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Title: The Cambridge natural history, Vol. 05 (of 10)
Author: Adam Sedgwick
David Sharp
Frederick Granville Sinclair
Editor: S. F. Harmer
Sir A. E. Shipley
Release date: November 6, 2023 [eBook #72052]
Language: English
Original publication: London: Macmillan and Co, 1895
Credits: Keith Edkins, Peter Becker and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK THE CAMBRIDGE NATURAL HISTORY, VOL. 05 (OF 10) ***
Transcriber's note: Text enclosed by underscores is in italics (_italics_).
A single underscore introduces a subscript (CO_2), and a caret a
superscript (B^1).
Page numbers enclosed by curly braces (for example: {25}) have been
incorporated to facilitate the use of the Alphabetical Index and other page
references in the text.
* * * * *
THE
CAMBRIDGE NATURAL HISTORY
EDITED BY
S. F. HARMER, M.A., Fellow of King's College, Cambridge; Superintendent of
the University Museum of Zoology
AND
A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge; University
Lecturer on the Morphology of Invertebrates
VOLUME V
[Illustration]
_Frontispiece._ MAP TO ILLUSTRATE THE GEOGRAPHICAL DISTRIBUTION OF
PERIPATUS.
PERIPATUS
By ADAM SEDGWICK, M.A., F.R.S., Fellow and Lecturer of Trinity College,
Cambridge
MYRIAPODS
By F. G. SINCLAIR, M.A., Trinity College, Cambridge
INSECTS
PART I. Introduction, Aptera, Orthoptera, Neuroptera, and a portion of
Hymenoptera (Sessiliventres and Parasitica)
By DAVID SHARP, M.A. (Cantab.), M.B. (Edinb.), F.R.S.
London
MACMILLAN AND CO.
AND NEW YORK
1895
_All rights reserved_
"Creavit in cœlo Angelos, in terra vermiculos: non superior in illis, non
inferior in istis. Sicut enim nulla manus Angelum, ita nulla posset
creare vermiculum."—SAINT AUGUSTINE, _Liber soliloquiorum animae ad
Deum_, Caput IX.
CONTENTS
PAGE
SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK ix
PERIPATUS
CHAPTER I
INTRODUCTION—EXTERNAL FEATURES—HABITS—BREEDING—ANATOMY—ALIMENTARY CANAL
—NERVOUS SYSTEM—THE BODY WALL—THE TRACHEAL SYSTEM—THE MUSCULAR SYSTEM
—THE VASCULAR SYSTEM—THE BODY CAVITY—NEPHRIDIA—GENERATIVE ORGANS
—DEVELOPMENT—SYNOPSIS OF THE SPECIES—SUMMARY OF DISTRIBUTION 3
MYRIAPODA
CHAPTER II
INTRODUCTION—HABITS—CLASSIFICATION—STRUCTURE—CHILOGNATHA—CHILOPODA
—SCHIZOTARSIA—SYMPHYLA—PAUROPODA—EMBRYOLOGY—PALAEONTOLOGY 29
INSECTA
CHAPTER III
CHARACTERISTIC FEATURES OF INSECT LIFE—SOCIAL INSECTS—DEFINITION OF THE
CLASS INSECTA—COMPOSITION OF INSECT SKELETON—NUMBER OF SEGMENTS—NATURE
OF SCLERITES—HEAD—APPENDAGES OF THE MOUTH—EYES—THORAX—ENTOTHORAX—LEGS
—WINGS—ABDOMEN OR HIND BODY—SPIRACLES—SYSTEMATIC ORIENTATION 83
CHAPTER IV
ARRANGEMENT OF INTERNAL ORGANS—MUSCLES—NERVOUS SYSTEM—GANGLIONIC CHAIN
—BRAIN—SENSE-ORGANS—ALIMENTARY CANAL—MALPIGHIAN TUBES—RESPIRATION
—TRACHEAL SYSTEM—FUNCTION OF RESPIRATION—BLOOD OR BLOOD-CHYLE—DORSAL
VESSEL OR HEART—FAT-BODY—OVARIES—TESTES—PARTHENOGENESIS—GLANDS 114
CHAPTER V
DEVELOPMENT
EMBRYOLOGY—EGGS—MICROPYLES—FORMATION OF EMBRYO—VENTRAL PLATE—ECTODERM
AND ENDODERM—SEGMENTATION—LATER STAGES—DIRECT OBSERVATION OF EMBRYO
—METAMORPHOSIS—COMPLETE AND INCOMPLETE—INSTAR—HYPERMETAMORPHOSIS
—METAMORPHOSIS OF INTERNAL ORGANS—INTEGUMENT—METAMORPHOSIS OF BLOWFLY
—HISTOLYSIS—IMAGINAL DISCS—PHYSIOLOGY OF METAMORPHOSIS—ECDYSIS 143
CHAPTER VI
CLASSIFICATION—THE NINE ORDERS OF INSECTS—THEIR CHARACTERS—PACKARD'S
ARRANGEMENT—BRAUER'S CLASSIFICATION—CLASSIFICATIONS BASED ON
METAMORPHOSIS—SUPER-ORDERS—THE SUBDIVISIONS OF ORDERS 171
CHAPTER VII
THE ORDER APTERA—DEFINITION—CHIEF CHARACTERISTICS—THYSANURA—CAMPODEA
—JAPYX—MACHILIS—LEPISMA—DIVERSITY OF INTERNAL STRUCTURE IN THYSANURA
—ECTOTROPHI AND ENTOTROPHI—COLLEMBOLA—LIPURIDAE—PODURIDAE
—SMYNTHURIDAE—THE SPRING—THE VENTRAL TUBE—ABDOMINAL APPENDAGES
—PROSTEMMATIC ORGAN—TRACHEAL SYSTEM—ANURIDA MARITIMA—COLLEMBOLA ON
SNOW—LIFE-HISTORIES OF COLLEMBOLA—FOSSIL APTERA—APTERYGOGENEA
—ANTIQUITY AND DISTRIBUTION OF CAMPODEA 180
CHAPTER VIII
ORTHOPTERA—FORFICULIDAE, EARWIGS—HEMIMERIDAE 198
CHAPTER IX
ORTHOPTERA _CONTINUED_—BLATTIDAE, COCKROACHES 220
CHAPTER X
ORTHOPTERA _CONTINUED_—MANTIDAE, SOOTHSAYERS 242
CHAPTER XI
ORTHOPTERA _CONTINUED_—PHASMIDAE, WALKING-LEAVES, STICK-INSECTS 260
CHAPTER XII
ORTHOPTERA _CONTINUED_—ACRIDIIDAE, LOCUSTS, GRASSHOPPERS 279
CHAPTER XIII
ORTHOPTERA _CONTINUED_—LOCUSTIDAE, GREEN GRASSHOPPERS, KATYDIDS 311
CHAPTER XIV
ORTHOPTERA _CONTINUED_—GRYLLIDAE, CRICKETS 330
CHAPTER XV
NEUROPTERA—MALLOPHAGA—EMBIIDAE 341
CHAPTER XVI
NEUROPTERA _CONTINUED_—TERMITIDAE, TERMITES OR WHITE ANTS 356
CHAPTER XVII
NEUROPTERA _CONTINUED_—PSOCIDAE (BOOK-LICE AND DEATH-WATCHES)—THE
FIRST FAMILY OF AMPHIBIOUS NEUROPTERA (PERLIDAE, STONE-FLIES) 390
CHAPTER XVIII
AMPHIBIOUS NEUROPTERA _CONTINUED_—ODONATA, DRAGON-FLIES 409
CHAPTER XIX
AMPHIBIOUS NEUROPTERA _CONTINUED_—EPHEMERIDAE, MAY-FLIES 429
CHAPTER XX
NEUROPTERA PLANIPENNIA—SIALIDAE, ALDER-FLIES, SNAKE-FLIES—PANORPIDAE,
SCORPION-FLIES—HEMEROBIIDAE, ANT-LIONS, LACEWINGS, ETC. 444
CHAPTER XXI
NEUROPTERA _CONTINUED_—TRICHOPTERA, THE PHRYGANEIDAE OR CADDIS-FLIES 473
CHAPTER XXII
HYMENOPTERA—HYMENOPTERA SESSILIVENTRES—CEPHIDAE—ORYSSIDAE—SIRICIDAE
—TENTHREDINIDAE OR SAWFLIES 487
CHAPTER XXIII
HYMENOPTERA PETIOLATA—PARASITIC HYMENOPTERA—CYNIPIDAE OR GALL-FLIES
—PROCTOTRYPIDAE—CHALCIDIDAE—ICHNEUMONIDAE—BRACONIDAE—STEPHANIDAE
—MEGALYRIDAE—EVANIIDAE—PELECINIDAE—TRIGONALIDAE 519
INDEX 567
SCHEME OF THE CLASSIFICATION (RECENT FORMS) ADOPTED IN THIS BOOK
PROTOTRACHEATA
PERIPATUS (p. 1)
MYRIAPODA
Order. Family.
CHILOGNATHA POLYXENIDAE (p. 43).
(= DIPLOPODA) GLOMERIDAE (p. 43).
SPHAEROTHERIIDAE (p. 43).
JULIDAE (p. 43).
BLANJULIDAE (p. 44).
CHORDEUMIDAE (p. 44).
POLYDESMIDAE (p. 44).
POLYZONIIDAE (p. 44).
CHILOPODA LITHOBIIDAE (p. 45).
SCOLOPENDRIDAE (p. 45).
NOTOPHILIDAE (p. 45).
GEOPHILIDAE (p. 46).
SCHIZOTARSIA CERMATIIDAE (= SCUTIGERIDAE) (p. 46).
SYMPHYLA. SCOLOPENDRELLIDAE (p. 46).
PAUROPODA PAUROPIDAE (p. 47).
INSECTA
Order. Division, Series, Family.
or Sub-Order.
APTERA THYSANURA CAMPODEIDAE (p. 183).
(p. 180) (p. 182) JAPYGIDAE (p. 184).
MACHILIDAE (p. 184).
LEPISMIDAE (p. 185).
COLLEMBOLA LIPURIDAE (p. 190).
(p. 189) PODURIDAE (p. 190).
SMYNTHURIDAE (p. 191).
Order. Division, Series, Family. Tribe or
or Sub-Order. Sub-Family.
ORTHOPTERA ORTHOPTERA FORFICULIDAE (p. 202).
(p. 198) CURSORIA
HEMIMERIDAE (p. 217).
BLATTIDAE Ectobiides.
(p. 220) Phyllodromiides.
Nyctiborides.
Epilamprides.
Periplanetides.
Panchlorides.
Blaberides.
Corydiides.
Oxyhaloides.
Perisphaeriides.
Panesthiides.
? Geoscapheusides.
MANTIDAE Amorphoscelides.
(p. 242) Orthoderides.
Mantides.
Harpagides.
Vatides.
Empusides.
PHASMIDAE Lonchodides.
(p. 260) Bacunculides.
Bacteriides.
Necroscides.
Clitumnides.
Acrophyllides.
Cladomorphides.
Anisomorphides.
Phasmides.
Aschipasmides.
Bacillides.
Phylliides.
ORTHOPTERA ACRIDIIDAE Tettigides.
SALTATORIA (p. 279) Pneumorides.
Mastacides.
Proscopiides.
Tryxalides.
Oedipodides.
Pyrgomorphides.
Pamphagides.
Acridiides.
LOCUSTIDAE Phaneropterides.
(p. 311) Meconemides.
Mecopodides.
Prochilides.
Pseudophyllides.
Conocephalides.
Tympanophorides.
Sagides.
Locustides.
Decticides.
Callimenides.
Ephippigerides.
Hetrodides.
Gryllacrides.
Stenopelmatides.
GRYLLIDAE Tridactylides.
(p. 330) Gryllotalpides.
Myrmecophilides.
Gryllides.
Oecanthides.
Trigonidiides.
Eneopterides.
Order. Division, Series, Family. Tribe or Group.
or Sub-Order. Sub-Family.
NEUROPTERA MALLOPHAGA Leiotheides.
(p. 345) Philopterides.
PSEUDO- EMBIIDAE (p. 351).
NEUROPTERA TERMITIDAE (p. 356).
PSOCIDAE (p. 390).
NEUROPTERA PERLIDAE (p. 398).
AMPHIBIO-
TICA ODONATA Anisopterides Gomphinae.
(p. 409) Cordulegasterinae.
Aeschninae.
Corduliinae.
Libellulinae.
Zygopterides Calepteryginae.
Agrioninae.
EPHEMERIDAE (p. 429).
NEUROPTERA SIALIDAE Sialides
PLANIPENNIA (p. 444) Raphidiides.
PANORPIDAE (p. 449).
HEMEROBIIDAE Myrmeleonides (p. 454).
(p. 453) Ascalaphides Holophthalmi.
(p. 459) Schizophthalmi.
Nemopterides (p. 462).
Mantispides (p. 463).
Hemerobiides Dilarina.
(p. 465) Nymphidina.
Osmylina.
Hemerobiina.
Chrysopides (p. 469).
Coniopterygides (p. 471).
TRICHOPTERA PHRYGANEIDAE Phryganeides (p. 480).
(p. 473) Limnophilides (p. 481).
Sericostomatides (p. 482).
Leptocerides (p. 482).
Hydropsychides (p. 482).
Rhyacophilides (p. 483).
Hydroptilides (p. 484).
HYMENOPTERA HYMENOPTERA CEPHIDAE (p. 504).
(p. 487) SESSILI- ORYSSIDAE (p. 506).
VENTRES SIRICIDAE (p. 507).
TENTHREDINIDAE (p. 510).
HYMENOPTERA CYNIPIDAE (p. 523).
PETIOLATA PROCTOTRYPIDAE (p. 533).
(part) CHALCIDIDAE (p. 539).
ICHNEUMONIDAE (p. 551).
BRACONIDAE (p. 558).
STEPHANIDAE (p. 561).
MEGALYRIDAE (p. 562).
EVANIIDAE (p. 562).
PELECINIDAE (p. 563).
TRIGONALIDAE (p. 564).
(_To be continued in Vol. VI._)
PERIPATUS
BY
ADAM SEDGWICK, M.A., F.R.S.
Fellow of Trinity College, Cambridge.
{3}CHAPTER I
PERIPATUS
INTRODUCTION–EXTERNAL FEATURES–HABITS–BREEDING–ANATOMY–ALIMENTARY CANAL–
NERVOUS SYSTEM–THE BODY WALL–THE TRACHEAL SYSTEM–THE MUSCULAR SYSTEM–THE
VASCULAR SYSTEM–THE BODY CAVITY–NEPHRIDIA–GENERATIVE ORGANS–DEVELOPMENT–
SYNOPSIS OF THE SPECIES–SUMMARY OF DISTRIBUTION.
The genus _Peripatus_ was established in 1826 by Guilding,[1] who first
obtained specimens of it from St. Vincent in the Antilles. He regarded it
as a Mollusc, being no doubt deceived by the slug-like appearance given by
the antennae. Specimens were subsequently obtained from other parts of the
Neotropical region and from South Africa and Australia, and the animal was
variously assigned by the zoologists of the day to the Annelida and
Myriapoda. Its true place in the system, as a primitive member of the group
Arthropoda, was first established in 1874 by Moseley,[2] who discovered the
tracheae. The genus has been monographed by Sedgwick,[3] who has also
written an account of the development of the Cape species.[4] A
bibliography will be found in Sedgwick's Monograph.
{4}There can be no doubt that _Peripatus_ is an Arthropod, for it possesses
the following features, all characteristic of that group, and all of
first-class morphological importance: (1) The presence of appendages
modified as jaws; (2) the presence of paired lateral ostia perforating the
wall of the heart and putting its cavity in communication with the
pericardium; (3) the presence of a vascular body cavity and pericardium
(haemocoelic body cavity); (4) absence of a perivisceral section of the
coelom. Finally, the tracheae, though not characteristic of all the classes
of the Arthropoda, are found nowhere outside that group, and constitute a
very important additional reason for uniting _Peripatus_ with it.
_Peripatus_, though indubitably an Arthropod, differs in such important
respects from all the old-established Arthropod classes, that a special
class, equivalent in rank to the others, and called Prototracheata, has had
to be created for its sole occupancy. This unlikeness to other Arthropoda
is mainly due to the Annelidan affinities which it presents, but in part to
the presence of the following peculiar features: (1) The number and
diffusion of the tracheal apertures; (2) the restriction of the jaws to a
single pair; (3) the disposition of the generative organs; (4) the texture
of the skin; and (5) the simplicity and similarity of all the segments of
the body behind the head.
The Annelidan affinities are superficially indicated in so marked a manner
by the thinness of the cuticle, the dermo-muscular body wall, the hollow
appendages, that, as already stated, many of the earlier zoologists who
examined _Peripatus_ placed it amongst the segmented worms; and the
discovery that there is some solid morphological basis for this
determination constitutes one of the most interesting points of the recent
work on the genus. The Annelidan features are: (1) The paired nephridia in
every segment of the body behind the first two (Saenger, Balfour[5]); (2)
the presence of cilia in the generative tracts (Gaffron). It is true that
neither of these features are absolutely distinctive of the Annelida, but
when taken in conjunction with the Annelidan disposition of the chief
systems of organs, viz. the central nervous system, and the main vascular
trunk or heart, may be considered as indicating affinities in that
{5}direction. _Peripatus_, therefore, is zoologically of extreme interest
from the fact that, though in the main Arthropodan, it possesses features
which are possessed by no other Arthropod, and which connect it to the
group to which the Arthropoda are in the general plan of their organisation
most closely related. It must, therefore, according to our present lights,
be regarded as a very primitive form; and this view of it is borne out by
its extreme isolation at the present day. _Peripatus_ stands absolutely
alone as a kind of half-way animal between the Arthropoda and Annelida.
There is no gradation of structure within the genus; the species are very
limited in number, and in all of them the peculiar features above mentioned
are equally sharply marked.
_Peripatus_, though a lowly organised animal, and of remarkable
sluggishness, with but slight development of the higher organs of sense,
with eyes the only function of which is to enable it to avoid the
light—though related to those animals most repulsive to the aesthetic sense
of man, animals which crawl upon their bellies and spit at, or poison,
their prey—is yet, strange to say, an animal of striking beauty. The
exquisite sensitiveness and constantly changing form of the antennae, the
well-rounded plump body, the eyes set like small diamonds on the side of
the head, the delicate feet, and, above all, the rich colouring and velvety
texture of the skin, all combine to give these animals an aspect of quite
exceptional beauty. Of all the species which I have seen alive, the most
beautiful are the dark green individuals of _Capensis_, and the species
which I have called _Balfouri_. These animals, so far as skin is concerned,
are not surpassed in the animal kingdom. I shall never forget my
astonishment and delight when on bearing away the bark of a rotten
tree-stump in the forest on Table Mountain, I first came upon one of these
animals in its natural haunts, or when Mr. Trimen showed me in confinement
at the South African Museum a fine fat, full-grown female, accompanied by
her large family of thirty or more just-born but pretty young, some of
which were luxuriously creeping about on the beautiful skin of their
mother's back.
EXTERNAL FEATURES.
The anterior part of the body may be called the head, though it is not
sharply marked off from the rest of the body (Fig. 1).
{6}[Illustration: FIG. 1.—_Peripatus capensis_, drawn from life. Life size.
(After Sedgwick.)]
[Illustration: FIG. 2.—Ventral view of hind-end of _P. Novae-Zealandiae_.
(After Sedgwick.) _g_, Generative opening; _a_, anus.
FIG. 3.—Ventral view of the head of _P. capensis_. (After Sedgwick.) _ant_,
Antennae; _or.p_, oral papillae; _F.1_, first leg; _T_, tongue.]
The head carries three pairs of appendages, a pair of simple eyes, and a
ventrally placed mouth. The body is elongated and vermiform; it bears a
number of paired appendages, each terminating in a pair of claws, and all
exactly alike. The number varies in the different species. The anus is
always at the posterior end of the body, and the generative opening is on
the ventral surface just in front of the anus; it may be between the legs
of the last pair (Fig. 2), or it may be behind them. There is in most
species a thin median white line extending the whole length of the dorsal
surface of the body, on each side of which the skin pigment is darker than
elsewhere. The colour varies considerably in the different species, and
even in different individuals of the same species. The ventral surface is
nearly always flesh-coloured, while the dorsal surface has a darker colour.
In the {7}South African species the colour of the dorsal surface varies
from a dark green graduating to a bluish gray, to a brown varying to a red
orange. The colour of the Australasian species varies in like manner, while
that of the Neotropical species (S. American and W. Indian) is less
variable. The skin is thrown into a number of transverse ridges, along
which wart-like papillae are placed. The papillae, which are found
everywhere, are specially developed on the dorsal surface, less so on the
ventral. Each papilla carries at its extremity a well-marked spine.
The appendages of the head are the antennae, the jaws and the oral
papillae.
The antennae, which are prolongations of the dorso-lateral parts of the
head, are ringed, and taper slightly till near their termination, where
they are slightly enlarged. The rings bear a number of spines, and the free
end of the antennae is covered by a cap of spiniferous tissue like that of
the rings.
[Illustration: FIG. 4.—Inner jaw-claw of _P. capensis_. (After Balfour.)
FIG. 5.—Outer jaw-claw of _P. capensis_. (After Balfour.)]
The mouth is at the hinder end of a depression called the buccal cavity,
and is surrounded by an annular tumid lip, raised into papilliform ridges
and bearing a few spines (Fig. 3). Within the buccal cavity are the two
jaws. They are short, stump-like, muscular structures, armed at their free
extremities by a pair of cutting blades or claws, and are placed one on
each side of the mouth. In the median line of the buccal cavity in front is
placed a thick muscular protuberance, which may be called the tongue,
though attached to the dorsal instead of to the ventral wall of the mouth
(Fig. 3). The tongue bears a row of small chitinous teeth. The jaw-claws
(Figs. 4 and 5), which resemble in all essential points the claws borne by
the feet, and like these are thickenings of the cuticle, are sickle-shaped.
They have their convex edge directed forwards and their concave or cutting
edge turned backwards. The inner cutting plate (Fig. 4) usually bears a
number of cutting teeth. The jaws appear to be used for tearing the food,
to which the mouth adheres by means of the tumid suctorial lips. The oral
papillae are placed at the sides of the head (Fig. 3). The {8}ducts of the
slime-glands open at their free end. They possess two main rings of
projecting tissue, and their extremities bear papillae irregularly
arranged.
The ambulatory appendages vary in number. There are seventeen pairs in _P.
capensis_ and eighteen in _P. Balfouri_, while in _P. Edwardsii_ the number
varies from twenty-nine to thirty-four pairs. They consist of two main
divisions, which we may call the leg and the foot (Figs. 6 and 7). The leg
(_l_) has the form of a truncated cone, the broad end of which is attached
to the ventro-lateral wall of the body, of which it is a prolongation. It
is marked by a number of rings of papillae placed transversely to its long
axis, the dorsal of which are pigmented like the dorsal surface of the
body, and the ventral like the ventral surface. At the narrow distal end of
the leg there are on the ventral surface three spiniferous pads, each of
which is continued dorsally into a row of papillae.
[Illustration: FIG. 6.—Ventral view of last leg of a male _P. capensis_.
(After Sedgwick.) _f_, Foot; _l_, leg; _p_, spiniferous pads. The white
papilla on the proximal part of this leg is characteristic of the male of
this species.]
[Illustration: FIG. 7.—Leg of _P. capensis_ seen from the front. (After
Sedgwick.) _f_, Foot; _l_, leg; _p_, spiniferous pads.]
The foot is attached to the distal end of the leg. It is slightly narrower
at its attached extremity than at its free end. It bears two sickle-shaped
claws and a few papillae. The part of the foot which carries the claws is
especially retractile, and is generally found more or less telescoped into
the proximal part. The legs of the fourth and fifth pairs differ from the
others in {9}the fact that the proximal pad is broken up into three, a
small central and two larger lateral. The enlarged nephridia of these legs
open on the small central division.
The males are generally rather smaller than the females. In those species
in which the number of legs varies, the male has a smaller number of legs
than the female.
HABITS.
They live beneath the bark of rotten stumps of trees, in the crevices of
rock, and beneath stones. They require a moist atmosphere, and are
exceedingly susceptible to drought. They avoid light, and are therefore
rarely seen. They move with great deliberation, picking their course by
means of their antennae and eyes. It is by the former that they acquire a
knowledge of the ground over which they are travelling, and by the latter
that they avoid the light. The antennae are extraordinarily sensitive, and
so delicate, indeed, that they seem to be able to perceive the nature of
objects without actual contact. When irritated they eject with considerable
force the contents of their slime reservoirs from the oral papillae. The
force is supplied by the sudden contraction of the muscular body wall. They
can squirt the slime to the distance of almost a foot. The slime, which
appears to be perfectly harmless, is extremely sticky, but it easily comes
away from the skin of the animal itself.
I have never seen them use this apparatus for the capture of prey, but
Hutton describes the New Zealand species as using it for this purpose. So
far as I can judge, it is used as a defensive weapon; but this of course
will not exclude its offensive use. They will turn their heads to any part
of the body which is being irritated and violently discharge their slime at
the offending object. Locomotion is effected entirely by means of the legs,
with the body fully extended.
Of their food in the natural state we know little; but it is probably
mainly, if not entirely, animal. Hutton describes his specimens as sucking
the juices of flies which they had stuck down with their slime, and those
which I kept in captivity eagerly devoured the entrails of their fellows,
and the developing young from the uterus. They also like raw sheep's liver.
They move their mouths in a suctorial manner, tearing the food with their
jaws. They have the power of extruding their jaws from {10}the mouth, and
of working them alternately backwards or forwards. This is readily observed
in individuals immersed in water.
BREEDING.
All species are viviparous. It has been lately stated that one of the
Australian species is normally oviparous, but this has not been proved. The
Australasian species come nearest to laying eggs, inasmuch as the eggs are
large, full of yolk, and enclosed in a shell; but development normally
takes place in the uterus, though, abnormally, incompletely developed eggs
are extruded.
The young of _P. capensis_ are born in April and May. They are almost
colourless at birth, excepting the antennae, which are green, and their
length is 10 to 15 mm. A large female will produce thirty to forty young in
one year. The period of gestation is thirteen months, that is to say, the
ova pass into the oviducts about one month before the young of the
preceding year are born. They are born one by one, and it takes some time
for a female to get rid of her whole stock of embryos; in fact, the embryos
in any given female differ slightly in age, those next the oviduct being a
little older (a few hours) than those next the vagina. The mother does not
appear to pay any special attention to her young, which wander away and get
their own food.
There does not appear to be any true copulation. The male deposits small,
white, oval spermatophores, which consist of small bundles of spermatozoa
cemented together by some glutinous substance, indiscriminately on any part
of the body of the female. Such spermatophores are found on the bodies of
both males and females from July to January, but they appear to be most
numerous in our autumn. It seems probable that the spermatozoa make their
way from the adherent spermatophore through the body wall into the body,
and so by traversing the tissues reach the ovary. The testes are active
from June to the following March. From March to June the vesiculae of the
male are empty.
There are no other sexual differences except in some of the South African
species, in which the last or penultimate leg of the male bears a small
white papilla on its ventral surface (Fig. 6).
Whereas in the Cape species embryos in the same uterus are all practically
of the same age (except in the month of April, when two broods overlap in
_P. capensis_), and birth takes place at a fixed season; in the Neotropical
species the uterus, which is {11}always pregnant, contains embryos of
different ages, and births probably take place all the year round.
In all species of _Peripatus_ the young are fully formed at birth, and
differ from the adults only in size and colour.
ANATOMY
THE ALIMENTARY CANAL (Fig. 8).
[Illustration: FIG. 8.—_Peripatus capensis_ dissected so as to show the
alimentary canal, slime glands, and salivary glands. (After Balfour.) The
dissection is viewed from the ventral side, and the lips (_L_) have been
cut through in the middle line behind and pulled outwards so as to expose
the jaws (_j_), which have been turned outwards, and the tongue (_T_)
bearing a median row of chitinous teeth, which branches behind into two.
The muscular pharynx, extending back into the space between the first and
second pairs of legs, is followed by a short tubular oesophagus. The latter
opens into the large stomach with plicated walls, extending almost to the
hind end of the animal. The stomach at its point of junction with the
rectum presents an S-shaped ventro-dorsal curve. _A_, Anus; _at_, antenna;
_F.1_, _F.2_, first and second feet; _j_, jaws; _L_, lips; _oe_,
oesophagus; _or.p_, oral papilla; _ph_, pharynx; _R_, rectum; _s.d_,
salivary duct; _s.g_, salivary gland; _sl.d_, slime reservoir; _sl.g_,
portion of tubules of slime gland; _st_, stomach; _T_, tongue in roof of
mouth.]
The buccal cavity, as explained above, is a secondary formation around the
true mouth, which is at its dorsal posterior end. It contains the tongue
and the jaws, which have already been described, and into the hind end of
it there opens ventrally by a median opening the salivary glands (_s.g_).
The mouth leads into a muscular pharynx (_ph_), which is connected by a
short oesophagus (_oe_) with a stomach (_st_). The stomach forms by far the
{12}largest part of the alimentary canal. It is a dilated soft-walled tube,
and leads behind into the short narrow rectum (_R_), which opens at the
anus. There are no glands opening into the alimentary canal.
NERVOUS SYSTEM.
The central nervous system consists of a pair of supra-oesophageal ganglia
united in the middle line, and of a pair of widely divaricated ventral
cords, continuous in front with the supra-oesophageal ganglia (Fig. 9).
The ventral cords at first sight appear to be without ganglionic
thickenings, but on more careful examination they are found to be enlarged
at each pair of legs (Fig. 9). These enlargements may be regarded as
imperfect ganglia. There are, therefore, as many pairs of ganglia as there
are pairs of legs. There is in addition a ganglionic enlargement at the
commencement of the oesophageal commissures, where the nerves to the oral
papillae are given off (Fig. 9, _or.g_).
[Illustration: FIG. 9.—Brain and anterior part of the ventral nerve-cords
of _Peripatus capensis_ enlarged and viewed from the ventral surface.
(After Balfour.) The paired appendages (_d_) of the ventral surface of the
brain are seen, and the pair of sympathetic nerves (_sy_) arising from the
ventral surface of the hinder part. From the commencement of the
oesophageal commissures pass off on each side a pair of nerves to the jaws
(_Jn_). The three anterior commissures between the ventral nerve-cords are
placed close together; immediately behind them the nerve-cords are swollen,
to form the ganglionic enlargements from which pass off to the oral
papillae a pair of large nerves on each side (_orn_). Behind this the cords
present a series of enlargements, one pair for each pair of feet, from
which a pair of large nerves pass off on each side to the feet (_pn_).
_atn_, Antennary nerves; _co_, commissures between ventral cords; _d_,
ventral appendages of brain; _E_, eye; _en_, nerves passing outwards from
ventral cord; _F.g.1_, ganglionic enlargements from which nerves to feet
pass off; _jn_, nerves to jaws; _org_, ganglionic enlargement from which
nerves to oral papillae pass off; _orn_, nerves to oral papillae; _pc_,
posterior lobe of brain; _pn_, nerves to feet; _sy_, sympathetic nerves.]
The ventral cords are placed each in the lateral compartments of the body
cavity, immediately within the longitudinal layer of muscles. They are
connected with each other, rather like the pedal nerves of _Chiton_ and the
lower Prosobranchiata, by a number of commissures. These commissures
exhibit a {13}fairly regular arrangement from the region included between
the first and the last pair of true feet. There are nine or ten of them
between each pair of feet. They pass along the ventral wall of the body,
perforating the ventral mass of longitudinal muscles. On their way they
give off nerves which innervate the skin.
Posteriorly the two nerve-cords nearly meet immediately in front of the
generative aperture, and then, bending upwards, fall into each other
dorsally to the rectum. They give off a series of nerves from their outer
borders, which present throughout the trunk a fairly regular arrangement.
From each ganglion two large nerves (_pn_) are given off, which, diverging
somewhat from each other, pass into the feet.
From the oesophageal commissures, close to their junction with the
supra-oesophageal ganglia, a nerve arises on each side which passes to the
jaws, and a little in front of this, apparently from the supra-oesophageal
ganglion itself, a second nerve to the jaws also takes its origin.
The supra-oesophageal ganglia (Fig. 9) are large, somewhat oval masses,
broader in front than behind, completely fused in the middle, but free at
their extremities. Each of them is prolonged anteriorly into an antennary
nerve, and is continuous behind with one of the oesophageal commissures. On
the ventral surface of each, rather behind the level of the eye, is placed
a hollow protuberance (Fig. 9, _d_), of which I shall say more in dealing
with the development. About one-third of the way back the two large optic
nerves take their origin, arising laterally, but rather from the dorsal
surface (Fig. 9). Each of them joins a large ganglionic mass placed
immediately behind the retina.
The histology of the ventral cords and oesophageal commissures is very
simple and uniform. They consist of a cord almost wholly formed of
nerve-fibres placed dorsally, and of a ventral layer of ganglion cells.
THE BODY WALL.
The skin is formed of three layers.
(1) The cuticle.
(2) The epidermis or hypodermis.
(3) The dermis.
The cuticle is a thin layer. The spines, jaws, and claws are special
developments of it. Its surface is not, however, smooth, {14}but is
everywhere, with the exception of the perioral region, raised into minute
secondary papillae, which in most instances bear at their free extremity a
somewhat prominent spine. The whole surface of each of the secondary
papillae just described is in its turn covered by numerous minute spinous
tubercles.
The epidermis, placed immediately within the cuticle, is composed of a
single layer of cells, which vary, however, a good deal in size in
different regions of the body. The cells excrete the cuticle, and they
stand in a very remarkable relation to the secondary papillae of the
cuticle just described. Each epidermis cell is in fact placed within one of
these secondary papillae, so that the cuticle of each secondary papilla is
the product of a single epidermis cell. The pigment which gives the
characteristic colour to the skin is deposited in the protoplasm of the
outer ends of the cells in the form of small granules.
At the apex of most, if not all, the primary wart-like papillae there are
present oval aggregations, or masses of epidermis cells, each such mass
being enclosed in a thickish capsule and bearing a long projecting spine.
These structures are probably tactile organs. In certain regions of the
body they are extremely numerous; more especially is this the case in the
antennae, lips, and oral papillae. On the ventral surface of the peripheral
rings of the thicker sections of the feet they are also very thickly set
and fused together so as to form a kind of pad (Figs. 6 and 7). In the
antennae they are thickly set side by side on the rings of skin which give
such an Arthropodan appearance to these organs in _Peripatus_.
THE TRACHEAL SYSTEM.
The apertures of the tracheal system are placed in the depressions between
the papillae or ridges of the skin. Each of them leads into a tube, which
may be called the tracheal pit (Fig. 10), the walls of which are formed of
epithelial cells bounded towards the lumen of the pit by a very delicate
cuticular membrane continuous with the cuticle covering the surface of the
body. The pits vary somewhat in depth; the pit figured was about 0.09 mm.
It perforates the dermis and terminates in the subjacent muscular layer.
Internally it expands in the transverse plane and from the expanded portion
the tracheal tubes arise in diverging bundles. Nuclei similar in character
to those in the walls of the tracheal {15}pit are placed between the
tracheae, and similar but slightly more elongated nuclei are found along
the bundles. The tracheae are minute tubes exhibiting a faint transverse
striation which is probably the indication of a spiral fibre. They appear
to branch, but only exceptionally. The tracheal apertures are diffused
over the surface of the body, but are especially developed in certain
regions.
[Illustration: FIG. 10.—Section through a tracheal pit and diverging
bundles of tracheal tubes taken transversely to the long axis of the body.
(After Balfour.) _tr_, Tracheae, showing rudimentary spiral fibre; _tr.c_,
cells resembling those lining the tracheal pits, which occur at intervals
along the course of the tracheae; _tr.o_, tracheal stigma; _tr.p_, tracheal
pit.]
THE MUSCULAR SYSTEM.
The general muscular system consists of—(1) the general wall of the body;
(2) the muscles connected with the mouth, pharynx, and jaws; (3) the
muscles of the feet; (4) the muscles of the alimentary tract.
The muscular wall of the body is formed of—(1) an external layer of
circular fibres; (2) an internal layer of longitudinal muscles.
The main muscles of the body are unstriated and divided into fibres, each
invested by a delicate membrane. The muscles of the jaws alone are
transversely striated.
THE VASCULAR SYSTEM.
The vascular system consists of a dorsal tubular heart with paired ostia
leading into it from the pericardium, of the pericardium, and the various
other divisions of the perivisceral cavity (Fig. 14, D). As in all
Arthropoda, the perivisceral cavity is a haemocoele; I.E. it contains blood
and forms part of the vascular system. The heart extends from close to the
hind end of the body to the head.
{16}THE BODY CAVITY.
The body cavity is formed of four compartments—one central, two lateral,
and a pericardial (Fig. 14, D). The former is by far the largest, and
contains the alimentary tract, the generative organs, and the slime glands.
It is lined by a delicate endothelial layer, and is not divided into
compartments nor traversed by muscular fibres. The lateral divisions are
much smaller than the central, and are shut off from it by the inner
transverse band of muscles. They are almost entirely filled with the
nerve-cord and salivary gland in front and with the nerve-cord alone
behind, and their lumen is broken up by muscular bands. They further
contain the nephridia. They are prolonged into the feet, as is the
embryonic body cavity of most Arthropoda. The pericardium contains a
peculiar cellular tissue, probably, as suggested by Moseley, equivalent to
the fat-bodies of insects.
NEPHRIDIA.
In _Peripatus capensis_ nephridia are present in all the legs. In all of
them (except the first three) the following parts may be recognised (Fig.
11):—
(1) A vesicular portion opening to the exterior on the ventral surface of
the legs by a narrow passage.
(2) A coiled portion, which is again subdivided into several sections.
(3) A section with closely packed nuclei ending by a somewhat enlarged
opening.
(4) The terminal portion, which consists of a thin-walled vesicle.
The last twelve pairs of these organs are all constructed in a very similar
manner, while the two pairs situated in the fourth and fifth pairs of legs
are considerably larger than those behind, and are in some respects very
differently constituted.
It will be convenient to commence with one of the hinder nephridia. Such a
nephridium from the ninth pair of legs is represented in Fig. 11. The
external opening is placed at the outer end of a transverse groove at the
base of one of the legs, while the main portion of the organ lies in the
body cavity in the base of the leg, and extends into the trunk to about the
level {17}of the outer edge of the nerve-cord of its side. The external
opening (_o.s_) leads into a narrow tube (_s.d_), which gradually dilates
into a large sac (_s_). The narrow part is lined by small epithelial cells,
which are directly continuous with and perfectly similar to those of the
epidermis. The sac itself, which forms a kind of bladder or collecting
vesicle for the organ, is provided with an extremely thin wall, lined with
very large flattened cells. The second section of the nephridium is formed
by the coiled tube, the epithelial lining of which varies slightly in the
different parts. The third section (_s.o.t_), constitutes the most distinct
portion of the whole organ. Its walls are formed of columnar cells almost
filled by oval nuclei, which absorb colouring matters with very great
avidity, and thus render this part extremely conspicuous. The nuclei are
arranged in several rows. It ends by opening into a vesicle (Fig. 14, D),
the wall of which is so delicate that it is destroyed when the nephridium
is removed from the body, and consequently is not shown in Fig. 11.
[Illustration: FIG. 11.—Nephridium from the 9th pair of legs of _P.
capensis_. _o.s_, External opening of segmental organ; _p.f_, internal
opening of nephridium into the body cavity (lateral compartment); _s_,
vesicle of segmental organ; _s.c.1_, _s.c.2_, _s.c.3_, _s.c.4_, successive
regions of coiled portion of nephridium; _s.o.t_, third portion of
nephridium broken off at _p.f_ from the internal vesicle, which is not
shown.]
The fourth and fifth pairs are very considerably larger than those behind,
and are in other respects peculiar. The great mass of each organ is placed
behind the leg on which the external opening is placed, immediately outside
one of the lateral nerve-cords. The external opening, instead of being
placed near the base of the leg, is placed on the ventral side of the third
ring (counting from the outer end) of the thicker portion of the leg. It
leads into a portion which clearly corresponds with the collecting vesicle
of the hinder nephridia. This part is not, however, dilated into a vesicle.
The three pairs of nephridia in the three foremost pairs of legs are
rudimentary, consisting solely of a vesicle and duct. The salivary glands
are the modified nephridia of the segment of the oral papillae.
{18}GENERATIVE ORGANS.
MALE.—The male organs (Fig. 12) consist of a pair of testes (_te_), a pair
of vesicles (_v_), vasa deferentia (_v.d_), and accessory glandular tubules
(_f_). All the above parts lie in the central compartment of the body
cavity. In _P. capensis_ the accessory glandular bodies or crural glands of
the last (17th) pair of legs are enlarged and prolonged into an elongated
tube placed in the lateral compartment of the body cavity (_a.g_).
[Illustration: FIG. 12.—Male generative organs of _Peripatus capensis_,
viewed from the dorsal surface. (After Balfour.) _a.g_, Enlarged crural
glands of last pair of legs; _F.16_, _17_, last pairs of legs; _f_, small
accessory glandular tubes; _p_, common duct into which the vasa deferentia
open; _te_, testis; _v_, seminal vesicle; _v.c_, nerve-cord; _v.d_, vas
deferens.]
The right vas deferens passes under both nerve-cords to join the left, and
form the enlarged tube (_p_), which, passing beneath the nerve-cord of its
side, runs to the external orifice. The enlarged terminal portion possesses
thick muscular walls, and possibly constitutes a spermatophore maker, as
has been shown to be the case in _P. N. Zealandiae_, by Moseley. In some
specimens a different arrangement obtains, in that the left vas deferens
passes under both nerve-cords to join the right.
FEMALE.—The ovaries consist of a pair of tubes closely applied together,
and continued posteriorly into the oviducts. The oviducts, after a short
course, become dilated into the uteruses, which join behind and open to the
exterior by a median {19}opening. The ovaries always contain spermatozoa,
some of which project through the ovarian wall into the body cavity.
Spermatozoa are not found in the uterus and oviducts, and it appears
probable that they reach the ovary directly by boring through the skin and
traversing the body cavity.[6] In the neotropical species there is a
globular receptaculum seminis opening by two short ducts close together
into the oviduct, and there is a small receptaculum ovorum with extremely
thin walls opening into the oviduct by a short duct just in front of the
receptaculum seminis. The epithelium of the latter structure is clothed
with actively moving cilia. In the New Zealand species there is a
receptaculum seminis with two ducts, but the receptacula ovorum has not
been seen.
There appear to be present in most, if not all, the legs some accessory
glandular structures opening just externally to the nephridia. They are
called the crural glands.
DEVELOPMENT.
As stated at the outset, _Peripatus_ is found in three of the great
regions, viz. in Africa, in Australasia, and in South America and the West
Indies. It is a curious and remarkable fact that although the species found
in these various localities are really closely similar, the principal
differences relating to the structure of the female generative organs and
to the number of the legs, they do differ in the most striking manner in
the structure of the ovum and in the early development. In all the
Australasian species the egg is large and heavily charged with food-yolk,
and is surrounded by a tough membrane. In the Cape species the eggs are
smaller, though still of considerable size; the yolk is much less
developed, and the egg membrane is thinner though dense. In the neotropical
species the egg is minute and almost entirely devoid of yolk. The
unsegmented uterine ovum of _P. Novae-Zealandiae_ measures 1.5 mm. in
length by .8 mm. in breadth; that of _P. capensis_ is .56 mm. in length;
and that of _P. Trinidadensis_ .04 mm. in diameter. In correspondence with
these differences in the ovum there are differences in the early
development, though the later stages are closely similar.
{20}[Illustration: FIG. 13.—A series of embryos of _P. capensis_. The hind
end of embryos B, C, D is uppermost in the figures, the primitive streak is
the white patch behind the blastopore. (After Sedgwick.) A, Gastrula stage,
ventral view, showing blastopore. B, Older gastrula stage, ventral view,
showing elongated blastopore and primitive streak. C, Ventral view of
embryo with three pairs of mesoblastic somites, dumb-bell-shaped blastopore
and primitive streak. D, Ventral view of embryo, in which the blastopore
has completely closed in its middle portion, and given rise to two
openings, the embryonic mouth and anus. The anterior pair of somites have
moved to the front end of the body, and the primitive groove has appeared
on the primitive streak. E, Side view of embryo, in which the hind end of
the body has begun to elongate in a spiral manner, and in which the
appendages have begun. _At_, antenna; _d_, dorsal projection; _p.s_,
preoral somite. F, Ventral view of head of embryo intermediate between E
and G. The cerebral grooves are wide and shallow. The lips have appeared,
and have extended behind the openings of the salivary glands, but have not
yet joined in the middle line. _At_, antennae; _c.g_, cerebral groove; _j_,
jaws; _j.s_, swelling at base of jaws; _L_, lips; _M_, mouth; _or.p_, oral
papillae; _o.s_, opening of salivary gland. G, Side view of older embryo
with the full number of appendages, to show the position in which the
embryos lie in the uterus.]
But unfortunately the development has only been fully worked out in one
species, and to that species—_P. capensis_—the following description
refers. The ova are apparently fertilised in the ovary, and they pass into
the oviducts in April and May. In May the brood of the preceding year are
born, and the new ova, which have meanwhile undergone cleavage, pass into
the uterus. There are ten to twenty ova in each uterus. The segmentation is
peculiar, and leads to the formation of a solid gastrula, consisting of a
cortex of ectoderm nuclei surrounding a central endodermal mass, which
consists of a much-vacuolated tissue with some irregularly-shaped nuclei.
The endoderm mass is exposed at one point—the blastopore (gastrula mouth).
The central vacuoles of the endoderm now unite and form the enteron of the
embryo, and at the same time the embryo elongates into a markedly oval
form, and an opacity—the primitive streak—appears at the hind end of the
blastopore (Fig. 13, B). This elongation of the embryo is accompanied by an
elongation of the blastopore, which soon becomes dumb-bell shaped (Fig. 13,
C). At the same time the mesoblastic somites (embryonic segments of
mesoderm) have made {21}their appearance in pairs at the hind end, and
gradually travel forward on each side of the blastopore to the front end,
where the somites of the anterior pair soon meet in front of the blastopore
(Fig. 13, D). Meanwhile the narrow middle part of the blastopore has closed
by a fusion of its lips, so that the blastopore is represented by two
openings, the future mouth and anus. A primitive groove makes its
appearance behind the blastopore (Fig. 13, D). At this stage the hind end
of the body becomes curved ventrally into a spiral (Fig. 13, E), and at the
same time the appendages appear as hollow processes of the body wall, a
mesoblastic somite being prolonged into each of them. The first to appear
are the antennae, into which the praeoral somites are prolonged. The
remainder appear from before backwards in regular order, viz. jaw, oral
papillae, legs 1-17. The full number of somites and their appendages is
not, however, completed until a later stage. The nervous system is formed
as an annular thickening of ectoderm passing in front of the mouth and
behind the anus, and lying on each side of the blastopore along the lines
of the somites. The praeoral part of this thickening, which gives rise to
the cerebral ganglia, becomes pitted inwards on each side (Fig. 13, F,
_c.g_). These pits are eventually closed, and form the hollow ventral
appendages of the supra-pharyngeal ganglia of the adult (Fig. 9, _d_). The
lips are formed as folds of the side wall of the body, extending from the
praeoral lobes to just behind the jaw (Fig. 13, F, _L_). They enclose the
jaws (_j_) mouth (_M_), and opening of the salivary glands (_o.s_), and so
give rise to the buccal cavity. The embryo has now lost its spiral
curvature, and becomes completely doubled upon itself, the hind end being
in contact with the mouth (Fig. 13, G). It remains in this position until
birth. The just-born young are from 10-15 mm. in length and have green
antennae, but the rest of the body is either quite white or of a reddish
colour. This red colour differs from the colour of the adult in being
soluble in spirit.
The mesoblastic somites are paired sacs formed from the anterior lateral
portions of the primitive streak (Fig. 13, C). As they are formed they
become placed in pairs on each side of the blastopore. The somites of the
first pair eventually obtain a position entirely in front of the blastopore
(Fig. 13, D). They form the somites of the praeoral lobes. The full
complement of somites is acquired at about the stage of Fig. 13, E.
{22}[Illustration: FIG. 14.—A series of diagrams of transverse sections
through _Peripatus_ embryos to show the relations of the coelom at
successive stages. (After Sedgwick.) A, Early stage: 1, gut; 2, mesoblastic
somite; no trace of the vascular space; endoderm and ectoderm in contact.
B, Endoderm has separated from the dorsal and ventral ectoderm. The somite
is represented as having divided on the left side into a dorsal and ventral
portion: 1, gut; 2, somite; 3, haemocoele. C, The haemocoele (3) has become
divided up into a number of spaces, the arrangement of which is
unimportant. The dorsal part of each somite has travelled dorsalwards, and
now constitutes a small space (triangular in section) just dorsal to the
gut. The ventral portion (2′) has assumed a tubular character, and has
acquired an external opening. The internal vesicle is already indicated,
and is shown in the diagram by the thinner black line: 1, gut; 2′,
nephridial part of coelom; 3, haemocoele; 3′, part of haemocoele which will
form the heart—the part of the haemocoele on each side of this will form
the pericardium; 4, nerve-cord. D represents the conditions at the time of
birth; numbers as in C, except 5, slime glands. The coelom is represented
as surrounded by a thick black line, except in the part which forms the
internal vesicle of the nephridium.]
The relations of the somites is shown in Fig. 14, A, which represents a
transverse section taken between the mouth and anus of an embryo of the
stage of Fig. 13, D. The history of these somites is an exceedingly
interesting one, and may be described shortly as follows:—They divide into
two parts—a ventral part, which extends into the appendage, and a dorsal
part (Fig. 14, B). The ventral part acquires an opening to the exterior
just outside the nerve-cord, and becomes entirely transformed into a
nephridium (Fig. 14, D, 2′). The dorsal part shifts dorsalwards and
diminishes relatively in size (Fig. 14, C). Its fate differs in the
different parts {23}of the body. In the anterior somites it dwindles and
disappears, but in the posterior part it unites with the dorsal divisions
of contiguous somites of the same side, and forms a tube—the generative
tube (Fig. 14, D, 2). The last section of this tube retains its connexion
with the ventral portion of the somite, and so acquires an external
opening, which is at first lateral, but soon shifts to the middle line, and
fuses with its fellow, to form the single generative opening. The praeoral
somite develops the rudiment of a nephridium, but eventually entirely
disappears. The jaw somite also disappears; the oral papilla somite forms
ventrally the salivary glands, which are thus serially homologous with
nephridia. The perivisceral cavity of _Peripatus_ is, as in all Arthropoda,
a haemocoele. Its various divisions develop as a series of spaces between
the ectoderm and endoderm, and later in the mesoderm. The mesoderm seems to
be formed entirely from the proliferation of the cells of the mesoblastic
somites. It thus appears that in _Peripatus_ the coelom does not develop a
perivisceral portion, but gives rise only to the renal and reproductive
organs.
SYNOPSIS OF THE SPECIES OF PERIPATUS.
PERIPATUS, Guilding.
Soft-bodied vermiform animals, with one pair of ringed antennae, one pair
of jaws, one pair of oral papillae, and a varying number of claw-bearing
ambulatory legs. Dorsal surface arched and more darkly pigmented than the
flat ventral surface. Skin transversely ridged and beset by wart-like
spiniferous papillae. Mouth anterior, ventral; anus posterior, terminal.
Generative opening single, median, ventral, and posterior. One pair of
simple eyes. Brain large, with two ventral hollow appendages; ventral
cords widely divaricated, without distinct ganglia. Alimentary canal
simple, uncoiled. Segmentally arranged, paired nephridia are present.
Body cavity is continuous with the vascular system, and does not
communicate with the paired nephridia. Heart tubular, with paired ostia.
Respiration by means of tracheae. Dioecious; males smaller and generally
less numerous than females. Generative glands tubular, continuous with
the ducts. Viviparous. Young born fully developed. They shun the light,
and live in damp places beneath stones, leaves, and bark of rotten
stumps. They eject when irritated a viscid fluid through openings at the
apex of the oral papillae.
Distribution: South Africa, New Zealand, and Australia, South America and
the West Indies [and in Sumatra?].
{24}SOUTH AFRICAN SPECIES.
With three spinous pads on the legs and two primary papillae on the
anterior side of the foot, and one accessory tooth on the outer blade of
the jaw; with a white papilla on the ventral surface of the last fully
developed leg of the male. Genital opening subterminal, behind the last
pair of fully-developed legs. The terminal unpaired portion of vas
deferens short. Ova of considerable size, but with only a small quantity
of food-yolk. (Colour highly variable, number of legs constant in same
species (?).)
P. CAPENSIS (Grube).—South African _Peripatus_, with seventeen pairs of
claw-bearing ambulatory legs. Locality, Table Mountain.
P. BALFOURI (Sedgwick).—South African _Peripatus_, with eighteen pairs of
claw-bearing ambulatory legs, of which the last pair is rudimentary. With
white papillae on the dorsal surface. Locality, Table Mountain.
P. BREVIS (De Blainville).—South African _Peripatus_, with fourteen pairs
of ambulatory legs. Locality, Table Mountain. (I have not seen this
species. Presumably it has the South African characters.)
P. MOSELEYI (Wood Mason).—South African _Peripatus_, with twenty-one and
twenty-two pairs of claw-bearing ambulatory legs. Locality, near
Williamstown, Cape Colony; and Natal.[7]
_Doubtful Species._
(1) South African _Peripatus_, with twenty pairs of claw-bearing
ambulatory legs (Sedgwick). Locality, Table Mountain. (Also Peters,
locality not stated.)
(2) South African _Peripatus_, with nineteen pairs of ambulatory legs
(Trimen). Locality, Plettenberg Bay, Cape Colony. (Also Peters, locality
not stated.)
AUSTRALASIAN SPECIES.
With fifteen pairs of claw-bearing ambulatory legs, with three spinous
pads on the legs, and a primary papilla projecting from the median dorsal
portion of the feet. Genital opening between the legs of the last pair.
Receptacula seminis present. Unpaired portion of vas deferens long and
complicated. Ova large and heavily charged with yolk. (Colour variable,
number of legs constant in same species (?).)
P. NOVAE ZEALANDIAE (Hutton).—Australasian _Peripatus_, without an
accessory tooth on the outer blade of the jaw, and without a white
papilla on the base of the last leg of the male. New Zealand.
P. LEUCKARTI (Saenger).—Australasian _Peripatus_, with an accessory tooth
on the outer blade of the jaw, and a white papilla on the base of the
last leg of the male. Queensland.
NEOTROPICAL SPECIES.
With four spinous pads on the legs, and the generative aperture between
{25}the legs of the penultimate pair. Dorsal white line absent. Primary
papillae divided into two portions. Inner blade of jaw with gap between
the first minor tooth and the rest. Oviducts provided with receptacula
ovorum and seminis. Unpaired part of vas deferens very long and
complicated. Ova minute, without food-yolk. (Colour fairly constant,
number of legs variable in same species (?).)
P. EDWARDSII.[8]—Neotropical _Peripatus_ from Caracas, with a variable
number of ambulatory legs (twenty-nine to thirty-four). Males with
twenty-nine or thirty legs, and tubercles on a varying number of the
posterior legs. The basal part or the primary papilla is cylindrical.
P. TRINIDADENSIS (n. sp.).—Neotropical _Peripatus_ from Trinidad, with
twenty-eight to thirty-one pairs of ambulatory legs, and a large number
of teeth on the inner blade of the jaw. The basal portion of the primary
papillae is conical.
P. TORQUATUS (Kennel).— Neotropical _Peripatus_ from Trinidad, with
forty-one to forty-two pairs of ambulatory legs. With a transversely
placed bright yellow band on the dorsal surface behind the head.
_Doubtful Species._
The above are probably distinct species. Of the remainder we do not know
enough to say whether they are distinct species or not. The following is
a list of these doubtful species, with localities and principal
characters:—
P. JULIFORMIS (Guilding).—Neotropical _Peripatus_ from St. Vincent, with
thirty-three pairs of ambulatory legs.
P. CHILIENSIS (Gay).—Neotropical _Peripatus_ from Chili, with nineteen
pairs of ambulatory legs.
P. DEMERARANUS (Sclater).—Neotropical _Peripatus_ from Maccasseema,
Demerara, with twenty-seven to thirty-one pairs of ambulatory legs and
conical primary papillae.
PERIPATUS FROM CAYENNE (Audouin and Milne-Edwards).—With thirty pairs of
legs. Named P. EDWARDSII by Blanchard.
PERIPATUS FROM VALENTIA LAKE, COLUMBIA (Wiegmann).—With thirty pairs of
legs.
PERIPATUS FROM ST. THOMAS (Moritz).—No description.
PERIPATUS FROM COLONIA TOWAR, VENEZUELA (Grube).—With twenty-nine to
thirty-one pairs of ambulatory legs. Named P. EDWARDSII by Grube.
PERIPATUS FROM SANTO DOMINGO, NICARAGUA (Belt).—With thirty-one pairs of
ambulatory legs.
PERIPATUS FROM DOMINICA (Angas).—Neotropical _Peripatus_, with twenty-six
to thirty (Pollard) pairs of ambulatory legs.
PERIPATUS FROM JAMAICA (Gosse).—With thirty-one and thirty-seven pairs of
ambulatory legs.
PERIPATUS FROM SANTARAM.—Neotropical _Peripatus_, with thirty-one pairs
of ambulatory legs.
PERIPATUS FROM CUBA.—No details.
{26}PERIPATUS FROM HOORUBEA CREEK, DEMERARA (Quelch).—With thirty pairs
of legs.
PERIPATUS FROM MARAJO (Branner).—No details.
PERIPATUS FROM UTUADO, PORTO RICO (Peters).—With twenty-seven, thirty,
thirty-one, and thirty-two pairs of legs.
PERIPATUS FROM SURINAM (Peters).—No details.
PERIPATUS FROM PUERTO CABELLO, VENEZUELA (Peters).—With thirty and
thirty-two pairs of legs.
PERIPATUS FROM LAGUAYRA, VENEZUELA (Peters).—No details.
PERIPATUS QUITENSIS (Schmarda).—From Quito, with thirty-six pairs of
legs.
PERIPATUS FROM SUMATRA (?).
P. SUMATRANUS (Horst).—_Peripatus_ from Sumatra, with twenty-four pairs
of ambulatory legs, and four spinous pads on the legs. The primary
papillae of the neotropical character with conical bases. Generative
opening between the legs of the penultimate pair. Feet with only two
papillae.[9]
SUMMARY OF DISTRIBUTION
DISTRIBUTION OF THE SOUTH AFRICAN SPECIES—
Slopes of Table Mountain, neighbourhood of Williamstown, Plettenberg
Bay—Cape Colony—Natal.
DISTRIBUTION OF THE AUSTRALASIAN SPECIES—
Queensland—Australia.
North and South Islands—New Zealand.
ORIENTAL REGION (?)—
Sumatra.
DISTRIBUTION OF THE NEOTROPICAL SPECIES—
Nicaragua.
Valencia Lake, Caracas, Puerto Cabello, Laguayra, Colonia
Towar—Venezuela.
Quito—Ecuador.
Maccasseema, Hoorubea Creek—Demerara.
Surinam (Peters).
Cayenne.
Santarem, Marajo, at the mouth of the Amazon—Brazil.
Chili.
And in the following West Indian Islands—Cuba, Dominica, Porto Rico
(Peters), Jamaica, St. Thomas, St. Vincent, Trinidad.
MYRIAPODA
BY
F. G. SINCLAIR, M.A.
(FORMERLY F. G. HEATHCOTE)
Trinity College, Cambridge.
{29}CHAPTER II
MYRIAPODA
INTRODUCTION–HABITS–CLASSIFICATION–STRUCTURE–CHILOGNATHA–CHILOPODA–
SCHIZOTARSIA–SYMPHYLA–PAUROPODA–EMBRYOLOGY–PALAEONTOLOGY.
_Tracheata_ with separated head and numerous, fairly similar segments. They
have one pair of antennae, two or three pairs of mouth appendages, and
numerous pairs of legs.
The Myriapoda are a class of animals which are widely distributed, and are
represented in almost every part of the globe. Heat and cold alike seem to
offer favourable conditions for their existence, and they flourish both in
the most fertile and the most barren countries.
They have not attracted much notice until comparatively recent times.
Compared with Insects they have been but little known. The reason of this
is not hard to find. The Myriapods do not exercise so much direct influence
on human affairs as do some other classes of animals; for instance,
Insects. They include no species which is of direct use to man, like the
silkworm or the cochineal insect, and they are of no use to him as food. It
is true that they are injurious to his crops. For instance, the species of
Millepede known as the "wire worm"[10] is extremely harmful; but this has
only attracted much notice in modern times, when land is of more value than
formerly, and agriculture is pursued in a more scientific manner, and the
constant endeavour to get the utmost amount of crop from the soil has
caused a minute investigation into the various species of animals which are
noxious to the growing crop. The species of {30}Myriapoda best known to the
ancients were those which were harmful to man on account of their poisonous
bite.
Some writers have supposed that the word which is translated "mole" in the
Bible (Lev. xi. 30) is really _Scolopendra_ (a genus of Centipede), and, if
this is so, it is the earliest mention of the Myriapods. They were rarely
noticed in the classical times; almost the only mention of them is by
Ælian, who says that the whole population of a town called Rhetium were
driven out by a swarm of Scolopendras. Pliny tells us of a marine
Scolopendra, but this was most probably a species of marine worm.
Linnaeus included Myriapods among the Insects; and the writers after him
till the beginning of this century classed them with all sorts of Insects,
with Spiders, Scorpions, and even among Serpents. It was Leach who first
raised them to the importance of a separate class, and Latreille first gave
them the name of Myriapoda, which they have retained ever since.
Myriapods are terrestrial animals, crawling or creeping on the ground or on
logs of wood, or even under the bark of trees. There is, however, a partial
exception to this; various naturalists have from time to time given
descriptions of marine Centipedes. These are not found in the sea, but
crawl about on the shore, where they are submerged by each tide. Professor
F. Plateau has given an account of the two species of Myriapods that are
found thus living a semi-aquatic life. They are named _Geophilus maritimus_
and _Geophilus submarinus_, and Plateau found that they could exist in sea
water from twelve to seventy hours, and in fresh water from six to ten
days. They thus offer a striking example of the power that their class
possess of existing under unfavourable circumstances.
With regard to their habits the different species differ very considerably.
On the one hand we have the Chilopoda, or Centipedes, as they are called in
this country, active, swift, and ferocious; living for the most part in
dark and obscure places, beneath stones, logs of wood, and dried leaves,
etc., and feeding on living animals. On the other hand, we have the
Chilognatha, or Millepedes, distinguished by their slow movements and
vegetable diet; inoffensive to man, except by the destruction they occasion
to his crops, and having as a means of defence no formidable weapon like
the large poison claws of the Centipedes, but only a peculiarly offensive
liquid secreted by special glands {31}known by the unpleasant though
expressive name of "stink glands," or by the more euphonious Latin name of
_glandulae odoriferae_.
As a general rule the larger species of Myriapods are found in the hotter
climates, some of the tropical species being very large, and some, among
the family of the Scolopendridae, extremely poisonous; and it is even said
that their bite is fatal to man.
[Illustration: FIG. 15.—_Scolopendra obscura._ (From C. L. Koch, _Die
Myriapoden_.)]
If, however, the Centipede is sometimes fatal to man, it does not always
have it its own way, for we read of man making food of Centipedes. It is
hard to believe that any human being could under any circumstances eat
Centipedes, which have been described by one naturalist as "a disgusting
tribe loving the darkness." Nevertheless, Humboldt informs us that he has
seen the Indian children drag out of the earth Centipedes eighteen inches
long and more than half an inch wide and devour them.
[Illustration: FIG. 16.—_Chordeuma sylvestre._ (From C. L. Koch, _Die
Myriapoden_.)]
This, I believe, is the only account of human beings using the Myriapoda as
food, if we except the accounts of the religious fanatics among the African
Arabs, who are said to devour Centipedes alive; though this is not a case
of eating for pleasure, for the Scolopendras are devoured in company with
leaves of the prickly pear, broken glass, etc., as a test of the unpleasant
things which may be eaten under the influence of religious excitement.
{32}A cold climate, however, is not fatal to some fairly large species of
Centipedes. A striking instance of this came under my own observation some
years ago. In 1886 I was travelling in the island of Cyprus—the "Enchanted
Island," as Mr. Mallock calls it in his book written about the same
time—with the intention of observing its natural history. This island
consists of a broad flat country crossed by two mountain ranges of
considerable height, thus offering the contrast of a hot climate in the
plains and a cold climate in the mountains. On the plain country I found
among the Myriapoda that the most common species were a large _Scolopendra_
and a large _Lithobius_. The _Scolopendra_ was fairly common, living for
the most part under large stones, and it was a pleasant task to search for
them in a ruined garden near Larnaca.
This garden was made for the public, and is situated about a quarter of a
mile from the old town of Larnaca. It has been suffered to fall into decay,
and is now quite neglected. Mr. Mallock has described many beautiful scenes
in his book, but I think he could have found few more beautiful than this
old garden with its deserted gardener's house, now a heap of ruins, but
overgrown with masses of luxuriant vegetation, with beautiful flowers
peeping out here and there as if charitably endeavouring to hide the
negligence of man, and to turn the desolation into a scene of beauty. I got
several prizes in this garden, but found the Myriapods were principally
represented by the species I have mentioned.
After leaving Larnaca I rode across the plain country through blazing heat,
which was rapidly parching up the ground to a uniform brown colour. At
every stopping-place I found the same species of _Scolopendra_ and of
_Lithobius_. After a few days I began to get up among the mountains of the
northern range, and the burning heat of the treeless plain was gradually
exchanged for the cool shade of the pine-trees and the fresh air of the
mountains. As I ascended higher and higher the temperature grew cooler till
I reached the top of Mount Troodos, the ancient Olympus. Here in the month
of May the snow still lingered in white patches, and the air was clear and
cold. I remained on the top of Troodos for a week, while I made a close
examination of the fauna to be found there. I was much surprised to find
the identical species of _Scolopendra_ and {33}_Lithobius_ with which I had
become acquainted in the heat of the low country, quite at home among the
snow, and as common as in, what I should have imagined to be, the more
congenial climate. Nor were they any the less lively. Far from exhibiting
any sort of torpor from the cold, the first one which I triumphantly seized
in my forceps wriggled himself loose and fastened on my finger with a
vigour which made me as anxious to get rid of him as I had formerly been to
secure him. However, he eventually went into my collecting box.
On the whole, we may say that the Chilopoda are most largely represented in
the hotter climates, where they find a more abundant diet in the rich
insect life of the tropical and semi-tropical countries. The more
brightly-coloured Myriapods, too, are for the most part inhabitants of the
warmer countries. The ease with which they are introduced into a country in
the earth round plants, and in boxes of fruit, may account to a great
extent for the wide distribution of the various species in different
countries. Mr. Pocock, who examined the Myriapods brought back from the
"Challenger" Expedition, informs us that of ten species brought from
Bermuda, four had been introduced from the West Indies. There is no doubt
that animals which can bear changes of temperature and deprivation of food,
and even a short immersion in the water, are well calculated to be
introduced into strange countries in many unexpected ways.
As might be expected from a class of animals so widely distributed,
Myriapods show an almost infinite variety of size and colour. We find them
so small that we can hardly see them with the naked eye, as in the case of
the tiny _Polyxenus_, the Pauropidae, and the Scolopendrellidae. We also
find them more than six inches in length, as the larger species of
Scolopendridae. I am afraid we must dismiss as an exaggeration an account
of Centipedes in Carthagena a yard in length, and more than six inches in
breadth. The giver of this account—Ulloa—informs us that the bite of this
gigantic serpent-like creature is mortal if a timely remedy be not applied.
It is certainly extremely probable that the bite of a Centipede of this
size would be fatal to any one. Some Centipedes are short and broad, and
composed of few segments, as _Glomeris_; some are long and thin, with more
than a hundred segments, as _Geophilus_. They may be beautifully coloured
with brilliant streaks of colour, as in some {34}of the Julidae or
Polydesmidae, or may be of a dull and rusty iron colour, or quite black.
One of the strangest peculiarities found among Myriapods is that some of
them (e.g. _Geophilus electricus_) are phosphorescent. As I was walking one
summer evening near my home in Cambridgeshire I saw what I thought was a
match burning. Looking more closely, I saw it move, and thinking it was a
glow-worm I picked it up, and was surprised to find that it was a
_Geophilus_ shining with a brilliant phosphorescent light. I let it crawl
over my hand, and it left a bright trail of light behind it, which lasted
some time. I have been told that this species is common in Epping Forest;
also in Cambridgeshire.[11]
Besides _G. electricus_, _G. phosphoreus_ has been described as a luminous
species by Linnaeus, on the authority of a Swedish sea captain, who
asserted that it dropped from the air, shining like a glow-worm, upon his
ship when he was sailing in the Indian Ocean a hundred miles from land.
What the use of this phosphorescence may be is not known with any degree of
certainty. It may be either a defence against enemies, or else a means of
attracting the two sexes to one another.
The places which the Myriapods select for their habitation vary as much as
their colour and size, though, with a few exceptions, they chose dark and
obscure places. A curious species of Myriapod is _Pseudotremia cavernarum_
(Cope), which is found in certain caves in America. The peculiar life it
leads in these caves seems to have a great influence on its colour, and
also affects the development of its eyes. Mr. Packard's account of them is
worth quoting: "Four specimens which I collected in Little Wyandotte cave
were exactly the same size as those from Great Wyandotte cave. They were
white tinged, dusky on the head and fore part of the body. The eyes are
black and the eye-patch of the same size and shape, while the antennae are
the same.
"Six specimens from Bradford cave, Ind. (which is a small grotto formed by
a vertical fissure in the rock, and only 300 to 400 yards deep), showed
more variation than those from the two Wyandotte caves. They are of the
same size and form, but slightly longer and a little slenderer.... The
antennae are much whiter than in those from the Wyandotte caves, and the
{35}head and body are paler, more bleached out than most of the Wyandotte
specimens.... It thus appears that the body is most bleached and the eyes
the most rudimentary in the Bradford cave, the smallest and most
accessible, and in which consequently there is the most variation in
surroundings, temperature, access of light and changed condition of air.
Under such circumstances as these we should naturally expect the most
variation."[12]
A strong contrast to these animals is afforded us by the Scutigeridae
(Schizotarsia). They are unknown in this country, but abound in some of the
Mediterranean countries and in parts of Africa. They remind one strongly of
spiders, with their long legs and their peculiar way of running on stones
and about the walls of houses.
[Illustration: FIG. 17.—_Cermatia (Scutigera) variegata._ (From C. L. Koch,
_Die Myriapoden_.)]
Some years ago I was in Malta, and I used to go and watch them on the
slopes outside Valetta, where they were to be found in great numbers. They
used to come out from beneath great stones and run about rapidly on the
ground or on the stones and rubbish with which the ground was covered, now
and again making a dart at some small insect which tempted them, and
seemingly not minding the blazing sun at all. As might be expected from
their habits, their eyes, far from being rudimentary, like those of the
cave-living _Pseudotremia_, or absent {36}like those of the Polydesmidae,
or of our own _Cryptops_, are highly developed, and form the only example
among the Myriapods of what are known as facetted eyes. The Scutigeridae
are also remarkable among Myriapods for the possession of a peculiar
sense-organ which is found in no other Myriapod.
The Myriapods most numerous in our own country are _Lithobius_ and _Julus_.
_Lithobius_, which will be described later on, may be found in almost any
garden under dried leaves, stones, etc. _Julus_, the common wire-worm, is
found crawling on plants and leaves and under the bark of trees, and does a
good deal of damage in a garden. _Polydesmus_ is also frequently found in
great numbers, and usually a great many of them together. _Glomeris_ is
also found, though it is not so common as the first two mentioned animals.
_Geophilus_ is also common, and especially in the south of England.
Scolopendridae are only represented by a single genus, _Cryptops_, which is
not very common, though by no means rare. The best place to find them is in
manure heaps. The animals of this species are small compared to most
Scolopendras, and have the peculiarity of being without any eyes.
_Scutigera_ is unrepresented in this country. One was found in Scotland
some years ago by Mr. Gibson Carmichael, but was shown to have been
imported, and not bred in the place.
The means of defence possessed by these animals also differ very much in
the different species of Myriapods. In the Centipedes the animals are
provided with a powerful weapon in the great poison claws which lie just
beneath the mouth, and which are provided with large poison glands, which
supply a fluid which runs through a canal in the hard substance of the claw
and passes into the wound made by the latter. The effect of this fluid is
instantaneous on the small animals which form the food of the Centipedes. I
have myself watched _Lithobius_ in this country creep up to a blue-bottle
fly and seize it between the poison claws. One powerful nip and the
blue-bottle was dead, as if struck by lightning. I have also seen them kill
worms and also other _Lithobius_ in the same way. When another _Lithobius_
is wounded by the poison claws it seems to be paralysed behind the wound.
The Millepedes, on the other hand, have no such offensive and defensive
weapon. They rely for protection on the fluid secreted by the _stigmata
repugnatoria_ (or _glandulae odoriferae_) mentioned before. This fluid has
been shown to contain prussic acid, and has a very unpleasant odour.
{37}[Illustration: FIG. 18.—_Polyxenus lagurus_ (From C. L. Koch, _Die
Myriapoden_).]
Most of the Millepedes are provided with these glands; but in the cave
Myriapods mentioned before, the animals have not to contend against so many
adversaries, and these glands almost disappear. Other Myriapods defend
themselves by means of the long and stiff bristles with which they are
provided, _e.g._ the little _Polyxenus_. This means of defence seems to
have been more common among the fossil Myriapods than among those still
living. Variations in the shape and size of the limbs are numerous, as
might be expected in so large a class of animals. One of the most curious
of such variations is found in a Centipede of the Scolopendra tribe, called
_Eucorybas_, in which the last limbs are flattened out and provided with
paddle-shaped lobes. The use of these is unknown, but it is probable that
they are concerned in some way with the breeding habits of the animal. The
habits of the Myriapods connected with their breeding are most interesting,
but have been very insufficiently investigated. There is no doubt that a
full inquiry into all such habits would be of great interest, and would
help to answer some of the problems which are still unsolved in these
forms. My own observations refer to two forms—_Julus terrestris_ among the
Millepedes, and _Lithobius forficatus_ among the Centipedes. _Julus
terrestris_ is one of the most common of the English Millepedes, and can be
easily obtained. I kept them in large shallow glass vessels with a layer of
earth at the bottom, and thus was able easily to watch the whole process.
They breed in the months of May, June, and July. The female _Julus_ when
about to lay her eggs sets to work to form a kind of nest or receptacle for
her eggs. She burrows down into the earth, and at some distance below the
surface begins the work. She moistens small bits of earth with the sticky
fluid secreted by her salivary glands, which become extraordinarily active
in the spring. She works up these bits of earth with her jaws and front
legs till they are of a convenient size and shape, and places them
together. When complete, the nest is shaped like a hollow sphere, the
inside being smooth and even, while the outside is rough and shows the
shape of the small knobs of earth of which it is composed. {38}She leaves a
small opening in the top. The size of the whole nest is about that of a
small nut. When she is ready to lay her eggs she passes them through the
hole in the top, and usually lays about 60 to 100 eggs at a time. The eggs,
which are very small, are coated with a glutinous fluid which causes them
to adhere together. When they are all laid she closes up the aperture with
a piece of earth moistened with her saliva; and having thus hermetically
sealed the nest, she leaves the whole to its fate. The eggs hatch in about
twelve days.
A naturalist named Verloef has lately found that the males of some Julidae
undergo certain changes in the form of the legs and other organs in autumn
and spring. These changes are probably connected with the breeding of the
animal, and remind us of the changes undergone during the breeding season
by salmon among the fishes.
_Julus_ breed very readily if carefully attended to and well supplied with
food. If they cannot obtain the food they like they will not breed so well.
I found that sliced apples with leaves and grass formed the best food for
them.
The process in the case of _Lithobius_ is much harder to watch. _Lithobius_
is not so plentiful as _Julus terrestris_, and the animals are more
impatient of captivity, more shy in their habits, and do not breed so
readily.
In January 1889 I was given the use of a room in the New Museums at
Cambridge, and was allowed to fit it up as I liked, so that I was able to
try the effect of different degrees of light and darkness, and of different
degrees of warmth. I succeeded in observing the whole process. The female
_Lithobius_ is furnished with two small movable hooks at the end of the
under surface of the body close to the opening of the oviduct. These small
hooks have been observed by many naturalists, but their use has, so far as
I know, never been described before. They play an important part in the
proceedings following the laying of the egg. The time of breeding in
_Lithobius_ is rather later than in _Julus_, and begins about June and
continues till August. There are first of all some convulsive movements of
the last segments of the body, and then in about ten minutes the egg
appears at the entrance of the oviduct. The egg is a small sphere (about
the size of a number five shot), rather larger than that of _Julus_, and is
covered with a sticky slime {39}secreted by the large glands inside the
body, usually called the accessory glands. When the egg falls out it is
received by the little hooks, and is firmly clasped by them. This is the
critical moment in the existence of the _Lithobius_ into which the egg is
destined to develop. If a male _Lithobius_ sees the egg he makes a rush at
the female, seizes the egg, and at once devours it. All the subsequent
proceedings of the female seem to be directed to the frustration of this
act of cannibalism. As soon as the egg is firmly clasped in the little
hooks she rushes off to a convenient place away from the male, and uses her
hooks to roll the egg round and round until it is completely covered by
earth, which sticks to it owing to the viscous material with which it is
coated; she also employs her hind legs, which have glands on the thighs, to
effect her purpose. When the operation is complete the egg resembles a
small round ball of mud, and is indistinguishable from the surrounding
soil. It is thus safe from the voracious appetite of the male, and she
leaves it to its fate. The number of eggs laid is small when compared with
the number laid by _Julus_.
The food in the case of _Lithobius_ consisted of worms and blue-bottles,
which were put alive into the glass vessel containing the _Lithobius_. I
tried raw meat chopped up, but they did not thrive on it in the same way
that they did on the living animals. I also put into their vessel bits of
rotten wood containing larvae of insects, etc.
I have succeeded in bringing back some specimens of _Polydesmus_ alive from
Madeira, and in getting them to breed in this country—of course in
artificial warmth—and their way of laying eggs and making a nest resembles
that of _Julus_. _Geophilus_ has one curious habit in connexion with the
fertilisation of the female. The male spins a web and deposits in the
middle of it a single spermatophore, and the female comes to the web to be
fertilised. The Scolopendridae are said to bring forth their young alive,
but I think the evidence for this is unsatisfactory. What have been taken
for the young Scolopendrae are perhaps the large spermatophores of the
male, which are not unlike a larval Myriapod in size and shape. I have
never been able to observe the process of breeding in this family. I have
had the spermatophores sent me from Gibraltar as "eggs," but a little
examination soon showed me their real character.
{40}The mode of progression in the Myriapods differs considerably, as might
be expected in a class in which the number of legs varies to such an
extent. The swiftest among them are the Scutigeridae with their long
spider-like legs. The Scolopendridae are also able to move with
considerable rapidity, and are also able to move tail forward almost as
well as in the ordinary manner. Where there are such a number of legs it
becomes a curious question as to the order in which the animal moves them;
and though several people have endeavoured to find this out, the number of
legs to be moved and the rapid movements have rendered accurate observation
impossible.
Some years ago Professor E. Ray Lankester tried to study the order in which
the legs of Centipedes moved, and came to the conclusion (recorded in an
amusing letter in _Nature_, 23rd May 1889) that if the animal had to study
the question itself, it would not get on at all. He finishes his letter
with the following verses:—
A Centipede was happy quite
Until a toad in fun
Said, "Pray which leg moves after which?"
This raised her doubts to such a pitch,
She fell exhausted in the ditch,
Not knowing how to run.
The progression of Millepedes is much slower than that of the Centipedes,
and it is remarkable that when the animal is in motion a sort of wave runs
down the long fringe-like row of feet. I have endeavoured to make out this
motion, but have never been able to understand it satisfactorily. My belief
was that the feet were moved in sets of five.
This wave-like peculiarity of motion is described in a curious old book,
_An Essay towards a Natural History of Serpents_. Charles Owen, D.D.
London, 1742: "The Ambua, so the natives of Brazil call the Millepedes and
the Centipedes, are serpents. Those reptiles of thousand legs bend as they
crawl along, and are reckoned very poisonous. In these Multipedes the
mechanism of the body is very curious; in their going it is observable that
on each side of their bodies every leg has its motion, one regularly after
another, so that their legs, being numerous, form a kind of undulation, and
thereby communicate to the body a swifter progression than one could
imagine where {41}so many short feet are to take so many short steps, that
follow one another rolling on like the waves of the sea."
Before proceeding to the classification of Myriapods, which will form the
next part of this account, a few words on the common names for them may not
be without interest.
In English we have the names Centipede and Millepede, and the Continental
nations have similar names implying the possession of a hundred or a
thousand legs, as the German "Tausendfüsse" and the French "Millepieds." Of
course these are general words, simply implying the possession of a great
number of legs. But we have also among the peasantry a name for Centipedes
which conveys a much more accurate idea of the number. The people of the
eastern counties (I daresay the term is more widely spread) call them
"forty legs." This is not quite accurate, but as _Lithobius_ has 17 legs on
each side, and _Scolopendra_ (_Cryptops_ is the English species) has 21 on
each side, it is a better approximation than Centipede. But another country
has a still more accurate term. I found some _Scolopendra_ in Beyrout, and
asked my native servant what he called them. He gave them what I afterwards
found was the common Arab name for them, "‘arba wál ‘arbarin," forty-four
legs. Now the Scolopendras, which in hotter climates are the chief
representatives of the Centipedes, have actually forty-two legs, or, if the
poison claws are counted, forty-four. In looking up the Arab term for
Centipede I came across a curious description given of them by Avicenna,
the great Arabian physician: "This is an animal known for its habit of
going into ears. For the most part it is a palm's length" [about four
inches, which is the average length of many species]. "On each side of the
body it has twenty-two feet, and moves equally well either backwards or
forwards."
With regard to its alleged habit of going into ears, the learned Arabian
has evidently made a false imputation on the character of our animal, and
has probably relied too much on the stories told him. He has also
exaggerated in stating that it goes equally well either backwards or
forwards. Some Centipedes can go backwards very easily and well, though not
so well as forwards. Perhaps he preferred examining dead specimens, which
afford an easy opportunity of counting their legs, to experimenting with
living animals, which might have resented liberties taken with them.
{42}The Persians have several words for them, less accurate than the Arabs
and more like our own terms. For instance, they call them "Hazarpa," or
thousand feet, like our Millepedes; also "Sadpa," or hundred feet,
equivalent to our Centipedes. Another term resembles our common term before
mentioned, "Chehlpa," forty feet. A more figurative term is "tasbih dud," a
worm resembling a rosary with a hundred beads; this word is translated in
Richardson's Persian Dictionary as "a venomous insect having eight feet and
a piked tail."
CLASSIFICATION OF THE MYRIAPODA.
Two of the principal writers on the classification of the Myriapods are
Koch and Latzel, both of whom have classified the whole group. I do not
wish for a moment to undervalue the many authors who have done excellent
work on the classification of different groups and families, but I wish
here to give an outline of a classification of the whole class, and I
naturally have recourse to the authors who have treated the subject as a
whole.
Koch's two works, the _System der Myriapoden_[13] and _Die Myriapoden_,[14]
cover the whole range of the class, and his divisions are clearly marked
out and are easily understood, but both works are comparatively old. He
does not include the Scolopendrellidae or the Pauropidae, which are now
included by all naturalists in the Myriapoda. Latzel is a more recent
writer, and though his work is entitled _The Myriapods of the
Austro-Hungarian Empire_,[15] he gives much information about Myriapods not
found in Europe, and his work is fairly entitled to be considered as
embracing the whole class. He divides the Myriapods into four Orders,
including the Scolopendrellidae and Pauropidae. On the whole, I think it
will be better here to take the classification of Koch, and to add to it
the two Orders before mentioned, viz. Symphyla containing one family the
Scolopendrellidae, and Pauropoda with one family the Pauropidae.
The Orders are as follows:—
{43}Order I. CHILOGNATHA (= DIPLOPODA)
Antennae 7 joints, three anterior body rings with one pair of legs to each
ring. Posterior rings with two pairs of legs to each. Genital organs
opening ventrally on the anterior rings of the posterior part of the body,
_i.e._ on one of the anterior of the segments bearing two pairs of legs;
usually the 7th.
This Order is divided into eight families:—
Family 1. _Polyxenidae._
Ten body rings, not counting the neck-plate. Thirteen pairs of limbs.
Eyes hard to find, on the lateral corner of the head (Fig. 18, p. 37).
Family 2. _Glomeridae._
11 body rings. 17 pairs of legs. Eyes arranged in a row curved outwards.
[Illustration: FIG. 19.—_Glomeris marginata._ (From C. L. Koch, _Die
Myriapoden_.)]
Family 3. _Sphaerotheriidae._
12 body rings. 19 pairs of legs. Eyes crowded together in a cluster.
[Illustration: FIG. 20.—_Sphaerotherium grossum._ (From C. L. Koch, _Die
Myriapoden_.)]
Family 4. _Julidae._
Body cylindrical. More than 30 body rings. Many eyes crowded together in
a cluster.
[Illustration: FIG. 21.—_Julus nemorensis._ (From C. L. Koch, _Die
Myriapoden_.)]
{44}Family 5. _Blanjulidae._
Thin cylindrical body with more than 30 body rings. Eyes either absent
or in a simple row beneath the edge of the forehead.
[Illustration: FIG. 22.—_Blanjulus guttulatus._ (From C. L. Koch, _Die
Myriapoden_.)]
Family 6. _Chordeumidae._
Resemble the _Polydesmidae_ (Fam. 7), but the head is longer and less
rounded in the forehead. The antennae are placed more at the side of the
head. Eyes small and numerous, in a cluster. Body rings always 30 (Fig.
16).
Family 7. _Polydesmidae._
Body cylindrical, with a lobe or keel on the posterior part of the upper
surface of the body ring. Always 19 body rings. No eyes.
[Illustration: FIG. 23.—_Polydesmus collaris._ (From C. L. Koch, _Die
Myriapoden_.)]
Family 8. _Polyzoniidae_.
Body with varying number of rings arched transversely downwards and sharp
at the sides. The anterior part of the ring somewhat hidden. The eyes in
a simple row. The stigmata very small and placed near the lateral corner
of the body ring. Head small in proportion to the body.
[Illustration: FIG. 24.—_Polyzonium germanicum._ (From C. L. Koch, _Die
Myriapoden_.)]
Order II. CHILOPODA (or SYNGNATHA).
Antennae with many joints, at least 14. Only one pair of legs to each body
ring. The genital opening on the last ring of the body. Bases of the legs
widely separate.
There are four families in this Order:—
{45}Family 1. _Lithobiidae._
Body with 9 principal and 6 subsidiary rings. On both principal and
subsidiary rings one pair of legs, except on the last ring of the body.
Many eyes; the posterior ones large and kidney-shaped. The antennae with
many rings.
[Illustration: FIG. 25.—_Lithobius erythrocephalus._ (From C. L. Koch,
_Die Myriapoden_.)]
Family 2. _Scolopendridae._
Body with 21 or 23 rings, no intermediate rings. Every ring with one pair
of legs. The last pair very long. Last pair at the point of the last
ring. Four or no eyes. Antennae with 17 or 20 joints. (Fig. 15, p. 31).
Family 3. _Notophilidae._
[Illustration: FIG. 26.—_Notophilus taeniatus._ (From C. L. Koch, _Die
Myriapoden_.)]
Body very long, 200 to 350 rings; alternate principal and subsidiary
rings. A pair of legs to each principal ring. No eyes. Maxillary palps
{46}very thick. Compact or very short limbs. The terminal point of the
last limb without claws.
Family 4. _Geophilidae._
Body long, 80 to 180 rings, principal and subsidiary. No eyes. The
maxillary palps not compact, and with first joint large. Last joint of
the last pair of legs with a sharp claw.
[Illustration: FIG. 27.—_Geophilus longicornis._ (From C. L. Koch, _Die
Myriapoden_.)]
Order III. SCHIZOTARSIA.
The tarsi of all the legs multiarticulate. The eyes facetted. Peculiar
sense organ beneath the head.
Family 1. _Cermatiidae_ (_Scutigeridae_)
Antennae with unequal number of joints. Body rings, each with one pair of
legs. Dorsal scutes not so large as ventral. Limbs long and
multiarticulate. (Fig. 17, p. 35).
Order IV. SYMPHYLA.
Myriapods resembling Thysanura. A pair of limbs to each segment. The
antennae are simple and multiarticulate with unequal joints. Eyes few.
Mandibles short. One pair of maxillae. No maxillipedes. Genital orifice in
the last segment of the body. A single pair of tracheae. Two abdominal
glands on the posterior part of the body. Two caudal appendages. Free
dorsal scutes. Ventral scutes often with parapodia.
Family 1. _Scolopendrellidae._
With the characters of the Order.
{47}Order V. PAUROPODA.
A pair of limbs to each segment. Antennae branched. Eyes few or none.
Labrum and labium indistinct. Genital orifice at the base of the second
pair of limbs. Free dorsal scutes. Nine pairs of feet (always?). Some
segments with sensitive hairs. Last segment the smallest.
Family 1. _Pauropidae._
Body slender. Dorsal scutes smooth. Limbs long and projecting from the
lateral margins of the body. Colour pale.
THE STRUCTURE OF THE MYRIAPODA.
Having now given a short view of the classification of the Class, I will
proceed to give a general account of their structure, the variations in
which have led to the divisions into the various Orders and Families. Their
structure shows resemblances to several widely different classes of
animals. One cannot help being impressed with their likeness to the Worms,
at the same time they have affinities with the Crustaceans, and still more
with the Insects. In the latter class the likeness of the Thysanuridae to
_Scolopendrella_ and _Pauropus_ have induced a celebrated Italian
anatomist, Professor Grassi, to claim the former as the ancestors of the
Myriapoda.
Myriapods have a body which is segmented, as it is termed; that is,
composed of a number of more or less similar parts or segments joined
together.
One of the most important characteristics which distinguish Myriapods from
other Arthropoda is the fact that they possess on the posterior segments of
the body true legs which are jointed and take part in locomotion. The head
is in all cases quite distinct from the body, and may be regarded as a
number of segments fused together into one mass. Their heads are always
provided with a single pair of _antennae_ and mouth appendages, consisting
of an upper lip, a pair of _mandibles_ or jaws, and one to two pairs of
_maxillae_. The mandibles resemble those of Insects, and are strongly
toothed. In the Chilognatha a pair of maxillae are fused so as to form a
single oval appendage. In the Chilopoda they each consist of a single blade
bearing a {48}short palp or feeler. The mouth parts may have the forms
known as chewing, biting, or suctorial (_Polyzonium_) mouth appendages.
With the exception of the terminal segment, and in many cases the first or
the seventh, each segment bears one or two pairs of limbs. These may be
very long, as in _Scutigera_, or very short, as in _Polyxenus_. They may be
attached close to one another near the ventral middle line of the body, or
may have their bases far apart from each other, as in the Chilopoda. The
exoskeleton or external armour is composed of chitin (Chilopoda) or of
chitin with calcareous salts deposited in it (Chilognatha).
Their internal structure has a great likeness to that of Insects.
The general position of the internal organs may be seen from Fig. 28, which
shows a _Lithobius_ dissected so as to exhibit the digestive and nervous
systems.
_The digestive canal_, which is a straight tube, extends throughout the
whole length of the body, and terminates in the last segment of the body.
It may be divided into the following parts:—
1. A narrow oesophagus, beginning with the mouth or buccal cavity, and
receiving the contents of two or more salivary glands (_d_).
2. A wide mesenteron or mid-gut (_n_) extending throughout almost the
whole length of the body.
3. A rectum which at its junction with the mid-gut receives the contents
of two or four _Malpighian tubes_ (_g_, _h_) which function as kidneys.
Their function was for a long time unknown, but the discovery of crystals
of uric acid in them placed the matter beyond doubt.
_The heart_ has the form of a long pulsating dorsal vessel which extends
through the whole length of the animal. It is divided into a number of
chambers, which are attached to the dorsal wall of the body, and are
furnished with muscles of a wing-like shape, which are known as the alary
muscles, and which govern its pulsations. The chambers are furnished with
valves and arteries for the exit of the blood, and slits known as _ostia_
for the return of the blood to the heart. The blood enters the chambers of
the heart from the body cavity through the {49}ostia, and passes out
through the arteries to circulate through the organs of the body and to
return by the ostia.
[Illustration: FIG. 28.—_Lithobius_ dissected. (After Vogt and Yung.) _a_,
antennae. _b_, poison claws. _c_, brain. _d_, salivary glands. _e_, legs.
_f_, nerve cord. _g_, Malpighian tube. _h_, Malpighian tube. _i_, vesicula
seminalis. _j_, accessory gland. _k_, accessory gland. _l_, testis. _m_,
thigh gland. _n_, digestive tube. ]
The two figures below (Figs. 29 and 30) show the position of the arteries
and the ostia in a single segment of the body. The heart is too small and
delicate to be seen with the naked eye; it therefore requires the aid of
the microscope. A freshly-killed animal was therefore taken and prepared in
the manner known to all microscopists, and extremely thin slices or
sections cut horizontally from its back. One of these sections cut the
whole length of the heart in one segment, which was accordingly drawn under
the microscope (Fig. 29), and shows a longitudinal {50}horizontal section
through the whole length of the heart in a single segment, with the two
ostia at each end of the segment and the two arteries in the middle.
The arteries, when they leave the body, pass into masses of fatty tissue on
either side of the heart, and the other figure (Fig. 30) is intended to
show the artery leaving the heart and penetrating into the fatty tissue.
The figure is taken from the same section as the former one, but is much
more highly magnified, so as to show more detail. The delicate coats of the
heart are shown, the artery being covered with a clothing of large cells.
[Illustration: FIG. 29.—Heart of _Julus terrestris_ showing ostia (_ost_)
and arteries (_Art_) magnified.]
[Illustration: FIG. 30.—Heart of _Julus terrestris_ showing structure of
artery (_Art._) and external coat of heart (_ext.c_), also fat body (_Fb_),
highly magnified. _Ht_, The cavity of the heart. The circular muscle fibres
which surrounds the heart are shown just below the external coat (_ext.c_).
_ogl_, Oil globules of the fat body.]
Myriapods breathe by means of _tracheae_, with the exception of the
Scutigeridae, which have an elementary form of lung which resembles that of
spiders, and will be mentioned further on. These tracheae, as in Insects,
are tubes lined with chitin, which is arranged in spiral bands. The
tracheae open to the exterior by openings called _stigmata_, through which
they receive the external air, which passes into the main tracheal tubes
and into their ramifications, and thus effects the aeration of the blood.
The _nervous system_ of the Myriapods consists, as in Insects, of a brain,
which may be more or less developed, a circumoesophageal ring embracing the
oesophagus, and a ventral chain of ganglia, and in some cases (Newport) of
a system of visceral {51}nerves. With the nervous system we may mention the
sense organs, the eyes, which are present in most cases, though wanting, as
has been already stated, in many groups. They are usually present as
clusters of ocelli or eye spots closely packed together, or (in
_Scutigera_) as peculiarly formed facetted eyes. The sensory hairs on the
antennae must be reckoned as sense organs, as also the tufts of sense hairs
on the head of _Polyxenus_. _Scutigera_ has also a peculiar sense organ
beneath the head, consisting of a sac opening on the under side of the head
full of slender hairs, each of which is connected at its base with a nerve
fibre. Except the eyes, the Myriapod sense organs have usually the form of
hairs or groups of hairs connected with nerve fibres, which communicate
with the central nervous system.
[Illustration: FIG. 31.—Under side of the head of _Scutigera coleoptrata_,
with sense organ. _eo_, Opening of sense organ to the exterior; _o_, sense
organ shown through the chitin; _m_, mouth; _oc_, eye; _mxl_, maxilla; _f_,
furrow in the chitin. (Heathcote, Sense organ in _Scutigera coleoptrata_.)]
[Illustration: FIG. 32.—Highly magnified section through head of _Polyxenus
lagurus_, showing sense organ. _ext.cut_, external cuticle; _t_, tube
surrounding base of sense hair; _gang.c_, ganglion cell. (Heathcote,
Anatomy of _Polyxenus lagurus_.)]
These two sense organs are shown in Figs. 31 and 32. Fig. 31 shows the
under side of the head of _Scutigera_ (Fig. 17), with the position of the
sense organ and its opening. Fig. 32 is part of a section through the head
of _Polyxenus_ with two of the sense hairs. Each spine or sense hair fits
into a cup in the chitin of the head; and the lower or internal part, which
is divided from the upper or external part by a rim, is joined to a
ganglionic nerve cell (_gang.c._).
The Myriapods are of separate sexes, and the generative organs in both
cases usually have the form of a long unpaired {52}tube, which in the male
is connected with accessory glands, and in the female is usually provided
with double receptacula seminis. The generative openings usually lie near
the base of the second pair of legs (Chilognatha), or at the posterior end
of the body (Chilopoda). In the Chilognatha there is usually in the male an
external copulatory organ at the base of the seventh pair of legs, remote
from the genital opening.
The preceding account of the anatomy of the Myriapods has shown us the
general characteristics of the whole group. I shall now take each of the
five Orders into which the class is divided in the classification adopted
in this account, and endeavour to explain the differences in anatomy which
have led to the establishment of the Order. The first Order with which we
have to do is that of the Chilognatha, which includes a large number of
Myriapods; no less than eight families, some of them including a great
number of forms.
ORDER I. CHILOGNATHA.
The Chilognatha differ from other Orders in the shape of the body. This is
in almost all cases, cylindrical or sub-cylindrical, instead of being more
or less flattened as in the other Orders.
The body, as in all other Myriapods, is composed of segments, but in the
Chilognatha these segments are composed, in almost all cases, of a complete
ring of the substance of which the exoskeleton (as the shell of the animal
is called) is composed. This substance is in the case of the Chilognatha
chitin (a kind of horny substance, resembling, for instance, the outer case
of a beetle's wing), containing a quantity of chalk salts and colouring
matter; the substance thus formed is hard and tough. In other Orders the
chitin of the exoskeleton is without chalky matter and is much more
flexible. The length of the body, as may be seen from the classification,
may be either very long, as in _Julus_, or very short, as in _Glomeris_.
The next anatomical character distinctive of the Order is the form of the
appendages. First, the antennae. These are, as a general rule, much shorter
than in the Chilopods, never reaching the length of half the body. They
are, as a rule, club-shaped, the terminal half being thicker than the half
adjoining the body.
{53}The next appendages to be mentioned are the _mouth parts_. These differ
in form from those of the other Orders, and their differences are connected
very largely with the fact that the Chilognatha live on vegetable
substances. Their mouth parts are adapted for chewing, except in the case
of the Polyzoniidae, the eighth family of the Order, in which, according to
Brandt, the mouth parts are adapted for sucking, and are prolonged into a
kind of proboscis. The mouth parts of the Chilognatha consist of—
(1) _An upper lip._ A transversely-placed plate, which is fused with the
rest of the head.
(2) A pair of powerful mandibles or jaws adapted for mastication, and
moved by powerful muscles. _f_ and _g_ in Fig. 33 shows these mandibles,
while the rest of the figure constitutes the broad plate (No. 3).
(3) A broad plate covering the under part of the head and partially
enclosing the mouth. This structure, which, as we shall afterwards see,
is formed by the fusion of two appendages which are distinct in the
animal when just hatched, has been called the deutomalae, the jaws
receiving the name of protomalae.
[Illustration: FIG. 33.—Mouth parts of _Chilognatha_. (From C. L. Koch,
_System der Myriapoden_.) _f_ and _g_, The mandibles. The parts marked _a_,
_b_, _c_, _d_, _e_ are firmly united and constitute the broad plate No. 3.
They have received the following names—_a_, _b_, Internal stipes; _c_,
external stipes; _d_, malellae; _e_, hypostoma.]
After the mouth parts we come to the legs. We first notice the fact that
the bases of the legs in each pair are closely approached to one another.
They are so set into the body that the basal joints, or, as they are
called, the coxal joints, nearly touch. This is the case in almost all
Chilognatha, except in the Polyxenidae, and it is a fact connected with
some important features in the internal anatomy. Then we have the
peculiarity in the Chilognatha which has formed the basis of most
classifications which have placed these animals in a group by themselves.
This is the possession in most segments of two pairs of legs. This
characteristic has caused the group to be called by some naturalists
Diplopoda. As a general rule, the first four segments {54}have only three
pairs of legs between them, one of them being without a pair of legs. This
legless or apodal segment is usually the third. From the fifth segment to
the end of the body all the segments have two pairs of legs each. The legs
are shorter than those of the Chilopods, and are all nearly equal in size.
This is not the case in the other Orders. The legs are commonly wanting in
the seventh segment of the male, and are replaced by a copulatory organ.
This peculiarity is related to the different position of the generative
openings in the Chilognatha. Another anatomical feature peculiar to the
Chilognatha is the possession of the stink glands—the _glandulae
odoriferae_ before mentioned. This, however, is a character which does not
hold for all the Chilognatha, since the Polyxenidae have none of these
glands. All the other families, however, possess them, and they are present
in none of the other Orders.
As regards the internal anatomy of the Chilognatha, the _digestive canal_
differs mainly in the glands which supply it with secretions. It receives
the saliva from two long tubular salivary glands, which open at the base of
the four-lobed plate which has been mentioned as the third of the mouth
appendages. The secretion of these glands is used, as has already been
said, in the process of preparing the nest for the eggs. We cannot fail to
be reminded of a similar function of salivary glands in those swallows,
which prepare the nests of which bird's-nest soup is made with the
secretion of the salivary glands. Another feature in the form of the
digestive tube is that in many cases, if not in all, it is marked with
constrictions which correspond with the segments of the body.
The _heart_ in the Chilognatha is not such a highly developed organ as in
the other Orders. The muscles which have already been mentioned as the
_alary_ muscles (or wing-shaped muscles) are not so highly developed, and
consist for the most part of a few muscular fibres. The muscular walls of
the heart, which consist of three layers, have the muscles less strongly
developed, and are in general adapted for a less energetic circulation.
The _tracheae_, which open into the stigmata, as has already been said,
branch into tufts of fine tubes, but the ramifications of these tufts never
join (or anastomose, as it is called), and consequently we never get, as in
the other Orders, long tracheal trunks running along the body.
{55}The _nervous system_, in addition to the existence of the visceral
nerve system described by Newport, shows a marked peculiarity in the form
of the ventral ganglionic chain. As has already been said, the nerve system
consists of a brain or mass of ganglia fused together and connected with
the ventral nervous cord by a collar of nervous substance surrounding the
oesophagus, and generally known as the _circumoesophageal_ collar. The
ventral nerve cord is a stout cord of nervous substance passing along the
whole length of the animal, and situated below (or ventral to) the
digestive tube and the generative system. This cord is enlarged at certain
points, and these enlargements or swellings are called ganglia, while from
the ganglia pass off nerves which supply the different organs of the body.
In the Chilognatha the cord has a compressed appearance as if the ganglia
were pressed into one another in such a way that it is very hard to
distinguish any ganglia at all. If we use the microscope and examine
sections cut transversely through the cord, we see that it is not a simple
cord. Even if we examine the nerve cord with a simple lens, we see that a
furrow runs longitudinally down it, and the use of the compound microscope
shows us that this furrow represents a division into two cords in such a
way that the single stout cord as it appeared to the naked eye is in
reality two cords running side by side, and so compressed together that the
substance is partly fused together. The ganglia too are double, being
swellings of the two cords and not a single enlargement on a single cord.
As we shall see in the other Orders, this arrangement constitutes a
characteristic distinction.
The _generative organs_ consist of a long tubular ovary or testis lying
along almost the whole length of the body and placed between the digestive
organ and the nervous system. Near its exit from the body the long tube
divides into two short tubes, the oviducts in the female or the vasa
_deferentia_ in the male. These ducts open in the third segment of the
body, unlike those of Myriapods belonging to other Orders. The accessory
glands present in most other Myriapods are not present in the Chilognatha.
The general arrangement of the organs of the Chilognatha may be seen from
Fig. 34, which represents a transverse section through the body of
_Polyxenus_ (Fig. 18). A comparison of {56}these two figures (Figs. 34 and
18) will show the position of the organs mentioned in this account. The
heart is shown with the suspensory and alary muscles attached.
[Illustration: FIG. 34.—Transverse section through _Polyxenus lagurus_:
_g.n.c_, _f.n.c_, ganglionic and fibrous parts of nerve cord; _Rec.sen_,
receptaculum seminis; _ori.dct_, oviduct; _Spmzoa_, spermatoza. (From
Heathcote, Anatomy of _Polyxenus lagurus_.)]
ORDER II. CHILOPODA.
The shape of the body differs from that of the Order which has been just
described (Chilognatha), inasmuch as it is not cylindrical but flattened,
the back, however, being more arched than the ventral surface. In this
respect, however, it cannot be said to differ from the other Orders which
we have yet to describe.
The segments are not formed by a single ring of the exoskeleton, which in
this Order is formed of chitin, and is tough and flexible rather than hard
and strong; but of two or three plates which form a covering to the
segment. The back is covered by a large plate known as the _tergum_, the
sides by two plates known as _pleura_, and the ventral part by a plate
called the _sternum_. The pleura and sternum are, however, in most cases
fused together or indistinguishable. In this, as in most of the anatomical
peculiarities, there is a much greater difference between the two Orders
Chilopoda and Chilognatha than between {57}the Chilopoda and the other
three Orders which have still to be described.
The Chilopoda have only one pair of appendages to each segment of the body
instead of two pairs like the Chilognatha.
The antennae of the Chilopoda are as a rule very long, and are always
longer than in the Chilognatha which we have just described. They differ
from those of the Schizotarsia (the third Order, which will be the next to
be described) in having the basal joints nearer together; in other words,
they are differently placed on the head. They differ from those of the
Pauropoda (the fifth Order) in being straight and not branched. As a rule
the antennae of the Chilopoda taper towards the extremity.
[Illustration: FIG. 35.—Mouth parts of _Lithobius_ (Latzel). A, Head of
_Lithobius_ seen from the under surface after removal of poison claws; _a_,
second maxilla; _b_, _c_, the two shafts of the first maxilla. B, One of
the mandibles. C, The two poison claws.]
The mouth parts are more numerous than in the Order we have just described
(the Chilognatha). They consist of—
1. An upper lip. This is a transverse plate as just described in the
case of the Chilognatha, but it is not always fused with the rest of the
head. It is also usually composed of three pieces, two lateral and a
middle piece.
2. A pair of _jaws_ or _mandibles_, which are not of so simple a form as
those of the Chilognatha, but rather resemble those of some of the
Crustacea.
3 and 4. Two pairs of appendages called maxillae resembling feet, but
used to aid the act of eating instead of locomotion. They are very
different in different Chilopods, but are mostly slender and weak and
usually provided with feelers (or palps) growing out of the main stem.
{58}5. The next pair of appendages are the first pair of the legs of the
body, which are also metamorphosed to serve a function different from the
ambulatory function of the other limbs. These are the _poison claws_, and
the possession of these forms another distinction between the Order we
are now discussing and that of the Chilognatha. At the same time the
third Order, that of the Schizotarsia, has poison claws, so that this
feature does not separate the Chilopoda from all the other Orders. These
poison claws are large curved claws connected with poison glands, the
secretion of which flows through a canal which opens near the point.
The _legs_ are longer than those of the Chilognatha, but not so long as
those in the next Order to be described (the Schizotarsia). Their number is
very various, from 15 pairs in _Lithobius_ to 173 in the Geophilidae.
Latzel notes a curious point in the number of the legs in this Order,
namely, the number of pairs of legs is always an uneven one. There are
always one pair to each segment. The last pair of legs is always longer
than the other pairs, and this is a peculiarity of the Order.
The _digestive tube_ resembles that of the other Orders, but the salivary
glands are not long and tubular but short (Fig. 28, _d_). It is, moreover,
not marked with constrictions corresponding with the segments of the body.
The _tracheal_ system or the system of respiration may be said to be more
highly developed in this Order than in any other. The tracheal branches
anastomose with one another (that is, the branches join), and in some cases
form long tracheal stems running along the body almost for its whole
length. The number of the tracheal openings or stigmata varies and does not
correspond with the number of segments.
The _nervous system_ differs considerably from that in the Order
Chilognatha; it resembles that in the Schizotarsia, and differs again from
that in the other two Orders, Symphyla and Pauropoda. The brain shows some
differences from other Orders chiefly in the development of the different
lobes which are connected with the sense organs, the eyes and antennae, for
instance; but the most marked difference is in the ventral ganglionic cord.
First, the ganglionic swellings are much more clearly marked than in the
Chilognatha. Secondly, the first three ganglia differ {59}from the others
in being nearer to one another and forming a single mass when seen by the
naked eye, though when examined by the aid of a microscope we can see all
the different parts are there. Thirdly, the division into two cords
mentioned in the Chilognatha is carried to a much greater extent. The
ganglia in each segment can be seen plainly to be double, and the cords
connecting the ganglia are two in number. We can plainly see that the
ventral nervous system of the Chilopoda consists of two cords lying
parallel to one another, and each having a ganglionic enlargement in every
segment. Whether a visceral nervous system is present in the group is
doubtful.
The eighth family of the Chilognatha, the Polyxenidae, show an approach to
the Chilopod nervous system.
The generative system differs chiefly in the opening of the genital
apparatus at the end of the body instead of in the third segment; though
this difference only separates the Order from the Chilognatha and not from
the other Orders. They also have two pairs of large accessory glands (as
they are called) connected with the genital openings.
ORDER III. SCHIZOTARSIA.
The third Order of Myriapods, the Schizotarsia, show a much greater
resemblance to the Chilopoda than to the first Order, the Chilognatha.
There are, however, important differences to distinguish them from all the
other Orders.
The shape of the body is short, thick, and very compact. The composition of
the individual segments resembles that found in Chilopoda rather than that
of Chilognatha.
The antennae are very long, longer than in any of the Chilopods, and are
composed of a great number of very small joints. The mouth parts show a
greater length and slenderness than do those of the other Orders mentioned
as yet. They consist of—
1. An _upper lip_ partly free, but fused at the sides with the rest of
the head. The upper lip is in three parts, as in the Chilopoda, but with
the middle part very small and the lateral pieces large.
2. A pair of _jaws_ or _mandibles_. These are provided not only with
teeth, as in the other Myriapods, but also with a sort of comb of stiff
bristles.
{60}3 and 4. Two pairs of _maxillae_ or foot jaws distinguished by their
length and slenderness.
5. The _poison claws_ long, slender, and not sharply curved. The bases of
the poison claws hardly fused together and short.
The _respiratory system_ in the Schizotarsia differs from that in all other
Myriapods in the fact before mentioned, that they breathe by means of lungs
and not by tracheae. There are, as before mentioned, eight dorsal scales in
these animals; each dorsal scale except the last bears one of the peculiar
organs which I have called lungs. At the hinder end of the scale there is a
slit which leads into an air sac, from which a number of short tubes
project into the blood in the space round the heart and serve to aerate it
before it enters the heart. The heart, therefore, sends aerated blood to
the organs, while in the tracheal-breathing Myriapods the blood is aerated
in the organs themselves by means of tracheae.
The poison claws are followed by segments bearing fifteen pairs of true
ambulatory legs. These are covered by eight large dorsal plates, increasing
in size from before to the middle of the body, the middle plate being the
largest, and then diminishing in size.
The _nervous system_ resembles that of the Chilopoda, but there is a
special pair of nerves which supply the sense organ, which has been
mentioned as peculiar to the Order. The ventral nerve cord shows a very
clear division into two, the ganglia of the two cords being almost entirely
separate. The first few ganglia are fused, as has been mentioned in the
Chilopoda.
The _digestive tube_ resembles that of the Chilopoda. The legs are very
long and slender, and the joints are beset with bristles. Both sexes have
small hook-like appendages at the sides of the genital openings.
The eyes have already been mentioned as being more highly developed than in
other classes, in correspondence with the more active habits of the animal.
The generative organs open at the hind end of the body, as in Chilopoda.
The heart is highly developed, quite as much so as the Chilopod heart, the
alary muscles being strong and broad, and the arteries being quite as
perfect as those in any Myriapod. The muscular coats which govern the
pulsations by their contractions are powerful and well developed.
{61}ORDER IV. SYMPHYLA.
We next come to one of the last two Orders which have been recently added
to the Myriapoda. These little animals have a great resemblance to the
Thysanura among the Insects, and especially to _Campodea_ among the
Thysanura. It will be well, therefore, to begin our account with a few of
the reasons which have induced naturalists to include them among the
Myriapods rather than among the Thysanura.
1. _Campodea_ has three pairs of mouth appendages, while _Scolopendrella_
has only two.
2. _Scolopendrella_ has broad plates covering the back, not only on the
anterior (thoracic) segments, but on the whole body.
3. The terminal appendages of _Scolopendrella_ differ from those in
_Campodea_.
4. _Scolopendrella_ has a sense organ which is absent in _Campodea_.
5. _Campodea_ breathes by means of three stigmata in the anterior part of
the body. The stigmata of _Scolopendrella_ are hard to see, and are not
in the same position.
6. _Scolopendrella_ has twelve pairs of legs, and _Campodea_, like all
Insects, has only three.
I will now go on to an account of their anatomy. The body is small and
slender, and is covered with a delicate shell or exoskeleton of chitin,
which is so thin as to be almost transparent.
The _antennae_ are long, and are composed of many joints of equal size.
The _mouth parts_ consist of—
1. An upper lip.
2. A pair of mandibles.
3. A pair of maxillae.
The segments are not all of equal size. Some are larger than others. The
larger and smaller segments are arranged alternately, and the smaller do
not bear legs. As before stated, there are twelve leg-bearing segments.
At the end of the body there are two hook-like appendages which are pierced
by a canal, through which is poured the secretion of a pair of glands. Near
the sides of these appendages are a pair of sense organs, consisting of
long hairs connected with nerves.
{62}The digestive canal is a long straight tube passing through the length
of the body. In the middle it is much enlarged, so as to form a stomach
with a glandular coat. Posterior to the stomach the digestive tube receives
the contents of two Malpighian tubes which act as kidneys.
The tracheal system consists of a single pair of stigmata on the under
surface of the head, and the tracheae connected with them.
ORDER V. PAUROPODA.
The Pauropoda, which form the fifth Order of Myriapods, are as yet very
imperfectly known. _Pauropus_ was discovered by Sir John Lubbock, and its
discovery was announced by him in 1866. He found this little Centipede in
his kitchen garden among some Thysanura, and at first considered it as a
larval form, but continued observation showed that it was a mature
creature. He described it as a small, white, bustling, intelligent little
creature about 1/25 inch in length.
The antennae are very curious and highly characteristic of the Order. They
resemble those of Crustacea rather than those of Myriapoda. Each antenna is
composed in the following manner. First there is a shaft of four joints.
From the fourth joint of this shaft spring two branches; one of these two
branches is narrower than the other, and ends in a long thin bristle
composed of a great number of joints. The other and broader branch bears
two such bristles, and between them a small pear-shaped or globular body,
the function of which is unknown.
The mouth parts consist of two minute pairs of appendages, the anterior
pair toothed and the posterior pointed. The body is rather narrower in
front; the segment behind the head has one pair of legs, the second, third,
fourth, and fifth behind the head two each. The posterior legs are the
longest; the genital organs open at the base of the second pair of legs,
between these and the third pair. The manner of breathing is as yet
unknown, tracheae not having been discovered.
_Pauropus_ at first looks most like a Chilopod, but differs from that
Order—
1. In the form of the antennae.
2. In the absence of poison claws and in the form of the mouth parts.
{63}3. The opening of the generative organs being in the front part of
the body.
It differs from Chilognatha in the following respects:—
1. The legs are not of equal length, the posterior legs being the
longest, as in Chilopods.
2. The mouth parts differ from those of Chilognaths almost as much as
from those of Chilopods.
3. The form of the antennae.
Only a few Pauropoda have been discovered as yet.
EMBRYOLOGY.
The preceding account of the anatomy of Myriapods would be incomplete
without some reference to the wonderful manner in which the different
organs of the body are built up; the whole of the complex organism
proceeding by a gradual and regulated process of development from a simple
cell called the ovum derived from the female body, and united with a cell
from the male body (called the spermatozoon). I hope to be able to give my
readers some idea of the interest which the pursuit of the difficult study
of embryology adds to anatomy, by offering us a key to the interpretation
of the relations between our knowledge of the forms at present living on
the earth and those which, we learn from Palaeontology, have inhabited our
planet in past ages.
[Illustration: FIG. 36.—Young ovum of _Julus terrestris_: _nucl_,
nucleolus; _nu_, nucleus; _R_, first appearance of yolk; _F_, follicle
cells.]
Like all living creatures with which we are acquainted, the starting-point
of Myriapod life is the _ovum_, as it is called. This _ovum_ is a _cell_
resembling the cells of which the body of all living animals are built up,
and which may be compared to the bricks of which a building is composed.
This cell or ovum is a small sphere of living transparent substance called
protoplasm, and it is _nucleated_—that is, it contains a small spot of
denser protoplasm called the nucleus, and within that a still smaller spot
of still more dense protoplasm called the nucleolus. In the process of
impregnation the ovum unites with the male cell, and the cell so formed is
called the impregnated ovum. This ovum has the property of dividing into
two cells, each resembling the {64}parent cell from which it is derived;
each of these cells has, like the parent cell, the same property of
dividing into two more, and so on. Thus from this continual process of
division or reproduction of every living cell, the materials are provided
for the building up of the body.
The regularity of the process of the division of the ovum, or, as it is
called, _segmentation of the ovum_, is interfered with by the presence of
_food yolk_. The cells formed by the process of cell division just
described need nourishment, and this nourishment is supplied to them by the
food yolk formed in the body of the ovum before the process of segmentation
begins. It is easy to understand that this yolk, which is not _alive_ like
the cells, cannot divide like them, and therefore the segmentation of the
ovum in Myriapods is _irregular_, as it is called.
[Illustration: FIG. 37.—Later stage: _nu_, nucleolus; _c.p_, nucleus;
_y.sp_, yolk spherules; _ch_, shell.]
I will now go back a little and describe what happens to the ovum before
the process of segmentation is complete. It increases in size and forms the
supply of food yolk which is to provide the nutriment of the ovum. Then
after impregnation the egg-shell is formed round it, and it becomes what we
know as the egg. This egg is not a perfect sphere, but is oval (in most
Myriapods) in shape. The egg is laid, and the process of segmentation
begins shortly after it is laid, as has already been described.
When it has been laid for about 36 hours, if we take an egg and, after
proper preparation, cut it into thin slices known to {65}microscopists by
the name of sections, and examine it by means of the microscope, we shall
see that segmentation has resulted in this. Just beneath the egg-shell
there is a thin layer of cells, one cell thick, which completely surrounds
the egg. Inside this coat of cells is the food yolk, with a few cells
scattered about in it at rare intervals, something like the raisins in a
plum-pudding.
With the next process the formation of the young Myriapod may be said to
begin. A strip along the length of the oval-shaped egg is thickened, and
this thick mass of cells represents the future ventral surface of the
animal. The rest of the thin layer of cells already mentioned just below
the shell will form the shell or exoskeleton of the future animal. The
thick strip of cells at the ventral surface has by this time split into
layers, so that, resorting to our microscope again, a section through the
short axis of the oval-shaped egg—a transverse section—will show us—
1. The egg-shell.
2. A layer of cells completely surrounding the egg, thin everywhere but
on the ventral surface. This layer is known to embryologists as the
_epiblast_. The thick part of the epiblast on the ventral surface gives
rise to the nervous system.
3 and 4. Two layers of cells connected in the middle, along the line of
the thick strip, but separate elsewhere, and not extending round the
whole of the inside. These layers constitute what is known as the
mesoblast, and give rise to the muscles and most of the internal organs.
5. The scattered cells in the yolk. They are known as the hypoblast and
give rise to the digestive canal.
After this point is reached the formation of the organs begins. The
segments are formed in order from before backwards. First the head, then
the next segment, and so on. When the number of segments with which the
animal will be hatched are formed, another process begins, and the tail end
of the animal, which can already be distinguished, is bent towards the
head. This is a process that takes place in many animals besides Myriapods,
and is called the formation of the ventral flexure. Shortly after this the
animal bursts the shell and comes {66}into the outer world. The various
processes may be understood by reference to the Figs. 36, 37, 38, 39, which
are successive stages in the development of a Chilognath. Figs. 37, 38, are
thin slices through the shorter diameter of the egg, which, as before
mentioned, is an oval in shape. Fig. 39 is a section through the longer
diameter of an egg in a more advanced stage of development, in fact just
about to burst the shell. The body of the future animal is marked by
constrictions, the future segments. Some of the organs are already formed,
as the brain and the digestive tube, the openings of which will form the
mouth (_st_) and the anus (_pr_).
[Illustration: FIG. 38.—Transverse section through next stage: _mk_,
keel-like mass of cells from which the mesoblast is produced; _ec_,
epiblast. (From Heathcote, Post. Emb. Dev. of _Julus terrestris_; _Phil.
Trans._ vol. 179, 1888, B.)]
[Illustration: FIG. 39.—Longitudinal section through later stage: _Segs._
2, 3, etc., segments; _Ceph. Seg_, head; _mes_, mesoblast; _en_, hypoblast;
_st_, future mouth; _pr_, future anus; _mesen_, gut; _mem.ex_, as in Fig.
41. (From Heathcote, Post. Emb. Dev. of _Julus terrestris_.)]
Myriapods are hatched at different stages of development. The Chilognatha
have only three appendages, which are so little developed that they are
only small shapeless stumps, while {67}the Chilopoda have the full number
of legs in some cases; in others only a small number of legs, but yet more
than the three pairs of legs of the Chilognatha, and fully developed
instead of stump-like. The eyes are usually developed late in the life of
the young animal. The bursting of the egg-shell is assisted in some
Myriapods by a special kind of spike on the back part of the head.
The Fig. 40 shows a young Chilognath which has just burst the shell and
come into the outer world. It is still surrounded with a membrane which has
been formed by its skin or epiblast within the egg. One eye-spot has been
formed.
[Illustration: FIG. 40.—Young _Julus terrestris_ just hatched.]
Fig. 41 shows a longitudinal section through the young Chilognath shown in
Fig. 40, and the next (Fig. 42) a transverse section through the same. In
comparing the two Figs. 41 and 42 it must be remembered that they are
_sections_ in different planes through the animal shown in Fig. 40, and
therefore they only show a small portion, a thin slice, of the organs.
[Illustration: FIG. 41.—Longitudinal section through late stage:
_Sup.oe.gl_, First appearance of brain; _st_, mouth; _pr_, anus; _mesen_,
gut; _n_, nerve cord; _n.gang_, nerve ganglion; _mem.ex_, membrane
surrounding the animal; _v.f_, ventral flexure; _mes_, mesoblast cells.
(Heathcote, Post. Emb. Dev. of _Julus terrestris_.)]
{68}The first appearance of the mouth appendages has been already
mentioned, and these are shown in Fig. 43, where the small stumps that
later on change to jaws are shown. The figure shows the head of a young
Chilognath seen from the lower side, and the second pair of stumps fuse
together later on and produce the broad plate already mentioned as the
characteristic mouth appendage of the Order.
[Illustration: FIG. 42.—_G_, gut; _Malp.T_, Malpighian tube; _N.C_, nerve
cord; _Tr.I_, deep invagination by which the tracheae are formed; _y.s_,
yolk spherules still present; _L_, first appearance of legs; _S.S_, part of
mesoblast. (Heathcote, Post. Emb. Dev. of _Julus terrestris_.)]
[Illustration: FIG. 43.—Under surface of the head of a young _Julus
terrestris_: _pro.m_, rudimentary jaws; _Deut.m_, rudimentary mouth plate;
_an_, antennae.]
After the animal is hatched it has still, in the case of most Myriapods
(those which are not hatched with all the segments complete), to undergo a
further development, and in particular the eyes are still unformed. The
process of development of the eye has only been followed out as yet in the
Chilognatha, and in only one form, _Julus_, and is so curious that a short
account may be of interest here. The development of the eye begins (in
_Julus_) on the fourth day after hatching, and continues until the animal
is full grown. A single {69}ocellus or eye-spot appears first, and the rest
are added one by one until the full number are reached.
The first appearances connected with the formation of the eye take place in
the cellular layer just beneath the chitinous exoskeleton. This layer,
called the hypodermis, plays an important part in the organisation of the
animal. It forms the inner layer of what we may call the skin of the
animal, and the cells of which it is composed secrete the chitin of which
the shell or exoskeleton of the animal is composed, and which is moulted
every year.
The first process in the formation of the eye-spot is the thickening of the
hypodermis beneath the chitin, just in the place where the eye will come.
At the same time the cells of this thickened mass of hypodermis secrete a
quantity of pigment of a dark red brown colour. Next the cells of the thick
mass of hypodermis begin to separate from one another in such a way that a
vesicle is formed. This vesicle is hollow inside, and the thick walls are
formed from the cells of the thickened hypodermic mass. This can be seen
from Fig. 44, which represents a section through an ocellus when it is
partly formed. From this vesicle the eye is formed.
The wall of the vesicle nearest the exoskeleton gives rise to the lens of
the eye, while the other walls of the vesicle form the retinal parts of the
eye. The cells from the brain grow out and form the optic nerve connecting
the retina with the brain. The whole eye spot is covered internally by a
thin membrane, formed not from the hypodermis but by cells from the inside
of the body (mesoblast cells).
[Illustration: FIG. 44.—Section through eye when first forming: _Hyp_,
hypodermis; _Ln_, lens; _F.W.V_, front wall of optic vesicle; _b.w.v_, back
wall of vesicle; _cap_, capsule.]
In the Chilognatha, the first Order of Myriapods, the young {70}animal
leaves the egg with three pairs of appendages; the first have already the
form of antennae, the second will form the jaws, but have not yet taken
their proper form, while the third pair will fuse together and alter their
shape so as to form the curious plate that has already been mentioned as
forming the second pair of mouth appendages. Behind the mouth appendages
will come the first three pairs of legs. The whole young animal on leaving
the egg is enveloped in two membranes. These membranes are secreted by the
outside layer of cells in the same way that the shell or exoskeleton of the
animal will be eventually formed, and represent the first two moults of the
animal, which continues to moult its shell every year throughout life.
Of the Chilopoda, the second Order of Myriapods, all the families leave the
egg-shell with the full number of legs, with the exception of the
Lithobiidae, which have seven pairs of legs including the poison-claws. The
Schizotarsia, the third Order, also have seven pairs of legs when hatched.
The legs make their appearance not one by one but in batches (in _Julus
terrestris_ in batches of five). The addition of legs and segments to the
body takes place, not at the end of the body, but between the end segment
and the penultimate.
This is a short sketch of the gradual development of the Myriapoda from the
ovum to the fully-grown animal. It is, I am aware, a short and insufficient
account of all the beautiful processes by which the different organs take
their rise, but space is insufficient here, and too much detail would be
out of place in a work of this nature, which only aims at giving an outline
sketch of the group, which shall be intelligible to the general reader who
has not made a special study of such matters. Before leaving the subject,
however, I must mention a few of the points of interest which are to be
learned from the examination of the course of development which has been
sketched here. One of the greatest puzzles in the natural history of the
Order Chilognatha has always been the double segments, as they are called;
that is, in fact, the possession of two pairs of legs to each segment,
which is, as we have already said, a distinguishing characteristic of the
Order. As we have seen, the Chilognatha at an early stage of existence do
not possess this characteristic, which is only peculiar to the adult
{71}and half-grown forms. Now what does this mean? Does each double segment
in the full-grown Millepede represent two segments which have become fused
together, or is each double segment, so called, a real segment resembling
the segments present in the other Orders (for instance, Chilopoda), which
has grown an extra pair of legs? Both these views have been advocated by
distinguished naturalists. Neither of them is, in my opinion, quite right
when viewed in the light cast on the subject by recent investigations into
the life history of the Chilognatha.
A close examination into the minutiae of the growth of the different organs
has shown us that the double characters of the double segments are more
deeply seated than was imagined. The circulatory system, the nerve cord,
and the first traces of segmentation in the mesoblast all show this double
character, and the only single part about the segment is the broad plate
covering the segment. Now in some of the most ancient of the fossil
Myriapods this broad plate shows traces of a division, as if it were in
reality two plates fused together. We have also to consider that the life
history of the Chilognatha allows us to believe that the peculiar
cylindrical shape of the body shown in the greatest degree in the Julidae
is attained by the unequal development of the dorsal and ventral surfaces
of the body; the ventral surface being compressed together till it is
extremely narrow, and the dorsal surface, as it were, growing round it till
the originally dorsal surface forms almost a complete ring round the body.
Taking all this into consideration, we are justified, in my opinion, in
concluding that each double segment in the Chilognatha is not two segments
fused together, nor a single segment bearing two pairs of legs, but is two
complete segments perfect in all particulars, but united by a large dorsal
plate which was originally two plates which have been fused together, and
which in most Chilognatha surrounds almost the whole of two segments in the
form of a ring.
Again in the Chilopoda we see that a great distinctive feature that
separates them from the Chilognatha is the character of the ventral nerve
cord, the cord being double and not single, a character connected with the
fact that the bases of the legs are widely separated from one another, and
not closely approached to each other, as in the Chilognatha. As we before
said, a more {72}minute anatomical examination showed us that this
difference was not so great as appeared at first sight, the cord showing
traces of a duplication. Well, are these traces superficial, or do they
represent a state of affairs more or less similar to that in the Chilopoda?
Embryology helps us to answer this question also. In the early stages of
the Chilognatha we find that the nerve cord has exactly the form of that in
Chilopoda, showing us that the appearances in the anatomy had led us to a
right conclusion, and giving us a valuable confirmation of our views. These
two examples will serve to show the kind of interest which attaches to
embryology.
PALAEONTOLOGY.
We have seen that embryology enables us to look at the structure of the
Myriapods from a new standpoint, and to correct and supplement the
knowledge gained from an examination of the adult animal. In the same way a
study of the forms of Myriapods which have become extinct on the globe, and
have been preserved to us in a fossil form, gives a further opportunity of
considering the relations of one form to another, and again of the
relations of our group to other groups of animals now existing on the
earth. Myriapod fossils have been found in strata of great antiquity. The
oldest of such fossils must have been among the first land animals. The
figure below shows a fossil Myriapod found in America, belonging to the
Order of the Protosyngnatha which are only found in the Palaeozoic strata.
It is a good example of the manner in which Myriapods were protected by
bundles of bristles in the same way as the _Polyxenus_ of the present time.
The oldest fossil Myriapods which have been discovered at the present time
are two species which have been found in the Old Red Sandstone in Scotland.
To realise the antiquity of these Myriapods, it will be worth while
recalling the typical fossils found in the Old Red Sandstone, so as to see
what the contemporaries of these ancient Myriapods were like. Among the
plants there were Algae, Ferns, and Conifers, belonging to the lower
divisions of the plant tribe. Among the animals there were Sponges, Corals,
Starfish, Worms, Shell-fish, and Fishes, but none of the more highly
organised of the animal or vegetable tribe {73}had appeared on the earth.
The Myriapods of the Old Red Sandstone, as has been before said, differ
considerably from those of the present day, and as we proceed towards the
species found in the more recent strata we find them more and more like the
ones at present living, till we get to the _Polyxenus_ and other species
found in amber, which are hardly to be distinguished from living forms.
The next oldest fossil Myriapods are found in the coal measures, when both
the animal and vegetable kingdoms were represented by more numerous and
more specialised forms. The fossil fauna of this period is characterised by
the number of gigantic Amphibia, many remains of which have been found. The
great forests and the abundant vegetation of this time must have been
favourable to the existence of our class, and accordingly we find no less
than 32 species of fossil Myriapods. Of these most have been found in
America, some in Great Britain, and some in Germany. One well-preserved
fossil of _Xylobius sigillariae_ was found by Dr. Dawson in America in the
stump of a tree in the remains of a fossil forest. The eyes, head, and legs
were plainly seen under the microscope. All these fossils belong to the
earliest or Palaeozoic period.
[Illustration: FIG. 45.—_Palaeocampa anthrax._ (After Meek and Worth.) From
Mazon Creek, Illinois.]
The figure below (Fig. 46) shows a fossil also from the coal formations of
Illinois, America, belonging to the family of the Euphoberiidae mentioned
further on. It shows a nearer approach to the Julidae of the present time.
The limbs, however, were of very curious shape, and may possibly have been
adapted to locomotion in water as well as on land, and the small supposed
branchiae on the ventral surface shown in Fig. 46, B, may possibly have
been an arrangement to render respiration in the water possible.
{74}In the secondary period the Myriapods were scantily represented, or, at
any rate, geologists have failed to find their fossils. The class is
represented by a single specimen found in the chalk in Greenland. This
fossil, which has been included in the Julidae under the name of _Julopsis
cretacea_, may perhaps belong to the Archipolypoda.
Passing on to the Tertiary or Recent period, we find the Myriapods again
numerous, and more nearly resembling those living at the present time. They
belong mostly to the Chilognatha and Chilopoda. They have been found in the
fresh-water gypsum of Provence in France, the brown coal of Germany, and
the green river formations of America. Several have been found in amber.
[Illustration: FIG. 46.—_Acantherpestes major._ (After Meek and Worth.)
Mazon Creek, America. A, The whole animal; B, branchiae on the ventral
surface.]
Fossil Myriapods have been divided into four Orders, two of which coincide
with the Orders of living Myriapods; the differences between the fossils
and the living Myriapods having been held insufficient to warrant the
establishment of a new Order. These two Orders are the Chilopoda and the
Diplopoda or Chilognatha (Diplopoda is another name used by some writers
for the group which we have hitherto called Chilognatha). The other two
Orders have sufficient differences from living forms to render it necessary
to include them in separate Orders.
The fossil Myriapods, then, are arranged as follows:—
Order I. Protosyngnatha.
Order II. Chilopoda.
Order III. Archipolypoda.
Order IV. Chilognatha (or Diplopoda).
The following table will show the species that have been discovered in the
different strata:—
Devonian, or } {75}
Old Red Sandstone } 2 species of _Archipolypoda_
Carboniferous { 1 species _Protosyngnatha_
{ 31 species _Archipolypoda_
Permian (Rothliegendes of Germany), 4 specimens belonging to the
_Julidae_ or _Archipolypoda_.
Cretaceous, 1 species { _Archipolypoda_ or
{ _Chilognatha_
Oligocene { 17 species _Chilopoda_
{
{ 23 species { _Diplopoda_
{ (_Chilognatha_)
Miocene, 1 species { _Diplopoda_
{ (_Chilognatha_)
I will now give a short account of the different Orders, and the fossil
forms which are included in them.
ORDER I. PROTOSYNGNATHA.
This Order is represented by a single fossil (Fig. 45), discovered in the
coal at Mazon Creek, Illinois, America, by Meek and Worth. It differs
greatly from any of those in existence at the present day. The body is
cylindrical, and composed of ten segments. The cephalic appendages (that
is, the antennae and mouth parts) are inserted into a single unsegmented
cephalic mass (the head). Each segment behind the head bears a single
dorsal and ventral plate of equal breadth and length. The limbs are placed
in these plates with a wide space between the base of each leg and that of
the opposite one of the pair. Along the back, bundles of bristles are
arranged in longitudinal rows.
ORDER II. CHILOPODA.
The fossil forms of this Order resemble those of the Chilopoda of the
present day. The oldest of them are found in amber. The following families
have been found:—
_Lithobiidae._ Several species have been found in amber.
_Scolopendridae._ One species in amber, several species in later Tertiary
formations.
_Geophilidae._ Three species in amber.
Two species resembling the Schizotarsia of the present day have been found
in amber.
{76}ORDER III. ARCHIPOLYPODA.
The most numerous of the fossil families. With a few exceptions, all the
Palaeozoic (that is, the oldest) Myriapods belong to this Order. The
Carboniferous Archipolypoda seem to be much more numerous in the coal of
America than in that of England. They resemble for the most part the
Myriapods of the present day, except that all the segments without
exception bear legs.
The families are three in number.
Family 1. _Archidesmidae._
Resemble the _Polydesmidae_ of the present day. Two species have been
found by Page in the Old Red Sandstone of Forfarshire. He named them
_Kampecaris_. One found by Peach in the same formation is called
_Archidesmus_.
Family 2. _Euphoberiidae._
They show some resemblance to the _Julidae_ of the present day, but the
dorsal scutes, or plates of the back, are more or less perfectly divided
into two divisions corresponding with the pairs of legs. The following
are the principal fossils of this family:—
_Acantherpestes._ Found by Meek and Worth in the coal at Mazon Creek in
America (Fig. 46).
_Euphoberia._ About 12 species found at the same place as the last
named.
_Amylispes._ Found by Scudder, Mazon Creek, America.
_Eileticus._ Scudder, Mazon Creek, America.
Family 3. _Archijulidae._
The dorsal plates nearly consolidated, but the division still apparent.
Fossil forms are—
_Trichijulus._ Scudder, Mazon Creek, America.
_Xylobius._ Dawson. Found in the coal in Nova Scotia. Two species found
at Mazon Creek, America.
ORDER IV. CHILOGNATHA.
Families corresponding to those of the present day. The oldest specimens
come from the chalk in Greenland; most of the others from amber.
Family 1. _Glomeridae._ One form, _G. denticulata_, has been found in
amber.
Family 2. _Polydesmidae._ Two species in amber.
Family 3. _Lysiopetalidae._ A number of species, amongst which are 6
_Craspedosoma_, mostly from amber.
{77}Family 4. _Julidae._ A number of species of this family have been
found, some in amber, some in other Tertiary strata. Amongst the latter a
probable example of _Julus terrestris_, living at the present time.
Family 5. _Polyxenidae._ Five species have been found in amber.
Now that we have considered the structure of the Myriapods and the groups
into which they are subdivided or classified, we may proceed to consider
what position they hold in the household of nature. That they present
certain features of similarity to other classes has been already mentioned,
and that this is the fact cannot be doubted when we look back at the way in
which they have been classified in the works of early writers. For example,
Lamarck, the great French naturalist, classifies them with spiders in his
well-known work, _La Philosophie Zoologique_, under the name of _Arachnides
antennistes_. Cuvier, the comparative anatomist, unites them with the
Insects, making them the first Order, while the Thysanura is the second. We
have already seen that one Order of Myriapods, the Symphyla, bears a great
resemblance to the Thysanura. The English naturalist Leach was the first to
establish Myriapods as a class, and his arrangement has been followed by
all naturalists after his time. But while their peculiarities of structure
and form are sufficiently marked to separate them as a class, it cannot be
denied that the older naturalists were right to recognise that they have
many essential characteristics in common with other classes of animals. And
recent investigations have emphasised this fact. For instance, let us
consider the recent discoveries of the Orders of Symphyla and Pauropoda,
Orders which, while bearing so many of the characters of Myriapods that
naturalists have agreed to place them in that class, yet resemble in many
important points the Insect Order of Thysanura. This seems to justify
Cuvier in claiming the close relationship for them that he did.
Recent investigations have also brought out more prominently the
resemblances to the Worms. Of late, considerable attention has been
directed to _Peripatus_ (see pp. 1-26), and the resemblances to the
Myriapods in its anatomy and development are such that Latzel has actually
included it in the Myriapods as an Order, Malacopoda. Now _Peripatus_ also
shows resemblances to the annelid Worms, and thus affords us a connexion to
the Worm type hardly less striking than that to the Insect. This
{78}resemblance to the Worms, which Myriapods certainly bear, was noticed
by the ancient writers, and as they had for the most part only external
appearances to consider, they pushed this idea to extremes in actually
including some of the marine Worms (Annelida) among the Centipedes. Pliny
talks of a marine _Scolopendra_ as a very poisonous animal, and there is
little doubt that he meant one of the marine worms. An old German
naturalist, Gesner, in a very curious book published in 1669 gives an
account of an annelid sea-worm which he calls _Scolopendra marina_, and
which is in all probability the sea Scolopendra which Pliny mentions. From
Gesner's account it seems to have been used as a medicine (externally
only). "The use of this animal in medicine. The animal soaked in oil makes
the hair fall off. So do its ashes mixed in oil." It was also pounded up
with honey.
This idea of Centipedes living in water survived among later naturalists.
Charles Owen, the author before quoted, mentions them as amphibious in
1742. "The Scolopendra is a little venomous worm and amphibious. When it
wounds any, there follows a blueness about the affected part and an itch
all over the body like that caused by nettles. Its weapons of mischief are
much the same with those of the spider, only larger; its bite is very
tormenting, and produces not only pruriginous pain in the flesh, but very
often distraction of mind. These little creatures make but a mean figure in
the ranks of animals, yet have been terrible in their exploits,
particularly in driving people out of their country. Thus the people of
Rhytium, a city of Crete, were constrained to leave their quarters for them
(Aelian, lib. xv. cap. 26)."
Myriapods have been considered to bear resemblances to the Crustacea, and
this to a certain extent is true, though only to a certain extent, the
resemblances being confined to the more general characteristics that they
share with other groups of animals.
Of late years attempts have been made to speculate about the origin of the
Myriapods—that is, to endeavour to obtain by means of investigation of
their anatomy, embryology, and palaeontological history, some idea of the
history of the group. Such attempts at research into the _phylogeny_, as it
is called, of a group must be more or less speculative until our knowledge
is much greater than {79}it is at present. But such inquiries have their
value, and the schemes of descent and phylogenetic trees, at any rate,
indicate a real relation to different groups, even if they do not provide
us with a real and actual history of the animals.
There have been two main theories about the descent of the Myriapoda. One
of these derives them directly from the Insecta through the forms known as
the Thysanura, which resemble in such a degree the Myriapod Orders of
Symphyla and Pauropoda. The other theory holds that the Myriapods, as well
as the Insecta, have been derived from some ancestor bearing a resemblance
to _Peripatus_. In other words, one theory claims that the relationship of
Myriapoda to Insecta is that of father and son; the other that the
relationship between the two is that of brother to brother. The arguments
by which these theories are respectively supported consist for the most
part of an analysis of the different characters of the anatomy and
embryology and the determination of the most primitive among them. For
example, the supporters of the theory that the Thysanura are the most
nearly allied to the Myriapod ancestor lay great weight on the fact that
some Myriapods are born with three pairs of legs only, and they compare
this stage in the life history of the Myriapoda to the metamorphosis and
larval stage of Insects. For the supporters of this view the Orders of
Symphyla and Pauropoda are the most primitive of the Myriapods. On the
other hand, the followers of the other theory do not allow that the
characters in which the Myriapods are like Insects are primitive ones, but
they lay more stress on the characters found in the early development, such
as the character of the process of the formation of the body segments, the
mesoblastic segmentation, and the origin of the various organs of the body.
It may be easily understood that such differences in the estimation of the
primitive characters of the embryology of a group may arise. Embryology has
been compared by one of the greatest of modern embryologists to "an ancient
manuscript with many of the sheets lost, others displaced, and with
spurious passages interpolated by a later hand." What wonder is it that
different people examining such a record should come to different
conclusions as to the more doubtful and difficult portions of it. It is
this very difficulty which makes the principal interest in the study, and
although our knowledge of the language in {80}which this manuscript is
written is as yet imperfect, still we hope that constant study may teach us
more and more, and enable us to read the great book of nature with more and
more ease and certainty.
If any of my readers should wish for a more full account of the natural
history of this group I must refer them to the following works, which I
have used in compiling the above account. In the first of these there is an
excellent bibliography of the subject:—
LATZEL, Die Myriapoden der Oesterreichisch-Ungarischen Monarchie, Wien,
1880.
ZITTEL, Handbuch der Palaeontologie, 1 Abth, II. Bd., Leipzig, 1881-1885.
KORSCHELT AND HEIDER, Lehrbuch der vergleichenden Entwicklungsgeschichte
der wirbellosen Thiere, Jena 1891.
INSECTA
BY
DAVID SHARP, M.A., M.B., F.R.S.
{83}CHAPTER III
CHARACTERISTIC FEATURES OF INSECT LIFE–SOCIAL INSECTS–DEFINITION OF THE
CLASS _INSECTA_–COMPOSITION OF INSECT SKELETON–NUMBER OF SEGMENTS–NATURE OF
SCLERITES–HEAD–APPENDAGES OF THE MOUTH–EYES–THORAX–ENTOTHORAX–LEGS–WINGS–
ABDOMEN OR HIND BODY–SPIRACLES–SYSTEMATIC ORIENTATION.
Insects form by far the larger part of the land animals of the world; they
outnumber in species all the other terrestrial animals together, while
compared with the Vertebrates their numbers are simply enormous. Yet they
attract but little attention from the ordinary observer, this being
probably primarily due to the small size of the individual Insect, which
leads the unreflecting to treat the creature as of little importance. "It
can be crushed in a moment" is perhaps the unformulated idea that underlies
the almost complete neglect of knowledge concerning Insects that prevails
even in the educated classes of society. The largest Insects scarcely
exceed in bulk a mouse or a wren, while the smallest are almost or quite
imperceptible to the naked eye, and yet the larger part of the animal
matter existing on the lands of the globe is in all probability locked up
in the forms of Insects. Taken as a whole they are the most successful of
all the forms of terrestrial animals.
In the waters of the globe the predominance of Insect life disappears. In
the smaller collections of fresh water many Insects find a home during a
portion of their lives, and some few contrive to pass their whole existence
in such places; but of the larger bodies of fresh water they invade merely
the fringes, and they make only the feeblest attempt at existence in the
ocean; the genus _Halobates_ containing, so far as we know, the sole
Insects {84}that are capable of using the ocean as a medium of existence at
a distance from the shore.
It will probably be asked, how has it come about that creatures so
insignificant in size and strength have nevertheless been so successful in
what we call the struggle for existence? And it is possible that the answer
will be found in the peculiar relations that exist in Insects between the
great functions of circulation and respiration; these being of such a
nature that the nutrition of the organs of the body can be carried on very
rapidly and very efficiently so long as a certain bulk is not exceeded.
Rapidity of growth is carried to an almost incredible extent in some
Insects, and the powers of multiplication—which may be considered as
equivalent to the growth of the species—even surpass the rapidity of the
increase of the individual; while, as if to augment the favourable results
attainable by the more usual routine of the physiological processes,
"metamorphosis" has been adopted, as a consequence of which growth and
development can be isolated from one another, thus allowing the former to
go on unchecked or uncomplicated by the latter. A very simple calculation
will show how favourable some of the chief features of Insect life are. Let
it be supposed that growth of the individual takes time in proportion to
the bulk attained, and let A be an animal that weighs one ounce, B a
creature that weighs ten ounces, each having the power of producing 100
young when full grown; a simple calculation shows that after the lapse of a
time necessary for the production of one generation of the larger creature
the produce of the smaller animal will enormously outweigh that of its
bulkier rival. Probably it was some consideration of this sort that led
Linnaeus to make his somewhat paradoxical statement to the effect that
three flies consume the carcase of a horse as quickly as a lion.[16]
Astonishing as may be the rapidity of the physiological processes of
Insects, the results attained by them are, it must be admitted, scarcely
less admirable: the structures of the Insect's body exhibit a perfection
that, from a mechanical point of view, is unsurpassed, while the external
beauty of some of the creatures makes them fit associates of the most
delicate flowers or no mean rivals of the most gorgeous of the feathered
world. The words {85}of Linnaeus, "Natura in minimis maxime miranda," are
not a mere rhetorical effort, but the expression of a simple truth. Saint
Augustine, too, though speaking from a point of view somewhat remote from
that of the great Swedish naturalist, expressed an idea that leads to a
similar conclusion when he said, "Creavit in coelum angelos, in terram
vermiculos; nec major in illis nec minor in istis."
The formation of organised societies by some kinds of Insects is a
phenomenon of great interest, for there are very few animals except man and
Insects that display this method of existence. Particulars as to some of
these societies will be given when we treat of the Termitidae, and of the
Hymenoptera Aculeata; but we will take this opportunity of directing
attention to some points of general interest in connexion with this
subject. In Insect societies we find that not only do great numbers of
separate individuals live together and adopt different modes of industrial
action in accordance with the position they occupy in the association, but
also that such individuals are profoundly modified in the structures of
their body and in their physiological processes in such ways as to
specially fit them for the parts they have to play. We may also see these
societies in what may be considered different stages of evolution; the
phenomena we are alluding to being in some species much less marked than
they are in others, and these more primitive kinds of societies being
composed of a smaller number of individuals, which are also much less
different from one another. We, moreover, meet with complex societies
exhibiting some remarkably similar features among Insects that are very
different systematically. The true ants and the white ants belong to groups
that are in structure and in the mode of growth of the individual
essentially dissimilar, though their social lives are in several important
respects analogous.
It should be remarked that the phenomena connected with the social life of
Insects are still only very imperfectly known; many highly important points
being quite obscure, and our ideas being too much based on fragments
gathered from the lives of different species. The honey bee is the only
social Insect of whose economy we have anything approaching to a wide
knowledge, and even in the case of this Insect our information is neither
so complete nor so precise as is desirable.
The various branches of knowledge connected with Insects {86}are called
collectively Entomology. Although entomology is only a department of the
great science of zoology, yet it is in practice a very distinct one; owing
to its vast extent few of those who work at other branches of zoology also
occupy themselves with entomology, while entomologists usually confine
themselves to work in the vast field thus abandoned to them.
Before passing to the consideration of the natural history and structure of
the members of the various Orders of Insects we will give a verbal
diagrammatic sketch, if we may use such an expression, with a view to
explaining the various terms that are ordinarily used. We shall make it as
brief as possible, taking in succession (1) the external structure, (2)
internal structure, (3) development of the individual, (4) classification.
In the course of this introductory sketch we shall find it necessary to
mention the names of some of the Orders of Insects that will only be
explained or defined in subsequent pages. We may therefore here state that
the term "Orthoptera" includes grasshoppers, locusts, earwigs, cockroaches;
"Neuroptera" comprises dragon-flies, May-flies, lacewings, stone-flies and
caddis-flies; to the "Hymenoptera" belong bees, wasps, ants, sawflies, and
a host of little creatures scarcely noticed by the ordinary observer:
"Coleoptera" are beetles; "Lepidoptera," butterflies and moths; "Diptera,"
house-flies, blue-bottles, daddy-longlegs, and such; "Hemiptera" or
"Rhynchota" are bugs, greenfly, etc.
CLASS INSECTA: OR INSECTA HEXAPODA.
_Definition_.—Insects are small animals, having the body divided into three
regions placed in longitudinal succession—head, thorax, and abdomen: they
take in air by means of tracheae, a system of tubes distributed throughout
the body, and opening externally by means of orifices placed at the sides
of the body. They have six legs, and a pair of antennae; these latter are
placed on the head, while the legs are attached to the thorax, or second of
the three great body divisions; the abdomen has no true legs, but not
infrequently has terminal appendages and, on the under surface,
protuberances which serve as feet. Very frequently there are two pairs of
wings, sometimes only one pair, in other cases none: the wings are always
placed on the thorax. Insects are transversely segmented—that is to say,
the body has the form of a succession of {87}rings; but this condition is
in many cases obscure; the number of these rings rarely, if ever, exceeds
thirteen in addition to the head and to a terminal piece that sometimes
exists. Insects usually change much in appearance in the course of their
growth, the annulose or ringed condition being most evident in the early
part of the individual's life. The legs are usually elongate and apparently
jointed, but in the immature condition may be altogether absent, or very
short; in the latter case the jointing is obscure. The number of jointed
legs is always six.
EXTERNAL STRUCTURE.
The series of rings of which the external crust or skeleton of Insects is
composed exhibits great modifications, not only in the various kinds of
Insects but even in the different parts of the same individual, and at
successive periods of its development; so that in the majority of mature
Insects the separate rings are readily distinguished only in the hind body
or abdomen. The total number of the visible rings, segments, somites, or
arthromeres, as they are variously called by different writers, is
frequently thirteen in addition to the head. This latter part is considered
to be itself composed of the elements of several rings, but morphologists
are not yet agreed as to their number, some thinking this is three while
others place it as high as seven; three or four being, perhaps, the figures
at present most in favour, though Viallanes, who has recently discussed[17]
the subject, considers six, the number suggested by Huxley, as the most
probable. Cholodkovsky is of a similar opinion. However this may be, the
three rings behind the head constitute the thorax, which is always largely
developed, though, like the head, its segmentation is usually very much
obscured by unequal development of different parts, or by consolidation of
some of them, or by both of these conditions. The third great division of
the body, the abdomen, is also usually much modified by one or more of the
terminal segments being changed in form, or even entirely withdrawn into
the interior of the body. The existence of ten segments in the hind body
can, however, be very frequently actually demonstrated, so that it is
correct to speak of ten as the normal number.
{88}[Illustration: FIG. 47—Diagram of exterior of insect: the two vertical
dotted lines indicate the divisions between H, head; T, thorax; and A,
abdomen: _a_, antenna; _b_, labrum; _c_, mandible; _d_, maxillary palpus;
_e_, labial palpus; _f_, facetted eye; _g_, pronotum; _h_, mesonotum; _i_,
metanotum; _k_, wings; _l_{1}_ to _l_{10}_, abdominal segments; _m_, the
internal membranous portions uniting the apparently separated segments;
_n_, cerci; _o_, stigma; _p_, abdominal pleuron bearing small stigmata;
_q_{1}_, _q_{2}_, _q_{3}_, pro-, meso-, meta-sterna; _r_{1}_, mesothoracic
episternum; _s_{1}_, epimeron, these two forming the mesopleuron; _r_{2}_,
_s_{2}_, metathoracic episternum and epimeron; _t_, coxa; _v_, trochanter;
_w_, femur; _x_, tibia; _y_, tarsus; _z_, gula.]
It is no reproach to morphologists that they have not yet agreed as to the
number of segments that may be taken as typical for an Insect, for all the
branches of evidence bearing on the point are still imperfect. It may be
well, therefore, to state the most extreme views that appear to be at all
admissible. Hagen[18] has recently stated the opinion that each thoracic
segment consists really of three segments—an anterior or wing-bearer, a
middle or leg-bearer, and a posterior or stigma-bearer. There seems to be
no reason for treating the stigma as being at all of the nature of an
appendage, and the theory of a triple origin for these segments may be
dismissed. There are, however, several facts that indicate a duplicity in
these somites, among which we may specially mention the remarkable
constancy of two pleural pieces on each side of each thoracic segment. The
hypothesis of these rings being each the representative of two segments
cannot therefore be at present considered entirely untenable, and in that
case the maximum and minimum numbers that can be suggested appear to be
twenty-four and eleven, distributed as follows:—
Maximum. Minimum. {89}
Head 7 3
Thorax 6 3
Abdomen 11 5
-- --
Total 24 11
Although it is not probable that ultimately so great a difference as these
figures indicate will be found to prevail, it is certainly at present
premature to say that all Insects are made up of the same number of primary
segments.
A brief account of the structure of the integument will be found in the
chapter dealing with the post-embryonic development.
The three great regions of the Insect body are functionally as well as
anatomically distinct. The head bears the most important of the sense
organs, viz. the antennae and ocular organs; it includes the greater of the
nerve-centres, and carries the mouth as well as the appendages, the trophi,
connected therewith. The thorax is chiefly devoted to the organs of
locomotion, bearing externally the wings and legs, and including
considerable masses of muscles, as well as the nerve centres by which they
are innervated; through the thorax there pass, however, in the longitudinal
direction, those structures by which the unity of the organisation is
completed, viz. the alimentary canal, the dorsal vessel or "heart" for
distributing the nutritive fluid, and also the nerve cords. The abdomen
includes the greater part of the organs for carrying on the life of the
individual and of the species; it also frequently bears externally, at or
near its termination, appendages that are doubtless usually organs of sense
of a tactile nature.
In the lower forms of Insect life there is little or no actual internal
triple division of the body; but in the higher forms such separation
becomes wonderfully complete, so that the head may communicate with the
thorax only by a narrow isthmus, and the thorax with the abdomen only by a
very slender link. This arrangement is carried to its greatest extreme in
the Hymenoptera Aculeata. It may be looked on as possibly a means for
separating the nutrition of the parts included in the three great body
divisions.
Along each side of the body extends a series of orifices for the admission
of air, the stigmata or spiracles; there are none of these on the head, but
on each side of most of the other segments {90}there is one of these
spiracles. This, however, is a rule subject to many exceptions, and it is
doubtful whether there is ever a spiracle on the last abdominal segment.
Even in the young stage of the Insect the number of these stigmata is
variable; while in the perfect Insect the positions of some of the stigmata
may be much modified correlatively with the unequal development or
consolidation of parts, especially of the thorax when it is highly modified
for bearing the wings.
The segments of the Insect are not separate parts connected with one
another by joints and ligaments; the condition of the Insect crust is in
fact that of a continuous long sac, in which there are slight constrictions
giving rise to the segments, the interior of the sac being always traversed
from end to end by a tube, or rather by the invaginated ends of the sac
itself which connect with an included second sac, the stomach. The more
prominent or exposed parts of the external sac are more or less hard, while
the constricted parts remain delicate, and thus the continuous bag comes to
consist of a series of more or less hard rings connected by more delicate
membranes. This condition is readily seen in distended larvae, and is shown
by our figure 48 which is taken from the same specimen, whose portrait,
drawn during life, will be given when we come to the Coleoptera, family
Cleridae. The nature of the concealed connexions between the apparently
separate segments of Insects is shown at _m_, Fig. 47, p. 88.
[Illustration: FIG. 48—_Tillus elongatus_, fully distended larva.]
As the number of segments in the adult Insect corresponds—except in the
head—with the number of divisions that appear very early in the embryo, we
conclude that the segmentation of the adult is, even in Insects which
change their form very greatly during growth, due to the condition that
existed in the embryo; but it must not be forgotten that important
secondary changes occur in the somites during the growth and development of
the individual. Hence in some cases there appear to be more than the usual
number of segments, e.g. _Cardiophorus_ larva, and in others the number of
somites is diminished by {91}amalgamation, or by the extreme reduction in
size of some of the parts.
Besides the division of the body into consecutive segments, another feature
is usually conspicuous; the upper part, in many segments, being
differentiated from the lower and the two being connected together by
intervening parts in somewhat the same sort of way as the segments
themselves are connected. Such a differentiation is never visible on the
head, but may frequently be seen in the thorax, and almost always in the
abdomen. A dorsal and a ventral aspect are thus separated, while the
connecting bond on either side forms a pleuron. By this differentiation a
second form of symmetry is introduced, for whereas there is but one upper
and one lower aspect, and the two do not correspond, there are two lateral
and similar areas. This bilateral symmetry is conspicuous in nearly all the
external parts of the body, and extends to most of the internal organs. The
pleura, or lateral regions of the sac, frequently remain membranous when
the dorsal and ventral aspects are hard. The dorsal parts of the Insect's
rings are also called by writers terga, or nota, and the ventral parts
sterna.
The appendages of the body are:—(1) a pair of antennae; (2) the trophi,
constituted by three pairs of mouth-parts; (3) three pairs of legs; (4) the
wings[19]; (5) abdominal appendages of various kinds, but usually jointed.
Before considering these in detail we shall do well to make ourselves more
fully acquainted with the elementary details of the structure of the trunk.
In the adult Insect the integument or crust of the body is more or less
hard or shell-like, sometimes, indeed, very hard, and on examination it
will be seen that besides the divisions into segments and into dorsal,
ventral, and pleural regions, there are lines indicating the existence of
other divisions, and it will be found that by dissection along these lines
distinct pieces can be readily separated. Each hard piece that can be so
separated is called a sclerite, and the individual sclerites of a segment
have received names from entomotomists. The sclerites are not really
{92}quite separate pieces, though we are in the habit of speaking of them
as if such were the case. If an Insect be distended by pressure from the
interior, many of the sclerites can be forced apart, and it is then seen
that they are connected by delicate membrane. The structure is thus made up
of hard parts meeting one another along certain lines of union—sutures—so
that the original membranous continuity may be quite concealed. In many
Insects, or in parts of them, the sclerites do not come into apposition by
sutures, and are thus, as it were, islands of hard matter surrounded by
membrane. A brief consideration of some of the more important sclerites is
all that is necessary for our present purpose: we will begin with the head.
[Illustration: FIG. 49.—Capsule of head of beetle, _Harpalus caliginosus_:
A, upper; B, under surface: _a_, clypeus; _b_, epicranium; _c_,
protocranium; _d_, gula; _e_, facetted eye; _f_, occipital foramen; _g_,
submentum; _h_, cavity for insertion of antenna.]
The head is most variable in size and form; as a part of its surface is
occupied by the eyes and as these organs differ in shape, extent, and
position to a surprising degree, it is not a matter for astonishment that
it is almost impossible to agree as to terms for the areas of the head. Of
the sclerites of the head itself there are only three that are sufficiently
constant and definite to be worthy of description here. These are the
clypeus, the epicranium, and the gula. The clypeus is situate on the upper
surface of the head-capsule, in front; it bears the labrum which may be
briefly described as a sort of flap forming an upper lip. The labrum is
usually possessed of some amount of mobility. The clypeus itself is
excessively variable in size and form, and sometimes cannot be delimited
owing to the obliteration of the suture of connexion with the more
posterior part of the head; it is rarely or never a paired piece.
Occasionally there is a more or less distinct piece interposed between the
clypeus and the labrum, and which is the source of considerable difficulty,
as it may be taken for the clypeus. Some authors call the clypeus the
epistome, but it is better to use this latter term for the purpose of
indicating the part that is immediately behind the labrum, whether that
part be the clypeus, or some other sclerite; the {93}term is very
convenient in those cases where the structure cannot be, or has not been,
satisfactorily determined morphologically.
In Figure 50 the parts usually visible on the anterior aspect of the head
and its appendages are shown so far as these latter can be seen when the
mouth is closed; in the case of the Insect here represented the bases of
the mandibles are clearly seen (_g_), while their apical portions are
entirely covered by the labrum, just below the lower margin of which the
tips of the maxillae are seen, looking as if they were the continuations of
the mandibles.
The labrum is a somewhat perplexing piece, morphologists being not yet
agreed as to its nature; it is usually placed quite on the front of the
head, and varies extremely in form; it is nearly always a single or
unpaired piece; the French morphologist Chatin considers that it is really
a paired structure.
[Illustration: FIG. 50.—Front view of head of field-cricket (_Gryllus_):
_a_, epicranium; _b_, compound eye; _c_, antenna; _d_, post-: _e_,
ante-clypeus; _f_, labrum; _g_, base of mandible; _h_, maxillary palpus;
_i_, labial palpus; _k_, apex of maxilla.]
The gula (Fig. 49, B _d_, and Fig. 47, _z_) is a piece existing in the
middle longitudinally of the under-surface of the head; in front it bears
the mentum or the submentum, and extends backwards to the great occipital
foramen, but in some Insects the gula is in front very distant from the
edge of the buccal cavity. The epicranium forms the larger part of the
head, and is consequently most inconstant in size and shape; it usually
occupies the larger part of the upper-surface, and is reflected to the
under-surface to meet the gula. Sometimes a transverse line exists (Fig.
49, A) dividing the epicranium into two parts, the posterior of which has
been called the protocranium; which, however, is not a good term. The
epicranium bears the antennae; these organs do not come out between the
epicranium and the clypeus, the foramen for their insertion being seated
entirely in the epicranium (see Fig. 50). In some Insects there are traces
of the epicranium being divided longitudinally along the middle line. When
this part is much modified the antennae may appear to be inserted on the
lateral portions of the head, or even {94}on its under-side; this arises
from extension of some part of the epicranium, as shown in Fig. 49, B,
where _h_, the cavity of insertion of the antenna, appears to be situate on
the under-surface of the epicranium, the appearance being due to an
infolding of an angle of the part.
There is always a gap in the back of the head for the passage of the
alimentary canal and other organs into the thorax; this opening is called
the occipital foramen. Various terms, such as frons, vertex, occiput,
temples, and cheeks, have been used for designating areas of the head. The
only one of these which is of importance is the gena, and even this can
only be defined as the anterior part of the lateral portion of the
head-capsule. An extended study of the comparative anatomy of the
head-capsule is still a desideratum in entomology. The appendages of the
head that are engaged in the operations of feeding are frequently spoken of
collectively as the trophi, a term which includes the labrum as well as the
true buccal appendages.
The appendages forming the parts of the mouth are paired, and consist of
the mandibles, the maxillae, and the labium, the pair in this latter part
being combined to form a single body. The buccal appendages are frequently
spoken of as gnathites. The gnathites are some, if not all, of them
composed of apparently numerous parts, some of these being distinct
sclerites, others membranous structures which may be either bare or
pubescent—that is, covered with delicate short hair. In Insects the mouth
functions in two quite different ways, by biting or by sucking. The Insects
that bite are called Mandibulata, and those that suck Haustellata. In the
mandibulate Insects the composition of the gnathites is readily
comprehensible, so that in nearly the whole of the vast number of species
of that type the corresponding parts can be recognised with something like
certainty. This, however, is not the case with the sucking Insects; in them
the parts of the mouth are very different indeed, so that in some cases
morphologists are not agreed as to what parts really correspond with some
of the structures of the Mandibulata. At present it will be sufficient for
us to consider only the mandibulate mouth, leaving the various forms of
sucking mouth to be discussed when we treat of the Orders of Haustellata in
detail.
The upper or anterior pair of gnathites is the mandibles, (Fig. 50, _g_).
There is no part of the body that varies more than {95}does the mandible,
even in the mandibulate Insects. It can scarcely be detected in some, while
in others, as in the male stag-beetle, it may attain the length of the
whole of the rest of the body; its form, too, varies as much as its size;
most usually, however, the pair of mandibles are somewhat of the form of
callipers, and are used for biting, cutting, holding, or crushing purposes.
The mandibles are frequently armed with processes spoken of as teeth, but
which must not be in any way confounded with the teeth of Vertebrates. The
only Insects that possess an articulated tooth are the Passalidae, beetles
armed with a rather large mandible bearing a single mobile tooth among
others that are not so. Wood Mason and Chatin consider the mandibles to be,
morphologically, jointed appendages, and the latter authority states that
in the mandible of _Embia_ he has been able to distinguish the same
elements as exist in the maxillae. In aculeate Hymenoptera the mandibles
are used to a considerable extent for industrial purposes.
[Illustration: FIG. 51.—Mandibles, maxillae, and labium of _Locusta
viridissima_: A, mandibles; B, maxillae (lateral parts) and labium (middle
parts) united: _a_, cardo; _b_, stipes; _c_, palpiger; _d_, max. palp.;
_e_, lacinia; _f_, galea; _g_, submentum; _h_, mentum; _i_, palpiger; _k_,
labial palpus; _l_, ligula; _m_, paraglossa (galea); _n_, lacinia; _o_,
lingua.]
The maxilla is a complex organ consisting of numerous pieces, viz. cardo,
stipes, palpiger, galea, lacinia, palpus. The galea and lacinia are
frequently called the lobes of the maxilla. The maxilla no doubt acts as a
sense organ as well as a mechanical apparatus for holding; this latter
function being subordinate to the other. In Fig. 68, p. 122, we have
represented a complex maxillary sense-organ.
The labium or lower lip has as its basal portion the {96}undivided mentum,
and closes the mouth beneath or behind, according as the position of the
head varies. In most Insects the labium appears very different from the
maxilla, but in many cases several of the parts corresponding to those of
the maxilla can be clearly traced in the labium.
[Illustration: FIG. 52.—Maxilla and lower lip of Coleoptera. A, Maxilla of
_Passalus_: _a_, cardo; _b_, stipes; _c_, palpiger; _d_, palpus; _e_, inner
or inferior lobe or lacinia; _f_, outer or superior lobe or galea: B,
Labium of _Harpalus caliginosus_: _a_, mentum; _b_, hypoglottis; _c_,
palpiger (support of the labial palp); _d_, palp; _e_, ligula; _f_,
paraglossa.]
The mentum is an undivided, frequently very hard, piece, continuous with
either the submentum or the gula, and anterior to this are placed the other
parts, viz. the labial palpi and their supports, the palpigers; beyond and
between these exists a central piece (Fig. 52, B, _e_), about whose name
some difference of opinion prevails, but which may be called the ligula
(languette of French authors), and on each side of this is a paraglossa. In
the Orthoptera the single median piece—the ligula of Coleopterists—is
represented by two divided parts. In some Insects (many Coleoptera) there
is interposed between the mentum and the palpigers a piece called the
hypoglottis (Fig. 52, B, _b_). It is not so well ascertained as it should
be, that the pieces of the lower lip bearing the same names in different
Orders are in all cases really homologous, and comparison suggests that the
hypoglottis of Coleoptera may possibly represent the piece corresponding to
the mentum of Orthopterists, the so-called mentum of beetles being in that
case the submentum of Orthopterists.
There is another part of the mouth to which we may call special attention,
as it has recently attracted more attention than it formerly did; it is a
membranous lobe in the interior of the mouth, very conspicuous in
Orthoptera, and called the tongue, lingua, or hypopharynx; it reposes, in
the interior of the mouth (Fig. 51, _o_), on the middle parts of the front
of the labium; it is probably not entirely lost in Coleoptera, but enters
into the composition of the {97}complex middle part of the lip by
amalgamation with the paraglossae. It has recently been proposed to treat
this lingua as the morphological equivalent of the labium or of the
maxillae, giving it the name of the endolabium, but the propriety of this
course remains to be proved;[20] the view is apparently suggested chiefly
by the structure of the mouth of _Hemimerus_, a very rare and most peculiar
Insect that has not as yet been sufficiently studied.
As the maxillae and labium are largely used by taxonomists in the
systematic arrangement of the mandibulate Insects, we give a figure of them
as seen in Coleoptera, where the parts, though closely amalgamated, can
nevertheless be distinguished. This Fig. 52 should be compared with Fig.
51.
In speaking of the segments of the body we pointed out that they were not
separate parts but constituted an uninterrupted whole, and it is well to
remark here that this is also true of the gnathites. Although the mouth
parts are spoken of as separate pieces, they really form only projections
from the great body wall. Fig. 51, B, shows the intimate connexion that
exists between the maxillae and labium; the continuity of the mandibles
with the membrane of the buccal cavity is capable of very easy
demonstration.
The head bears, besides the pieces we have considered, a pair of antennae.
These organs, though varying excessively in form, are always present in the
adult Insect, and exist even in the majority of young Insects. They are
very mobile, highly sensitive organs, situate on or near the front part of
the head. The antennae arise in the embryo from the procephalic lobes, the
morphological import of which parts is one of the most difficult points
connected with Insect embryology.
The eyes of Insects are of two sorts, simple and compound. The simple eyes,
or ocelli, vary in number from one to as many as eighteen or twenty; when
thus numerous they are situated in groups on each side of the head. In
their most perfect form, as found in adult aculeate Hymenoptera, in
Orthoptera and Diptera, ocelli are usually two or three in number, and
present the appearance of small, perfectly transparent lenses inserted in
the integument. In their simplest form they are said to consist of some
masses of pigment in connexion with a nerve.
{98}[Illustration: FIG. 53.—Two ommatidia from the eye of _Colymbetes
fuscus_, × 160. (After Exner.) _a_, Cornea; _b_, crystalline cone; _c_,
rhabdom; _d_, fenestrate membrane with nerve structures below it; _e_,
iris-pigment; _f_, retina-pigment.]
The compound, or facetted, eyes are the most remarkable of all the
structures of the Insect, and in the higher and more active forms, such as
the Dragon-flies and hovering Diptera, attain a complexity and delicacy of
organisation that elicit the highest admiration from every one who studies
them. They are totally different in structure and very distinct in function
from the eyes of Vertebrata, and are seated on very large special lobes of
the brain (see Fig. 65), which indeed are so large and so complex in
structure that Insects may be described as possessing special ocular brains
brought into relation with the lights, shades, and movements of the
external world by a remarkably complex optical apparatus. This instrumental
part of the eye is called the dioptric part in contradistinction from the
percipient portion, and consists of an outer corneal lens (_a_, Fig. 53),
whose exposed surface forms one of the facets of the eye; under the lens is
placed the crystalline cone (_b_), this latter being borne on a rod-like
object (_c_), called the rhabdom. There are two layers of pigment, the
outer (_e_), called the iris-pigment, the inner (_f_), the retinal-pigment;
underneath, or rather we should say more central than, the rhabdoms is the
fenestrate membrane (_d_), beyond which there is an extremely complex mass
of nerve-fibres; nerves also penetrate the fenestrate membrane, and their
distal extremities are connected with the delicate sheaths by one of which
each rhabdom is surrounded, the combination of sheath and nerves forming a
retinula. Each set of the parts above the fenestrate membrane constitutes
an ommatidium, and there may be many of these ommatidia in an eye; indeed,
it is said that the eye of a small beetle, _Mordella_, contains as many as
25,000 ommatidia. As a rule the larvae of Insects with a complete
metamorphosis bear only simple eyes. In the young of Dragon-flies, as well
as of some other Insects having a less perfect metamorphosis, the compound
eyes exist in the early stages, but they {99}have then an obscure
appearance, and are probably functionally imperfect.
In the interior of the head there exists a horny framework called the
tentorium, whose chief office apparently is to protect the brain. It is
different in kind according to the species. The head shows a remarkable and
unique relation to the following segments. It is the rule in Insect
structure that the back of a segment overlaps the front part of the one
following it; in other words, each segment receives within it the front of
the one behind it. Though this is one of the most constant features of
Insect anatomy, it is departed from in the case of the head, which may be
either received into, or overlapped by, the segment following it, but never
itself overlaps the latter. There is perhaps but a single Insect
(_Hypocephalus_, an anomalous beetle) in which the relation between the
head and thorax can be considered to be at all similar to that which exists
between each of the other segments of the body and that following it; and
even in _Hypocephalus_ it is only the posterior angles of the head that
overlap the thorax. Although the head usually appears to be very closely
connected with the thorax, and is very frequently in repose received to a
considerable extent within the latter, it nevertheless enjoys great freedom
of motion; this is obtained by means of a large membrane, capable of much
corrugation, and in which there are seated some sclerites, so arranged as
to fold together and occupy little space when the head is retracted, but
which help to prop and support it when extended for feeding or other
purposes. These pieces are called the cervical sclerites or plates. They
are very largely developed in Hymenoptera, in many Coleoptera, and in
Blattidæ, and have not yet received from anatomists a sufficient amount of
attention. Huxley suggested that they may be portions of head segments.
[Illustration: FIG. 54.—Extended head and front of thorax of a beetle,
_Euchroma_: _a_, back of head; _b_, front of pronotum; _c_, chitinous
retractile band; _d_, cervical sclerites.]
THORAX.
The thorax, being composed of the three consecutive rings behind the head,
falls naturally into three divisions—pro-, meso-, {100}and metathorax.
These three segments differ greatly in their relative proportions in
different Insects, and in different stages of the same Insect's life. In
their more highly developed conditions each of the three divisions is of
complex structure, and the sclerites of which it is externally made up are
sufficiently constant in their numbers and relative positions to permit of
their identification in a vast number of cases; hence the sclerites have
received names, and their nomenclature is of practical importance, because
some, if not all, of these parts are made use of in the classification of
Insects. Each division of the thorax has an upper region, called
synonymically dorsum, notum, or tergum; an inferior or ventral region,
called sternum; and on each side a lateral region, the pleuron. These
regions of each of the three thoracic divisions are further distinguished
by joining to their name an indication of the segment spoken of, in the
form of the prefixes pro-, meso-, and meta-; thus the pronotum, prosternum,
and propleura make up the prothorax. The thoracic regions are each made up
of sclerites whose nomenclature is due to Audouin.[21] He considered that
every thoracic ring is composed of the pieces shown in Fig. 55, viz. (1)
the sternum (B', _a_), an unpaired ventral piece; (2) the notum (A),
composed of four pieces placed in consecutive longitudinal order (A'), and
named praescutum (_a_), scutum (_b_), scutellum (_c_), and post-scutellum
(_d_); (3) lateral pieces, of which he distinguished on each side an
episternum (B', _c_), epimeron (_e_), and parapteron (_d_), these together
forming the pleuron. We give Audouin's Figure, but we cannot enter on a
full discussion of his views as to the thorax; they have become widely
known, though the constancy of the parts is not so great as he supposed it
would prove to be. Sometimes it is impossible to find all the elements he
thought should be present in a thoracic ring, while in other cases too many
sclerites exist. As a rule the notum of the meso- and metathoraces is in
greater part composed of two pieces, the scutum and the scutellum; while in
the pronotum only one dorsal piece can be satisfactorily distinguished,
though a study of the development may show that really two are frequently,
if not usually, present. On the other hand, one, or more, of the notal
sclerites in some cases shows evidence of longitudinal division along the
middle. The sternum or ventral piece, though varying greatly in form, is
{101}the most constant element of a thoracic segment, but it has sometimes
the appearance of consisting of two parts, an anterior and a posterior. The
pleuron nearly always consists quite evidently of two parts, the
episternum, the more anterior and inferior, and the epimeron.[22] The
relations between these two parts vary much; in some cases the episternum
is conspicuously the more anterior, while in others the epimeron is placed
much above it, and may extend nearly as far forwards as it. It may be said,
as a rule, that when the sternum extends farther backwards than the notum,
the epimeron is above the episternum, as in many Coleoptera; but if the
sternum be anterior to the notum, then the episternum is superior to the
epimeron, as in dragon-flies. We would here again reiterate the fact that
these "pieces" are really not separate parts, but are more or less
indurated portions of a continuous integument, which is frequently entirely
occupied by them; hence a portion of a sclerite that in one species is
hard, may in an allied form be wholly or partly membranous, and in such
case its delimitation may be very evident on some of its sides, and quite
obscure on another.
[Illustration: FIG. 55.—Mesothorax of _Dytiscus_, after Audouin. A, notum;
A', pieces of the notum separated: _a_, praescutum; _b_, scutum; _c_,
scutellum; _d_, post-scutellum: B, the sternum and pleura united; B', their
parts separated: _a_, sternum; _c_, episternum; _d_, parapteron; _e_,
epimeron.]
{102}The parapteron of Audouin does not appear to be really a distinct
portion of the pleuron; in the case of _Dytiscus_ it is apparently merely a
thickening of an edge. Audouin supposed this part to be specially connected
with the wing-articulation, and the term has been subsequently used by
other writers in connexion with several little pieces that exist in the
pleural region of winged Insects.
The prothorax is even more subject to variation in its development than the
other divisions of the thorax are. In the Hymenoptera the prosternum is
disconnected from the pronotum and is capable, together with the first pair
of legs, of movement independent of its corresponding dorsal part, the
pronotum, which in this Order is always more or less completely united with
the meso-thorax; in the Diptera the rule is that the three thoracic
segments are closely consolidated into one mass. In the majority of Insects
the prothorax is comparatively free, that is to say, it is not so closely
united with the other two thoracic segments as they are with one another.
The three thoracic rings are seen in a comparatively uniform state of
development in a great number of larvae; also in the adult stages of some
Aptera, and among winged insects in some Neuroptera such as the Embiidae,
Termitidae, and Perlidae. In Lepidoptera the pronotum bears a pair of
erectile processes called patagia; though frequently of moderately large
size, they escape observation, being covered with scales and usually
closely adpressed to the sides of the pronotum.
The two great divisions of the body—the mesothorax and the metathorax—are
usually very intimately combined in winged Insects, and even when the
prothorax is free, as in Coleoptera, these posterior two thoracic rings are
very greatly amalgamated. In the higher forms of the Order just mentioned
the mesosternum and mesopleuron become changed in direction, and form as it
were a diaphragm closing the front of the metasternum. The meso- and
meta-thorax frequently each bear a pair of wings.
We have described briefly and figured (Fig. 55) the sclerites of the
mesothorax, and those of the metathorax correspond fairly well with them.
In addition to the sclerites usually described as constituting these two
thoracic divisions, there are some small pieces at the bases of the wings.
Jurine discriminated and named no less than seven of these at the base of
the anterior {103}wing of a Hymenopteron. One of them becomes of
considerable size and importance in the Order just mentioned, and seems to
be articulated so as to exert pressure on the base of the costa of the
wing. This structure attains its maximum of development in a genus (?
nondescript) of Scoliidae, as shown in Fig. 56. The best name for this
sclerite seems to be that proposed by Kirby and Spence, tegula. Some
writers call it paraptère, hypoptère, or squamule, and others have termed
it patagium; this latter name is, however, inadmissible, as it is applied
to a process of the prothorax we have already alluded to.
[Illustration: FIG. 56.—Head and thorax of wasp from Bogota: _t_, tegula;
_b_, base of wing.]
To complete our account of the structure of the thorax it is necessary to
mention certain hard parts projecting into its interior, but of which there
is usually little or no trace externally. A large process in many Insects
projects upwards from the sternum in a forked manner. It was called by
Audouin the entothorax; some modern authors prefer the term apophysis.
Longitudinal partitions of very large size, descending from the dorsum into
the interior, also exist; these are called phragmas, and are of great
importance in some Insects with perfect flight, such as Hymenoptera,
Lepidoptera, and Diptera. There is no phragma in connection with the
pronotum, but behind this part there may be three. A phragma has the
appearance of being a fold of the dorsum; it serves as an attachment for
muscles, and may probably be of service in other ways. More insignificant
projections into the interior are the little pieces called apodemes (Fig.
57, _e_); these are placed at the sides of the thorax near the wings. The
apophyses are no doubt useful in preserving the delicate vital organs from
shocks, or from derangement by the muscular movements and the changes of
position of the body.
[Illustration: FIG. 57.—Transverse section of skeleton of metathorax of
_Goliathus druryi_, seen from behind: _a_, metanotum; _b_, metasternum;
_c_, phragma; _d_, entothorax (apophysis or furca); _e_, apodeme; _f_,
tendon of articulation. (After Kolbe.)]
The appendages of the thorax are (_a_) inferior, the legs; (_b_)
{104}superior, the wings. The legs are always six in number, and are
usually present even in larvae, though there exist many apodal larvae,
especially in Diptera. The three pairs of legs form one of the most
constant of the characters of Insects. They are jointed appendages and
consist of foot, otherwise tarsus; tibia, femur, trochanter, and coxa;
another piece, called trochantin more or less distinctly separated from the
coxa, exists in many Insects. The legs are prolongations of the body sac,
and are in closer relation with the epimera and with the episterna than
with other parts of the crust, though they have a close relation with the
sternum. If we look at the body and leg of a neuropterous Insect (Fig. 58)
we see that the basal part of the leg—the coxa—is apparently a continuation
of one of the two pleural pieces or of both; in the latter case one of the
prolonged pieces forms the coxa proper, and the tip of the other forms a
supporting piece, which may possibly be the homologue of the trochantin of
some Insects. In some Orthoptera, especially in Blattidae, and in
Termitidae, there is a transverse chitinised fold interposed between the
sternum and the coxa, and this has the appearance of being the same piece
as the trochantin of the anterior legs of Coleoptera.
[Illustration: FIG. 58.—Hind leg of _Panorpa_: _a_, episternum; _a′_,
epimeron; _b_, coxa; _b′_, coxal fold of epimeron; _c_, trochanter; _d_,
femur; _e_, tibia; _f_, tarsus.]
Beyond the coxa comes the trochanter; this in many Hymenoptera is a double
piece, though in other Insects it is single; usually it is the most
insignificant part of the leg. The femur is, on the whole, the least
variable part of the leg; the tibia, which follows it, being frequently
highly modified for industrial or other purposes. The joint between the
femur and the tibia is usually bent, and is therefore the most conspicuous
one in the leg; it is called the knee. The other joints have not
corresponding names, though that between the tibia and the tarsus is of
great importance. The spines at the tip of the tibia, projecting beyond it,
are called spurs, or calcares. The tarsus or {105}foot is extremely
variable; it is very rarely absent, but may consist of only one
piece—joint, as it is frequently called[23]—or of any larger number up to
five, which may be considered the characteristic number in the higher
Insect forms. The terminal joint of the tarsus bears normally a pair of
claws; between the claws there is frequently a lobe or process, according
to circumstances very varied in different Insects, called empodium,
arolium, palmula, plantula, pseudonychium, or pulvillus. This latter name
should only be used in those cases in which the sole of the foot is covered
with a dense pubescence. The form of the individual tarsal joints and the
armature or vestiture of the lower surface are highly variable. The most
remarkable tarsus is that found on the front foot of the male _Dytiscus_.
It has been suggested that the claws and the terminal appendage of the
tarsus ought to be counted as forming a distinct joint; hence some authors
state that the higher Insects have six joints to the feet. These parts,
however, are never counted as separate joints by systematic entomologists,
and it has recently been stated that they are not such originally.
The parts of the foot at the extremity of the last tarsal joint proper are
of great importance to the creature, and vary greatly in different Insects.
The most constant part of this apparatus is a pair of claws, or a single
claw. Between the two claws there may exist the additional apparatus
referred to above. This in some Insects—notably in the Diptera—reaches a
very complex development. We figure these structures in _Pelopaeus
spinolae_, a fossorial Hymenopteron, remarking that our figures exhibit the
apparatus in a state of retraction (Fig. 59). According to the nomenclature
of Dahl and Ockler[24] the plate (_b_) on the dorsal aspect is the pressure
plate (_Druck-Platte_), and acts as an agent of pressure on the sole of the
pad (C, _e_); _c_ and _d_ on the underside are considered to be
extension-agents; _c_, extension-plate; _d_, extension-sole
(_Streck-Platte_, _Streck-Sohle_). These agents are assisted in acting on
the pad by means of an elastic bow placed in the interior of the latter.
The pad (_e_) is a very remarkable structure, capable of much extension and
retraction; {106}when extended it is seen that the pressure plate is bent
twice at a right angle so as to form a step, the distal part of which runs
along the upper face of the basal part of the pad; the apical portion of
this latter consists of two large lobes, which in repose, as shown in our
Figure (_f_), fall back on the pad, something in the fashion of the
retracted claws of the cat, and conceal the pressure-plate.
The mode in which Insects are able to walk on smooth perpendicular surfaces
has been much discussed, and it appears highly probable that the method by
which this is accomplished is the exudation of moisture from the foot;
there is still, however, much to be ascertained before the process can be
satisfactorily comprehended. The theory to the effect that the method is
the pressure of the atmosphere acting on the foot when the sole is in
perfect apposition with the object walked on, or when a slight vacuum is
created between the two, has apparently less to support it.
[Illustration: FIG. 59.—Foot of _Pelopaeus_, a fossorial wasp: A, tarsus
entire; B, terminal joint, upper side; C, under side. _a_, claw; _b_, base
of pressure-plate; _c_, extension-plate; _d_, extension-sole; _e_, pad;
_f_, lobe of pad retracted.]
The legs of the young Insect are usually more simple than those of the
adult, and in caterpillars they are short appendages, and only imperfectly
jointed. If a young larva, with feet, of a beetle, such as _Crioceris
asparagi_ be examined, it may be seen that the leg is formed by
protuberance of the integument, which becomes divided into parts by simple
creases; an observation suggesting that the more highly developed jointed
leg is formed in a similar manner. This appears to be really the case,
{107}for the actual continuity of the limb at the chief joint—the knee—can
be demonstrated in many Insects by splitting the outer integument
longitudinally and then pulling the pieces a little apart; while in other
cases even this is not necessary, the knee along its inner face being
membranous to a considerable extent, and the membrane continuous from femur
to tibia.
Turning to the wings, we remark that there may be one or two pairs of these
appendages. When there is but one pair it is nearly always mesothoracic,
when there are two pairs one is invariably mesothoracic, the other
metathoracic. The situation of the wing is always at the edge of the notum,
but the attachment varies in other respects. It may be limited to a small
spot, and this is usually the case with the anterior wing; or the
attachment may extend for a considerable distance along the edge of the
notum, a condition which frequently occurs, especially in the case of the
posterior wings. The actual connexion of the wings with the thorax takes
place by means of strong horny lines in them which come into very close
relation with the little pieces in the thorax which we have already
described, and which were styled by Audouin articulatory epidemes. There is
extreme variety in the size, form, texture, and clothing of the wings, but
there is so much resemblance in general characters amongst the members of
each one of the Orders, that it is usually possible for an expert, seeing
only a wing, to say with certainty what Order of Insects its possessor
belonged to. We shall allude to these characters in treating of the Orders
of Insects.
Each wing consists of two layers, an upper and a lower, and between them
there may be tracheae and other structures, especially obvious when the
wings are newly developed. It has been shown by Hagen that the two layers
can be separated when the wings are recently formed, and it is then seen
that each layer is traversed by lines of harder matter, the nervures. These
ribs are frequently called wing-veins, or nerves, but as they have no
relation to the anatomical structures bearing those names, it is better to
make use of the term nervures. The strength, number, form and
inter-relations of these nervures vary exceedingly; they are thus most
important aids in the classification of Insects. Hence various efforts have
been made to establish a system of nomenclature that shall be uniform
throughout the different Orders, but at present success has not
{108}attended these efforts, and it is probable that no real homology
exists between the nervures of the different Orders of Insects. We shall
not therefore discuss the question here. We may, however, mention that
German savants have recently distinguished two forms of nervures which they
consider essentially distinct, viz. convex and concave. These, to some
extent, alternate with one another, but a fork given off by a convex one is
not considered to be a concave one. The terms convex and concave are not
happily chosen; they do not refer to the shape of the nervures, but appear
to have been suggested by the fact that the surface of the wing being
somewhat undulating the convex veins more usually run along the ridges, the
concave veins along the depressions. The convex are the more important of
the two, being the stronger, and more closely connected with the
articulation of the wing.
The wings, broadly speaking, may be said to be three-margined: the margin
that is anterior when the wings are extended is called the costa, and the
edge that is then most distant from the body is the outer margin, while the
limit that lies along the body when the wings are closed is the inner
margin.
The only great Order of Insects provided with a single pair of wings is the
Diptera, and in these the metathorax possesses, instead of wings, a pair of
little capitate bodies called halteres or poisers. In the abnormal
Strepsiptera, where a large pair of wings is placed on the metathorax,
there are on the mesothorax some small appendages that are considered to
represent the anterior wings. In the great Order Coleoptera, or beetles,
the anterior wings are replaced by a pair of horny sheaths that close
together over the back of the Insect, concealing the hind-wings, so that
the beetle looks like a wingless Insect: in other four-winged Insects it is
usually the front wings that are most useful in flight, but the elytra, as
these parts are called in Coleoptera, take no active part in flight, and it
has been recently suggested by Hoffbauer[25] that they are not the
homologues of the front wings, but of the tegulae (see Fig. 56), of other
Insects. In the Orthoptera the front wings also differ in consistence from
the other pair over which they lie in repose, and are called tegmina. There
are many Insects in which the wings {109}exist in a more or less
rudimentary or vestigial condition, though they are never used for purposes
of flight.
The abdomen, or hind body, is the least modified part of the body, though
some of the numerous rings of which it is composed may be extremely altered
from the usual simple form. Such change takes place at its two extremities,
but usually to a much greater extent at the distal extremity than at the
base. This latter part is attached to the thorax, and it is a curious fact
that in many Insects the base of the abdomen is so closely connected with
the thorax that it has all the appearance of being a portion of this latter
division of the body; indeed it is sometimes difficult to trace the real
division between the two parts. In such cases a further differentiation may
occur, and the part of the abdomen that on its anterior aspect is
intimately attached to the thorax may on its posterior aspect be very
slightly connected with the rest of the abdomen. Under such circumstances
it is difficult at first sight to recognise the real state of the case.
When a segment is thus transferred from the abdomen to the metathorax, the
part is called a median segment. The most remarkable median segment exists
in those Hymenoptera which have a stalked abdomen, but a similar though
less perfect condition exists in many Insects. When such a union occurs, it
is usually most complete on the dorsal surface, and the first ventral plate
may almost totally disappear: such an alteration may involve a certain
amount of change in the sclerites of the next segment, so that the
morphological determination of the parts at the back of the thorax and
front of the abdomen is by no means a simple matter. A highly modified
hind-body exists in the higher ants, Myrmicidae. In Fig. 60 we contrast the
simple abdomen of _Japyx_ with the highly modified state of the same part
in an ant.
[Illustration: FIG. 60.—Simple abdomen of _Japyx_ (A) contrasted with the
highly modified one of an ant, _Cryptocerus_ (B). The segments are numbered
from before backwards.]
Unlike the head and thorax, the abdomen is so loosely knitted together that
it can undergo much expansion and contraction. {110}This is facilitated by
an imbricated arrangement of the plates, and by their being connected by
means of membranes admitting of much movement (Fig. 47, _m_, p. 88). In
order to understand the structure of the abdomen it should be studied in
its most distended state; it is then seen that there is a dorsal and a
ventral hard plate to each ring, and there is also usually a stigma; there
may be foldings or plications near the line of junction of the dorsal and
ventral plates, but these margins are not really distinct pieces. The
pleura, in fact, remain membranous in the abdominal region, contrasting
strongly with the condition of these parts in the thorax. The proportions
of the plates vary greatly; sometimes the ventral are very large in
proportion to the dorsal, as is usually the case in Coleoptera, while in
the Orthoptera the reverse condition prevails.
Cerci or other appendages frequently exist at the extremity of the abdomen
(Fig. 47, _n_, p. 88); the former are sometimes like antennae, while in
other cases they may be short compressed processes consisting of very few
joints. The females of many Insects possess saws or piercing instruments
concealed within the apical part of the abdomen; in other cases an elongate
exserted organ, called ovipositor, used for placing the eggs in suitable
positions, is present. Such organs consist, it is thought, either of
modified appendages, called gonapophyses, or of dorsal, ventral, or pleural
plates. The males frequently bear within the extremity of the body a more
or less complicated apparatus called the genital armour. The term
gonapophysis is at present a vague one, including stings, some ovipositors,
portions of male copulatory apparatus, or other structures, of which the
origin is more or less obscure.
The caterpillar, or larva, of the Lepidoptera and some other Insects, bears
a greater number of legs than the three pairs we have mentioned as being
the normal number in Insects, but the posterior feet are in this case very
different from the anterior, and are called false legs or prolegs. These
prolegs, which are placed on the hind body, bear a series of hooks in
Lepidopterous larvae, but the analogous structures of Sawfly larvae are
destitute of such hooks.
Placed along the sides of the body, usually quite visible in the larva, but
more or less concealed in the perfect Insect, are little apertures for the
admittance of air to the respiratory {111}system. They are called spiracles
or stigmata. There is extreme variety in their structure and size; the
largest and most remarkable are found on the prothorax of Coleoptera,
especially in the groups Copridae and Cerambycidae.
The exact position of the stigmata varies greatly, as does also their
number. In the Order Aptera there may be none, while the maximum number of
eleven pairs is said by Grassi[26] to be attained in _Japyx solifugus_: in
no other Insect have more than ten pairs been recorded, and this number is
comparatively rare. Both position and number frequently differ in the early
and later stages of the same Insect. The structure of the stigmata is quite
as inconstant as the other points we have mentioned are.
[Illustration: FIG. 61.—Membranous space between pro- and meso-thoraces of
a beetle _Euchroma_, showing stigma (_st_); _a_, hind margin of pronotum;
_b_, front leg; _c_, front margin of mesonotum; _d_, base of elytra; _e_,
mesosternum.]
The admission of air to the tracheal system and its confinement there, as
well as the exclusion of foreign bodies, have to be provided for. The
control of the air within the system is, according to Landois[27] and
Krancher,[28] usually accomplished by means of an occluding apparatus
placed on the tracheal trunk a little inside of the stigma, and in such
case this latter orifice serves chiefly as a means for preventing the
intrusion of foreign bodies. The occluding apparatus consists of muscular
and mechanical parts, which differ much in their details in different
Insects. Lowne supposes that the air is maintained in the tracheal system
in a compressed condition, and if this be so, this apparatus must be of
great importance in the Insect economy. Miall and Denny[29] state that in
the anterior stigmata of the cockroach the valves act as the occluding
agents, muscles being attached directly to the inner face of the valves,
and in some other Insects the spiracular valves appear to act partially by
muscular agency, but there are many stigmata having valves destitute of
muscles. According to Lowne[30] there exist valves in the blowfly at the
entrance to the trachea proper, and he gives the following as the
arrangement of parts for the admission of air:—there is a spiracle
{112}leading into a chamber, the atrium, which is limited inwardly by the
occluding apparatus; and beyond this there is a second chamber, the
vestibule, separated from the tracheae proper by a valvular arrangement. He
considers that the vestibule acts as a pump to force the air into the
tracheae.
[Illustration: FIG. 62.—Diagrammatic Insect to explain terms of position.
A, apex; B, base: 1, tibia; 2, last abdominal segment; 3, ideal centre.]
SYSTEMATIC ORIENTATION.
Terms relating to position are unfortunately used by writers on entomology
in various, even in opposite senses. Great confusion exists as to the
application of such words as base, apex, transverse, longitudinal. We can
best explain the way in which the relative positions and directions of
parts should be described by reference to Figure 62. The spot 3 represents
an imaginary centre, situated between the thorax and abdomen, to which all
the parts of the body are supposed to be related. The Insect should always
be described as if it were in the position shown in the Figure, and the
terms used should not vary as the position is changed. The creature is
placed with ventral surface beneath, and with the appendages extended, like
the Insect itself, in a horizontal plane. In the Figure the legs are, for
clearness, made to radiate, but in the proper position the anterior pair
should be approximate in front, and the middle and hind pairs directed
backwards under the body. The legs are not to be treated as if they were
hanging from the body, though that is the position they frequently actually
assume. The right and left sides, and the upper and lower faces (these
latter are frequently also spoken of as sides), are still to retain the
same nomenclature even when the position of the specimen is reversed. The
base of an organ is that margin that is nearest to the ideal centre, the
apex that which is most distant. {113}Thus in Fig. 62, where 1 indicates
the front tibia, the apex (A) is broader than the base (B); in the antennae
the apex is the front part, while in the cerci the apex is the posterior
part; in the last abdominal segment (2) the base (B) is in front of the
apex (A). The terms longitudinal and transverse should always be used with
reference to the two chief axes of the body-surface; longitudinal referring
to the axis extending from before backwards, and transverse to that going
across, _i.e._ from side to side.
{114}CHAPTER IV
ARRANGEMENT OF INTERNAL ORGANS–MUSCLES–NERVOUS SYSTEM–GANGLIONIC CHAIN–
BRAIN–SENSE-ORGANS–ALIMENTARY CANAL–MALPIGHIAN TUBES–RESPIRATION–TRACHEAL
SYSTEM–FUNCTION OF RESPIRATION–BLOOD OR BLOOD-CHYLE–DORSAL VESSEL OR
HEART–FAT-BODY–OVARIES–TESTES–PARTHENOGENESIS–GLANDS.
The internal anatomy of Insects may be conveniently dealt with under the
following heads:—(1) Muscular system; (2) nervous system; (3) alimentary
system (under which may be included secretion and excretion, about which in
Insects very little is known); (4) respiratory organs; (5) circulatory
system; (6) fat-body; (7) reproductive system.
[Illustration: FIG. 63.—Diagram of arrangement of some of the internal
organs of an Insect: _a_, mouth; _b_, mandible; _c_, pharynx; _d_,
oesophagus; _e_, salivary glands (usually extending further backwards);
_f_, eye; _g_, supra-oesophageal ganglion; _h_, sub-oesophageal ganglion;
_i_, tentorium; _j_, aorta; _k_{1}_, _k_{2}_, _k_{3}_, entothorax;
_l_{1}-l_{8}_, ventral nervous chain; _m_, crop; _n_, proventriculus; _o_,
stomach; _p_, Malpighian tubes; _q_, small intestine; _r_, large intestine;
_s_, heart; _t_, pericardial septum; _u_, ovary composed of four egg-tubes;
_v_, oviduct; _w_, spermatheca (or an accessory gland); _x_, retractile
ovipositor; _y_, cercus; _z_, labrum.]
{115}Many of the anatomical structures have positions in the body that are
fairly constant throughout the class. Parts of the respiratory and muscular
systems and the fat-body occur in most of the districts of the body. The
heart is placed just below the dorsal surface; the alimentary canal extends
along the middle from the head to the end of the body. The chief parts of
the nervous system are below the alimentary canal, except that the brain is
placed above the beginning of the canal in the head. The reproductive
system extends in the abdomen obliquely from above downwards, commencing
anteriorly at the upper part and terminating posteriorly at the lower part
of the body cavity.
In Fig. 63 we show the arrangement of some of the chief organs of the body,
with the exception of the muscular and respiratory systems, and the
fat-body. It is scarcely necessary to point out that the figure is merely
diagrammatic, and does not show the shapes and sizes of the organs as they
will be found in any one Insect.
MUSCLES.
The muscular system of Insects is very extensive, Lyonnet[31] having found,
it is said, nearly 4000 muscles in the caterpillar of the goat-moth; a
large part of this number are segmental repetitions, nevertheless the
muscular system is really complex, as may be seen by referring to the study
of the flight of dragon-flies by von Lendenfeld.[32]
The minute structure of the muscles does not differ essentially from what
obtains in Vertebrate animals. The muscles are aggregations of minute
fibrils which are transversely striated, though in variable degree. Those
in the thorax are yellow or pale brown, but in other parts the colour is
more nearly white. The muscles of flight are described as being penetrated
by numerous tracheae, while those found elsewhere are merely surrounded by
these aerating tubules.
The force brought into play by the contractions of Insect muscles is very
great, and has been repeatedly stated to be much superior to that of
Vertebrate animals; very little reliance can, however, be {116}placed on
the assumptions and calculations that are supposed to prove this, and it is
not supported by Camerano's recent researches.[33]
Some of the tendons to which the muscles are attached are very elaborate
structures, and are as hard as the chitinous skeleton, so as to be like
small bones in their nature. A very elaborate tendon of this kind is
connected with the prothoracic trochantin in Coleoptera, and may be readily
examined in _Hydrophilus_. It has been suggested that the entothorax is
tendinous in its origin, but other morphologists treat it, with more
reason, as an elaborate fold inwards of the integument.
[Illustration: FIG. 64.—Cephalic and ventral chain of ganglia: A, larva of
_Chironomus_; B, imago of _Hippobosca_. (After Brandt.)]
NERVOUS SYSTEM.
Insects are provided with a very complex nervous system, which may be
treated as consisting of three divisions:—(1) The cephalic system; (2) the
ventral, or ganglionic chain; (3) an accessory sympathetic system, or
systems. All these divisions are intimately connected. We will consider
first the most extensive, viz. the ventral chain. This consists of a series
of small masses of nervous matter called ganglia which extend in the
longitudinal direction of the body along the median line of the lower
aspect, and are connected by longitudinal commissures, each ganglion being
joined to that following it by two threads of nervous matter. Each of the
ganglia of the ventral chain really consists of two ganglia placed side by
side and connected by commissures as well as cellular matter. In larvae
some of the ganglia may be contiguous, so that the commissures do not
exist. From the ganglia motor nerves proceed to the various parts of the
{117}body for the purpose of stimulating and co-ordinating the contractions
of the muscles. The number of the ganglia in the ventral chain differs
greatly in different Insects, and even in the different stages of
metamorphosis of the same species, but never exceeds thirteen. As this
number is that of the segments of the body, it has been considered that
each segment had primitively a single ganglion. Thirteen ganglia for the
ventral chain can, however, be only demonstrated in the embryonic state; in
the later stages of life eleven appears to be the largest number that can
be distinguished, and so many as this are found but rarely, and then
chiefly in the larval stage. The diminution in number takes place by the
amalgamation or coalescence of some of the ganglia, and hence those Insects
in which the ganglia are few are said to have a highly concentrated nervous
system. The modes in which these ganglia combine are very various; the most
usual is perhaps that of the combination of the three terminal ganglia into
one body. As a rule it may be said that concentration is the concomitant of
a more forward position of the ganglia. As a result of this it is found
that in some cases, as in Lamellicorn beetles, there are no ganglia situate
in the abdomen. In the perfect state of the higher Diptera, the thoracic
and abdominal ganglia are so completely concentrated in the thorax as to
form a sort of thoracic brain. In Fig. 64 we represent a very diffuse and a
very concentrated ganglionic chain; A being that of the larva of
_Chironomus_, B that of the imago of _Hippobosca_. In both these sketches
the cephalic ganglia as well as those of the ventral chain are shown.
Turning next to the cephalic masses, we find these in the perfect Insect to
be nearly always two in number: a very large and complex one placed above
the oesophagus, and therefore called the supra-oesophageal ganglion; and a
smaller one, the sub- or infra-oesophageal, placed below the oesophagus.
The latter ganglion is in many Insects so closely approximated to the
supra-oesophageal ganglion that it appears to be a part thereof, and is
sometimes spoken of as the lower brain. In other Insects these two ganglia
are more remote, and the infra-oesophageal one then appears part of the
ventral chain. In the embryo it is said that the mode of development of the
supra-oesophageal ganglion lends support to the idea that it may be the
equivalent of three ganglia; there being at one {118}time three lobes,
which afterwards coalesce, on each side of the mouth. This is in accordance
with the view formulated by Viallanes[34] to the effect that this great
nerve-centre, or brain, as it is frequently called, consists essentially of
three parts, viz. a Proto-, a Deuto-, and a Trito-cerebron. It is, however,
only proper to say that though the brain and the ventral chain of ganglia
may appear to be one system, and in the early embryonic condition to be
actually continuous, these points cannot be considered to be fully
established. Dr. L. Will has informed us[35] that in Aphididae the brain
has a separate origin, and is only subsequently united with the ganglionic
chain. Some authorities say that in the early condition the sub-oesophageal
ganglion is formed from two, and the supra-oesophageal from the same number
of ganglia; the division in that case being 2 and 2, not 3 and 1, as
Viallanes' views would suggest. The inquiries that are necessary to
establish such points involve very complex and delicate investigations, so
that it is not a matter of surprise that it cannot yet be said whether each
of these views may be in certain cases correct. The supra- and
sub-oesophageal ganglia are always intimately connected by a commissure on
each side of the oesophagus; when very closely approximated they look like
one mass through which passes the oesophagus (Fig. 66, A). The large
supra-oesophageal ganglion supplies the great nerves of the cephalic
sense-organs, while the smaller sub-oesophageal centre gives off the nerves
to the parts of the mouth. From the lower and anterior part of the
supra-oesophageal ganglion a nervous filament extends as a ring round the
anterior part of the oesophagus, and supplies a nerve to the upper lip.[36]
This structure is not very well known, and has been chiefly studied by
Liénard,[37] who considers that it will prove to be present in all Insects.
Whether the two cephalic ganglia be considered as really part of a single
great ganglionic chain, or the reverse, they are at any rate always
intimately connected with the ventral ganglia. We have already stated that
the two cephalic masses are themselves closely approximated in many
Insects, and may add that in some Hemiptera the first thoracic ganglion of
the ventral chain is amalgamated into one body with the sub-oesophageal
ganglion, {119}and further that there are a few Insects in which this
latter centre is wanting. If the cephalic ganglia and ventral chain be
looked on as part of one system, this may be considered as composed
originally of seventeen ganglia, which number has been demonstrated in some
embryos.
The anatomy of the supra-oesophageal ganglion is very complex; it has been
recently investigated by Viallanes[38] in the wasp (_Vespa_) and in a
grasshopper (_Caloptenus italicus_). The development and complication of
its inner structure and of some of its outer parts appear to be
proportional with the state of advancement of the instinct or intelligence
of the Insect, and Viallanes found the brain of the grasshopper to be of a
more simple nature than that of the wasp.
[Illustration: FIG. 65.—Brain of Worker Ant of _Formica rufa_. (After
Leydig, highly magnified.) Explanation in text.]
Brandt, to whom is due a large part of our knowledge of the anatomy of the
nervous system in Insects, says that the supra-oesophageal ganglion varies
greatly in size in various Insects, its mass being to a great extent
proportional with the development of the compound eyes; hence the absolute
size is not a criterion for the amount of intelligence, and we must rather
look to the complication of the structure and to the development of certain
parts for an index of this nature. The drone in the honey-bee has,
correlatively with the superior development of its eyes, a larger brain
than the worker, but the size of the hemispheres, and the development of
the gyri cerebrales is superior in the latter. In other words, the mass of
{120}those great lobes of the brain that are directly connected with the
faceted eyes must not be taken into account in a consideration of the
relation of the size and development of the brain to the intelligence of
the individual. The weight of the brain in Insects is said by Lowne to vary
from 1/150 to 1/2500 of the weight of the body.
Figure 65 gives a view of one side of the supra-oesophageal ganglion of the
worker of an ant,—_Formica rufa_,—and is taken from Leydig, who gives the
following elucidation of it: _A_, primary lobe, _a_, homogeneous granular
inner substance, _b_, cellular envelope; _B_, stalked bodies (gyri
cerebrales), _a_, _b_, as before; _C_, presumed olfactory lobes, _c_, inner
substance, _d_, ganglionic masses; _D_, ocular lobes, _e_, _f_, _g_, _h_,
various layers of the same; _E_, origin of lateral commissures; _F_, median
commissure in interior of brain; _G_, lower brain (sub-oesophageal
ganglion); _H_, ocelli; _J_, faceted eye.
[Illustration: FIG. 66.—Stomato-gastric nerves of Cockroach: A, with brain
_in situ_, after Koestler; B, with the brain removed, after Miall and
Denny: _s.g_, supra-oesophageal ganglion; _o_, optic nerve; _a_, antennary
nerve; _f.g_, frontal ganglion; _oe_, oesophagus; _c_, connective; _p.g_,
paired ganglia; _v.g_, crop or ventricular ganglion; _r_, recurrent nerve.]
Besides the brain and the great chain of ganglia there exists an accessory
system, or systems, sometimes called the sympathetic, vagus, or visceral
system. Although complex, these parts are delicate and difficult of
dissection, and are consequently not so well known as is the ganglionic
chain. There is a connecting or median nerve cord, communicating with the
longitudinal commissures of each segment, and itself dilating into ganglia
at intervals; this is sometimes called the unpaired system. There is
another group of nerves having paired ganglia, {121}starting from a small
ganglion in the forehead, then connecting with the brain, and afterwards
extending along the oesophagus to the crop and proventriculus (Fig. 66).
This is usually called the stomatogastric system. The oesophageal ring we
have already spoken of.
By means of these accessory nervous systems all the organs of the body are
brought into more or less direct relation with the brain and the ganglionic
chain.
Our knowledge of these subsidiary nervous systems is by no means extensive,
and their nomenclature is very unsettled; little is actually known as to
their functions.
ORGANS OF SENSE.
Insects have most delicate powers of perception, indeed they are perhaps
superior in this respect to the other classes of animals. Their senses,
though probably on the whole analogous to those of the Vertebrata, are
certainly far from corresponding therewith, and their sense organs seem to
be even more different from those of what we call the higher animals than
the functions themselves are. We have already briefly sketched the
structure of the optical organs, which are invariably situate on the head.
This is not the case with the ears, which certainly exist in one Order,—the
Orthoptera,—and are placed either on the front legs below the knee, or at
the base of the abdomen. Notwithstanding their strange situation, the
structures alluded to are undoubtedly auditory, and somewhat approximate in
nature to the ear of Vertebrates, being placed in proximity to the inner
face of a tense membrane; we shall refer to them when considering the
Orthoptera. Sir John Lubbock considers—no doubt with reason—that some ants
have auditory organs in the tibia. Many Insects possess rod-like or
bristle-like structures in various parts of the body, called chordotonal
organs; they are considered by Graber[39] and others to have auditory
functions, though they are not to be compared with the definite ears of the
Orthoptera.
The other senses and sense organs of Insects are even less known, and have
given rise to much perplexity; for though many structures have been
detected that may with more or less probability be looked on as sense
organs, it is difficult to assign a {122}particular function to any of
them, except it be to the sensory hairs. These are seated on various parts
of the body. The chitinous covering, being a dead, hard substance, has no
nerves distributed in it, but it is pierced with orifices, and in some of
these there is implanted a hair which at its base is in connexion with a
nerve; such a structure may possibly be sensitive not only to contact with
solid bodies, but even to various kinds of vibration. We give a figure
(Fig. 67) of some of these hairs on the caudal appendage of a cricket,
after Vom Rath. The small hairs on the outer surface of the chitin in this
figure have no sensory function, but each of the others probably has; and
these latter, being each accompanied by a different structure, must, though
so closely approximated, be supposed to have a different function; but in
what way those that have no direct connexion with a nerve may act it is
difficult to guess.
The antennae of Insects are the seats of a great variety of sense organs,
many of which are modifications of the hair, pit and nerve structure we
have described above, but others cannot be brought within this category.
Amongst these we may mention the pits covered with membrane (figured by
various writers), perforations of the chitin without any hair, and
membranous bodies either concealed in cavities or partially protruding
therefrom.
[Illustration: FIG. 67.—Longitudinal section of portion of caudal appendage
of _Acheta domestica_ (after Vom Rath): _ch_, chitin; _hyp_, hypodermis;
_n_, nerve; _h^1_, integumental hairs, not sensitive; _h^2_, ordinary hair;
_h^3_, sensory hair; _h^4_, bladder-like hair; _sz_, sense-cell.]
[Illustration: FIG. 68.—Longitudinal section of apex of palpus of _Pieris
brassicae_: _sch_, scales; _ch_, chitin; _hyp_, hypodermis; _n_, nerve;
_sz_, sense cells; _sh_, sense hairs. (After Vom Rath.)]
Various parts of the mouth are also the seats of sense organs of different
kinds, some of them of a compound character; in such cases there may be a
considerable number of hairs seated on branches of a common nerve as
figured {123}by Vom Rath[40] on the apex of the maxillary palp of _Locusta
viridissima_, or a compound organ such as we represent in Fig. 68 may be
located in the interior of the apical portion of the palp.
The functions of the various structures that have been detected are, as
already remarked, very difficult to discover. Vom Rath thinks the cones he
describes on the antennae and palpi are organs of smell, while he assigns
to those on the maxillae, lower lip, epipharynx, and hypopharynx the _rôle_
of taste organs, but admits he cannot draw any absolute line of distinction
between the two forms. The opinions of Kraepelin, Hauser, and Will, as well
as those of various earlier writers, are considered in Sir John Lubbock's
book on this subject.[41]
ALIMENTARY AND NUTRITIVE SYSTEM.
The alimentary canal occupies the median longitudinal axis of the body,
being situated below the dorsal vessel, and above the ventral nervous
chain; it extends from the mouth to the opposite extremity of the body. It
varies greatly in the different kinds of Insects, but in all its forms it
is recognised as consisting essentially of three divisions: anterior,
middle, and posterior. The first and last of these divisions are considered
to be of quite different morphological nature from the middle part, or true
stomach, and to be, as it were, invaginations of the extremities of a
closed bag; it is ascertained that in the embryo these invaginations have
really blind extremities (see Fig. 82, p. 151), and only subsequently
become connected with the middle part of the canal. There are even some
larvae of Insects in which the posterior portion of the canal is not opened
till near the close of the larval life; this is the case with many
Hymenoptera, and it is probable, though not as frequently stated certain,
that the occlusion marks the point of junction of the proctodaeum with the
stomach. The anterior and posterior parts of the canal are formed by the
ectoderm of the embryo, and in embryological and morphological language are
called respectively the stomodaeum and proctodaeum; the true stomach is
formed from the endoderm, {124}and the muscular layer of the whole canal
from the mesoderm.
[Illustration: FIG. 69.—Digestive system of _Xyphidria camelus_ (after
Dufour): _a_, head capsule; _b_, salivary glands; _c_, oesophagus; _d_,
crop; _e_, proventriculus; _f_, chyle, or true stomach; _g_, small
intestine; _h_, large intestine; _i_, Malpighian tubes; _k_, termination of
body.]
The alimentary canal is more complex anatomically than it is
morphologically, and various parts are distinguished, viz. the canal and
its appendicula; the former consisting of oesophagus, crop, gizzard, true
stomach, and an intestine divided into two or more parts. It should be
remarked that though it is probable that the morphological distinctions
correspond to a great extent with the anatomical lines of demarcation, yet
this has not been sufficiently ascertained: the origin of the proctodaeum
in _Musca_ is indeed a point of special difficulty, and one on which there
is considerable diversity of opinion. In some Hemiptera the division of the
canal into three parts is very obscure, so that it would be more correct,
as Dufour says, to define it as consisting in these Insects of two main
divisions—one anterior to, the other posterior to, the insertion of the
Malpighian tubes.
It should be borne in mind that the alimentary canal is very different in
different Insects, so that the brief general description we must confine
ourselves to will not be found to apply satisfactorily to any one Insect.
The oesophagus is the part behind the mouth, and is usually narrow, as it
has to pass through the most important nervous centres; extremely variable
in length, it dilates behind to form the crop. It may, too, have a
dilatation immediately behind the mouth, and in such case a pharynx is
considered to exist. The crop is broader than the oesophagus, and must be
looked on as a mere dilatation of the latter, as no line of
{125}demarcation can be pointed out between the two, and the crop may be
totally absent.
In some of the sucking Insects there is a lateral diverticulum, having a
stalk of greater or less length, called the sucking-stomach; it is by no
means certain that the function this name implies is correctly assigned to
the organ.
The gizzard or proventriculus (French, _gésier_; German, _Kaumagen_) is a
small body interposed in some Insects between the true stomach and the crop
or oesophagus. It is frequently remarkable for the development of its
chitinous lining into strong toothed or ridged processes that look as if
they were well adapted for the comminution of food. The function of the
proventriculus in some Insects is obscure; its structure is used by
systematists in the classification of ants. The extremity of the
proventriculus not infrequently projects into the cavity of the stomach.
The true stomach, or chylific ventricle (_Magen_ or _Mitteldarm_ of the
Germans), is present in all the post-embryonic stages of the Insect's life,
existing even in the imagines of those who live only for a few hours, and
do not use the stomach for any alimentary purpose. It is so variable in
shape and capacity that no general description of it can be given.
Sometimes it is very elongate, so that it is coiled and like an intestine
in shape; it very frequently bears diverticula or pouches, which are placed
on the anterior part, and vary greatly in size, sometimes they are only two
in number, while in other cases they are so numerous that a portion of the
outside of the stomach looks as if it were covered with villi. A division
of the stomach into two parts is in some cases very marked, and the
posterior portion may, in certain cases, be mistaken for the intestine; but
the position of the Malpighian tubes serves as a mark for the distinction
of the two structures, the tubes being inserted just at the junction of the
stomach with the intestine.
The intestine is very variable in length: the anterior part is the smaller,
and is frequently spoken of as the colon; at the extremity of the body the
gut becomes much larger, so as to form a rectum. There is occasionally a
diverticulum or "caecum" connected with the rectum, and in some Insects
stink-glands. In some Hemiptera there is no small intestine, the Malpighian
tubes being inserted at the junction of the stomach with the {126}rectum.
The total length of the alimentary canal is extremely variable; it is
necessarily at least as long as the distance between the mouth and anal
orifice, but sometimes it is five or six times as long as this, and some of
its parts then form coils in the abdominal cavity.
The alimentary canal has two coats of muscles: a longitudinal and a
transverse or annular. Both coexist in most of its parts. Internal to these
coats there exists in the anterior and posterior parts of the canal a
chitinous layer, which in the stomach is replaced by a remarkable
epithelium, the cells of which are renewed, new ones growing while the old
are still in activity. We figure a portion of this structure after Miall
and Denny, and may remark that Oudemans[42] has verified the correctness of
their representation. The layers below represent the longitudinal and
transverse muscles.
[Illustration: FIG. 70.—Epithelium of stomach of Cockroach (after Miall and
Denny): the lower parts indicate the transverse and longitudinal muscular
layers.]
In addition to the various diverticula we have mentioned, there are two
important sets of organs connected with the alimentary canal, viz. the
salivary glands and the Malpighian tubes.
The salivary glands are present in many Insects, but are absent in others.
They are situate in the anterior portion of the body, and are very variable
in their development, being sometimes very extensive, in other cases
inconspicuous. They consist either of simple tubes lined with cells, or of
branched tubes, or of tubes dilated laterally into little acini or groups
of bags, the arrangement then somewhat resembling that of a bunch of
grapes. There are sometimes large sacs or reservoirs connected with the
efferent tubes proceeding from the secreting portions of the glands. The
salivary glands ultimately discharge into the mouth, so that the fluid
secreted by them has to be {127}swallowed in the same manner as the food,
not improbably along with it. The silk so copiously produced by some larvae
comes from very long tubes similar in form and situation to the simple
tubes of the salivary glands.
The Malpighian tubules are present in most Insects, though they are
considered on good authority to be absent in many Collembola and in some
Thysanura. They are placed near the posterior part of the body, usually
opening into the alimentary canal just at the junction of the stomach and
the intestine, at a spot called the pylorus. They vary excessively in
length and in number,[43] being sometimes only two, while in other cases
there may be a hundred or even more of them. In some cases they are budded
off from the hind-gut of the embryo when this is still very small; in other
cases they appear later; frequently their number is greater in the adult
than it is in the young. In _Gryllotalpa_ there is one tube or duct with a
considerable number of finer tubes at the end of it. There is no muscular
layer in the Malpighian tubes, they being lined with cells which leave a
free canal in the centre. The tubes are now thought, on considerable
evidence, to be organs for the excretion of uric acid or urates, but it is
not known how they are emptied. Marchal has stated[44] that he has seen the
Malpighian tubes, on extraction from the body, undergo worm-like movements;
he suggests that their contents may be expelled by similar movements when
they are in the body.
The functions of the different portions of the alimentary canal, and the
extent to which the ingested food is acted on by their mechanical
structures or their products is very obscure, and different opinions
prevail on important points. It would appear that the saliva exercises a
preparatory action on the food, and that the absorption of the nutritive
matter into the body cavity takes place chiefly from the true stomach,
while the Malpighian tubes perform an excretory function. Beyond these
elementary, though but vaguely ascertained facts, little is known, though
Plateau's[45] and Jousset's researches on the digestion of Insects throw
some light on the subject.
{128}RESPIRATORY ORGANS.
The respiration of Insects is carried on by means of a system of vessels
for the conveyance of air to all parts of the body; this system is most
remarkably developed and elaborate, and contrasts strongly with the
mechanism for the circulation of the blood, which is as much reduced as the
air system is highly developed, as well as with the arrangement that exists
in the Vertebrates. There are in Insects no lungs, but air is carried to
every part of the body directly by means of tracheae. These tracheae
connect with the spiracles—the orifices at the sides of the body we have
already mentioned when describing the external structures—and the air thus
finds its way into the most remote recesses of the Insect's body. The
tracheae are all intimately connected. Large tubes connect the spiracles
longitudinally, others pass from side to side of the body, and a set of
tracheae for the lower part of the body is connected with another set on
the upper surface by means of several descending tubes. From these main
channels smaller branches extend in all directions, forking and giving off
twigs, so that all the organs inside the body can be supplied with air in
the most liberal manner. On opening a freshly deceased Insect the abundance
of the tracheae is one of the peculiarities that most attracts the
attention; and as these tubes have a peculiar white glistening appearance,
they are recognised without difficulty. In Insects of active flight,
possibly in some that are more passive, though never in larvae, there are
air-sacs, of more than one kind, connected with the tracheae, and these are
sufficiently capacious to have a considerable effect in diminishing the
specific gravity of the Insect. The most usual situation for these sacs is
the basal portion of the abdominal cavity, on the great lateral tracheal
conduits. In speaking of the external structure we have remarked that the
stigmata, or spiracles, by which the air is admitted are very various in
their size and in the manner in which they open and close. Some spiracles
have no power of opening; while others are provided with a muscular and
valvular apparatus for the purpose of opening and closing effectually.
The structure of the tracheae is remarkable: they are elastic and consist
of an outer cellular, and an inner chitinous layer; this latter is
strengthened by a peculiar spiral fibre, which gives {129}to the tubes,
when examined with the microscope, a transversely, closely striated
appearance. Packard considers[46] that in some tracheae this fibre is not
really spiral, but consists of a large number of closely placed rings. Such
a condition has not, however, been recorded by any other observer. The
spiral fibre is absent in the fine capillary twigs of the tracheal system,
as well as from the expanded sacs. The mode of termination of the capillary
branches is not clear. Some have supposed that the finest twigs anastomose
with others; on the other hand it has been said that they terminate by
penetrating cells, or that they simply come to an end with either open or
closed extremities. Wistinghausen[47] states that in the silk-glands the
tracheal twigs anastomose, and he is of opinion that the fine terminal
portions contain fluid. However this may be, it is certain that all the
organs are abundantly supplied with a capillary tracheal network, or
arboreal ramification, and that in some cases the tubes enter the substance
of tissues. Near their terminations they are said to be 1/30 to 1/60
millimetre in diameter.
[Illustration: FIG. 71.—Portion of the abdominal part of tracheal system of
a Locust (_Oedipoda_): _a_, spiracular orifices; _b_, tracheal tubes; _c_,
vesicular dilatations; _d_, tracheal twigs or capillaries. (After Dufour.)]
We must repeat that such a system as we have just sketched forms a striking
contrast to the imperfect blood-vascular system, and that Insects differ
profoundly in these respects from Vertebrate animals. In the latter the
blood-vessels penetrate to all {130}the tissues and form capillaries, while
the aerating apparatus is confined to one part of the body; in Insects the
blood-circulating system is very limited, and air is carried directly by
complex vessels to all parts; thus the tracheal system is universally
recognised as one of the most remarkable of the characters of Insects. Many
Insects have a very active respiratory system, as is shown by the rapidity
with which they are affected by agents like chloroform; but the exact
manner in which the breathing is carried on is unknown. In living Insects
rapid movements of contraction and expansion of parts of the body, chiefly
the abdomen, may be observed, and these body contractions are sometimes
accompanied by opening and shutting the spiracular orifices: it has been
inferred that these phenomena are respiratory. Although such movements are
not always present, it is possible that when they occur they may force the
air onwards to the tissues, though this is by no means certain. It is clear
that the tracheal system is the usual means of supplying the organisation
with oxygen, but it appears to be improbable that it can also act as the
agent for removing the carbonaceous products of tissue-changes. It has been
thought possible that carbonic acid might reach the spiracles from the
remote capillaries by a process of diffusion,[48] but it should be
recollected that as some Insects have no tracheal system, there must exist
some other mode of eliminating carbonic acid, and it is possible that this
mode may continue to operate as an important agent of purification, even
when the tracheal system is, as a bearer of air to the tissues, highly
developed. Eisig[49] has suggested that the formation of chitin is an act
of excretion; if so this is capable of relieving the system of carbonic
acid to some extent. Others have maintained that transpiration takes place
through the delicate portions of the integument. Lubbock[50] has shown that
Melolontha larvae breathe "partly by means of their skin." The mode in
which the carbon of tissue-change, and the nitrogen of inspiration are
removed, is still obscure; but it appears probable that the views expressed
by Réaumur, Lyonnet, and Lowne[51] as to inspiration and expiration may
prove to be nearer the truth than those which are more widely current. In
{131}connexion with this it should be recollected that the outer integument
consists of chitin, and is cast and renewed several times during the life
of the individual. Now as chitin consists largely of carbon and nitrogen,
it is evident that the moulting must itself serve as a carbonaceous and
nitrogenous excretion. If, as is suggested by Bataillon's researches,[52]
the condition accompanying metamorphosis be that of asphyxia, it is
probable that the secretion of the new coat of chitin may figure as an act
of excretion of considerable importance. If there be any truth in this
suggestion it may prove the means of enabling us to comprehend some points
in the development of Insects that have hitherto proved very perplexing.
Peyrou has shown[53] that the atmosphere extracted from the bodies of
Insects (_Melolontha_) is much less rich in oxygen than the surrounding
atmosphere is, and at ordinary temperatures always contains a much larger
proportion of carbonic acid: he finds, too, that as in the leaves with
which he makes a comparison, the proportion of oxygen augments as the
protoplasmic activity diminishes. Were such an observation carried out so
as to distinguish between the air in the tracheal system and the gas in
other parts of the body the result would be still more interesting.
We know very little as to the animal heat produced by insects, but it is
clear from various observations[54] that the amount evolved in repose is
very small. In different conditions of activity the temperature of the
insect may rise to be several degrees above that of the surrounding medium,
but there seems to be at present no information as to the physiological
mode of its production, and as to the channel by which the products—whether
carbonic acid or other matters—may be disposed of.
In the order Aptera (Thysanura and Collembola) the tracheal system is
highly peculiar. In some Collembola it apparently does not exist, and in
this case we may presume with greater certainty that transpiration of gases
occurs through the integument: in other members of this Order tracheae are
present in a more or less imperfect state of development, but the tracheae
of different segments do not communicate with one another, {132}thus
forming a remarkable contrast to the amalgamated tracheal system of the
other Orders of Insects, where, even when the tracheal system is much
reduced in extent (as in Coccidae), it is nevertheless completely unified.
_Gryllotalpa_ is, however, said by Dohrn[55] to be exceptional in this
respect; the tracheae connected with each spiracle remaining unconnected.
Water Insects have usually peculiarities in their respiratory systems,
though these are not so great as might _à priori_ have been anticipated.
Some breathe by coming to the surface and taking in a supply of air in
various manners, but some apparently obtain from the water itself the air
necessary for their physiological processes. Aquatic Insects are frequently
provided with gills, which may be either wing-like expansions of the
integument containing some tracheae (Ephemeridae larvae), or bunches of
tubes, or single tubes (Trichoptera larvae). Such Insects may either
possess stigmata in addition to the gills, or be destitute of them. In
other cases air is obtained by taking water into the posterior part of the
alimentary canal (many dragon-flies), which part is then provided with
special tracheae. Some water-larvae appear to possess neither stigmata nor
gills (certain Perlidae and Diptera), and it is supposed that these obtain
air through the integument; in such Insects tracheal twigs may frequently
be seen on the interior of the skin. In the imago state it is the rule that
Water Insects breathe by means of stigmata, and that they carry about with
them a supply of air sufficient for a longer or shorter period. A great
many Insects that live in water in their earlier stages and breathe there
by peculiar means, in their perfect imago state live in the air and breathe
in the usual manner. There are, in both terrestrial and aquatic Insects, a
few cases of exsertile sacs without tracheae, but filled with blood
(_Pelobius_ larva, _Machilis_, etc.); and such organs are supposed to be of
a respiratory nature, though there does not appear to be any positive
evidence to that effect.
BLOOD AND BLOOD-CIRCULATION.
Owing to the great complexity of the tracheal system, and to its general
diffusion in the body, the blood and its circulation are very different in
Insects from what they are in Vertebrates, so {133}that it is scarcely
conducive to the progress of physiological knowledge to call two fluids
with such different functions by one name. The blood of Insects varies
according to the species, and in all probability even in conformity with
the stage of the life of the individual. Its primary office is that of
feeding the tissues it bathes, and it cannot be considered as having any
aerating function. It is frequently crowded with fatty substances. Graber
says: "The richness of Insect blood in unsaponified or unelaborated fat
shows in the plainest manner that it is more properly a mixture of blood
and chyle; or indeed we might say with greater accuracy, leaving out of
consideration certain matters to be eliminated from it, that it is a
refined or distilled chyle." Connected in the most intimate manner with the
blood there is a large quantity of material called vaguely the fat-body;
the blood and its adjuncts of this kind being called by Wielowiejski[56]
the blood-tissue. We shall return to the consideration of this tissue after
sketching the apparatus for distributing the refined chyle, or blood as we
must, using the ordinary term, call it.
There is in Insects no complete system of blood-vessels, though there is a
pulsating vessel to ensure distribution of the nutritive fluid. This dorsal
vessel, or heart as it is frequently called, may be distinguished and its
pulsations watched, in transparent Insects when alive. It is situate at the
upper part of the body, extending from the posterior extremity, or near it,
to the head or thorax, and is an elongate tube, consisting as it were of a
number of united chambers; it is closed behind, except in some larvae, but
is open in front, and has several orifices at the sides; these orifices, or
ostia, are frequently absent from the front part of the tube, which portion
is also narrower, being called the aorta—by no means a suitable term. Near
the lateral orifices there are delicate folds, which act to some extent as
valves, facilitating, in conjunction with the mode of contraction of the
vessel, a forward movement of the blood. The composition of the tube, or
series of chambers, is that of a muscular layer, with internal and external
membranous coverings, the intima and adventitia. Olga Poletajewa states[57]
that in _Bombus_ the dorsal vessel consists of five chambers placed in
longitudinal succession, and not very intimately connected, and that there
is but little {134}valvular structure. In _Cimbex_ she finds a similar
arrangement, but there are ten chambers, and no aorta.
The dorsal vessel is connected with the roof of the body by some short
muscles, and is usually much surrounded by fat-body into which tracheae
penetrate; by these various means it is kept in position, though only
loosely attached; beneath it there is a delicate, incomplete or fenestrate,
membrane, delimiting a sort of space called the pericardial chamber or
sinus; connected with this membrane are some very delicate muscles, the
alary muscles, extending inwards from the body wall (_b_, Fig. 72): the
curtain formed by these muscles and the fenestrate membrane is called the
pericardial diaphragm or septum. The alary muscles are not directly
connected with the heart.
[Illustration: FIG. 72.—Dorsal vessel (_c_), and alary muscles (_b_), of
_Gryllotalpa_ (after Graber); _a_, aorta. _N.B._—The ventral aspect is here
dorsal, and nearly the whole of the body is removed to show these parts.]
[Illustration: FIG. 73.—Diagram of transverse section of pericardial sinus
of _Oedipoda coerulescens_. (After Graber, _Arch. Mikr. Anat._ ix.) H,
heart; _s_, septum; _m_, muscles—the upper suspensory, the lower alary.]
It has been thought by some that delicate vessels exist beyond the aorta
through which the fluid is distributed in definite channels, but this does
not appear to be really the case, although the fluid may frequently be seen
to move in definite lines at some distance from the heart.
There is still much uncertainty as to some of the details of the action of
the heart, and more especially as to the influence of the alary muscles.
The effect of the contraction of these must be to increase the area of the
pericardial chamber by rendering {135}its floor or septum less arched, as
shown in our diagram (Fig. 73), representing a transverse section through
the pericardial chamber, H being the dorsal vessel with _m_ its suspensory
muscles, and _s_ its septum, with _m_ the alary muscles. The contraction of
these latter would draw the septum into the position of the dotted line,
thus increasing the area of the sinus above; but as this floor or septum is
a fenestrated structure, its contraction allows fluid to pass through it to
the chamber above; thus this arrangement may be looked on as a means of
keeping up a supply of fluid to the dorsal vessel, the perforated septum,
when it contracts, exerting pressure on the tissues below; these are
saturated with fluid, which passes through the apertures to the enlarged
pericardial chamber.
Some misconception has prevailed, too, as to the function of the
pericardial chamber. This space frequently contains a large quantity of
fat-body—pericardial tissue—together with tracheae, and this has given rise
to the idea that it might be lung-like in function; but, as Miall and
Denny[58] have pointed out, this is erroneous; the tissues in Insects have
their own ample supplies of air. It has also been supposed that the alary
muscles cause the contraction of the heart, but this is not directly the
case, for they are not attached to it, and it pulsates after they have been
severed. It has been suggested that the contractions of this vessel are
regulated by small ganglia placed on, or in, its substance. However this
may be, these contractions vary enormously according to the condition of
the Insect; they may be as many, it is said, as 100 or more in a minute, or
they may be very slow and feeble, if not altogether absent, without the
death of the Insect ensuing.
The expulsion of the blood from the front of the dorsal vessel seems to be
due to the rhythm of the contraction of the vessel as well as to its
mechanical structure. Bataillon says,[59] confirming an observation of
Réaumur, that at the period when the silkworm is about to change to the
chrysalis condition, the circulation undergoes periodical changes, the
fluid moving during some intervals of about ten minutes' duration in a
reversed direction, while at other times the blood is expelled in front and
backwards simultaneously, owing apparently to a rhythmical change in the
mode of contraction of the dorsal vessel.
{136}As the dorsal vessel consists of a number of distinct chambers, it has
been suggested that there is normally one of these for each segment of the
body; and it appears that the total number is sometimes thirteen, which is
frequently that of the segments of the body without the head. The number of
chambers differs, however, greatly, as we have previously stated, and
cannot be considered to support the idea of an original segmental
arrangement of the chambers. The dorsal vessel, though in the adult a
single organ, arises in the embryo from two lateral, widely separated parts
which only in a subsequent stage of the embryonic development coalesce in
the median line.
FAT-BODY.
In discussing the tracheae we remarked on the importance of their function
and on their abundant presence in the body. Equally conspicuous, and
perhaps scarcely less important in function, is the fat-body, which on
opening some Insects, especially such as are in the larval stage, at once
attracts attention. It consists of masses of various size and indefinite
form distributed throughout the body, loosely connected together, and more
or less surrounding and concealing the different organs. The colour varies
according to the species of Insect. This fat-body is much connected with
fine tracheal twigs, so that an organisation extending throughout the body
is thus formed. It may be looked on as a store of nutritious matter which
may be added to or drawn on with great rapidity; and it is no doubt on this
that many of the internal parasites, so common in the earlier stages of
Insects' lives, subsist before attacking the more permanent tissues of
their hosts. There is some reason to suppose that the fat-body may have
some potency in determining the hunger of the Insect, for some parasitised
larvae eat incessantly.
The matter extracted from the food taken into the stomach of the Insect,
after undergoing some elaboration—on which point very little is known—finds
its way into the body-cavity of the creature, and as it is not confined in
any special vessels the fat-body has as unlimited a supply of the nutritive
fluid as the other organs: if nutriment be present in much greater quantity
than is required for the purposes of immediate activity, metamorphosis or
reproduction, it is no doubt taken up by the {137}fat-body which thus
maintains, as it were, an independent feeble life, subject to the demands
of the higher parts of the organisation. It undoubtedly is very important
in metamorphosis, indeed it is possible that one of the advantages of the
larval state may be found in the fact that it facilitates, by means of the
fat-body, the storage in the organisation of large quantities of material
in a comparatively short period of time.
A considerable quantity of fat tissue is found in the pericardial sinus,
where it is frequently of somewhat peculiar form, and is spoken of as
pericardial cells, or pericardial tissue. Some large cells, frequently of
pale yellow colour, and containing no fat, are called oenocytes by
Wielowiejski. They are connected with the general fat-body, but are not
entirely mingled with it; several kinds have been already distinguished,
and they are probably generally present. The phagocytes, or leucocytes, the
cells that institute the process of histolysis in the metamorphosis of
_Muscidae_, are a form of blood cell; though these cells are amoeboid some
writers derive them from the fat-body. The cells in the blood have no doubt
generally an intimate relation with the fat-body, but very little accurate
information has been obtained as to these important physiological points,
though Graber has inaugurated their study.[60]
ORGANS OF SEX.
The continuation of the species is effected in Insects by means of two
sexes, each endowed with special reproductive organs. It has been stated
that there are three sexes in some Insects—male, female, and neuter; but
this is not correct, as the so-called neuters are truly sexed
individuals,—generally females,—though, as a rule, they are not occupied
with the direct physiological processes for continuing the species.
The offspring is usually produced in the shape of eggs, which are formed in
ovaries. These organs consist of egg-tubes, a cluster of which is placed on
each side of the body, and is suspended, according to Leydig[61] and
others, to the tissue connected with the heart by means of the thread-like
terminations of the tubes.
{138}[Illustration: FIG. 74.—Sex organs of female of _Scolia interrupta_
(after Dufour); _a_, egg-tubes; _b_, oviducts; _c_, poison glands; _d_,
duct of accessory gland (or spermatheca); _e_, external terminal parts of
body.]
The number of egg-tubes varies greatly in different Insects; there may be
only one to each ovary (_Campodea_), but usually the number is greater, and
in the queen-bee it is increased to about 180. In the Queens of the
Termitidae, or white ants, the ovaries take on an extraordinary
development; they fill the whole of the greatly distended hind-body. Three
thousand egg-tubes, each containing many hundred eggs, may be found in a
Queen Termite, so that, as has been said by Hagen,[62] an offspring of
millions in number is probable. There is considerable variety in the
arrangements for the growth of the eggs in the egg-tubes. Speaking
concisely, the tubes may be considered to be centres of attraction for
nutritive material, of which they frequently contain considerable stores.
Next to the terminal thread, of which we have already spoken, there is a
greater or smaller enlargement of the tube, called the terminal chamber;
and there may also be nutriment chambers, in addition to the dilatations
which form the egg-chambers proper. Korschelt[63] distinguishes three
principal forms of egg-tubes, viz. (1) there are no special nutriment
chambers, a condition shown in Figure 74; (2) nutriment chambers alternate
with the egg-chambers, as shown in our Figure of an egg-tube of _Dytiscus
marginalis_; (3) the terminal chamber takes on an unusual development,
acting as a large nutriment chamber, there being no other special nutriment
chambers. This condition is found in _Rhizotrogus solstitialis_. The
arrangements as to successive or simultaneous production of the eggs in the
tubes seem to differ in different Insects. In some forms, such as the white
ants, the process of egg-formation (oogenesis) attains a rapidity that is
almost incredible, and is continued, it is said, for periods of many
months. There is no point in which Insects differ more than in that of the
number of eggs produced by one {139}female. The egg-tubes are connected
with a duct for the conveyance of the eggs to the exterior, and the
arrangements of the tubes with regard to the oviduct also vary much. An
interesting condition is found in _Machilis_ (see Fig. 94, p. 188), where
the seven egg-tubes are not arranged in a bunch, but open at a distance
from one another into the elongated duct. The two oviducts usually unite
into one chamber, called the azygos portion or the uterus, near their
termination. There are a few Insects (Ephemeridae) in which the two
oviducts do not unite, but have a pair of orifices at the extremity of the
body. Hatchett-Jackson has recently shown[64] that in _Vanessa io_ of the
Order Lepidoptera, the paired larval oviducts are solid, and are fixed
ventrally so as to represent an Ephemeridean stage; that the azygos system
of ducts and appended structures develop separately from the original
oviducts, and that they pass through stages represented in other Orders of
Insects to the stage peculiar to the Lepidoptera. _Machilis_, according to
Oudemans, is a complete connecting link between the Insects with single and
those with paired orifices.
There are in different Insects more than one kind of diverticula and
accessory glands in connexion with the oviducts or uterus; a receptaculum
seminis, also called spermatheca, is common. In the Lepidoptera there is
added a remarkable structure, the bursa copulatrix, which is a pouch
connected by a tubular isthmus with the common portion of the oviduct, but
having at the same time a separate external orifice, so that there are two
sexual orifices, the opening of the bursa copulatrix being the lower or
more anterior. The organ called by Dufour in his various contributions
_glande sébifique_, is now considered to be, in some cases at any rate, a
spermatheca. The special functions of the accessory glands are still very
obscure.
[Illustration: FIG. 75.—Egg-tube of _Dytiscus marginalis_; _e.c_,
egg-chamber; _n.c_, nutriment chamber; _t.c_, terminal chamber; _t.t_,
terminal thread. (After Korschelt.)]
The ovaries of the female are replaced in the male by a pair {140}of
testes, organs exhibiting much variety of form. The structure may consist
of an extremely long and fine convoluted tube, packed into a small space
and covered with a capsule; or there may be several shorter tubes. As
another extreme may be mentioned the existence of a number of small
follicles opening into a common tube, several of these small bodies forming
together a testis. As a rule each testis has its own capsule, but cases
occur—very frequently in the Lepidoptera—in which the two testes are
enclosed in a common capsule; so that there then appears to be only one
testis. The secretion of each testis is conveyed outwards by means of a
slender tube, the vas deferens, and there are always two such tubes, even
when the two testes are placed in one capsule. The vasa deferentia differ
greatly in their length in different Insects, and are in some cases many
times the length of the body; they open into a common duct, the ductus
ejaculatorius. Usually at some part of the vas deferens there exists a
reservoir in the form of a sac or dilatation, called the vesicula
seminalis. There are in the male, as well as in the female, frequently
diverticula, or glands, in connexion with the sexual passages; these
sometimes exhibit very remarkable forms, as in the common cockroach, but
their functions are quite obscure. There is, as we have already remarked,
extreme variety in the details of the structure of the internal
reproductive apparatus in the male, and there are a few cases in which the
vasa deferentia do not unite behind, but terminate in a pair of separate
orifices. The genus _Machilis_ is as remarkable in the form of the sexual
glands and ducts of the male as we have already mentioned it to be in the
corresponding parts of the female.
[Illustration: FIG. 76.—_Tenthredo cincta._ _a_, _a_, testes; _b_, _b_,
vasa deferentia; _c_, _c_, vesiculæ seminales; _d_, extremity of body with
copulatory armature. (After Dufour.)]
Although the internal sexual organs are only fully developed in the imago
or terminal stage of the individual life, yet in reality their rudiments
appear very early, and may be detected from the embryo state onwards
through the other preparatory stages.
The spermatozoa of a considerable number of Insects, especially of
Coleoptera, have been examined by {141}Ballowitz;[65] they exhibit great
variety; usually they are of extremely elongate form, thread-like, with
curious sagittate or simply pointed heads, and are of a fibrillar
structure, breaking up at various parts into finer threads.
EXTERNAL SEXUAL ORGANS.—The terminal segments of the body are usually very
highly modified in connexion with the external sexual organs, and this
modification occurs in such a great variety of forms as to render it
impossible to give any general account thereof, or of the organs
themselves. Some of these segments—or parts of the segments, for it may be
dorsal plates or ventral plates, or both—may be withdrawn into the
interior, and changed in shape, or may be doubled over, so that the true
termination of the body may be concealed. The comparative anatomy of all
these parts is especially complex in the males, and has been as yet but
little elucidated, and as the various terms made use of by descriptive
entomologists are of an unsatisfactory nature we may be excused from
enumerating them. We may, however, mention that when a terminal chamber is
found, with which both the alimentary canal and the sexual organs are
connected, it is called a cloaca, as in other animals.
PARTHENOGENESIS.
There are undoubted cases in Insects of the occurrence of parthenogenesis,
that is, the production of young by a female without concurrence of a male.
This phenomenon is usually limited to a small number of generations, as in
the case of the Aphididae, or even to a single generation, as occurs in the
alternation of generations of many Cynipidae, a parthenogenetic alternating
with a sexual generation. There are, however, a few species of Insects of
which no male is known (in Tenthredinidae, Cynipidae, Coccidae), and these
must be looked on as perpetually parthenogenetic. It is a curious fact that
the result of parthenogenesis in some species is the production of only one
sex, which in some Insects is female, in others male; the phenomenon in the
former case is called by Taschenberg[66] Thelyotoky, in the latter case
Arrhenotoky; Deuterotoky being applied to the cases in which two sexes are
produced. In some forms of {142}parthenogenesis the young are produced
alive instead of in the form of eggs. A very rare kind of parthenogenesis,
called paedogenesis, has been found to exist in two or three species of
Diptera, young being produced by the immature Insect, either larva or pupa.
GLANDS.
Insects are provided with a variety of glands, some of which we have
alluded to in describing the alimentary canal and the organs of sex; but in
addition to these there are others in connexion with the outer integument;
they may be either single cells, as described by Miall in _Dicranota_
larva,[67] or groups of cells, isolated in tubes, or pouches. The minute
structure of Insect glands has been to some extent described by Leydig;[68]
they appear to be essentially of a simple nature, but their special
functions are very problematic, it being difficult to obtain sufficient of
their products for satisfactory examination.
{143}CHAPTER V
DEVELOPMENT
EMBRYOLOGY–EGGS–MICROPYLES–FORMATION OF EMBRYO–VENTRAL PLATE–ECTODERM AND
ENDODERM–SEGMENTATION–LATER STAGES–DIRECT OBSERVATION OF EMBRYO–
METAMORPHOSIS–COMPLETE AND INCOMPLETE–INSTAR–HYPERMETAMORPHOSIS–
METAMORPHOSIS OF INTERNAL ORGANS–INTEGUMENT–METAMORPHOSIS OF BLOWFLY–
HISTOLYSIS–IMAGINAL DISCS–PHYSIOLOGY OF METAMORPHOSIS–ECDYSIS.
The processes for the maintenance of the life of the individual are in
Insects of less proportional importance in comparison with those for the
maintenance of the species than they are in Vertebrates. The generations of
Insects are numerous, and the individuals produced in each generation are
still more profuse. The individuals have as a rule only a short life;
several successive generations may indeed make their appearances and
disappear in the course of a single year.
Although eggs are laid by the great majority of Insects, a few species
nevertheless increase their numbers by the production of living young, in a
shape more or less closely similar to that of the parent. This is well
known to take place in the Aphididae or green-fly Insects, whose rapid
increase in numbers is such a plague to the farmer and gardener. These and
some other cases are, however, exceptional, and only emphasise the fact
that Insects are pre-eminently oviparous. Leydig, indeed, has found in the
same _Aphis_, and even in the same ovary, an egg-tube producing eggs while
a neighbouring tube is producing viviparous individuals.[69] In the Diptera
pupipara the young are {144}produced one at a time, and are born in the
pupal stage of their development, the earlier larval state being undergone
in the body of the parent: thus a single large egg is laid, which is really
a pupa.
The eggs are usually of rather large size in comparison with the parent,
and are produced in numbers varying according to the species from a few—15
or even less in some fossorial Hymenoptera—to many thousands in the social
Insects: somewhere between 50 and 100 may perhaps be taken as an average
number for one female to produce. The whole number is frequently deposited
with rapidity, and the parent then dies at once. Some of the migratory
locusts are known to deposit batches of eggs after considerable intervals
of time and change of locality. The social Insects present extraordinary
anomalies as to the production of the eggs and the prolongation of the life
of the female parent, who is in such cases called a queen.
The living matter contained in the egg of an Insect is protected by three
external coats: (1) a delicate interior oolemm; (2) a stronger, usually
shell-like, covering called the chorion; (3) a layer of material added to
the exterior of the egg from glands, at or near the time when it is
deposited, and of very various character, sometimes forming a coat on each
egg and sometimes a common covering or capsule for a number of eggs. The
egg-shell proper, or chorion, is frequently covered in whole or part with a
complex minute sculpture, of a symmetrical character, and in some cases
this is very highly developed, forming an ornamentation of much delicacy;
hence some Insects' eggs are objects of admirable appearance, though the
microscope is of course necessary to reveal their charms. One of the
families of butterflies, the Lycaenidae, is remarkable for the complex
forms displayed by the ornamentation of the chorion (see Fig. 78, B).
[Illustration: FIG. 77.—Upper or micropylar aspect of egg of _Vanessa
cardui_. (After Scudder.)]
The egg-shell at one pole of the egg is perforated by one or more minute
orifices for the admission to the interior of the spermatozoon, and it is
the rule that the shell hereabouts is symmetrically sculptured (see Fig.
77), even when it is {145}unornamented elsewhere: the apertures in question
are called micropyles. They are sometimes protected by a micropyle
apparatus, consisting of raised processes, or porches: these are developed
to an extraordinary extent in some eggs, especially in those of
Hemiptera-Heteroptera (see Fig. 78, C). Some of these peculiar structures
have been described and figured by Leuckart.[70] The purpose they serve is
quite obscure.
[Illustration: FIG. 78.—Eggs of Insects: A, blowfly (after Henking); B,
butterfly, _Thecla_ (after Scudder); C, Hemipteron (Reduviid).]
FORMATION OF EMBRYO.
The mature, but unfertilised, egg is filled with matter that should
ultimately become the future individual, and in the process of attaining
this end is the seat of a most remarkable series of changes, which in some
Insects are passed through with extreme rapidity. The egg-contents consist
of a comparatively structureless matrix of a protoplasmic nature and of
yolk, both of which are distributed throughout the egg in an approximately
even manner. The yolk, however, is by no means of a simple nature, but
consists, even in a single egg, of two or three kinds of spherular or
granular constituents; and these vary much in their appearance and
arrangement in the early stages of the development of an egg, the yolk of
the same egg being either of a homogeneously granular nature, or consisting
of granules and larger masses, as well as of particles of fatty matter;
these latter when seen through the microscope looking sometimes like
shining, nearly colourless, globules.
{146}[Illustration: FIG. 79.—Showing the two extruded polar bodies P_{1},
P_{2} now nearly fused and reincluded, and the formation of the spindle by
junction of the male and female pronuclei. (After Henking.)]
The nature of the matrix—which term we may apply to both the protoplasm and
yolk as distinguished from the minute formative portions of the egg—and the
changes that take place in it have been to some extent studied, and
Kowalewsky, Dohrn,[71] Woodworth,[72] and others have given some
particulars about them. The early changes in the formative parts of the
mature egg have been observed by Henking in several Insects, and
particularly in _Pyrrhocoris_, his observations being of considerable
interest. When the egg is in the ovary and before it is quite mature,—at
the time, in fact, when it is receiving nutriment from ovarian cells,—it
contains a germinal vesicle including a germinal spot, but when the egg is
mature the germinal vesicle has disappeared, and there exists in its place
at one portion of the periphery of the egg-contents a cluster of minute
bodies called chromosomes by Henking, whom we shall follow in briefly
describing their changes. The group divides into two, each of which is
arranged in a rod or spindle-like manner, and may then be called a
directive rod or spindle. The outer of these two groups travels quite to
the periphery of the egg, and there with some adjacent matter is extruded
quite outside the egg-contents (not outside the egg-coverings), being in
its augmented form called a polar or directive body. While this is going on
the second directive spindle itself divides into two groups, the outer of
which is then extruded in the manner we have already described in the case
of the first polar body, thus completing the extrusion of two directive
bodies. The essential parts of the bodies that are successively formed
during these processes are the aggregates, called chromosomes; the number
of these chromosomes appears to be constant in each species; their
movements and dispositions are of a very interesting character, the systems
they form in {147}the course of their development having polar and
equatorial arrangements. These we cannot further allude to, but may mention
that the extrusion of the directive bodies is only temporary, they being
again included within the periphery of the egg by the growth and extension
of adjacent parts which meet over and thus enclose the bodies.
The arrangements and movements we have briefly alluded to have been limited
to the unfertilised condition of the egg (we should rather say, the
fertilising element has taken no part in them), and have as their result
the union of the chromosomes existing after the extrusion of the two polar
bodies, into a small body called the female pronucleus or egg-nucleus
(Eikern), while the position of the movements has been an extremely minute
portion of the egg near to its outer surface or periphery. The introduction
of a sperm, or male, element to the egg through the micropyle gives rise to
the formation of another minute body placed more in the interior of the
egg, and called the sperm-nucleus. The egg-nucleus, travelling more into
the interior of the egg, meets the sperm-nucleus; the two amalgamate,
forming a nucleus or body that goes through a series of changes resulting
in its division into two daughter-bodies. These two again divide, and by
repetitions of such division a large number of nuclei are formed which
become arranged in a continuous manner so as to form an envelope enclosing
a considerable part (if not quite the whole) of the egg-mass. This envelope
is called the blastoderm, and together with its contents will form the
embryo. We must merely allude to the fact that it has been considered that
some of the nuclei forming the blastoderm arise directly from the egg-mass
by a process of amalgamation, and if this prove to be correct it may be
admitted that some portions of the embryo are not entirely the result of
division or segmentation of combined germ and sperm-nuclei. Wheeler
states[73] that some of the nuclei formed by the first differentiation go
to form the vitellophags scattered throughout the yolk. We should also
remark that, according to Henking, the blastoderm when completed shows at
one part a thickening, immediately under which (_i.e._ included in the area
the blastoderm encloses) are the two polar bodies, which, as we have seen,
were formed by the germinating body at an earlier stage of its activity.
Fig. 79 {148}represents a stage in the development of _Pyrrhocoris_,
showing the interior of the egg after a body has been formed by the union
of the sperm and egg-nuclei; this body is about to undergo division or
segmentation, and the equatorial arrangement where this will take place is
seen. The two polar bodies P_{1}, P_{2}, after having been excluded, are
nearly reincluded in the egg.
THE VENTRAL PLATE.
The next important change after the formation of the blastoderm is the
partial detachment of a part of its periphery to become placed in the
interior of the other and larger portion. The way in which this takes place
will be gathered from the accompanying diagrammatic figures taken from
Graber: a thickened portion (_a_ _b_) of the blastoderm becomes indrawn so
as to leave a fold (_c_ _d_) at each point of its withdrawal, and these
folds afterwards grow and meet so as to enclose the thickened portion. The
outer envelope, formed in part by the original blastoderm and in part by
the new growth, is called the serosa (_e_ _f_), the inner layer (_g_) of
the conjoined new folds being termed the amnion: the part withdrawn to the
interior and covered by the serosa and amnion is called the ventral plate,
or germinal band (_Keimstreif_), and becomes developed into the future
animal. The details of the withdrawal of the ventral plate to the interior
are very different in the various Insects that have been investigated.
[Illustration: FIG. 80.—Stages of the enclosure of the ventral plate: A,
_a_, _b_, ventral plate; B, _c_, _d_, folds of the blastoderm that form the
commencement of the amnion and serosa; C, _e_, _f_, part of the serosa;
_g_, amnion.]
One of the earliest stages in the development is a differentiation of a
portion of the ventral plate into layers from which the future parts of the
organisation will be derived. This separation of endoderm from ectoderm
takes place by a sort of invagination, analogous with that by which the
ventral plate itself is formed. A longitudinal depression running along the
middle of the ventral plate appears, and forms a groove or channel, which
becomes obliterated as to its outer face by the meeting together of the two
margins of the groove (except on the {149}anterior part, which remains
open). The more internal layer of the periphery of this closed canal is the
origin of the endoderm and its derivatives. Subsequently the ventral plate
and its derivatives grow so as to form the ventral part and the internal
organs of the Insect, the dorsal part being completed much later by growths
that differ much in different Insects; Graber, who has specially
investigated this matter, informing us[74] that an astonishing
multifariousness is displayed. It would appear that the various modes of
this development do not coincide with the divisions into Orders and
Families adopted by any systematists.
We should observe that the terms ectoderm, mesoderm, and endoderm will
probably be no longer applied to the layers of the embryo when
embryologists shall have decided as to the nature of the derived layers,
and shall have agreed as to names for them. According to the nomenclature
of Graber[75] the blastoderm differentiates into Ectoblast and Endoblast;
this latter undergoing a further differentiation into Coeloblast and
Myoblast. This talented embryologist gives the following table of the
relations of the embryonic layers and their nomenclature, the first term of
each group being the one he proposed to use:—
Periblast-------Ectoblast Part of yolk cells.
(Epiblast, \ (Ectoderm, outer /
/ blastoderm).\ layer). /
/ \ /
Protoblast. \ / Coeloblast
\ Centroblast Endoblast or--------(Endoderm in narrower
\(Yolk-cells, Hypoblast, \ sense).
hypoblast, inner layer. \ _Darmdrüsenblatt_.
endoderm (Mesoblast of \
in part of Balfour.) \
Balfour.) Mesoderm and Myoblast (Mesoderm
endoderm. of most authors).
_Darmmuskelblatt_
Nussbaum considers[76] that "there are four layers in the cockroach-embryo,
viz. (1) _epiblast_, from which the integument and nervous system are
developed; (2) _somatic layer of mesoblast_, mainly converted into the
muscles of the body-wall; (3) _splanchnic layer of mesoblast_, yielding the
muscular coat of the alimentary canal; and (4) _hypoblast_, yielding the
epithelium of the mesenteron."
{150}[Illustration: FIG. 81.—Early stages of the segmentation of a beetle
(_Lina_): A, segmentation not visible, 1 day; B, segmentation of head
visible; C, segmentation still more advanced, 2¼ days; PC, procephalic
lobes; _g^1_, _g^2_, _g^3_, segments bearing appendages of the head; _th_,
thorax; _th^1_, _th^2_, _th^3_, segments of the thorax; _a^1_, _a^2_,
anterior abdominal.]
Turning our attention to the origin of the segmentation, that is so marked
a feature of Insect structure, we find that evidence of division or
arrangement of the body into segments appears very early, as shown in our
Figure of some of the early stages of development of _Lina_ (a beetle),
Fig. 81. In A the segmentation of the ectoderm has not commenced, but the
procephalic lobes (_P C_) are seen; in B the three head segments are
distinct, while in C the thoracic segmentation has occurred, and that of
the abdomen has commenced. Graber considers that in this species the
abdomen consists of ten segmental lobes, and a terminal piece or telson.
According to Graber[77] this is not a primitive condition, but is preceded
by a division into three or four parts, corresponding with the divisions
that will afterwards be head, thorax, and abdomen. This primary
segmentation, he says, takes place in the Hypoblast (Endoderm) layer of the
ventral plate; this layer being, in an early stage of the development of a
common grasshopper (_Stenobothrus variabilis_), divided into four sections,
two of which go to form the head, while the others become thorax and
abdomen respectively. In _Lina_ the primary segmentation is, Graber says,
into three instead of four parts. Graber's opinion on the primary
segmentation does not appear to be generally accepted, and Wheeler, who has
studied[78] the {151}embryology of another Orthopteron, considers it will
prove to be incorrect. When the secondary segmentation occurs the anterior
of the two cephalic divisions remains intact, while the second divides into
the three parts that afterwards bear the mouth parts as appendages. The
thoracic mass subsequently segments into three parts, and still later the
hind part of the ventral plate undergoes a similar differentiation so as to
form the abdominal segments; what the exact number of these may be is,
however, by no means easy to decide, the division being but vague,
especially posteriorly, and not occurring all at once, but progressing from
before backwards.
The investigations that have been made in reference to the segmentation of
the ventral plate do not at present justify us in asserting that all
Insects are formed from the same number of embryonic segments. The matter
is summarised by Lowne, to the effect that posterior to the procephalic
lobes there are three head segments and three thoracic segments, and a
number of abdominal segments, "rarely less than nine or more than eleven."
It will be seen by referring to Figure 81 that the segmentation appears,
not simultaneously, but progressively from the head backwards; this of
course greatly increases the difficulty of determining by means of a
section the real number of segments.
[Illustration: FIG. 82.—Embryo of a moth (_Zygaena_) at the fifth day
(after Graber): _am_, amnion; _s_, serosa; _p_, procephalic lobes; _st_,
stomodaeum; _pr_, proctodaeum; _g^1_, _g^2_, _g^3_, the mouth parts or head
appendages; _th^1_, _th^2_, _th^3_, appendages of the thoracic segments;
_a^1_-_a^{10}_, abdominal segments; _s.g_, salivary gland.]
The later stages in the development of Insects are already proved to be so
various that it would be impossible to attempt to follow them in detail;
but in Fig. 82 we represent a median section of the embryo of _Zygaena
filipendula_ at the fifth day. It shows well some of the more important of
the general features of the development at a stage subsequent to those
represented in Fig. 81, A, B, C. The very distinct stomodaeum (_st_) and
proctodaeum (_pr_) are seen as inflexions of the external wall of the body;
the segmentation and the development of the {152}ventral parts of the
embryo are well advanced, while the dorsal part of the embryo is still
quite incomplete.
The method of investigation by which embryologists chiefly carry on their
researches is that of dividing the egg after proper preparation, into a
large number of thin sections, which are afterwards examined in detail, so
as to allow the arrangement to be completely inferred and described.
Valuable as this method is, it is nevertheless clear that it should, if
possible, be supplemented by direct observation of the processes as they
take place in the living egg: this method was formerly used, and by its aid
we may still hope to obtain exact knowledge as to the arrangements and
rearrangements of particles by which the structures develop. Such questions
as whether the whole formative power in the egg is absolutely confined to
one or two small centres to which the whole of the other egg contents are
merely, as it were, passive accessories, or whether an egg is a combination
in which some portion of the powers of rearrangement is possessed by other
particles, as well as the chromosomes, in virtue of their own nature or of
their position at an early period in the whole, can scarcely be settled
without the aid of direct observation of the processes during life.
The importance of the yolk is recognised by most of the recent writers.
Nussbaum states (_loc. cit._) that "scattered yolk-cells associate
themselves with the mesoblast cells, so that the constituents of the
mesoblast have a twofold origin." Wheeler finds[79] that amoeboid cells—he
styles them vitellophags—traverse the yolk and assist in its rearrangement;
he insists on the importance both as regards quantity and quality of the
yolk.
The eggs of some insects are fairly transparent, and the process of
development in them can, to a certain extent, be observed by simple
inspection with the microscope; a method that was used by Weismann in his
observations on the embryology of _Chironomus_. There is a moth (_Limacodes
testudo_), that has no objection to depositing its eggs on glass
microscope-slides. These eggs are about a millimetre long, somewhat more
than half that width, are very flat, and the egg-shell or chorion is very
thin and perfectly transparent. When first laid the contents of this egg
appear nearly homogeneous and evenly distributed, a finely granular
appearance being presented throughout; but in {153}twenty-four hours a
great change is found to have taken place. The whole superficial contents
of the egg are at that time arranged in groups, having the appearance of
separate rounded or oval masses, pressed together so as to destroy much of
their globular symmetry. The egg contents are also divided into very
distinct forms, a granular matter, and a large number of transparent
globules, these latter being the fatty portion of the yolk; these are
present everywhere, though in the centre there is a space where they are
very scanty, and they also do not extend quite to the circumference. But
the most remarkable change that has taken place is the appearance in the
middle of the field of an area different from the rest in several
particulars; it occupies about one-third of the width and one-third of the
length; it has a whiter and more opaque appearance, and the fat globules in
it are fewer in number and more indistinct. This area is afterwards seen to
be occupied by the developing embryo, the outlines of which become
gradually more distinct. Fig. 83 gives an idea of the appearance of the egg
about the middle period of the development. In warm weather the larva
emerges from this egg ten or eleven days after it has been deposited.
[Illustration: FIG. 83.—A, Egg of _Limacodes testudo_ about the middle of
the development of the embryo; B, micropyles and surrounding sculpture of
chorion.]
The period occupied by the development of the embryo is very different in
the various kinds of Insects; the blowfly embryo is fully developed in less
than twenty-four hours, while in some of the Orthoptera the embryonic stage
may be prolonged through several months. According to Woodworth the
blastoderm in _Vanessa antiopa_ is complete in twenty-four hours after the
deposition of the egg, and the involution of the ventral plate is
accomplished within three days of deposition.
METAMORPHOSIS.
The ontogeny, or life history of the individual, of Insects is peculiar,
inasmuch as a very large part of the development takes {154}place only late
in life and after growth has been completed. Insects leave the egg in a
certain form, and in that condition they continue—with, however, a greater
or less amount of change according to kind—till growth is completed, when,
in many cases, a very great change of form takes place. Post-embryonic
development, or change of form of this kind, is called metamorphosis. It is
not a phenomenon peculiar to Insects, but exists to a greater or less
extent in other groups of the Metazoa; while simpler post-embryonic
development occurs in nearly all, as in scarcely any complex animals are
all the organs completely formed at the time the individual becomes
possessed of a separate existence. In many animals other than Insects the
post-embryonic development assumes most remarkable and complex forms,
though there are perhaps none in which the phenomenon is very similar to
the metamorphosis of Insects. The essential features of metamorphosis, as
exhibited in the great class we are writing of, appear to be the separation
in time of growth and development, and the limitation of the reproductive
processes to a short period at the end of the individual life. The peculiar
phenomena of the post-embryonic development of the white ants show that
there exists some remarkable correlation between the condition of the
reproductive organs and the development of the other parts of the
organisation. If we take it that the post-embryonic physiological processes
of any individual Insect are of three kinds,—growth, development, and
reproduction,—then we may say that in the higher Insects these three
processes are almost completely separated, and go on consecutively, the
order being,—first, growth; second, development; third, reproduction.
While, if we complete the view by including the processes comprised in the
formation of the egg and the development therein, the series will be—(1)
oogenesis, or egg-growth; (2) development (embryonic); (3) growth
(post-embryonic); (4) development (post-embryonic); (5) reproduction.
The metamorphosis of Insects is one of the most interesting parts of
entomology. It is, however, as yet very little known from a scientific
point of view, although the simpler of its external characters have for
many ages past attracted the attention and elicited the admiration of
lovers of nature. It may seem incorrect to say that little is yet known
scientifically of a phenomenon concerning which references almost
{155}innumerable are to be found in literature: nevertheless the
observations that have been made as to metamorphosis, and the analysis that
has been commenced of the facts are at present little more than sufficient
to show us how vast and complex is the subject, and how great are the
difficulties it presents.
There are three great fields of inquiry in regard to metamorphosis, viz.
(1) the external form at the different stages; (2) the internal organs and
their changes; (3) the physiological processes. Of these only the first has
yet received any extensive attention, though it is the third that precedes
or underlies the other two, and is the most important. We will say a few
words about each of these departments of the inquiry. Taking first the
external form—the instar. But before turning to this we must point out that
in limiting the inquiry to the post-embryonic development, we are making
one of those limitations that give rise to much misconception, though they
are necessary for the acquisition of knowledge as to any complex set of
phenomena. If we assume five well-marked stages as constituting the life of
an Insect with extreme metamorphosis, viz. (1) the formation and growth of
the egg; (2) the changes in the egg culminating in its hatching after
fertilisation; (3) the period of growth; (4) the pupal changes; (5) the
life of the perfect Insect; and if we limit our inquiry about development
to the latter three, we are then shutting out of view a great preliminary
question, viz. whether some Insects leave the egg in a different stage of
development to others, and we are consequently exposing ourselves to the
risk of forgetting that some of the distinctions we observe in the
subsequent metamorphosis may be consequential on differences in the
embryonic development.
INSTAR AND STADIUM.
Figs. 84 and 85 represent corresponding stages in the life of two different
Insects, Fig. 84 showing a locust (_Acridium_), and Fig. 85 a white
butterfly. In each A represents the newly-hatched individual; B, the insect
just before its perfect state; C, the perfect or imago stage. On comparing
the two sets of figures we see that the C stages correspond pretty well as
regards the most important features (the position of the wings being
unimportant), that the A stages are moderately different, {156}while the B
states are not to be recognised as equivalent conditions.
[Illustration: FIG. 84.—Locust (_Acridium peregrinum_): A, newly hatched;
B, just antecedent to last ecdysis; C, perfect Insect.]
[Illustration: FIG. 85.—Butterfly (_Pieris_): A, the newly hatched young,
or larva magnified; B, pupa (natural size) just antecedent to last ecdysis;
C, perfect Insect.]
Every Insect after leaving the egg undergoes during the process of growth
castings of the skin, each of which is called a moult or ecdysis. Taking
for our present purpose five as the number of ecdyses undergone by both the
locust and butterfly, we may express the differences in the successions of
change we portray in Figs. 84 and 85 by saying that previous to the first
ecdysis the two Insects are moderately dissimilar, that the locust
undergoes a moderate change before reaching the fifth ecdysis, and
undergoes another moderate change at this moult, thus reaching its perfect
condition by a slight, rather gradual series of {157}alterations of form.
On the other hand, the butterfly undergoes but little modification,
remaining much in the condition shown by A, Fig. 85, till the fourth, or
penultimate, ecdysis, but then suffers a complete change of form and
condition, which apparently is only inferior to another astonishing change
that takes place at the fifth or final moult. The chief, though by no means
the only, difference between the two series consists in the fact that the
butterfly has interposed between the penultimate and the final ecdyses a
completely quiescent helpless condition, in which it is deprived of
external organs of sense, locomotion, and nutrition; while in the locust
there is no loss of these organs, and such quiescent period as exists is
confined to a short period just at the fifth ecdysis. The changes exhibited
by the butterfly are called "complete metamorphosis," while this phenomenon
in the locust is said to be "incomplete." The Insect with complete
metamorphosis is in its early stage called a larva, and in the quiescent
state a pupa. The adult state in both butterfly and locust is known as
imago or perfect Insect.
The most conspicuous of the differences between Insects with complete and
those with incomplete metamorphosis is, as we have remarked, the existence
in the former of a pupa. The pupal state is by no means similar in all the
Insects that possess it. The most anomalous conditions in regard to it
occur in the Order Neuroptera. In some members of that Order—the
Caddis-flies for instance—the pupa is at first quiescent, but becomes
active before the last ecdysis; while in another division—the May-flies—the
last ecdysis is not preceded by a formed pupa, nor is there even a distinct
pupal period, but the penultimate ecdysis is accompanied by a change of
form to the winged condition, the final ecdysis being merely a casting of
the skin after the winged state has been assumed. In the _Odonata_ or
Dragon-flies there is no pupal stage, but the change of form occurring at
the last ecdysis is very great. In those Insects where the interval between
the last two moults is not accompanied by the creature's passing into a
definite, quiescent pupa, the individual is frequently called then a nymph;
but the term nymph has merely a distinctive meaning, and is not capable of
accurate definition, owing to the variety of different conditions covered
by the word. Eaton, in describing this term as it is used for
_Ephemeridae_, says, "Nymphs are young which lead an {158}active life,
quitting the egg at a tolerably advanced stage of morphological
development, and having the mouth-parts formed after the same main type of
construction as those of the adult insect."[80]
The intervals between the ecdyses are called stadia, the first stadium
being the period between hatching and the first ecdysis. Unfortunately no
term is in general use to express the form of the Insect at the various
stadia; entomologists say, "the form assumed at the first moult," and so
on. To avoid this circumlocution it may be well to adopt a term suggested
by Fischer,[81] and call the Insect as it appears at hatching the first
instar, what it is as it emerges from the first ecdysis the second instar,
and so on; in that case the pupa of a Lepidopteron that assumed that
condition at the fifth ecdysis would be the sixth instar, and the butterfly
itself would be the seventh instar.
Various terms are used to express the differences that exist in the
metamorphoses of Insects, and as these terms refer chiefly to the changes
in the outer form, we will here mention them. As already stated, the locust
is, in our own language, said to have an incomplete metamorphosis, the
butterfly a complete one. The term Holometabola has been proposed for
Insects with complete metamorphosis, while the appellations Ametabola,
Hemimetabola, Heterometabola, and Paurometabola have been invented for the
various forms of incomplete, or rather less complex, metamorphosis. Some
writers use the term Ametabola for Insects that are supposed to exhibit no
change of external form after quitting the egg, the contrasted series of
all other Insects being then called Metabola. Westwood and others use the
word Homomorpha for Insects in which the condition on hatching more or less
resembles that attained at the close of the development, and Heteromorpha
for those in which the form on emergence from the egg differs much from
what it ultimately becomes.
HYPERMETAMORPHOSIS.
There are certain unusual changes to which the term hypermetamorphosis has
been applied; these we can here only briefly allude to.
{159}Insects that have complete metamorphoses, and are not supplied with
food by their parents or guardians, are provided during their larval life
with special modifications of extremely various kinds to fit them for the
period of life during which they are obtaining food and growing. Thus
caterpillars possess numerous adaptations to fit them for the period during
which they live on leaves, while maggots have modifications enabling them
to live amongst decomposing flesh. Some larvae are greatly modified in this
adaptive way, and when the adaptations change greatly during the life of
the larva, hypermetamorphosis is said to exist. As an instance we may
mention some beetle larvae that are born with legs by whose aid they can
cling to a bee, and so get carried to its nest, where they will in future
live on the stores of food the bee provides for its own young. In order
that they may be accommodated to their totally different second
circumstances, they change their first form, losing their legs, and
becoming almost bladder-like creatures, fitted for floating on the honey
without being injured by it. Such an occurrence has been described by
Fabre[82] in the case of _Sitaris humeralis_, and his figures have been
reproduced in Sir John Lubbock's book on the metamorphoses of Insects,[83]
as well as in other works, yet they are of so much interest that we give
them again, especially as the subject is still only in its infancy; we at
present see no sufficient reason for the later of these larval states.
Little is, we believe, known as to the internal anatomy of the various
instars in these curious cases.
[Illustration: FIG. 86.—Preparatory stages of _Sitaris humeralis_: 9, 10,
11, 12, first, second, third, and fourth larval instars; 13, pupa. (After
Lubbock and Fabre.)]
{160}There are certain minute Hymenoptera that deposit their eggs inside
the eggs of other Insects, where the beings hatched from the parasitic eggs
subsequently undergo their development and growth, finding their sustenance
in the yolk or embryo contained in the host-egg. It is evident that such a
life is very anomalous as regards both food and the conditions for
respiration, and we consequently find that these tiny egg-parasites go
through a series of changes of form of a most remarkable character.[84] It
would appear that in these cases the embryonic and post-embryonic
developments are not separated in the same way as they are in other
Insects. We are not aware that any term has yet been proposed for this very
curious kind of Insect development, which, as pointed out by Brauer,[85] is
doubtless of a different nature from the hypermetamorphosis of _Sitaris_.
CHANGES IN INTERNAL ORGANS.
In relation to the post-embryonic development of the internal organs of the
body there is but little exact generalisation to be made, the anatomical
condition of these organs at the time of emergence from the egg having been
ascertained in but few Insects. We know that in Holometabolous Insects the
internal anatomy differs profoundly in the larval and imaginal instars. As
to Insects with more imperfect metamorphosis very little information
exists, but it appears probable that in many no extensive distinctions
exist between the newly-hatched and the adult forms, except in the
condition of the reproductive organs. Differences of minor importance
doubtless exist, but there is almost no information as to their extent, or
as to the periods at which the changes occur; so that we do not know to
what extent they may be concentrated at the final ecdysis. In Insects with
perfect metamorphosis the structures of the internal organs are, as we have
said, in many cases totally different in the larval and imaginal periods of
the life; but these changes are far from being uniform in all Holometabola.
The nervous system in some cases undergoes a great concentration of the
ganglia, in others does not, and important distinctions exist in this
respect even within the limits of a single Order, such as the Coleoptera.
{161}Some Insects take the same kind of food throughout their lives, but
many others change totally in this respect, and their organs for the
prehension and digestion of food undergo a corresponding change.
Butterflies suck food in the form of liquid juices from flowers by means of
a delicate and long proboscis, while the young butterfly—the
caterpillar—disdains sweets, and consumes, by the assistance of powerful
mandibles, a great bulk of leaves. Other Holometabola undergo no such total
change of habits; the tiger-beetle, for instance, is as ferocious a
consumer of the juices of Insects in its young stage as it is in the adult
condition. Hence Brauer[86] divides Insects, as regards this point, into
three categories. The forms in which both the young and adult take food by
suction he calls Menorhyncha; those in which both the imago and immature
forms feed by mandibles he calls Menognatha; while his Metagnatha consists
of those insects that take food by jaws when young, but by suction with
tubular mouths when mature. Besides these main divisions there are some
exceptional cases to which we need not here allude, our present object
being to indicate that in the Metagnatha the digestive organs are of a very
different nature in the young and in the adult states of existence.
The internal organs for the continuance of the species are known to be
present in a rudimentary stage in the embryo, and it is a rule that they do
not attain their full development until growth has been completed; to this
rule there may possibly be an exception in the case of the Aptera. But
little information of a comparative character exists as to the dorsal
vessel and the changes it undergoes during metamorphosis. There is
considerable difficulty in connexion with the examination of this
structure, but it appears probable that it is one of the organs that
changes the least during the process of metamorphosis.
The exact nature of the internal changes that occur during metamorphosis is
almost a modern subject. It is of course a matter of great difficulty to
observe and record changes that go on in the interior of such small
creatures as Insects, and when the phenomena occur with great rapidity, as
is frequently the case in Insect metamorphosis, the difficulty is much
increased. Nevertheless the subject is of such great interest that it has
been investigated with a skill and perseverance that call for the
{162}highest admiration. The greater part of the information obtained
refers to a single Insect, the blowfly; and amongst those who have made
important contributions to it we may mention Weismann,[87] Viallanes,[88]
Ganin,[89] and Van Rees,[90] and it is at present under investigation by
Lowne. A good deal, too, is becoming known about the processes in the case
of the silkworm.
INTEGUMENT AND ECDYSIS.
The integument consists of a cellular layer, usually called the hypodermis,
situated on a basement membrane. The hypodermis, or layer of chitinogenous
cells, excretes a matter which remains attached to the body, forming the
hard outer layer of the skin. This layer consists of chitin and has no
vitality, but its presence no doubt exerts a very important influence on
the physiological processes of the Insect. The chitinous investment varies
much in thickness and in other properties; in some Insects it is hard, even
glassy, so as to be difficult to pierce with a pin, in others it is
pliable, and in some very delicate. Chitin is a substance very difficult to
investigate; according to the recent researches of Krawkow[91] it may prove
to be of somewhat variable chemical composition.
After a time the hypodermis excretes a fresh supply of chitin, and,
possibly by the commencement of this process, the older chitinous
investment becomes separated and is shed. The details have, however, not
been ascertained, though their importance has been suggested by Hatchett
Jackson.[92] The newly exposed layer of integument is pallid, but
afterwards becomes coloured in a manner varying according to the species,
the process being possibly due to some secondary exudation permeating the
freshly exposed chitin, or modifying some part of its exterior.
Lowne informs us that in the imago of the blowfly the great majority of the
hypodermic cells themselves enter into the composition of the chitinous
integument; and it is perhaps not a matter for surprise that the cells
should die on the completion of their functional activity, and should form
a part of the chitinous {163}investment. Some writers say that the
chitinous layer may be shown to be covered by a delicate extima or outer
coat.
The number of ecdyses varies greatly in Insects, but has been definitely
ascertained in only a few forms outside the Order Lepidoptera. In
_Campodea_ Grassi says there is a single fragmentary moult, and in many
Hymenoptera the skin that is cast is extremely delicate, and the process
perhaps only occurs twice or three times previous to the pupal stage. In
most Insects, however, ecdysis is a much more important affair, and the
whole of the chitinous integument is cast off entire, even the linings of
the tracheae, and of the alimentary canal and its adjuncts being parted
with. Sir John Lubbock observed twenty-three moults in a May-fly of the
genus _Cloëon_,[93] this being the maximum yet recorded, though Sommer
states[94] that in _Macrotoma plumbea_ moulting goes on as long as life
lasts, even after the Insect has attained its full size.
Some Insects get quit of a considerable quantity of matter by their
ecdyses, while in others the amount is comparatively slight. It has been
thought that the moulting is effected in order to permit of increase of
size of the Insect, but there are facts which point to the conclusion that
this is only a factor of secondary importance in the matter. One of these
is that many Insects make their first ecdysis almost immediately after they
leave the egg; this is the case with the young larva of the blowfly, which,
according to Lowne, moults within two hours of its emergence from the egg.
We have already referred to the important suggestion made by Eisig[95]
that, since chitin is a nitrogenous substance, the ecdyses may be a means
of getting rid of waste nitrogenous matter; to which we have added that as
chitin also consists largely of carbon, its excretion may be of importance
in separating carbonaceous products from the blood.
METAMORPHOSIS OF BLOWFLY.
The phenomena of metamorphosis are displayed to their greatest extent in
the transformations and physiological processes of the _Muscid Diptera_, of
which the common blowfly is an {164}example. We will briefly consider the
information that has been obtained on this subject.
The development of the embryo in the egg of the blowfly is unusually rapid,
occupying only a period of twenty to twenty-four hours. After its first
moult the blowfly larva grows rapidly during a period of about ten to
fourteen days, during which it undergoes moults, the number of which
appears not to be definitely ascertained. After becoming full-fed the larva
loses its active state, and passes for a period into a condition of
comparative quiescence, being spoken of in this state as a resting larva.
This quiet period occurs in most full-grown larvae, and is remarkable for
the great variation that may occur in its duration, it being in many
Insects subject to prolongation for months, in some cases possibly even for
years, though in favourable circumstances it may be very short. Lowne
informs us that in the blowfly this period of the life is occupied by very
great changes in the internal organs, which are undergoing very extensive
processes of destruction and rebuilding. After some days the outer skin of
the resting larva shrivels, and is detached from the internal living
substances, round which it hardens and forms the sort of cocoon or capsule
that is so well known. This using of the cast larval skin as a cocoon is,
however, limited to certain of the two-winged flies, and perhaps a few
other Insects, and so must be considered an exceptional condition. The
capsule conceals from view a most remarkable state, known to the old
naturalist Réaumur as the "spheroidal condition," but called by more recent
writers the pronymph. The pronymphal state may be looked on as being to a
great extent a return of the animal to the condition of an egg, the
creature becoming an accumulation of soft creamy matter enclosed in a
delicate skin. This spheroidal condition, however, really begins in the
resting larva, and Van Rees and others think that the delicate membrane
enclosing the substance of the pronymph is really the hypodermis of the
integument of the larva. Although this seems probable, from the resemblance
this condition would in that case present to the phenomena usual in
ecdysis, it is not generally admitted, and there is much difficulty in
settling the point. Lowne is of a contrary opinion, looking on the limiting
membrane as a subsequent formation; he calls it the paraderm. The process
of forming the various organs goes on in the pronymph, till the
{165}"nymph" has completed its development, the creature having then again
taken on a definite form which apparently corresponds to the pupa of
Hymenoptera. Great doubt, however, exists as to this equivalence, and
indeed as to any exact correspondence between the metamorphic stadia of
different Insects, a view which long since was expressed by Sir John
Lubbock[96] and Packard. The term nymph is used in this case not because
there is any resemblance to the condition similarly named in Insects with
less complete metamorphosis, but because the term pupa is applied to the
outer case together with the contained nymph. The transformation of the
nymph into the perfect blowfly occupies a period very variable according to
the temperature.
HISTOLYSIS.—The processes by which the internal organs of the maggot are
converted into those of the fly are of two kinds,—histolysis or breaking
down, histogenesis or building up, of tissue. The intermediary agents in
histolysis are phagocytes, cells similar to the leucocytes or white
corpuscles of the blood: the intermediary agents in histogenesis are
portions of tissue existing in the larval state incorporated with the
different organs, or preserving a connexion therewith even when they are to
a great extent separated therefrom. In this latter case they are called
imaginal discs, though Professor Miall prefers to term them imaginal
folds.[97] The two processes of histolysis and histogenesis, though to some
extent mutually dependent (for the material to be built up has to be
largely obtained by previous destruction), do not go on _pari passu_,
though they are to a great extent contemporaneous. In the resting larva
histolysis is predominant, while in the nymph histogenesis is more
extensive. Microscopic observation shows that the phenomena connected with
the histolysis of the muscular tissue are scarcely distinguishable from
those of an inflammatory process, and Viallanes[98] dilates on this fact in
an instructive manner. The phagocytes attach themselves to, or enter, the
tissues which are to be disintegrated, and becoming distended, assume a
granular appearance. By this pseudo-inflammatory process the larval
structures are broken down into a creamy substance; the buds, or germs,
from which the new organs are to be developed being exempt from the
destruction. These buds, of which about sixty or upwards have already been
detected, undergo {166}growth as they are liberated, and so the new
creature is formed, the process of growth in certain parts going on while
destruction is being accomplished in others. Considerable discrepancy
prevails as to the extent to which the disintegration of some of the
tissues is carried.
[Illustration: FIG. 87.—Imaginal discs of _Muscidae_ in process of
development: A, Brain and ventral ganglion of a larva 7 mm. long of _M.
vomitoria_; _v_, ventral ganglion; _c_, cephalic ganglion; _h_, head
rudiment; _vc_, portion of ventral chain; _pd_, prothoracic rudiment;
_vc_{3}_, third nerve; _md_, mesothoracic rudiment: B, mesothoracic
rudiment, more advanced, in a pupa just formed of _Sarcophaga carnaria_,
showing the base of the sternum and folds of the forming leg, the central
part (_f_) representing the foot: C, the rudimentary leg of the same more
advanced; _f_, femur; _t_, tibia; _f_{1}_, _f_{5}_, tarsal joints: D, two
discs from a larva 20 mm. long of _Sarcophaga_, attached to tracheae;
_msw_, mesonotal and wing-rudiment; _mt_, metathoracic rudiment: E, _r_,
mesothoracic rudiment of a 7 mm. long larva attached to a tracheal twig.
(After Weismann and Graber.)]
According to Kowalevsky[99] it would appear that after the phagocytes have
become loaded with granules they serve as nutriment for the growing
tissues, and he thinks they become blood-cells in the imago. The process of
histolysis has been chiefly studied in the blowfly, and not much is known
of it in other Insects, yet it occurs to a considerable extent, according
to Bugnion[100] and others, in the metamorphosis of Lepidoptera. Indeed it
would almost seem that the processes of histolysis and histogenesis may be
looked on as exaggerated forms of the phenomena of the ordinary life of
tissues, due to greater rapidity and discontinuity of tissue nutrition.
{167}IMAGINAL DISCS.—The imaginal discs are portions of the larval
hypoderm, detached from continuity with the main body of the integument,
but connected therewith by strings or pedicels which may be looked on as
portions of the basement membrane. Whether these discs, or histoblasts as
they are called by Künckel d'Herculais,[101] are distinguished by any
important character from other buds or portions of regenerative tissue
that, according to Kowalevsky,[102] Korschelt and Heider,[103] and others,
exist in other parts of the body, does not appear to be at present
ascertained.
We give some figures, taken from Weismann and Graber, of the imaginal
rudiments existing in the larvae of _Muscidae_. Although by no means good,
they are the best for our purpose we can offer to the reader. Other figures
will be found in Lowne's work on the blowfly now in course of publication.
Weismann's paper[104] is now thirty years old, and, when it was written, he
was not aware of the intimate connexion the rudiments have with the
integument; this has, however, now been demonstrated by several observers.
Pratt states[105] that the formation of the imaginal discs in _Melophagus
ovinus_ takes place in the later stages of the embryonic development, and
after the manner formerly suggested by Balfour, viz. invagination of the
ectoderm.
[Illustration: FIG. 88.—Median longitudinal section through larva of
blowfly during the process of histolysis. (After Graber.) Explanation in
text.]
Both the regenerative buds and the rudimentary sexual glands are known to
be derived directly from the embryo; neither of them undergoes any
histolysis, so that we have in them embryonic structures which exist in a
quiescent condition during the period in which the larva is growing with
great rapidity, and which when the larva has attained its full growth and
is disintegrating, then {168}appropriate the products of the disintegration
so as to produce the perfect fly.
Our Fig. 88, taken from Graber, represents a longitudinal median section of
a full-grown larva of _Musca_, in which the processes of metamorphosis are
taking place. The position of some of the more important imaginal rudiments
is shown by it: _b^1_, _b^2_, _b^3_, rudiments of the three pairs of legs
of the imago; _an_, of antennae; between _an_ and _w_, rudiment of eye;
_w_, of wings; _h_, of halteres; _f_, fat-body; _d_, middle of alimentary
canal; _n_, ventral chain; _st_, stigma; 6, 7, sixth and seventh body
segments.
PHYSIOLOGY OF METAMORPHOSIS.
Many years ago, Harvey perceived the probable existence of a physiological
continuity between the earlier and later stages of the Insect's life.
Modern investigation has shown that in the blowfly a remarkable analogy
exists between the conditions of the pupa and the egg. The outer shell of
the pupa corresponds to the chorion or egg-shell, and the delicate outer
membrane of the pronymph to the oolemn or lining membrane of the egg; the
creamy matter corresponds with the yolk, and the regenerative buds are
analogous to the formative portions of the developing egg. The process of
histolysis as carried out by the phagocytes of the later life appears also
to find a parallel in the vitellophags of the embryonic life.[106] It
appears probable that the physiological processes of the post-embryonic
metamorphosis may be essentially a repetition—or an interrupted
continuation—of those of the embryonic period.
The inquiry as to what are the determining causes of the metamorphic
changes of the blowfly and other Insects has as yet but little advanced.
Why does the larva grow up to a certain period with great rapidity, then
cease its appropriating power and break up the parts that have been so
rapidly and recently formed? And why do the imaginal buds remain quiescent
till the other tissues are being disintegrated, and then, instead of
sharing the general condition of disintegration, commence a career of
development? To these questions no satisfactory answer has yet been given,
though the remarkable studies, already referred to, of Bataillon on the
later larval life {169}of the silkworm suggest the direction in which
knowledge may be found, for they show that the physiological conditions of
the later larval life are different from those of the earlier life,
possibly as the direct result of the mere aggregation of matter, and the
consequent different relations of the parts of the organism to atmospheric
and aqueous conditions.
If we wish to understand metamorphosis, we must supplement the old opinion
that ecdysis is merely an occurrence to facilitate expansion, by the more
modern conception that it is also an important physiological process. That
shedding the skin is done solely to permit of enlargement of size is a view
rendered untenable by many considerations. The integument can increase and
stretch to an enormous extent without the aid of moulting; witness the
queen-termite, and the honey-bearers of the _Myrmecocystus_ ants. Many
moults are made when increase of size does not demand them, and the
shedding of the skin at the time of pupation is accompanied by a decrease
in size. And if moulting be merely connected with increase of size, it is
impossible to see why _Cloëon_ should require two dozen moults, while
_Campodea_ can do with one, or why a collembolon should go on moulting
during the period of life subsequent to the cessation of growth.
The attention of entomologists has been chiefly directed to the ecdyses
connected with the disclosure of the pupal and imaginal instars. Various
important transformations may, however, occur previous to this, and when
they do so it is always in connexion with ecdyses. Caterpillars frequently
assume a different appearance and change their habits or character at a
particular ecdysis; and in Orthoptera each ecdysis is accompanied by a
change of form of the thoracic segments; this change is very considerable
at one of the intermediate ecdyses.
The assumption of the pupa state is the concomitant of an ecdysis, and so
also is the appearance of the imago; but the commencement of each of these
two stages precedes the ecdysis, which is merely the outward mark of the
physiological processes. The ecdysis by which the pupa is revealed occurs
after the completion of growth and when great changes in the internal
organs have occurred and are still taking place; the ecdysis by which the
imago appears comes after development has been quite or nearly completed.
Although the existence of a pupa is to the eye the most {170}striking of
the differences between Insects with perfect and those with imperfect
metamorphosis, yet there is reason for supposing that the pupa and the
pupal period are really of less importance than they at first sight appear
to be. In Fig. 85 we showed how great is the difference in appearance
between the pupa and the imago. The condition that precedes the appearance
of the pupa is, however, really the period of the most important change. In
Fig. 89 we represent the larva and pupa of a bee; it will be seen that the
difference between the two forms is very great, while the further change
that will be required to complete the perfect Insect is but slight. When
the last skin of the larva of a bee or of a beetle is thrown off, it is, in
fact, the imago that is revealed; the form thus displayed, though
colourless and soft, is that of the perfect Insect; what remains to be done
is a little shrinking of some parts and expansion of others, the
development of the colour, the hardening of certain parts. The colour
appears quite gradually and in a regular course, the eyes being usually the
first parts to darken. After the coloration is more or less
perfected—according to the species—a delicate pellicle is shed or rubbed
off, and the bee or beetle assumes its final form, though usually it does
not become active till after a farther period of repose.
[Illustration: FIG. 89.—Larva and pupa of a bee, _Xylocopa violacea_: A,
larva; B, pupa, ventral aspect; C, pupa, dorsal aspect. (After Lucas.)]
{171}CHAPTER VI
CLASSIFICATION—THE NINE ORDERS OF INSECTS—THEIR CHARACTERS—PACKARD'S
ARRANGEMENT—BRAUER'S CLASSIFICATION—CLASSIFICATIONS BASED ON
METAMORPHOSIS—SUPER-ORDERS—THE SUBDIVISIONS OF ORDERS.
CLASSIFICATION.
We have already alluded to the fact that Insects are the most numerous in
species and individuals of all land animals: it is estimated that about
250,000 species have been already described and have had scientific names
given to them, and it is considered that this is probably only about
one-tenth of those that really exist. The classification in a
comprehensible manner of such an enormous number of forms is, it will be
readily understood, a matter of great difficulty. Several methods or
schemes have since the time of Linnaeus been devised for the purpose, but
we shall not trouble the reader to consider them, because most of them have
fallen into disuse and have only a historical interest. Even at present
there exists, however, considerable diversity of opinion on the question of
classification, due in part to the fact that some naturalists take the
structure of the perfect or adult Insect as the basis of their arrangement,
while others prefer to treat the steps or processes by which the structure
is attained, as being of primary importance. To consider the relative
values of these two methods would be beyond our scope, but as in practice a
knowledge of the structures themselves must precede an inquiry as to the
phases of development by which the structures are reached; and as this
latter kind of knowledge has been obtained in the case of a comparatively
small portion of the known forms,—the embryology and metamorphosis having
been investigated in but {172}few Insects,—it is clear that a
classification on the basis of structure is the only one that can be at
present of practical value. We shall therefore for the purposes of this
work make use of an old and simple system, taking as of primary importance
the nature of the organs of flight, and of the appendages for the
introduction of food to the body by the perfect Insect. We do not attempt
to disguise the fact that this method is open to most serious objections,
but we believe that it is nevertheless at present the most simple and
useful one, and is likely to remain such, at any rate as long as knowledge
of development is in process of attainment.
ORDERS.
The great groups of Insects are called Orders, and of these we recognise
nine, viz. (1) Aptera, (2) Orthoptera, (3) Neuroptera, (4) Hymenoptera, (5)
Coleoptera, (6) Lepidoptera, (7) Diptera, (8) Thysanoptera, (9) Hemiptera.
These names are framed to represent the nature of the wings; and there is
some advantage in having the Orders named in a uniform and descriptive
manner. The system we adopt differs but little from that proposed by
Linnaeus.[107] The great Swedish naturalist did not, however, recognise the
Orders Orthoptera and Thysanoptera; and his order Aptera was very different
from ours.
These Orders may be briefly defined as follows,—the reader being asked to
recall the fact that by a mandibulate mouth we understand one in which the
mandibles, or the maxillæ, or both, are fitted for biting, crushing, or
grasping food; while the term suctorial implies that some of the mouth
parts are of a tubular form or are protrusible as a proboscis, which
assists, or protects, a more minute and delicate sucking apparatus:—
1. _Aptera_ (ἀ without, πτερόν a wing). Wingless[108] Insects; mouth
mandibulate or very imperfectly suctorial. Metamorphosis very little.
2. _Orthoptera_ (ὀρθός straight, πτερόν a wing). Four wings are present,
the front pair being coriaceous (leather-like), usually smaller than the
other pair, which are of more delicate texture, and contract in repose
after the manner of a fan. Mouth mandibulate. Metamorphosis slight.
3. _Neuroptera_ (νεῦρον nerve, πτερόν a wing). Four wings of membranous
{173}consistency, frequently with much network; the front pair not much,
if at all, harder than the other pair, the latter with but little or no
fanlike action in closing. Mouth mandibulate. Metamorphosis variable, but
rarely slight.
4. _Hymenoptera_ (ὑμήν membrane, πτερόν a wing). Four wings of membranous
consistency; the front pair larger than the hind, which are always small
and do not fold up in repose. Mouth mandibulate, sometimes provided also
with a tubular proboscis. Metamorphosis very great.
5. _Coleoptera_ (κολεός sheath, πτερόν a wing). Four wings; the upper
pair shell-like in consistency, and forming cases which meet together
over the back in an accurate line of union, so as to entirely lose a
winglike appearance, and to conceal the delicate membranous hind pair.
Mouth mandibulate. Metamorphosis great.
6. _Lepidoptera_ (λεπίς scale, πτερόν a wing). Four large wings covered
with scales. Mouth suctorial. Metamorphosis great.
7. _Diptera_ (δίς double, πτερόν a wing). Two membranous wings. Mouth
suctorial, but varying greatly. Metamorphosis very great.
8. _Thysanoptera_ (θύσανος fringe, πτερόν a wing). Four very narrow
fringed wings. Mouth imperfectly suctorial. Metamorphosis slight.
9. _Hemiptera_ (ἡμι half, πτερόν a wing). Four wings; the front pair
either leather-like with more membranous apex, or entirely parchment-like
or membranous. Mouth perfectly suctorial. Metamorphosis usually slight.
We must again ask the reader to bear in mind that numerous exceptions exist
to these characters in most of the great Orders; for instance, wingless
forms are not by any means rare in several of the Orders.
Before remarking further on this system we will briefly sketch two other
arrangements of the Orders of Insects, for which we are indebted to Packard
and Brauer.
PACKARD'S CLASSIFICATION.
Packard has devoted much attention to the subject, and has published two or
three successive schemes, of which the following is the most recent:[109]
the definitions are those of the author himself, but the information in
brackets is given to institute a concordance with the system we adopt:—
1. _Thysanura._ Wingless; often with a spring (equivalent to our
_Aptera_).
2. _Dermaptera._ Front wings minute, elytra-like (= _Forficulidae_, a
part of our _Orthoptera_).
3. _Orthoptera._ Wings net-veined; fore wings narrow, hind wings folded
(= our _Orthoptera_ after subtraction of _Dermaptera_).
{174}4. _Platyptera._ Four net-veined wings; mouth parts adapted for
biting (= _Termitidae_ and _Mallophaga_, parts of our _Neuroptera_).
5. _Odonata._ Wings net-veined, equal (= _Odonata_, a division of our
_Neuroptera_).
6. _Plectoptera._ Wings net-veined, unequal (= _Ephemeridae_, a part of
our _Neuroptera_).
7. _Thysanoptera._ Mouth beaklike but with palpi (= our _Thysanoptera_).
8. _Hemiptera._ Mouth parts forming a beak for sucking. No palpi (= our
_Hemiptera_).
The above eight Orders form the group AMETABOLA, while the following eight
constitute the METABOLA:—
9. _Neuroptera._ Wings net-veined; metamorphosis complete (= a small part
of our _Neuroptera_).
10. _Mecaptera._ Wings long and narrow (for a small part of our
_Neuroptera_; the _Panorpatae_ of Brauer).
11. _Trichoptera._ Wings not net-veined (= our division of _Neuroptera_
with the same name).
12. _Coleoptera._ Fore wings sheathing the hinder ones (= our
_Coleoptera_).
13. _Siphonaptera._ Wingless, parasitic. Flea (= a division of
_Diptera_).
14. _Diptera._ One pair of wings (= our _Diptera_ after subtraction of
_Siphonaptera_).
15. _Lepidoptera._ Four wings (and body) scaled (= our _Lepidoptera_).
16. _Hymenoptera._ Four clear wings; hinder pair small; a tongue (= our
_Hymenoptera_).
Although this system of the Orders of Insects has some valuable features it
is open to very serious objections, to which we can only briefly allude.
The Order Hemiptera with its extensive divisions, Heteroptera, Homoptera,
Coccidae, and Anoplura exhibiting great differences in structure and
considerable divergence in metamorphosis, is treated as only equivalent to
the little group Panorpatae (scorpion-flies); these latter being considered
a distinct order, although they are not very different in structure or
metamorphosis from the Orders he calls Neuroptera and Trichoptera. The
arrangement appears to be specially designed with the view of making the
Orders adopted in it fall into the two groups Ametabola and Metabola. The
propriety of such a course is more than doubtful since very few of the
Ametabola are really without metamorphosis, in the wide sense of that term,
while the Metabola include Insects with various kinds of metamorphosis.
Indeed if we substitute for the term Ametabola the more correct expression,
"Insects with little metamorphosis," and for Metabola the definition,
"Insects with more metamorphosis but of various kinds," we then recognise
that the arrangement {175}is, like all others, a quite artificial one,
while it is of little value, owing to the development of so few Insects
being hitherto fully ascertained.
BRAUER'S CLASSIFICATION.
Professor Brauer has recently proposed[110] to adopt 17 Orders or chief
groups of Insects, arranging them as follows:—
I. APTERYGOGENEA (with one order).
1. _Synaptera_ (= _Aptera_ of our system).
II. PTERYGOGENEA (= all the other Insects of our arrangement).
2. _Dermaptera_ (= _Orthoptera_, Fam. _Forficulidae_ in our
arrangement).
3. _Ephemeridae_ (= a division of _Neuroptera_ in our arrangement).
4. _Odonata_ (= a division of _Neuroptera_ in our arrangement).
5. _Plecoptera_ (= _Neuroptera_, Fam. _Perlidae_ in our
arrangement).
6. _Orthoptera_ (= our _Orthoptera_ - _Forficulidae_ and +
_Embiidae_).
7. _Corrodentia_ (= the families _Termitidae_, _Psocidae_, and
_Mallophaga_, of our _Neuroptera_).
8. _Thysanoptera_ (as with us).
9. _Rhynchota_ (= _Hemiptera_ with us).
10. _Neuroptera_ (= the families _Hemerobiidæ_ and _Sialidæ_ of our
_Neuroptera_).
11. _Panorpatae_ (= the family _Panorpidae_ of our _Neuroptera_).
12. _Trichoptera_ (= the division _Trichoptera_ of _Neuroptera_).
13. _Lepidoptera_ (= as with us).
14. _Diptera_ (= our _Diptera_ - _Aphaniptera_).
15. _Siphonaptera_ (= _Aphaniptera_, a division of _Diptera_ with
us).
16. _Coleoptera_ (= _Coleoptera_).
17. _Hymenoptera_ (as with us).
The chief characters on which Brauer bases his system are: (1) The
existence or absence of wings. (2) The condition of the mouth, and whether
it undergoes radical changes in the ontogeny, arriving thus at the
categories Menognatha, Metagnatha, and Menorhyncha, as we have mentioned on
p. 161. (3) The metamorphosis; the grouping adopted being Ametabola,
Hemimetabola, Metabola. (4) The number of the Malpighian tubules;
Oligonephria, Polynephria. (5) The nature of the wings, the relative
proportions of the thoracic segments, and some other characters.
Brauer's treatise is accompanied by a valuable and in many respects very
sagacious consideration of the generalised characters of the Insecta; as a
classification based partly on generalisations and partly on structures, it
is, so far as the present {176}condition of our knowledge goes, a good one.
But it is of little value as a practical guide, and as a basis for
theoretical speculation it cannot be treated as of importance, because the
generalisations it makes use of are premature, owing to the small
proportion of the forms that have been examined. And even now the groups
adopted are known to be subject to many exceptions.
Thus it begins by a division of Insecta into winged and wingless; but the
winged division is made to comprehend an enormous number of wingless
Insects, whole subdivisions of Orders such as the Mallophaga being placed
in the winged series, although all are without wings. This first division
is indeed entirely theoretical; and if a classification on generalisations
were adopted, it would be more natural to begin with the old division into
Homomorpha and Heteromorpha, and treat the Order Aptera as the first
division of the Homomorpha, while the Heteromorpha would commence with the
Ephemeridae and Odonata, in which, though the individual in the early part
of the ontogeny is very different from the perfect Insect, there is no
marked division of the later larval and the pupal stages. Brauer's system
is also defective inasmuch as it takes no account of the embryological or
oogenetic processes, though these are of equal importance with the later
phases of the Ontogeny. Even as regards the division into Orders, it is far
from being free from reproach; for instance, the separation of the
Dermaptera from the Orthoptera, while Rhynchota remains intact, although
including a more extensive series of heterogeneous forms; the division of
the Neuroptera into widely separated groups, each of which is treated as
equivalent to the great Orders, such as Coleoptera (in which Strepsiptera
are included), Hymenoptera, and Diptera, is not reasonable. The association
of Mallophaga and Termitidae, while Dermaptera are separated from
Orthoptera, is also undeniably arbitrary, and other similar disparities are
to be seen on scrutinising the details of the system.
On comparing the three arrangements we have outlined, it will be seen that
the chief discrepancies they present come under two heads: (1) The
treatment of the Neuroptera, opinions differing as to whether these Insects
shall be grouped as a single Order, or shall be divided into numerous
Orders; and as to what, if this latter course be adopted, the divisions
shall be. (2) The treatment of the parasitic groups Mallophaga,
Aphaniptera, etc. {177}It must be admitted that whichever of the three
systems we have sketched be adopted, the result is, as regards both these
points, open to criticism. The Order Neuroptera, if we take it in the broad
sense, differs from the other Orders in the greater variety of
metamorphosis exhibited by its members; while if, on the contrary, it be
dismembered, we get a number of groups of very unequal extent and not
distinguished from one another by the same decisive and important
characters as are the other Orders of which they are considered equivalent.
The discrepancy exists in nature, and can scarcely be evaded by any system.
A similar observation may be made as to the parasitic groups, viz.
Mallophaga, Anoplura, Aphaniptera, and Strepsiptera. If these be treated as
separate Orders the result is not satisfactory; while, if they be
associated with the larger groups to which they are respectively nearest
allied, it is almost equally unsatisfactory.
We may mention that Packard and Brauer have in their treatises discussed
the question of super-orders, and have gone so far as to propose names for
them. These two authorities do not however agree in their conclusions; and
as the names proposed are of little practical value, and are but rarely met
with, we need not explain them or discuss the comparative merits of the two
systems.
The divisions of inferior value to the Order are, after repeated scrutiny
by many naturalists, becoming of a more satisfactory character, and
notwithstanding various anomalies, may be, many of them, considered fairly
natural.[111] Unfortunately entomologists have not been able to agree on a
system of terminology, so that for these subdivisions terms such as
sub-order, series, legion, section, tribe, etc., are used by different
authorities in ways so various as to cause much confusion. In the following
pages the terms sub-order and series will be used in a somewhat vague
manner, the term sub-order being preferred where the group appears to be an
important one and of a fairly natural character, while the word series will
be adopted when the groups are connected in a conventional manner. The
designation "family" will be used for groups of subordinate importance; and
as regards this term we may remark that systematic entomologists are making
genuine efforts to define the "families" in an accurate and comprehensible
manner. The endeavour to make these systematic {178}families dependent
throughout the Class Insecta on characters of similar morphological value
has, however, scarcely been entered on, and it is perhaps not desirable,
seeing how very small a portion of the Insects of the world have been
critically examined, that much effort should be yet expended on an attempt
of the kind. It must be admitted that the species of Insects should be
obtained before they can be satisfactorily classified, and it is
estimated[112] that at least nine-tenths of the Insects of the world are
still unknown to entomologists.
GEOLOGICAL RECORD.—Although Insects have a very long pedigree, it is as yet
a very imperfect one. The remains of creatures that can be referred to the
Class Insecta have been found, it is said, in Silurian strata; only one or
two of these very early forms are at present known, and the information
about them is by no means satisfactory; if Insects at all—as to which some
doubt exists—they apparently belong to very different forms, though, like
all the earliest fossil Insects, they are winged. In the strata of the
Carboniferous epoch numerous Insects have been detected, in both Europe and
North America. These earlier Insects are by Scudder called
Palaeodictyoptera, and separated from the Insects around us on the ground
that he considers there existed amongst these palaeozoic Insects no ordinal
distinctions such as obtain in the existing forms, but that the primeval
creatures formed a single group of generalised Hexapods. Brauer does not
accept this view, considering that the earlier Insects can be referred to
families existing at the present time and forming parts of the Orthoptera,
Neuroptera, and Hemiptera. The discrepancy between these two authorities
depends to a great extent on the different classifications of existing
Insects that they start from; Scudder treating the wings as of primary
importance, while Brauer assigns to them only a subordinate value. From the
point of view taken in the present work Scudder's view appears to be in the
main correct, though his expression as to the primary fossil Insects
forming a single homogeneous group is erroneous. The Neuroptera, still in
existence, certainly form a heterogeneous group, and it is clear that the
Palaeozoic fossils represent a more diverse assemblage than the present
Neuroptera do.[113]
{179}In the more recent rocks Insect remains become comparatively numerous,
and in Mesozoic strata forms that can satisfactorily be referred to
existing Orders are found, the Palaeodictyoptera of Goldenberg and Scudder
having mostly disappeared; the Blattidae or cockroaches do not apparently
present any great discontinuity between their Palaeozoic and Mesozoic
forms. The Tertiary rocks afford us fairly satisfactory evidence to the
effect that Insects were then more numerous in species than they are at the
present day. At Florissant in Colorado the bed of an ancient lake has been
discovered, and vast quantities of Insect remains have been found in it,
the geographical conditions indicating that the creatures were not brought
from a distance, but were the natural fauna of the locality; and if so we
can only conclude that Insects must have been then more abundant in species
than they are now.
Scudder has informed us[114] that not only were Insects abundant in the
Tertiaries, but that their remains indicate conditions of existence very
similar to what we find around us. "Certain peculiarities of secondary
sexual dimorphism accompanying special forms of communistic life, such as
the neuters and workers in Hymenoptera and the soldiers among the
Termitina, are also found, as would be expected, among the fossils, at
least through the whole series of the Tertiaries. The same may be said of
other sexual characteristics, such as the stridulating organs of the
Orthoptera, and of peculiarities of oviposition, as seen in the huge
egg-capsules of an extinct Sialid of the early Tertiaries. The viviparity
of the ancient Aphides is suggested, according to Buckton, by the
appearance of one of the specimens from the Oligocene of Florissant, while
some of the more extraordinary forms of parasitism are indicated at a time
equally remote by the occurrence in amber of the triungulin larva of
_Meloe_, already alluded to, and of a characteristic strepsipterous Insect;
not only, too, are the present tribes of gall-making Insects abundant in
the Tertiaries, but their galls as well have been found."
{180}CHAPTER VII
THE ORDER APTERA–DEFINITION–CHIEF CHARACTERISTICS–THYSANURA–CAMPODEA–
JAPYX–MACHILIS–LEPISMA–DIVERSITY OF INTERNAL STRUCTURE IN THYSANURA–
ECTOTROPHI AND ENTOTROPHI–COLLEMBOLA–LIPURIDAE–PODURIDAE–SMYNTHURIDAE–
THE SPRING–THE VENTRAL TUBE–ABDOMINAL APPENDAGES–PROSTEMMATIC ORGAN–
TRACHEAL SYSTEM–ANURIDA MARITIMA–COLLEMBOLA ON SNOW–LIFE-HISTORIES OF
COLLEMBOLA–FOSSIL APTERA–APTERYGOGENEA–ANTIQUITY AND DISTRIBUTION OF
CAMPODEA.
ORDER I. APTERA.
_Small Insects with weak outer skin, destitute throughout life of wings
or their rudiments, but with three pairs of legs; antennae large or
moderate in size._
The above definition is the only one that can at present be framed to apply
to all the Insects included in our Aptera. Unfortunately it is far from
diagnostic, for it does not enable us to distinguish the Aptera from the
larvae or young individuals of many Insects of other Orders. There are,
however, certain characters existing in many species of Aptera that enable
their possessors to be recognised with ease, though, as they are quite
wanting in other members, they cannot correctly be included in a definition
applying to the whole of the Order.
We are thus brought in view of two of the most important generalisations
connected with the Aptera, viz. that these Insects in their external form
remain throughout their life in a condition resembling the larval state of
other Insects, and that they nevertheless exhibit extreme variety in
structural characters.
The more important of the special characters alluded to above {181}as being
possessed by some but not by all members of the Order are (1) a remarkable
leaping apparatus, consisting of two elongate processes at the under side
of the termination of the body; (2) a peculiar ventral tube, usually seen
in the condition of a papilla with invaginated summit, and placed on the
first abdominal segment (see Fig. 100, p. 194); (3) the scales covering the
body; (4) the existence of abdominal appendages in the form of long cerci
or processes at the termination of the body, or of short processes on the
sides of the under surface of the abdominal segments.
Throughout the Order the general shape approximates to that of a larva;
this is shown by the diagrammatic section of the body of _Machilis_ (Fig.
90). There is a succession of rings differing little from one another,
except so far as the head is concerned; even the division of thorax from
abdomen is but little evident, and although in some of the forms the three
thoracic segments may differ considerably among themselves, yet they never
assume the consolidated form that they do to a greater or less extent in
the imago stage of the other Orders. Fig. 90 shows the larva-like structure
of the body, and also exhibits the inequalities in size between some of the
dorsal and the corresponding ventral plates. This phenomenon is here
displayed only to a small extent, so that the true relations of the dorsal
and ventral plates can be readily detected; but in the higher Insects want
of correspondence of this kind may be much more extensive.
[Illustration: FIG. 90.--Section of body of _Machilis_: _o_, ovipositor.
(After Oudemans.)]
The respiratory system is in many of these Insects very inferior in
development, and may even be, so far as tracheae and spiracles are
concerned, entirely absent, but in other members of the Aptera it is well
developed. In the other internal organs there is also great variety, as
there is in the external structure.
A brief explanation as to the term Aptera, which we have adopted as the
name of this Order, is necessary. This name was used by Linnaeus for our
Insects, but as he associated with them various other heterogeneous forms
which were afterwards separated, his "Aptera" became completely broken up
and ceased {182}to be recognised as an Order of Insects. The term was,
however, revived by Haeckel and Balfour several years since, and applied
quite properly to the Insects we have in view. Subsequently Packard and
Brauer, recognising the claims of these Insects to an isolated position,
proposed for them the names Synaptera and Apterygogenea, and Packard has
also used the term Cinura. There is, however, clearly an advantage in
retaining the termination "ptera" for each of the Orders of Insects; and as
the fact that "Aptera" of Linnaeus included many Insects is not a
sufficient reason for refusing to apply the term to a portion of the forms
he used it for, we may, it is clear, make use of the Linnaean name with
propriety, it being explicitly stated that the Order does not include by
any means all the apterous forms of Insects.
The Order includes two sub-orders, viz. (1) _Thysanura_, in which the hind
body (abdomen) is composed of ten segments, and there is no ventral tube on
its first segment; and (2) _Collembola_, in which the hind body consists of
not more than six segments, the first of which is furnished beneath with a
peculiar tube or papilla.
THYSANURA.
Our knowledge of this important sub-order has been recently much increased
by the works of Grassi[115] and Oudemans.[116] Very little is known,
however, of the extra-European forms, there being great difficulties in the
way of collecting and preserving specimens of these Insects in such a way
as to render them available for study and accurate comparison. Grassi and
Rovelli[117] recognise four families among the few European species of
Thysanura, viz. Campodeidae, Japygidae, Machilidae, Lepismidae. Campodeidae
is perhaps limited to a single species, only one having been satisfactorily
established, though several descriptions have been made of what are
supposed to be other species.
This Insect (_Campodea staphylinus_) is, so far as external form goes, well
known, from its having been figured in many works on natural history on
account of its having been supposed to be {183}the nearest living
representative of a primitive or ancestral Insect. The creature itself is
but little known even to entomologists, although it is one of the commonest
of Insects over a large part of Europe. It is numerous in the gardens and
fields about London and Cambridge, and abounds in damp decaying wood in the
New Forest; if there be only one species, it must possess an extraordinary
capacity for adapting itself to extremes of climate, as we have found it at
midsummer near the shores of the Mediterranean in company with the
subtropical white ants, and within a day or two of the same time noticed it
to be abundant on the actual summit of Mount Canigou, one of the higher
Pyrenees, where the conditions were almost arctic, and it was nearly the
only Insect to be found. The species is said to exist also in North America
and in East India. It is a fragile, soft Insect of white colour, bending
itself freely to either side like a Myriapod; the legs are rather long, the
antennae are long and delicate, and the two processes, or cerci, at the
other extremity of the body are remarkably similar to antennae. It has no
eyes and shuns the light, disappearing very quickly in the earth after it
has been exposed. If placed in a glass tube it usually dies speedily, and
is so extremely delicate that it is difficult to pick it up even with a
camel's hair brush without breaking it; so that we may fear it to be almost
hopeless to get enough specimens from different parts of the world to learn
what differences may exist amongst the individuals of this so-called
primitive Insect. Meinert, a very able entomologist, considers that there
is really more than one species of _Campodea_.
[Illustration: FIG. 91.—_Campodea staphylinus._ (After Lubbock, × 15.)]
Campodeidae as a family may be briefly defined as Thysanura with the trophi
buried in the head and with the body terminated by antenna-like processes.
We shall consider some of the anatomical peculiarities of this interesting
Insect after we have {184}briefly reviewed some of the external characters
of the other Thysanura.
The second family (Japygidae) consists of one genus _Japyx_, of which there
are, no doubt, several different species in various parts of the world,
such having already been detected in tropical Africa, in Malasia, and in
Mexico, as well as in Madeira and Europe. The commoner species of the
latter continent, _Japyx solifugus_, lives in moss or in shady places on
the edges of woods. It possesses a great resemblance to a newly-hatched
earwig, and the writer has found it in France under a stone in company with
a number of the tiny creatures it was so much like. This species has been
found as far north as Paris, but has not been met with in Britain. The
family Japygidae is, like the Campodeidae, entotrophous, and is
distinguished by the body being terminated behind by a pair of forceps
instead of antennary organs.
The other two families of Thysanura, Machilidae and Lepismidae, are
ectotrophous—that is, the parts of the mouth are not buried in the head,
but are arranged in the fashion usual in mandibulate Insects.
Only one genus of Machilidae is known, but it is no doubt very numerous in
species, and probably is distributed over most of the globe. _Machilis
maritima_ is common in some places on the coast of England. Another species
(_M. polypoda_) occurs amongst dead leaves in the New Forest, and we have
also observed a species of the genus under the loose stones that frequently
form the tops of the "dykes" or piled walls in Scotland. In more southern
Europe species of _Machilis_ are commonly met with on the perpendicular
faces of very large stones or rocks, over which they glide with wonderful
facility. The scales on the bodies of these rock-inhabiting species form
pretty patterns, but are detached with such facility that it is almost
impossible to obtain specimens in satisfactory condition for examination.
In Machilidae the dorsal plates of the hind body are reflexed to the under
surface so as to form an imbrication covering the sides of the ventral
plates, and the eyes are largely developed; by which characters the family
is distinguished from the Lepismidae. The pair of large compound eyes (Fig.
92, _O_) is a remarkable feature, being indeed unique in the Aptera. The
structures (_o_, _o′_) that Oudemans considers to be simple eyes have, in
external appearance, a resemblance to the fenestrae of the {185}Blattidae;
Grassi states, however, that not only are they eyes, but that they are of
almost unique structure, being, in fact, intermediate between simple and
compound eyes.
The mode of development of the compound eyes of _Machilis_ is of
considerable interest, but unfortunately very little is known about it,
even the period at which the eyes appear being uncertain. Judging from
analogy with the Orthoptera, we should suppose them to be present when the
Insect leaves the egg, and Oudemans apparently considers this to be the
case, but Bolivar states[118] that in the early stages of _Machilis_ the
eyes are only simple eyes; these being replaced by compound eyes in the
later life. The writer has observed very young individuals of _Machilis
polypoda_, and found the eyes to be evidently compound.
[Illustration: FIG. 92.—Head of _Machilis maritima_ (after Oudemans): _A_,
base of antenna; _C_, clypeus; _F_, vertex; _P_, fold; _O_, eye; _o_, _o′_,
supposed simple eye; _M_, mandible; _m_, maxilla; _L_, upper lip; _l_,
lower lip; _T_, portion of maxillary palp; _t_, of labial palp. × 20.]
[Illustration: FIG. 93.—_Lepisma cincta._ (After Oudemans.) × 4. (The line
indicates the natural length.)]
The remaining family of Thysanura, the Lepismidae, is in certain respects
the most highly developed of the Order. The covering of scales found on the
body is very remarkable in some of the species, especially in the genus
_Lepisma_ (Fig. 93, _L. cincta_); the thoracic segments are different from
one another {186}and from those of the abdomen, and the tracheal system is
more highly developed than it is in the Machilidae. Several genera are
known, but only two members of the family have yet been detected in
Britain. One of them (_Lepisma saccharina_), occurs only in houses, and is
sometimes called the silver fish; it is, when full grown, less than half an
inch long, and is covered with scales that give it a feebly metallic
lustre. Like the other Thysanura, its movements are very perfect. It is
said that it is occasionally injurious by nibbling paper, but the writer's
observations lead him to doubt this; its usual food is doubtless
farinaceous or saccharine matter. _Thermobia furnorum_, our other British
Lepismid, has only recently been discovered; it is found in bakehouses at
Cambridge and elsewhere. The bakers call these Insects fire-brats,
apparently considering them to be fond of heat.
Much valuable information as to the anatomy of Thysanura has been obtained
by Grassi and Oudemans, and is of great interest. Taking four genera, viz.
_Campodea_, _Japyx_, _Machilis_, and _Lepisma_, to represent the four
families constituting the sub-order, we will briefly enumerate some of the
more remarkable of the characters of their internal anatomy. _Campodea_ has
a very inferior development of the tracheal system; there are three pairs
of spiracles, which are situate on the thoracic region; the tracheae
connected with each spiracle remain distinct, not uniting with those coming
from another spiracle; there are thus six separate small tracheal systems,
three on each side of the body. _Japyx solifugus_ has eleven pairs of
spiracles, of which four are thoracic; the tracheae are united into one
system on each side by means of lateral tubes; thus there are two extensive
tracheal systems situate one on each side of the body, there being a single
transverse tube, placed near the posterior extremity, uniting the two
lateral systems. In _Machilis_ there are nine pairs of stigmata, two of
them thoracic, seven abdominal; the tracheae from each spiracle remain
unconnected, so that there are eighteen separate tracheal systems, some of
which are considerably more developed than others. The Lepismidae have ten
pairs of stigmata, and the tracheae connected with them are completely
united into one system by longitudinal and transverse tubes. Besides these
differences there are others, of considerable importance, in the position
of the stigmata.
{187}All the Thysanura possess salivary glands. In _Campodea_ there are
about sixteen extremely short Malpighian tubules, or perhaps glands
representing these organs; _Japyx_ is destitute of these structures;
_Machilis maritima_ has twenty elongate tubules; in _Lepisma_ also they are
long, and apparently vary in number from four to eight in different
species. The proportions of the three divisions of the alimentary canal
differ extremely; there is a very large proventriculus in _Lepisma_, but
not in the other families; coecal diverticula are present on the anterior
part of the true stomach in _Machilis_ and in _Lepisma_, but are wanting in
_Campodea_ and in _Japyx_.
The dorsal vessel seems not to present any great differences in the
sub-order. Grassi says there are no alary muscles present, but Oudemans
describes them as existing in _Machilis_, but as being excessively
delicate.
The ventral chain of nerve-ganglia consists in _Campodea_ of one cephalic
ganglion, one sub-oesophageal (which clearly belongs to the ventral series
of ganglia), three thoracic, and seven abdominal. In the other families
there are eight instead of seven abdominal ganglia.
The structure of the internal sexual organs is very remarkable in the
Thysanura. In _Campodea_ there is one extremely large, simple tube on each
side of the body. In _Japyx_ there are seven small tubes on each side,
placed one in each of the successive abdominal segments, and opening into a
common duct. In _Machilis_ there are also seven tubes opening into a common
duct, but the arrangement is no longer a distinctly segmental one. In
_Lepisma_ there are five egg-tubes on each side, the arrangement being
segmental in the young state but not in the adult condition. In _Campodea_
nutrient cells alternate with the eggs in the tubes, but this is not the
case in the other families. Fig. 94 shows the ovaries in three of the
Thysanura; in the drawing representing this part in _Machilis_ (C), one of
the two ovaries is cut away for the sake of clearness.
The male organs in _Campodea_ are very similar in size and arrangement to
the ovaries, there being a single large tube or sac and a short vas
deferens on each side of the body. In _Japyx_ there is a sac on each side,
but it is rendered double by a coecum at its base, and there are long and
tortuous vasa deferentia. In _Lepisma_ there are three pairs of coeca on
each {188}side, segmentally placed and opening into a common duct. In
_Machilis_ there are three retort-shaped sacs on each side opening near one
another into a common duct, the vasa deferentia are elongate, and are very
curiously formed, being each double for a considerable length, and the
separated portions connected at intervals by five transverse commissural
ducts.
[Illustration: FIG. 94.—Ovaries of Thysanura: A, of _Campodea_; B, of
_Japyx_; C, of _Machilis_. (After Grassi and Oudemans.)]
One of the characteristic features of Insect structure is the restriction
of articulated legs to the thoracic region. In the Thysanura there exist
appendages occupying a position on the hind body somewhat similar to that
of the legs on the thorax. These appendages are quite small bodies, and are
placed at the hind margins of the ventral plates of the abdomen, one near
each side; they are connected by a simple joint to the sternite and are
provided with muscles. They are found in _Campodea_ on segments 2 to 7; in
_Lepisma_ on 8 and 9, in the allied _Nicoletia_ on 2 to 9; in _Japyx_ on 1
to 7, being, however, more rudimentary than they are in _Campodea_. In
_Machilis_ they attain perhaps their greatest development and exist on
segments 2 to 9; moreover, in this genus such appendages occur also on the
coxae of the second and third pairs of thoracic legs. Oudemans thinks they
help to support the abdomen, and that they also assist in leaping; Grassi
considers that they are supporting agents to some extent, but that they are
essentially tactile organs. He calls them false legs "Pseudozampe."
Still more remarkable and obscure in function are the vesicles found near
the appendages; we figure a pair after Oudemans, showing them in the
exserted state. In the retracted state the outer portion of the vesicles is
withdrawn into the basal part _P_ (Fig. 95), so that the vesicles are then
only just visible, being {189}concealed by the ventral plate. The abdominal
appendage is not retractile. In _Machilis_ there are twenty-two of these
vesicles, arranged either two or four on one ventral plate of the hind
body. They are also present in _Campodea_, where there are six pairs. They
are usually said to be absent in _Japyx_ and in _Lepisma_, but Haase
shows[119] that _Japyx_ possess a pair placed behind the second ventral
plate of the abdomen. The vesicles appear to be exserted by the entrance of
blood into them, and to be retracted by muscular agency. Much difference of
opinion prevails as to their function; it appears probable that they may be
respiratory, as suggested by Oudemans.
The scales found on the bodies of the Ectotrophous Thysanura may be looked
on as modified hairs, and are essentially similar to those of the
Lepidoptera, and they drop off as readily as do those of the Lepidoptera.
Stummer-Traunfels, who has recently published[120] the results of his
researches on the mouth-organs of Thysanura and Collembola, confirms the
division of the Thysanura into Entotrophi and Ectotrophi, and considers
that the Collembola agree with the former group. The German author
therefore proposes to divide our Aptera, not into Thysanura and Collembola,
but into Ectognathi and Entognathi, the former group consisting of
Machilidae and Lepismidae, the latter of Campodeidae, Japygidae and the
various families of Collembola. We think it far more natural, however, to
retain the older division into Thysanura and Collembola.
[Illustration: FIG. 95.—Abdominal appendage and exsertile vesicles of
_Machilis_. _A_, appendage; _V_, vesicles protruded; _P_, basal portion;
_R_, muscles, × 70.]
COLLEMBOLA.
The sub-order Collembola, which we have defined on p. 182, consists of
small Insects, many of which possess the capacity of leaping, or springing
suddenly, and when disturbed or alarmed naturally make use of this means of
escaping. Their leaps, however, appear to be made quite at random, and very
frequently do {190}not have the result of taking the creature into
concealment, and in such circumstances they may be rapidly and frequently
repeated until the Insect feels itself, as we may suppose, in a position of
safety. Three families may be very readily distinguished, viz. (1)
Lipuridae, in which no leaping apparatus is present; (2) Poduridae, a
leaping apparatus exists near the extremity of the abdomen; the body is
subcylindric and evidently segmented; (3) Smynthuridae, a leaping apparatus
exists: the body is sub-globular with comparatively large head and abdomen,
the intervening thoracic region being small; the segmentation of the body
is obscure.
The study of the Collembola is much less advanced than that of the
Thysanura, comparatively little having been added to our knowledge of the
group since Lubbock's monograph of the British forms was published by the
Ray Society in 1873. Why the Collembola should be neglected when the
Thysanura attract so much attention is as inexplicable as many other
fashions are.
The family Lipuridae consists of a few very small and obscure Insects of
soft consistence. They move slowly, and, owing to the absence of any
leaping power, attract attention less readily than the other Collembola do.
Two genera are generally recognised, and they should probably form separate
families; indeed, in Lubbock's arrangement they do so. In one of the genera
(_Anoura_) the mouth is very imperfect, no mandibles or maxillae having
been detected, while in the other genus (_Lipura_) these organs exist.
In the members of the family Poduridae, including the Degeeriidae of
Lubbock, a saltatory apparatus is present in the form of appendages
attached to the fifth abdominal segment (Degeeriides), or to the fourth
(Podurides). These appendages are during life flexed beneath the body, but
in dead specimens usually project backwards, having the appearance of a
bifid tail. Poduridae are of elongate form, somewhat like small
caterpillars, and are frequently prettily marked with variegate colours.
Fig. 97 represents an arctic form closely allied to our native genus
_Isotoma_.
[Illustration: FIG. 96.—_Lipura burmeisteri_. (After Lubbock.)]
{191}The peculiar shape of the members of the Smynthuridae is sufficient
for their identification. They possess a very convex abdomen, and very near
to it a large head, the intervening chink being occupied by the small
thorax. The segmentation of the body is not easily distinguished. Nicolet
states that the thorax consists of three segments and the abdomen of the
same number, and that when the Insect emerges from the egg these divisions
can be perceived. In after life the posterior part of the thorax becomes
amalgamated with the abdomen, so that it is difficult to trace the
divisions, but there appears to be no information as to the manner in which
this change occurs. Some of these minute Insects frequent trees and bushes,
and their leaping powers are very perfect, so that it is difficult to
capture them. The family includes both the Smynthuridae and the Papiriidae
of Lubbock.
[Illustration: FIG. 97.—_Corynothrix borealis_: _a_, ventral tube; _b_, the
spring. (After Tullberg.)]
[Illustration: FIG. 98.—_Smynthurus variegatus_, with spring extended.
(After Tullberg.)]
The two most characteristic organs of the Collembola are the spring and the
ventral tube. The first of these is an elongate structure attached to the
underside of the abdomen near its extremity, either on the penultimate or
ante-penultimate segment. It consists of a basal part, and of two
appendages attached thereto. It is carried under the Insect bent forwards,
and is retained in this position by means of a catch which projects from
the under surface of the third segment of the body, descending between the
two branches of the spring, and passing under the extremity of its basal
segment. It is considered that the spring is elastic, is flexed under the
body by muscular action, and, being retained in this position {192}of
restraint by the catch, when the latter is removed the spring extends by
reason of its elasticity, and the leap is thus executed. Whether this is
really the exact method of leaping is, however, doubtful, for Lubbock says
that the catch "only exists in certain genera"; while in its structure it
does not appear to be well calculated to retain in position an organ that
by virtue of its elasticity is constantly exerting a considerable force.
[Illustration: FIG. 99.—_Smynthurus fuscus_, with exsertile vesicle (_a_)
protruded from ventral tube; _b_, the spring extended.]
The ventral tube is an anomalous and enigmatic structure. In the lower
forms, such as _Lipura_ or _Anurida_, it consists merely of a papilla (Fig.
100, A, _a_) more or less divided by fissure into two parts. In the
Smynthuridae it is more highly developed, and protects two long delicate
tubes that are capable of being protruded, as shown in the outline profile
of _Smynthurus fuscus_ (Fig. 99), which is taken from specimens preserved
in balsam by Mr. J. J. Lister. The nature and use of this ventral tube have
given rise to much discussion. Lubbock considered, and others have agreed
with him, that it serves to attach the Insect to bodies to which it may be
desirable the Insect should, when in the perpendicular position, adhere.
Reuter[121] assigns a quite different function to this singular structure.
He states that the hairs of the body are hygroscopic, and that the peculiar
claws of the Insect having collected the moisture from the hairs, the
ventral tube becomes the means of introducing the liquid into the body.
These Insects possess, however, a mouth, and there seems to be no reason
why a complex apparatus should be required in addition to it for so simple
a purpose as the introduction of moisture to the interior of the body.
Haase finds[122] that Collembola can crawl on glass without the aid of the
ventral tube; he considers its function to be physiological, and that it
may probably be respiratory as it has been suggested is the case with the
vesicles of Thysanura. The function of the ventral tube is certainly not
yet satisfactorily elucidated. The vesicles contained in it are said to be
extruded by blood-pressure, and withdrawn by muscular action in a manner
similar to that which we have described as occurring {193}in the case of
the exsertile vesicles of the Thysanura. The processes in _Smynthurus_ bear
glandular structures at their extremities. It has been suggested that the
ventral tube of Collembola is the homologue of a pair of ventral
appendages. The term Collophore has been applied to it somewhat
prematurely, seeing the doubt that still exists as to its function.
Some of the Collembola possess a very curious structure called the
prostemmatic or ante-ocular organ; its nature and function have been very
inadequately investigated. The ocular organs of the Collembola consist,
when they are present, of isolated ocelli placed at the sides of the head
like the corresponding organs of caterpillars; the prostemmate is placed
slightly in front of the group of ocelli, and has a concentric arrangement
of its parts, reminding one somewhat of the compound eyes of the higher
Insects. This structure is represented in Fig. 100, B, C; it is said by Sir
John Lubbock to be present in some of the Lipuridae that have no ocelli,
and he therefore prefers to speak of it as the "post-antennal" organ.
A very characteristic feature in the Collembola is the slight development
of the tracheal system. Although writers are far from being in accord as to
details, it seems that stigmata and tracheae are usually absent. In
_Smynthurus_ there are, however, according to Lubbock,—whose statement is
confirmed by Meinert and Tullberg,—a pair of stigmata situate on the head
below the antennae, and from these there extends a tracheal system
throughout the body. Such a position for stigmata is almost, if not quite
unique in Insects; Grassi, however, seems to have found something of the
kind existing in the embryo of the bee.
At present only a small number of species of the Order Aptera are known;
Lubbock recognised about sixty British species, and Finot sixty-five as
found in France. The North American forms have not received so much
attention as the European, and the Aptera of other countries, though they
are probably everywhere fairly numerous, are scarcely known at all. A few
have been described from the Indo-Malayan region and some from Chili, and
the writer has seen species from the West Indian and Sandwich Islands. All
the exotic forms as yet detected are very similar to those of Europe.
The Thysanura are probably not very numerous in species, and appear to be
in general intolerant of cold. With the Collembola {194}the reverse is the
case. They are excessively numerous in individuals; they are found nearly
everywhere on the surface of the ground in climatic conditions like those
of our country, while no less than sixteen species have been found in Nova
Zembla and one each in Kerguelen and South Georgia. One species, if not
more, of _Podura_, lives on the surface of stagnant waters, on which the
minute creatures may frequently be seen leaping about in great numbers
after being disturbed.
In 1874 the plain of Gennevilliers in France was copiously irrigated; in
the following year the soil was still very damp, and there existed numerous
pools of stagnant water, on the surface of which _Podura aquatica_ was
developed in such prodigious quantity as to excite the astonishment of the
inhabitants of the region.
Accounts have been frequently given of the occurrence on snow and glaciers
of Insects spoken of as snow-fleas, or snow-worms. These mostly relate to
Poduridae, which are sometimes found in countless number in such
situations. The reason for this is not well understood. According to F.
Löw,[123] on the 17th of March at St. Jacob in Carinthia, Parson Kaiser
observed, on the occurrence of the first thaw-weather, enormous numbers of
a Podura (? _Achorutes murorum_) on the surface of the snow for an extent
of about half a mile, the snow being rendered black in appearance by them;
eleven days afterwards they were found in diminished numbers on the snow,
but in large quantity on the water left by its melting. This account
suggests that the occurrence of the Insects on the snow was merely an
incident during their passage from the land, where they had been
hibernating, to the surface of the water.
One little member of the Lipuridae, _Anurida maritima_ (_Lipura maritima_
of Lubbock), has the habit, very unusual for an Insect, of frequenting salt
water. It lives amongst the rocks on the shores of the English Channel,
between high and low tide-marks. Its habits have been to some extent
observed by Laboulbène[124] and Moniez[125]; it appears to be gregarious,
and when the tide is high, to shelter itself against the commotions of the
water in chinks of the rocks and other positions of advantage. When the
tide is out the Insects apparently delight to {195}congregate in masses on
the surface of the rock pools. This _Anurida_ can endure prolonged
immersion; but both the observers we are quoting say that it is, when
submerged, usually completely covered with a coat of air so that the water
does not touch it. The little creature can, however, it would appear,
subsist for some time in the pools of salt water, even when it is not
surrounded by its customary protecting envelope of the more congenial
element. Its food is said, on very slender evidence, to consist of the
remains of small marine animals, such as Molluscs. We reproduce some of
Laboulbène's figures (Fig. 100); the under-surface shows at a the divided
papilla of the ventral tube; B, C represent the peculiar prostemmatic
organ, alluded to on p. 193, in its mature and immature states.
[Illustration: FIG. 100.—_Anurida maritima_: A, under-surface; _a_, papilla
of ventral tube; B, prostemmatic organ of young; C, of adult. (After
Laboulbène.)]
Very little information exists as to the life-history of the Aptera; as for
their food, it is generally considered to consist of refuse vegetable or
animal matter. It is usual to say that they are completely destitute of
metamorphosis, but Templeton says of _Lepisma niveo-fasciata_ that "the
young differ so much from the mature Insect that I took them at first for a
distinct species; the thoracic plates are proportionately less broad, and
the first is devoid of the white marginal band." As regards the moults, it
would appear that in this, as in so many other points, great diversity
prevails, Grassi stating that in _Campodea_ there is a single fragmentary
casting of the skin; and Sommer informing us that in _Macrotoma plumbea_
the moults are not only numerous, but continue, after the creature has
attained its full growth, throughout life.
A very marked feature of the Aptera is their intolerance of a dry
atmosphere. Although _Campodea_ can exist under very diverse conditions, it
dies very soon after being placed in a dry closed tube; and the same
susceptibility appears to be shared by all the other members of the Order,
though it is not so extreme in all; possibly it may be due to some
peculiarity in the structure {196}of the integument. So far as tolerance of
heat and cold goes, the Aptera can apparently exist in any climate, for
though some of the species extend to the Arctic regions, others are
peculiar to the tropics.
_Thysanura_ are recorded by Klebs and Scudder as occurring commonly in
amber; the latter author has described a fossil, supposed to be a
_Lepisma_, found in the Tertiary deposits at Florissant. Scudder has also
described another fossil, likewise from Florissant, which he considers to
form a special sub-order of Thysanura—_Ballostoma_—but it is extremely
doubtful whether this anomalous creature should be assigned to the Order at
all. A still older fossil, _Dasyleptus lucasii_ Brongniart, from the
Carboniferous strata in France, is considered to belong to the Order
Aptera, but it must be admitted there is some doubt on this point.
The interest aroused in the minds of naturalists by the comparatively
simple forms of these purely wingless and therefore anomalous Insects has
been accompanied by much discussion as to their relations to other Insects,
and as to whether they are really primitive forms, or whether they may
perhaps be degenerate descendants from some less unusual states of
Insect-life. Mayer and Brauer dissociated our Aptera entirely from other
Insects, and proposed to consider the Hexapoda as being composed of two
groups—(1) the Apterygogenea, consisting of the few species we have been
specially considering; and (2) the Pterygogenea, including all the rest of
the immense crowd of Insect forms. They were not, however, able to
accompany their proposed division by any satisfactory characters of
distinction, and the subsequent progress of knowledge has not supported
their view, all the best investigators having found it necessary to
recognise the extremely intimate relations of these Insects with the
Orthoptera. Meinert thought that _Lepisma_ must be included in the
Orthoptera; Grassi proposes to consider the Thysanura as a distinct
division of Orthoptera; and Oudemans recognises the close relations
existing between _Machilis_ and Orthoptera proper. Finot includes the
Aptera in his Orthoptères de la France, and a species of _Japyx_ has
actually been described by a competent entomologist as an apterous earwig.
At present, therefore, we must conclude that no good distinction has been
found to justify the separation of the Aptera from all other Insects.
{197}The taxonomy of the Collembola has not yet been adequately treated,
and it is possible that more grounds will be found for separating them as a
distinct Order from the Thysanura,—a course that was advocated by
Lubbock,—than exist for dividing these latter from the Orthoptera proper.
There are apparently no grounds for considering the Aptera to be degenerate
Insects, and we may adopt the view of Grassi, that they are primitive, or
rather little evolved forms. It must be admitted that there are not at
present any sufficient reasons for considering these Insects to be
"ancient" or "ancestral." The vague general resemblance of _Campodea_ to
many young Insects of very different kinds is clearly the correlative of
its simple form, and is no more proof of actual ancestry to them than their
resemblances _inter se_ are proofs of ancestry to one another. But even if
deprived of its claim to antiquity and to ancestral honours, it must be
admitted that _Campodea_ is an interesting creature. In its structure one
of the most fragile of organisms, with a very feeble respiratory system,
inadequate organs of sense, only one pair of ovarian tubes, very imperfect
mouth-organs, and a simple alimentary canal, it nevertheless flourishes
while highly-endowed Insects become extinct. In the suburban gardens of
London, on the shores of the Mediterranean, on the summits of the higher
Pyrenees, in North America even it is said in the caves of Kentucky, and in
India, _Campodea_ is at home, and will probably always be with us.
{198}CHAPTER VIII
ORTHOPTERA—FORFICULIDAE, EARWIGS—HEMIMERIDAE
ORDER II.—ORTHOPTERA.
_Insects with the mouth parts conspicuous, formed for biting, the four
palpi very distinct, the lower lip longitudinally divided in the middle.
The tegmina (mesothoracic wings), of parchment-like consistence, in
repose closed on the back of the Insect so as to protect it. The
metathoracic wings, of more delicate consistence, ample, furnished with
radiating or divergent nervures starting from the point of articulation,
and with short cross nervules forming a sort of network; in repose
collapsing like a fan, and more or less completely covered by the tegmina
(except in certain Phasmidae, where, though the wings are ample, the
tegmina are minute, so that the wings are uncovered). In a few forms
(winged Forficulidae and some Blattidae) the metathoracic wings are, in
addition to the longitudinal folding, contracted by means of one or two
transverse folds. The mode of growth of each individual is a gradual
increase of size, without any abrupt change of form, except that the
wings are only fully developed in the final condition. There is no
special pupal instar. Species in which the wings are absent or
rudimentary are numerous._
The Orthoptera are Insects of comparatively large size. The Order, indeed,
includes the largest of existing Insects, while none are so minute as many
of the members of the other Orders are; three millimetres is the least
length known for an Orthopterous Insect, and there are very few so small,
though this is ten times the length of the smallest beetle. The Order
includes earwigs, cockroaches, soothsayers or praying-insects, stick- and
leaf-insects, grasshoppers, locusts, green grasshoppers, and crickets.
{199}The changes of form that accompany the growth of the individual are
much less abrupt and conspicuous than they are in most other Insects. The
metamorphosis is therefore called Paurometabolous. It has been supposed by
some naturalists that Orthoptera go through a larger portion of their
development in the egg than other Insects do. This does not clearly appear
to be the case, though it seems that there are distinctions of a general
character in the embryology; the period of development in the egg is
prolonged, and the yolk is said by Wheeler[126] to be more than usually
abundant in comparison with the size of the young embryo. The embryonic
development may in tropical countries be accomplished in three weeks (see
Mantidae), but in countries where winter supervenes, the period may in some
species be extended over seven or eight months.
The external features of the post-embryonic development—a term that is more
convenient in connexion with Orthoptera than metamorphosis—are as follows:
the wings are never present when the Insect is first hatched, but appear
subsequently, and increase in size at the moults; the form and proportions
of the segments of the body—especially of the thorax—undergo much change;
an alteration of colour occurs at some of the moults, and the integument
becomes harder in the adult condition. Neither the development of the
internal organs, nor the physiological processes by which the changes of
external form are effected, appear to have been studied to any great
extent.
Many of the Orthoptera do not possess wings fit for flight, and some
species even in the adult state have no trace whatever of such organs.
Flight, indeed, appears to be of minor importance in the Order; in many
cases where the wings exist they are purely musical organs, and are not of
any use for flight. The apterous and the flightless conditions are not
confined to one division of the Order, but are found in all the families
and in many of their subdivisions. As the front pair of wings in Orthoptera
do not really carry out the function of flight, and as they differ in
several particulars from the hinder pair, or true wings, it is usual to
call them tegmina. The musical powers of the Orthoptera are confined to the
saltatorial group of families.
{200}[Illustration: FIG. 101.—_Poecilimon affinis_ ♂. Bulgaria. Alar organs
serving only as musical organs. The ear on front tibia and aural orifice of
prothorax are well shown.]
The Cursoria are dumb or nearly so; it is a remarkable fact that also in
this latter division the alar organs, though frequently present, have but
little value for flight, and are in some cases devoted to what we may call
purposes of ornament or concealment. This is specially the case in the
Phasmidae and Mantidae, where the effectiveness of colour and pattern of
these parts becomes truly astonishing. The tegmina frequently exhibit an
extraordinary resemblance to vegetable structures, and this appearance is
not superficial, for it may be seen that the nervures of the wings in their
disposition and appearance resemble almost exactly the ribs of leaves. One
of the most remarkable of the features of Orthoptera is that a great
difference frequently exists between the colours of the tegmina and of the
wings, _i.e._ the front and hind wings; the latter are concealed in the
condition of repose, but when activity is entered on and they are
displayed, the individual becomes in appearance a totally different
creature. In some cases, contrary to what usually occurs in Insects, it is
the female that is most remarkable; the male in Mantidae and Phasmidae
being frequently a creature of quite inferior appearance and power in
comparison with his consort. The musical powers of the saltatorial
Orthoptera are, however, specially characteristic of the male sex. There is
evidence that these powers are of great importance to the creatures, though
in what way is far from clear. Some parts of the structures of the body are
in many of these musical species clearly dominated by the musical organs,
and are apparently specially directed to securing their efficiency. We find
in some Locustidae that the tegmina are nothing but sound-producing
instruments, while the pronotum is prolonged to form a hood that protects
them without encumbering their action. In the males of the Pneumorides,
where the phonetic organ is situated on the abdomen, this part of the body
is inflated and tense, no doubt with the result of increasing the volume
and quality of the sound. In the genus _Methone_ (Fig. 185) we find a
grasshopper whose great hind legs have no saltatorial function, and but
little power of locomotion, but act as parts of a sound-producing
{201}instrument, and as agents for protecting some parts of the body in
repose. Further particulars of these cases must be looked for in our
accounts of the different groups.
The eggs of many Orthoptera are deposited in capsules or cases; these
capsules may contain only one egg, or a great many.
The Order includes many species of Insects, though in Britain it is poorly
represented: we have only about forty species, and this small number
includes some that are naturalised. Only a few of the forty extend their
range to Scotland. A revision of the species found in Britain has recently
been made by Mr. Eland Shaw.[127] In continental Europe, especially in the
south, the species become more numerous; about 500 are known as inhabitants
of geographical Europe. In countries where the face of nature has been less
transformed by the operations of man, and especially in the tropical parts
of the world, Orthoptera are much more abundant.
The lowest number at which the species now existing on the surface of the
earth can be estimated is 10,000. This, however, is probably far under the
mark, for the smaller and more obscure species of Orthoptera have never
been thoroughly collected in any tropical continental region, while new
forms of even the largest size are still frequently discovered in the
tropics.
We shall treat the Order as composed of eight families:—
Series, _Cursoria_: hind legs but little different from the others.
{ 1. Forficulidae—Tegmina short, wings complexly folded; body
{ armed at the extremity with strong forceps.
{ 2. Hemimeridae—Apterous: head exserted, constricted behind.
{ 3. Blattidae—Coxae of the legs large, exserted, protecting
{ the lower part of the body.
{ 4. Mantidae—Front legs very large, raptorial, armed with spines.
{ 5. Phasmidae—Mesothorax large as compared with the prothorax.
Series, _Saltatoria_: hind legs elongate, formed for leaping, their
femora usually thickened.
{ 6. Acridiidae—Antennae short, not setaceous, of not more than
{ 30 joints, tarsi three-jointed.
{ 7. Locustidae—Antennae very long, setaceous, composed of a
{ large number of joints, tarsi four-jointed.
{ 8. Gryllidae—Antennae very long, setaceous, tarsi two- or
{ three-jointed.
The first five of these subdivisions are amongst the most distinct of any
that exist in the Insecta, there being no connecting links between them.
The three groups forming the {202}Saltatoria are much more intimately
allied, and should, taken together, probably have only the same taxonomic
value as any one of the other five groups.
Owing partly to the inherent difficulties of the subject, and partly to the
fragmentary manner in which it has been treated by systematists, it has
been impossible till recently to form any clear idea of the classification
of Orthoptera. During the last twenty years Henri de Saussure and Brunner
von Wattenwyl have greatly elucidated this subject. The latter of these two
distinguished naturalists has recently published[128] a revision of the
system of Orthoptera, which will be of great assistance to those who may
wish to study these Insects. We therefore reproduce from it the characters
of the tribes, placing the portion relating to each family at the end of
our sketch thereof.
FAM. I. FORFICULIDAE—EARWIGS.
(DERMAPTERA OR DERMATOPTERA OF BRAUER AND OTHERS)
_Insects of elongate form, with an imbricate arrangement of the segments
of the body; bearing at the posterior extremity a pair of callipers or
more distorted instruments. The hind wings (when present) folded in a
complex manner, and covered, except at their tips, by a pair of short
wing-covers (tegmina), of a leather-like consistence. Wingless forms are
very numerous. The young is very similar to the adult._
[Illustration: FIG. 102.—_Pygidicrana hugeli._ Java.]
Although earwigs are said to be rare in most parts of the world, yet in
Europe no Insect is better known than _Forficula auricularia_, the common
earwig, it being very abundant even in gardens and cultivated places. In
certain seasons it not unfrequently enters our houses, in which case it too
often falls a {203}victim to prejudices that have very little to justify
them. This Insect is a good type of the winged earwigs. In the parts of the
mouth it exhibits the structures usual in the Orthoptera; there is a large
labrum, a pair of maxillae, each provided with two lobes and a palpus
consisting of two very short basal joints and three longer joints beyond
these; the mandibles are strong, with curvate pointed extremities; in the
lower lip there is a ligula exposed in front of a very large mentum; it
consists of two pieces, not joined together along the middle, but each
bearing on its lateral edge a palpus with two elongate joints and a short
basal one; this lip is completed by the lingua, which reposes on the upper
face of the part, and completely overlaps and protects the chink left by
the want of union along the middle line of the external parts of the lip.
The antennae are elongate, filiform, and are borne very near the front of
the exserted head. There are rather large facetted eyes, but no ocelli. The
three segments of the thorax are distinct, the prothorax being quite free
and capable of movement independent of the parts behind it: the meso- and
meta-nota are covered by the tegmina and wings; these latter project
slightly from underneath the former in the shape of small slips, that are
often of rather lighter colour; the wing-covers are short, not extending
beyond the insertion of the hind legs, and repose flat on the back, meeting
together in a straight line along the middle. These peculiar flat,
abbreviated wing-covers, with small slips (which are portions of the folded
wings) projecting a little from underneath them, are distinctive marks of
the winged Forficulidae.
The legs are inserted far from one another, the coxae being small; each
sternum of the three thoracic segments projects backwards, forming a
peculiar long, free fold, underlapping the front part of the following
segment. The hind body or abdomen is elongate, and is formed of ten
segments; the number readily visible being two less in the female than it
is in the male. The segments are fitted together by a complex imbrication,
which admits of great mobility and distension, while offering a remarkable
power of resistance to external pressure: each segment is inserted far
forward in the interior of that preceding it, and each also consists of
separate upper and lower plates that much overlap where they meet at the
sides (see Fig. 103). The body is always terminated by a pair of horny,
pincer-like {204}processes, which are differently shaped according to the
sex of the individual.
[Illustration: FIG. 103.—Lateral view of _Forficula auricularia_ L. Female
abdomen distended showing spiracles, S, and the small 8th and 9th dorsal
plates (7 and 8 in Fig.).]
The structure of the abdomen in the earwig has given rise to considerable
discussion. In Fig. 103 we reproduce Westwood's diagram of it as seen
fully distended in a female specimen; in this state the minute spiracles
can be detected, though in the normal condition of the body they cannot be
seen, being placed on the delicate membranes that connect the chitinous
plates. Westwood's interpretation of the structure was not, however, quite
correct, as the part which he considered to be the first dorsal plate is
really the second; so that the segments numbered 7, 8, 9 in our figure are
really 8, 9, 10. The common earwig is interesting as exhibiting, in an
imperfect state, the union of the first dorsal plate of the abdomen with
the thorax; a condition which is carried to so great an extent in the
Hymenoptera as to quite obscure the nature of the parts, and which has
consequently given rise to much perplexity and discussion. We represent
this structure as seen in the common earwig in Fig. 104, where _a_
represents the pronotum, _b_ the mesonotum, _c_ the metanotum, _d_ the
first, _f_ the second abdominal segment; _e_ being a delicate membrane of
considerable size that intervenes between the two, and which is more
exposed than are the corresponding membranes connecting the subsequent
rings; a condition similar to that which is found in _Cimbex_, _Cephus_,
and some other Hymenoptera.
[Illustration: FIG. 104.—Dorsal portions of the middle segments of body of
_Forficula auricularia_ (tegmina and wings removed).]
On the under surface of the abdomen of the earwig the full number of 10
plates cannot be superficially distinguished; but it is found by dissection
that in the female the short eighth and ninth dorsal rings are joined on
the ventral aspect by a delicate membrane, while the tenth ventral is of a
less delicate {205}nature, and forms a triangular plate at the base of each
half of the forceps. Between the branches of the forceps there is a
perpendicular plate, the pygidium of Orthopterists, possibly the unpaired
terminal portion of the body seen in some embryos, and called the telson.
The pygidium is a separate sclerite, though it looks as if it were only a
portion of the large tenth dorsal plate bent downwards, and in some
descriptive works is erroneously described as being such.
[Illustration: FIG. 105.—_Chelidura dilatata_, male. Pyrenees.]
[Illustration: FIG. 106.—Tegmina and wings (visible in part or invisible)
of apterous earwigs. 1, _Chelidura_ sp.; 2, _Chelidura dilatata_; 3,
_Anisolabis moesta_; 4. _A. maritima_. _a_, First thoracic segment; _b_,
second; _c_, third; _d_, basal portion of abdomen.]
A very large number of species of Forficulidae have the organs of flight
undeveloped. Fig. 105 represents _Chelidura dilatata_, an apterous form
that is very common in the Eastern Pyrenees. The condition of the meso- and
meta-nota—the parts from which the tegmina and wings are developed, and to
which they are attached when present—is very remarkable in these forms, and
exhibits much variety. In Fig. 106 we represent the conditions of these
parts in a few apterous forms. The tegmina or the segment from which they
are developed (_b_), are seen in the shape of a plate which may extend all
across the middle and be undivided (No. 4); in which case the appearance
indicates entire absence of the tegmina; these are, on the contrary,
evidently present in the form of slips grafted one to each side of the
second thoracic segment in _Anisolabis_ (No. 3); or they may look like
short broad slips extending all across the body, and marking off a piece
frequently called a scutellum, but which is really the mesonotum (some
species of _Chelidura_, as No. 2); or, again, they may be nearly free
tegmina, somewhat similar to those of the winged forms; this is the case
with some species of _Chelidura_, as represented by No. 1. This last figure
is taken from a species from the Sierra Nevada, apparently undescribed,
allied to _C. bolivari_.
In the cases we are considering no analogous structures exist on {206}the
metanotum (the part of the body that in the winged forms bears the wings,
and which is marked _c_ in our diagrams, Fig. 106), so that the tegmina are
to all appearance less rudimentary (or vestigial) than the wings. The
metanotum forms a sort of flap, called by Fischer[129] "involucrum alarum";
he considered the part immediately behind this to be the metanotum; this
piece is, however, no doubt really part of the abdomen (_d_ in our Figure).
This is apparently the view taken by Brunner.[130] The structure of these
parts is important as bearing on the subject of the nature and origin of
Insects' wings, a question to which no satisfactory answer has yet been
given. The appearances we have remarked on are to some extent similar to
the conditions existing in the immature state of the organs of flight in
the common earwig (see Fig. 112, p. 212), but whether the varieties
presented by the wingless forms have parallels in the immature conditions
of the various winged forms is quite uncertain, the life-histories of
earwigs being almost unknown.
[Illustration: FIG. 107.—Wing of _Forficula auricularia_. A, Wing expanded,
explanation in text; B, wing folded and packed.]
The developed wings of earwigs are worthy of attention, both as regards
their actual structure and the manner in which they are folded up in
repose. When expanded they have a shape curiously suggestive of the human
ear. The chief parts of the wing, as shown in Fig. 107, A, are _a_, _b_,
two portions of the horny piece that forms the scale which covers the more
delicate parts of the wing when it is folded, and which, according to
Brunner, represents the radial and ulnar fields of the wings of Acridiidae
and Locustidae (see Fig. 167); _c_ is the small apical field limited below
by the vena dividens; _d_ is the vena plicata which runs along the under
side of the scale as far as the apical field, where it gives off the
axillary nerves; _e_ is a vena spuria, or adventitious vein such as exists
in many other Orthoptera with delicate wings. On the front part of the
scale, _a_, and on a different plane so that it is not shown in our figure,
there is a very delicate small band which is supposed to {207}represent the
marginal field of the wing of other Orthoptera. There are, however, grave
difficulties in the way of accepting this view of the earwig's wing,
amongst which we may mention the position of the vena dividens and its
relation to the so-called radial and ulnar fields of the wing. The wings
are remarkable for their delicacy; moreover, the way in which they fold up
so as to be packed in the manner shown in B, Fig. 107, is very interesting,
there being, in fact, no other Insects that fold up their wings in so
complicated and compact a fashion as the earwigs do. The process is carried
out somewhat as follows: the longer radii come a little nearer together,
the delicate membrane between them falling into folds somewhat like those
of a paper fan; a transverse fold, or turn-over, then occurs at the point
where the radii, or axillary nerves, start from the vena plicata; then a
second transverse fold, but in a reversed direction, occurs affecting the
wing just close to the spots where the shorter radial nervures are dilated;
then by a contraction close to the scale the whole series of complex folds
and double are brought together and compressed.
It is quite a mystery why earwigs should fold their wings in this complex
manner, and it is still more remarkable that the Insects very rarely use
them. Indeed, though _Forficula auricularia_ is scarcely surpassed in
numbers by any British Insect, yet it is rarely seen on the wing; it is
probable that the majority of the individuals of this species may never
make use of their organs of flight or go through the complex process of
unfolding and folding them. It should be remarked that no part of the
delicate membranous expanse of the wing is exposed when the wings are
packed in their position of repose; for the portion that projects from
under the tegmina—and which, it will be remembered, is always present, for
when wings exist in earwigs they are never entirely concealed by the
tegmina—is, it is curious to note, of hard texture, and is frequently
coloured and sculptured in harmony with the tegmen; in fact, one small part
of the wing forms in colour and texture a most striking contrast to the
rest of the organ, but agrees in these respects with the wing-covers. This
condition is seen in Fig. 108, where B shows the sculpture of the tegmina
_t_, and of the projecting tips of the wings _w_. There are numerous other
instances in Orthoptera where one part of a wing or wing-case {208}is
exposed and the other part concealed, and the exposed portion is totally
different in colour and texture from the concealed portion.
The wings of earwigs are attached to the body in a very unusual manner;
each wing is continued inwards on the upper surface of the metanotum, as if
it were a layer of the integument meeting its fellow on the mesial line;
the point of contact forming two angles just behind the metanotum.
Some writers have considered that the tegmina of earwigs are not the
homologues of those of other Orthoptera, but are really tegulae (cf. Fig.
56, p. 103). We are not aware that any direct evidence has been produced in
support of this view.
The pair of forceps with which the body is armed at its extremity forms
another character almost peculiar to the earwigs, but which exists in the
genus _Japyx_ of the Thysanura. These forceps vary much in the different
genera of the family; they sometimes attain a large size and assume very
extraordinary and distorted shapes. They are occasionally used by the
Insects as a means of completing the process of packing up the wings, but
in many species it is not probable that they can be used for this purpose,
because their great size and peculiarly distorted forms render them
unsuitable for assisting in a delicate process of arrangement; they are,
too, always present in the wingless forms of the family. Their importance
to the creature is at present quite obscure; we can only compare them with
the horns of Lamellicorn Coleoptera, which have hitherto proved
inexplicable so far as utility is concerned. No doubt the callipers of the
earwigs give them an imposing appearance, and may be of some little
advantage on this account; they are not known to be used as offensive
instruments for fighting, but they are occasionally brought into play for
purposes of defence, the creatures using them for the infliction of nips,
which, however, are by no means of a formidable character.
[Illustration: FIG. 108.—_Anechura scabriuscula._ Himalaya. A, Outline of
the Insect; B, tegmina, _t_, and tips of wings, _w_, showing their similar
sculpture.]
{209}These forceps are, in the case of the common earwig—and they have not
been studied from this point of view in any other species—remarkable,
because of the great variation in their development in the male, a
character which again reminds us of the horns of Lamellicorn beetles: in
the female they are comparatively invariable, as is also the case in the
few species of Lamellicornia, which possess horned females. A and B in
Figure 109 represent the forceps of different males of the common earwig, C
showing those of the other sex. The subject of the variation of the male
callipers of the earwig has been considered by Messrs. Bateson and
Brindley,[131] who examined 1000 specimens captured on the same day on one
of the Farne islands off the coast of Northumberland; 583 of these were
mature males, and the pincers were found to vary in length from about 2½
mm. to 9 mm. (A and B in Fig. 109 represent two of the more extreme forms
of this set of individuals.) Specimens of medium size were not, as it might
perhaps have been expected they would be, the most common; there were, in
fact, only about 12 individuals having the forceps of the medium length—4¾
to 5¼ mm., while there were no less than 90 individuals having forceps of a
length of about 7 mm., and 120 with a length of from 2¾ to 3¼. Males with a
medium large length of the organ and with a medium small length thereof
were the most abundant, so that a sort of dimorphism was found to exist.
Similar relations were detected in the length of the horns of the male of a
Lamellicorn beetle examined by these gentlemen. In the case of the set of
earwigs we have mentioned, very little variation existed in the length of
the forceps in the female sex.
[Illustration: FIG. 109.—Forceps of the common earwig: A, of large male; B,
of small male; C, of female.]
In many earwigs—including _F. auricularia_—there may be seen on each side
of the dorsal aspect of the true fourth, or of the fourth and neighbouring
segments of the hind body a small elevation, called by systematists a plica
or fold, and on examination the fold will be found to possess a small
orifice on its posterior aspect. These folds are shown in Figs. 105 and
108; {210}they have been made use of for purposes of classification, though
no functional importance was attached to them. Meinert, however,
discovered[132] that there are foetid glands in this situation, and
Vosseler has recently shown[133] that the folds are connected with
scent-glands, from which proceed, in all probability, the peculiar odour
that is sometimes given off by the earwig. The forms destitute of the
folds, e.g. _Labidura_, are considered to have no scent glands. There is a
very peculiar series of smooth marks in the earwigs on the dorsal aspect of
the abdominal segments, and these are present in the glandless forms as
well as in the others.
The internal anatomy has been to some extent investigated by Dufour and
Meinert. Dufour dissected _F. auricularia_ and _Labidura riparia_, and
found[134] that salivary glands exist in the latter Insect (called by him
_Forficula gigantea_), though he was unable to discover them in the common
earwig. According to Meinert,[135] there are, however, salivary glands
affixed to the stipes of the maxillae in _F. auricularia_, while (in
addition?) _L. riparia_ possesses very elongate glands seated in the middle
or posterior part of the breast. The alimentary canal is destitute of
convolutions, but oesophagus, crop, and gizzard all exist, and the
intestine behind the stomach consists of three divisions. The Malpighian
tubes are numerous, 30 or 40, and elongate. The respiratory system is not
highly developed. Earwigs—the European species at least—have, as already
mentioned, very small powers of flight; the tracheal system is
correspondingly small, and is destitute of the vesicular dilatations that
are so remarkable in the migratory Locusts.
[Illustration: FIG. 110.—_Labidura riparia_, male. Europe.]
The three thoracic spiracles[136] are readily observed in living
{211}individuals. There are seven pairs of abdominal spiracles, which,
however, are very minute, and can only be found by distending the body as
shown in Fig. 103. The ventral chain consists of nine ganglia (the
sub-oesophageal centre is not alluded to by Dufour); the three thoracic are
equidistant and rather small; the hindmost of the six abdominal ganglia is
considerably larger than any one of the other five.
The ovaries of _Labidura riparia_ and _Forficula auricularia_ are extremely
different. In _L. riparia_ there are on each side five tubes, each
terminating separately in an obliquely directed lateral part of the
oviduct. In _F. auricularia_ there is but one tube on each side, but it is
covered by three longitudinal series of very short sub-sessile, grape-like
bodies, each of the two tubes being much dilated behind the point where
these bodies cease.
The testes in earwigs are peculiar and simple; they consist, on each side,
of a pair of curvate tubular bodies, connected at their bases and prolonged
outwards in the form of an elongate, slender vas deferens. The structures
in the males of several species have been described at some length by
Meinert,[137] who finds that in some species a double ejaculatory duct
exists.
[Illustration: FIG. 111.—Ovaries of _Labidura riparia_, A; and _Forficula
auricularia_, B. (After Dufour.)]
The young is similar to the adult in form; in the winged forms it is always
easy to distinguish the adult by the full development of the wings, but in
the wingless forms it can only be decided with certainty that a specimen is
not adult by the softer and weaker condition of the integuments. Scarcely
anything appears to be known as to the life-history, except a few
observations that have been made on the common earwig; Camerano found[138]
that this Insect has certainly three ecdyses, and possibly {212}an earlier
one which he failed to notice, and his observation confirms the vague
previous statement of Fischer. The eggs, in the neighbourhood of Turin, are
deposited and hatched in the early spring; in one case they were laid on
the 10th March, and the Insects issuing from them had completed their
growth and were transformed into perfect Insects on the 22nd May. In the
immature state the alar structures of the future imago may be detected. The
tegmina-bearing sclerites, _t_, Fig. 112, look then somewhat like those of
some of the apterous forms (Fig. 106) and, as shown in A and B, Fig. 112,
do not differ greatly in the earlier and later stages. The wings, however,
change much more than the tegmina do; at first (Fig. 112, A) there is but
little difference between the two, though in the interior of the wing-flap
some traces of a radiate arrangement can be seen, as shown at _W_ in A,
Fig. 112; in a subsequent condition the wing-pads are increased in size and
are more divided, the appearance indicating that the wings themselves are
present and packed about a centre, as shown in _W_ of B, Fig. 112.
[Illustration: FIG. 112.—Notal plates from which the tegmina and wings of
_Forficula auricularia_ are developed in young, A, and more advanced, B,
nymph.]
In the young of the common earwig the number of joints[139] in the antennae
increases with age. Camerano, _l.c._, says that before emergence from the
egg there are apparently only 8 joints in the antennae, and Fischer states
that the larvae of _F. auricularia_ have at first only 8 antennal joints;
later on 12 joints are commonly found, and, according to Bateson,[140] this
number occasionally persists even in the adult individual. Meinert
says[141] that the newly hatched _Forficula_ has either 6 or 8 joints, and
he adds that in the later portion of the preparatory stage the number is
12. Considerable discrepancy prevails in books as to the normal number of
joints in the antennae of the adult _F. auricularia_, the statements
varying from 13 to 15. The latter number may be set aside as erroneous,
although it is, curiously {213}enough, the one given in the standard works
of Fischer, Brunner, and Finot. Meinert gives without hesitation 14 as the
number; Bateson, _l.c._, found that 14 joints occurred in 70 or 80 per cent
of adult individuals, that 13 was not uncommon, that 12 or 11 occasionally
occurred, and that the number may differ in the two antennae of the same
individual. These variations, which seem at first sight very remarkable,
may with probability be considered as due to the fact that in the young
state the number of joints increases with age, and that the organs are so
fragile that one or more of the joints is very frequently then lost, the
loss being more or less completely repaired during the subsequent
development. Thus a disturbing agency exists, so that the normal number of
14 joints is often departed from, though it appears to be really natural
for this species. Bateson has also pointed out that when the normal number
of articulations is not present, the relative proportions of joints 3 and 4
are much disturbed. It is, however, probable that the increase in number of
the joints takes place by division of the third or third and fourth joints
following previous growth thereof, as in Termitidae; so that the
variations, as was suggested by Bateson, may be due to mutilation of the
antennae, and consequent incompletion of the normal form of the parts from
which the renovation takes place; growth preceding segmentation—in some
cases the growth may be like that of the adult, while the segmentation
remains more incomplete. In the young the forceps of the two sexes differ
but slightly; the form of the abdominal rings is, on the contrary,
according to Fischer, already different in the two sexes in the early
stage.
The common earwig has a very bad reputation with gardeners, who consider it
to be an injurious Insect, but it is probable that the little creature is
sometimes made the scapegoat for damage done by other animals; it appears
to be fond of sweets, for it often makes its way to the interior of fruits,
and it no doubt nibbles the petals, or other delicate parts of flowers and
vegetables. Camerano, however, states, _l.c._, that the specimens he kept
in confinement preferred dead Insects rather than the fruits he offered
them. Rühl considers the earwig to be fond of a carnivorous diet, eating
larvae, small snails, etc., and only attacking flowers when these
fail.[142] It has a great propensity for concealing {214}itself in places
where there is only a small crevice for entry, and it is possible that its
presence in fruits is due to this, rather than to any special fondness for
the sweets. This habit of concealing itself in chinks and crannies in
obscure places makes it an easy matter to trap the Insect by placing pieces
of hollow stalks in the situations it affects; inverted flower-pots with a
little hay, straw, or paper at the top are also effectual traps. We have
remarked that it is very rarely seen on the wing, and though it has been
supposed to fly more freely at night there is very little evidence of the
fact. Another British species, _Labia minor_, a smaller Insect, is,
however, very commonly seen flying.
Earwigs have the reputation of being fond of their young, and Camerano
describes the female of the common earwig as carefully collecting its eggs
when scattered, lifting them with its mandibles and placing them in a heap
over which it afterwards brooded. De Geer[143] more than a century ago
observed a fondness of the mother for the young. After the eggs were
hatched, Camerano's individual, however, evinced no interest in the young.
A larger species, _Labidura riparia_ (Fig. 110) is said to move its eggs
from place to place, so as to keep them in situations favourable for their
development.
The name "earwig" is said to be due to an idea that these creatures are
fond of penetrating into the ears of persons when asleep. Hence these
Insects were formerly much dreaded, owing to a fear that they might
penetrate even to the brain. There does not appear to be on record any
occurrence that could justify such a dread, or the belief that they enter
the ears. If they do not do so, it is certainly a curious fact that a
superstition of the kind we have mentioned occurs in almost every country
where the common earwig is abundant; for it has, in most parts of Europe, a
popular name indicating the prevalence of some such idea. It is known as
_Ohren-wurm_ in German, as _perce-oreille_ in French, and so on. The
expanded wing of the earwig is in shape so very like the human ear, that
one is tempted to suppose this resemblance may in former ages have given
rise to the notion that the earwig has some connexion with the human ear;
but this explanation is rendered very improbable by the fact that the
earwig is scarcely ever seen with its wings expanded, and that it is a most
difficult matter to unfold them {215}artificially, so that it is very
unlikely that the shape of the wings should have been observed by untutored
peoples.
The group Forficulidae seems to be most rich in species in warm and
tropical regions; several unwinged species are met with in the mountainous
districts of Europe; indeed, in some spots their individuals are extremely
numerous under stones. In Britain we have a list of six species, but only
two of these are to be met with; the others have probably been introduced
by the agency of man, and it is doubtful whether more than one of these
immigrants is actually naturalised here. One of these doubtfully native
species is the fine _Labidura riparia_ (Fig. 110), which was formerly found
near Bournemouth. Altogether about 400 species of earwigs are known at the
present time, and as they are usually much neglected by Insect collectors,
it is certain that this number will be very largely increased, so that it
would be a moderate estimate to put the number of existing species at about
2000 or 3000. None of them attain a very large size, _Psalis americana_
being one of the largest and most robust of the family; a few display
brilliant colours, and some exhibit a colour ornamentation of the surface;
there are two or three species known that display a general resemblance to
Insects of other Orders. The remarkable earwig represented in Fig. 102 (and
which appears to be a nondescript form—either species or variety—closely
allied to _P. marmoricauda_) was found by Baron von Hügel on the mountains
of Java; the femora in this Insect have a broad face which is turned
upwards instead of outwards, the legs taking a peculiar position; and it is
curious that this exposed surface is ornamented with a pattern. The feature
that most attracts attention on inspecting a collection of earwigs is,
however, the forceps, and this is the most marked collective character of
the group. These curious organs exhibit a very great variety; in some cases
they are as long as the whole of the rest of the body, in others they are
provided with tynes; sometimes they are quite asymmetrical, as in
_Anisolabis tasmanica_ (Fig. 113); in _Opisthocosmia cervipyga_, and many
others they are curiously distorted in a variety of ways. The
classification of the earwigs is still in a rudimentary state; the number
of joints in the antennae, the form of the feet, and (in the terrestrial
forms) the shape of the rudimentary wing-cases and wings being the
characters that have been made most use of by {216}systematists; no
arrangement into sub-families or groups of greater importance than genera
is adopted.
The only particulars we have as to the embryological development of the
earwig are due to Heymons.[144] The forceps spring from the eleventh
abdominal segment, and represent the cerci of other Orthoptera. An
egg-tooth is found to be present on the head for piercing the egg-shell.
The embryo reverses its curved position during the development, as other
Orthoptera have been observed to do, but in a somewhat different manner,
analogous to that of the Myriapods.
Several fossil Forficulidae are known; specimens belonging to a peculiar
genus have been described from the Lower Lias of Aargau and from the
Jurassic strata in Eastern Siberia, but the examples apparently are not in
a very satisfactory state of preservation. In the Tertiary formations
earwigs have been found more frequently. Scudder has described eleven
species of one peculiar genus from the Lower Miocene beds at Florissant in
Colorado; some of these specimens have been found with the wings expanded,
and no doubt that they were fully developed Forficulidae can exist. The
fossil species of earwigs as yet known do not display so remarkable a
development of the forceps as existing forms do.
[Illustration: FIG. 113.—_Anisolabis tasmanica_ ♂.]
Brauer and others treat the Forficulidae as a separate Order of
Insects—Dermaptera—but the only structural characters that can be pointed
out as special to the group are the peculiar form of the tegmina and hind
wings—which latter, as we have said on p. 206, are considered by some to be
formed on essentially the same plan as those of other Orthoptera—the
imbrication of the segments, and the forceps terminating the body. The
development, so far as it is known, is that of the normal Orthoptera. Thus
the Forficulidae are a very distinct division of Orthoptera, the characters
that separate them being comparatively slight, though there are no
intermediate forms. Some of those who treat the Dermaptera as a sub-Order
equivalent to the rest of the divisions of the Order, call the latter
combination Euorthoptera.
{217}FAM. II. HEMIMERIDAE.
_Apterous, blind Insects with exserted head, having a constricted neck,
mouth placed quite inferiorly; the thoracic sterna large, imbricate. Hind
body elongate, the segments imbricate, the dorsal plates being large and
overlapping the ventral; the number of visible segments being different
according to sex: a pair of long unsegmented cerci at the extremity.
Coxae small, widely separated. Development intra-uterine._
[Illustration: Fig. 114.—_Hemimerus hanseni_, female. Africa. (After
Hansen.)]
[Illustration: FIG. 115.—Under side of head and front of prothorax of
_Hemimerus_. _a_, base of antenna; _b_, articulation of antenna; _c_,
labrum; _d_, mandible; _e_, condyle of mandible; _f_, articular membrane of
mandible; _g_, stipes of maxilla; _h_, exterior lobe; _i_, palpus of
maxilla; _k_, submentum; _l_, mentum; _m_, terminal lobe of labium; _n_,
labial palp; _o_, plate between submentum and sternum; _p_, prosternum;
_q_, cervical sclerites. (After Hansen.)]
In describing the labium of Mandibulata, p. 97, we alluded to the genus
_Hemimerus_ as reputed to possess a most peculiar mouth. When our remarks
were made little was known about this Insect; but a very valuable
paper[145] by Dr. H. J. Hansen on it has since appeared, correcting some
errors and supplying us with information on numerous points. M. de Saussure
described the Insect as possessing two lower lips, each bearing articulated
palpi, and he therefore proposed to treat _Hemimerus_ as the representative
of a distinct Order of Insects, to be called Diploglossata. It now appears
that the talented Swiss entomologist was in this case deceived by a bad
preparation, and that the mouth shows but little departure from the
ordinary mandibulate type. There is a large inflexed labrum; {218}the
mandibles are concealed by the maxillae, but are large, compressed, and on
their inner edge toothed. The maxillae are well developed, are surmounted
by two lobes and bear five-jointed palpi. The ligula appears to be broad
and short, and formed of two parts longitudinally divided; the short palpi
consist of three segments. The mentum is very large. The lingua is present
in the form of a free pubescent lobe with a smaller lobe on each side. The
structure of the pleura is not fully understood; that of the abdomen seems
to be very like the earwigs, with a similar difference in the sexes. The
cerci are something like those of Gryllidae, being long, flexible, and
unsegmented. The legs have rather small coxae, and three-jointed tarsi, two
of which are densely studded with fine hairs beneath, as in Coleoptera. It
is difficult to detect the stigmata, but Dr. Hansen believes there are ten
pairs.
[Illustration: FIG. 116.—Foetus of _Hemimerus_. (After Hansen.) _a_,
Antenna; _b_, organ from the neck; _c_, cerci; _d_, membrane (? cast
skins).]
[Illustration: FIG. 117.—_Hemimerus talpoides_. Africa. (After de
Saussure.) A, Upper; B, under surface.]
The species described by Dr. Hansen as _H. talpoides_ is probably distinct
from that of Walker, though both come from equatorial West Africa. Dr.
Hansen's species, which may be called _H. hanseni_, has been found living
on the body of a large rat, _Cricetomys gambianus_; the Insect occurred on
a few specimens only of the mammal, but when found was present in
considerable numbers; it runs with rapidity among the hairs and apparently
also springs. The nature of its food is by no means clear. Not the least
remarkable fact in connexion with this peculiar Insect is its gestation.
The young are borne inside the mother, {219}apparently about six at a time,
the larger one being of course the nearest to the orifice. Dr. Hansen
thinks the young specimens are connected with the walls of the maternal
passages by means of a process from the neck of each. But the details of
this and other points are insufficiently ascertained; it is, indeed,
difficult to understand how, with a process of the kind of which a fragment
is shown in Fig. 116, _b_, the Insect could fix itself after a detachment
for change of position. The young is said to be very like the adult, but
with a simpler structure of the antennae and abdomen. On the whole, it
appears probable that _Hemimerus_ is, as stated by Dr. Hansen, a special
family of Orthoptera allied to Forficulidae; further information both as to
structure and development are, however, required, as the material at the
disposition of the Swedish entomologist was very small.
{220}CHAPTER IX
ORTHOPTERA CONTINUED—BLATTIDAE, COCKROACHES
FAM. III. BLATTIDAE—COCKROACHES.
_Orthoptera with the head deflexed, in repose concealed from above, being
flexed on to the under-surface with the anterior part directed backwards.
All the coxae large, free, entirely covering the sternal surfaces of the
three thoracic segments, as well as the base of the abdomen. The sternal
sclerites of the thoracic segments little developed, being weak and
consisting of pieces that do not form a continuous exo-skeleton; tegmina
and wings extremely variable, sometimes entirely absent. The wings
possess a definite anal region capable of fan-like folding; rarely the
wing is also transversely folded. The three pairs of legs differ but
little from one another._
[Illustration: FIG. 118.—_Heterogamia aegyptiaca_. A, male; B, female.
(After Brunner.)]
The Blattidae, or cockroaches, are an extensive family of Insects, very
much neglected by collectors, and known to the ordinary observer chiefly
from the fact that a few species have {221}become naturalised in various
parts of the world in the houses of man. One such species is abundant in
Britain, and is the "black beetle" of popular language; the use of the word
beetle in connexion with cockroaches is, however, entomologically
incorrect. One or two members of the family are also well known, owing to
their being used as the "corpora vilia" for students commencing anatomical
investigation of the Arthropoda; for this purpose they are recommended by
their comparatively large size and the ease with which an abundant supply
of specimens may always be procured, but it must be admitted that in some
respects they give but a poor idea of Insect-structure, and that to some
persons they are very repulsive.
The inflexed position of the head is one of the most characteristic
features of the Blattidae; in activity it is partially released from this
posture, but the mouth does not appear to be capable of the full extension
forwards that is found in other Insects that inflex the head in repose. The
labium is deeply divided, the lingua forms a large lobe reposing on the
cleft. The maxillary palpi have two basal short joints, and three longer
joints beyond these; the labial palps consist of three joints of moderate
length. The under-surface of the head is formed in large part by the
submentum, which extends back to the occipital foramen.
[Illustration: FIG. 119.—Under-surface of _Periplaneta australasiae_. _c_,
Coxae.]
The front of the head is the aspect that in repose looks directly
downwards; the larger part of it is formed by the clypeus, which is
separated from the epicranium by a very fine suture angulate in the middle;
there is a large many-facetted eye on each side; near to the eye a circular
space serves for the insertion of the antenna; close to this and to the eye
there is a peculiar small area of paler colour, frequently membranous,
called the fenestra, and which in the males of _Corydia_ and
{222}_Heterogamia_ is replaced by an ocellus. The antennae are very
elongate and consist of a large number of minute rings or joints,
frequently about 100. The head is not inserted directly in the thorax, as
is the case in so many Insects; but the front of the thorax has a very
large opening, thus the neck between it and the head is of more than usual
importance; it includes six cervical sclerites.
The pronotum is more or less like a shield in form, and frequently entirely
conceals the head, and thus looks like the most anterior part of the body;
usually it has no marked angles, but in some of the apterous forms the hind
angles are sharp and project backwards. In contrast to the pronotum the
prosternum is small and feeble, and consists of a slender lateral strip on
each side, the two converging behind to unite with a median piece, the
prosternum proper. None of these pieces of the ventral aspect of the
prothorax are ordinarily visible, the side-pieces being covered by the
inflexed head, and the median piece by the great coxae. In some of the
winged Blattidae (_Blabera_, e.g.) there is at the base of each anterior
coxa a small space covered by a more delicate membrane, that suggests the
possibility of the existence of a sensory organ there (Fig. 120, _i_).[146]
At the base of—above and behind—the front coxa the prothoracic spiracle is
situate.
[Illustration: FIG. 120.—Base of front leg and portion of prothorax of
_Blabera gigantea_. _a_, Under-side of pronotum; _b_, fold of pronotum?;
_c_, epimeron?; _d_, episternum?; _e_, trochantin; _f_, coxa; _g_,
trochanter; _h_, base of femur; _i_, presumed sense organ.]
The meso- and meta-thoracic segments differ but slightly from one another;
the notal or dorsal pieces are moderately large, while the sternal or
ventral are remarkably rudimentary, and are frequently divided on the
middle line. Connected with the posterior part of each sternum there is a
piece, bent upwards, called by some anatomists the furca; when the sterna
are divided the furca may extend forwards between them; in other {223}cases
it is so obscure externally as to leave its existence in some doubt.
The sterna in Blattidae are remarkable for their rudimentary structure.
This is probably correlated with the great development of the coxae, which
serve as shields to the lower part of the body. The pieces of the sterna
are not only small, but are also of feeble consistence—semi-membranous, in
fact—and appear like thicker portions of the more extensive and delicate
membrane in which they are situate; they sometimes differ considerably in
the sexes of the same species. The coxae have very large bases, and between
them and the sterna are some pieces that are grooved and plicate, so that
it is not easy to decide as to their distinctions and homology (Fig. 120).
The second breathing orifice is a slit placed in a horny area in the
membrane between the middle and hind coxae.
The legs are remarkable for the large and numerous spines borne by the
tibiae, and frequently also by the femora: the trochanters are distinct and
of moderate size; the tarsi are five-jointed, frequently the basal four
joints are furnished with a pad beneath; the fifth joint is elongate, bears
two claws, and frequently between these a projecting lobe or arolium; this
process scarcely exists in the young of _Stilopyga orientalis_, the common
cockroach, though it is well developed in the adult. The hind body or
abdomen is always large, and its division into rings is very visible, but
the exact number of these that can be seen varies according to age, sex,
species, and to whether the dorsal or ventral surface be examined. The
differences are chiefly due to the retraction and inflexion of the apical
segments; the details of the form of these parts differ in nearly every
species. It is, however, considered that ten dorsal and ventral plates
exist, though the latter are not so easily demonstrated as the former. The
basal segment is often much diminished, the first dorsal plate being
closely connected with the metanotum, while the first ventral may be still
more rudimentary; much variety exists on this point. In the female two of
the ventral terminal plates are frequently inflexed, so as to be quite
invisible without dissection. From the sides of the tenth segment spring
the cerci, flat or compressed processes very various in size, length, and
form, usually more or less distinctly jointed. Systematists call the
seventh ventral plate of the {224}female the "lamina subgenitalis," or the
"lamina subgenitalis spuria," the concealed eighth plate being in this
latter case considered the true subgenital plate. In the male this term is
applied to the ventral plate of the ninth segment, the corresponding dorsal
plate being called the "lamina supra-analis." These terms are much used in
the systematic definitions of the genera and larger groups.
The males, in addition to the cerci alluded to as common to both sexes, are
provided on the hind margin of the lamina subgenitalis with a pair of
slender styles. These are wanting in the females, but in the common
cockroach the young individuals of that sex are provided, like the male,
with these peculiar organs. M. Peytoureau has described[147] the mode of
their disappearance, viz. by a series of changes at the ecdyses.
Cholodkovsky, who has examined the styles, considers them to be
embryologically the homologues of true legs.[148] These styles are said not
to be present in any shape in some species—_Ectobia_, _Panesthia_, etc.;
this probably refers only to the adults. In some cases a curious condition
occurs, inasmuch as one of the two styles is absent, and is replaced by a
notch on the right side, thus causing an asymmetry—_Phyllodromia_,
_Temnopteryx_, etc.
It has been found in several species that there are eight pairs of
abdominal spiracles, making, with the two thoracic, ten pairs in all. The
first of the abdominal spiracles is larger than the others, and in the
winged species may be easily detected by raising the tegmina and wings, it
being more dorsal in position than those following, which are in some
species exposed on the ventral surface owing to the cutting away of the
hind angles of the ventral plates; but the terminal spiracles are in all
cases difficult to detect, and it is possible that the number may not be
the same in all the species of the family. The cerci exhibit a great deal
of variety. In the species with elongate tegmina and wings the cerci are
elongate, and are like antennae in structure; in many of the purely
apterous forms the cerci appear to be entirely absent (cf. Fig. 130,
_Gromphadorhina_), but on examination may be found to exist in the form of
a small plate, or papilla scarcely protuberant. In the males of
_Heterogamia_ they are, on the {225}contrary, very like little antennae; in
the unwinged females of this genus they are concealed in a chink existing
on the under-surface of the apex of the body.
The alar organs of Blattidae are of considerable interest from several
points of view. They exist in various conditions as regards size and
development, and in some forms are very large; each tegmen in some species
of the genus _Blabera_ (Fig. 132) may attain a length of nearly three
inches; in other cases wings and tegmina are entirely absent, and various
intermediate conditions are found. In Fig. 121 we give a diagram of the
tegmen or front wing, A, and the hind wing, B, to explain the principal
nervures and areas. The former are four in number, and, adopting Brunner's
nomenclature[149] for them, are named proceeding from before backwards
mediastinal, _a_; radial, _b_; infra-median (or ulnar), _c_; and dividens,
_d_. An adventitious vein, vena spuria, existing in the hind wings of
certain genera is marked _sp_ in B.
[Illustration: FIG. 121.—Diagram of tegmen, A, and wing, B, in Blattidae.
Nervures: _a_, mediastinal; _b_, radial; _c_, ulnar or infra-median; _d_,
dividens; _sp_, spuria. Areas: 1, mediastinal or marginal; 2, scapular or
radial; 3, median; 4, anal or axillary.]
The vena dividens is of great importance, as it marks off the anal or
axillary field, which in both tegmen and wing has a different system of
minor veins from what obtains in the rest of the organ; the veins being in
the anterior region abundantly branching and dichotomous (Fig. 132), while
in the anal field there is but little furcation, though the nervures
converge much at the base. The mediastinal gives off minor veins towards
the front only, the radial gives off veinlets at first towards the front,
but nearer the tip of the wings sends off minor veins both backwards and
forwards. The infra-median or ulnar vein is very variable; it is frequently
{226}abbreviated, and on the whole is of subordinate importance to the
other three. These latter thus form four chief areas or fields, viz.—1,
mediastinal or marginal; 2, scapular or radial; 3, median; and 4, anal.
These nervures and divisions may be traced in a large number of existing
and fossil Blattidae, but there are forms existing at present which it is
difficult to reduce to the same plan. In _Euthyrhapha_, found in the
Pacific Islands, the hind wings are long and project beyond the tegmina,
and have a very peculiar arrangement of the nervures; the species of
_Holocampsa_ also possess abnormal alar organs, while the structure of
these parts in _Diaphana_ (Fig. 122) is so peculiar that Brunner wisely
refrains from attempting to homologise their nervures with those of the
more normal Blattidae. The alar organs are frequently extremely different
in the two sexes of the same species of Blattidae, and the hind wing may
differ much from the tegmen as regards degree of departure from the normal.
So that it is not a matter for surprise that the nervures in different
genera cannot be satisfactorily homologised.
[Illustration: FIG. 122.—_Diaphana fieberi._ Brazil. A, The Insect, natural
size; B, tegmen, and C, wing, magnified. (After Brunner.)]
But the most peculiar wings in the family are the folded structures found
in some forms of the groups Ectobiides and Oxyhaloides [Anaplectinae and
Plectopterinae of de Saussure]. These have been studied by de
Saussure,[150] and in Fig. 123 we reproduce some of his sketches, from
which it will be seen that in B and C the wing is divided by an unusual
cross-joint into two parts, the apical portion being also longitudinally
divided into two pieces _a_ and _b_. Such a form of wing as is here shown
has no exact parallel in any of the other groups of Insects, though the
earwigs and some of the Coleoptera make an approach to it. This structure
permits a very perfect folding of the wing in repose. The peculiarities
exhibited have been explained by de Saussure somewhat as follows. In the
ordinary condition of Orthoptera the axillary or anal field (P) when the
wings are {227}closed collapses like a fan, and also doubles under the
anterior part (H) of the wing along the line _a a_, in Fig. 123, A, the
result being similar to that shown by our Fig. 124. It will be noticed in
Fig. 123, A, that a small triangular area (_t_) exists at the tip of the
wing just where the fold takes place, so that when the wing is shut this
little piece is liberated, as shown in _t_, Fig. 124. In many Blattidae,
e.g. _Blabera_ (Fig. 132), no trace of this little intercalated piece can
be found, but in others it exists in various degrees of development
intermediate between what is shown in _Thorax porcellana_ (Fig. 123, A) and
in _Anaplecta azteca_ (123, B), so that _a_, _b_ of the latter may be
looked on as a greater development of the condition shown in A at _t_. It
will be noticed that the superadded part of the wing of 123, B, possesses
no venation, being traversed only by the line along which it folds; but in
the wing of _Diploptera silpha_, 123, C, the corresponding part is
complexly venated. This venation, as Brunner says,[151] is not an extension
of the ordinary venation of the wing, but is _sui generis_. It is curious
that though all the degrees of development between A and B exist in various
forms of the tribes Ectobiides and Oxyhaloides, yet there is nothing to
connect the veined apex of Diploptera with the unveined one of _Anaplecta_.
[Illustration: FIG. 123.—Hind wings of Blattidae. A, _Thorax porcellana_;
B, _Anaplecta azteca_; C, _Diploptera silpha_. (After de Saussure.)]
[Illustration: FIG. 124.—Hind wing of _Blatta_ folded. _t_, Free triangular
area. (After de Saussure.)]
The internal anatomy of Blattids has been investigated in only one or two
species. There are no great peculiarities, but some features of minor
interest exist. The alimentary canal (Fig. 125) is remarkable {228}on
account of the capacious crop, and the small gut-like, chylific ventricle;
eight elongate pouches are situate on this latter part at its junction with
the gizzard.
The Malpighian tubules are very numerous and delicate; there are extensive
salivary glands and reservoirs; and on the anterior part of the true
stomach there are eight caecal diverticula. The great chain of the nervous
system consists in all of eleven ganglia—two cephalic, three thoracic, and
six abdominal.
The ovaries in _Stilopyga orientalis_ consist each of eight egg-tubes,
placed at the periphery of a common receptacle or oviduct, the pair of
receptacles themselves opening into a common chamber—the uterus—which is
surrounded by a much branching serific or colleterial gland. In this
chamber the egg-case is formed from the secretion of the gland just
mentioned. According to Miall and Denny,[152] there is a spermatheca which
opens not into the uterus but into the cloacal chamber behind it. Lowne
doubts this diverticulum being a true spermatheca. The manner in which the
eggs are fertilised and their capsule modelled is uncertain.[153]
[Illustration: FIG. 125.—Alimentary canal of _Stilopyga orientalis_. (After
Dufour.) _a_, Head; _b_, salivary glands; _c_, salivary reservoir; _d_,
crop; _e_, diverticula placed below proventriculus; _f_, stomach; _g_,
small intestine; _h_, rectum; _i_, Malpighian tubes; _k_, extremity of hind
body.]
The internal reproductive organs of the male are very complex in _Stilopyga
orientalis_; each testis consists of a number (30 to 40) of vesicles placed
on a tube which is prolonged to form the vas deferens. There is a very
peculiar large complex gland consisting of longer and shorter utricles,
opening into the vesiculae seminales, and forming a "mushroom-shaped
gland."[154] {229}This gland is much larger than the testes proper, which,
it is said, lose early their functional activity in the species in
question, and shrivel. There is another important accessory gland, the
conglobate gland of Miall and Denny, opening on a portion of the external
copulatory armour.
Although some species of Blattidae are domesticated in our houses, and
their bodies have been dissected by a generation of anatomists, very little
is known as to their life histories. The common "black beetle" of the
kitchen is said by Cornelius to be several years in attaining the adult
state. Observations made at Cambridge by the writer, as well as others now
being carried on there by Mr. H. H. Brindley, quite confirm this view, the
extent of growth accomplished in several months being surprisingly little,
and the amount of food consumed very small. It is therefore not improbable
that the life of an individual of this species may extend to five years.
_Phyllodromia germanica_, a species that is abundant in the dwellings of
the peoples of north-eastern Europe, attains its full development in the
course of a few months.
We have already alluded to the fact that in the Blattidae the eggs are laid
in a capsule formed in the interior of the mother-Insect. This capsule is a
horny case varying much in size and somewhat less in form in the different
species; it is borne about for some time by the mother, who may not
infrequently be seen running about with it protruding from the hinder part
of the body. Sooner or later the capsule is deposited in a suitable
situation, and the young cockroaches emerge; it is said that they are
sometimes liberated by the aid of the mother. Mr. Brindley has found it
very difficult to procure the hatching of the young from their capsules.
[Illustration: FIG. 126.—Egg-capsules of European Blattidae. A, _Ectobia
lapponica_; B, _Phyllodromia germanica_; C, _Heterogamia aegyptiaca_.
(After Brunner.)]
It is known that some Blattidae are viviparous. In the case of one such
species, _Panchlora viridis_, it appears probable that the egg-capsule is
either wanting, or is present in only a very imperfect form.[155]
On emerging the young _Blatta_ is in general form very similar to the
parent, though usually much paler in colour. After casting {230}the skin
an uncertain number of times—not less than five, probably as many as
seven—it reaches the adult condition, the changes of outer form that it
undergoes being of a gradual nature, except that at the last ecdysis the
wings—in the case of the winged species—make their appearance, and the
terminal segments of the body undergo a greater change of form. What
mutations of shape may be undergone by the thoracic segments previous to
the final production of the wings has not apparently been accurately
recorded, Fischer's opinion being evidently based on very slight
observation. The little that has been recorded as to the post-embryonic
development since the observations of Hummel[156] and Cornelius[157] will
be found in the works of Brunner.[158] According to this latter authority,
in the wingless species the terminal segments of the body have the same
form in the early stages as they have in the adult state, so that this
latter condition can only be recognised by the greater hardness of the
integument. When tegmina or wings are present in a well-developed form in a
Blattid, it is certain that the Insect is adult; and when there can be seen
at the side of the mesonotum or metanotum a piece, however small, separated
by a distinct suture, it may be correctly assumed that the individual is an
adult of a species having only rudimentary alar organs. The adult female of
the common _Stilopyga orientalis_ shows this phenomenon.
The cockroaches are remarkable for the excessive rapidity with which they
run, or rather scurry, their gait being very peculiar. The common domestic
forms, when alarmed, disappear with great agility, seeking obscure corners
in which to hide themselves, it being part of their instinct to flee from
light. Hence they are called lucifugous, and are most of them entirely
nocturnal in their activities. In the South of Europe and other warmer
regions many Blattidae may, however, be found on bushes and foliage in the
daytime; these, when alarmed, fall down and run off with such speed and in
so tortuous a manner, that it is a very difficult matter to seize them. It
is recorded that the males of the genus _Heterogamia_ are attracted by
lights, though their apterous females keep themselves concealed underground
in sandy places.
{231}We may take this opportunity of alluding to the attraction that light
exerts on Insects. Many species that conceal themselves during the daytime
and shun light as if it were disagreeable, are at night-time so fascinated
by it that it is the cause of their destruction. The quantity of Insects
killed in this way by electric and other bright lights is now enormous; in
many species the individuals immolate themselves by myriads. It would
appear that only nocturnal and winged species are so attracted. So far as
we know, light has no fascination for Insects except when they are on the
wing. The phenomenon is not understood at present.
The food of Blattidae is believed to be of a very mixed character, though
Brunner considers that dead animal matter is the natural nutriment of the
members of this family. It is well known that the common cockroach eats a
variety of peculiar substances; its individuals undoubtedly have the
somewhat too economical habit of eating their own cast skins and empty
egg-capsules, but in this they only act like many other much admired
Insects. _S. orientalis_ is gregarious, and the individuals are very
amicable with one another; small specimens sit on, or run over the big
individuals, and even nestle under them without their displaying the least
resentment. The common cockroach is a rather amusing pet, as the creatures
occasionally assume most comical attitudes, especially when cleaning their
limbs; this they do somewhat after the fashion of cats, extending the head
as far as they can in the desired direction, and then passing a leg or
antenna through the mouth; or they comb other parts of the body with the
spines on the legs, sometimes twisting and distorting themselves
considerably in order to reach some not very accessible part of the body.
There is very little information extant as to the domestic Blattidae found
in parts of the world outside Europe, but it seems that there are numerous
species that prefer the dwellings of man, even though they only tolerate
the owners. Belt says[159] "the cockroaches that infest the houses of the
tropics are very wary, as they have numerous enemies—birds, rats,
scorpions, and spiders; their long trembling antennae are ever stretched
out, vibrating as if feeling the very texture of the air around them; and
their long legs quickly take them out of danger. Sometimes {232}I tried to
chase one of them up to a corner where on a wall a large cockroach-eating
spider stood motionless looking out for his prey; the cockroach would rush
away from me in the greatest fear, but as soon as it came within a foot of
its mortal foe nothing would force it onwards, but back it would double,
facing all the danger from me rather than advance nearer to its natural
enemy." To this we may add that cockroaches are the natural prey of the
fossorial Hymenoptera of the group Ampulicides, and that these wasps
sometimes enter houses in search of the Insects.
[Illustration: FIG. 127.—_Nocticola simoni_. A, male; A_{1}, tegmen and
rudiment of wing; A_{2}, front of head; B, female. The cerci are broken, in
B the right one is restored in outline. (After Bolivar.)]
We have already noticed the considerable difference that exists in many
cases between the sexes of the same species. This is sometimes carried to
such an extent that nothing but direct observation could make us believe
that the males and females are of one kin. Fig. 118 (p. 220) shows a case
of this kind. Though the young as a rule are excessively similar to the
adults, yet this is by no means invariably the case. In some of the more
amply winged forms, such as _Blabera_, the young is about as different from
the adult as the female of _Heterogamia_ {233}is from its male. In
Blattidae it is always the case—so far as is yet known—that when there is a
difference as regards the alar organs between the two sexes, it is the male
that has these structures most developed, and this even when they can be of
little or no use for purposes of flight.
Among the most interesting forms of the family are the two species of the
genus _Nocticola_, recently discovered by M. Simon in caves in the
Philippine Islands.[160] They are amongst the smallest of the Orthoptera,
the male being scarcely ⅛ of an inch long. In the larval state of _N.
simoni_ the ocular organs exist as three ocelli, or facets, on each side of
the head, and in the perfect state the number is increased somewhat, as
shown in Fig. 127, A_{2}. In the second species of the genus the female is
quite blind (the male being still undiscovered). The fenestræ in
_Nocticola_ are absent; the tegmina and wings are totally wanting in the
female (Fig. 127, B), but are present in a very peculiar condition in the
male (Fig. 127, A_{1}). There are other anomalies in the structure of these
cavernicolous Insects, the cerci being apparently of peculiar structure,
and the spines of the legs more hair-like than usual. The condition of the
eyes is remarkable; the peculiarity in their development is worthy of
study.
[Illustration: FIG. 128.—_Corydia petiveriana_, with tegmina extended, A;
closed, B.]
To those who are acquainted with Blattidae only through our domestic "black
beetle" it may seem absurd to talk of elegance in connexion with
cockroaches. Yet there are numerous forms in which grace and beauty are
attained, and some exhibit peculiarities of ornamentation that are worthy
of attention. _Corydia petiveriana_ (Fig. 128) is a common cockroach in
East India. It has an effective system of coloration, the under wings and
the sides of the body being vividly coloured with orange yellow; when the
tegmina are closed the upper surface of the body is of a velvet-black
colour, with cream-coloured marks; these spots are different {234}on the
two tegmina, as shown in Fig. 128, A, but are so arranged that when the
tegmina are closed (Fig. 128, B) a symmetrical pattern is produced by the
combination of the marks of the two differently spotted tegmina. It is very
curious to notice the great difference in the colour of the part of the
right tegmen that is overlapped by the edge of the left one; this part of
the tegmen being coloured orange yellow in harmony with the wings. The
result of the remarkable differentiation of the colours of the two tegmina
may be summarised by saying that on the right one the colour of a part is
abruptly contrasted with that of the rest of the organ, so as to share the
system of coloration of the under-wings and body, while the corresponding
part of the other tegmen is very different, and completes the system of
symmetrical ornamentation of the upper surface.
Many other members of the Blattidae have an elegant appearance, and depart
more or less from their fellows in structural characters, with the result
of adding to their graceful appearance; in such cases, so far as at present
known, these Insects are brightly coloured. Thus _Hypnorna amoena_ (Fig.
129) has the antennae banded in white, black, and red, while the
overlapping part of the tegmina is arranged so as to bring the line of
junction between them nearly straight along the middle line of the body,
and thus produce a more symmetrical appearance than we find in other
cockroaches. The head in this Insect is not so concealed as usual, and this
undoubtedly adds somewhat to the effective appearance of this cockroach.
This visibility of the front of the head in _Hypnorna_ is not, as would be
supposed, owing to its being less inflexed than usual. On the contrary, the
head is quite as strongly inflexed as it is in other Blattidae, but the
part just at the front of the thorax is unusually elongate, so that the
eyes are exposed and the Insect has a larger field of vision. This
interesting Insect belongs to the tribe Oxyhaloides [Plectopterinae
Sauss.], in which group the most highly developed folded wings occur.
[Illustration: FIG. 129.—_Hypnorna amoena_. Central America. Tribe
Oxyhaloides. (After de Saussure.)]
The wingless forms never exhibit the grace and elegance possessed by some
of the more active of the winged Blattidae. {235}One of them,
_Gromphadorhina portentosa_, found in Madagascar (Fig. 130), is a very
robust Insect, and attains a length of 78 millim.—somewhat more than 3
inches. This Insect has projections on the thorax that remind us of the
horns that exist in some of the Lamellicorn beetles.
Little has been yet written as to the resemblances of Blattidae to other
species of their own family, or to other creatures, but it is probable that
such similarities will be found to prevail to a considerable extent. W. A.
Forbes has called attention[161] to the larva of a Blattid from Brazil as
being remarkable for its superficial resemblance to an Isopod crustacean.
Some of the wingless forms have a great resemblance to the small rolling-up
Myriapods of the group Glomerides; _Pseudoglomeris fornicata_, of which we
figure the female (Fig. 131), has received its name from this resemblance.
The females of the S. African genus _Derocalymma_ possess this Glomerid
appearance, and have a peculiar structure of the prothorax, admitting of a
more complete protection of the head. Brunner states that the wingless
kinds of _Derocalymma_ roll themselves up like wood-lice. In many of the
forms of this tribe—Perisphaeriides—the males are winged, though the
females are so like Myriapods. According to de Saussure[162] the gigantic
_Megaloblatta rufipes_ bears an extreme resemblance in appearance to the
large cockroaches of the genus _Blabera_.
[Illustration: FIG. 130.—_Gromphadorhina portentosa_, × ⅔. Tribe
Perisphaeriides. (After Brunner.)]
[Illustration: FIG. 131.—_Pseudoglomeris fornicata_, ♀. Burma. Tribe
Perisphaeriides. (After Brunner.)]
Some of the species of _Holocompsa_ remind us strongly of Hemiptera of the
family Capsidae; they have an arrangement of colours similar to what
prevails in that group, and their tegmina and wings which, as being those
of Blattids may be said to be abnormally formed, resemble in texture and
the distribution of the venation those of the Hemiptera. These Insects are
closely allied to _Diaphana_, of which genus we have figured a species
(Fig. 122).
{236}There is very little evidence on which to base an estimate of the
number of species of Blattidae existing in the world at present. Probably
the number extant in collections may amount to 1000 or thereabouts, and the
total existing in the world may be as many as 5000. The species of
Blattidae cannot tolerate cold, and are consequently only numerous in
tropical regions. Europe possesses about twenty species, and in Britain
there are only three that are truly native; these are all small Insects
belonging to the genus _Ectobia_, and living out of doors, amongst leaves,
under bushes, and in various other places. We have, however, several other
species that have been introduced by the agency of man, and these all live
under cover, where there is artificial warmth and they are protected from
the inclemencies of the winter season. The commonest of these forms is
_Stilopyga orientalis_, the "black beetle" of our kitchens and bakehouses.
This Insect is said to have been brought to Europe from "Asia" about 200
years ago, but the evidence as to its introduction, and as to the country
of which it is really a native, is very slight. It is indeed said[163] that
_S. orientalis_ has been found in peat in Schleswig-Holstein. _Periplaneta
americana_ is a larger Insect, and is common in some places; it is
apparently the species that is most usually found on board ships, where it
sometimes multiplies enormously, and entirely devours stores of farinaceous
food to which it obtains access: it is known that sometimes a box or barrel
supposed to contain biscuits, on being opened is found to have its edible
contents entirely replaced by a mass of living cockroaches. Fortunately
_Periplaneta americana_ has not spread widely in this country, though it is
found in great numbers in limited localities; one of the best known of
which is the Zoological Gardens in the Regent's Park at London.
_Periplaneta australasiae_ is very similar to _P. americana_, but has a
yellow mark on the shoulder of each tegmen. This has obtained a footing in
some of the glass-houses in the Botanic Gardens at Cambridge and Kew; and
it is said to be fairly well established in Belfast. Another of our
introduced domestic cockroaches is _Phyllodromia germanica_, a much smaller
Insect than the others we have mentioned. It has only established itself at
a few places in this country, but it is extremely abundant in some parts of
Northern and Eastern Europe. It has been increasing in numbers in Vienna,
where, according to Brunner, it is {237}displacing _Stilopyga orientalis_.
In addition to these, _Rhyparobia maderae_ and species of the genus
_Blabera_ have been met with in our docks, and are possibly always to be
found there. They are Insects of much larger size than those we have
mentioned. We figure the alar organs of one of these species of _Blabera_
of the natural size: the species in this genus are extremely similar to one
another. Blaberae are known in the West Indies as drummers, it being
supposed that they make a noise at night,[164] but details in confirmation
of this statement are wanting.
[Illustration: FIG. 132.—Alar organs of _Blabera_ sp. A, tegmen; B, wing.]
It is a remarkable fact that no satisfactory reasons can be assigned for
the prevalence of one rather than another of these domestic cockroaches in
particular localities. It does not seem to depend at all on size, or on the
period of development, for the three species _Stilopyga orientalis_,
_Periplaneta americana_, and _Phyllodromia germanica_, which are the most
abundant, differ much in these respects, and replace one another in
particular localities, so that it does not appear that any one is gaining a
permanent or widespread superiority as compared with another. There are,
however, no sufficient records on these points, and further investigation
may reveal facts of which we are at present ignorant, and which will throw
some light on this subject. We may remark that Mr. Brindley has found it
more difficult to obtain hatching of the young from the egg-capsules of
_Periplaneta americana_ and _Phyllodromia germanica_ at Cambridge, than
from those of _Stilopyga orientalis_.
Although much work has been done on the embryology of Blattidae, the
subject is still very incomplete. The recent memoirs of Cholodkovsky[165]
on _Phyllodromia germanica_ contain so much of general interest as to the
development of the external parts of the body that we may briefly allude to
them. The earliest appearance of segmentation appears to be due to the
centralisation of numerous {238}cells round certain points in the ventral
plate. The segmentation of the anterior parts is first distinct, and the
appearance of the appendages of the body takes place in regular order from
before backwards, the antennae appearing first; the mandibles, however,
become distinct only subsequent to the maxillae and thoracic appendages.
There are in the course of the development appendages to each segment of
the body (he counts eleven abdominal segments); the cerci develop in a
similar manner to the antennae; the first pair of abdominal appendages—at
first similar to the others—afterwards assume a peculiar stalked form. The
abdominal appendages subsequently disappear, with the exception of the
ninth pair, which form the ventral styles, and the eleventh pair, which
become the cerci. The last ventral segment is said to be formed by the
union of the tenth and eleventh embryonic ventral segments.
[Illustration: FIG. 133.—A, Tegmen(?) of _Palaeoblattina douvillei_; B, of
_Etoblattina manebachensis_. (After Brauer and Scudder.)]
As regards their Palaeontological forms Blattidae are amongst the most
interesting of Insects, for it is certain that in the Carboniferous epoch
they existed in considerable number and variety. A still earlier fossil has
been found in the Silurian sandstone of Calvados; it consists of a fragment
(Fig. 133, A), looking somewhat like an imperfect tegmen of a Blattid; it
was described by Brongniart under the name of _Palaeoblattina douvillei_,
and referred by him, with some doubt, to this family. Brauer has, however,
expressed the opinion[166] that the fragment more probably belonged to an
Insect like the mole-cricket, and in view of this discrepancy of
authorities we may be pardoned for expressing our own opinion to the effect
that the relic has no connexion with the Insecta. The figure given by
Scudder[167] has not, however, so uninsect-like an appearance as that we
have copied from Brauer. Whatever may prove to be the case with regard to
_Palaeoblattina_, it is certain, as we {239}have already said, that in the
Palaeozoic epoch Insects similar to our existing cockroaches were abundant,
their remains being found in plenty in the coal-measures both of Europe and
North America. Fig. 133, B, shows a fossil tegmen of _Etoblattina
manebachensis_ from the upper Carboniferous beds of Ilmenau in Germany. It
will be noticed that the disposition of the nervures is very much like that
which may be seen in some of our existing Blattidae (cf. the tegmen of
_Blabera_, Fig. 132, A), the vena dividens (_a_) being similarly placed, as
is also the mediastinal vein on the front part of the organ. The numerous
carboniferous Blattidae have been separated as a distinct Order of Insects
by Scudder under the name Palaeoblattariae, but apparently rather on
theoretical grounds than because of any ascertained important structural
distinctions. He also divided the Palaeoblattariae into two groups,
Mylacridae and Blattinariae, the former of which was supposed to be
peculiar to America. Brongniart has, however, recently discovered that in
the Carboniferous deposits of Commentry in France Mylacridae are as common
as in America. This latter authority also states that some of the females
of these fossil Blattidae are distinguished by the presence of an elongate
exserted organ at the end of the body. He considers this to have been an
ovipositor by which the eggs were deposited in trees or other receptacles,
after a manner that is common in certain Orthoptera at the present day. If
this view be correct these Carboniferous Insects must have been very
different from the Blattidae of our own epoch, one of whose marked
characteristics is the deposition of the eggs in a capsule formed in the
body of the parent.
In the strata of the secondary epoch remains of Blattidae have also been
discovered in both Europe and America, in Oolitic, Liassic, and Triassic
deposits. From the Tertiary strata, on the other hand, comparatively few
species have been brought to light. A few have been discovered preserved in
amber.
[Illustration: FIG. 134.—Front leg of _Periplaneta australasiae_.]
The classification of the Blattidae is attended with considerable
difficulty on account of the numerous wingless forms, and of the
{240}extreme difference in the organisation of the two sexes of many
species. It has, however, been brought to a fairly satisfactory state by
the reiterated labours of Brunner von Wattenwyl, and we reproduce his
recently perfected exposition of their characters. His first division is
made by means of a structure which is very easily observed, viz. whether
the femora are armed with spines, as in Fig. 134, or not. The terms used in
connexion with the wings and other parts of the body we have already
explained.
Brunner's system is adopted by de Saussure,[168] who, however, proposes to
replace the names Ectobiides and Oxyhaloides by Anaplectinae and
Plectopterinae. He also proposes to apply the generic name _Blatta_ to the
Insect that is now so frequently called _Phyllodromia germanica_ in
zoological works. If that view be adopted, Brunner's group Phyllodromiides
will be called Blattides.
Table of the tribes of Blattidae, after Brunner:—
1. Femora spiny beneath.[169]
2. The last ventral plate of the female large, without valves.
3. Supra-anal lamina of both male and female transverse, narrow.
Wings, when present, furnished with a triangular apical field.
Posterior femora unarmed beneath, or armed with two spines on the
anterior margin. Egg-capsules furnished with a longitudinal suture.
Tribe 1. ECTOBIIDES. [Anaplectinae Saussure.]
3′. Supra-anal lamina of each sex more or less produced, triangular,
or emarginate. Wings, when present, without apical field. Posterior
femora with both edges spiny.
4. Supra-anal lamina of each sex triangular, not notched. Cerci
projecting much beyond this lamina.
5. Pronotum and elytra smooth (_i.e._ without peculiarity of
surface other than punctuation). The radial nervure of the wing
giving off several parallel branches, pectinate on the anterior
margin (except in the genus _Abrodiaeta_). Tarsal joints without
pads. Tribe 2. PHYLLODROMIIDES. [Blattinae Saussure.]
5′. Pronotum and elytra holosericeous. Radial nervure of the
wings giving off irregular branches on the anterior margin (ulnar
vein many-branched). Tarsal joints furnished with pads. Tribe 3.
NYCTIBORIDES.
4′. Supra-anal lamina of males more or less four-sided, with obtuse
angles, of females broad, rounded, or lobed. Cerci not projecting
beyond the lamina. (Tarsal joints with distinct pads.) Ulnar
nervure of the wings giving off parallel branches towards the vena
dividens. Tribe 4. EPILAMPRIDES.
{241}2′. The last ventral plate of the female furnished with valves.
Tribe 5. PERIPLANETIDES.[170] (Fig. 119, _Periplaneta australasiae_.)
1′. Femora unarmed beneath. (In the tribe Panesthiides the anterior
femora are frequently armed with two spines.)
2. Supra-anal lamina of each sex more or less produced, posterior
margin notched.
3. A distinct pad between the claws. Tribe 6. PANCHLORIDES.
3′. No pad between the claws, or only an excessively small one.
4. Wings with a folded fan-like anal field. Pronotum smooth. Tribe
7. BLABERIDES. (Fig. 132, _Blabera_ sp. wings.)
4′. Anal field of the wing with a single fold. Pronotum more or
less pilose. Tribe 8. CORYDIIDES. (Fig. 128, _Corydia petiveriana_.
Fig. 118, _Heterogamia aegyptiaca_.)
2′. Supra-anal lamina of each sex, short, transverse, posterior margin
straight or rounded.
3. Subgenital lamina of the male somewhat produced, furnished with a
single style. Tarsal claws with a distinct pad (except in the genus
_Paranauphoeta_).
4. Anterior portion of the wings pointed, either the apical field
of the wing very much produced, or the wings twice as long as the
tegmina, folded in repose. Tribe 9. OXYHALOIDES. [Plectopterinae
Saussure.] (Fig. 129, _Hypnorna amoena_.)
4′. Anterior portion of wing, when present, rounded, with no apical
field. Tribe 10. PERISPHAERIIDES. (Fig. 130, _Gromphadorhina
portentosa_; Fig. 131, _Pseudoglomeris fornicata_.)
3′. Subgenital lamina of males extremely small, without styles. No
pad between claws. Tribe 11. PANESTHIIDES.
To the above tribes another one—GEOSCAPHEUSIDES—has been recently added by
Tepper,[171] for an extraordinary Australian Insect of fossorial habits,
with front legs formed somewhat like those of _Gryllotalpa_.
{242}CHAPTER X
ORTHOPTERA _CONTINUED_—MANTIDAE—SOOTHSAYERS
FAM. IV. MANTIDAE—SOOTHSAYERS OR PRAYING INSECTS.
_Orthoptera with exserted but deflexed head and elongate prothorax, the
first pair of legs largely developed, raptorial, the coxae elongate,
free, femora and tibiae armed with spines: second and third pair of legs
simple and similar; the tarsi five-jointed, without a pad (arolium)
between the claws; a pair of jointed cerci near the extremity of the
body._
The Mantidae are an extensive family of Orthoptera, showing extreme variety
in the shapes and outlines of the body, and characterised by the very
remarkable front legs; the function of these legs being to seize and hold
their prey, which consists of living Insects, Mantidae being carnivorous
and highly voracious.
The labium is deeply divided, each half exhibiting a very near approach to
the structure of a maxilla; there is a large membranous lingua reposing on
the inner face of the lower lip. The head is quite free from the thorax,
its front part being deflexed, and even somewhat inflexed, so that the
mouth is directed downwards and somewhat backwards: it is very mobile,
being connected to the thorax by a comparatively slender neck, which is,
however, concealed by the pronotum. There are two large, prominent eyes,
the antennae are frequently very slender, but they sometimes differ
according to sex, and in some genera are pectinate in the male; just above
and between their insertion are three ocelli placed in a triangle, two
above, one below; between the antennae and the clypeus there is an interval
called the scutellar space. In some forms of Mantidae the head assumes most
extraordinary shapes; the eyes may become {243}elongate and horn-like;
there may be a projection between them bearing the ocelli, and attaining
occasionally a great length; the scutellar space also may have a remarkable
development, the whole thus forming a peculiar ornamental structure, as in
Fig. 136.
[Illustration: FIG. 135.—_Deroplatys sarawaca_, female. Borneo. (After
Westwood.)]
The prothorax is elongate, but there are a few genera, _e.g._
_Eremiaphila_, in which it is exceptionally short, and there are several
others in which the elongate form is more or less masked by foliaceous
expansions of the sides. The pronotum shows near the front a transverse
depression or seam, which marks the position of an internal chitinous
ridge. The anterior legs are {244}inserted near the front of the
prosternum, which extends less far forwards than the pronotum does; the
posterior part of the prosternum is very elongate, and is completely
separated from the anterior part by the base of the coxae and the membranes
attached to them; the pronotum and sternum are closely connected at the
sides till near the posterior part where they diverge, the space so formed
being occupied by a membrane in which the prothoracic stigma is situated.
The mesothorax is as long as broad, and the front wings are attached to the
whole length of the sides; the mesosternum is a triangular piece pointed
behind, and bearing very large side-pieces, to the hinder portion of which
the middle coxae are attached; these latter are large and quite free, and
repose on the metasternum which they cover; the mesothoracic stigma may be
detected as a slit situated on a slight prominence just behind and a little
below the membranous hind-margin of the tegmen. The metathorax differs
comparatively little in size and structure from the mesothorax; the
membranous hind wings are attached to the sides of the notum along nearly
the whole length of the latter. The abdomen is moderately long; in each sex
ten dorsal plates may be detected, and there is a pair of ringed cerci
projecting from beneath the sides of the tenth plate. The number of ventral
plates is more difficult to verify, the first one being much reduced; eight
other plates can be demonstrated in the male and six in the female.
[Illustration: FIG. 136.—Head of _Harpax variegatus_, seen from the front.]
The anterior legs are formed in a remarkable manner in the Mantidae, and
are, in fact, the most characteristic feature of the family. Attached near
the front of the thorax there is a very long coxa, to the apex of which is
articulated the triangular trochanter; this bears the elongate femur, which
is furnished on its lower face with sharp spines and teeth; the tibia which
follows is much shorter and smaller than the femur; its lower face bears
also an armature of teeth, and it is so articulated with {245}the femur
that it can be completely closed thereon, its teeth fitting in among those
of the femur (Fig. 137, B); the latter has one or more longer spines
overlapping the apical part of the tibia when contracted. The tarsus is
slender, five-jointed, without pad. The other two pairs of legs are simple;
the hinder usually a little the longer, and in some species that possess
powers of leaping (_Ameles_), with the femora a little thicker at the base.
[Illustration: FIG. 137.—Front leg of _Empusa pauperata_, female: A, with
tibia extended and tarsus wanting; B, more magnified (the basal parts
removed), showing the mode of closure.]
The alar organs of the Mantidae are as regards the nervures and areas
fairly similar to those of the Blattidae. The tegmina are usually narrow,
and exhibit three well-marked areas; the one in front or external
(according as the wing is expanded or closed) is the mediastinal area; it
is usually more elongate and occupies a larger portion of the surface of
the tegmen than in Blattidae. The middle area, forming the larger part of
the wing, is occupied by the branches of the radial and ulnar nervures. The
third area, the anal, possesses a sort of appendage in the form of a small
space of a more delicately membranous nature at the inner part of the base.
The tegmina are often more or less leaf-like in texture and consistence;
this character is as a rule not very marked, but there are a few species
with the tegmina very like foliage, this being more marked in the female;
in some, if not in all, of these cases the mediastinal area is considerably
increased. One tegmen overlaps the other, as in Blattidae, but to a less
extent, and the correlative asymmetry is but slight: there is frequently a
pallid spot close to the main vein on the principal area, nearer to the
base than to the extremity. The hind wings are more ample than the front,
and of much more delicate consistence; they possess numerous veins
converging to the base; the anterior part of the wing is firmer in
consistence, and its veins are more numerously furcate; there are many more
or less distinct minute cross-veinlets, and an elegant tinting is not
infrequent. They close in a fan-like manner, transverse folding being
unknown in the family.
{246}But little has been written on the internal anatomy of the Mantidae.
Dufour has described only very partially that of _M. religiosa_. The
salivary glands are largely developed, salivary receptacles exist; the
alimentary canal possesses eight elongate coecal diverticula placed on the
chylific ventricle; there are about one hundred Malphigian tubules. In each
ovary there are about 40 egg-tubes, and they are joined at their bases in
clusters of about half a dozen; each cluster has a common sinus; these
sinuses are placed at intervals along a tube, which is one of two branches
whose union forms the oviduct; there are a large number of "serific glands"
of two kinds in the female. The testes are unusually complex in their
structure.
According to Schindler[172] the Malphigian tubes in _Mantis_ are not
inserted, as usual, at the base of the intestine, but on the intestine
itself at about one-third of its length from the base. There is some doubt
about this observation. Schindler considers the fact, if it be such,
unique.
The eggs of the Mantidae are deposited in a singular manner: the female,
placing the extremity of the body against a twig or stone, emits some
foam-like matter in which the eggs are contained. This substance dries and
forms the ootheca; whilst attaining a sufficient consistence it is
maintained in position by the extremity of the body and the tips of the
elytra, and it is shaped and fashioned by these parts. The eggs are not, as
might be supposed, distributed at random through the case, but are lodged
in symmetrically-arranged chambers, though how these chambers come into
existence by the aid of so simple a mode of construction does not appear.
The capsule is hard; it quite conceals the eggs, which might very naturally
be supposed to be efficiently protected by their covering: this does not,
however, appear to be the case, as it is recorded that they are subject to
the attacks of Hymenopterous parasites. The time that elapses after the
eggs are laid and before they hatch varies greatly according to
circumstances. In France, _Mantis religiosa_ deposits its eggs in
September, but they do not hatch until the following June; while in E.
India the young of another species of _Mantis_ emerge from the eggs about
twenty days after these have been deposited. Trimen has recorded some
particulars as to the formation of its egg-case by a _Mantis_ in S. Africa.
This {247}specimen constructed four nests of eggs at intervals of about a
fortnight, and Trimen states that the four were "as nearly as possible of
the same size and of precisely similar shape." He also describes its mode
of feeding, and says that it was fond of house-flies, and would eat
"blue-bottles," i.e. _Musca vomitoria_, but if while eating one of the
latter a house-fly were introduced, the "blue-bottle" was generally
dropped, even though it might be in process of being devoured. The young
have to escape from the chambers in which they are confined in these
egg-cases; they do so in a most curious manner; not by the use of the feet,
but by means of spines directed backwards on the cerci and legs, so that
when the body is agitated advance is made in only one direction. The eggs
last deposited are said to be the first to hatch. On reaching the exterior
the young Mantids do not fall to the ground, but remain suspended, after
the manner of spiders, to the ootheca by means of two threads attached to
the extremities of the cerci; in this strange position they remain for some
days until the first change of skin is effected, after which they commence
the activity of their predatory life.
[Illustration: FIG. 138.—Egg-case of _Mantis_ with young escaping: A, the
case with young in their position of suspension; B, cerci magnified,
showing the suspensory threads. (After Brongniart.)]
Dr. Pagenstecher has given an account[173] of the development of _Mantis
religiosa_, from which it would appear that the statements of Fischer and
others as to the number of moults are erroneous, owing to the earliest
stages not having been observed. When the young _Mantis_ emerges from the
egg it bears little resemblance to the future Insect, but looks more like a
tiny pupa; the front legs, that will afterwards become so remarkable, are
short and not different from the others, and the head is in a curious
mummy-like state, with the mouth-parts undeveloped and is inflexed on the
breast: there are, he says, nine abdominal segments. The first ecdysis soon
takes place and the creature is thereafter recognisable as a young
_Mantis_. Pagenstecher's specimens at first would only eat Aphididae, but
at a later stage of the {248}development they devoured other Insects
greedily: the number of ecdyses is seven or eight. The ocelli appear for
the first time when the wing rudiments do so; the number of joints in the
antennae increases at each moult. Dr. Pagenstecher considers that this
Insect undergoes its chief metamorphosis immediately after leaving the egg,
the earlier condition existing apparently to fit the Insect for escaping
from the egg-case. In the immature stage of the Mantidae the alar organs
appear (Fig. 139) as adjuncts of the sides of the meso- and meta-notum,
projecting backwards and very deeply furrowed and ribbed in a wing-like
manner. According to Pagenstecher, this wing-like appearance only commences
in the fifth stadium, but he has not given particulars of the conditions of
these parts in the preceding instars. According to de Saussure[174] the
wings of the females of some species remain permanently in this undeveloped
or nymphal state.
[Illustration: FIG. 139.—Tegmina (_t_) and wings (_w_) of immature
_Mantis_.]
[Illustration: FIG. 140.—_Iris oratoria_, female. South Europe. Natural
size.]
The Mantidae, as a rule, have a quiet unobtrusive mien, and were it not for
their formidable front legs would look the picture of innocence; they,
however, hold these legs in such manner as to greatly detract from the
forbidding appearance thereof, stretching them out only partially so as to
give rise to an appearance of supplication or prayer;[175] this effect is
increased by their holding themselves in a semi-erect position, standing on
the hind and middle legs with the upper parts of the body directed somewhat
forwards, hence they are called by various names indicating prayer or
supplication, and it is said that in some countries they are considered
sacred. Some of the older {249}writers went so far as to say that a
_Mantis_ would indicate the road a child should take by stretching out one
of its arms in the right direction. The traveller Burchell, speaking of a
species since described by Westwood under the name of _Tarachodes
lucubrans_, says: "I have become acquainted with a new species of _Mantis_,
whose presence became afterwards sufficiently familiar to me by its never
failing, on calm warm evenings, to pay me a visit as I was writing my
journal, and sometimes to interrupt my lucubrations by putting out the
lamp. All the _Mantis_ tribe are very remarkable Insects; and this one,
whose dusky sober colouring well suits the obscurity of night, is certainly
so, by the very late hours it keeps. It often settled on my book, or on the
press where I was writing, and remained still, as if considering some
affair of importance, with an appearance of intelligence which had a
wonderful effect in withholding my hand from doing it harm. Although
hundreds have flown within my power, I never took more than five. I have
given to this curious little creature the name of _Mantis lucubrans_; and
having no doubt that he will introduce himself to every traveller who comes
into this country [Southern Africa] in the months of November and December,
I beg to recommend him as a harmless little companion, and entreat that
kindness and mercy may be shown to him." This appearance of innocence and
quietness must have struck all who have seen these Insects alive;
nevertheless, it is of the most deceptive character, for the creature's
activity consists of a series of wholesale massacres carried on day after
day, the number of victims it sacrifices being enormous. The _Mantis_ does
not even spare its own kind; it is well known that the female not
unfrequently devours its own mate. A very different picture to that of
Burchell has been drawn by Potts, who observed the habits of a species in
New Zealand.[176] He informs us that when about making an attack it
approaches its intended prey with slow, deliberate movements, its anterior
limbs folded in an innocent fashion, now and then raising itself or lifting
the prothorax in a stealthy quiet manner, perhaps to judge accurately of
its distance; when near enough, with one swift dart the victim is secured.
The prey is held {250}firmly in the formidable trap formed by the anterior
leg, and is thus brought near the mouth. The _Mantis_ usually commences its
feast by taking off some portions of the head of its wretched victim, and
displays an absolute indifference to its struggling or kicking; the
mandibles having seized a portion of the food, the legs holding it move
away, thus leaving a fragment in the mouth. Portions only of a captured
Insect are consumed, much being cast away; and Mr. Potts states that he has
seen one of these voracious creatures kill and devour parts of fourteen
small flies within a very brief space of time. This voracity and waste of
animal food is very remarkable when we recollect that many Insects have
such perfect powers of assimilation that during their whole period of
growth they only consume a mass of food—and that vegetable—but little
larger in size than the bulk they themselves attain. This fact is well
known in the case of _Bruchus_, _Caryoborus_, and other seed-feeding
Insects. Burmeister has stated good grounds for believing that some of the
larger Mantidae do not confine themselves to Insect diet, but attack and
devour small Vertebrates.[177] He has given a circumstantial account of a
case at Buenos Ayres, where a small bird was secured by the wingless female
of a large _Mantis_, which had commenced devouring its head when the
observer took possession of the creature and its booty. Dubois states[178]
that when a decapitated, but living, _Mantis_ was suspending itself to a
roll of drapery by its four posterior legs, a person could detach with the
fingers the left anterior leg (of the four) and the right posterior, or
conversely the left posterior and right anterior, without the interference
producing any action on the part of the creature; but if one of the other
legs was also interfered with, which would necessarily have changed the
position of the body, then immediately one of the two unoccupied legs was
placed by the creature in a proper position to assure its stability. This
reflex action altogether resembled in appearance a conscious action, and
was as effectually performed.
The combination in Mantidae of voracious and destructive instincts with
helpless and inert attitudes gives rise to the idea that these latter are
adopted for the purpose of deceiving the living prey and of thus more
easily obtaining the means of subsistence. {251}It appears, however, more
probable that the helpless attitudes have no such origin, but are due to
the structure and form of the creature. The front legs being wonderfully
well formed for raptorial purposes, have no capacity for locomotion or for
supporting the Insect in the usual manner, so that the body has to be borne
by the hinder two pairs of legs; at the same time the raptorial pair of
limbs—which, it will be recollected, are of great size and attached to the
anterior part of an unusually long prothorax—have to be held in such a
position as will not derange the equilibrium maintained by the posterior
part of the body; moreover, these large raptorial legs are entirely
exserted, and have no trace of any articulatory cavity that might act as a
mechanical aid to their support. Thus they could not be held extended
without great muscular exhaustion; hence we can well believe that the
sedentary and helpless attitudes of the creature are not the results of any
guile.
A _Mantis_ has been recorded as bearing a close resemblance to a Phasmid of
the genus _Bacillus_ and having only small front legs; it was suggested by
Bates[179] that the Mantis would probably be found to feed on the
_Bacillus_. Though the case is of considerable interest, no further
information about it has been obtained.
[Illustration: FIG. 141.—_Mantoida luteola_ Westw., male. Santarem.]
The simplest forms of the family are found in the groups Amorphoscelides
and Orthoderides. From our figure of one of these (Fig. 141, _Mantoida
luteola_ ♂), it will be seen that the peculiarities of the family can
scarcely be detected, the raptorial legs being very little developed and
the prothorax short. The sexes, too, differ but little in these simple
forms. Most of them are very rare in collections, but Wood-Mason
states[180] that _Amorphoscelis annulicornis_ is frequently found about
Calcutta on the trunks of trees, to the bark of which it is so similar that
it is only discovered with difficulty. In its rapid movements it resembles
the cockroaches or _Machilis_, more than it does the more differentiated
forms of its own group.
{252}In the genus _Pyrgomantis_ (Fig. 142, _P. singularis_, female) the
male has the tegmina and wings of normal size, while in the female they are
rudimentary.
[Illustration: FIG. 142.—_Pyrgomantis singularis_, female. S. Africa.
(After Westwood.)]
[Illustration: FIG. 143.—Outline of _Chaeradodis cancellata_ ♀, nymph.
(After Wood-Mason.)]
The variety of shape and external appearance in this family is very great;
de Saussure considers it to be a mimetic group. In certain species some
parts of the body—more especially the tegmina—have very much the appearance
of foliage, and usually in such cases this appearance is confined to the
female, the males in this family having, as we have said, the organs of
flight more transparent and colourless; in the former sex the alar organs,
when present, are frequently but little adapted for flying. In some species
the prothorax is expanded at the sides (Fig. 135, _Deroplatys sarawaca_;
and Fig. 143, _Choeradodis cancellata_), and in such cases the outline of
the natural thorax—if we may use such an expression—may be detected
occupying the middle of the unusual expansion. The European _Mantis
religiosa_ varies much in colour; in some examples the tegmina are
leaf-green, while in others they are brown or gray. There is some evidence
extant making it probable that in some species the colour of an individual
changes at different times—Colonel Bowker saying of {253}_Harpax ocellata_
that it "beats the Chameleon hollow in changing colour."
Some of the species of the old genus _Eremiaphila_ (Fig. 144) are of very
unusual form. De Saussure considers that some species of this genus are
more highly modified than any other animals for maintaining their existence
in desert regions. They are said to be found in places where no vegetation
exists, and to assimilate in appearance with the sandy soil, the species
varying in colour, so that the individuals agree in tint with the soil on
which they dwell. These Insects are referred to the group Orthoderides, and
have a short prothorax, the alar organs being unsuited for flight. What
they live on is not actually known; although other Insects are the natural
food of Mantids, it is said that these desert-frequenting species occur in
spots where no other Insect life is known to exist. Lefebvre[181] met with
these Eremiaphilas in the desert between the Nile and the Northern Oasis,
El Bahryeh, but was quite unable to discover their mode of subsistence.
These Insects are very rare in collections, and the information we possess
about them is very meagre.
[Illustration: FIG. 144.—_Eremiaphila turcica._ (After Westwood.)]
Mr. Graham Kerr found on the Pilcomayo river a species of Mantidae living
on branches of trees amongst lichens, which it so exactly resembled that it
was only detected by the movement of a limb; it was accompanied by a
Phaneropterid grasshopper, which bore a similar resemblance to the lichens.
One of the rarest and most remarkable forms of Mantidae is the genus
_Toxodera_, in which the eyes project outwards as pointed cones (Fig. 145).
These Insects offer an interesting problem for study, since we are entirely
ignorant about them. Brunner places the Toxoderae in his tribe Harpagides,
but with the remark that "these Insects of antediluvian shapes differ
essentially from all other Mantidae."
Wood-Mason informs us[182] that the young of _Hymenopus bicornis_
{254}beautifully simulate blossoms of different colours. And it has been
stated by Dr. Wallace, on the authority of a communication made to him by
Sir Charles Dilke, that a small _Mantis_ found in Java exactly resembles a
pink Orchis-flower, and this species "was not only said to attract Insects,
but even the kind of Insects (butterflies) which it allures and devours was
mentioned." We do not know of what species or genus this Insect may be, but
_Hymenopus bicornis_ is a peculiar form of the tribe Harpagides, and has,
together with its younger state, been figured long ago by Caspar Stoll in
his quaint and interesting old book.[183] Though it has very peculiar
foliaceous expansions on the two hinder pairs of legs, these dilatations
are very different from those seen in the curious _Gongylus gongylodes_,
the female of which we figure (Fig. 146). This latter, according to the
information we shall quote, is also a "floral simulator." Specimens of _G.
gongylodes_ were shown to the members of the Asiatic Society of Bengal in
1877 by Dr. J. Anderson,[184] who at the same gave some information about
them which we shall reproduce in full, because, incomplete as it is, it is
apparently almost the sole piece of definite information we possess as to
this curious Insect, or any of its congeners:—
[Illustration: FIG. 145.—_Toxodera denticulata_, male. Java. (After
Serville.)]
"These Insects all came from the same locality, having been {255}forwarded
to Mr. Buckland by Mr. Larymore of the Central Jail at Midnapur. Mr.
Larymore had procured them from the neighbouring country district, where
Santál women and children had hunted them out and brought them in, hanging
on branches or twigs of a bush, somewhat like a wild plum-tree. They are
also said to be found upon rose-bushes, and in connexion with this it was
observed that, in Midnapur, they were known as rose-leaf Insects, from the
circumstance that when the Insect is more developed and furnished with
wings, the foliaceous appendages are said greatly to increase in size, and
exactly to resemble rose-leaves. Dr. Anderson, however, was disposed to
think that more than one species might probably occur in the Midnapur
district, and that these Insects with the larger foliaceous expansions
might be distinct from the species now before the Society.
[Illustration: FIG. 146.—_Gongylus gongylodes_, female. East India.]
{256}"Mr. Buckland had made over these Insects to Dr. Anderson, and since
that time they have been regularly fed upon house-flies and grasshoppers;
the latter, however, appear to be rather too strong for them, and they
therefore prefer the flies. They have been tried with small fragments of
plaintain and custard-apple, which they not only eat, but the juice of
which they seem to suck with considerable avidity, Dr. Anderson, however,
thought that it was the moisture of these fruits that was the chief
attraction to these Insects, for the entire character of their organisation
indicated a raptorial habit.
"Dr. Anderson went on to say that he had succeeded in identifying the three
larger Insects by means of a single dried specimen in the Indian Museum,
which, however, was fully mature and provided with wings. These remarkable
Insects proved to be the pupae of a peculiar species of _Mantis_ which was
known to Aldrovandus, who figured it more than a century and a half before
the first appearance of the Systema Naturae of Linnaeus, to whom it was
known as _Gryllus gongylodes_, and also as _Mantis gongylodes_; and since
the time of Aldrovandus it had been figured in a variety of works on
Natural History, but apparently in every instance from mature, and
seemingly dried specimens, so that the colours of the Insect during life
had never been correctly described.
"So much by way of introduction to these remarkable pupal Mantises, the
recognised scientific name of which is _Gongylus gongylodes_ L.
"The reason which induced Dr. Anderson to bring them to the notice of the
Society had now to be pointed out. On looking at the Insects from above,
they did not exhibit any very striking features beyond the leaf-like
expansion of the prothorax and the foliaceous appendages to the limbs, both
of which, like the upper surface of the Insect, are coloured green, but on
turning to the under surface the aspect is entirely different. The
leaf-like expansion of the prothorax; instead of being green, is a clear,
pale lavender-violet, with a faint pink bloom along the edges of the leaf,
so that this portion of the Insect has the exact appearance of the corolla
of a plant, a floral simulation which is perfected by the presence of a
dark, blackish brown spot in the centre, over the prothorax, and which
mimics the opening to the tube of a corolla. A favourite position of this
Insect is to hang head {257}downwards among a mass of green foliage, and,
when it does so, it generally remains almost motionless, but, at intervals,
evinces a swaying movement as of a flower touched by a gentle breeze; and
while in this attitude, with its fore-limbs banded violet and black, and
drawn up in front of the centre of the corolla, the simulation of a
papilionaceous flower is complete. The object of the bright colouring of
the under surface of the prothoracic expansion is evident, its purpose
being to act as a decoy to Insects, which, mistaking it for a corolla, fly
directly into the expectant, serrated, sabre-like, raptorial arms of the
simulator. It is no new fact that many Insects resemble the leaves of
plants and trees, and that they manifest forms and colours which serve to
protect them in the struggle for existence, but so far as Dr. Anderson had
ascertained, this was the first recorded instance of an Insect simulating
the corolla of a flower for the evident purpose of attracting Insects
towards it for its sustenance. It is even more remarkable than this, for it
is a localised adaptation for such a purpose, a portion of the Insect being
so modified in form and colour that the appearance of the corolla of a
plant is produced, in conjunction with the remainder of the long attenuated
prothorax, which at a distance resembles the flower stem; the anterior
limbs when in repose even adding to and heightening the deception."
That we should have no more precise information as to a large Insect of
such remarkable habits and appearance, and one that has been known to
naturalists for upwards of three centuries, is a matter for regret. Careful
observation as to the habits, food, and variation of these floral
simulators, and as to whether they seek for spots specially suitable to
their coloration, would be of great interest. A European congener of this
Insect, _Empusa pauperata_, has small foliaceous expansions on the legs,
but its habits have not been noticed in detail.
The very curious Insect represented in Fig. 147, _Stenophylla cornigera_,
is a member of the tribe Vatides; the form of the cerci at the end of the
body is very peculiar. This extremely rare, if not absolutely unique,
Insect is a native of the interior of Brazil.
Dufour has recorded that _Mantis religiosa_ possesses the power of
producing a mournful sound by rubbing the extremity of the body against the
wings; it is stated that a hissing sound is {258}produced by other species,
and Wood-Mason has suggested[185] that a special structure exists on the
tegmina for the purpose.
There are probably about 600 species of Mantidae known; they are
distributed over all the warmer parts of the earth, but there are none in
the cooler regions. Europe possesses some twelve or fourteen species, most
of them confined to the Mediterranean sub-region; a single species, _Mantis
religiosa_, is frequently found in Central France, and has been recorded as
occurring as far north as Havre. Although no species is a native of
Britain, it is not difficult to keep them alive here. Denny records[186]
that an egg-case of a _Mantis_ was sent from Australia to England, and that
the hatching of the eggs was completed after its arrival. The young fed
readily on flies, and we are informed that in the neighbourhood of
Melbourne, where this _Mantis_ is plentiful, specimens are placed by the
citizens on the window-blinds of their houses, so that the rooms may be
cleared from flies by means of the indefatigable voracity of the _Mantis_.
[Illustration: FIG. 147.—_Stenophylla cornigera._ Brazil. (After
Westwood.)]
The geological record as to Mantidae is very meagre and unsatisfactory. The
genus _Mantis_ is said to occur in amber, and Heer has referred to the same
genus an ill-preserved fossil from the upper Miocene beds of Central
Europe; a fragment {259}of a hind wing found in the Jurassic strata of
Siberia has been assigned to the family; and until recently _Lithomantis_
from the Carboniferous beds of Scotland was considered to belong to
Mantidae. Scudder, however, has rejected it therefrom, placing it in the
Neuropteroid division of Palaeodictyoptera, and Brongniart, adding another
species to the genus from the Carboniferous strata in France, proposed to
treat the two as a distinct family, which he called Palaeomantidae.[187]
This naturalist has, however, since renewed his study[188] of these
Insects, has become convinced that they have no relations with existing
Mantidae, and has consequently removed them to the family Platypterides in
the Order Neuroptera.
Six tribes of Mantidae are recognised by Brunner and de Saussure.
Table of the tribes of Mantidae:—
1. Anterior tibiae with the outer edge unarmed beneath or only furnished
with very minute tubercles. (Pronotum not longer than the anterior
coxae.) Tribe 1. AMORPHOSCELIDES. (Fig. 141, _Mantoidea luteola_.)
1′. Anterior tibiae with the outer edge spinose beneath.
2. Anterior femora having the inner edge armed beneath with equal
spines, or with spines in which only the alternate are smaller.
Antennae of the male simple, rarely unipectinate.
3. Tibiae and also the intermediate and hind femora even above.
4. Legs and body with no lobe-like processes. (Antennae simple in
each sex.)
5. Pronotum not forming any dilatation above the insertion of the
coxae, its lateral margins straight or (in the genus
_Choeradodis_) strongly dilated with the anterior margin not
rounded. Tribe 2. ORTHODERIDES. (Fig. 142, _Pyrgomantis_; Fig.
143, _Choeradodis_; Fig. 144, _Eremiaphila turcica_.)
5′. Pronotum dilated above the insertion of the coxae, there with
the lateral margins broadened in a round manner, the anterior
margin rounded. Tribe 3. MANTIDES. (Fig. 140, _Iris oratoria_.)
4′. Legs or body furnished with lobes. (Posterior femora or
segments of the body with lobes, or vertex of the head conically
prolonged.) Tribe 4. HARPAGIDES. (Fig. 136, _Harpax variegatus_;
Fig. 135, _Deroplatys sarawaca_.)
3′. Tibiae as well as the intermediate and hind femora carinate
above. (Pronotum elongate, with the posterior part, behind the
transverse groove, three times as long as the anterior part.) Tribe
5. VATIDES. (Fig. 147, _Stenophylla cornigera_.)
2′. Anterior femora beneath, with the inner edge armed between the
longer teeth with shorter teeth, usually three in number. Antennae of
the male bipectinate. (Vertex conically prolonged.) Tribe 6. EMPUSIDES.
(Fig. 146, _Gongylus gongylodes_.)
{260}CHAPTER XI
ORTHOPTERA _CONTINUED_—PHASMIDAE—WALKING-LEAVES—STICK-INSECTS
FAM. V. PHASMIDAE—STICK AND LEAF INSECTS.
_Head exserted; prothorax small, not elongate; mesothorax very elongate;
the six legs differing but little from one another, the front pair not
raptorial, the hind pair not saltatorial. The cerci of the abdomen not
jointed, consisting of only one piece; the tarsi five-jointed. Tegmina
usually small, or entirely absent, even when the wings are present and
ample. The sexes frequently very dissimilar. Absence of alar organs
frequent._
These Insects are amongst the most curious of natural objects. They are
frequently of large size, some attaining 9 inches in length (Fig. 162,
_Palophus centaurus_, one-half natural length). Their variety of form could
scarcely be surpassed; their resemblance to products of the vegetable
kingdom is frequently very great: some of the more linear species (Fig.
148, _Lonchodes nematodes_) look like sticks or stems of grass; some have a
moss-like appearance, while others resemble pieces of lichen-covered bark.
The members of the tribe Phylliides are leaf-like. A certain number of
other Phasmids are covered with strong spines, like thorns (Fig. 149). The
plant-like appearance is greatest in the female sex. When there is a
difference between the two sexes as to the organs of flight, these are more
fully developed in the male.
{261}[Illustration: FIG. 148.—_Lonchodes nematodes._ Malay Archipelago.
(After Westwood.)]
The antennae are usually many-jointed, but the number of joints varies from
8 to more than 100; the head is exserted; the eyes are more or less
prominent; ocelli are present in some cases. The prothorax is always small,
and it is a remarkable fact that it undergoes but little elongation even in
those species that are most linear and elongate in form (see Fig. 148,
_Lonchodes nematodes_), and that have the meso- and metathoraces extremely
long; it is very simple in structure, consisting apparently merely of a
dorsal and of a sternal plate, nearly the whole of the side being occupied
by the large space in which the coxae are inserted; the edges of the
pronotum are not free. The mesothorax is frequently six times as long as
the prothorax, though in the leaf-like and a few other forms it does not
possess this great extension; still it is always of large size relatively
to the other two thoracic segments. This is peculiar inasmuch as in other
groups where the mesothorax is relatively large there are powerful
mesothoracic wings; whereas the Phasmidae are remarkable for the
obsolescence of the mesothoracic alar appendages. The middle legs and the
tegmina or elytra, when present, are attached only to the posterior part of
the mesothorax; the notum and the sternum are separated by two narrow slips
on each side, the epimeron and episternum. The metathorax is formed like
the mesothorax, except that the posterior part of the dorsal surface is
considered to consist of the first ventral segment consolidated with the
posterior part of the metanotum, the two being distinct enough in the
winged forms. The hind body or abdomen is elongated except in the
Phylliides; it consists of ten dorsal plates; the first frequently looks
like a portion of the metanotum, and is treated as really such by Westwood,
who describes the abdomen as consisting of nine segments. The flat apical
appendages are attached behind the tenth dorsal plate. The ventral plates
are similar to the dorsal in arrangement, except that in the female the
eighth plate forms a sort of spoon-like or gutter-like process to assist in
carrying or depositing the eggs, and that the two following segments are
concealed by it, and are sometimes of more delicate texture. The legs vary
greatly in the details of {262}their shape: the coxae are short, oval, or
round, never large; the trochanter is small; the front femora often have
the basal part narrower than the apical, and they are frequently so formed
that they can be stretched out in front of the head, concealing its sides
and outline and entirely encasing the antennae. There is an arolium or
cushion between the claws of the five-jointed tarsi. The front legs are
frequently longer than the others. Only a very slight study has been made
of the alar organs of Phasmidae; but according to Redtenbacher and Brauer,
they differ greatly from those of Blattidae and Mantidae, inasmuch as the
costal vein is placed not on the actual margin of the wing but in the field
thereof, and in this respect they more resemble the Orthoptera saltatoria.
Very little information exists as to the internal anatomy of the Phasmidae.
Many years ago a memoir of a fragmentary and discursive nature was
published on the subject by J. Müller,[189] but his conclusions require
confirmation; the nervous system, according to his account, which refers to
_Arumatia ferula_, has the anterior ganglia small, the supra-oesophageal
ganglion being apparently not larger than those forming the ventral chain.
[Illustration: FIG. 149.—_Heteropteryx grayi_, male. Borneo. One-half
natural size.]
Joly's more recent memoir on the anatomy of _Phyllium crurifolium_[190] is
also meagre; he states that the nervous system resembles that of the
locusts (Acridiidae), though there are at least ten pairs of ganglia—one
supra-, one infra-oesophageal, three thoracic, and five abdominal. He found
no salivary glands; the Malpighian tubules are slender, elongate, and very
numerous. The tracheal system has no air-vesicles. He found no distinction
{263}of crop and proventriculus, but the true stomach appears to consist of
two different parts, the anterior being remarkably uneven externally,
though destitute of coeca, while on the posterior part there are peculiar
vermiform processes. There are eighteen or twenty tubes in each ovary.
[Illustration: FIG. 150.—_Aschipasma catadromus_, female. Sumatra. Natural
size. (After Westwood.)]
When the young Insect is in the egg, ready for emergence, the meso- and
meta-thorax are not remarkably elongate, so that the femora are not very
far apart, but by the time the creature has fairly emerged from the prison
of its embryonic life the thoracic segments have attained their usual
proportions; much expansion of the body takes place as the Insect leaves
the egg, so that it appears a marvel how it could have been contained
therein; this expansion affects the parts of the body unequally.
The records as to the post-embryonic development of Phasmidae are very
scanty, but indicate great differences in the length of time occupied by
it. _Bacillus patellifer_ is said to moult several times, _Diapheromera
femorata_ only twice. This latter species becomes full grown in six weeks,
while, according to Murray,[191] _Phyllium scythe_ required fifteen or
sixteen months for growth, and did not moult until ten months after
hatching; the number of ecdyses in the case of the _Phyllium_ was three. At
each change of skin an immediate increase in size, similar to that we have
noticed as occurring on leaving the egg, takes place; each limb on being
freed becoming about a fourth longer and larger than the corresponding part
of the envelope from which it has just been withdrawn. After the second
moult of _Phyllium_ the tegmina and wings made their appearance, but
remained of very {264}small size until after the third moult, when they
suddenly shot out to their full size; they came out of little cases about a
quarter of an inch long, and in the course of a few minutes attained their
full size of about two and a half inches of length. In the apterous species
the difference between the young and adults in external characters is very
slight.
[Illustration: FIG. 151.—_Ceroys saevissima._ Brazil. (After Westwood.)]
Phasmidae are very sensitive to cold; both in North America and Australia
their lives are terminated by the occurrence of frost. They are all
vegetable feeders, the cannibalism that has been attributed to them by
several writers being probably imaginary. They are, however, excessively
voracious, so that a pair will destroy a great quantity of foliage; they
are consequently in some parts of the world classed amongst injurious
Insects. In Fiji and the Friendly Islands, _Lopaphus cocophagus_ eats the
cocoa-nut foliage and causes a scarcity of food, so that it becomes a
matter of necessity to destroy these Insects. One writer has gone so far as
to attribute the occurrence of cannibal habits amongst the inhabitants of
some of these islands to the want of food caused by the ravages of this
Insect. Some, if not all, of the Phasmidae have the habit of ejecting a
stinking fluid, that is said to be very acrid, and occasionally, when it
strikes the eye, to cause blindness; this liquid comes from glands placed
in the thorax. Some Phasmidae are much relished as food by birds;
_Diapheromera femorata_ is sucked by several bugs as well as eaten by
birds, and another species is recorded to have harboured Ichneumon-flies in
its body without suffering any apparent inconvenience from their presence
or from their emergence. Notwithstanding the great amount of food they
consume and their want of activity, they produce comparatively few eggs.
From twelve to twenty or thirty is frequently mentioned as about the
{265}number, but in the case of _Diapheromera femorata_ Riley speaks of
upwards of one hundred. These eggs are not deposited in any careful way,
but are discharged at random, simply dropping from the female; the noise
caused by the dropping of the eggs of _Diapheromera femorata_ from the
trees on which the Insects are feeding to the ground is said to resemble
the pattering of raindrops. The eggs of this species often remain till the
second year before they hatch. The eggs in the Phasmidae generally are of a
most remarkable nature, and nearly every one who mentions them speaks of
their extreme resemblance to seeds. Göldi[192] has suggested that this is
for the purpose of deceiving Ichneumons; it is, however, on record that the
eggs are actually destroyed by Ichneumons. It is worthy of notice that the
eggs are shed like seeds, being dropped loosely and, as we have said,
remaining on the ground or elsewhere, sometimes for nearly two years,
without other protection than that they derive from their coverings. Each
egg is really a capsule containing an egg, reminding us thus of the capsule
of the Blattidae, which contains, however, always a number of eggs. Not
only do the eggs have a history like that of seeds, and resemble them in
appearance, but their capsule in minute structure, as we shall subsequently
show, greatly resembles vegetable tissue. The egg-capsule in Phasmidae is
provided with a lid, which is pushed off when the Insect emerges (Fig.
157). This capsule induced Murray to suppose that the egg contained within
is really a pupa, and he argued therefrom that in the Orthoptera the larval
stages are passed in the egg, and that the Insect after its emergence
should be looked on as an active pupa that takes food.
[Illustration: FIG. 152.—Eggs of Phasmidae: A, _Lonchodes duivenbodi_; B,
_Platycrania edulis_; C, _Haplopus grayi_; D, _Phyllium siccifolium_.
(After Kaup.)]
The individuals of this group of Insects possess the power of reproducing a
lost limb; and Scudder, who has made some experiments as to this,[193]
states that if a leg be cut off beyond the {266}trochantero-femoral
articulation, the parts remaining outside of this joint are dropped before
the next moult, and are afterwards renewed either as a straight short stump
in which the articulations are already observable, or as a miniature leg,
the femur of which is straight and the tibia and tarsus curved into a
nearly complete circle; in the former case, the leg assumes at the next
moult the appearance that it has in the second case; this latter form is
always changed at the succeeding moult into a leg resembling the normal
limb in every respect excepting size, and the absence of the fourth tarsal
joint (Fig. 153). If the leg be removed nearer to the body than the
trochantero-femoral articulation the limb is not replaced.
The sexes are frequently extremely different; the female is usually very
much larger than the male. This latter sex often possesses wings when they
are quite wanting in the other sex; the resemblance to portions of plants
is often very much greater in the female than it is in the male.
[Illustration: FIG. 153.—_Cyphocrania aestuans_; individual in which the
right front leg has been renewed. Senegal. (After Westwood.)]
We have pointed out that the tegmina or upper wings are usually of small
size or absent (Fig. 150, _Aschipasma catadromus_), even in the species
where the lower wings are very largely developed; in such cases the latter
organs are folded in a complicated, fan-like manner, and repose on the
back, looking as if they were really the tegmina (Fig. 159, _Calvisia
atrosignata_); this appearance, moreover, is in some species enhanced much
by the fact that the part of the wing which is outermost in the folded
state is quite differently {267}coloured from the rest of the organ. The
colour of the body in many Phasmidae is said to be very variable, and if
the tints be owing to chlorophyll or other plant juices, finding their way
amongst the Insect-tissues, this is readily understood; in _Diapheromera_
the young Insect is brownish on hatching, becomes green after feeding, and
turns brown again when the leaves do so. The ocelli, too, are said to be
very variable, and M‘Coy goes so far as to state[194] that they may be
either present or absent in different individuals though of the same
species and sex,—a statement so remarkable as to require minute
examination, though it is to some extent confirmed by the remarks of other
entomologists.
[Illustration: FIG. 154.—_Phyllium scythe_, female. Sylhet. (After
Westwood.)]
The resemblance presented by different kinds of Orthoptera to leaves is so
remarkable that it has attracted attention even in countries where Natural
History is almost totally neglected; in many such places the inhabitants
are firmly convinced that the Insects are truly transformed leaves, by
which they understand a bud developing into a leaf and subsequently
becoming a walking-leaf or Insect. To them the change is a kind of
metamorphosis of habit; it grew as a leaf and then took to walking.[195] It
is usually the tegmina that display this great resemblance to vegetable
structures, and there is perhaps no case in which the phenomenon is more
marked than it is in the genus _Phyllium_, the members of which occur only
in the tropical regions of the Old World, where they extend from Mauritius
and the Seychelles to the Fiji Islands—possibly even more to the East—and
have, it would appear, a peculiar penchant for insular life.
{268}[Illustration: FIG. 155.—_Phyllium scythe_, male. Sylhet. (After
Murray.)]
The genus _Phyllium_ constitutes by itself the tribe Phylliides. Although
the characters and affinities of this group have been only very
inadequately investigated, it will probably prove to be a very distinct and
isolated one. The species are not well known, but are probably numerous,
and the individuals are believed not to be rare, though the collections of
entomologists are very badly supplied with them. The resemblance of the
tegmina or front wings to leaves is certainly of the most remarkable
nature. During the early life the Insect does not possess the tegmina, but
it is said then to adapt itself to the appearance of the leaves it lives
on, by the positions it assumes and the movements[196] it makes. When
freshly hatched it is of a reddish-yellow colour. The colour varies at
different periods of the life, but "always more or less resembles a leaf."
After the young Insect has commenced eating the leaves it speedily becomes
bright green; and when the metamorphosis is completed the female Insect is
possessed of the leaf-like tegmina shown in Figs. 154, 156. Before its
death the specimen described by Murray passed "through the different hues
of a decaying leaf." Brongniart has had opportunities of observing one of
these leaf-Insects, and has, with the aid of M. Becquerel, submitted their
colouring matter to spectral analysis,[197] with the result of finding
{269}that the spectrum exhibits slight distinctions from that of solutions
of chlorophyll, but does not differ from that of living leaves. Mr. J. J.
Lister when in the Seychelles brought away living specimens of _Phyllium_;
and these becoming short of food, nibbled pieces out of one another just as
they might have done out of leaves. The Phasmidae are purely vegetable
feeders, and these specimens did not seriously injure one another, but
confined their depredations to the leaf-like appendages and expansions.
The males of this genus are totally different from the females; the
foliaceous tegmina being replaced by appendages that are not leaf-like,
while the posterior wings, which are large and conspicuous parts of the
body, have no leaf-like appearance (Fig. 155).
[Illustration: FIG. 156.—Alar organs and one side of thorax of _Phyllium
crurifolium_: A, tegmen; B, rudiment of wing; C, pronotum; D, anterior
division of mesonotum; E, posterior division; F, metanotum; _a_, _b_, _c_,
_d_, _e_, chief wing-nervures; _a_, mediastinal; _b_, radial; _c_, ulnar;
_d_, dividens?; _e_, plicata?.]
In the female _Phyllium_ the hind wings are not present, being represented
by a minute process (Fig. 156, B). The tegmen of the female _Phyllium_ is,
from various points of view, a remarkable and exceptional structure. It is
the rule that when there is in Insects a difference between the alar organs
of the two sexes it is the male that has them largest; this is the case in
_Phyllium_ so far as the hind wings are concerned, but in the fore-wings
the rule is departed from, the leaf-like tegmina of the female being very
much larger than the rudimentary wing-covers of the male. In Phasmidae it
is the rule that the tegmina are atrophied, even when the hind wings are
largely developed. This is the case in the male of _Phyllium_, but in the
female this normal condition is reversed. Although the alar organs of
Phasmidae have received hitherto but a small amount of attention, it is
probable that the female tegmen of _Phyllium_ is as peculiar
morphologically as it is in other respects. In Fig. 156 we give an accurate
representation of the chief nervures in the tegmen of a female _P.
crurifolium_. It is interesting to compare this with the diagrams we give
of the tegmina of a Blattid (Fig. 121) and of an Acridiid {270}(Fig. 167);
the tegmen of the _Phyllium_ is very different, the radial vein and all the
parts behind it being placed quite close to the posterior edge of the
structure. A similar view is taken by both Redtenbacher and Brauer. The
latter says,[198] "In _Phyllium_ (the walking-leaf) almost the whole of the
front wing is formed by the praecostal and subcostal fields; all the other
fields with their nervures, including even the costa, are compressed
towards the hind margin into a slender stripe. In the hind wing the costa
is, however, marginal." Unfortunately no examination appears to have been
made of the male tegmen, so that we do not know whether that of the female
differs from it morphologically as strongly as it does anatomically. It is,
however, clear that the tegmina of the female _Phyllium_ not only violate a
rule that is almost universal in the Insecta, but also depart widely from
the same parts of its mate, and are totally different—and, for a Phasmid,
in an almost if not quite unique fashion—from the other pair of alar organs
of its own body.
[Illustration: FIG. 157.—Egg of _Phyllium scythe_. (After Murray.) A, The
whole egg, natural size; A', magnified; B, the capsule broken, showing the
true egg inside, natural size; B', magnified.]
{271}[Illustration: FIG. 158.—Portion of a longitudinal section of the egg
capsule of _Phyllium crurifolium_: _a_, external; _b_, middle; _c_, inner
zones; _d_, elongate alveoli. × 100. (After Henneguy.)]
We have already alluded to the resemblance to seeds displayed by the eggs
of Phasmidae. The eggs of _Phyllium_ have been studied by several
entomologists, and their resemblance to seeds excites general astonishment.
Murray describes the egg-capsule of _Phyllium scythe_, and says: "It looks
uncommonly like some seeds; if the edges of the seed of _Mirabilis jalapa_
were rubbed off, the seed might be mistaken for the egg. The ribs are all
placed at equal distances, except two, which are wider apart, and the space
between them flatter, so that on the egg falling it rolls over till it
comes to this flatter side, and there lies.... At the top there is a little
conical lid, fitting very tightly to the mouth.... On removing the lid we
see a beautiful porcelain chamber of a pale French-white colour, bearing a
close resemblance to the texture of a hen's egg, but it is not calcareous,
and has more the appearance of enamel." The eggs of _P. crurifolium_ have
been examined by Joly and Henneguy; their account confirms that of Murray.
Henneguy adds that a prominent lozenge on the egg represents the surface by
which the achene of an umbelliferous plant is united to the column, and
that the micropyles are placed on this lozenge. The minute structure of the
capsule has also been examined by several entomologists; and Henneguy,[199]
who has described and figured some of the details of the capsule of _P.
crurifolium_, says, "Almost every botanist, on examining for {272}the first
time a section of this capsule, would declare that he is looking at a
vegetable preparation."
We may remark that, although there is difference of opinion on the point,
the evidence extant goes to show that the egg-capsules are formed in the
egg-tubes, only one egg being produced at a time in a tube,[200] the others
in it remaining quite rudimentary.
About 600 species of the family are known; there are only four or five
kinds found in Europe, and they are all confined to the south, only one of
them extending as far north as Central France. The males of these European
_Bacilli_ are extremely rare in comparison with the females, which are
common Insects. Phasmidae are of almost universal distribution in the warm
parts of the world, and even the species whose individuals are of large
size seem to be able to continue their existence in comparatively small
islands. Australia is perhaps the region where they are most largely
developed at present. Macleay says of _Podacanthus wilkinsoni_ that it is
rare in any part of Australia to find in the summer season a gum-tree
without a few of these Insects grazing on it; and occasionally this Insect
has been so abundant there that the trees for miles around have been
denuded of their foliage by it, and the dead and dying Insects have been
found lying beneath the trees almost in heaps. There are several Phasmidae
in New Zealand, all wingless forms, and different from those found in
Australia. In Brazil a species of the genus _Prisopus_ has the peculiar
habit of seeking shelter under the stones submerged in the mountain
streams; to enable it to do this it is remarkably constructed, the under
side of the body being hollowed, and various parts set with a dense fringe
of hairs; the Insect is supposed to expel the air from the body in order to
adhere to the upper surface of a stone, where it sits with its fore legs
extended in front of its head, which is directed against the current.
Attention has been called to a still more remarkable form said to be allied
to the Prisopi, by Wood-Mason,[201] who calls the Insect _Cotylosoma
dipneusticum_. This Insect is apparently known only by a single example of
the female sex; it is 3 or 4 inches in length, has rudimentary organs of
flight, and along the lower margins of the metathorax there are said to be
on each side five {273}conspicuous fringed plates of the nature of tracheal
gills; these coexist with open stigmata for aerial respiration, as in the
imago of _Pteronarcys_. The writer has examined this curious Insect, and
thinks it very doubtful whether the plates are branchiae at all. The
locality for this Insect is the island of Taviuni, not Borneo, as stated by
Wood-Mason. These and one or two Acridiidae are the only Insects of the
Order Orthoptera at present believed to possess aquatic habits.
[Illustration: FIG. 159.—_Calvisia atrosignata_, female. Tenasserim. (After
Brunner.)]
Although the number of species of Phasmidae is small in comparison with
what we find in many of the large families of Insecta, yet there is
probably no other family that equals it in multiplicity of form and
diversity of external appearance.
{274}[Illustration: FIG. 160.—_Eurycantha_ (_Karabidion_) _australis_,
male. Lord Howe's Island. (After Westwood.)]
[Illustration: FIG. 161.—_Anisomorpha pardalina._ Chili. (After Westwood.)]
_Karabidion_ (Fig. 160), a genus found in some of the islands of the
southern hemisphere, has the hind legs enormously thickened in the male.
Some Phasmids, e.g. _Orxines zeuxis_, have the hind wings marked and
coloured after the manner of butterflies or moths. _Lamponius laciniatus_
has an elaborately irregular outline, looking like a mass of moss, and some
species of _Bacteria_ are so very slender that the linear body is scarcely
equal in size to one of the legs it bears. Among the most interesting forms
are the Insects for which the genera _Agathemera_ and _Anisomorpha_ (Fig.
161) have been established; they are remarkably broad and short, have the
mesothorax but little elongated, with the tegmina attached to it in the
form of two short, thick, leathery lobes; while the wings are seen as marks
on the metanotum looking like a mere sculpture of the surface; these
Insects {275}have quite the appearance of larval forms, and it is worthy of
note that the elongation of the mesothorax, which is one of the most marked
features of the Phasmidae, is in these forms only very slight.
[Illustration: FIG. 162.—_Palophus centaurus._ Old Calabar. Half natural
size. (After Westwood.[202])]
{276}[Illustration: FIG. 163.—_Titanophasma fayoli._ Carboniferous
formation at Commentry. × ⅕. (From Zittel.)]
[Illustration: FIG. 164.—_Titanophasma fayoli_ (restoration). × ⅒.]
Some Insects said to belong to the genera _Phasma_ and _Bacteria_ have been
found in amber. A single Insect-fossil found in the Tertiary strata in
North America has recently been referred by Scudder to the family, and even
to a genus still existing in the New World—_Agathemera_; the fragment is,
however, so defective, and the characteristic points of the Phasmidae are
so little evident in it, that not much reliance can be placed on the
determination. No Phasmid has been unearthed from Mesozoic strata, so that,
with the exception of the fragment just mentioned, nothing that evidently
belongs to the Phasmidae has been discovered older than the remains
preserved in amber. In the Carboniferous layers of the Palaeozoic epoch
there are found remains of gigantic Insects that may possibly be connected
with our living Phasmidae. These fossils have been treated by Brongniart
and Scudder as forming a distinct family called Protophasmidae. The first
of these authors says[203] that our Phasmidae were represented in the
Carboniferous {277}epoch by analogous types differing in the nature of the
organs of flight: these ancient Insects were of larger size than their
descendants, being 25 to 50 centimetres long, and as much as 70 in spread
of wing. To this group are referred, on somewhat too inferential grounds,
the fossil wings found in the Carboniferous layers, and called by
Goldenberg _Dictyoneura_.
We reproduce from Zittel's handbook a figure (Fig. 162) of one of these
gigantic Insects, and add an attempt at a restoration of the same after the
fashion of Scudder (Fig. 163). From these figures it will be seen that the
relation to our existing Phasmidae must at best have been very remote.[204]
It will be noted that the larger of the two figures is on a ⅕ scale.
The classification of Phasmidae was left in a very involved state by Stål,
but has recently been brought into a more satisfactory condition by Brunner
von Wattenwyl. We give a translation of his table of the tribal
characters:—
1. Tibiae beneath carinate to the apex, without an apical area.
2. Antennae much longer than the front femora, many jointed, the joints
being above 30 in number and only distinct at the base and towards the
apex.[205]
3. Median [true first abdominal] segment much shorter than the
metanotum.[206] The species all apterous.
4. The anal segment of the males roof-like, more or less bilobate.
The female has a supra-anal lamina. The species inhabit the Old
World. Tribe 1. LONCHODIDES (Fig. 148, _Lonchodes nematodes_.)
4′. The anal segment of the males arched, straight behind. No
supra-anal lamina in the female. The species are American. Tribe 2.
BACUNCULIDES.
3′. Median segment as long as, or longer than the metanotum. Species
with the male or both sexes winged.
4. Females apterous or rarely possessed of short wings.[207] Males
winged. Femora dentate beneath, or lobed, or at least armed with
one tooth. Species occur both in America and in the Old World.
Tribe 3. BACTERIIDES. (Fig. 162, _Palophus centaurus_.) {278}4′.
Each sex winged. Femora smooth beneath. The species belong to the
Old World. Tribe 4. NECROSCIDES. (Fig. 159, _Calvisia
atrosignata_.)
2′. Antennae (at any rate in the females) shorter than the front
femora, the joints distinct, not more than 28 in number. The species
belong to the Old World.
3. Median segment shorter than the metanotum. Apterous species. Cerci
plump. Tribe 5. CLITUMNIDES. (Fig. 160, _Eurycantha australis_.)
3′. Median segment longer than the metanotum. Species usually winged.
Cerci (except in some genera of the group _Platycraninae_) flattened,
elongate. Tribe 6. ACROPHYLLIDES. (Fig. 153, _Cyphocrania aestuans_.)
1′. Tibiae furnished beneath with a triangular apical area.
2. Antennae many jointed, longer than the front femora.
3. Median segment shorter than the metanotum. Apterous species.[208]
4. Either head, thorax, or legs spiny or lobed. Tribe 7.
CLADOMORPHIDES. (Fig. 149, _Heteropteryx grayi_.)
4′. Head, thorax and legs unarmed. Tribe 8. ANISOMORPHIDES. (Fig.
161, _Anisomorpha pardalina_.)
3′. Median segment longer than the metanotum.
4. Claws unarmed. Tegmina lobe-like, either perfectly developed or
entirely absent. The winged species are all American, the apterous
are both African and Australian. Tribe 9. PHASMIDES.
4′. Claws toothed on the inner side. Tegmina spine-like. Wings well
developed. The species are Asiatic. Tribe 10. ASCHIPASMIDES. (Fig.
150, _Aschipasma catadromus_.)
2′. Antennae shorter than the anterior femora,[209] formed of not more
than 20 joints. Old World species.
3. Body slender. Apterous. Tribe 11. BACILLIDES.
3′. Body very broad, lamina-like. Either wings or tegmina present.
Tribe 12. PHYLLIIDES. (Fig. 155, _Phyllium scythe_, male; Fig. 154,
_idem._, female.)
{279}CHAPTER XII
ORTHOPTERA _CONTINUED_—ACRIDIIDAE
FAM. VI. ACRIDIIDAE—LOCUSTS AND GRASSHOPPERS.
_Orthoptera with the hind legs differing from the others by being more
elongate and having their femora broader near the base. Antennae short,
with less than 30 joints. No exserted ovipositor in female. Tarsi short,
with three distinct joints. The auditory organ placed on the side of the
upper part of the first abdominal segment._
[Illustration: FIG. 165.—_Tryxalis nasuta_, female. Natural size. Europe.]
We commence the consideration of the saltatorial Orthoptera with the family
Acridiidae. It includes the grasshoppers of our native fields as well as
the destructive migratory locusts of foreign countries, and is the most
numerous in species and individuals of any of the Orthopterous families.
Our native grasshoppers, though of small size, give a very good idea of the
Acridiidae. Active little Insects, with large head, conspicuous {280}eyes,
laterally somewhat compressed body, long hind legs with femur directed
upwards and backwards, the knee-joint forming an acute angle, the organs of
flight pressed to the sides of the body, our common grasshoppers represent
the Acridiidae quite as truly as do the gigantic exotic forms, some of
which measure 9 or 10 inches across the expanded wings.
[Illustration: FIG. 166.—Front of head of _Porthetis_ sp. Transvaal.]
The large head is immersed behind in the thorax; the front is deflexed, or
even inflexed, so as to be placed in a plane at an acute angle with that of
the vertex (Fig. 165); the compound eyes are placed at the sides of the
head and rather widely separated; in front there are three small ocelli.
Two of these are placed one on each side close to the eye between the eye
and the base of the antenna; the third ocellus being in the middle just in
front of the insertion of the antennae, between the edges of the margined
space that usually runs down the middle of the front. The positions of
these ocelli and the shape of the front and upper parts of the head are of
importance in the classification of the family; the ocelli vary much in
their development, being in some species beautifully clear and prominent
(Fig. 166), while in others they are small, not easily detected, apparently
functionally imperfect. The antennae are never very long, are sometimes
compressed and pendent from the front of the head. The parts of the mouth
are very large. The prothorax is much arched; it is often carinate or
crested along the middle of the notum; this part is frequently prolonged
backwards, forming a sort of hood over the base of the wings; the surface
may be rugged or warty, forming in some species inexplicable structures;
the legs are widely separated, all of them being placed at the sides of the
body; the edge of the pronotum is distinct and situate close to the base of
the leg; the prosternum frequently bears a large projection extending
directly downwards between the front legs. The mesothorax is short, its
chief sternal piece is very broad, the middle legs being very widely
separated. The metathorax is larger; its sternal plate usually exhibits
behind a sort of embrasure filled up by a portion of the first ventral
plate.
{281}[Illustration: FIG. 167.—Alar organs of Acridiidae (_Bryodema
tuberculata_). A, Left tegmen; B, left wing: _ar.med_, area mediastina;
_ar.sc_, area scapularis; _ar.disc_, area discoidalis; _ar.an_, anal area;
_v.m_, vena mediastina; _v.r_, vena radialis; _v.r.a_, vena radialis
anterior; _v.r.m_, vena radialis media; _v.r.p_, vena radialis posterior;
_v.i_, vena intercalata; _v.u.a_, vena ulnaris anterior; _v.u.p_, vena
ulnaris posterior; _v.d_, vena dividens; _v.pl_, vena plicata. (After
Brunner.)]
The hind body is elongate, and shows distinctly eight dorsal segments,
behind which are the pieces forming—in the female, the fossorial organs
which replace an ovipositor—in the male, the modified parts connected with
the terminal segment. The alar organs (Fig. 167) exhibit, according to
Brunner, the same areas as we have described in Blattidae. According,
however, to Redtenbacher[210] the tegmina of the Acridiidae and other
saltatorial Orthoptera differ from those of the cursorial group (with the
exception of the Phasmidae) in that they possess a praecostal field, due to
the fact that the vein which in the Cursoria is costal, _i.e._ forms the
front margin, in the Saltatoria lies, on the contrary, in the field of the
wing. If this view be correct the mediastinal area of Brunner is not
homologous in the two divisions. The tegmina are long and comparatively
narrow; they are of firm parchment-like texture, with several longitudinal
veins, which divide beyond the middle, so as to become more numerous as
they reach the extremity of the wing; there is much reticulation, dividing
the surface into numerous small cells. The hind wings are much more ample,
and of more delicate texture; the longitudinal veins fork but little, the
numerous cross veinlets are fine. In repose the hind wings fold together in
a fan-like manner, and are entirely concealed by the upper wings. The front
and middle legs are similar and small, the coxae are quite small, and do
not completely fill the articular cavities, which are partly covered by
membrane; all the tarsi are three-jointed. The basal joint, when looked at
beneath, is seen to bear three successively placed pads, so that from
beneath the tarsi look as if they were five-jointed {282}(Fig. 185, C). The
hind legs are occasionally very long; their femora, thicker towards the
base, are generally peculiarly sculptured, bearing longitudinal ridges or
grooves, which are more or less spinose, and are also very frequently
marked with short parallel lines meeting a central longitudinal line at
similar angles, so as to give rise to a well-marked pattern; where the legs
are broader the pattern is more complex (Fig. 168). The long tibiae bear
two rows of spines on their upper or posterior edge; this part of the hind
leg can be completely bent in under the femur. The stigmata consist of one
prothoracic, one metathoracic, and eight abdominal pairs.
[Illustration: FIG. 168.—Hind leg of _Porthetis_ sp. Transvaal.]
In reference to the ocelli, which are shown in Fig. 166, we may remark that
the Acridiidae is one of the large groups of Insects in which the
coexistence of compound and single eyes is most constant, though in some of
the wingless forms the ocelli are very imperfect. We know at present of
nothing in the habits of Acridiidae to render two kinds of eyes specially
necessary. We shall subsequently see that a similar condition in regard to
the function of hearing is believed to exist in this family.
Acridiidae are remarkable amongst the Orthoptera for the possession of air
sacs or vesicular dilatations in the interior of the Insect in connexion
with the tracheae (Fig. 176). Such vesicles are found in many of the higher
winged Insects, but not in larval forms, or in those that are destitute of
powers of flight.[211] They, no doubt, assist the Insect in its movements
in the air. The body of a large grasshopper or locust is naturally of
considerable weight, and it is more than probable that true flight can only
be accomplished when these vesicles are dilated and filled with air. The
exact mode in which the sacs are dilated is not known; possibly it may be
accomplished by the elasticity of the structure of the vesicles coming into
action when the other contents of the {283}body are not completely
developed, or are temporarily diminished. Although air vessels are absent
in the neighbouring groups of Orthoptera, Dufour says they are present even
in apterous forms of Acridiidae, but he gives no particulars.[212] Packard
has given an account[213] of the arrangement of these remarkable sacs in
the Rocky Mountain Locust. He finds that there are two sets: a thoracic
group, consisting of a pair of very large size, with which are connected
some smaller sacs placed in the head; and an abdominal set, which forms a
very remarkable series. The figures we give (Fig. 176, A, B) show that
these sacs are of such large size that if fully distended they must
interfere with the development of the ovaries, and that they must be
themselves greatly diminished, if not obliterated, by the distension of the
alimentary canal. We may look on them as only coming into full play when
the normal distension of the canal is prevented, and there is only small
development of the reproductive organs. Under such circumstances the locust
becomes a sort of balloon, and migrates. In addition to the air sacs there
are many dilatable tracheae, placed chiefly in parts of the body where
there is not space for the large air sacs. These are, for the sake of
clearness, omitted from our figure.
The ganglia constituting the brain are simpler in Acridiidae than they are
in the higher Insects, such as bees and wasps, and have been specially
studied by Packard[214] and Viallanes.[215] The other ganglia of the
nervous cord are eight in number, three thoracic and five abdominal.
[Illustration: FIG. 169.—Ovaries of _Oedipoda caerulescens_: _a_, calyx;
_b_, its gut-like appendage; _c_, sebific gland; _d_, termination of body.
(After Dufour.)]
The salivary glands are small. The alimentary canal is capacious but not
coiled. It has no gizzard, but the crop has a peculiar structure,
apparently as a substitute. There are diverticula connected with the true
stomach. The Malpighian tubes are elongate {284}and extremely numerous. The
pair of testes is united in a single envelope. The form and arrangement of
the ovaries is remarkable (Fig. 169); the egg-tubes are united by the
convergence of their terminal threads into a single mass; outside of each
ovary there extends a large calyx, into which the tubes open; each calyx is
prolonged at its extremity, and forms a long, convoluted tube.
[Illustration: FIG. 170.—Inner face of femur of _Stenobothrus_, male,
showing line, _a-a_, of musical beads. (After Landois, magnified three
times.)]
Acridiidae possess structures for the production of sound, together with
others that are, no doubt, for hearing. The chirping of grasshoppers is
accomplished by rubbing together the outer face of the upper wing and the
inner face of the hind femur. This latter part bears a series of small
bead-like prominences placed on the upper of the two lower ridges that run
along the side that is nearest to the body (Fig. 170); the tegmen or
wing-case has projecting veins, one of which is slightly more prominent,
and has a sharp edge; by scraping this edge over the beads of the femur the
wing is thrown into a state of vibration and a musical sound is produced.
The apparatus for producing sound was for long supposed to be confined to
the male sex of grasshoppers; it was indeed known that females made the
movements appropriate for producing music, but as they appeared to be
destitute of instruments, and as no sound was known to follow from their
efforts, it was concluded that these were merely imitative. Graber has,
however, discovered[216] that rudimentary musical organs do exist in the
females of various species of _Stenobothrus_ (Fig. 171, B). It is true that
in comparison with those of the male (Fig. 171, A) they are minute, but it
would appear that they are really phonetic, though we can hear no sounds
resulting from their use.
[Illustration: FIG. 171.—A, Some of the knobs projecting from the surface
of the femur of _Stenobothrus melanopterus_, male; B, same of the female.
Highly magnified. (After Graber.)]
Graber considers that the musical pegs of Acridiidae are {285}modified
hairs, and he states that in certain females the stages intermediate
between hair and peg can be found. There is apparently much variety in the
structure of these instruments in different species, and even in
individuals of the same species. In _Stenobothrus lineatus_, instead of
pegs, the instrument consists of raised folds.
In some of the aberrant forms of Acridiidae—certain Eremobiides and
Pneumorides—the males are provided with sound-producing instruments
different to those we have described, both as regards situation and
structure.
[Illustration: FIG. 172.—Middle of body of _Pachytylus nigrofasciatus_, to
show tympanum, _e_. (After Brunner.)]
[Illustration: FIG. 173.—Mecostethus grossus: A, Insect with wings
expanded; B, profile of head and prothorax. (After Brunner.)]
If the dorsal aspect of the first segment of the hind body of an Acridian
Insect be carefully examined there may be seen in the majority of species
an organ which has somewhat the appearance of an ear (Fig. 172), and which
there is great reason for believing to be really an organ of that nature.
It is situate a little over the articulation of the hind leg, very close to
the spot where the sound is, as above described, produced. There are three
forms of these Acridian ears as described by Brunner:[217] (1) a membrane
surrounded by a rim; (2) the membrane somewhat depressed, a portion of the
segment projecting a little over it; (3) the depression very strongly
marked, and the sides projecting over it so much that all that is seen
externally is a sort of broad slit with a cavity beneath it. This last is
the condition in which the ear exists in the genera _Mecostethus_ (Fig.
173) and _Stenobothrus_, which are among our few native grasshoppers. On
minute examination this ear proves to consist of a tympanum supplied
internally with nerve and ganglion in addition to {286}muscles, and
tracheal apparatus of a complex nature; it is no doubt delicately sensitive
to some forms of vibration. Unlike the stridulating organ, these ears exist
in both sexes; they are found in a great majority of the species of
Acridiidae. The forms in which the ears are absent are usually at the same
time wingless and destitute of organs of stridulation; but, on the other
hand, there are species—some of them wingless—that are, so far as is known,
incapable of stridulation and yet possess these ears.
It is, indeed, a matter of great difficulty to decide as to the exact
function of these ear-like acoustic organs, which, we may remind the
reader, are peculiar to the saltatorial Orthoptera, and we must refer for a
full discussion of the subject to Graber's masterly works,[218] contenting
ourselves with a brief outline, which we may commence by saying that the
Orthoptera with ears are believed to be sensitive to sounds by means other
than these organs. This suggests that the latter exist for some purpose of
perception of special sound. But if so what can this be? Only the males
possess, so far as we know, effective sound-producing organs, but both
sexes have the special ears; moreover, these structures are present in
numerous species where we do not know of the existence of phonetic organs
in either sex. Thus it appears at present impossible to accept these organs
as being certainly special structures for the perception of the music of
the species. It is generally thought that the females are charmed by the
music of the males, and that these are stimulated to rivalry by the
production of the sounds; and Dufour[219] has suggested that this process
reacts on the physiological processes of the individual. There has not been
a sufficient amount of observation to justify us in accepting these views,
and they do not in any way dispose of the difficulty arising from the
existence of the acoustic organs in species that do not, so far as we know,
produce special sounds. It is possible that the solution of the difficulty
may be found in the fact that these apparently dumb species do really
produce some sound, though we are quite ignorant as to their doing so. It
is well known that sounds inaudible to some human ears are perfectly
distinct to others. Tyndall, in his work on Sound, has illustrated this by
a fact that is of special interest from our present point of view.
"Crossing {287}the Wengern Alp with a friend," he says, "the grass on each
side of the path swarmed with Insects which to me rent the air with their
shrill chirruping. My friend heard nothing of this, the Insect world lying
beyond his limit of audition." If human ears are so different in their
capacities for perceiving vibrations, it of course becomes more probable
that auditory organs so differently constituted as are those of Insects
from our own may hear sounds when the best human ear can detect nothing
audible. On the whole, therefore, it would appear most probable that the
Orthoptera provided with acoustic organs, and which we consider dumb, are
not really so, but produce sounds we cannot hear, and do so in some manner
unknown to us. If this be the case it is probable that these ears are
special organs for hearing particular sounds.
Scudder, who has given considerable attention to the subject of Orthopteran
music, says that in N. America "the uniformity with which each species of
_Stenobothrus_ plays its own song is quite remarkable. One kind,
_Stenobothrus curtipennis_, produces about six notes per second, and
continues them from one and a half to two and a half seconds; another, _S.
melanopleurus_, makes from nine to twelve notes in about three seconds. In
both cases the notes follow each other uniformly, and are slower in the
shade than in the sun."
Some of the species of Acridiidae, it should be noticed, produce a noise
during their flights through the air, due to the friction of the wings;
whether this has a definite importance, or whether it may be entirely
incidental, has scarcely yet been considered.
Information of a satisfactory kind as to the post-embryonic development of
the Acridiidae is but scanty. We have represented in Fig. 84, A, the
condition in which a migratory locust, _Schistocerca peregrina_, leaves the
egg, and we will here complete the account of its growth; following
Brongniart,[220] whose statement is confirmed by Lestage and other
naturalists. Immediately on leaving the egg the young locust casts its
skin, and is then of a clear green colour, but it rapidly becomes brown,
and in twelve hours is black. At this early age the gregarious instinct,
possessed by this and some other species of Acridiidae, becomes evident. In
six days the individual undergoes a second moult, after which it is black,
spotted and banded with white, and with a rose-coloured streak on each side
of the hind body. The {288}third ecdysis occurs in six or eight days after
the second; the rose colour becomes more distinct, and the head is of a
brown tint instead of black. After eight days the fourth ecdysis occurs;
the creature is then about 35 millimètres long; its colour has much
changed, the position of the markings is the same, but the rose colour is
replaced by citron yellow, the line of the spiracles is marked with white,
and at this time the creature has the "first rudiments of wings," and is
very voracious. In ten days another ecdysis takes place, the yellow colour
is more vivid, the prothorax is definitely speckled with white, and the
hind body is increasing much in size. In fifteen or twenty days the sixth
moult occurs, and the Insect appears in its perfect form; the large tegmina
now present are marked with black in the manner so well known, and the
surface generally is variegated with bluish and rosy marks. Although this
is the colour in Algeria, yet apparently it is not so farther south; the
Insects that arrive thence in the French colony are on some occasions of a
different colour, viz. reddish or yellowish, those of this latter tint
being, it is believed, older specimens of the reddish kind. M. Brongniart
points out that some Phasmidae—of the _Phyllium_ group—undergo an analogous
series of colour-changes in the course of the individual development,
though other species do not.
[Illustration: FIG. 174.—Development of wings in _Caloptenus spretus_: the
upper row gives a lateral view of the thoracic segments, and the lower row
a dorsal view of these segments; 1, second instar; 2, third instar; 3,
fourth instar; 4, fifth instar. (After Riley.) _t_, tegmen; _w_, wing.]
{289}[Illustration: FIG. 175.—_Caloptenus spretus._ North America. A, Newly
hatched, much magnified; B, adult, natural size. (After Riley.)]
Riley and Packard have given an account[221] of some parts of the
post-embryonic development of the Rocky Mountain Locust, which enables us
to form a satisfactory conception of the stages of development of the
wings. Fig. 175, A, represents the first instar, the young locust, just
emerged from the egg and colourless. Fig. 174 shows some of the subsequent
stages of development of the wings, the upper line of figures giving a
profile view of the thoracic segments, and the lower line showing their
dorsal aspects; 1 shows the condition of the parts in the second instar,
the chief difference from the first instar being the development of colour;
in the third instar there is an evident slight development of the future
alar organs, exhibited chiefly in the outgrowth and lobing of the free
posterior angles of the meso- and metanota, as shown in Fig. 174, 2. After
the third moult there is a great difference; the instar then disclosed—the
fourth—has undergone a considerable change in the position of the meso- and
metathoraces, which are thrust forward under the pronotum; this has become
more enlarged and hood-like (Fig. 174, 3); at the same time the
wing-rudiments have become free and detached, the metathoracic pair being
the larger, and overlapping the other pair. The fifth instar (Fig. 174, 4)
differs but little from the fourth, except in the larger size of the
pronotum and wing-rudiments. The sixth—shown in Fig. 175, {290}B—is the
perfect Insect, with the alar organs free and large, the prothorax much
changed in form, the colour different. From the above it will be seen that
the chief changes occurred at the third and fifth ecdyses, after each of
which a considerable difference in the form of the Insect was revealed. In
the first three instars the sexes can scarcely be distinguished, in the
fourth they are quite distinct, and in the fifth coupling is possible,
though usually it does not occur till the final stage is attained.
The discovery that Orthoptera change their colours in the course of their
development, and even after they have become adult, is important, not only
from a physiological point of view, but because it throws some light on the
questions as to the number of species and the geographical distribution of
the migratory locusts, as to which there has existed a great confusion.
The Acridiidae are considered to be exclusively vegetable feeders, each
individual consuming a very large quantity of food. The mode in which the
female deposits her eggs has been described by Riley,[222] and is now
widely known, his figures having been frequently reproduced. The female has
no elongate ovipositor, but possesses instead some hard gonapophyses
suitable for digging purposes; with these she excavates a hole in the
ground, and then deposits the eggs, together with a quantity of fluid, in
the hole. She prefers hard and compact soil to that which is loose, and
when the operation is completed but little trace is left of it. The fluid
deposited with the eggs hardens and forms a protection to them,
corresponding to the more definite capsules of the cursorial Orthoptera.
The details of the process of oviposition and of the escape of the young
from their imprisonment are of much interest. According to Künckel
d'Herculais[223] the young _Stauronotus maroccanus_ escapes from the
capsule by putting into action an ampulla formed by the membrane between
the head and the thorax; this ampulla is supposed to be dilated by fluid
from the body cavity, and is maintained in the swollen condition by the
Insect accumulating air in the crop beneath it. In order to dislodge the
lid of the capsule, six or seven of the young ones inside combine their
efforts to push it off by means of their ampullae. The ampulla
{291}subsequently serves as a sort of reservoir, by the aid of which the
Insect can diminish other parts of the body, and after emergence from the
capsule, penetrate cracks in the earth so as to reach the surface.
Immediately after doing this the young _Stauronotus_ moults, the skin it
casts being called by Künckel an amnios. The cervical ampulla reappears at
subsequent moults, and enables the Insect to burst its skin and emerge from
it.
The process is apparently different in _Caloptenus spretus_, which,
according to Riley, ruptures the egg-shell and works its way out by the
action of the spines at the apex of the tibiae. This latter Insect when it
emerges moults a pellicle, which Riley considers to be part of the
embryonic membranes.
Riley states that a female of _Caloptenus spretus_ makes several
egg-masses. Its period of ovipositing extends over about 62 days, the
number of egg-masses being four and the total number of eggs deposited
about 100. The French naturalists have recently observed a similar fact in
Algeria, and have ascertained that one of the migratory
locusts—_Schistocerca peregrina_—may make a deposit of eggs at more than
one of the places it may alight on during its migration.
It has been ascertained that the eggs of Acridiidae are very nutritious and
afford sustenance to a number of Insects, some of which indeed appear to
find in them their sole means of subsistence. Beetles of the family
Cantharidae frequent the localities where the eggs are laid and deposit
their eggs in the egg-masses of the Orthoptera, which may thus be entirely
devoured. Two-winged flies of the family Bombyliidae also avail themselves
of these eggs for food, and a mite is said to be very destructive to them
in North America. Besides being thus destroyed in enormous quantities by
Insects, they are eaten by various birds and by some mammals.
Most of the Insects called locusts in popular language are members of the
family Acridiidae, of which there are in different parts of the world very
many species, probably 2000 being already known. To only a few of these can
the term Locust be correctly applied. A locust is a species of grasshopper
that occasionally increases greatly in number, and that moves about in
swarms to seek fresh food. There are many Orthoptera that occasionally
greatly increase in numbers, and that then extend their usual area more or
less; and some Acridiidae multiply {292}locally to a great extent—very
often for one or two seasons only,—and are then called locusts. The true
migratory locusts are species that have gregarious habits strongly
developed, and that move over considerable distances in swarms. Of these
there are but few species, although we hear of their swarms in many parts
of the world.
The migratory locusts do much more damage than the endemic species. In
countries that are liable to their visitations they have a great influence
on the prosperity of the inhabitants, for they appear suddenly on a spot in
huge swarms, which, in the space of a few hours, clear off all the
vegetable food that can be eaten, leaving no green thing for beast or man.
It is difficult for those who have not witnessed a serious invasion to
realise the magnitude of the event. Large swarms consist of an almost
incalculable number of individuals. A writer in _Nature_[224] states that a
flight of locusts that passed over the Red Sea in November 1889 was 2000
square miles in extent, and he estimated its weight at 42,850 millions of
tons, each locust weighing 1/16 of an ounce. A second similar, perhaps even
larger, flight was seen passing in the same direction the next day. That
such an estimate may be no exaggeration is rendered probable by other
testimony. From official accounts of locusts in Cyprus we find that in
1881,[225] up to the end of October, 1,600,000,000 egg-cases had been that
season collected and destroyed, each case containing a considerable number
of eggs. By the end of the season the weight of the eggs collected and made
away with amounted to over 1300 tons, and, notwithstanding this, no less
than 5,076,000,000 egg-cases were, it is believed, deposited in the island
in 1883.
When we realise the enormous number of individuals of which a large swarm
of locusts may consist we can see that famine is only a too probable
sequence, and that pestilence may follow—as it often has done—from the
decomposition of the bodies of the dead Insects. This latter result is said
to have occurred on some occasions from locusts flying in a mass into the
sea, and their dead bodies being afterwards washed ashore.
Locust swarms do not visit the districts that are subject to their
invasions every year, but, as a rule, only after intervals of a
considerable number of years. It has been satisfactorily {293}ascertained
that in both Algeria and North America large swarms occur usually only at
considerable intervals. In North America Riley thought[226] the average
period was about eleven years. In Algeria the first invasion that occurred
after the occupation of the country by the French was in 1845, the second
in 1864, the third in 1866, since which 1874 and 1891 have been years of
invasion. These breaks seem at first strange, for it would be supposed that
as locusts have great powers of increase, when once they were established
in any spot in large numbers, there would be a constant production of
superfluous individuals which would have to migrate as regularly as is the
case with swarms of bees. The irregularity seems to depend on three facts:
viz. that the increase of locusts is kept in check by parasitic Insects;
that the eggs may remain more than one year in the ground and yet hatch out
when a favourable season occurs; and that the migratory instinct is only
effective when great numbers of superfluous individuals are produced.
It is not known that the parasites have any power of remaining in abeyance
as the locust eggs may do; and the bird destroyers of the locusts may
greatly diminish in numbers during a year when the Insects are not
numerous; so that a disproportion of numbers between the locusts and their
destroyers may arise, and for a time the locusts may increase rapidly,
while the parasites are much inferior to them in numbers. If there should
come a year when very few of the locusts hatch, then the next year there
will be very few parasites, and if there should then be a large hatching of
locusts from eggs that have remained in abeyance, the parasites will not be
present in sufficient quantity to keep the destructive Insects in check;
consequently the next year the increase in number of the locusts may be so
great as to give rise to a swarm.
It is well established that locusts of the migratory species exist in
countries without giving rise to swarms, or causing any serious injuries;
thus _Pachytylus cinerascens_—perhaps the most important of the migratory
locusts—is always present in various localities in Belgium, and does not
give rise to swarms. When migration of locusts does occur it is attended by
remarkable manifestations of instinct. Although several generations may
elapse without a migration, it is believed that the locusts when {294}they
migrate do so in the direction taken by predecessors. Their movements are
to a large extent dependent on the wind, and it is said that they make
trial flights to ascertain its direction. When on the wing probably very
little muscular effort is necessary. Their bodies contain elastic air sacs
in communication with the tracheae, and at the time of flight it may be
presumed that the body is comparatively empty, food being wanting, and the
internal organs of reproduction, which occupy a large space when in
activity, yet undeveloped, hence the sacs have full room for expansion, as
explained on p. 283. Thus the Insects exert but little effort in their
aerial movements, and are, it is believed, chiefly borne by the wind.
Should this become unfavourable it is said that they alight and wait for a
change.
The most obscure point in the natural history of the migratory locusts
appears to be their disappearance from a spot they have invaded. A swarm
will alight on a locality, deposit there a number of eggs, and then move
on. But after a lapse of a season or two there will be few or none of the
species present in the spot invaded. This appears to be partly due to the
young locusts dying for want of food after hatching; but in other cases
they again migrate after growth to the land of their ancestors. The latter
fact is most remarkable, but it has been ascertained by the U.S.
Entomological Commission that these return swarms do occur.
[Illustration: FIG. 176.—Portions of body of _Caloptenus spretus_ to show
some of the air-sacs. (Modified from Packard.) A, Dorsal aspect of anterior
parts; B, lateral aspect of posterior parts of body; _a_, enlargements of
tracheae in head; _b_, pair of large sacs in thorax; _c_, sacs on the
tracheal trunks of abdomen; _s_, spiracles.]
In South Africa it would appear that the movements of the migratory locusts
are frequently made before the Insects have acquired their wings. Mrs.
Barber, in an account of "Locusts and Locust-Birds in South Africa,"[227]
has illustrated many points in the {295}Natural History of these Insects.
The South African species manifests the gregarious and migratory
disposition when the individuals are quite young, so that they travel in
flocks on foot, and are called by the Dutch "Voetgangers." After hatching,
the various families of young amalgamate, so that enormous numbers come
together. Having denuded the neighbourhood of all its food-supplies, they
move off in search of fresh crops and pastures new. They take advantage of
roads, and sometimes a good many miles will be traversed in a day; they
proceed by means of short leaps, rapidly repeated. When the "Voetgangers"
are thus returning northwards towards the lands in the interior from which
their progenitors departed, no obstacles can stay their course. Forests or
rivers may intervene, diverting them for a while from their line of march,
but they succeed ultimately in continuing their journey to the interior.
The manner in which these wingless locusts occasionally cross broad rivers
is interesting, as it has some bearing on the difficult question of the
possibility of winged locusts crossing seas of considerable width. Mrs.
Barber refers to an instance that took place on the Vaal River in the
spring of the year 1871, shortly after the discovery of the Diamond-fields.
The country was at that time swarming with young locusts; every blade of
grass was cleared off by them. One day a vast swarm of the "Voetgangers"
made their appearance on the banks of the Vaal River; they appeared to be
in search of a spot for crossing, which they could not find, the river
being somewhat swollen. For several days the locusts travelled up the
stream; in the course of doing this they paused for some time at an abrupt
bend in the river where a number of rocks were cropping out, as if in doubt
whether to attempt a passage at this place. They, however, passed on, as if
with the hope of finding a better ford; in this apparently they were
disappointed, for three days afterwards they returned to the same bend of
the river, and there plunged in vast multitudes into the stream, where,
assisted by a favourable current and the sedges and water-plants which grew
upon the projecting rocks, they managed to effect a crossing, though great
numbers were drowned and carried away by the flooded river. Mrs. Barber
adds that "Voetgangers" have been known to attempt the passage of the
Orange River when it was several hundred yards in breadth, pouring their
vast swarms into the flooded stream regardless of the consequences, until
they {296}became heaped upon each other in large bodies. As the living mass
in the water accumulated, some portions of it were swept away by the strong
current from the bank to which they were clinging, and as the living
locusts tightly grasped each other and held together, they became floating
islands, the individuals continually hopping and creeping over each other
as they drifted away. Whether any of the locust-islands succeeded in
reaching the opposite bank is unknown; probably some of them were drifted
on land again. They are by no means rapid swimmers; they do not perish
easily in the water when in masses, their habit of continually changing
places and hopping and creeping round and round upon each other being very
advantageous as a means of preservation. It is a common practice for the
young locusts to form a bridge over a moderately broad stream by plunging
indiscriminately into it and holding on to each other, grappling like
drowning men at sticks or straws, or, in fact, anything that comes within
their reach, and that will assist in floating them; meanwhile those from
behind are eagerly pushing forward over the bodies of those that are
already in the stream and hurrying on to the front, until at length by this
process they reach the opposite bank of the river; thus a floating mass of
living locusts is stretched across the stream, forming a bridge over which
the whole swarm passes. In this manner few, comparatively speaking, are
drowned, because the same individuals do not remain in the water during the
whole of the time occupied by the swarm in crossing, the Insects
continually changing places with each other; those that are beneath are
endeavouring to reach the surface by climbing over others, whilst those
above them are, in their turn, being forced below. Locusts are exceedingly
tenacious of life, remaining under water for a considerable time without
injury. An apparently drowned locust will revive beneath the warm rays of
the sun, if by chance it reaches the bank or is cast on shore. Mrs. Barber
relates an interesting case where the instinct of the "Voetgangers" was at
fault, they plunging into a river from a steep sandy bank, only to find
another similar sandy precipice on the other side. On this they could gain
no footing, and all perished in the stream, where they putrefied, and
caused the death of the fish, which floated likewise on the surface; so
powerful were the effluvia produced that no one was able to approach the
river.
{297}Locusts are able to travel considerable distances, though how far is
quite uncertain. Accounts vary as to their moving by night. It has,
however, been recently proved that they do travel at night, but it is not
ascertained how long they can remain in the air without descending. The
ocean is undoubtedly a source of destruction to many swarms; nevertheless,
they traverse seas of considerable width. They have been known to reach the
Balearic Islands, and Scudder gives[228] a well-authenticated case of the
occurrence of a swarm at sea. On the 2nd of November 1865 a ship on the
voyage from Bordeaux to Boston, when 1200 miles from the nearest land, was
invaded by a swarm of locusts, the air and the sails of the ship being
filled with them for two days. The species proved to be _Acridium_
(_Schistocerca_) _peregrinum_. This is an extraordinary case, for locusts
do not fly with rapidity, being, indeed, as we have remarked, chiefly
carried by the wind. Possibly some species may occasionally rest on the
water at night, proceeding somewhat after the fashion of the "Voetgangers"
when passing over rivers as described by Mrs. Barber. In Sir Hans Sloane's
history of Jamaica an account of an occurrence of this kind is given on the
authority of Colonel Needham, who states that in 1649 locusts devastated
the island of Tenerife, that they were seen to come from Africa when the
wind was blowing thence, that they flew as far as they could, then alighted
on the water, one on the other, till they made a heap as big as the
greatest ship, and that the next day, being refreshed by the sun, they took
flight again and landed in clouds at Tenerife. De Saussure says[229] that
the great oceans are, as a rule, impassable barriers, and that not a
species of the tribe Oedipodides has passed from the Old World to the New.
It is, however, possible that _Acridium peregrinum_, of the tribe
Acridiides, may have originally been an inhabitant of America, and have
passed from thence to the Old World.
{298}[Illustration: FIG. 177.—European migratory locust, _Pachytylus
cinerascens_ ♀.]
The species of Acridiidae that have been ascertained to be migratory are
not numerous.[230] The most abundant and widely distributed of them is
_Pachytylus cinerascens_ (Fig. 177), which has invaded a large part of the
Eastern hemisphere, extending from the Atlantic Ocean to China. It exists
in numerous spots in the Oriental region and the Asiatic Archipelago, and
even in New Zealand. It is the commoner of the locusts of Europe. Its
congener, _P. migratorius_, is much less widely distributed, its migrations
being, according to de Saussure, limited to Turkestan and Eastern Europe. A
third species, _P. migratorioides_, inhabits Eastern Africa, and a variety
of it is the "Yolala" or locust of Madagascar. Mr. Distant has informed the
writer that this migratory locust is found in South Africa. _P._
(_Oedaleus_) _marmoratus_ has almost as wide a distribution in the Eastern
hemisphere as _P. cinerascens_, except that it is more exclusively
tropical; it is thus excluded from New Zealand. _P._ (_Oedaleus_)
_nigrofasciatus_ has a more northern distribution than its congener, but
has extended to Africa and the Asiatic Archipelago. This Insect is so
variable that the distinctions of its races from other species of the same
genus are not yet clear. All the above-mentioned locusts belong to the
tribe Oedipodides. _Acridium peregrinum_, now more frequently called
_Schistocerca peregrina_, belongs to the tribe Acridiides. It is a large
locust (Fig. 84), and has a wide distribution. It is the chief species in
North Africa, and is probably the locust of the plagues of Egypt mentioned
in the book of Exodus. It is also, according to Cotes,[231] the chief
locust of North-West India. In this latter country _Pachytylus cinerascens_
and some other species also occur. With the exception of _S. peregrina_,
the species of the genus _Schistocerca_ are confined to the New World. In
North America locusts are more usually called grasshoppers. Several species
of the genus _Caloptenus_ are injurious in that country, but the chief
migratory species is _C. spretus_ (Fig. 175). This genus belongs to
Acridiides. A large locust, _Schistocerca americana_, is also migratory to
a small extent in the United States. In South America other species of
_Schistocerca_ are migratory; it is not known how many there may be, and it
is possible that one or more may prove to be the _S. peregrina_ of the Old
World. A Chilian species, according to Mr. E. C. Reed,[232] {299}exhibits
distinctions of colour similar to those that have been observed in _S.
peregrina_ in Algeria.
[Illustration: FIG. 178.—_Cephalocoema lineata_, female, × ⅔. S. America.
(After Brunner.)]
In Britain we are now exempt from the ravages of locusts, though swarms are
said to have visited England in 1693 and 1748. Individuals of the migratory
species are, however, still occasionally met with in England and the south
of Scotland. _P. cinerascens_ has been recorded from Kerry in Ireland, but
erroneously, the Insect found being _Mecostethus grossus_ (Fig. 173).
According to Miss Ormerod,[233] large locusts are imported to this country
in fodder in considerable numbers, but are usually dead; living individuals
are, however, sometimes found among the others. In 1869 living specimens of
_Schistocerca peregrina_ were found in various parts of the country,
having, in all probability, arrived here by crossing the German Ocean.
_Pachytylus cinerascens_ has also, it is believed, occurred here, the
specimens that have been recorded at different times under the name of _P.
migratorius_ being more probably the former species.
Although the majority of the very large number of species included in
Acridiidae are recognised with ease from their family likeness as belonging
to the group, yet there are others that present an unusual aspect. This is
specially the case with the members of the small tribes Tettigides,
Proscopides, and Pneumorides, and with some of the apterous forms of the
Oedipodides. The tribe Proscopides (Fig. 178, _Cephalocoema lineata_,
female) includes some of the most curious of the Acridiidae. Breitenbach
gives[234] a brief account of the habits of certain species which he met
with near Porto Alegre in South America. On a stony hill there was some
grass which, by several months' exposure to the sun's rays, had {300}become
withered and brown. Apparently no live thing was to seen on this hillock
except the ubiquitous ants, but after a while he noticed some
"lightning-like" movements, which he found were due to specimens of
Proscopia. The Insects exactly resemble the withered vegetation amongst
which they sit, and when alarmed seek safety with a lengthy and most rapid
leap. When attention was thus directed to them he found the Insects were
really abundant, and was often able to secure fifty specimens on a single
afternoon. These Insects bear a great general resemblance to the Phasmides,
but there is no evidence at present to show that the two kinds of Insects
live in company, as is the case with so many of the Insects that resemble
one another in appearance. Although the linear form and the elongation of
the body are common to the stick-Insects and the Proscopides, yet this
structure is due to the growth of different parts in the two families. In
the Phasmidae the prothorax is small, the mesothorax elongate, while in the
Proscopides the reverse is the case. The elongation of the head is very
curious in these Insects; the mouth is not thus brought any nearer to the
front, but is placed on the under side of the head, quite close to the
thorax. The tribe Tryxalides contains Insects (Fig. 165) that approach the
Proscopides in the form of the head and other characters. In most cases the
sexes of the Proscopides differ from one another so strongly that it is
difficult to recognise them as being of the same species. Usually both
sexes are entirely apterous, but the Chilian genus _Astroma_ exhibits a
remarkable exception and an almost unique condition of the alar organs, the
mesonotum being in each sex entirely destitute of such appendages, while
the female has on the metanotum rudiments of wings which are absent in the
male.
[Illustration: FIG. 179.—_Tettix bipunctatus._ Britain. A, The Insect
magnified; B, part of the middle of the body; _a_, prolongation of
pronotum; _b_, tegmen; _c_, wing.]
The tribe Tettigides is a very extensive group of small Acridiidae, in
which the pronotum extends backwards as a hood and covers the body, the
tegmina and wings being more or less modified. In our British species (Fig.
179) this condition does not greatly modify the appearance of the Insect,
but in many exotic species (Fig. 180) the hood assumes {301}remarkable
developments, so that the Insects have no longer the appearance of
Orthoptera. It would be impossible, without the aid of many figures, to
give an idea of the variety of forms assumed by this prothoracic expansion.
It is a repetition of what occurs in the Order Hemiptera, where the
prothoracic hoods of the Membracides exhibit a similar, though even more
extraordinary, series of monstrous forms. So great is the general
similarity of the two groups that when the genus _Xerophyllum_ (Fig. 180,
A) was for the first time described, it was treated by the describer as
being a bug instead of a grasshopper. This genus includes several species
from Africa. The curious _Cladonotus_ (Fig. 180, B) is a native of Ceylon,
where it is said to live in sandy meadows, after the fashion of our
indigenous species of _Tettix_ (Fig. 179). Very little is known as to the
habits of these curious Tettigides, but it has been ascertained that some
of the genus _Scelimena_ are amphibious, and do not hesitate to enter the
water and swim about there; indeed it is said that they prefer plants
growing under water as food. This habit has been observed both in Ceylon
and the Himalayas. The species are said to have the hind legs provided with
dilated foliaceous appendages useful for swimming.
[Illustration: FIG. 180.—Tettigides: A, _Xerophyllum simile_ Fairm.; B,
_Cladonotus humbertianus_. (After Bolivar.)]
[Illustration: FIG. 181.—A, _Mastax_ (_Erianthus_) _guttatus_, male.
Sumatra. (After Westwood.) B, profile; C, front of head.]
The tribe Mastacides includes thirty or forty species of Acridiidae with
short antennae and vertical head (Fig. 181, _Mastax guttatus_); they are
apparently all rare and little {302}known, but are widely distributed in
the tropics of the Old and New Worlds. Nothing whatever seems to be known
of their habits or of their development.
The tribe Pneumorides includes a still smaller number of species of very
aberrant and remarkable grasshoppers, of large size, with short antennae,
and with the pronotum prolonged and hood-like; they are peculiar to South
Africa. Although amongst the most remarkable of Insects, we are not able to
give any information as to their habits. It would appear from the form of
their legs that they have but little power of hopping. The species of which
we figure the female (Fig. 182) is very remarkable from the difference in
colour of the sexes. The female is so extravagantly coloured that she has
been said to look as if "got up" for a fancy-dress ball. She is of a gay
green, with pearly white marks, each of which is surrounded by an edging of
magenta; the white marks are very numerous, especially on the parts of the
body not shown in our figure; the face has magenta patches and a large
number of tiny pearly-white tubercles, each of which, when placed on a
green part, is surrounded by a little ring of mauve colour. Though the
female is certainly one of the most remarkably coloured of Insects, her
consort is of a modest, almost unadorned green colour, and is considerably
different in form. He is, however, provided with a musical apparatus, which
it is possible may be a means of pleasing his gorgeous but dumb spouse. It
consists of a series of ridges placed on each side of the inflated abdomen,
which, as we have previously (p. 200) remarked, has every appearance of
being inflated with the result of improving its resonance.
[Illustration: FIG. 182.—_Pneumora scutellaris_, female. South Africa.]
{303}The Pyrgomorphides[235] is a small tribe of about 120 described
species, two of which are found in the south of Europe (Fig. 183,
_Pyrgomorpha grylloides_). The tribe includes a number of large and curious
Insects, among them the species of _Phymateus_ and _Petasia_, with peculiar
excrescences on the pronotum and vivid colours on some parts of the body or
its appendages, which are apparently common Insects in South Africa.
The tribe Tryxalides includes a great many species of grasshoppers. In them
the front of the head joins the upper part at an acute angle (Figs. 165 and
173). This tribe and the Acridiides are the most numerous in species of the
family. To the latter belong most of the migratory locusts of the New World
(Fig. 175, _Caloptenus spretus_). A Spanish species of this tribe,
_Euprepocnemis plorans_, though provided with well-developed wings,
possesses the remarkable habit of seeking shelter by jumping into the water
and attaching itself below the surface to the stems of plants.
[Illustration: FIG. 183.—_Pyrgomorpha grylloides._ South Europe. (After
Fischer.)]
[Illustration: FIG. 184.—_Xiphocera_ (_Hoplolopha_) _asina_. S. Africa.
(After de Saussure.)]
The tribe Pamphagides[236] includes some 200 species, found chiefly in
Africa and the arid regions near the Mediterranean Sea. They are mostly
apterous forms, and this circumstance has, according to de Saussure,
exercised a marked influence on the geographical distribution of the
species. Although the tribe consists chiefly of apterous forms, several
species possess {304}well-developed wings; sometimes this is the case of
the male but not of the female. Some of the species are highly modified for
a desert life, and exhibit a great variation in the colour of the
individuals in conformity with the tint of the soil they inhabit.
_Xiphocera asina_ (Fig. 184) is thought by Péringuey to be the prey of the
extraordinary South African tiger-beetles of the genus _Manticora_.
We have already mentioned the tribe Oedipodides[237] as including most of
the species of migratory locusts of the Old World. Some striking cases of
variation in colour occur amongst the winged Oedipodides. In certain
species the hind wings may be either blue or rosaceous in colour; it is
thought that the latter is the tint natural in the species, and that it is
due to the mixture of a red pigment with the pale blue colour of the wing;
hence the blue-coloured wings are analogous to cases of albinism. But the
most remarkable fact is that this colour difference is correlative with
locality. Brunner von Wattenwyl says[238] that the blue variety of _Oe.
variabilis_ occurs only in a few localities in Europe—he mentions Vienna
and Sarepta,—and that where it occurs not a single red example can be met
with. Similar phenomena occur in other species in both Europe and North
America, and L. Bruner has suggested[239] that the phenomena in the latter
country are correlative with climatic conditions.
The group Eremobiens, a subdivision of Oedipodides, includes some of the
most interesting forms of Acridiidae. Its members have several modes of
stridulation. _Cuculligera flexuosa_ and other of the winged forms,
according to Pantel,[240] produce sounds by the friction of the middle
tibia against the wing, both of these parts being specially modified for
the purpose in the male sex. The most peculiar members of the Eremobiens
are some very large Insects, modified to an extraordinary extent for a
sedentary life in deserts and arid places. Trimen says[241] that a South
African species, _Trachypetra bufo_, which lives amongst stones, is so
coloured that he had much difficulty in detecting it, and that he noticed
in certain spots, often only a few square yards in extent, where the stones
lying on the ground were darker, lighter, or more mottled than usual, that
the individuals of the grasshopper were of a similar colour to the stones.
{305}[Illustration: FIG. 185.—_Methone anderssoni_, female. S. Africa. _a_,
Front of head; _b_, posterior leg; _c_, _d_, front and hind feet. (_c_ and
_d_ magnified, the others natural size.)]
The Insect referred to by Trimen is, we believe, the _Batrachotettix whiti_
of de Saussure. In this species the alar organs are completely absent, and
the pronotum forms a sort of hood that protects the base of the hind body.
Some of the desert Eremobiens vary so much that the differences found among
individuals of the same species {306}are said by Brunner and de Saussure to
be so great as to affect even the generic characters, and give rise to the
idea of an "uncompleted species-formation."
[Illustration: FIG. 186.—Portions of middle of the body and hind leg of
_Methone anderssoni_ ♂: _a_, femur; _b_, an inferior fold; _c_,
rattling-plate; _d_, striated surface; _e_, the adjoining sculpture; _f_,
grooved portion of tegmen. The part _e_ is really, like _d_, a portion of
the second abdominal segment, not of the third, as might be supposed from
the figure.]
_Methone anderssoni_, an inhabitant of the Karoo Desert of South Africa, is
one of the largest of the Acridiidae. A female of this species is
represented of the natural size in Fig. 185. This Insect is remarkable on
account of the complex organs for producing sound, and for the great
modification of the posterior legs (Fig. 185, _b_), which do not possess
locomotive functions, but serve as a portion of the sound-producing
apparatus, and as organs for protecting the sides of the body. This Insect
is said to be very efficient in making a noise. The sexes differ
considerably in their sound-producing organs, a portion of which are
present in the female as well as in the male (Fig. 186). Connected with the
first abdominal segment, but extending backwards on the second, there is a
peculiar swelling bearing two or three strongly raised chitinous folds
(Fig. 186, _c_). When the leg is rotated these folds are struck by some
peg-like projections situate on the inner face of the base of the femur,
and a considerable noise is thus produced. The pegs cannot be seen in our
figure. This apparatus is equally well developed in female and male. On the
second abdominal segment, immediately behind the creaking folds we have
described, there is a prominent area, densely and finely striated (Fig.
186, _d_): this is rubbed by some fine asperities on the inner part of the
femur near its base. Sound is produced by this friction on the striated
surface, the sculpture of which is abruptly contrasted with that of the
contiguous parts: these structures seem to be somewhat better developed in
the male than they are in the female, and to be phonetic, at any rate in
the former sex. {307}The male has the rudimentary tegmina (Fig. 186, _f_)
much longer than they are in the female (Fig. 185), and their prolonged
part is deeply grooved, so as to give rise to strong ridges, over which
plays the edge of the denticulate and serrate femur. There is nothing to
correspond to this in the female, and friction over the surface of this
part of the male produces a different and louder sound. There can be little
doubt that this is a phonetic structure peculiar to the male. It
approximates in situation to the sound-producing apparatus of the males of
the Stenobothri and other Acridiidae. _Methone anderssoni_ has large
tympanal organs: the small tegmina cover them up completely. In the female
the tips of the tegmina seem to be adapted for forming covering-flaps for
the tympana. In both sexes there is a sac (Fig. 186, _b_) adjoining the
structures we have mentioned, but which is not directly phonetic, though it
may be an adjunct of the apparatus.
There is no other Orthopteron in which the phonetic organs are so complex
as they are in the male of _Methone anderssoni_, and it would appear
probable that this Insect possesses the power of producing two, if not
more, distinct sounds, one in common with the female, and peculiar to this
and one or two other species; the other somewhat similar to that of other
Acridiids, and more specially developed in the male, if not absolutely
confined to it.
This Insect is of a very sedentary disposition, and when disturbed
apparently seeks safety rather by the noise it can make than by flight. Its
powers of locomotion indeed are very feeble. The alar organs are quite
rudimentary, and of no assistance whatever for movement. The hind legs seem
to be almost equally useless for this purpose; they are broader than they
are in other Acridiidae, and have different functions. When _Methone_ moves
it does so by means of the anterior four legs, on which it walks propped up
as if on stilts. When at rest the hind legs are pressed close to the body,
and the tibiae are inflexed and not seen, the creature in this position
greatly resembling a clod of earth. We know nothing of the life history of
this Insect, except that the young resemble the adult in appearance, and
are provided with the sound-producing apparatus, or some portion thereof.
The geographical distribution of the Eremobiens corresponds with that of
the Pamphagides, with two important differences, viz. that in the Old World
the former group occupies a somewhat {308}more restricted area, and that it
is represented in the New World by two peculiar North American genera,
_Haldmanella_ and _Brachystola_. _B. magna_ is an Insect nearly equal in
size to _Methone anderssoni_. Its peculiar form and movements have procured
for it in Texas and Colorado the popular names of "buffalo hopper" and
"lubber grasshopper." This Insect has not—like _Methone_—the colours of the
desert sands; it is of a green tint, with comparatively smooth body, and
during the day rests concealed under tufts of grass. It has apparently no
sound organs, though de Saussure thinks there are structures present that
are vestiges or rudiments thereof.
The family Acridiidae includes a large part of the species that make up our
meagre list of British Orthoptera. Indeed, the only native Orthoptera at
the present time sufficiently common to attract general attention are, in
addition to the earwig, the species of the genera _Stenobothrus_ and
_Gomphocerus_, whose musical instruments we have described previously. We
have eight species of these Insects. They are the little grasshoppers, so
common in our fields and gardens, the hunting of which is a source of much
amusement to children. The Insect goes off with a sudden and long hop just
as it is going to be seized, and this is appreciated by the child as very
clever. The hunt, as a rule, does not result in much damage to the
grasshoppers, the ingenious escape being the greater part of the pleasure.
These _Stenobothri_ are remarkable for their variation in colour, and it is
thought by some that they frequent spots where they find themselves a match
with their surroundings. There is, however, little or no information of
importance on this point extant. _Mecostethus grossus_ (Fig. 173), though
larger, is very like the common field grasshoppers, but appears to have
become rare since the fens were drained. The two curious little
grasshoppers of the genus _Tettix_ (Fig. 179) are not uncommon. In addition
to these Acridiidae, three species of migratory locusts are occasionally
met with in Britain, viz. _Pachytylus cinerascens_ (Fig. 177), _P.
migratorius_, and _Schistocerca peregrina_ (Fig. 84); this latter we have
already alluded to as being probably the locust mentioned in the book of
Exodus.
Acridiidae have never been found in amber, owing possibly to their large
size and strength. There are but few fossil forms known, and these do not
extend farther back in time than the Mesozoic {309}epoch. Several forms,
including three peculiar genera, have been found in the Tertiary strata at
Florissant. The remains from the Mesozoic layers are apparently very
fragmentary and obscure.
Brongniart has instituted a family of Insects under the name
Palaeacrididae[242] for some fossil Insects from the Carboniferous strata
at Commentry. He considers that these Insects were abundant in the epoch of
the Carboniferous strata.
The very large number of genera and species of Acridiidae have been
recently arranged in nine tribes by Brunner von Wattenwyl:—
1. Feet without a claw-pad.[243] [Pronotum covering all the body.]
Tegmina lobe-like. Tribe 1. TETTIGIDES. (Figs. 179, 180, _Tettix_,
_Xerophyllum_, _Cladonotus_.)
1′. Feet with a claw-pad.
2. Antennae shorter than the anterior femora.
3. Head short, as if compressed from in front.
4. Body bladder-like, inflated.[244] [Pronotum covering half the
abdomen.] South African species. Tribe 2. PNEUMORIDES. (Fig. 182,
_Pneumora scutellaris_.)
4′. Body ordinary. Tribe 3. MASTACIDES. (Fig. 181, _Mastax
guttatus_.)
3′. Head very elongate. [Body apterous or sub-apterous.] Tribe 4.
PROSCOPIIDES. (Fig. 178, _Cephalocoema lineata_.)
2′. Antennae longer than the anterior femora.
3. Prosternum unarmed.
4. The plane of the vertex of the head meeting the plane of the
front of the head as an angle. The former produced or declivous.
The face looking down. Tribe 5. TRYXALIDES. (Fig. 165, _Tryxalis
nasuta_; Fig. 173, _Mecostethus grossus_.)
4′. Planes of the vertex and front of the head connected in a
rounded manner. Face looking forwards. Tribe 6. OEDIPODIDES.
(Fig. 177, _Pachytylus_; Fig. 185, _Methone_.)
3′. Prosternum with an elevated lamina in front, either irregularly
swollen or mucronate.
4. Foveoles of the vertex superior, contiguous, forming the apex of
the vertex. Face looking much downwards. Tribe 7. PYRGOMORPHIDES.
(Fig. 183, _Pyrgomorpha grylloides_.)
4′. Foveoles of the vertex, either superior (but not forming the
apex of the vertex), or lateral, or inferior, or quite obsolete.
{310}5. Foveoles superior, open behind. Prosternum irregularly
swollen, rarely mucronate. Tribe 8. PAMPHAGIDES. (Fig. 184,
_Xiphocera asina_.)
5′. Foveoles lateral or inferior, closed behind or (usually)
entirely obsolete. Prosternum distinctly mucronate or
tuberculate. Tribe 9. ACRIDIIDES. (Fig. 84, _Acridium
peregrinum_; Fig. 176, _Caloptenus spretus_.)
{311}CHAPTER XIII
ORTHOPTERA _CONTINUED_—LOCUSTIDAE, GREEN GRASSHOPPERS, KATYDIDS
FAM. VII. LOCUSTIDAE—GREEN GRASSHOPPERS.
_Orthoptera, with very long delicate antennae composed of many more than
thirty joints; hind legs longer than the others, thicker at the base.
Tarsi with four joints. Front tibiae usually provided with tympanal
organs placed below the knee; stridulating apparatus of males, when
present, situate on the basal part of the tegmina. Females usually with
an elongate exserted ovipositor, formed by the apposition of six pieces.
Wingless forms numerous._
[Illustration: FIG. 187.—_Cyrtophyllus crepitans_, male. West Indies.]
An unfortunate confusion has long existed as to the term Locustidae, and
has resulted in the application of the name to a group of Insects that
contains none of the locusts of ordinary language. Some entomologists
therefore use the term Phasgonuridea for this family, but the great
majority prefer the term Locustidae.
{312}[Illustration: FIG. 188.—Development of wings in _Platycleis grisea_:
A, B, C, D, E, consecutive stages; _p_, prothorax; _m_, mesothorax; _mt_,
metathorax; _t_, tegmen; _w_, wing; _ab′_, position of first abdominal
segment. In C, D, and E, _m_ points to the part by which the _m_, shown in
A and B, is concealed; in D and E only the positions of _mt_ are indicated.
(After Graber.)]
The Locustidae are, as a rule, more fragile Insects than the Acridiidae,
from which they can be readily distinguished by the characters we have
mentioned in our definition. According to Dufour, there are no air vesicles
connected with the tracheal system in this family; possibly to this it may
be due that none of the family undertake the long flights and migratory
wanderings that have made some of the Acridiidae so notorious. Very little
is known as to the life histories of the members of this extensive family
of Orthoptera. Graber, however, has given some particulars as to the
development of _Platycleis grisea_, and of one or two other species. He
recognises five instars, but his first is probably really the second, as he
did not observe the Insect in its youngest condition. Although his figures
are very poor, we reproduce them, as they give some idea of the mode of
growth of the wings, and of the correlative changes in the thoracic
segments. It will be seen that in the first three of these instars the alar
organs appear merely as prolongations of the sides of the posterior two
thoracic rings, and that in D a great change has occurred in the position
of these segments, so that the alar organs are free processes, the two
posterior thoracic rings being insignificant in size in comparison with the
now greatly developed prothorax. In E the tegmen is shown fully developed,
the positions of some {313}of the rings covered by it being indicated by
the letters _m_, _mt_, _ab′_. These changes are very similar to those we
have described in Acridiidae, the chief difference being the greater
development of the dependent wing-pads previous to the fourth instar.
[Illustration: FIG. 189.—Front of head of _Copiophora cornuta_, female.
Demerara.]
The ocelli in Locustidae are much more imperfect than they are in
Acridiidae, and are frequently rudimentary or nearly totally absent, or
there may be but one instead of three. They are, however, present in a
fairly well-developed state in some species, and this is the case with the
one whose face we portray in Fig. 189, where the anterior of the three
ocelli is quite conspicuous, the other two being placed one on each side of
the curious frontal cone near its base. The peculiar head ornament shown in
this figure exists in both sexes, and something similar occurs in a large
number of Conocephalides. We have not the slightest idea of its import.
Individuals of one or more species of this curious South American genus are
occasionally met with alive in gardens near London. They are, no doubt,
imported as eggs, for they are sometimes met with in the juvenile state,
but in what way they are introduced is not known.
The ovipositor frequently attains a great length in these Insects, so as to
exceed that of the body. It is used in different ways, some of the family
depositing their eggs in the earth, perhaps in vegetable matter under the
surface; but other species place the ova in twigs or stems of plants,
arranging them in a very neat and compact manner in two series, as depicted
by Riley[245] in the case of _Microcentrum retinerve_ (Fig. 190). These
eggs are laid in the autumn, and in the following spring become more
swollen before hatching. The Insect undergoes a moult during the process of
emerging from the egg. By the time the emergence is completed the
_Microcentrum_ has expanded so much {314}in size that it is a matter of
astonishment how it can ever have been packed in the egg; the young
commence jumping and eating leaves in a few minutes. Including the ecdysis
made on leaving the egg, they cast their skins five times. The
post-embryonic development occupies a period of about ten weeks. The larvae
eat their cast skins. When the final moult occurs the tegmina and wings are
at first quite soft and colourless, but within an hour they assume their
green colour. These Insects, as remarked by Riley, make interesting pets.
The people of the Amazon valley are in the habit of keeping a species in
cages, and our British _Locusta viridissima_ does very well in confinement.
One of the most curious habits of these Locustidae is a constant licking of
the front paws. Riley says that _M. retinerve_ bestows as much attention on
its long graceful antennæ as many a maiden does upon her abundant tresses,
the antennæ being drawn between the jaws and smoothed by the palpi. This
American naturalist also tells us that he reared three successive broods in
confinement, and that the Insects gradually deteriorated, so that the eggs
of the third generation failed to hatch.
[Illustration: FIG. 190.—Eggs of Katydid (_Microcentrum retinerve_): A, the
two series at deposition; B, side view of a single series. (After Riley.)]
The ovipositor, which is one of the most characteristic features of the
Locustidae, is not present in the newly-hatched Locustid (Fig. 191, A), the
organ being then represented only by two papillae placed on the penultimate
segment. The structure and development of the ovipositor in _Locusta
viridissima_ have been described by Dewitz.[246] Fig. 191, A, shows the
young Insect taken from the egg just as it is about to emerge. The abdomen
consists of ten segments, the terminal one bearing at its extremity two
processes, the cerci, _a′_. These persist throughout the life of the
Insect, and take no part in the formation of the ovipositor. The tenth
segment subsequently divides into two (_a_, _a'′_, Fig. 191, C), giving
rise to the appearance of eleven abdominal segments, and of the ovipositor
springing from the antepenultimate.
{315}[Illustration: FIG. 191.—Development of ovipositor of _Locusta
viridissima_: _a_, terminal segment; _a′_, cerci; _a″_, secondary division
of terminal segment; _b_, penultimate (ninth) segment; _b′_, primary
papillae of this segment; _b″_, secondary divisions thereof; _c_, eighth
segment; _c′_, its papillae. (After Dewitz.) A, embryo ready for emergence;
B, portion of integument of the ventral plates of eighth and ninth
segments; C, the appendages in a condition somewhat more advanced than they
are in A.]
[Illustration: FIG. 192.—Structure of ovipositor of _Locusta viridissima_:
A, arrangement of parts at base, _c′_ being separated and turned outwards;
B, transverse section. The parts of the appendage bear the same lettering
as in Fig. 191. (After Dewitz.)]
Near to one another, on the middle of the ventral aspect of the true ninth
abdominal segment, are seen the two papillae (_b′_), which at first are the
only visible indications of the future ovipositor. If, however, the
integument be taken off and carefully examined, it will be found that there
exist on the eighth abdominal plate two spots, where there is a slight
thickening and prominence of the integument (Fig. 191, B, _c_). From these
two spots the two lower rods of the ovipositor are produced; these two,
together with the two growths from the ninth segment, form the four
external rods of the ovipositor. Inside these there exist in the completed
structure two other rods (Fig. 192, B, _b'′_). These are produced by a
growth from the inner parts of the two papillae of the ninth segment. The
relations of the six rods in their early condition are shown in Fig. 191,
C, where the two primary papillae _b′_ of the ninth segment are seen with
their secondary offshoots _b″_; _c′_ being the papillae of the eighth
segment. The subsequent relations of the pieces are shown in Fig. 192; A
exhibiting the base of the organ with the lower rods turned on one side to
show the others, the shaded parts indicating {316}muscular attachments; B
is a transverse section of the organ. In these figures the different parts
of the appendages bear the same lettering as they do in Fig. 191. It will
be seen that in the completed structures the parts _c′_ have become very
intimately connected with the parts _b′_ and _b″_, which belong to another
segment.
The Locustidae resemble the Acridiidae in the possession of specialised
ears and sound-producing organs; neither of these is, however, situate in
the same part of the body as in Acridiidae. The ears of Locustidae are
placed on the front legs, below the knee; a tympanum (Fig. 193, A), or a
crack giving entrance to a cavity in which the tympanum is placed (Fig.
193, B), being seen on each side of each of the anterior pair of limbs. In
this family, as in the Acridiidae, three kinds of ear are recognised
according to the condition of the tympanum, which is either exposed (Fig.
193, A) or closed by an overgrowth of the integument (Fig. 193, B), or in a
condition to a certain extent different from either of these. The existence
of ears placed on the legs is a curious fact, but it is beyond doubt in the
Locustidae, and there is good reason for believing that analogous organs
exist in this situation in other Insects that have special means of
sound-production, such as the ants and the Termites.
[Illustration: FIG. 193.—Ears of Locustidae: A, portion of front leg of
_Odontura serricauda_, adult; _p_, prominence of integument; _r_, rim of
ear; _T_, tympanum; _b_, thickened area thereof; _Fu_, remains of groove in
which the structure was developed. B, portion of front leg of _Thamnotrizon
apterus_; _i_, inner margin; _a_, slit-like external aperture of ear; _di_,
overlapping cover of the ear. (After Graber.)]
The structure of these organs in the Locustidae has been investigated by
Graber,[247] and their acoustic functions placed beyond doubt, though to
what special kind of sounds they may be sensitive is not ascertained, this
point being surrounded by even greater difficulties than those we have
discussed in the case of the Acridiidae. In the Locustidae there is a
special structure of a remarkable nature in connexion with the ears. In
Acridiidae {317}a stigma is placed close to the ear, and supplies the
internal structures of the organ with air. There are no stigmata on the
legs of Insects, consequently admission of air to the acoustic apparatus in
Locustidae is effected by means of a gaping orifice at the back of the
prothorax, just over the base of the front leg (Fig. 101); this
communicates with its fellow of the other side, and from them there extend
processes along the femora into the tibiae, where they undergo dilatation,
so as to form vesicular cavities, one of which is in proximity to each drum
of the ear. These leg-tracheae are not connected with the ordinary tracheal
system; the prothoracic stigma exists in close proximity to the acoustic
orifice we have described, but is much smaller than it. It is not yet clear
why the acoustic apparatus should require a supply of air apart from that
which could be afforded by the ordinary tracheal system. This special
arrangement—to which there is hardly a parallel in Insect anatomy—has still
to be accounted for; we do not know whether the necessity for it may be
connected with the respiratory system or the acoustic organ.
[Illustration: FIG. 194.—Diagram of arrangement of parts of the ear as seen
in transverse section of the tibia of a Locustid. A, J, V, H, outer, inner,
anterior, posterior aspects of leg; _a_, _d_, thin part of integument
forming anterior tympanum; _b_, _c_, thicker portion of same; _f_, _g_,
posterior tympanum; _a_, _f_, and _d_, _h_, _g_, thick portions of
integument; _i_, _k_, internal protuberances of same; _l_, _m_, _n_, _o_,
walls of the anterior tracheal vesicle, _vTr_; _p_, _q_, _s_, _r_, walls of
the posterior tracheal vesicle, _hTr_; _o″_, projection of tympanal orifice
of prothorax; _tr-n_, tracheal nerve-end organ, _crista acustica_; _st_,
rod; _de_, curtain-membrane; _hn_, _e_, supra-tympanal, nerve-end organ;
_hn_, ganglion cells; _st′_, rods; _e_, point of integumental fixation of
nerve endings. (After Graber.)]
The chief features of the acoustic apparatus of the legs of Locustidae will
be gathered from the accompanying diagrammatic transverse section through
the tibia. In this figure the deep black parts indicate the outer wall of
the tibia and its prolongations, the white spaces indicate the parts filled
with air, while the dotted portions are occupied by blood or some of the
body organs;[248] the {318}circular space _o″_ is not part of the actual
structure, but represents the area of the external acoustic orifice of the
prothorax; it is not, however, so large as it should be.
Although the tibial ears of Locustidae are very perfect organs, there is
great difficulty in deciding on the exact nature of their functions. They
would appear to be admirably adapted to determine the precise locality from
which a sound proceeds, especially in those cases—and they are the highest
forms—in which the tympanum is placed in a cavity the external orifice of
which is a slit (Fig. 193, B); for the legs can be moved in the freest
manner in every direction, so as to bring the drum into the most direct
line of the vibrations. But as to what kinds of vibrations may be
perceived, and the manner in which they may be transmitted to the nerves,
there is but little evidence. On reference to the diagram it will be
noticed that the tympanum, the tympanal vesicles, and the nervous apparatus
are not in close connexion, so that even the mode by which the impulses are
transmitted is obscure.
The musical organs of the Locustidae are different from those of the
Acridiidae, and are invariably situate on the basal part of the tegmina.
They are found, in the great majority of cases, only in the male; in the
tribes Ephippigerides and Callimenides they exist in each sex. One of the
wings bears a file on its inner surface, while the other—on the right side
of the body—is provided with a sharp edge placed on a prominent part of its
inner margin. By slightly tilting the tegmina and vibrating them rapidly,
the edge passes under the file, and a musical sound is produced. These
structures are limited to the small anal area of the wing, and when the
tegmina are very greatly reduced in size, it is this part that still
remains. There is much variety in the details of the structure. The
nervures of this part of the tegmina are different in the male from what
they are in the female, and, moreover, the two wing-covers of the male
differ from one another. It is apparently the vibrations of the right
tegmen that produce the sound, and this part usually bears a space of a
glassy nature, which probably improves the character of the sound produced.
Our chief British songster of this group, _Locusta viridissima_, is only
provided with phonetic organs (Fig. 195) of a somewhat imperfect character,
but in the genus _Mecopoda_ there is great perfection of the structures.
The anal areas of the two tegmina are in this case {319}very different;
that of the left one, which bears the file, being similar in texture to the
rest of the wing-cover, while the corresponding part of the other tegmen is
rigid and transparent, and greatly distorted, so as to create a cavity
which, no doubt, improves the sound; the scraper too is very perfectly
formed. The difference between this form of musical organ and that of _L.
viridissima_ is curious, inasmuch as in the better instrument the important
modifications are confined to one tegmen, while in the other form both
tegmina are largely changed. The difference appears to be that in _Locusta_
the left tegmen, as well as the right one, acts as a sounding-board, while
in _Mecopoda_ it does not do so, but when the wings are closed quite covers
and conceals the musical instrument.
The Locustidae, notwithstanding the fact that their alar organs are
generally more ample than those of the Acridiidae, seem to be, as a rule,
of more sedentary habits, and more nocturnal in their activity. The musical
powers of the different species are very varied. _Locusta viridissima_
produces a shrill and monotonous but not disagreeable, sound, and is
capable of sustaining it for a quarter of an hour without any intermission,
except a break for the sake of starting again immediately with greater
force, like a performer on a flute. It occasionally chirps in the day, but
the act is then very brief. Bates informs us that one of these singing
grasshoppers, called Tananá by the natives of the Amazon valley, is much
admired for its singing, and is kept in little cages. The Amazonian
naturalist thought the music of this species superior to that of any other
Orthopterous Insect he had heard. The name of this grasshopper is
_Thliboscelus camellifolius_. It is very similar in appearance to
_Cyrtophyllus crepitans_, the Insect we have represented in Fig. 187.
[Illustration: FIG. 195.—Inner face of base of tegmina of _Locusta
viridissima_: A, the two wing-covers separated; B, in natural position with
mesonotum connecting them, showing file and edge scraping it; _a_, the
stridulating file; _b_, the rudimentary file on other tegmen.]
The most notorious of the musical Locustids are the Katydids {320}of North
America. There are several species of them—they belong, indeed, to more
than one genus,—but it seems that sounds somewhat resembling the words
Katy-did are perceptible in most of their performances. These sounds are
frequently repeated with slight variations—Katy-did, O-she-did,
Katy-did-she-did. Riley describes the music of the Katydid we represent in
Fig. 196 as follows:[249] "The first notes from this Katydid are heard
about the middle of July, and the species is in full song by the first of
August. The wing-covers are partially opened by a sudden jerk, and the
notes produced by the gradual closing of the same. The song consists of a
series of from twenty-five to thirty raspings, as of a stiff quill drawn
across a coarse file. There are about five of these raspings or trills per
second, all alike, and with equal intervals, except the last two or three,
which, with the closing of the wing-covers, run into each other. The whole
strongly recalls the slow turning of a child's wooden rattle, ending by a
sudden jerk of the same; and this prolonged rattling, which is peculiar to
the male, is invariably and instantly answered by a single sharp 'chirp' or
'tschick' from one or more females, who produce the sound by a sudden
upward jerk of the wings."
[Illustration: FIG. 196.—Katydid, _Microcentrum retinerve_. N. America.
(After Riley.)]
Pertinacity is one of the most curious features of the performance of
musical Locustids. One would say they desire to distinguish themselves as
much as possible. Harris says that _Cyrtophyllus concavus_ mounts on the
uppermost twigs of trees and there performs its Katy-did-she-did in rivalry
with others. He says even the female in this species gives forth a feeble
noise. Scudder says that some of the Katydids sing both by day and night,
but their day song differs from that of the night. "On a summer's day it is
curious to observe these little creatures suddenly {321}changing from the
day to the night song at the mere passing of a cloud, and returning to the
old note when the sky is clear. By imitating the two songs in the daytime
the grasshoppers can be made to respond to either at will; at night they
have but one note."
Although but little is known as to the habits of Locustidae, it is
ascertained that they are less exclusively herbivorous in their food habits
than the Acridiidae are; many seem to prefer a mixed diet. _Locusta
viridissima_ will eat various leaves and fruits, besides small quantities
of flesh. It has been recorded that a specimen in confinement mastered a
humble-bee, extracted with its mandibles the honey-bag, and ate this
dainty, leaving the other parts of the bee untouched. Many of the
Locustidae are believed to be entirely carnivorous. Brunner considers a
minority to be exclusively phytophagous. The species very rarely increase
to large numbers; this, however, occurs sometimes with _Orphania
denticauda_ and _Barbitistes yersini_ in Europe, and _Anabrus purpurascens_
in North America. We have already mentioned that the eggs of some species
are deposited in parts of plants, and of others in the earth. The British
_Meconema varium_ deposits its eggs in the galls of _Cynips_ in the autumn;
these eggs do not hatch till the following spring. _Xiphidium ensiferum_
has somewhat similar habits in North America, the gall selected for the
reception of the eggs being the scales formed by a species of _Cecidomyia_
on the leaves of willows. It has been ascertained that the development of
the embryo in the last-named species is commenced in the autumn, but is
suspended during the winter, being only completed in the following spring,
eight or nine months afterwards. We owe to Wheeler[250] a memoir on the
embryology of this Insect.
Some of the species have the peculiar habit of dwelling in caves. This is
especially the case with the members of the tribe Stenopelmatides (Fig.
197), which frequently possess enormously long antennae and legs, and are
destitute of alar organs and ears. The species with this habit, though
found in the most widely separated parts of the world, have a great general
resemblance, so that one would almost suppose the specimens found in the
caves of Austria, in the Mammoth cave of Kentucky, and in the rock-cavities
of New Zealand to be one {322}species, although they are now referred by
entomologists to different genera.
[Illustration: FIG. 197.—_Dolichopoda palpata_, male. Dalmatia. (After
Brunner.)]
[Illustration: FIG. 198.—Leaf-like tegmen of _Pterochroza ocellata_: _a_,
_a_, _a_, marks like those made by Insects on leaves.]
The Locustidae display in the greatest possible perfection that resemblance
of the tegmina to leaves which we mentioned when speaking of the general
characters of the Orthoptera. The wing-covers are very leaf-like in colour
and appearance in many Locustidae, but it is in the tribe Pseudophyllides
and in the South American genus _Pterochroza_ (Fig. 198) that the
phenomenon is most remarkable. The tegmina in the species of this genus
look exactly like leaves in certain stages of ripeness or decay. In the
tegmina of some of the species not only are the colours of faded leaves
exactly reproduced, but spots are present like those on leaves due to
cryptogamic growths. Perhaps the most remarkable feature of these
resemblances is the one pointed out by Brunner von Wattenwyl,[251] viz.
that the tracks and spots formed on leaves by the mining of Insects in
their tissues are also represented in the leaf-like wing-covers of the
_Pterochroza_; transparent spots (_a_, _a_, Fig. 198) being present, just
as they are in many leaves that have been attacked by Insects. Brunner was
so much impressed by these facts that he came to the conclusion that they
cannot be accounted for on the grounds of mere utility, {323}and proposed
the term Hypertely to express the idea that in these cases the bounds of
the useful are transcended. We will mention here another peculiar case of
resemblance described by Brunner as occurring in a Locustid. Two specimens
of a little Phaneropterid were brought from the Soudan by the Antinori
expedition, and have been described by Brunner under the name of
_Myrmecophana fallax_. The Insect is said to bear an extraordinary
resemblance to an ant. The most peculiar feature in the resemblance is
shown in Fig. 199, A, B. The most characteristic point in the external form
of an ant is the stalked abdomen, this structure being at the same time
quite foreign to the Orthoptera. In the other parts of the body and in the
colour generally, the _Myrmecophana_ resembles an ant, but the abdomen of
the Orthopteron is not stalked; it has, however, the appearance of being
so, in consequence of certain parts being of a white colour, as shown in
our figure. If abstraction be made of the white parts, the form of the
stalked abdomen of the ant is nicely reproduced. The specimens brought from
the Soudan were wingless and destitute of ovipositor, and may be immature,
but Brunner suggests that they may prove to be really mature, the
ovipositor, tegmina, and wings being permanently absent. The existence of a
long ovipositor would certainly detract greatly from the ant-like
appearance of the Orthopteron.
[Illustration: FIG. 199.—_Myrmecophana fallax._]
It is certain that the plant-like appearance of some of the Locustidae
renders them inconspicuous to the human eye in the situations they
frequent. It is a matter of common observation that though the noise of
their chirpings may be heard to such an extent as to make it certain that
many individuals must be in the immediate neighbourhood, yet at the same
time it may be most difficult to detect even a single individual. M. Boutan
noticed this phenomenon in the case of _Ephippigera rugosicollis_, and
tells us that the human eye can, with a little practice, acquire the art of
detecting these concealed creatures. This consists {324}apparently in
making use, not of a general inspection, but of a scrutiny of the outlines
of the leaves and twigs of a tree. By this means, when the eye is
accustomed to the task, the Insects can be detected with comparative ease;
much in the same way, M. Boutan says, as a figure, placed in an engraving
in such a way as to elude the eye, is appreciated with ease after the eye
has once perceived it.
Some of the Locustidae are provided with means of defence of a positive
nature. The Algerian _Eugaster guyoni_ ejects two jets of a caustic
orange-coloured fluid from two pores situate on the sides of the
mesosternum, and covered by the anterior coxae. This species is carnivorous
as well as herbivorous, and produces a sound more like humming than
stridulation.[252]
[Illustration: FIG. 200.—_Phasmodes ranatriformis_,female. Australia.
(After Westwood.)]
We have previously pointed out that some of the Acridiidae resemble the
stick-Insects rather than the members of their own group; and similar cases
occur amongst the Locustidae. Such a resemblance has, however, only been
found in a few species of the tribe Prochilides. We figure one of these,
_Phasmodes ranatriformis_, a native of South-West Australia. The very
elongate linear form and the total absence of alar organs give this Insect
a considerable resemblance to the stick-Insects or apterous Phasmidae.
_Prochilus australis_ is allied to this curious Locustid, but the alar
organs are present in both sexes, and the Insect bears a great resemblance
to the winged Phasmidae. This is due not only to the general form and
colour, but also to the fact that the tegmina are very narrow, which
{325}causes them to look like the coloured slip on the anterior parts of
the wings of some of the Phasmidae (cf. p. 266). Another case of a Locustid
with elongate, slender form is found in the extraordinary _Peringueyella
jocosa_ of South Africa, a member of the tribe Sagides. It has minute
organs of flight, and reproduces, to a considerable extent, the form and
appearance of Proscopides or of some Tryxalides.[253]
[Illustration: FIG. 201.—_Schizodactylus monstrosus_, male. Natural size.
East India.]
We follow Brunner in placing among the Locustidae the large Insect we
represent in Fig. 201. It is remarkable on account of its tegmina and
wings; these have their extremities much prolonged and curled; moreover,
the flat interior area and the abruptly {326}deflexed exterior area make
them look more like the wings of Gryllidae. This species has no ocelli, and
is said to be destitute of ears. The inflated condition of the anterior and
middle tibiae suggest that it possesses auditory structures, though there
appears to be no external opening for them. This Insect is found in India,
where it is said to be common on the banks of sandy rivers, living there in
burrows of the depth of three feet. Very little is known, however, as to
this curious Insect. It has recently been reported[254] as being injurious
to tobacco and other crops on high ground in Durbungha by cutting off their
roots. The local name for the Insect is _bherwa_. We should think it
somewhat doubtful whether this refers really to _S. monstrosus_.
[Illustration: FIG. 202.—_Anostostoma australasiae_, male. Australia.]
In number of species the Locustidae are perhaps scarcely inferior to the
Acridiidae, and in variety of form they surpass this latter family. Many of
the most gigantic forms are apterous, and these very often have a repellant
aspect. The genus _Anostostoma_ is remarkable for its large head. Allied to
it is _Deinacrida heteracantha_, the "Weta-punga" of the New Zealand
natives, an Insect formerly abundant in the forests north of Auckland, but
of late years become extremely rare. The head and body of this Insect may
measure more than 2½ inches in length, and when the antennae and legs are
stretched out the total length may be 14 or 15 inches. Although bulky and
absolutely wingless, yet, as Buller informs us,[255] it climbs with
agility, and is sometimes found on the topmost branches of lofty trees.
When disturbed it produces a clicking, accompanied by a slow movement
{327}of its hind legs. A second species, _D. thoracica_, lives in decayed
wood, and a third, _D. megacephala_, is remarkable from the very large size
of the head and mandibles in the male sex. The fact that a clicking noise
is produced by the Weta-punga is of some interest, for the genus
_Deinacrida_ is among the Locustidae that possess ears, but are said to be
destitute of sound-producing organs.
Amongst the most remarkable of the Locustidae are the two species of which
Brongniart has recently formed the genus _Eumegalodon_ and the tribe
Eumegalodonidae, which is not included in Brunner's table of the tribes of
Locustidae. The ovipositor is large and sabre-shaped; the male is unknown.
The genus _Megalodon_ is placed by Brunner in the tribe Conocephalides; it
also consists of extremely remarkable Insects.
[Illustration: FIG. 203.—_Eumegalodon blanchardi_, female. Borneo. × ⅘.
(After Brongniart.)]
The Locustidae appear to be of slow growth, and the autumns of Britain are
usually not warm enough for them. Hence we have but nine British species,
and of this number only three or four are known to occur north of the
Thames. The only one that attracts attention is _Locusta viridissima_,
which in some districts of the south of England occurs in considerable
numbers, and attests its presence by its peculiar music. It is called the
green grasshopper.
{328}The geological record is rather obscure in the matter of Locustidae.
Scudder considers that a fair number of Tertiary forms are known, and says
that they represent several of the existing tribes and genera. One or two
have been found in Mesozoic rocks.
TABLE OF THE TRIBES OF LOCUSTIDAE
1. Tarsi more or less depressed.
2. Front tibiae furnished with auditory cavities.
3. Antennae less distant from the summit of the occiput than from the
labrum; inserted between the eyes.[256]
4. First two joints of the tarsi laterally smooth. (Posterior
tibiae furnished on each side with an apical spine.) Tribe 1.
PHANEROPTERIDES. (Fig. 196, _Microcentrum_; Fig. 199,
_Myrmecophana_. Fig. 101, _Poecilimon affinis_.)
4′. First two joints of the tarsi laterally, longitudinally
sulcate.
5. Foramina of the anterior tibiae normally open. (Fig. 193, A.)
6. Posterior tibiae furnished on each side with apical spines.
7. Prosternum unarmed. Tribe 2. MECONEMIDES.
7′. Prosternum bispinose or bituberculate. Tribe 3.
MECOPODIDES.
6′. Posterior tibiae with no apical spines. (Head prognathous.)
Tribe 4. PROCHILIDES. (Fig. 200, _Phasmodes_.)
5′. Foramina of the anterior tibiae forming a chink, or protected
by a scale. (Fig. 193, B.)
6. Anterior tibiae with no apical spines.
7. Margins of the scrobes[257] of the antennae prominent.
Tribe 5. PSEUDOPHYLLIDES. (Fig. 187, _Cyrtophyllus
crepitans_; Fig. 198, _Pterochroza ocellata_.)
7′. Margins of the scrobes of the antennae not prominent.
8. Posterior tibiae furnished above on each side with
apical spines, or with a single spine on the side.
9. Posterior tibiae either furnished with apical spines
on each side, or only on the inner side. Tribe 6.
CONOCEPHALIDES. (Fig. 189, _Copiophora cornuta_.)
9′. Posterior tibiae furnished above with an apical spine
placed only on the outer side. Tribe 7. TYMPANOPHORIDES.
8′. Posterior tibiae without apical spines. Tribe 8.
SAGIDES.
6′. Anterior tibiae furnished with an apical spine on the inner
side.[258]
{329}7. The first joint of the posterior tarsi destitute of a
free sole-lobe. Tribe 9. LOCUSTIDES.
7′. The first joint of the posterior tarsi furnished with a
free sole-lobe. Tribe 10. DECTICIDES.
3′. Antennae more distant from the summit of the occiput than from
the labrum, inserted either beneath the eyes or on their inferior
border. Tegmina and wings greatly abbreviate, scale-like; when
tegmina are present they are furnished in each sex with a tympanum.
4. Third joint of the posterior tarsi shorter than the second. Both
anterior and posterior tibiae furnished on each side with a spine.
Tribe 11. CALLIMENIDES.
4′. Third joint of posterior tarsi longer than the second joint.
Anterior tibiae with no apical spine on the inner side, and
posterior tibiae with no apical spine on the outer side.
5. Antennae inserted at the edge of the eyes. Pronotum unarmed.
Tegmina present in each sex. Anterior tibiae furnished on the
outer side with an apical spine. Posterior tibiae furnished
beneath with four apical spines. Tribe 12. EPHIPPIGERIDES.
5′. Antennae inserted distinctly below the eyes. Pronotum
spinous. Elytra in the females wanting. Anterior tibiae without
apical spine on either side. Posterior tibiae beneath with two
apical spines or with none. Tribe 13. HETRODIDES.
2′. Anterior tibiae without auditory cavities. Tegmina with no
tympanum. Tribe 14. GRYLLACRIDES. (Fig. 201, _Schizodactylus
monstrosus_.)
1′. Tarsi distinctly compressed (most of the species apterous.) Tribe 15.
STENOPELMATIDES. (Fig. 202, _Anostostoma australasiae_; Fig. 197,
_Dolichopoda palpata_.)
{330}CHAPTER XIV
ORTHOPTERA _CONTINUED_—GRYLLIDAE, CRICKETS
FAM. VIII. GRYLLIDAE—CRICKETS.
_Antennae very slender, generally long and setaceous; hind legs long,
saltatorial. Tegmina with the outer portion deflexed on to the side of
the body, and with the inner part lying flat on the body. Tarsi usually
three-jointed (rarely two- or four-jointed). Female with a long
ovipositor (except in Gryllotalpides). Apterous forms numerous._
The Gryllidae are closely connected with the Locustidae, the musical and
auditory organs being in both similarly situate, and the female in both
possessing, in most of the tribes, an elongate exserted ovipositor. The two
families differ in the number of joints of the tarsi, in the form of the
tegmina, and in the fact that in Gryllidae the portion of the wing modified
for musical purposes consists of a larger portion of the organ—according to
de Saussure, the discoidal as well as the anal area.
[Illustration: FIG. 204.—House-cricket, _Gryllus_ (_Acheta_) _domesticus_,
male.]
The family would be a very natural one if we were to exclude from it the
mole-crickets which have fossorial front legs and no ovipositor, and the
Tridactylides, which also are {331}destitute of ovipositor, and have short
antennae, consisting of about ten joints.
The head is generally very large; ocelli are present, though usually
imperfect; the extremity of the body bears a pair of remarkably long cerci.
The hind tibiae are usually armed with very strong spines; the first joint
of the hind tarsus is elongate, and terminates in two spines, between which
the small second joint is often almost completely concealed; the feet are
not provided beneath with pads, but only bear remote setae.
The alar organs are difficult of comprehension, and different opinions
prevail as to their morphology. The tegmina are extremely different to the
hind wings, and never attain large dimensions, neither do they exhibit any
leaf-like or ornamental structures. In the genus _Pteroplistus_ they are
formed somewhat like the elytra of Coleoptera, and close over the back of
the Insect in a fashion very like that found in beetles. According to
Brunner the larger part of the tegmen—which, as we have said, reposes flat
on the back of the Insect—represents merely the anal area, and all the
other parts must be sought in the smaller, deflexed portion of the
wing-cover. De Saussure's opinion, to a somewhat different effect, we have
already mentioned. The tegmina of the male are extremely different from
those of the female, so that it is a matter of much difficulty to decide
what nervures correspond.[259]
[Illustration: FIG. 205.—Tegmina (sinistral) of the house-cricket. A, male,
inner aspect; B, female, outer aspect: _a_, inner margin; _b_, outer
margin; _c_, nervure bearing stridulating file.]
The wing-covers of the male differ from those of the Locustidae, inasmuch
as the pair are of similar formation, each bearing a stridulating file on
its lower aspect. This file projects somewhat inwards, so that its position
is marked on the outer aspect of the wing-cover by a depression. Usually
the right tegmen overlaps the other, an arrangement contrary to that which
prevails in other Orthoptera. The wings are ample and delicate; they
possess numerous nervures that are not much forked and have a {332}simple,
somewhat fan-like arrangement; the little transverse nervules exhibit only
slight variety. These wings are frequently rolled up at the apex, and
project beyond the body like an additional pair of cerci (Fig. 204). The
abdomen is chiefly remarkable for the large development of the pleura, the
stigmata being consequently very conspicuous. The cerci are not jointed,
though they are flexible and, often, very long; they bear a variety of
sense-organs (Fig. 67). The saltatorial powers of the crickets are
frequently considerable.
Graber has observed the post-embryonic development of the field-cricket,
_Gryllus campestris_, though unfortunately not from the very commencement,
so that we do not know whether there are five, six, or seven ecdyses; the
number is probably either six or seven. The manner in which the alar organs
are developed is similar to that we have described and figured in the
Locustidae. In the earlier instars there is a slight prolongation of each
side of the meso- and meta-notum, but about the middle of the development a
considerable change occurs—the rudimentary organs then become free
appendages and assume a different position.
The Gryllidae possess a pair of tympana on each front leg, but these organs
contrast with those of the Locustidae in that the pair on each leg usually
differ from one another, the one on the outer or posterior aspect being
larger than that on the inner or front face of the leg.
The ears of the Gryllidae have not been so well investigated as those of
the Locustidae, but are apparently of a much less perfect nature. No
orifice for the admission of air other than that of the prothoracic stigma
has been detected, except in _Gryllotalpa_. On the other hand, it is
said[260] that in addition to the tibial organs another pair of tympana
exists, and is seated on the second abdominal segment in a position
analogous to that occupied by the ear on the first segment of Acridiidae.
The musical powers of the crickets are remarkable, and are familiar to all
in Europe, as the performance of the house-cricket gives a fair idea of
them. Some of the Insects of the family are able to make a very piercing
noise, the note of _Brachytrypes megacephalus_ having been heard, it is
said, at a distance of a mile from where it was being produced. The mode of
{333}production is the same as in the Locustidae, rapid vibration of the
tegmina causing the edge of one of them to act on the file of the other.
The mole-cricket, _Gryllotalpa vulgaris_—the _Werre_ of the Germans,
_Courtilière_ of the French—is placed with a few allies in a special group,
Gryllotalpides, characterised by the dilated front legs, which are
admirably adapted for working underground. Like the mole, this Insect has a
subterranean existence. It travels in burrows of its own formation, and it
also forms beneath the surface a habitation for its eggs and family. Its
habits have been alluded to by Gilbert White,[261] who tells us that "a
gardener at a house where I was on a visit, happening to be mowing, on the
6th of May, by the side of a canal, his scythe struck too deep, pared off a
large piece of turf, and laid open to view a curious scene of domestic
economy: there were many caverns and winding passages leading to a kind of
chamber, neatly smoothed and rounded, and about the size of a moderate
snuff-box. Within this secret nursery were deposited near a hundred eggs of
a dirty yellow colour, and enveloped in a tough skin, but too lately
excluded to contain any rudiments of young, being full of a viscous
substance. The eggs lay but shallow, and within the influence of the sun,
just under a little heap of fresh moved mould like that which is raised by
ants."
[Illustration: FIG. 206.—Front leg of the mole-cricket. A, outer; B, inner
aspect: _e_, ear-slit.]
The front legs are remarkable structures (Fig. 206), being beautifully
adapted for burrowing; the tibiae and tarsi are arranged so as to act as
shears when it may be necessary to sever a root. The shear-like action of
the tarsus and tibia is very remarkable; the first and second joints of the
former are furnished with hard processes, which, when the tarsus is moved,
pass over the edges of the tibial teeth in such a way as to be more
effective than a pair of shears. In consequence of its habit of cutting
roots, {334}the mole-cricket causes some damage where it is abundant. It is
now a rare Insect in England, and is almost confined to the southern
counties, but in the gardens of Central and Southern Europe it is very
abundant. Its French name _courtilière_ is supposed to be a corruption of
the Latin _curtilla_. Its fondness for the neighbourhood of water is well
known. De Saussure says that in order to secure specimens it is only
necessary to throw water on the paths between the flower-beds of gardens
and to cover the wetted places with pieces of board; in the morning some of
these Insects are almost sure to be found under the boards disporting
themselves in the mud. The Gryllotalpae swim admirably by aid of their
broad front legs.
Ears exist in the mole-cricket, and are situate on the front leg below the
knee, as in other Gryllidae, although it seems strange that a leg so
profoundly modified for digging and excavating as is that of the
mole-cricket should be provided with an ear. In _Gryllotalpa_ the ear is
concealed and protected by being placed in a deep slit or fold of the
surface, and this depression is all that can be seen by examination of the
exterior (Fig. 206, _e_). In the allied genus _Scapteriscus_ the tympanal
membrane is, however, destitute of special protection, being completely
exposed on the surface of the leg.
Although the tegmina or upper wings in _Gryllotalpa_ are of small size, yet
the true wings are much more ample; they are of delicate texture and
traversed by many nearly straight radii, so that they close up in the most
complete manner, and form the two long delicate, flexible processes that in
the state of repose may be seen projecting not only beyond the tegmina, but
actually surpassing the extremity of the body hanging down behind it, and
looking like a second pair of cerci.
The mole-cricket is believed to be chiefly carnivorous in its diet, though,
like many other Orthoptera, it can accommodate its appetite to parts of the
vegetable as well as of the animal kingdom. The Insect is capable of
emitting a sound consisting of a dull jarring note, somewhat like that of
the goat-sucker. For this purpose the tegmina of the males are provided
with an apparatus of the nature we have already described, but which is
very much smaller and less elaborate than it is in the true crickets.
{335}[Illustration: FIG. 207.—Alimentary canal and appendages of the
mole-cricket: _a_, head; _b_, salivary glands and receptacle; _c_, lateral
pouch; _d_, stomato-gastric nerves; _e_, anterior lobes of stomach; _f_,
peculiar organ; _g_, neck of stomach; _h_, plicate portion of same; _i_,
rectum; _k_, lobulate gland; _l_, extremity of body; _m_, Malpighian tubes.
(After Dufour.)]
The alimentary canal and digestive system of _Gryllotalpa_ present
peculiarities worthy of notice. Salivary glands and reservoirs are present;
the oesophagus is elongate, and has on one side a peculiar large pouch
(Fig. 207, _c_); beyond this is the gizzard, which is embraced by two lobes
of the stomach. This latter organ is, beyond the lobes, continued backwards
as a neck, which subsequently becomes larger and rugose-plicate. On the
neck of the stomach there is a pair of branching organs, which Dufour
considered to be peculiar to the mole-cricket, and compared to a spleen or
pancreas. The single tube into which the Malpighian tubules open is seated
near the commencement of the small intestine. These tubules are very fine,
and are about one hundred in number. The arrangement by which the
Malpighian tubules open into a common duct instead of into the intestine
itself appears to be characteristic of the Gryllidae, but is said to occur
also in _Ephippigera_, a genus of Locustidae. According to Leydig[262] and
Schindler the Malpighian tubules are of two kinds, differing in colour,
and, according to Leydig, in contents and histological structure. Near the
posterior extremity of the rectum there is a lobulated gland having a
reservoir connected with it; this is the chief source of the foetid
secretion the mole-cricket emits when seized. The nervous chain consists of
three thoracic and four abdominal ganglia; these latter do not extend to
the extremity of the body; {336}the three anterior of the four ganglia are
but small, the terminal one being much larger.
The number of eggs deposited by a female mole-cricket is large, varying, it
is said, from 200 to 400. The mother watches over them carefully, and when
they are hatched, which occurs in a period of from three to four weeks
after their deposition, she supplies the young with food till their first
moult; after this occurs they disperse, and begin to form burrows for
themselves.
It has been said that the young are devoured by their parents, and some
writers have gone so far as to say that 90 per cent of the progeny are thus
disposed of. M. Decaux, who has paid considerable attention to the economy
of the mole-cricket,[263] acquits the mother of such an offence, but admits
that the male commits it. The number of eggs in one nest is said to be
about 300.
The embryonic development of the mole-cricket has been studied by
Dohrn[264] and Korotneff,[265] and is considered by the former to be of
great interest. The tracheae connected with each stigma remain isolated,
while, according to Korotneff, the development of the alimentary canal is
not completed when the young mole-cricket is hatched. Perhaps it may be
this condition of the digestive organs that necessitates the unusual care
the mother bestows on her young.
[Illustration: FIG. 208.—_Cylindrodes kochi._ Australia. A, outline of the
Insect with five of the legs and the extremity of the body mutilated; B,
middle leg. (After de Saussure.)]
The genus _Cylindrodes_ (Fig. 208, _C. kochi_) comprises some curious and
rare Insects of elongate, slender form. They are natives of Australia,
where the first species known of the genus was found in Melville Island by
Major Campbell, from whom we learn that these Insects burrow in the stems
of plants, and are so destructive that he was unable to keep a single plant
in his greenhouse on account of the ravages of _Cylindrodes campbellii_.
The form of these Insects is beautifully adapted to {337}their habits, the
body being contracted in the middle in such a way as to permit the middle
and hind legs to be packed against it, so that the cylindrical form is not
interfered with by these appendages while the excavating anterior legs are
at work in front of the Insect. The abdomen has nine segments; the terminal
one, said to be remarkably long and destitute of cerci, is not shown in our
figure.
The genus _Tridactylus_ is considered by de Saussure to form, with its ally
_Rhipipteryx_, a division of Gryllotalpinae, but they are treated, perhaps
more correctly, by Brunner as a separate tribe. _T. variegatus_ (Fig. 209)
is a small Insect, abundant in sandy places on the banks of rivers in
Southern Europe,—extending on the Rhone as far north as Geneva,—and is
remarkable for its great power of leaping, and for the rapidity with which
it can burrow in the sand. This anomalous Insect has only ten joints to the
antennae. Its alar organs are imperfect, and not like those of other
Gryllidae in either form or neuration. The hind legs are of peculiar
structure, the tibiae terminating in two processes between which is situate
a rudimentary tarsus. Near the extremity of the tibia there are some
plates, forming two series, that can be adpressed to the tibia, or extended
as shown in our figure. The body is terminated by four rather short, very
mobile processes; the upper pair of these are each two-jointed, and are
thought by de Saussure and Haase[266] to be cerci; the inferior pair, being
articulated processes of the anal segment, their presence in addition to
cerci is remarkable. It is difficult to distinguish the sexes of this
Insect.
[Illustration: FIG. 209.—_Tridactylus variegatus_, France.]
The exotic genus _Rhipipteryx_ is allied to _Tridactylus_. It is widely
distributed in South America, but the little Insects that {338}compose it
are rare in collections, their saltatorial powers no doubt making it
difficult to catch them; little is known as to their habits. In the
undescribed Amazonian species we figure (Fig. 210), the wings, instead of
being mere rudiments, as in _Tridactylus_, are elongate and project beyond
the body; they are of a blue-black colour, and arranged so as to look as if
they were the abdomen of the Insect; they, moreover, have a transverse
pallid mark, giving rise to an appearance of division. It is difficult to
form any surmise as to the nature of so curious a modification of the
wings.
The Tridactylides have no tympana on the legs, and their affinity with the
Gryllidae is very doubtful. Dufour thought _T. variegatus_ to be more
allied to the Acridiidae. He based this opinion chiefly on some points of
the internal anatomy, but pointed out that _Tridactylus_ differs from the
Acridiidae in having no air-sacs in the body.
[Illustration: FIG. 210.—_Rhipipteryx_ sp., Amazon valley.]
Not many of the Gryllidae are so peculiar as the forms we have mentioned.
The family consists in larger part of Insects more or less similar to the
common cricket, though exhibiting a great variety of external form. The
common cricket of our houses, _Gryllus (Acheta) domesticus_ (Fig. 204), has
a very wide distribution in the Old World, and is also found in North
America. It is believed to have had its natural distribution extended by
commerce, though really nothing is known as to its original habitat. The
shrill chirping of this little Insect is frequently heard at night in
houses, even in the most densely inhabited parts of great cities. Neither
the female nor the young are musical, yet the chirping may be heard at all
seasons of the year, as young and adults coexist independent of season. The
predilection of _Gryllus domesticus_ for the habitations of man is very
curious. The Insect is occasionally found out of doors in the neighbourhood
of dwelling-houses in hot weather, but it does not appear that this species
leads anywhere a truly wild life. It is fond of heat; though it rarely
multiplies in dwelling-houses to any great extent, it is sometimes found in
profusion in {339}bake-houses. Usually the wings in the cricket are
elongate, and project backwards from under the tegmina like an additional
pair of cerci; a variety, however, occurs in which these tails are absent,
owing to abbreviation of the wings.
There is no beauty in the appearance of any of the Gryllidae, though many
of them are very bizarre in shape. Very few of them venture to leave the
surface of the earth to climb on plants. The species of _Oecanthus_,
however, do so, and may be found sitting in flowers. They have a more
Locustoid appearance than other Gryllidae. One of the most curious forms of
the family is _Platyblemmus_, a genus of several species found in the
Mediterranean region, the male of which has the head prolonged into a
curious process (Fig. 211); this varies greatly in development in the males
of the same species. It would seem that this organ is of a similar nature
to the extraordinary structures we have figured in Locustidae (Fig. 189)
and Mantidae (Fig. 136), though it appears impossible to treat the cephalic
appendages of _Platyblemmus_ as ornamental objects; their import is at
present quite obscure.
A curious form of variation occurs in this family, and is called
micropterism by de Saussure; we have already mentioned its occurrence in
the house-cricket. The hind wings, which are usually ample, and frequently
have their extremities rolled up and protruding like cerci, are sometimes
much smaller in size, and not visible till the tegmina are expanded. De
Saussure at one time supposed these micropterous individuals to be distinct
species; it is now, however, known that intermediate examples can be found
by examining a great many specimens. Some species are always micropterous.
[Illustration: FIG. 211.—_Platyblemmus lusitanicus_, male. A, front of
head; B, profile of Insect with most of the appendages removed.]
In Britain we have only four representatives of the Gryllidae, viz. the
mole-cricket, the house-cricket, and two field-crickets, one of which,
_Nemobius sylvestris_, is considerably smaller than the house-cricket,
while the other, _Gryllus campestris_, the true field-cricket, is a larger
Insect. Its habits have been described in an interesting manner in Gilbert
White's 88th letter. {340}This Insect, like so many others, is apparently
becoming rare in this country.
A single fossil from the Lias has been described as belonging to the
Gryllidae, but in the Tertiary strata a variety of members of the family
have been discovered both in Europe and North America.
The classification of Gryllidae is due to de Saussure,[267] and is said by
Brunner to be very natural. In the following synopsis of the tribes of
crickets we give de Saussure's arrangement, except that we follow Brunner
in treating Tridactylides as a distinct tribe:—
1. Antennae ten-jointed; posterior tarsi aborted. Tribe 1. TRIDACTYLIDES.
(Fig. 209, _Tridactylus variegatus_; Fig. 210, _Rhipipteryx_ sp.)
1′. Antennae many jointed; posterior tarsi normal.
2. Tarsi compressed, the second joint minute.
3. Anterior legs fossorial; anterior tibiae at the apex with two to
four divisions. Pronotum elongate, ovate, rounded behind. Female
without ovipositor. Tribe 2. GRYLLOTALPIDES. (Fig. 206, front legs of
_Gryllotalpa_; Fig. 208, _Cylindrodes kochi_.)
3′. Anterior legs formed for walking. Ovipositor of the female
visible (either elongate or rudimentary).
4. Posterior tibiae biseriately serrate. Tribe 3. MYRMECOPHILIDES.
4′. Posterior tibiae biseriately spinose. Ovipositor straight.
5. Antennae short, thickish, almost thread-like. Facial
scutellum exserted between antennae. Posterior tibiae dilated.
Gen. _Myrmecophila_.[268]
5′. Antennae elongate, setaceous. Facial scutellum transverse,
visible below the antennae. Tibiae slender.
6. Posterior tibiae armed with two strong spines, not serrate
between the spines. Tribe 4. GRYLLIDES. (Fig. 204, _Gryllus
domesticus_; Fig. 211, _Platyblemmus lusitanicus_.)
6′. Posterior tibiae slender, armed with slender spines, and
serrate between them. Tribe 5. OECANTHIDES.
2′. Second joint of the tarsi depressed, heart-shaped.
3. Posterior tibiae not serrate, but biseriately spinose.
4. The spines on each side three and mobile; apical spurs on the
inner side only two in number. Ovipositor short, curved. Tribe 6.
TRIGONIDIIDES.
4′. The spines numerous, fixed. Ovipositor elongate, straight. Gen.
_Stenogryllus_.
3′. Posterior tibiae serrate and spinose on each side, the apical
spurs, as usual, three on each side. Ovipositor straight or curved.
Tribe 7. ENEOPTERIDES.
{341}CHAPTER XV
NEUROPTERA—MALLOPHAGA—EMBIIDAE
ORDER III. NEUROPTERA.
_Imago with biting mouth; with two pairs of wings, the anterior as well as
the posterior membranous, usually with extensive neuration, consisting of
elongate nervures and either of short cross-nervules forming numerous cells
or of a complex minute mesh-work. (One division, Mallophaga, consists
entirely of wingless forms; in Termitidae some of the individuals of each
generation become winged, but others do not: except in these cases adult
wingless forms are few.) The metamorphosis differs in the several
divisions._
[Illustration: FIG. 212.—_Osmylus chrysops_, New Forest.]
The Neuroptera form a heterogeneous, though comparatively small, Order of
Insects, including termites, stone-flies, dragon-flies, may-flies,
caddis-flies, lace-wings, scorpion-flies, ant-lions, etc. Bird-lice are
also included in Neuroptera, though they have no trace of wings.
We treat the Order as composed of eleven distinct families, {342}and, as a
matter of convenience, arrange them in five divisions:—
1. _Mallophaga_.—Permanently wingless Insects, living on the bodies of
birds or mammals. (Development very imperfectly known.) Fam. 1.
Mallophaga.
2. _Pseudoneuroptera_.—Insects with wings in adult life (in some cases
wings are never acquired). The wings are developed in a visible manner
outside the body. There is no definite pupa. Live entirely on land. Fam.
2. Embiidae; 3. Termitidae; 4. Psocidae.
3. _Neuroptera amphibiotica_.—Wings developed as in division 2. Three
ocelli usually exist. Life aquatic in the early stages. Fam. 5. Perlidae;
6. Odonata; 7. Ephemeridae.
4. _Neuroptera planipennia_.—Wings developed internally; not visible in
early stages, but becoming suddenly evident when the pupal form is
assumed. Mandibles present in the adult Insect. Life in early stages
aquatic or terrestrial. Fam. 8. Sialidae; 9. Panorpidae; 10.
Hemerobiidae.
5. _Trichoptera_.—Development as in division 4. Mandibles absent in the
adult Insect. Life aquatic in the early stages. Fam. 11. Phryganeidae.
The families we have enumerated in the preceding scheme are now generally
adopted by entomologists. Great difference of opinion exists, however, as
to the groups of greater value than the family, and for a long time past
various schemes have been in vogue. Though it is necessary to allude to the
more important of these systems, we can do so only in the briefest manner.
Some of the families of Neuroptera are similar in many points of structure
and development to Insects of other Orders; thus Termitidae are somewhat
allied to Blattidae, Perlidae to Phasmidae in Orthoptera, while the
Phryganeidae or Trichoptera make a considerable approach to Lepidoptera.
Some naturalists—among whom we may mention Burmeister and Grassi—unite our
Aptera, Orthoptera, and most of our Neuroptera into a single Order called
Orthoptera. Others treat our Neuroptera as consisting of eight or nine
distinct Orders; these, together with the names proposed for them, we have
already alluded to in our chapter on classification, pp. 171-177.
Erichson, impressed by the variety existing in Neuroptera, separated some
of the groups into a sub-Order called Pseudoneuroptera; this sub-Order
comprised our Termitidae, Psocidae, Ephemeridae, and Libellulidae. This
division is still adopted in several treatises; the Pseudoneuroptera are
indeed by some naturalists retained as an Order distinct from both
Orthoptera {343}and Neuroptera. Gerstaecker subsequently made use of a
system somewhat different from that of Erichson, uniting the Perlidae,
Ephemeridae, and Odonata into a group called _Orthoptera amphibiotica_,
from which the Termitidae and Psocidae were excluded. The divisions we have
here adopted differ but little from those of Gerstaecker, though we have
arranged them in a very different manner. It is probable that not one-tenth
part of the Neuroptera existing in the world have yet been examined by
entomologists, and of those that are extant in collections, the
life-histories and development are very imperfectly known. We have,
therefore, not considered it wise to adopt a system that would involve
great changes of nomenclature, while there can be little hope of its
permanency.
FOSSILS.—When considering the subject of fossil Insects we briefly alluded
to the discussions that have occurred as to whether the fossils of the
palaeozoic period should be referred to existing Orders. Since the pages we
allude to were printed, M. Brongniart's very important work[269] on the
Insects of that epoch has appeared. He considers that these ancient fossils
may be classified with the existing Orders of Insects, though they cannot
be placed in existing families; and he assigns the palaeozoic fossil
Insects at present known, to the Orders Neuroptera and Orthoptera, and to
the homopterous division of Hemiptera. The greater part of the species he
looks on as Neuroptera, and places in six families—Megasecopterides,
Protephemerides, Platypterides, Stenodictyopterides, Protodonates, and
Protoperlides. Of these he considers the ancient Protephemerides,
Protodonates, and Protoperlides as the precursors, which, we presume, we
may interpret as the actual ancestors, of our existing Ephemeridae,
Odonata, and Perlidae.
Some of the fossils restored and described by the French entomologist are
of great interest. We shall notice the Protephemerides, Protodonates, and
Protoperlides in connexion with the families to which they are specially
allied, and shall now only allude to the quite extinct families of
Neuroptera, the Megasecopterides, Platypterides, and Stenodictyopterides.
It is a peculiarity of these ancient Insects that they were much larger
creatures than the corresponding forms that now exist. This may be due, to
some extent, to the fact that tiny, {344}fragile forms have not been
preserved in the rocks, or have not attracted the attention of collectors;
but as some of the palaeozoic Insects were absolutely the largest
known—surpassing considerably in size any Insects at present existing—it is
probable that, even if small forms existed at the remote epoch we are
alluding to, the average size of the individual was greater than it is at
present. The Megasecopterides of the carboniferous epoch were Insects of
large size, with long, narrow wings, a small prothorax, and large meso- and
meta-thorax, these two segments being equal in size; the abdomen was
elongate and moderately voluminous, and was terminated by a pair of very
elongate, slender filaments like those of the may-flies. The family
includes several genera and species found at Commentry. One of these forms,
_Corydaloides scudderi_, is of great interest, as it is believed by
Brongniart that the imago possessed tracheal gills situated on the sides of
the abdomen, analogous with those that exist at present in the immature
condition of certain Ephemeridae. They are of interest in connexion with
the gills found at the present time in the imagos of _Pteronarcys_ (see p.
401). Although these fossils are of such enormous antiquity, the tracheae
can, M. Brongniart says, be still perceived in these processes.
The Platypterides include also a considerable number of Insects of large
size, with four large equal wings, frequently spotted or variegate. Some of
these Insects were provided with expansions or lobes on the sides of the
prothorax (Fig. 213); these are looked on as analogous to the expansions of
meso- and meta-thorax, which are supposed by some writers to have been the
rudiments from which wings were developed. These prothoracic
wing-rudiments, if such they be, are said to have a system of nervures
similar to what we find in true wings. The genus _Lithomantis_ includes a
Scotch fossil, and has already been mentioned by us on p. 259.
[Illustration: FIG. 213.—_Lithomantis carbonaria_. Carboniferous strata of
Commentry, France. (After Brongniart.)]
The third family of extinct carboniferous Neuroptera is the
Stenodictyopterides, in which Brongniart places the _Dictyoneura_ of
{345}Goldenberg, the North American _Haplophlebium_, and several genera
from Commentry. Some of them were very large Insects, with robust bodies,
and possessed wing-like expansions on the prothorax, and lateral gill-like
appendages on the sides of the abdomen.
It is worthy of note that though so large a number of carboniferous
Neuroptera have now been discovered, no larvae or immature forms have been
found.
We now pass to the consideration of the divisions of Neuroptera still
living.
FAM. I. MALLOPHAGA—BIRD-LICE OR BITING LICE.
_Small Insects, wingless, with large head; thorax usually of two, rarely
of one or three segments; prothorax always distinct; hind body consisting
of eight to ten segments, in addition to the posterior two thoracic
segments which usually are but little or not at all separated from it.
The metamorphosis is very slight. The creatures live on the skins of
birds or mammals, finding nourishment in the epidermal products._
The whole of the Insects of this family live a parasitic, or rather
epizoic, life. They all creep about those parts that are near to the skin,
the feathers of birds or the hair of mammals; they rarely come quite to the
surface, so that they are not detected on a superficial examination. It is
curious that under these circumstances they should exhibit so great a
variety of form and of anatomical characters as they do.
[Illustration: FIG. 214.—_Trinoton luridum_. Lives on the common duck and
various species of _Anas_. (After Giebel.)]
They are very depressed, that is, flat, Insects, with a large head, which
exhibits a great variety of shape; frequently it is provided in front of
the antennae with some peculiar tubercles called trabeculae, which in some
cases are mobile. The antennae are never large, frequently very small; they
consist of from three to five joints, and are sometimes concealed in a
cavity on the under side of the head.
{346}[Illustration: FIG. 215.—Under-surface of head of _Lipeurus
heterographus_. (After Grosse.) _ol_, Labium; _md_, mandible; _mx_,
maxilla; _ul_, labium.]
[Illustration: FIG. 216.—Under lip of _Nirmus_, A; and of _Tetrophthalmus
chilensis_, B. (After Grosse.) _m_, Mentum; _g_, ligula; _pl_, palp; _pg_,
paraglossa; _hy_, lingua.]
The eyes are very rudimentary, and consist of only a small number of
isolated facets placed behind the antennae; sometimes they are completely
absent. The mouth parts are situated entirely on the under-surface of the
head and in a cavity. The upper lip is frequently of remarkable form, as if
it were a scraping instrument (_ol_, Fig. 215). The mandibles are sharply
toothed and apparently act as cutting instruments. The maxillae have been
described in the principal work on the family[270] as possessing in some
cases well-developed palpi. According to Grosse[271] this is erroneous; the
maxillae, he says, are always destitute of palpi, and are of peculiar form,
being each merely a lobe of somewhat conical shape, furnished on one aspect
with hooks or setae. The under lip is peculiar, and apparently of very
different form in the two chief groups of Mallophaga. The large mentum
bears, in Liotheides (Fig. 216, B), on each side a four-jointed palpus, the
pair of palps being very widely separated; the ligula is broad and
undivided; on each side there is a paraglossa bearing an oval process, and
above this is a projection of the hypopharynx. In Philopterides (Fig. 216,
A) the palpi are absent, and the parts of the lower lip are—with the
exception of the paraglossae—but little differentiated. The lingua
(hypo-pharynx) in Mallophaga is largely developed, {347}and bears near the
front a chitinous sclerite corresponding with another placed in the
epipharynx.
The prothorax in Mallophaga is a distinct division of the body even when
the meso- and meta-thorax appear to be part of the abdomen. The mesothorax
is frequently very small; it and the metathorax are sometimes intimately
connected. In other cases (_Laemobothrium_) the metathorax appears to
differ from the following abdominal segment only by having the third pair
of legs attached to it. In _Trinoton_ (Fig. 214) the three thoracic
segments are well developed and distinct. The abdominal segments visible,
vary in number from eight to ten; there is sometimes a difference according
to sex, the male having one segment taken into the interior in connexion
with the reproductive organs. The legs have short, broad coxae and small
tarsi of one or two joints; very rarely three joints are present; there are
either one or two claws; the legs with one claw being adapted for clinging
to or clutching hairs. The front pair of legs is used not for locomotion so
much as for grasping the food and bringing it within the range of the
mouth. No trace of wings has been detected in any species.
[Illustration: FIG. 217.—Ganglia of nervous system of _Lipeurus bacillus_.
(After Giebel.) _a_, Cavity of head.]
The nervous system has been examined by Giebel in _Lipeurus bacillus_;
there is a supra- and an infra-oesophageal ganglion, and three thoracic,
but no abdominal ganglia. The supra-oesophageal is remarkably small, in
fact not larger than the infra-oesophageal; it consists evidently of two
conjoined halves. The alimentary canal has a slender, elongate oesophagus,
dilated behind into a crop; this is frequently received between two cornua
formed by the anterior part of the stomach, which, except for these, is
simply tubular in form, though somewhat narrower at the posterior
extremity. In some forms—Philopterides—the crop is of a very peculiar
nature (Fig. 218), forming an abrupt paunch separated from the stomach by
the {348}posterior portion of the oesophagus. There are only four
Malpighian tubes; in some species the basal half of each tube is much
dilated. The two divisions of the intestine are short and are separated by
the intervention of a glandular girdle. Salivary glands exist; Giebel
figures what we may consider to be an enormous salivary reservoir as
existing in _Menopon leucostomum_.
The testes and ovaries are of a simple nature. The former consist of two or
three capsules, each having a terminal thread; the vasa deferentia are
tortuous and of variable length; they lead into the anterior part of the
ejaculatory duct, where also opens the elongate duct proceeding from the
bicapsular vesicula seminalis; these structures have been figured by
Grosse[272] as well as by Giebel. The ovaries consist of three to five
short egg-tubes on each side; the two oviducts combine to form a short
common duct with which there is connected a receptaculum seminis.
[Illustration: FIG. 218.—Alimentary canal of _Docophorus fuscicollis_.
(After Giebel.) _a_, Oesophagus; _b_, paunch; _a′_, posterior division of
oesophagus; _c_, chylific ventricle or stomach; _d_, Malpighian tubes; _e_,
small intestine; _f_, glandular girdle; _g_, rectum.]
The eggs of some Mallophaga have been figured by Melnikow;[273] they
possess at one extremity a cover with a multiple micropyle-apparatus, and
at the opposite pole are provided with seta-like appendages. They are very
like the eggs of the true lice, and are said in some cases to be suspended
by threads to the hairs or feathers after the fashion of the eggs of
Pediculi.
Little is known as to the development; the young are extremely like the
adult, and are thought to moult frequently; the duration of life is quite
unknown.
It has been stated by some writers that the mouth is truly of the sucking
kind, and that the Mallophaga feed on the blood of their hosts. This is,
however, erroneous; they eat the delicate portions of the feathers of
birds, and of mammals perhaps the young hair. Their fertility is but small,
and it is believed that {349}in a state of nature they are very rarely an
annoyance to their hosts. The majority of the known species live on birds;
the forms that frequent mammals are less varied and have been less studied;
most of them have only one claw to the feet (Fig. 220), while the greater
portion of the avicolous species have two claws.
[Illustration: FIG. 219.—_Lipeurus ternatus_, male; inhabits _Sarcorhamphus
papa_. (After Giebel.)]
[Illustration: FIG. 220.—_Trichodectes latus_, male; inhabits the dog,
_Canis familiaris_.]
Most of the forms have the anterior legs small, and they are usually drawn
towards the mouth, owing, it is believed, to their being used after the
manner of hands to bring the food to the mouth; hence in some of our
figures (219, 220) the body looks as if it had only four legs.
Very diverse statements have been made as to whether allied forms of
Mallophaga are found only on allied birds. It would appear that this is the
case only to a limited extent, as certain species are found on quite a
variety of birds; moreover, some birds harbour several species of
bird-lice, even five genera having been found, it is said, on one species
of bird. _Docophorus icterodes_ has been recorded as occurring on many
kinds of ducks and geese; the swan, however, harbours a distinct species,
_Docophorus cygni_, and this is said to have also been found on the
bean-goose.
At least five species, belonging to three distinct genera, have been found
on the common fowl. The parasite most frequently met with on this valuable
creature is _Menopon pallidum_ (Fig. {350}221), which is said to have been
figured by Redi two hundred years ago under the name of _Pulex capi_. This
species multiplies to a considerable extent; it is of very active habits,
and passes readily from one bird to another, so that it is found on other
species besides the domestic fowl. It is even said that horses kept near
hen-roosts have been seriously troubled by _Menopon pallidum_, but it is
suggested by Osborn that these attacks may perhaps have been really due to
itch-mites. There is, however, no doubt that this species may infest
poultry, especially if sickly, to an enormous extent. The dust-baths in
which poultry are so fond of indulging are considered to be of great use in
keeping down the numbers of this Insect.
[Illustration: FIG. 221.—_Menopon pallidum_; inhabits the common fowl,
_Gallus domesticus_. (After Piaget.)]
A table of the birds and mammals on which Mallophaga have been found,
together with the names of the latter, has been given by Giebel.[274] The
classification of the group, so far as the principal divisions are
concerned, by no means accords with the kind of animals that serve as
hosts, for the only two genera peculiar to quadrupeds (_Trichodectes_, Fig.
220; and _Gyropus_) belong to the two chief divisions of Mallophaga. The
genus _Menopon_ includes numerous species found on birds, and three or four
others peculiar to mammals.
Two very natural divisions, Philopterides and Liotheides, were adopted by
Giebel and Nitzsch, but unfortunately the chief character they made use of
for diagnosing the two groups—the presence or absence of maxillary
palpi—was illusory. Apparently the labial palps will serve the purpose of
distinguishing the two divisions, they being present in the Liotheides and
absent in the Philopterides. A table of the characters of the avicolous
genera of these two groups is given by Grosse.[275]
The Liotheides are more active Insects, and leave their host after its
death to seek another. But the Philopterides do not do so, and die in about
three days after the death of their host. Possibly Mallophaga may be
transferred from one bird to another {351}by means of the parasitic
two-winged flies that infest birds. The writer has recorded[276] a case in
which a specimen of one of these bird-flies captured on the wing was found
to have some Mallophaga attached to it.
We should perhaps point out that these Mallophaga, though called bird-lice,
have nothing to do with the true lice which are so frequently found with
them, and that live by sucking the blood of their hosts. It would in fact
be better to drop the name of bird-lice altogether, and call the Mallophaga
biting lice. _Trichodectes latus_, according to this method, would be known
as the biting louse of the dog, the true or sucking louse of which animal
is _Haematopinus piliferus_, and belongs to the anoplurous division of
Hemiptera.
FAM. II. EMBIIDAE.
_Elongate feeble Insects; with small prothorax, elongate meso- and
meta-thorax, which may either bear wing or be without them. In the former
case these organs are not caducous, are delicately membranous, and all of
one consistence, with three or four indefinite longitudinal nervures and
a few cross-veinlets. The development is incompletely known. The
individuals do not form organised societies._
[Illustration: FIG. 222.—_Oligotoma michaeli._ (After M‘Lachlan.)]
The Embiidae are one of the smallest families of Insects; not more than
twenty species are known from all parts of the world, and it is probable
that only a few hundred actually exist. They are small and feeble Insects
of unattractive appearance, and shrivel so much after death as to render it
difficult to ascertain their characters. They require a warm climate. Hence
{352}it is not a matter for surprise that little should be known about
them.
[Illustration: FIG. 223.—Under-surface of _Embia_ sp. Andalusia.]
The simple antennae are formed of numerous joints, probably varying in
number from about fifteen to twenty-four. The mouth is mandibulate. Chatin
states[277] that the pieces homologous with those of a maxilla can be
detected in the mandible of _Embia_. The labium is divided. The legs are
inserted at the sides of the body, the coxae are widely separated (Fig.
223), the hind pair being, however, more approximate than the others. The
abdomen is simple and cylindrical, consisting of ten segments, the last of
which bears a pair of biarticulate cerci. In the male sex there is a slight
asymmetry of these cerci and of the terminal segment. The thorax is
remarkable on account of the equal development of the meso- and meta-thorax
and their elongation in comparison to the prothorax. When they bear wings
there is no modification or combination of the segments for the purposes of
flight, the condition of these parts being, even then, that of wingless
Insects; so that the Embiidae that have wings may be described as
apterous-like Insects provided with two pairs of inefficient wings. The
wings are inserted on a small space at the front part of each of the
segments to which they are attached. The legs have three-jointed tarsi, and
are destitute of a terminal appendage between the claws.
[Illustration: FIG. 224.—Anterior wing of _Oligotoma saundersii_: A, the
wing; B, outline of the wing, showing nervures. (After Wood-Mason.) 1,
Costal; 2, subcostal; 3, radial; 4, discoidal; 5, anal nervure.]
The wings in Embiidae are very peculiar; they are extremely {353}flimsy,
and the nervures are ill-developed; stripes of a darker brownish colour
alternate with pallid spaces. We figure the anterior wing of _Oligotoma
saundersii_, after Wood-Mason; but should remark that the neuration is
really less definite than is shown in these figures; the lower one
represents Wood-Mason's interpretation of the nervures. He considers[278]
that the brown bands "mark the original courses of veins which have long
since disappeared." A similar view is taken by Redtenbacher,[279] but at
present it rests on no positive evidence.
One of the most curious features of the external structure is the complex
condition of the thoracic sternal sclerites. These are shown in Fig. 223,
representing the under-surface of an _Embia_ of uncertain species recently
brought by Mr. Bateson from Andalusia.
According to Grassi[280] there are ten pairs of stigmata, two thoracic and
eight abdominal; these are connected by longitudinal and transverse
tracheae into a single system. The ganglia of the ventral chain are, one
suboesophageal, three thoracic, and seven abdominal; these are segmentally
placed, except that there is no ganglion in the fifth abdominal segment.
There is a stomato-gastric system but no "sympathetic." Salivary glands are
present. The stomodaeal portions of the alimentary canal are remarkably
capacious; the stomach is elongate and slender, without diverticula; the
Malpighian tubes are elongate and slender; they vary in number with the age
of the individual, attaining that of twenty in the adult. The ovaries are
arranged somewhat after the fashion of those of _Japyx_, there being in
each five short egg-tubes, opening at equal intervals into a straight duct.
The testes are remarkably large; each one consists of five masses of
lobules, and has a large vesicula seminalis, into the posterior part of
which there open the ducts of two accessory glands. The large joint of the
front tarsus includes glands whose secretion escapes by orifices at the
tips of certain setae interspersed between the short spines that are placed
on the sole.
Species of this genus occur in the Mediterranean region, but their
characters have not yet been examined. Our information {354}as to these is
chiefly to be found in Grassi's work. The two species studied by him were
wingless. They live under stones, where they spin webs by means of the
front feet, whose first joint is, as we have said, enlarged and contains
glands; the Insect uses the webs as a means of support in progression,
acting on them by means of papillae and a comb-like structure placed on the
four posterior feet.
Grassi informs us that these Insects are not uncommon under stones in
Catania; they require moisture as well as warmth, but not too much;
sometimes there is only one individual found under a stone, at others eight
or ten. In the winter and spring their galleries are found on the surface
of the earth, but in the hot months of summer they secure the requisite
amount of moisture by sinking their galleries to the depth of ten or
fifteen centimetres. Their food consists chiefly of vegetable matter. They
may be reared with ease in glass vessels. Other species of the family
attain wings; the details of the process are not well known. _Oligotoma
michaeli_ (Fig. 222) was discovered in a hothouse in London among some
orchid roots brought from India, and was found in more than one stage of
development; the young greatly resemble the adult, except in the absence of
wings. A nymph-form is described by M‘Lachlan[281] as possessing wings of
intermediate length, and Hagen has suggested that this supposed nymph is
really an adult female with short wings. If this latter view be correct,
nothing is known as to the mode of development of wings in the family. It
is still uncertain whether female Embiidae ever possess wings. Wood-Mason
and Grassi have shown that there are wingless females in some species, and
we know that there are winged males in others, but what the usual relation
of the sexes may be in this respect is quite uncertain. These Insects have
been detected in various parts of the world. In the Sandwich Islands
_Oligotoma insularis_ was discovered by the Rev. T. Blackburn in the wood
and thatch forming the roofs of natives' houses. A species has been found
in Prussian amber, and Grassi thinks that _Embia solieri_—one of the
Mediterranean species—is not to be distinguished with certainty from the
Insect found in amber.
Embiidae still remains one of the most enigmatic of the families of
Insects. Although Grassi's recent observations are {355}of great value from
an anatomical point of view, they rather add to, than diminish, the
difficulties we encounter in endeavouring to understand the lives of these
obscure creatures. That Embiidae form webs has long been known, and it was
thought by some that the webs, like those of spiders, might be of
assistance in procuring food. We may, however, infer from Grassi's
observations that this is not the case, but that the silken tunnels or
galleries—as he calls them—serve chiefly as a means of locomotion and
protection, the feet of the Insects being highly modified in conformity
with this mode of life. Grassi seems to be of opinion that the galleries
are also useful in preserving a proper degree of humidity round the
Insects. We have already alluded to the mystery that surrounds the mode of
growth of their wings. Nearly all that is known as to the Embiidae is
contained in Grassi's paper, or is referred to in Hagen's monograph of the
family.[282]
Considerable difference of opinion has prevailed as to the allies of these
obscure Insects. It would seem that they are most nearly allied to
Termitidae and Psocidae. Grassi, however, considers these affinities only
remote, and suggests that Embiidae should form a separate Order, to be
placed in a super-Order Orthoptera, which would include our Aptera, the two
families mentioned above, Mallophaga, Embiidae, and the ordinary
Orthoptera. Brauer places the family in his Orthoptera genuina.
{356}CHAPTER XVI
NEUROPTERA _CONTINUED_—TERMITIDAE, TERMITES OR WHITE ANTS
FAM. III. TERMITIDAE—WHITE ANTS, TERMITES.
[Illustration: FIG. 225.—_Termes_ (_Hodotermes_) _mossambicus_. Winged
adult. (After Hagen.)]
_Each species is social, and consists of winged and wingless individuals.
The four wings are, in repose, laid flat on the back, so that the upper
one only is seen except just at the bases; they are membranous and very
elongate, so that they extend far beyond the apex of the abdomen; the
hind pair is remarkably similar in size, form, and consistence to the
front pair: near the base of each wing there is a suture, or line of
weakness, along which the wings can be broken off, the stumps in that
case remaining as short horny flaps reposing on the back. Ligula
channelled but not divided into two parts. The wingless individuals are
very numerous, and have the head and thirteen body segments distinct; the
body {357}is terminated by a pair of short cerci. The metamorphosis is
slight and gradual, and in some individuals is dispensed with._
The term White Ants has been so long in use for the Termitidae that it
appears almost hopeless to replace it in popular use by another word. It
has, however, always given rise to a great deal of confusion by leading
people to suppose that white ants differ chiefly from ordinary ants by
their colour. This is a most erroneous idea. There are scarcely any two
divisions of Insects more different than the white ants and the ordinary
ants. The two groups have little in common except that both have a social
life, and that a very interesting analogy exists between the forms of the
workers and soldiers of these two dissimilar Orders of Insects, giving rise
to numerous analogies of habits. The word Termites—pronounced as two
syllables—is a less objectionable name for these Insects than white ants.
The integument in Termites is delicate, and the chitinous plates are never
very hard; frequently they are so slightly developed that the creature
appears to consist of a single membranous sac with creases in it, the head
alone being very distinct. The head is exserted, frequently of large size,
sometimes as large as all the rest of the body together. Termites may be
quite blind, or possess facetted and simple eyes, the latter when present
being two in number and always accompanied by facetted eyes. The antennae
are simple, consisting of from nine to thirty-one joints, which differ but
little from one another; the number in each individual increases as the
development progresses. The parts of the mouth are large, the ligula
consists of one piece (Fig. 226, A), but often has the appearance of being
formed by two united pieces; on its extremity are seated two pairs of
lobes.
[Illustration: FIG. 226.—_Termes bellicosus._ Labium, A, maxilla, B, of
winged adult; lower face of each. (After Hagen.)]
The head is articulated to the thorax by means of two very large cervical
sclerites on each side, placed at right angles to one another, and visible
on the under-surface. The prothorax is well developed and distinct from the
parts behind it. The {358}pronotum, of variable form and size, is very
distinct in the perfect Insects; with it are connected the largely
developed pleura. The episternum is very peculiar, consisting of an
elongate chitinous slip on each side hanging downwards, the two not quite
meeting in the middle; they thus form the margin of the very large anterior
orifice, and are in contiguity with the cervical sclerites; behind them are
the very large epimera. The prosternum appears to be usually entirely
membranous; in some cases the sclerite in it is small and delicate, and
apparently differs according to the species. The meso- and meta-thorax are
sub-equal in size; the mesosternum forms a peculiar, large, adpressed fold.
The metasternum is membranous, but is terminated behind by a sclerite
apparently of variable form. The hind body is voluminous, simple in form,
consisting of ten segments and bearing at the extremity two short distant
cerci of a variable number of joints. The terminal ventral sclerites differ
greatly in form according to the species and sometimes according to the
sex; there are sometimes, if not always, present near the extremity two
peculiar minute biarticulate styles, called appendices anales. The coxae
are all large, free, and exserted; at the base of each is a transverse
trochantin. The femora are articulated with the trochanters, not with the
coxae; both femora and tibiae are slender, the tarsi small, four-jointed;
the terminal joint elongate.
[Illustration: FIG. 227.—Front tibia and tarsus of _Calotermes rugosus_
larva, showing auditory organ. × 90. (After F. Müller.)]
It is now well established that Termites have a means of communication by
sounds. The individuals have a peculiar way of jerking themselves, as has
been frequently noticed by observers of the Insects; these convulsive
movements may possibly be connected with the production of sound, which may
perhaps be evoked by contact between the back of the head and the pronotum;
the exact mode by which the sounds are produced is not, however, known. The
existence of an auditory organ in the front tibia has been demonstrated by
Fritz Müller,[283] and we reproduce (Fig. 227) one of his figures. The
structure seems to {359}be in plan and position similar to the ear of
Locustidae, though much less perfect.
[Illustration: FIG. 228.—Wings of Termites: A, _Termes lucifugus_; B,
_Hodotermes brunneicornis_; C, _Culotermes nodulosus_. (After Redtenbacher:
B and C diagrammatic.) III, V, VII, homologous areas and nervures according
to Redtenbacher. 1, Costal; 2, subcostal; 3, median; 4, submedian nervures
according to Hagen.]
The wings of Termitidae are not like those of any other Insects; their
neuration is very simple, but nevertheless the wings of the different forms
exhibit great differences in the extent to which they are made up of the
various fields. This is shown in Fig. 228, where the homologous nervures
are numbered according to the systems of both Hagen and Redtenbacher. The
area, VII, that forms the larger part of the wing in C, corresponds to the
small portion at the base of the wing in B. The most remarkable feature of
the wing is, however, its division into two parts by a suture or line of
weakness near the base, as shown in Fig. 225. The wings are used only for a
single flight, and are then shed by detachment at this suture; the small
basal portion of each of the four wings is horny and remains attached to
the Insect, serving as a protection to the dorsal surface of the thorax.
The nature of the suture that enables the Termites to cast their wings with
such ease after swarming is not yet understood. There are no true
transverse veinlets or nervules in Termites. Redtenbacher suggests[284]
that the transverse division of the wing at its base, as shown in Fig. 225,
along which the separation of the wing occurs at its falling off, may have
arisen from a coalescence of the subcostal vein with the eighth concave
vein of such a wing as that of Blattidae. The same authority also informs
us that the only point of resemblance between the wings of Termitidae and
those of Psocidae is that both have an unusually small number of concave
veins.
The information that exists as to the internal anatomy of {360}Termites is
imperfect, and refers, moreover, to different species; it would appear that
considerable diversity exists in many respects, but on this point it would
be premature to generalise. What we know as to the respiratory system is
chiefly due to F. Müller.[285] The number of spiracles is ten; Hagen says
three thoracic and seven abdominal, Müller two thoracic and eight
abdominal. In fertile queens there usually exist only six abdominal
stigmata. There is good reason for supposing that the respiratory system
undergoes much change correlative with the development of the individual;
it has been suggested that the supply of tracheae to the sexual organs is
deficient where there is arrest of development of the latter.
The alimentary canal is only of moderate length. Salivary glands exist, as
also do salivary reservoirs; these latter are large, in some species
remarkably so. The oesophagus is slender, but abruptly enlarged behind to
form a large crop; a proventriculus is apparently either present or absent;
the chylific ventricle, or stomach, is slender and simple. The Malpighian
tubules are very long; their number is probably from four to eight in the
adult, and in the earlier stages less. Behind the tubes the alimentary
canal forms a large paunch, and after this there is a small intestine and
rectum. The paunch is a peculiar structure, and probably of great
importance in the economy of Termites.
These creatures emit minute quantities of a secretion that is corrosive,
and can act on metal and even glass;[286] its nature and source are not
understood. Hagen describes peculiar structures in the rectum to which he
is inclined[287] to ascribe the origin of this substance, but this is very
uncertain.
[Illustration: FIG. 229.—Head and alimentary canal of _Termes lucifugus_
(nymph). _a_, head; _b_, salivary glands; _c_, salivary receptacles; _d_,
crop; _e_, stomach; _f_, intestinal paunch; _g_, small, _h_, large
intestine; _i_, Malpighian tubes; _k_, extremity of body. (After Dufour.)]
The brain is small; the infra-oesophageal ganglion is placed
{361}immediately under the supra-oesophageal; there are three thoracic and
six abdominal ganglia. The nervous system apparently differs but little in
the various forms, or in the different stages of life, except that in the
fertile females the abdominal ganglia become so much enlarged that they
even exceed the brain in size.
The testes are unusually simple; each consists of eight capsules opening
into the vas deferens; the two vasa converge and are continued as a short
ejaculatory duct; at the point of convergence there is a pair of curled
vesiculae seminales.
The ovarian system is also simple; there is a variable number of elongate
egg-tubes, each of which opens separately into the oviduct; the two ducts
unite to form a short uterus, on which there is placed first a spermatheca,
and near the extremity a convolute tubular sebific gland. The number of
egg-tubes is subject to extraordinary variation, according to the species,
and according to the age of the fertilised individual.
SOCIAL LIFE.—Termites live in communities that consist sometimes of
enormous numbers of individuals. The adult forms found in a community are
(1) workers; (2) soldiers; (3) winged males and females; (4) some of these
winged forms that have lost their wings. Some species have no worker caste.
The individuals of the third category are only present for a few days and
then leave the nest in swarms. In addition to the adult individuals there
are also present various forms of young. The individuals that have lost
their wings are usually limited to a single pair, king and queen; there may
be more than one king and queen, but this is not usual. The king and queen
may be recognised by the stumps of their cast wings, which exist in the
form of small triangular pieces folded on the back of the thorax (Fig.
235). The continuance of the community is effected entirely by the royal
pair; they are the centres of activity of the community, which is thrown
into disorder when anything happens to them. Usually the pair are
physically incapable of leaving the nest, especially the queen, and
frequently they are enclosed in a cell which they cannot leave. In
consequence of the disorganisation that arises in the community in the
absence of a royal pair, Termites keep certain individuals in such a state
of advancement that they can rapidly be developed into royalties should
occasion require it. These reserve individuals are called complementary by
Grassi; when {362}they become royalties they are usually immature as
regards the condition of the anterior parts of the body, and are then
called by Grassi and others neoteinic, as is more fully explained on p.
380.
SWARMS.—As a result of the Termite economy large numbers of superfluous
individuals are frequently produced; these, in the winged state, leave the
community, forming swarms which are sometimes of enormous extent, and are
eagerly preyed on by a variety of animals including even man. Hagen has
given particulars[288] of a swarm of _T. flavipes_ in Massachusetts, where
the Insects formed a dark cloud; they were accompanied by no less than
fifteen species of birds, some of which so gorged themselves that they
could not close their beaks.
There is but little metamorphosis in Termitidae. Young Termites are very
soft; they have a thin skin, a disproportionately large head, and are of a
peculiar white colour as if filled with milk. This condition of milkiness
they retain, notwithstanding the changes of form that may occur during
their growth, until they are adult. The wings first appear in the form of
prolongations of the meso- and meta-nota, which increase in size, the
increment probably taking place at the moults. The number of joints of the
antennae increases during the development; it is effected by growth of the
third joint and subsequent division thereof; hence the joints immediately
beyond the second are younger than the others, and are usually shorter and
altogether more imperfect. The life-histories of Termites have been by no
means completely followed; a fact we can well understand when we recollect
that these creatures live in communities concealed from observation, and
that an isolated individual cannot thrive; besides this the growth is, for
Insects, unusually slow.
NATURAL HISTORY.—The progress of knowledge as to Termites has shown that
profound differences exist in the economy of different species, so that no
fair general idea of their lives can be gathered from one species. We will
therefore briefly sketch the economy, so far as it has been ascertained, in
three species, viz. _Calotermes flavicollis_, _Termes lucifugus_, and _T.
bellicosus_.
{363}[Illustration: FIG. 230.—Some individuals of _Calotermes flavicollis_:
A, nymph with partially grown wing-pads; B, adult soldier; C, adult winged
individual. (After Grassi.)]
_Calotermes flavicollis_ inhabits the neighbourhood of the Mediterranean
Sea; it is a representative of a large series of species in which the
peculiarities of Termite life are exhibited in a comparatively simple
manner. There is no special caste of workers, consequently such work as is
done is carried on by the other members of the community, viz. soldiers,
and the young and adolescent. The habits of this species have recently been
studied in detail in Sicily by Grassi and Sandias.[289] The Insects dwell
in the branches and stems of decaying or even dead trees, where they
nourish themselves on those parts of the wood in which the process of decay
is not far advanced; they live in the interior of the stems, so that
frequently no sign of them can be seen outside, even though they may be
heard at work by applying the ear to a branch. They form no special
habitation, the interior of the branch being sufficient protection, but
they excavate or increase the natural cavities to suit their purposes. It
is said that they line the galleries with proctodaeal cement; this is
doubtful, but they form barricades and partitions where necessary, by
cementing together the proctodaeal products with matter from the salivary
glands or regurgitated from the anterior parts of the alimentary canal. The
numbers of a community only increase slowly and remain always small; rarely
do they reach 1000, and usually remain very much below this. The king and
queen move about, and their family increases but slowly. After fifteen
months of their union they may be surrounded by fifteen or twenty young; in
another twelve months the number may have increased to fifty, and by the
time it has reached some five hundred or upwards the increase ceases. This
is due to the fact that the fertility of the queen is at first progressive,
but ceases to be so. A queen three or four years old produces at the time
of maximum production four to six eggs a day. When the community is
small—during its first two years—the winged individuals that depart from it
are about eight or ten annually, but the numbers of the swarm augment with
the increase of the {364}population. The growth of the individuals is slow;
it appears that more than a year elapses between the hatching of the egg
and the development of the winged Insect. The soldier may complete its
development in less than a year; the duration of its life is not known;
that of the kings and queens must be four or five years, probably more.
After the winged Insects leave the colony they associate themselves in
pairs, each of which should, if all goes well, start a new colony.
The economy of _Termes lucifugus_, the only European Termite besides
_Calotermes flavicollis_, has been studied by several observers, the most
important of whom are Lespès[290] and Grassi and Sandias. This species is
much more advanced in social life than _Calotermes_ is, and possesses both
workers and soldiers (Fig. 231, 2, 3); the individuals are much smaller
than those of _Calotermes_. Burrows are made in wood of various kinds,
furniture being sometimes attacked. Besides making excavations this species
builds galleries, so that it can move from one object to another without
being exposed; it being a rule—subject to certain exceptions—that Termites
will not expose themselves in the outer air. This is probably due not only
to the necessity for protection against enemies, but also to the fact that
they cannot bear a dry atmosphere; if exposed to a drying air they speedily
succumb. Occasionally specimens may be seen at large; Grassi considers
these to be merely explorers. Owing to the extent of the colonies it is
difficult to estimate with accuracy the number of individuals composing a
community, but it is doubtless a great many thousands. Grassi finds the
economy of this species in Sicily to be different from anything that has
been recorded as occurring in other species; there is never a true royal
pair. He says that during a period of six years he has examined thousands
of nests without ever finding such a pair. In place thereof there are a
considerable number of complementary queens—that is, females that have not
gone through the full development to perfect Insects, but have been
arrested in various stages of development. In Fig. 231, Nos. 4 and 5 show
two of these abnormal royalties; No. 4 is comparatively juvenile in form,
while No. 5 is an individual that has been substituted in an orphaned nest,
and is nearer to the natural condition of perfect development. We have no
information as to whether any {365}development goes on in these individuals
after the state of royalty is assumed, or whether the differences between
these neoteinic queens are due to the state of development they may happen
to be in when adopted as royalties. Kings are not usually present in these
Sicilian nests; twice only has Grassi found a king, but he thinks that had
he been able to search in the months of August and September he would then
have found kings. It would appear therefore that the complementary kings
die, or are killed after they have fertilised the females. Parthenogenesis
is not thought to occur, as Grassi has found the spermathecae of the
complementary queens to contain spermatozoa.
[Illustration: FIG. 231.—Some of the forms of _Termes lucifugus_. 1, Young
larva; 2, adult worker; 3, soldier; 4, young complementary queen; 5, older
substitution queen; 6, perfect winged Insect. (After Grassi.)]
{366}The period of development apparently occupies from eighteen to
twenty-three months. At intervals swarms of a great number of winged
individuals leave the nest, and are usually promptly eaten up by various
animals. After swarming, the wings are thrown off, and sometimes two
specimens or three may be seen running off together; this has been supposed
to be preliminary to pairing, but Grassi says this is not the case, but
that the object is to obtain their favourite food, as we shall mention
subsequently.
Although these are the usual habits of _Termes lucifugus_ at present in
Sicily, it must not be concluded that they are invariable; we have in fact
evidence to the contrary. Grassi has himself been able to procure in
confinement a colony—or rather the commencement of one—accompanied by a
true royal pair; while Perris has recorded[291] that in the Landes he
frequently found a royal pair of _T. lucifugus_ under chips; they were
accompanied in nearly every case by a few eggs. And Professor Perez has
recently placed a winged pair of this species in a box with some wood, with
the result that after some months a young colony has been founded. It
appears probable therefore that this species at times establishes new
colonies by means of royal pairs derived from winged individuals, but after
their establishment maintains such colonies as long as possible by means of
complementary queens. It is far from improbable that distinctions as to the
use of true and complementary royalties may be to some extent due to
climatic conditions. In some localities _T. lucifugus_ has multiplied to
such an extent as to be very injurious, while in others where it is found
it has never been known to do so.
The Termitidae of Africa are the most remarkable that have yet been
discovered, and it is probably on that continent that the results of the
Termitid economy have reached their climax. Our knowledge of the Termites
of tropical Africa is chiefly due to Smeathman, who has described the
habits of several species, among them _T. bellicosus_. It is more than a
century since Smeathman travelled in Africa and read an account of the
Termites to the Royal Society.[292] His information was the first of any
importance about Termitidae that was given to the world; it is, as may be
well understood, deficient in many details, but is nevertheless of great
value. Though his statements have been doubted they are truthful, and have
been confirmed by Savage.[293]
{367}[Illustration: FIG. 232.—Royal cell of _Termes bellicosus_, partially
broken open to show the queen and her attendants. (After Smeathman.) B,
Antenna of the queen; _b_, _b_, line of entrances to the cell; A, A, an
entrance, in this line, closed by the Termites. × ⅞.]
{368}_T. bellicosus_ forms buildings comparable to human dwellings; some of
them being twenty feet in height and of great solidity. In some parts of
West Africa these nests were, in Smeathman's time, so numerous that they
had the appearance of villages. Each nest was the centre of a community of
countless numbers of individuals; subterranean passages extended from them
in various directions. The variety of forms in one of these communities has
not been well ascertained, but it would seem that the division of labour is
carried to a great extent. The soldiers are fifteen times the size of the
workers. The community is dependent on one royal couple. It is the opinion
of the natives that if that couple perish so also does the community; and
if this be correct we may conclude that this species has not a perfect
system of replacing royal couples. The queen attains an almost incredible
size and fertility. Smeathman noticed the great and gradual growth of the
abdomen, and says it enlarges "to such an enormous size that an old queen
will have it increased so as to be fifteen hundred or two thousand times
the bulk of the rest of her body, and twenty or thirty thousand times the
bulk of a labourer, as I have found by carefully weighing and computing the
different states." He also describes the rate at which the eggs are
produced, saying that there is a constant peristaltic movement[294] of the
abdomen, "so that one part or other alternately is rising and sinking in
perpetual succession, and the matrix seems never at rest, but is always
protruding eggs to the amount (as I have frequently counted in old queens)
of sixty in a minute, or eighty thousand and upward in one day of
twenty-four hours."
This observer, after giving an account of the great swarms of perfect
winged Insects that are produced by this species, and after describing the
avidity with which they are devoured by the Hymenopterous ants and other
creatures, adds: "I have discoursed with several gentlemen upon the taste
of the white ants; and on comparing notes we have always agreed that they
are most {369}delicious and delicate eating. One gentleman compared them to
sugared marrow, another to sugared cream and a paste of sweet almonds."
From the preceding brief sketch of some Termitidae we may gather the chief
points of importance in which they differ from other Insects, viz. (1) the
existence in the community of individuals—workers and soldiers—which do not
resemble their parents; (2) the limitation of the reproductive power to a
single pair, or to a small number of individuals in each community, and the
prolongation of the terminal period of life. There are other social Insects
besides Termitidae: indeed, the majority of social Insects—ants, bees, and
wasps—belong to the Order Hymenoptera, and it is interesting to note that
analogous phenomena occur in them, but nevertheless with such great
differences that the social life of Termites must be considered as totally
distinct from that of the true ants and other social Hymenoptera.
DEVELOPMENT.—Social Insects are very different to others not only in the
fact of their living in society, but in respect of peculiarities in the
mode of reproduction, and in the variety of habits displayed by members of
a community. The greatest confusion has arisen in reference to Termitidae
in consequence of the phenomena of their lives having been assumed to be
similar to those of Hymenoptera; but the two cases are very different,
Hymenoptera passing the early parts of their lives as helpless maggots, and
then undergoing a sudden metamorphosis to a totally changed condition of
structure, intelligence, and instinct.
The development of what we may look on as the normal form of
Termitidae—that is, the winged Insects male and female—is on the whole
similar to that we have sketched in Orthoptera; the development in earwigs
being perhaps the most similar. The individuals of Termitidae are, however,
in the majority of cases if not in all, born without eyes; the
wing-rudiments develop from the thoracic terga as shorter or longer lobes
according to the degree of maturity; as in the earwigs the number of joints
in the antennae increases as development advances. All the young are, when
hatched, alike, the differences of caste appearing in the course of the
subsequent development; the most important of these differences are those
that result in the production of two special classes—only met with in
social Insects—viz. worker and soldier. Of these the workers are
individuals whose {370}development is arrested, the sexual organs not going
on to their full development, while other organs, such as the eyes, also
remain undeveloped; the alimentary canal and its adjuncts occupy nearly the
whole of the abdominal cavity. The adult worker greatly resembles—except in
size—the young. Grassi considers that the worker is not a case of simple
arrest of development, but that some deviation accompanies the arrest.
The soldier also suffers an arrest of development in certain respects
similar to the worker; but the soldier differs in the important fact that
the arrest of the development of certain parts is correlative with an
extraordinary development of the head, which ultimately differs greatly
from those of either the worker or of the sexual males and females.
[Illustration: FIG. 233.—The pairs of mandibles of different adult
individuals of _Termes_ sp. from Singapore. A, Of worker; B, of soldier; C,
of winged male; D, of winged female.]
SOLDIER.—All the parts of the head of the soldier undergo a greater or less
change of form; even the pieces at its base, which connect it by means of
the cervical sclerites with the prothorax, are altered. The parts that
undergo the greatest modification are the mandibles (Fig. 233, B); these
become much enlarged in size and so much changed in form that in a great
many species no resemblance to the original shape of these organs can be
traced. It is a curious fact that the specific characters are better
expressed in these superinduced modifications than they are in any other
part of the organisation (except, perhaps, the wings). The soldiers are not
alike in any two species of Termitidae so far as we know, and it seems
impossible to ascribe the differences that exist between the soldiers of
different species of Termitidae to special adaption for the work they have
to perform. Such a suggestion is justifiable only in the case of the Nasuti
(Fig. 234, 1), where the front of the head is prolonged into a point: a
duct opens at the extremity of this point, from which is exuded a fluid
that serves as a cement for {371}constructing the nest, and is perhaps also
used to disable enemies. Hence the prolongation and form of the head of
these Nasuti may be fairly described as adaptation to useful ends. As
regards the great variety exhibited by other soldiers—and their variety is
much greater than it is in the Nasuti—it seems at present impossible to
treat it as being cases of special adaptations for useful purposes. On the
whole it would be more correct to say that the soldiers are very dissimilar
in spite of their having to perform similar work, than to state that they
are dissimilar in conformity with the different tasks they carry on.
[Illustration: FIG. 234.—Soldiers of different species of Termites. (After
Hagen.) 1, _Termes armiger_; 2, _T. dirus_; 3, _Calotermes flavicollis_; 4,
_T. bellicosus_; 5, _T. occidentis_; 6, _T. cingulatus (?)_; 7, _Hodotermes
quadricollis (?)_; 8, _T. debilis (?)_, Brazil.]
The Termite soldier is a phenomenon to which it is difficult to find a
parallel among Insects. The soldier in the true ants is usually not
definitely distinguished from the worker, but it is possible that in the
leaf-cutting ants, the so-called soldier may prove to be more similar in
its nature to the Termite soldier. The soldiers of any one species of
Termite are apparently {372}extremely similar to one another, and there are
no intermediates between them and the other forms, except in the stages of
differentiation. But we must recollect that but little is yet known of the
full history of any Termite community, and it is possible that soldiers
which in the stage of differentiation promise to be unsatisfactory may be
killed and eaten,—indeed there is some evidence to this effect. There is
too in certain cases some difference—larger or smaller size being the most
important—between the soldiers of one species, which may possibly be due to
the different stage of development at which their differentiation
commenced.
It would at present appear that, notwithstanding the remarkable difference
in structure of the soldiers and workers of the white ants, there is not a
corresponding difference of instinct. It is true that soldiers do more of
certain things than workers do, and less of others, but this appears to be
due solely to their possession of such very different structures; and we
are repeatedly informed by Grassi that all the individuals in a community
take part, so far as they are able, in any work that is going on, and we
find also in the works of other writers accounts of soldiers performing
acts that one would not have expected from them. The soldiers are not such
effective combatants as the workers are. Dudley and Beaumont indeed
describe the soldiers as merely looking on while the workers fight.[295] So
that we are entitled to conclude that the actions of the soldiers, in so
far as they differ from those of the rest of the community, do so because
of the different organisation and structures of these individuals. We
shall, when speaking of food, point out that the condition of the soldier
in relation to food and hunger is probably different from that of the other
forms.
VARIOUS FORMS OF A COMMUNITY.—The soldiers and workers are not the only
anomalous forms found in Termitid communities; indeed on examining a large
nest a variety of forms may be found that is almost bewildering. Tables
have been drawn up by Grassi and others showing that as many as fifteen
kinds may be found, and most of them may under certain circumstances
coexist. Such tables do not represent the results of actual examination in
any one case, and they by no means adequately represent the number that,
according to the most recent observations of Grassi, may be present; but we
give one taken {373}from Grassi, as it conveys some idea of the numerous
forms that exist in certain communities. In this table the arrangement,
according to A, B, C, D, E, represents successive stages of the
development:—
_Forms of Termes lucifugus_. (After Grassi.) _Zool. Anz._ xii. 1889, p.
360.
A 1. Young, undifferentiated larvae.
|
+----------------------+--------------------------+
| | |
B 2. Larvae that will 3. Larvae that will 4. Reserves for royal
not mature the sexual mature the sexual specimens:(only present
organs. organs. when 14, 15, and 11 are
| | wanting, or when 14 and
| | 15 are present in
| | insufficient numbers).
| |
+-----+-----+ +------------+-------------=
| | | | |
C 5. Larvae 6. Larvae 9. Nymphs of 10. Nymphs 11. Reserves for
of soldiers. of workers. the first of the royal pairs (only
| | form. second present when 14,
| | | form. 15, and 4 are
| | | | wanting, or when
| | | | the two latter
D 7. Soldiers. 8. Workers. +----+-----+ | are present in
| | | insufficient
12. Winged 13. Reserve | numbers).
Insects royal pairs? |
| |
E 14. True royal 15. Substitution
couple. royal pairs.
On inspecting this table it will be perceived that the variety of forms is
due to three circumstances—(1) the existence of castes that are not present
in ordinary Insects; (2) the coexistence of young, of adolescents, and of
adults; and (3) the habit the Termites have of tampering with forms in
their intermediate stages, the result of which may be the substitution of
neoteinic individuals in place of winged forms.
This latter procedure is far from being completely understood, but to it
are probably due the various abnormal forms, such as soldiers with
rudiments of wings, that have from time to time been discovered in Termite
communities, and have given rise to much perplexity.
In connexion with this subject we may call attention to the necessity, when
examining Termite nests, of taking cognisance of the fact that more than
one species may be present. Bates found different Termites living together
in the Amazons Valley, and Mr. Haviland has found as many as five species
of Termitidae and three of true ants in a single mound in South Africa. In
this latter case observation showed that, though in such close proximity,
there was but little further intimacy between the species. There are,
however, true inquiline, or guest, Termites, {374}of the genus _Eutermes_,
found in various parts of the world living in the nests of other
Termitidae.
ORIGIN OF THE FORMS.—The interest attaching to the various forms that exist
in Termites, more particularly to the worker and soldier, is evident when
we recollect that these never, so far as we know, produce young. In the
social Hymenoptera it has been ascertained that the so-called neuters
(which in these Insects are always females) can, and occasionally do,
produce young, but in the case of the Termites it has never been suggested
that the sexual organs of the workers and soldiers, whether male or female,
ever become fruitful; moreover, the phenomena of the production of young by
the white ants are of such a nature as to render it in the highest degree
improbable that either workers or soldiers ever take any direct part in it.
Now the soldier is extremely different from the sexual individuals that
produce the young, and seeing that its peculiarities are not, in the
ordinary sense of the word, hereditary, it must be of great interest to
ascertain how they arise.
Before stating the little information we possess on this subject, it is
necessary to reiterate what we have already said to the effect that the
soldiers and workers are not special to either sex, and that all the young
are born alike. It would be very natural to interpret the phenomena by
supposing the workers to be females arrested in their development—as is the
case in social Hymenoptera—and by supposing the soldiers to be males with
arrested and diverted development.
The observations already made show that this is not the case. It has been
thoroughly well ascertained by Lespès and Fritz Müller that in various
species of _Calotermes_ the soldiers are both males and females. Lespès and
Grassi have shown that the workers of _Termes lucifugus_ are of male and
female sex, and that this is also true of the soldiers. Although the view
of the duality of the sexes of these forms was received at first with
incredulity, it appears to be beyond doubt correct. Grassi adds that in all
the individuals of the workers and soldiers of _Termes lucifugus_ the
sexual organs, either male or female, are present, and that they are in the
same stage of development whatever the age of the individual. This
statement of Grassi's is of importance because it seems to render
improbable the view that the difference of form of the soldier and worker
arises from the arrest of the {375}development of their sexual organs at
different periods. The fact that sex has nothing whatever to do with the
determination of the form of workers and soldiers may be considered to be
well established.
The statement that the young are all born alike is much more difficult to
substantiate. Bates said that the various forms could be detected in the
new-born. His statement was made, however, merely from inspection of the
nests of species about which nothing was previously known, and as it is
then very difficult to decide that a specimen is newly hatched, it is
probable that all he meant was that the distinction of workers, soldiers,
and sexual forms existed in very small individuals—a statement that is no
doubt correct. Other observers agree that the young are in appearance all
alike when hatched, and Grassi reiterates his statement to this effect.
Hence it would appear that the difference of form we are discussing arises
from some treatment subsequent to hatching. It may be suggested,
notwithstanding the fact that the young are apparently alike when hatched,
that they are not really so, but that there are recondite differences which
are in the course of development rendered conspicuous. This conclusion
cannot at present be said with certainty to be out of the question, but it
is rendered highly improbable by the fact ascertained by Grassi that a
specimen that is already far advanced on the road to being an ordinary
winged individual can be diverted from its evident destination and made
into a soldier, the wings that were partially developed in such a case
being afterwards more or less completely absorbed. This, as well as other
facts observed by Grassi, render it probable that the young are truly, as
well as apparently, born in a state undifferentiated except as regards sex.
Fig. 230 (p. 363) is designed to illustrate Grassi's view as to this
modification; the individual A is already far advanced in the direction of
the winged form C, but can nevertheless be diverted by the Termites to form
the adult soldier B.
According to the facts we have stated, neither heredity nor sex nor arrest
of development are the causes of the distinctions between worker and
soldier, though some arrest of development is common to both; we are
therefore obliged to attribute the distinction between them to other
influences. Grassi has no hesitation in attributing the anatomical
distinctions that arise between the soldiers, workers, and winged forms to
alimentation. {376}Food, or the mode of feeding, or both combined, are,
according to the Italian naturalist, the source of all the distinctions,
except those of sex, that we see in the forms of any one species of
Termite.
FEEDING.—Such knowledge as we possess of the food-habits of Termitidae is
chiefly due to Grassi; it is of the very greatest importance, as giving a
clue to much that was previously obscure in the Natural History of these
extraordinary creatures.
In the abodes of the Termites, notwithstanding the enormous numbers of
individuals, cleanliness prevails; the mode by which it is attained appears
to be that of eating all refuse matter. Hence the alimentary canal in
Termitidae contains material of various conditions of nutritiveness. These
Insects eat their cast skins and the dead bodies of individuals of the
community; even the material that has passed through the alimentary canal
is eaten again, until, as we may presume, it has no further nutritive
power. The matter is then used for the construction of their habitations or
galleries, or is carried to some unfrequented part of the nest, or is
voided by the workers outside of the nests; the pellets of frass, _i.e._
alimentary rejectamenta, formed by the workers frequently betraying their
presence in buildings when none of the Insects themselves are to be seen.
The aliments of _Calotermes flavicollis_ are stated by Grassi and Sandias
to be as follows: (1) wood; (2) material passed from the posterior part of
the alimentary canal or regurgitated from the anterior part; (3) the matter
shed during the moults; (4) the bodies of other individuals; (5) the
secretion of their own salivary glands or that of their fellows; (6) water.
Of these the favourite food is the matter passed from the posterior part of
the alimentary canal. We will speak of this as proctodaeal food. When a
_Calotermes_ wishes food it strokes the posterior part of another
individual with the antennae and palpi, and the creature thus solicited
yields, if it can, some proctodaeal food, which is then devoured. Yielding
the proctodaeal food is apparently a reflex action, as it can be induced by
friction and slight pressure of the abdomen with a small brush. The
material yielded by the anterior part of the alimentary canal may be called
stomodaeal product. It makes its appearance in the mouth in the form of a
microscopic globule that goes on increasing in size till about one
millimetre in diameter, when it is {377}either used for building or as food
for another individual. The mode of eating the ecdysial products has also
been described by Grassi and Sandias. When an individual is sick or
disabled it is frequently eaten alive. It would appear that the soldiers
are great agents in this latter event, and it should be noticed that owing
to their great heads and mandibles they can obtain food by other means only
with difficulty. Since they are scarcely able to gnaw wood, or to obtain
the proctodaeal and stomodaeal foods, their condition may be considered to
be that of permanent hunger, only to be allayed by carnivorous proceedings.
When thrown into a condition of excitement the soldiers sometimes exhibit a
sort of Calotermiticidal mania, destroying with a few strokes five or six
of their fellows. It is, however, only proper to say that these strokes are
made at random, the creature having no eyes. The carnivorous propensities
of _Calotermes_ are apparently limited to cannibalism, as they slaughter
other white ants (_Termes lucifugus_) but never eat them.
The salivary food is white and of alkaline nature; when excreted it makes
its appearance on the upper lip. It is used either by other individuals or
by the specimen that produced it; in the latter case it is transferred to
the lower lip and swallowed by several visible efforts of deglutition. The
aliments we have mentioned are made use of to a greater or less extent by
all the individuals except the very young; these are nourished only by
saliva: they commence taking proctodaeal and stomodaeal food before they
can eat triturated wood.
ROYAL PAIRS.—The restriction of the reproductive powers of a community to a
single pair (or to a very restricted number of individuals) occurs in all
the forms of social Insects, and in all of them it is concomitant with a
prolongation of the reproductive period far exceeding what is natural in
Insects. We are not in a position at present to say to what extent the
lives of the fertile females of Termitidae are prolonged, there being great
difficulties in the way of observing these Insects for long periods owing
to their mode of life; living, as they do, concealed from view, light and
disturbance appear to be prejudicial to them. We have every reason to
believe, however, that the prolongation extends as a rule over several
years, and that it is much greater than that of the other individuals of
the community, although the lives of even these latter are longer than is
usual in Insects; but this {378}point is not yet satisfactorily
ascertained. As regards the males there is reason to think that
considerable variety as to longevity prevails. But the belief is that the
royal males of Termitidae also form an exception to other Insects in the
prolongation of the terminal periods of their lives. In Hymenoptera, male
individuals are profusely produced, but their lives are short, and their
sole duty is the continuation of the species by a single act. We have seen
that Grassi is of opinion that a similar condition of affairs exists at
present with _Termes lucifugus_ in Sicily, but with this exception it has
always been considered that the life of the king Termite is, roughly
speaking, contemporaneous with that of the queen; it is said that in
certain species the king increases in bulk, though not to an extent that
can be at all compared with the queen.
It must be admitted that the duration of life of the king has not been
sufficiently established, for the coexistence of a king with a queen in the
royal cell is not inconsistent with the life of the king being short, and
with his replacement by another. Much that is imaginary exists in the
literature respecting Termites, and it is possible that the life of the
king may prove to be not so prolonged as has been assumed.
[Illustration: FIG. 235.—Royal pair of _Termes_ sp. from Singapore, taken
out of royal cell. A, A, King, lateral and dorsal views; B, B, queen,
dorsal and lateral views. Natural sizes.]
Returning to the subject of the limitation of the reproduction of the
community to a single pair, we may remark that _a priori_ one would suppose
such a limitation to be excessively unfavourable to the continuation of the
species; and as it nevertheless is the fact that this feature is almost, if
not quite, without exception {379}in Insect societies, we may conclude that
it is for some reason absolutely essential to Insect social life. It is
true that there are in Termitidae certain partial exceptions, and these are
so interesting that we may briefly note them. When a royal cell is opened
it usually contains but a single female and male, and when a community in
which royal cells are not used is inspected it is usually found that here
also there are present only a single fertile female and a single king.
Occasionally, however, it happens that numerous females are present, and it
has been noticed that in such cases they are not fully matured females, but
are imperfect, the condition of the wings and the form of the anterior
parts of the body being that of adolescent, not adult Insects. It will be
recollected that the activity of a community of Termites centres round the
great fertility of the female; without her the whole community is, as
Grassi graphically puts it, orphaned; and the observations of the Italian
naturalist make it clear that these imperfect royalties are substitution
queens, derived from specimens that have not undergone the natural
development, but have been brought into use to meet the calamity of
orphanage of the community. The Termites apparently have the power of
either checking or stimulating the reproductive organs apart from other
organs of the body, and they appear to keep a certain number of individuals
in such a condition that in case of anything going wrong with the queen,
the reserves may be brought as soon as possible into a state of
reproductive activity. The individuals that are in such a condition that
they can become pseudo-royalties are called complementary or reserve
royalties, and when actually brought into use they become substitution
royalties. It is not at present quite clear why the substitution royalties
should be in such excess of numbers as we have stated they were in the case
we have figured (Fig. 236), but it may be due to the fact that when the
power of the community is at a certain capacity for supporting young a
single substitution royalty would not supply the requisite producing power,
and consequently the community adopts a greater number of the substitution
forms. Termites are utterly regardless of the individual lives of the
members of the community, and when the reproductive powers of the company
of substitution royalties become too great, then their number is reduced by
the effective method of killing and eating them.
According to Grassi's observations, the communities of _Termes
{380}lucifugus_ are now kept up in Sicily almost entirely by substitution
royalties; the inference being that the age of each community has gone
beyond the capacity for life of any single royal queen.
The substitution royalties are, as we have said, called neoteinic (νεος,
youthful, τείνω, to belong to), because, though they carry on the functions
of adult Insects, they retain the juvenile condition in certain respects,
and ultimately die without having completed the normal development. The
phenomenon is not quite peculiar to Insects, but occurs in some other
animals having a well-marked metamorphosis, notably in the Mexican
Axolotl.[296]
[Illustration: FIG. 236.—Pair of neoteinic royalties, taken from the royal
chamber of _Termes_ sp. at Singapore by Mr. G. D. Haviland. The queen was
one of thirteen, all in a nearly similar state. A, king; B, C, queen.]
A point of great importance in connexion with the neoteinic royalties is
that they are not obtained from the instar immediately preceding the adult
state, but are made from Insects in an earlier stage of development. The
condition immediately preceding the adult state is that of a nymph with
long wing-pads; such specimens are not made into neoteinic royalties, but
nymphs of an earlier stage, or even larvae, are preferred. It is apparently
by an interference with one of these earlier stages of development that the
"nymphs of the second form," which have for long been an enigma to
zoologists, are produced.
POST-METAMORPHIC GROWTH.—The increase of the fertility of the royal female
is accompanied by remarkable phenomena of growth. Post-metamorphic growth
is a phenomenon almost unknown in Insect life, except in these Termitidae;
distension not infrequently occurs to a certain extent in other Insects,
and {381}is usually due to the growth of eggs inside the body, or to the
repletion of other parts. But in Termitidae there exists post-metamorphic
growth of an extensive and complex nature; this growth does not affect the
sclerites (_i.e._ the hard chitinous parts of the exo-skeleton), which
remain of the size they were when the post-metamorphic growth commenced,
and are consequently mere islands in the distended abdomen (Fig. 236, B,
C). The growth is chiefly due to a great increase in number and size of the
egg-tubes, but there is believed to be a correlative increase of various
other parts of the abdominal as distinguished from the anterior regions of
the body. A sketch of the distinctions existing between a female of a
species at the time of completion of the metamorphosis and at the period of
maximum fertility does not appear to have been yet made.
NEW COMMUNITIES.—The progress of knowledge in respect of Termitidae is
bringing to light a quite unexpected diversity of habits and constitution.
Hence it is premature to generalise on important matters, but we may refer
to certain points that have been ascertained in connexion with the
formation of new communities. The duration of particular communities and
the modes in which new ones are founded are still very obscure. It was
formerly considered that swarming took place in order to increase the
number of communities, and likewise for promoting crossing between the
individuals of different communities. Grassi, however, finds as the result
of his prolonged observations on _Termes lucifugus_ that the swarms have no
further result than that the individuals composing them are eaten up. And
Fritz Müller states[297] that in the case of the great majority of forms
known to him the founding of a colony by means of a pair from a swarm would
be just about as practicable as to establish a new colony of human beings
by placing a couple of newly-born babes on an uninhabited island. It was
also thought that pairs, after swarming, re-entered the nests and became
royal couples. It does not, however, appear that any one is able to produce
evidence of such an occurrence. The account given by Smeathman of the
election of a royal couple of _Termes bellicosus_ is imperfect, as, indeed,
has already been pointed out by Hagen. It suggests, however, that a winged
pair after leaving the nest do again enter it to become king {382}and
queen. The huge edifices of this species described by Smeathman are clearly
the result of many years of labour, and at present substitution royalties
are not known to occur in them, so that it is not improbable Smeathman may
prove to be correct even on this point, and that in the case of some
species mature individuals may re-enter the nest after swarming and may
become royal couples. On the whole, however, it appears probable that
communities of long standing are kept up by the substitution royalty
system, and that new communities when established are usually founded by a
pair from a swarm, which at first are not in that completely helpless
condition to which they come when they afterwards reach the state of
so-called royalty. Grassi's observations as to the sources of food remove
in fact one of the difficulties that existed previously in regard to the
founding of new colonies, for we now know that a couple may possibly bear
with them a sufficient supply of proctodaeal and stomodaeal aliment to last
them till workers are hatched to feed them, and till soldiers are developed
and the community gradually assumes a complex condition. Professor Perez
has recently obtained[298] the early stages of a community from a winged
pair after they had been placed in captivity, unattended by workers.
Müller's observation, previously quoted, is no doubt correct in relation to
the complete helplessness of royal pairs after they have been such for some
time; but that helplessness is itself only gradually acquired by the royal
pair, who at first are able to shift for themselves, and produce a few
workers without any assistance.
ANOMALOUS FORMS.—Müller has described a _Calotermes_ under the name of _C.
rugosus_, which is interesting on account of the peculiar form of the young
larva, and of the changes by which it subsequently becomes similar in form
to other species of the genus. We represent the development of this larva
in Fig. 237. We may call attention to the fact that this figure illustrates
the large size of the paunch, which is so extraordinary in some of the
states of the Termitidae.
It will be recollected that the genus _Calotermes_ is destitute of workers.
There is another genus, _Anoplotermes_, in which the reverse condition
prevails, and the soldier is absent; this is the only case yet known in
which such a state of affairs exists. {383}The species is called _A.
pacificus_ by Fritz Müller; it differs from other Termitidae in possessing
a proventriculus destitute of triturating ridges. The nests of this species
are utilised by a little _Eutermes_ (_E. inquilinus_ Müller) for its own
advantage; whether by first destroying the _Anoplotermes_ or whether by
merely taking possession of the nests abandoned by their owners is not
known. It is a most remarkable fact that the _Eutermes_ resembles the
_Anoplotermes_ so extremely that the two can scarcely be distinguished,
though anatomically they are quite different. The resemblance is indeed so
great that it deceived Von Jhering into supposing that the two genera were
alternate generations of a single species, one generation possessing
soldiers, the other being without them. Subsequently, by anatomical
investigation, he recognised[299] the error into which he had fallen—an
error that, under such peculiar circumstances, was quite pardonable.
[Illustration: FIG. 237.—Changes in external form of the young larva of
_Calotermes rugosus_. A, Newly hatched with nine joints in antennae, × 8;
B, older larva with ten joints, × 8; C, next stage with eleven joints, × 8;
D, larva with twelve joints; the position of the parts of the alimentary
canal are shown—_v_, crop; _m_, stomach; _b_, paunch; _e_, intestine; _r_,
dorsal vessel, × 16/3 (After Fritz Müller.)]
Hagen has suggested[300] that _Hodotermes japonicus_ never produces winged
forms. Very little, however, is actually known as to this species.
MARCHING AND HARVESTING TERMITES.—Smeathman alluded to a remarkable
_Termes_ seen by him in Africa, giving it the name of _T. viarum_. Nothing
further is known of this Insect, which, according to Smeathman's account,
may possibly be the most remarkable of the family. _T. viarum_ is said to
be larger than _T. bellicosus_, and was discovered issuing in large numbers
from a hole in the ground and marching in columns consisting of workers
directed by soldiers of enormous size, some of whom {384}climbed up plants
and gave audible signals to the army, which immediately responded with a
hissing noise and by increasing their pace with the utmost hurry; they
continued marching by the spot where Smeathman observed them for upwards of
an hour. He was not able to find their nests, and no specimens have been
preserved; both soldiers and workers possessed eyes. Marching in this way
by daylight is contrary to the nature of ordinary Termites, and some doubt
has existed as to the correctness of Smeathman's observation, which has in
fact remained for upwards of a century without confirmation.
[Illustration: FIG. 238.—Eyed, grass-cutting Termite, _Hodotermes
havilandi_, A, soldier; B, worker. South Africa. In life the head is
carried horizontally, so the piece of grass sticks up like a flag-pole.]
Mr. G. D. Haviland has, however, this year discovered in Natal a Termite
which shows that there are species in Africa of the kind described by
Smeathman, the workers and soldiers being possessed of facetted eyes. Mr.
Haviland states that the workers of this species issue from holes in the
ground during the heat of the day and cut grass both dead and green. They
carry it, in lengths of about two inches, to the mouths of the holes, often
leaving it there and going at once to fetch more. Under acacia bushes they
carry acacia leaflets as well as grass. In the middle of the day more grass
accumulates at the entrance to the holes than can be taken in, but as the
heat of the day diminishes the workers cease to forage and take in the
accumulation. When the grass is all in they sometimes close the mouth of
the hole with moistened pellets of earth brought in their mouths. The
soldiers remain in the holes; when disturbed they jerk themselves like
soldiers of other species to frighten away the intruder; when they bite,
their grip is very tenacious. The holes are about ⅓ of an inch in diameter,
and there are usually several of them a few yards apart; around each
{385}of them is a patch over which the grass has been cut quite short. Mr.
Haviland followed these holes by digging for a distance of 20 feet and to a
depth of 5½ feet; they remain uniform in size except that near the entrance
there may be one or two chambers in which the grass is temporarily stored,
but these do not hold more than would be collected in an hour or two. As
the burrow descends it is occasionally joined by another, and at the point
of junction there is usually a considerable widening. Sometimes they run
straight for 6 or 7 feet, sometimes they curve abruptly, sometimes they are
nearly horizontal, but near the mouth may be almost vertical in direction.
These Termites are very local, but the specimens are numerous when found.
Mr. Haviland dug for these Insects at two places on the Tugela river, one
of them being at Colenso. It is much to be regretted that he was unable to
reach the nest. We figure a soldier selected from specimens sent by Mr.
Haviland to the Cambridge University Museum. This Insect is apparently much
smaller than Smeathman's _T. viarum_. Other species of Termitidae have been
described[301] as forming underground tunnels in Africa, but none of the
species have yet been satisfactorily identified.
It was stated by Smeathman that some species of Termites had chambers in
their habitations in which grew a kind of fungus used by the Insects for
food; Mr. Haviland is able to confirm Smeathman in this particular; he
having found fungus-chambers in the nests of more than one species both in
Singapore and South Africa (Fig. 240).
HABITATIONS.—In nothing do Termites differ more than in the habitations
they form. Sometimes, as we have mentioned in the case of _Calotermes_,
there is no real structure formed; only a few barriers being erected in
burrows or natural hollows in wood. In other cases very extensive
structures are formed, so that the work of the Termites becomes a
conspicuous feature in the landscape. This is of course only the case in
regions that are not much interfered with by man; the great dwellings
spoken of by Smeathman and others soon disappear from the neighbourhood of
settlements, but in parts of Africa and in Australia large dwellings are
still formed by these creatures. In the latter part of the world there
exists a very remarkable one, formed by an {386}undetermined species called
by the officers and crew of her Majesty's ship _Penguin_ the "compass ant."
The outline of one of the structures formed by this Termite we represent in
Fig. 239. Mr. J. J. Walker, to whom we are indebted for the sketch from
which this figure is taken, has also favoured us with the following extract
from his diary, of date 4th August 1890: "The most interesting feature in
the scenery (about forty miles inland from Port Darwin) was the constant
succession of huge mounds raised by the Termites, of which I had seen some
comparatively small examples in my rambles near Port Darwin; but these
exceeded in dimensions all I had ever seen. The most frequent as well as
the largest kind was usually of a reddish or ferruginous colour outside,
and generally almost cylindrical in shape with obtusely-pointed top, but
nearly always more or less weather-worn, with great irregular buttresses
and deep ruts down the sides; many of them look like ruined towers in
miniature. Their usual height was from 8 to 10 feet, but many were much
higher, and some attained an (estimated) elevation of at least 20 feet.
Another kind, seen only in one or two places along the line, was of a much
more singular character; they averaged only 4 to 5 feet high, were built of
a dark-gray mud, and in shape were like thin flat wedges set upright (see
Fig. 239), reminding one of tombstones in a churchyard. But the most
remarkable feature about these mounds was that they had all the same
orientation, viz. with the long faces of the wedge pointing nearly north
and south. Why this is so I am quite at a loss to imagine, and I much
regret that I had no opportunity of closely examining these most singular
structures. A third kind of mound, usually not exceeding 2 feet in height,
was of a simple, acute, conical figure, and generally of a gray colour
somewhat paler than the last."
[Illustration: FIG. 239.—Termitarium of compass or meridian Termite of
North Australia. A, face extending south and north; B, cross-section.]
The material used for the construction of the dwellings is either earth,
wood, or the excrement of the Termites. The huge edifices mentioned by
Smeathman are composed of earth cemented {387}together so as to look like
stone or brick, and the buildings appear to be almost as strong as if they
were actually constructed with these materials. In many cases the substance
used is comminuted wood that has passed one or more times through the
alimentary canal of the Insects, and may therefore be called excrement.
Whether the stone-like material is made from earth that has passed through
the alimentary canal or from grains gathered for the purpose has not been
well ascertained. In any case the material is cemented together by means of
the secretions of glands. Dudley and Beaumont have described the process of
construction, in a species observed by them, saying that earth is brought
and placed in position by the mandibles, and cemented by liquid from the
abdomen.[302] Von Jhering says[303] that some species form the exterior
walls of their dwellings of stone-like material, but make use of woody
matter for the construction of the interior. Smeathman has described the
nest of _Termes bellicosus_. The whole of the very strong external wall
consists of clay-like material, cemented by the secretions of the Termites
to a very firm consistence. The royal cell is built of the same material as
the framework of the nest; whilst the nurseries in which the young are
chiefly found are built of woody material, and are always covered with a
kind of mould—the mycelium of a fungus—and plentifully sprinkled with small
white bodies, which, under the microscope, are found to be filled with a
number of oblong, spore-like cells.
[Illustration: FIG. 240.—Fragment of Termitarium of _Termes angustatus_, S.
Africa, showing fungus chambers and orifices of communication.]
These nurseries rest on the clay-like framework of the nest, but are not
attached thereto; they in no way support it, or one another, indeed they
have the appearance of being constantly added to on their upper margins and
constantly eaten away on their under parts. Fig. 240 represents the
appearance of the upper boundary of a nursery taken from a nest of _Termes
angustatus_. The small white bodies, mentioned above, have disappeared: the
mycelium of the fungus, though not shown in the {388}figure, is still
visible on the specimen from which it was drawn, and gives rise to a
whitish, glaucous appearance.
In various parts of the world nests formed on trees by Termites are to be
seen; these tree nests are, it would appear, in some cases only parts of a
community, and are connected with the main body by galleries. In other
cases nests are formed in various positions of advantage; Messrs. Hubbard
and Hagen have given us an account[304] of some of these—probably the work
of _Eutermes ripperti_—as seen in Jamaica. They describe the nests as
spherical or conical masses, looking externally as if composed of loamy
earth; they are placed on trees, fences, or walls; they vary in size from
that of a man's fist to that of a hogshead; they appear to be composed of
finely comminuted wood fastened together by saliva. These nests are formed
on the same principle as those of the wasps that make nests hanging to
trees and bushes, as they consist of an external protecting envelope
covering a comb-like mass in the interior. At the bottom of the nest there
is a covered gallery leading to the earth, where the main nest appears to
be situate; galleries also are constructed so as to lead to the tops of
trees and other places, in such a manner that the Termite can still keep up
its peculiarity of working and travelling in tunnels and yet roam over a
large area; the activity of these Termites continues day and night. In each
nest there is a queen, who lays eggs that are removed by the worker
Termites to the bottom of the nest. The young are fed on a prepared food,
consisting apparently of comminuted vegetable matter, of which considerable
masses are laid in store. Some of the nests are rich in containing many
pounds' weight of this material, while others are apparently quite
destitute of it. There is a soldier form and at least two kinds of workers.
Some species of true ant frequently shares the nest of these white ants,
but on what terms the two kinds of Insects live together is not stated.
TERMITE RAVAGES.—In countries whose climate is favourable to their
constitutions certain kinds of Termites become of great importance to our
own species. Owing to their taste for woody matter and to their habit of
working in concealment, it is no uncommon thing for it to be discovered
that Termites have obtained access to a building and have practically
destroyed the wooden materials used in its construction; all the interior
of the {389}wood being eaten away and only a thin outer shell left intact.
A Termite, _T. tenuis_, was introduced—in what manner is not certainly
known[305]—to the Island of St. Helena, and committed such extensive
ravages there that Jamestown, the capital, was practically destroyed and
new buildings had to be erected. Other such cases are on record.
Destructive species can sometimes be destroyed by placing in the nests a
portion of arsenicated food. This is eaten by some individuals, who perish
in consequence; and their dead bodies being consumed by their comrades, the
colony becomes checked if not exterminated.
The number of described species of Termitidae does not much exceed 100, but
this is certainly only a small portion of those existing, the total of
which may probably reach 1000 species.
Termitidae are classed by some naturalists with the Orthoptera, and they
have a great deal in common with some of the cursorial division of that
Order, more particularly Forficulidae and Blattidae; but they differ from
Orthoptera in the nature and form of the wings. They are also classed by
some, with a few other forms, as a separate Order of Pseudo-Neuroptera
called Corrodentia, but this is not a very satisfactory course, as the
Termitidae do not agree closely with the forms associated with them, while
the aggregate so formed is far from being very distinct from other forms of
Neuroptera. On the whole the best plan appears to be to treat the
Termitidae as forming a distinct family of the Order Neuroptera, or to make
it a distinct Order, as proposed by Grassi. Packard now associates Termites
in an Order with the biting-lice, and calls it Platyptera.
FOSSIL TERMITES.—Termitidae were very abundant in Tertiary times, and the
genera appear to have been then much the same as at present. In Mesozoic
strata the remains of true Termitidae apparently exist in the Lias in
Europe, but farther back than this the family has not been satisfactorily
traced. It was formerly supposed that Termitidae existed in the
Carboniferous strata, but this appears to be very doubtful; and the fossil
remains of that epoch, which were presumed to be those of Termites, are now
referred by Scudder and others to the Neuropteroid division of the Order
Palaeodictyoptera, an Order which is formed entirely of Palaeozoic fossil
remains.
{390}CHAPTER XVII
NEUROPTERA _CONTINUED_—PSOCIDAE (BOOK-LICE AND DEATH-WATCHES)—THE FIRST
FAMILY OF AMPHIBIOUS NEUROPTERA (PERLIDAE, STONE-FLIES).
FAM. IV. PSOCIDAE—BOOK-LICE, DEATH-WATCHES.
_Minute Insects with slender, thread-like, or hair-like antennae; four
delicate membranous wings, the front pair of which are the larger; their
neuration is not abundant and is irregular, so that the cells are also
irregularly arranged; the transverse nervules are only one or two in
number.[306] Prothorax very small, in the winged forms quite concealed
between the head and the large mesothorax; this latter closely connected
with, or fused with, the metathorax. Species quite wingless, or with
wings unfitted for flight, exist; in them the prothorax is not so
extremely small, while the mesothorax is smaller than in the winged
forms. Tarsi of two or three segments. Metamorphosis slight, marked
chiefly by the development of wings and ocelli._
[Illustration: FIG. 241.—_Psocus fasciatus_, England. (After M‘Lachlan.)]
The Psocidae are without exception small and soft-bodied Insects, and are
only known to those who are not entomologists by the wingless forms that
run about in uninhabited or quiet apartments, and are called dust-lice or
book-lice. They are perhaps more similar to Termitidae than to any other
Insects, but the two families differ much in the structure of their wings,
and are totally dissimilar in the nature of their lives.
{391}[Illustration: FIG. 242.—Transverse horizontal section of head of
_Psocus_: _f_, fork or pick; _t_, lingua; _mx_, left maxilla; _c_, cardo;
_p_, stipes; _m.m_, muscles; _m.s_, socket of mandible.]
[Illustration: FIG. 243.—A, Front of head of _Psocus heteromorphus_; _cl_,
post-clypeus; _g_, epicranium: B, transverse horizontal section of
post-clypeus of _Psocus_: _cl_, post-clypeus; _c.m_, clypeal muscles; _g_,
epicranium; _t_, tendons; _l.m_, labial muscle in section; _oe_,
oesophagus; _oe.b_, oesophageal bone. (After Burgess and Bertkau.)]
The antennae consist of eleven to twenty-five joints, or even more, about
thirteen being the usual number; the basal two are thicker than the others,
and are destitute of setae or pubescence such as the others possess. The
maxillae and labium are remarkable. The former possesses a peculiar hard
pick or elongate rod; this is considered by many naturalists to be the
inner lobe, but Burgess thinks it more probably an independent organ,[307]
as it has no articulation of any kind with the outer lobe. The latter is
remarkably thick and fleshy; the palpus is 5-jointed. Other authorities
consider the pick to be certainly the inner lobe; if it be not, the latter
is quite wanting. Hagen agrees with Burgess in stating that the pick slides
in the outer lobe as in a sheath. The labium has a large mentum and a
ligula divided anteriorly into two lobes; at each outer angle in front
there is a globular projection, which is doubtless the labial palpus;
reposing on the labium there is a large free lingua. The labrum is large,
attached to a distinct clypeus, behind which there is a remarkable
post-clypeus, which is usually prominent as if inflated; to its inner face
are attached several muscles which converge to be inserted on a plate
placed below the anterior part of the oesophagus, and called by Burgess the
{392}oesophageal bone; under or within the lingua there is a pair of
lingual glands. Judging from Grosse's study of the mouth of Mallophaga, we
may conclude that the oesophageal bone will prove to be a sclerite of the
hypopharynx. The eyes of the winged forms are frequently remarkably convex,
and there are also three ocelli, triangularly placed on the vertex. The
head is free and very mobile. The coxae are rather small, exserted,
contiguous; the sterna small. The abdomen has usually ten segments, though
sometimes only nine can be detected.
The thorax in Psocidae usually looks as if it consisted of only two
segments. This is due to two opposite conditions: (1) that in the winged
forms the prothorax is reduced to a plate concealed in the fissure between
the head and the mesothorax bearing the first pair of wings; (2) that in
the wingless forms (Fig. 247), though the prothorax is distinct, the meso-
and metathorax are fused into one segment.
[Illustration: FIG. 244.—Reproductive organs of _Clothilla pulsatoria_. A,
Male; _a_, vesiculae seminales; _b_, testes; _c_, vasa deferentia; _d_,
ejaculatory duct. B, Female; _a_, _b_, egg-tubes; _c_, oviduct; _d_,
uterus, containing egg; _e_, accessory gland (the enveloping sac in
section); _f_, its duct. (After Nitzsch.)]
The internal anatomy is only very incompletely known. Nitzsch[308] has,
however, described the alimentary canal and the reproductive organs of
_Clothilla pulsatoria_. The former is remarkably simple: no proventriculus
or crop was found; the stomach is very elongate, and consists of a sac-like
anterior portion and an elongate, tubular posterior part. There are four
Malpighian tubes. The posterior part of the canal is remarkably short, the
small intestine being scarcely as long as the rectum. The ovaries (Fig.
244, B) consist of five egg-tubes on each side; connected with the oviduct
there is a peculiar accessory gland consisting of a sac containing other
small sacs each {393}with an elongate efferent duct; the number of the
secondary sacs varies from one to four according to the individual. The
testis (Fig. 244, A, _b_) is a simple capsule; connected with the base of
the ejaculatory duct there is a pair of elongate accessory glands or
vesiculae seminales.
The life-history has never been satisfactorily sketched. The young greatly
resemble the old, but have no ocelli or wings, and sometimes the tarsi are
of two joints, while in the adult they have three. The antennae have also
in these cases a less number of joints in the young stage. The food is
animal or vegetable refuse substances; many live on fungoid matter of
various kinds, mouldy chaff being, it is said, a favourite pabulum; the
mould on palings is a source of food to many; others live on the rust-fungi
of leaves, and many frequent the bark of trees. They are able to spin webs,
probably by the aid of the lingual glands; the eggs are deposited, in some
cases, on leaves and covered with a web. Hagen says that a peculiar organ,
possibly a gland—he calls it a hose[309]—exists at the base of the tarsal
claws. In our climate most of the species pass the winter in the egg-state.
There may be two generations in a year, perhaps more.
The nomenclature of the wing-veins of Psocidae has given rise to much
discussion.[310] The system shown in the accompanying figure is probably
the most convenient; the subcostal vein (2) is always obscure, and
sometimes can only be detected by very minute examination. Some interesting
information as to the minute structure and mode of formation of the wings
and their nervures has been given by Hagen.[311]
[Illustration: FIG. 245.—Anterior wing of _Elipsocus brevistylus_. (After
Reuter.) 1, Costal vein; 2, subcostal; 3, radial; 4, cubitus; 4_a_,
branches of cubitus; 5, sector of the radius; 5_a_, forks thereof.]
In the young the wings first appear as buds, or outgrowths of the sides of
the meso- and meta-thorax; afterwards the prothorax decreases, while the
other two thoracic segments and the wing-rudiments attached to them
increase. The wings from their very origin appear to be different from
those of the Orthoptera, and the changes that take place in the thoracic
{394}segments in the course of the development, differ from those that
occur in Orthoptera.
[Illustration: FIG. 246.—Micropterous form of _Mesopsocus unipunctatus_.
_a_, _a_, Wings. (After Bertkau.)]
There are several peculiarities connected with the wings. Frequently they
exist, though of no use for flight; some Psocidae that have
perfectly-formed wings are so reluctant to use them that, M‘Lachlan says,
they will allow themselves to be crushed without seeking to escape by
flight. At certain periods, however, some Psocidae float on the wing in
considerable numbers, especially in a moist still atmosphere, and then
drift about like the winged Aphididae, which are frequently found with
them. There is evidence that individuals, or generations, of some of the
winged species occur with only rudimentary wings; although this has been
denied by Kolbe, there can be no doubt about it. The form figured above
(Fig. 246) was described by Bertkau[312] as a distinct genus, but was
afterwards recognised by him[313] to be a short-winged form of _Mesopsocus
unipunctatus_. It is probable that the adult female of this species has the
wings always micropterous, while the male has these organs of the full
size. In other species the condition of the rudimentary wings seems to be
quite constant. The facts concerning the wings of Psocidae are so peculiar
that Kolbe came to the conclusion that the organs exist not because they
are of use for flight, so much as because it is the nature of an Insect to
develop wings.[314]
Some of the species of Psocidae have never any trace of wings. These
apterous forms are mostly included in the division Atropinae, and are
usually very minute; it has been again and again erroneously stated that
they are the young state of winged forms. Hagen kept a large colony of
_Atropos divinatoria_ for some years in confinement, so that he saw
numerous generations as well as many specimens. He found the apterous
condition quite constant.
{395}The association of ocelli with wings is nearly constant in Psocidae.
The genus _Clothilla_—allied to _Atropos_—possesses very rudimentary wings
but no ocelli. Hagen, however, found[315] that in a certain locality no
less than 12 per cent of the individuals of this species were provided with
ocelli,—a most extraordinary variation.
In some of these apterous forms there is found on each side of the
prothorax a tubercular prominence which, according to Hagen, can be
considered only as the rudiment of a wing that never develops. Though no
existing Insect is known to possess rudimentary wings on the prothorax, we
have previously mentioned (p. 344) that in the Carboniferous epoch
appendages of the nature alluded to were not very rare.
A genus of living forms—_Hyperetes_—in which the three thoracic segments
are well developed, but in which there are no alar appendages or rudiments,
is considered by Hagen to be more primitive than the Psocidae found in
amber to which we shall subsequently allude.
The number of described species of Psocidae does not reach two hundred; we
have, however, thirty species or more in Britain.[316] Nietner observed
about the same number in the immediate vicinity of his house in Ceylon. The
isolated and remote Hawaiian group of islands is remarkably rich in
Psocidae. Two thousand is a moderate estimate of the number of existing
species. The largest forms yet discovered belong to the Brazilian genus
_Thyrsophorus_; they attain, however, a breadth of only about one inch with
the wings fully expanded. The Cuban genus _Embidopsocus_ is said to be of
great interest from its approximation to Embiidae. It is at present very
inadequately known.
One (or more) very minute Insects of this family—_Clothilla pulsatoria_
according to Hagen, _Atropos[317] divinatoria_ according to some other
authors—is widely known under the name of the death-watch, owing to its
being believed to make a peculiar {396}ticking noise, supposed to be
prophetic of the decease of some individual—a human being we fancy, not a
death-watch. It is difficult to believe that so minute and soft an Insect
can produce a sound audible to human ears, and many entomologists are of
opinion that the sound in question is really produced by a beetle—of the
genus _Anobium_—which lives in wood, and that as the beetle may be
concealed in a hole, while the _Clothilla_ is seen running about, the sound
is naturally, though erroneously, attributed to the latter. But the rapping
of the _Anobium_ is well known, is produced while the Insect is at large,
and is said to be a different noise from that of the Psocid; evidence too
has been given as to the production of the sound in a workbox when the
Psocid was certainly present, and the most careful search failed to reveal
any beetle.
[Illustration: FIG. 247.—A, _Atropos divinatoria_; B, _Clothilla
pulsatoria_. (After M‘Lachlan.)]
The Rev. W. Derham, who two hundred years ago was Rector of Upminster, in
Essex, and was well known as a distinguished writer and philosopher, gave
an account of the ticking of death-watches to the Royal Society.[318] This
gentleman was a most accurate and minute observer; he was well acquainted
with the ticking of the greater death-watch—_Anobium_—which he describes
very accurately, as well as the acts accompanying it, the details he
mentions being exactly such as occur at the present time. He not only heard
the ticking of the Psocid or lesser death-watch, but repeatedly witnessed
it. He says: "I am now so used to, and skilful in the matter as to be able
to see, and show them, beating almost when I please, by having a paper with
some of them in it conveniently placed and imitating their pulsation, which
they will readily answer." He also states that he could only hear them
beating when it was done on paper, and that this death-watch will tick for
some hours together without intermission, with intervals between each beat,
so that it much resembles the ticking of a watch. The act of ticking was
{397}accompanied by rapping the front of the head on the paper, but Mr.
Derham could not be sure that the sound was produced in that manner,
because each stroke was also accompanied by a peculiar shudder, or recoil.
After a prolonged ticking he observed that another individual of the other
sex made its appearance. The species figured by Mr. Derham more resembles a
_Hyperetes_ than it does either of our two known book-lice, _Atropos_ and
_Clothilla_.
[Illustration: FIG. 248.—The lesser death-watch of Upminster. (After
Derham.) A, magnified; B, natural size.]
[Illustration: FIG. 249.—_Sphaeropsocus kunowii._ From amber. × 30. (After
Hagen.)]
Numerous species of Psocidae are preserved in amber; Hagen[319] has made a
careful study, based on a considerable number of specimens, of about
thirteen such species. They belong to no less than nine genera and five
sub-families. _Sphaeropsocus_ is the most remarkable; this Insect has a
well-developed prothorax, as is the case in the wingless Psocids, and a
pair of large wings or tegmina meeting by a straight suture along the back,
as is usual in beetles, though quite unknown in existing Psocidae. Another
species, _Amphientomum paradoxum_, has the body and appendages covered with
scales like a butterfly or moth; other species, found in gum-copal or still
living, have scales on various parts of the body, but not to so great an
extent as this amber species. The genus _Amphientomum_ is still represented
in Ceylon and elsewhere by living forms; Packard has figured some of the
scales;[320] they appear to be extremely similar to those of Lepidoptera or
Thysanura. The facts connected with this fauna of amber Psocidae would seem
to show that the family was formerly more extensive and important than it
is at present; we should therefore expect to find numerous fossil forms in
strata of date {398}anterior to that of the amber; but this is not the
case, all that is known as to fossil Psocidae being that Scudder has
recently ascribed traces of an Insect found in the Tertiary rocks of Utah
to this family as a distinct genus.
FAM. V. PERLIDAE.
_Insects of moderate or large size, furnished with four membranous wings;
these are usually complexly reticulate; the hind pair are much the
larger, and have a large anal area of more simple venation, which becomes
plicate when folded. The coxae are small, the legs widely separated. The
larvae are aquatic in habits; the metamorphosis is slight._
[Illustration: FIG. 250.—_Pteronarcys frigida_, male. (After Gerstaecker.)]
The Perlidae form a small family of Insects unattractive in their general
appearance. The life-history of each individual consists of two abruptly
contrasted portions; the earlier stage being entirely aquatic, the later
aerial. Hence the Perlidae come into the amphibious division of Neuroptera.
The definition we have given above would, except as regards the texture of
the front wings and the aquatic habits of the larvae, apply to many Insects
of the Order Orthoptera. The Phryganeidae, another {399}family of
Neuroptera, have aquatic larvae and wings somewhat similar in form to those
of the Perlidae, but the members of the two families cannot be confounded,
as the Phryganeidae have hairy front wings and large and contiguous coxae.
The antennae of the Perlidae are long, very flexible, and composed of a
very large number of joints. The parts of the mouth vary a good deal. The
mandibles and maxillae are usually rather small, and all the parts of the
mouth are of feeble consistence or even membranous; the maxillary palpi
are, however, well developed and exserted from the mouth, five-jointed. The
labium is short and but little conspicuous. The mandibles in some forms are
almost membranous, but in other genera they are firmer and are toothed. The
labium is composed of a very large mentum, beyond which is a large piece,
usually undivided, bearing the four terminal lobes; the three-jointed
palpus is seated on the side of the large middle sclerite, which is no
doubt of composite nature. Considerable variety as to the lower lip
prevails. The head is broad and flat; there is an indistinctly-indicated
clypeus, three—more rarely two—ocelli, and on each side an eye neither very
large nor perfect. The prothorax is free, and has a flat, margined notum.
The meso- and the meta-thorax are large, equal segments. The pro-, meso-,
and meta-sternum are large pieces; between the first and second, and
between the second and third there is an intervening membrane. The
metasternum is much prolonged backwards, and has on each side a peculiar
slit; similar orifices exist on the other sterna (Fig. 254, _o_). Newport,
who has examined them in _Pteronarcys_, says that they are blind
invaginations of the integument; he calls them the sternal or furcal
orifices.[321] According to this naturalist these very peculiar openings
pass into the body "as strong bone-like tubes, diverging from the axis to
the periphery of the body in the immediate vicinity of some of the
principal tracheae, but that they do not in any way communicate with them,
as they terminate abruptly as caecal structures." He thinks them analogous
with the endo-skeleton of other Insects; a view which cannot be considered
sufficiently established. Laboulbène states[322] that when _Perla parisina_
is seized and placed on its back, it does not move, but emits a liquid at
the base of the articulation of the legs. {400}This suggests that it may
come from these sternal orifices. The abdomen consists of ten dorsal
plates, the first being short, and of nine ventral; the dorsal plates are
much more ample transversely than the ventral. Frequently the hind body is
terminated by two long, many-jointed cerci, looking like antennae. The
coxae are small, not prominent, and are directed outwards. The legs are
slender, the tibiae often grooved. The tarsi are three-jointed, terminating
in two claws and a more or less distinct pad. In the genus _Isopteryx_ an
auditory organ has been described as existing in the legs, in a position
similar to that of the analogous structures in Termitidae and Blattidae.
The wings when closed repose flat on the back, and fold and overlap so that
only one is seen (Fig. 251); in this state the costal portion of each front
wing is turned downwards, so as to protect to some extent, the sides of the
body.
[Illustration: FIG. 251.—_Perla maxima._ (After Pictet.)]
[Illustration: FIG. 252.—_Perla_ sp., nymph, showing tracheal gills.
Pyrénées orientales.]
The early stages are known, but have not been described minutely, and there
appears to be very little information as to the youngest life. All the
species are, when immature, aquatic in their habits; the larvae greatly
resemble the perfect Insects in form, though differing in not possessing
wings and in the ocelli being merely opaque spaces. They have rather large
compound eyes; the future wings are represented by lobe-like
prolongations—varying in length according to age—of the meso- and
meta-notum. In the Nemourae the cerci are absent in the imago though
present in the young. The larvae of Perlidae are carnivorous {401}and are
able to swim well, the legs being provided with abundant swimming hairs;
they, however, as a rule, prefer to walk at the bottom of the pool, or on
rocks or boulders in the water they live in.
One of the most peculiar features of the Perlidae is their respiratory
system. Unfortunately the greatest differences of opinion have prevailed on
various matters in connexion with this subject, and there are several
points about which it is not possible at present to express a decided
opinion.
[Illustration: FIG. 253.—Tracheal gill and portion of a trachea of
_Pteronarcys_. (After Newport.)]
The larvae have no stigmata; it appears to be generally agreed that there
is in them no means of admitting air to the tracheal system by means of
orifices. Some breathe entirely through the integument, the process being
aided by the accumulation of tracheae at the spots where the breathing
orifices should be, and where the integument is more delicate. Others,
however, possess gills in the form of protruded bunches of filaments,
connected with tracheae in the manner shown in Fig. 253. These filamentous
branchiae occur in numerous species of the family, and are situate on
various parts of the body, but many species are destitute of them in
genera, other members of which possess the filaments. In some Nemourae
instead of bunches of filaments there are tubular projections on the
prothoracic segment; and in _Dictyopteryx signata_ similar structures occur
even in the cephalic region, Hagen stating[323] that there exists a pair on
the submentum and another on the membrane between the head and the thorax.
In the imago state, stigmata are present in the normal fashion, there being
two thoracic and six abdominal pairs. In several species the filaments
persist in the imago, so that in these cases we meet with the curious
condition of the coexistence of branchiae with a well-developed and
functionally active system of spiracles; this is the more curious because
the creatures usually have then nothing to do with the water, it having
been ascertained that in these cases the species live out of the water as
other terrestrial and aerial Insects do. These instances of persistence
{402}of branchiae during the aerial life have been the source of some
perplexity; the condition was shown to exist in _Pteronarcys_ by Newport,
and has since been demonstrated in various other forms. Newport believed
that the imago of _Pteronarcys_ breathes by means of the gills, although it
lives out of the water and possesses spiracles; and he informs us that Mr.
Barnston observed the Insect when on the wing "constantly dipping on the
surface of the water." Hence Newport concluded that _Pteronarcys_ in the
winged state is "an amphibious animal." That a winged Insect should live in
the air and yet breathe by means of gills would be truly extraordinary, and
there can be little doubt that Newport's idea was erroneous. Hagen[324] was
able to examine living imagos of the species in question. He found that
they avoided the water, and though he placed some individuals therein, yet
they did not use the gills. He also informs us that the branchiae have,
during life, a shrivelled appearance, indicating that they are not
functionally active, but are merely useless organs carried over to the
imago from the previous instar, in which they were truly the means of
obtaining air. Hagen also ascertained that the spiracles of the imago are
in a normal state, being adapted for breathing, even as far back as the
seventh abdominal segment.
[Illustration: FIG. 254.—Under side of body of _Pteronarcys regalis_,
imago. (After Newport.) _g_, Tracheal gills; _o_, sternal orifices.]
Great difference of opinion has prevailed as to the relations of the
branchiae to the stigmata, it having been contended that the falling off of
some of the branchiae left the stigmatic orifices. The facts appear to be
only consistent with the conclusion that the two are totally independent
organs. This subject has been investigated by Palmén,[325] who finds that
in Perlidae—contrary to what occurs in may-flies—the species are either
entirely destitute of gills, or these organs are persistent throughout
life. It is not to be inferred from this that the gills in the
{403}perennibranchiate Perlidae are as conspicuous as they are in the
exceptional _Pteronarcys_: for it appears that at the final moult the gills
usually become very much contracted and concealed by the new integument; in
some cases they merely appear as slight prominences in the neighbourhood of
the stigmata.
Pictet, Dufour, Newport, and Imhof[326] have studied the internal anatomy.
The alimentary canal is remarkable for the enormous oesophagus; there is no
distinction between this and the crop. A proventriculus is quite absent,
and there are no chitinous folds in the position it usually occupies. The
true stomach is small, and only commences in the fourth abdominal segment.
It has a prolonged lobe on each side in front, and in addition to this
eight sacs; thus there are formed ten diverticula, fastened to the
posterior part of the oesophagus by ligaments. The terminal portion of the
stomach is small, and apparently only distinguished from the short
intestine by the point of insertion of the Malpighian tubes; these vary in
number from about twenty to sixty. There are two pairs of large salivary
glands. In _Pteronarcys_ the caecal diverticula of the stomach are wanting.
In some Perlidae the terminal parts of the gut are more complex than in
_Perla maxima_; Newport figures both an ilium and colon very strongly
differentiated, and states that these parts differ much in _Perla_ and
_Pteronarcys_. According to him the stomach is embraced by a network of
tracheae, and Imhof tells us that he found the stomach to contain only air.
[Illustration: FIG. 255.—Alimentary canal and outline of body of _Perla
maxima_. (After Imhof.) _l_, Upper lip; _mh_, buccal cavity; _ap_, common
termination of salivary ducts; _o_, oesophagus; _s_, salivary glands; _ag_,
duct of salivary gland; _b_, anterior diverticula of stomach; _lg_, their
ligaments of attachment; _mp_, Malpighian tubes; _r_, rectum; _af_, anal
orifice.]
The brain is small, but, according to Imhof, consists of four amalgamated
divisions; the infra-oesophageal ganglion is small, {404}and placed very
near the brain. There are three thoracic and six abdominal ganglia on the
ventral chain. The nerves to the wings are connected with the longitudinal
commissures of the ventral chain by peculiar, obliquely-placed, short
commissures. The reproductive glands are peculiar, inasmuch as in each sex
the pair of principal glands is connected together in the middle. The
testes thus form an arch consisting of a large number of sub-spherical or
pear-shaped follicles; the vasa deferentia are short in _Perla maxima_, and
there are no vesiculae seminales; the ejaculatory duct is divided into
three parts by constrictions. In _Pteronarcys_ and in _Perla bicaudata_,
according to Newport and Dufour, the vasa deferentia are very long and
tortuous, and there are elongate vesiculae seminales. The arrangement of
the extremely numerous egg-tubes is analogous to that of the follicles of
the testes, so that, as Dufour says, there is but a single ovary; connected
with the short, unpaired portion of the oviduct, there is a large
receptaculum seminis, and near the terminal orifice of the duct there is in
_P. maxima_ an eight-lobed accessory gland.
[Illustration: FIG. 256.—The pair of united ovaries of _Perla maxima_: _o_,
egg-tubes; _ov_, oviduct; _r_, receptaculum seminis concealing the orifice
of the duct and an accessory gland.]
[Illustration: FIG. 257.—Egg of _Perla maxima_. (After Imhof.) _c_,
chorion; _d_, oolemn; _gs_, glass-like covering of micropyle apparatus;
_l_, cavity under same; _g_, canals penetrating chorion.]
The eggs are produced by Perlidae in enormous numbers: they are rather
small, but peculiar in form, and possess at one extremity a micropyle
apparatus, covered by a glassy substance through which Imhof could find no
orifice. On the other hand, the chorion on another part of the egg is
perforated by several canals.
{405}The Perlidae being of aquatic habits in their early stages, and,
notwithstanding their ample wings, very poor adepts in the art of flying,
are rarely found at any considerable distance from their native element.
They are specially fond of running water, and delight in the neighbourhood
of waterfalls, or other spots where the current is broken by obstacles so
that a foaming water results. It is probable that the larvae which breathe
by means of gills find an advantage in living in strongly-aerated water.
Mountain streams and torrents are therefore specially affected by them; but
Pictet informs us that they do not like the waters descending from
glaciers. The food of the larvae is believed to be chiefly young may-flies,
or other small, soft creatures, and it may possibly be owing to the absence
of these that the Perlidae do not affect the glacier streams. Although
Perlidae are remarkable for their capacity for enduring cold, it is
possible that they may require warmth of the water at some period of their
development, and this the glacier-streams cannot offer to them. They are
among the earliest Insects to appear in the spring in Europe. Mr. Barnston
says that on the Albany river in Canada the nymph of _Capnia vernalis_
comes up frequently in the cracks of the ice and casts its skin there; "it
frequently comes up when the thermometer stands at freezing." Of _Nemoura
glacialis_, which inhabits similar localities, he says that "it appears in
the spring (end of March or beginning of April) when the ice becomes
honeycombed, and even before then, at the same time as _Capnia vernalis_.
It pairs in the crevices of decaying ice. The male has long antennae, and
his wings are generally rumpled as if glued together." Newport entertained
the idea that those Perlidae that live at low temperatures are of lower
organisation than the other forms of the family.
It is a remarkable fact that several Perlidae frequently have—like _Nemoura
glacialis_—the wings of the male much reduced in size; this being the
contrary of the rule that usually prevails among Insects to the effect
that, when there is a difference in the powers of flight, or even in the
size of the wings, it is the male that is superior. Mr. J. J. Lister met
with a very interesting Perlid at Loch Tanna in Arran at the beginning of
April 1892. In this Insect, which is, according to Mr. M‘Lachlan, a form of
_Isogenus nubecula_, the wings of the female (Fig. 258, B) are reduced to a
size much less than those of ordinary {406}Perlidae, while those of the
male (Fig. 258, A) are mere useless rudiments. Morton has pointed out that
in Scotland more than one species of _Taeniopteryx_ occasionally produces
micropterous males, and he associates this phenomenon with the early time
of their appearance "almost in winter."[327] In _Nemoura trifasciata_ this
reduction of the wings takes another but equally curious form; the hind
wings of the male being long enough to cover the body, while the anterior
pair are reduced to mere rudiments.
[Illustration: FIG. 258.—_Isogenus nubecula_, Loch Tanna. A, Male; A',
wings of male more magnified; B, wings of female.]
The phenomena of micropterism in Perlidae are well worthy of more detailed
investigation. Mr. Morton informs the writer that the male of _Perla
maxima_ (Fig. 251) in North Britain has the wings so short that they cannot
be of any use as organs of flight. In Central Europe the wings are ample,
as shown in our figure. In _Perla cephalotes_ the male is short-winged in
both Britain and Central Europe; of the male of _Dictyopteryx microcephala_
only the micropterous form is known to exist. In _Isogenus nubecula_ (Fig.
258) it appears that the wings of the female are always more ample than
those of the male of the same locality, and that local micropterism affects
the two sexes unequally. Within the Arctic circle this Insect is usually of
the Scotch form, though the male there occasionally has more ample wings.
It has been observed that in some Perlidae the eggs, after they have been
extruded, are carried about by the female; for what reason is not at all
known. They are said to be enclosed in a membranous capsule at the apex of
the abdomen. The number of eggs deposited is sometimes very large,
amounting to five or six thousand, and they are often of very minute size.
About twenty-four species of Perlidae occur in Britain.[328] The
{407}species from all parts of the world existing in collections probably
scarcely exceed two hundred. The insignificance of this number is no doubt
chiefly due to the fact that these unattractive Insects are rarely captured
by collectors, and are so fragile that unless good care is taken of them,
specimens soon go to destruction after being dried. Perlidae are known to
occur in most parts of the world, so that the number of species really
existing may reach two or three thousand. They are known to anglers as
stone-flies and creepers and are a favourite bait for trout.
The family in its character comes near to the Orthoptera, especially to the
more simple forms of Phasmidae, but the two groups differ in the texture of
the front wings and in the structure of the mouth-parts, as well as in the
different proportions of the mesothorax and metathorax. According to
Pictet, in the Australian genus _Eusthenia_ the trophi (Fig. 259) approach
nearer to those of the Orthoptera, so that it appears possible that a more
intimate connexion will be found to exist as more forms are discovered. Of
the groups we include in Neuroptera, Perlidae are in structure most allied
to Sialidae, but the development in the two groups exhibits very important
distinctions. Brauer treats the Perlidae as forming a distinct Order called
Plecoptera, a name applied to the family by Burmeister many years ago.
[Illustration: FIG. 259.—A, Maxilla, B, labium of _Eusthenia spectabilis_.
(After Pictet.)]
Several species of Perlidae, considered to belong to existing genera, have
been found in amber. A fossil from the Eocene deposits in the Isle of Wight
and another from the Miocene of Continental Europe are referred to the
family. Brauer has recently described[329] some fossils from the Jurassic
formation in East Siberia as forming three genera, now extinct, of
Perlidae.
Brongniart informs us[330] that several fossils have been found {408}in the
Carboniferous strata of Commentry that justify us in asserting that allies
of Perlidae then existed. He considers these Carboniferous Insects to have
belonged to a separate family, Protoperlides. The fragments are, however,
so small that we must await further information before forming a definite
opinion as to these Protoperlides.
{409}CHAPTER XVIII
AMPHIBIOUS NEUROPTERA _CONTINUED_—ODONATA, DRAGON-FLIES
FAM. VI. ODONATA—DRAGON-FLIES.
(LIBELLULIDAE OF SOME AUTHORS)
_Elongate Insects with very mobile head and large eyes, with small and
inconspicuous antennae ending in a bristle; with four elongate wings
sub-equal in size and similar in texture, of papyraceous consistency and
having many veinlets, so that there exists a large number of small cells.
All the legs placed more anteriorly than the wings. The earlier stages of
the life are aquatic; there is great change in the appearance of the
individual at the final ecdysis, but there is no pupal instar._
The dragon-flies form a very natural and distinct group of Insects. All the
species are recognised with ease as belonging to the family. They are
invariably provided with wings in the perfect state, and many of them are
amongst the most active of Insects. Their anatomy is, in several respects,
very remarkable.
The head is large and is concave behind; it is attached to the thorax in
such a way that it rotates on two cervical sclerites that project forwards,
and in some cases almost meet in a point in front; hence it possesses
extreme mobility, the power of rotation being very great.
The eyes are always large; in some cases they are even enormous, and occupy
the larger part of the area of the head: the upper facets of the eye are in
many cases larger than the lower, and in a few forms the line of division
is sharply marked transversely. There are three ocelli, which, when the
size of the compound eyes is not too great, are placed in the usual
{410}manner as a triangle on the vertex; but in the forms where the
compound eyes are very large the portion of the head between is, as it
were, puffed out so as to form a projection just in front of where the eyes
meet, and one ocellus is then placed on each side of this projection, an
antenna being inserted quite close to it; the third ocellus is placed in
front of the projection we have mentioned, by which it is often much
concealed; this anterior ocellus is in some cases of unusually large size,
and oval or transverse in form.
[Illustration: FIG. 260.—_Anax formosus_, Britain. (After Migneaux.) (The
legs are not in a natural position.)]
The parts of the mouth are very peculiar, especially the lower lip: we will
briefly allude to its characters in the highly modified forms, premising
that in the smaller and less active species it is less remarkable. The
Libellulidae are carnivorous, their prey being living Insects which are
captured by the dragon-fly on the wing; it is believed that the mouth is
largely instrumental in the capture, though the flight of these Insects is
so excessively rapid that it is difficult, if not impossible, to verify the
action of the mouthpieces by actual observation.
{411}[Illustration: FIG. 261.—A, Maxilla of _Libellula quadrimaculata_; B,
labium of _Aeschna grandis_. _p_, _p′_, Palpus; _a_, terminal spine of
palpus; _c_, cardo; _t_, stipes; _s_, squama; _le_, outer lobe of maxilla,
partly covered by, _li_, inner lobe; _m_, mentum; _r_, intervening lobe.
(After Gerstaecker.)]
For the purpose of securing the prey a mouth that can change its capacity
to a considerable extent and with rapidity is a desideratum, and these
qualities are present in the mouths of those Libellulidae that capture
their prey while hawking. The upper lip is very mobile, is pendent, and
closes the mouth above, while the lower lip entirely closes the under part
by means of two mobile plates; these in some forms (_Libellula_) meet
together in the mesial line, while in others a third plate separates them
in the middle (Fig. 261, B, _li_). These plates are, according to
Gerstaecker's view,[331] portions of the much changed labial palpi, the
part that separates them in _Aeschna_ being the inner lobes of the labial
maxillae; in _Libellula_, where the dilated and valve-like joints of the
palpi meet in the middle line, the labial lobes remain small and are
overlapped by the dilated portions of the palpi. The maxillae proper (Fig.
261, A) are less peculiar, their chief character being that the inner and
outer lobes are not separated, and that the palpus is of only one joint.
Some entomologists take, however, another view of this structure, looking
on the palp-like outer part (_p_ of our figure) as the true outer lobe of
the maxillae, the palpus proper being in that case considered to be
entirely absent. The mandibles are very powerful, and armed with largely
developed teeth. In the interior of the mouth there is a large, free,
semi-membranous lingua, the posterior part of its delicate inferior lamina
being connected with the mentum; the upper lamina of the lingua is stronger
and is pilose. The antennae of the dragon-flies are always small, and
consist of two stouter joints at the {412}base, and a terminal part which
is very slender and pointed, and formed of four or five joints.
The prothorax is always small; the pronotum is distinct, though in some
forms it is quite concealed in the concavity of the back of the head; the
sternum is small; the anatomy of the pleura and basal pieces of the legs is
obscure.
[Illustration: FIG. 262.—A, _Agrion pulchellum_, natural size; B, _Aeschna
cyanea_, profile; C, same from front to show position of legs. ⅔ natural
size.]
The meso- and meta-thorax are very intimately combined, and their relations
are such that the former is placed much above the latter. This peculiarity
is carried to its greatest extent in some of the Agrioninae (Fig. 262, A),
where not only are the wings placed at a considerable distance behind the
three pairs of legs, but also the front pair of wings is placed almost
directly above the hind pair. In the Anisopterides these peculiarities are
much less marked (Fig. 262, B), nevertheless even in them the three pairs
of legs are placed quite in front of the wings. This peculiar structure of
the wing-bearing segments is accompanied by an unusual development of the
pleura, which, indeed, actually form the larger part, if not nearly the
whole, of the front region of the dorsal aspect of these two segments. We
shall not enter into more minute particulars as to the structure of the
thorax, for difference of opinion prevails as to the interpretation of the
parts.[332] The abdomen is remarkable for its elongation; it is never
broad, and in some genera—_Mecistogaster_, _e.g._—it attains a length and
slenderness which are not {413}reached by any other Insects. It consists of
ten segments and a pair of terminal calliper-like or flap-like processes of
very various sizes and forms.
The wings of the dragon-flies are usually transparent and provided with a
multitude of small meshes. The hind wings are about as large as the front
pair, or even a little larger; the main nervures have a sub-parallel
course, and are placed in greater part on the anterior region of each wing.
The relations of the more constant nervures and the cells of which they are
parts form a complex subject, and are amongst the most important of the
characters used in classifying these Insects. The wings are always elongate
in comparison to their breadth and have no folds; they are held partially
extended, or are placed so as to project backwards, or backwards and
outwards. They exhibit another peculiarity, inasmuch as the front or costal
margin is slightly uneven before or near the middle, giving rise to an
appearance such as might result from the breaking and subsequent mending of
the marginal rib at the spot in question, which is called the nodus. In
some forms a peculiar character exists in the shape of a small opaque space
called the membranule, lying close to the body of the Insect in the anal
area of the wing, as shown in Fig. 260.
The legs are slender and are chiefly remarkable for the beautiful series of
hair-like spines with which they are armed, and which in some forms (_e.g._
_Platycnemis_, Fig. 264) are of considerable length. We believe that the
legs are of great importance in capturing the prey, they being held
somewhat in the position shown in Fig. 262, C. The tarsi are three-jointed.
In the male of _Libellago caligata_ the legs exhibit a remarkable
condition, the tibiae being dilated, and on the upper side of a vivid red
colour, while below they are white. This coloration and form are each
unusual in the family. The male of _Platycnemis pennipes_, a British
species (Fig. 264), shows a similar dilatation of the tibiae, but to a less
extent and without any great difference in the colour of the two faces of
the dilatation. This dilatation reaches its maximum in _Psilocnemis
dilatipes_ M‘Lach. The position of the legs in relation to the other parts
of the body is peculiar to the dragon-flies; the legs seem to be unfit for
walking, the Insects never using them for that purpose.
{414}Several peculiarities in the internal anatomy deserve notice. The
alimentary canal in _Libellula_ is about as long as the body, the
oesophagus and chylific stomach being elongate, while the intestine is
short and divided into only two parts; there is no definite proventriculus.
The Malpighian tubules are shorter than usual; they are about forty in
number. The male has no vesiculae seminales; the vasa deferentia are
elongate, and the ejaculatory duct is very short, being in fact merely a
common sinus formed by the terminations of the vasa deferentia. The opening
of this duct is situated on the penultimate ventral plate; the organs of
intromission are, however, placed much anterior to this, on the under side
of the second segment. The mode in which the fertilising fluid is
transferred from the ninth to the second segment is not well understood,
but it is known that the abdomen is flexed by the Insect so as to bring the
ninth ventral plate into contact with the second. The three thoracic
ganglia of the nervous chain are all contiguous, though not completely
amalgamated; the abdominal ganglia are seven in number, and are all
separated, the terminal one being larger than the others. Dufour, after
repeated dissections, was unable to find any salivary glands, but Olga
Poletajewa[333] states that they exist.
The Odonata must be ranked among the most highly-organised Insects so far
as external structure and powers of locomotion are concerned; the peculiar
modifications of the thoracic segments and the relative positions of the
wings and legs mark a great departure from the normal type of Insect
structure. Their prey consists of living Insects, which they capture on the
wing by their own superior powers of flight. They destroy a great many
Insects, their appetite for food being, as in the cases of the Mantidae and
of the tiger-beetles, apparently almost insatiable. They are admirably
constructed for the purposes of their predatory lives; they fly with great
swiftness and change the direction of their flight with admirable facility.
They are, however, dependent on sunshine, and conceal themselves in dull
and cloudy weather. The larger Insects of the family belong to the division
Anisopterides (Fig. 260, _Anax formosus_) and some of these may, in our own
country, usually be seen, in the bright sunshine of the summer and autumn,
engaged in hawking in their favourite haunts. Places where other Insects
{415}abound are naturally those most frequented; the glades of woods,
country lanes and hedge-sides, the borders of streams and the margins of
sheets of water are the places they most affect. They inspire the rustics
with some feeling of fear, and hence have received the name of
"horse-stingers," and in North America are called "devil's
darning-needles." The aversion to dragon-flies may perhaps be due to their
appearance, which is certainly, in the case of some of our species of
_Aeschna_, _Cordulegaster_, and _Gomphus_, very remarkable, consisting of a
dark ground-colour with bars and spots of vivid green or yellow, giving, it
must be admitted, a peculiar, even savage appearance to the Insects.
Whatever the reason may be, they are, it is certain, held in much fear, and
it is difficult to induce a country lad to touch one even when it is
captured and held by another person. The idea of dragon-flies being
dangerous to anything but their Insect victims is, however, entirely
erroneous; they may be captured and handled without their inflicting any
injury. It is probable that the life of the imago may endure for several
weeks if not months. It is known that _Sympycna fusca_—a common European
though not British dragon-fly—hibernates in the imago state.
In the case of the large dragon-flies we have mentioned, each individual
appears to have a domain, as it were, of its own. Westwood tells us that he
has seen what he believed to be the same individual hawking daily for
several weeks together over a small pond. The writer observed a specimen of
_Cordulegaster annulatus_ to frequent a particular bush, to which it
returned—frequently to the same leaf—after an excursion in search of food.
The way in which these Insects actually seize their prey has not yet been
made clear; it is certain that they capture flying Insects, and it seems
most probable, as we have already said, that this is done by means of the
legs. These, as we have said, are inserted so as to be very near to the
mouth; they are directed forwards, and are held bent at right angles so as
to form a sort of net, and are armed with a beautiful system of fine
spines; it is probable that if the dragon-fly pursue an Insect on the wing
and strike it with the trap, formed by its six legs (Fig. 262, C), then
these immediately come together under the mouth, so that the victim,
directly it is captured by the leg-trap of its pursuer, finds itself in the
jaws of its destroyer. It is perhaps impossible to {416}verify this by
actual observation, as the act of capture and transfer is so very brief and
is performed in the midst of a rapid dash of flight, but it seems more
probable that the prey is first struck by the legs than that the mouth is
the primary instrument of capture. The excessive mobility of the head
permits the victim to be instantly secured by the mouth, and the captured
fly is turned about by this and the front pair of legs, and is nipped
rapidly so that the wings and drier parts fall off; the more juicy parts of
the prey are speedily squeezed into a little ball, which is then swallowed,
or perhaps we should rather say that the mouth closes on it, and submits it
to further pressure for the extraction of the juices. We have already noted
that many of these large and active dragon-flies, particularly in the
Libellulinae and Aeschninae, have their eyes distinctly divided into two
parts, the facets in the lower part of the eye being different from those
of the upper part. Exner considers[334] that the upper division is for the
perception of movement, the lower for the perception of the form of resting
objects. Plateau thinks[335] that the dragon-flies perceive only movement,
not form.
[Illustration: FIG. 263.—Inner view of a portion of the left side of body
of _Libellula depressa_, showing a part of the mechanism of flight, viz.
some of the chitinous ridges at base of the upper wing, and some of the
insertions of the tendons of muscles. A, line of section through base of
upper wing, the wing being supposed to be directed backwards; C, upper
portion of mechanism of the lower wing; _b_, lever extending between the
pieces connected with the two wings. (After von Lendenfeld.)]
The splendid acts of flight of the Anisopterid Odonata are accomplished by
the aid of a complex arrangement of chitinous pieces at the bases of the
wings (Fig. 263). In Insects with considerable powers of flight the hind
wings are usually subordinate in functional importance to the anterior, to
which they are attached by a series of hooks, or some other simple
mechanism, on the wings. {417}In the Odonata the two wings of each pair are
quite free, but they are perhaps brought into correlative action by means
of a lever of unusual length existing amongst the chitinous pieces in the
body wall at the base of the wings (Fig. 263, _b_). The wing muscles are
large; according to von Lendenfeld[336] there are three elevator, five
depressor, and one adductor muscles to each wing: he describes the wing
movements as the results of the correlative action of numerous muscles and
ligaments, and of a great number of chitinous pieces connected in a jointed
manner.
Amans[337] has suggested that the mechanism of flight of the dragon-fly
would form a suitable model for a flying-machine, to be propelled by
electricity.
[Illustration: FIG. 264.—_Platycnemis pennipes_, ♂, Britain.]
The Zygopterides—the second of the two divisions of the Odonata—are Insects
different in many respects from the large and robust Anisopterides. The
division comprises the delicate Insects called "demoiselles," damsel-flies,
by the French (Fig. 262, A, and Fig. 264). Great power of flight is not
possessed by these more fragile Insects; they flit about in the most gentle
and airy manner from stem to stem of the aquatic plants and grasses that
flourish in the localities they love. To this group belong the fairy-like
Insects of the genus _Calepteryx_, in which various parts of the body and
wings are suffused with exquisite {418}metallic tints, while sometimes the
two sexes of one species have differently coloured wings. The smallest and
most delicate dragon-flies that are known are found in the tropics; some of
the genera allied to _Agrion_ consist of Insects of extraordinary fragility
and delicacy.
Although the mature Odonata are so pre-eminently endowed for an aerial and
active life, yet in the earlier stages of their existence they are very
different; they are then, without exception, of aquatic habits; though
carnivorous also in this period of their existence, they are sluggish in
movement, lurking in concealment and capturing their prey by means of a
peculiar conformation of the mouth, that we shall subsequently describe.
Their life-histories are only very imperfectly known.
The eggs are deposited either in the water or in the stem of some aquatic
plant, the female Insect occasionally undergoing submersion in order to
accomplish the act. The young on hatching are destitute of any traces of
wings (Fig. 265), and the structure of the thoracic segments is totally
different from what it is in the adult, the rectal respiratory system (Fig.
265, _x_) to which we shall subsequently allude, being, however, already
present. The wings are said to make their first appearance only at the
third or fourth moult. At this time the pleura of the second and third
thoracic segments have grown in a peculiar manner so as to form a lateral
plate (Fig. 266, B, shows this plate at a later stage), and the wing-pads
appear as small projections from the membranes at the upper margins of
these pleural plates (Fig. 266, A, B). The plates increase in size during
the subsequent stadia, and meet over the bases of the wing-pads, which also
become much longer than they were at first. The number of moults that occur
during growth has not been observed in the case of any species, but they
are believed to be numerous. There is no pupa, nor is there any well-marked
quiescent stage preceding the assumption of the winged form at the last
ecdysis, although at the latter part of its life the nymph appears to be
more inactive than usual. When full grown, the nymph is more like the
future perfect Insect than it was at first, and presents the appearance
shown in Figs. 266 and 270. At this stage it crawls out of the water and
clings to some support such as the stem or leaf of an aquatic plant; a few
minutes after doing so the skin of the back of the thoracic region splits,
and the imago emerges from the nymphal skin.
{419}[Illustration: FIG. 265.—Larva of _Diplax_ just hatched. _n_, a
ganglion of the ventral chain; _d_, dorsal vessel; _x_, tracheal network
round rectum. (After Packard, _P. Boston Soc._ xi. 1868, p. 365.)]
[Illustration: FIG. 266.—_Ictinus_ sp., nymph, Himalaya. A, Dorsal, B,
lateral view. (After Cabot.)]
The nymphs never have the body so elongate as the perfect Insect, the
difference in this respect being frequently great, and the nymphs of the
subfamily Libellulinae being very broad (Fig. 266, nymph of _Ictinus_ sp.);
consequently the creature on emergence from the nymph-skin is very much
shorter than it will soon become. Extension begins to take place almost
immediately; it has been thought by some that this is accomplished by
swallowing air; this is, however, uncertain. At first the wings have only
the length of the wing-pads of the nymph, and their apical portion is an
unformed mass. The colour of the perfect Insect is not present when the
emergence takes place. The wing grows quickly until the full length is
attained. In the genus _Agrion_ {420}the expansion of the wings is
accompanied by frequent elevations and depressions of the body, and
occupies an hour or so; the elongation of the abdomen is not so soon
completed, and its brilliant colours do not appear for several hours.
[Illustration: FIG. 267.—Young nymph of _Aeschna_ sp. (Cambridge) about
fourth moult.]
The mouth of the nymph bears a remarkable structure called the mask (Fig.
268). It is apparently formed by a backward growth of the bases of the
labium and lingua, a hinge being formed between the two at the most
posterior point of their growth. The prolonged portions of these parts are
free: usually the mask is folded under the head, but it can be unfolded and
thrust forward, remaining then attached to the head by means of the more
anterior parts of the lingua and by the maxillae, the whole of the elongate
apparatus being, when used, extended from this anterior part of its
attachment. The front parts of the labium form a prehensile apparatus armed
with sharp teeth, so that the structures make altogether a very effectual
trap, that can be extended in order to secure the prey.
[Illustration: FIG. 268.—Under side of head of _Calepteryx virgo_, nymph,
with mask unfolded. _a_, Lingua; _b_, line from which the mask swings; _c_,
line of doubling up; _d_, lower lip proper; _e_, articulated lateral
processes thereof.]
The fact that the dragon-fly passes suddenly, in the middle of its
existence, from an aquatic to an aerial life, makes the condition of its
respiratory organs a subject for inquiry of more than usual interest.
Réaumur was of opinion that the nymph was, in spite of its aquatic
existence, provided with an extensive system of stigmata or orifices for
breathing air; this was, however, denied by Dufour, and his opinion seemed
to be supported by the fact that other means of obtaining air were
discovered to exist in these nymphs. The inquiries connected with the
respiration {421}of Odonata are still very incomplete, but some interesting
points have been ascertained, the most important of which is perhaps the
existence in some forms of a respiratory system in connexion with the
posterior part of the alimentary canal (Fig. 269). In the nymphs of
Anisopterides the system consists of four main tracheal trunks, traversing
the length of the body, and by their ramifications and inosculations
forming an extensive apparatus. Connected with the four main trunks we have
described, there is a shorter pair confined to the abdomen, where it
supplies a large number of branches to the walls of the stomach. The dorsal
pair of the main tubes give numerous subsidiary branches to the outside of
the rectum, and the ventral pair furnish a smaller number. The walls of the
gut are penetrated by the branches, which inside the rectum form numerous
loops; these, covered by a membrane, project into the interior in the form
of multitudinous papillae (Æschninae). In the Libellulinae the papillae are
replaced by more flattened processes or lamellae. The structures attain a
remarkable development, there being in _Aeschna cyanea_ upwards of 24,000
papillae.
[Illustration: FIG. 269.—Portion of tracheal system of nymph of _Aeschna
cyanea_. _R_, _R_, _R_, _R_, rectum; _A_, anus; _td_, dorsal; _tv_,
ventral, tracheal tubes; _M_, Malpighian tubes. (After Oustalet.)]
These rectal gills obtain air from water admitted into the rectum for the
purpose; the extremity of the body being armed with projections of variable
form, that can be separated to allow ingress and egress of the fluid, or
brought into close apposition so as to close the orifice. The water so
taken in can, by some species, be ejected with force, and is used
occasionally as a means of locomotion. These rectal branchiae can absorb
free air, as well as air dissolved in water. If the fluid in which the
creatures are placed has been previously boiled, so as to expel the air
from it, the nymphs then thrust the {422}extremity of the body out of the
water and so obtain a supply of air.
Oustalet and Palmén state that at the last ecdysis the lamellae, or the
papillae, do not disappear, but remain quite empty, and are consequently
functionless, while on the tracheal trunks there are developed air vesicles
to fit the creature for its aerial career. Hagen says that in _Epitheca_
the whole structure of the gills is shed at the final moult.
The subject of the rectal branchiae of _Libellula_ has been discussed and
illustrated by Chun,[338] who states that Leydig has made known that in
_Phryganea grandis_ a structure is found connecting the rectal branchiae of
_Libellula_ with the rectal glands of some other Insects. We have not been
able to find a confirmation of this in the writings of Leydig or elsewhere.
[Illustration: FIG. 270.—_Calepteryx virgo_, mature nymph, Britain.]
In the nymphs of the Zygopterides the highly-developed rectal branchiae
found in the Aeschninae and Libellulinae do not exist, and the respiration
seems to be of a complex character. In one division of the
Zygopterides—Calepteryginae—rectal gills of an imperfect character are said
by Hagen and others to exist.[339] The nymphs of the Zygopterides are
provided with three mobile processes at the extremity of the body (Fig.
270); these serve the purposes of locomotion. They are believed to possess
also a respiratory function, but this must be of an accessory nature, for
the nymphs live after the removal of the processes, and indeed reproduce
them; the skin of these processes is harder than is usual in Insect gills.
In the nymph of _Euphaea_—a genus of Calepteryginae found in tropical
Asia—there are also external {423}abdominal gills, and in this case
respiration may, according to Hagen,[340] take place in four different
manners: (1) by ten pairs of stigmata; (2) by lateral branchiae well
furnished with tracheae; (3) by caudal branchiae; (4) by rectal branchiae.
It is further said that in this Insect the lateral branchiae persist in the
imago.
Although the means of respiration of the nymphs have been fairly well
ascertained, yet the mode in which the nymph is prepared for the sudden
change from the aquatic to aerial life is still obscure, the condition of
the stigmata not being thoroughly elucidated. It appears probable, however,
that the young nymph has no stigmata; that these organs appear in the
course of its development, being at first quite impervious, but becoming—at
any rate in the case of the larger and more important pair—open previous to
the final ecdysis. We have mentioned the contradictory opinions of Réaumur
and Dufour, and will now add the views of some modern investigators.
Oustalet says[341] that there are two pairs of spiracles in the nymphs; the
first pair is quite visible to the naked eye, and is situate between pro-
and meso-notum; it is in the nymph closed by a membrane. The other pair of
spiracles is placed above the posterior pair of legs, is small and
completely closed. He does not state what stage of growth was attained by
the nymphs he examined. Palmén was of opinion that not only thoracic but
abdominal spiracles exist in the nymph,[342] and that they are completely
closed so that no air enters them; he says that the spiracles have tracheae
connected with them, that at each moult the part closing the spiracles is
shed with some of the tracheal exuviae attached to it. The breathing
orifices are therefore for a short time at each ecdysis open, being
subsequently again closed by some exudation or secretion. This view of
Palmén's has been thought improbable by Hagen and Dewitz, who operated by
placing nymphs in alcohol or warm water and observing the escape of bubbles
from the spots where the supposed breathing orifices are situate. Both
these observers found much difference in the results obtained in the cases
of young and of old nymphs. Hagen concludes that the first pair of thoracic
spiracles are functionally active, and that abdominal stigmata exist though
{424}functionless; he appears to be of opinion that when the first thoracic
stigma is closed this is the result of the abutting against it of a closed
trachea. Dewitz found[343] that in the adult nymph of _Aeschna_ the
thoracic stigma is well developed, while the other stigmata—to what number
and in what position is not stated—are very small. In a half-grown Aeschnid
nymph he found the thoracic stigma to be present in an undeveloped form. On
placing a full-grown nymph in alcohol, gas escaped from the stigma in
question, but in immature nymphs no escape of gas occurred although they
were subjected to a severe test. A specimen that, when submitted to the
above-mentioned immersion, emitted gas, subsequently moulted, and
thereafter air escaped from the spiracle previously impervious. The
observations of Hagen and Dewitz are perhaps not so adverse to the views of
Palmén as has been supposed, so that it would not be a matter for surprise
if Palmén's views on this point should be shown to be quite correct.
The number of species of Odonata or Libellulidae that have been described
is somewhat less than two thousand, but constant additions are made to the
number, and when the smaller and more fragile forms from the tropics are
collected and worked out it will probably be found that the number of
existing species is somewhere between five and ten thousand. They are
distributed all over the world, but are most numerous in species in the
warmer regions, and their predominance in any one locality is very much
regulated by the existence of waters suitable for the early stages of their
lives.
A good work on the British Odonata is still a desideratum.[344] In Britain
about forty-six species are believed to be native. They are said to be of
late years less numerous than they used to be. Notwithstanding their great
powers of flight, dragon-flies are destroyed by birds of various kinds;
several hawks are said to be very fond of them, and _Merops persicus_ to
line its nest with their wings. The number of Insects killed by
dragon-flies in places where they are abundant must be enormous; the
nymphs, too, {425}are very destructive in the waters they inhabit, so that
dragon-flies have no doubt been no mean factor in maintaining that
important and delicate balance of life which it is so difficult for us to
appreciate. The nymphs are no doubt cannibals, and this may perhaps be an
advantage to the species, as the eggs are sometimes deposited in large
numbers in a limited body of water, where all must perish if the nymphs did
not, after exhausting other food, attack one another. Martin, speaking of
the Odonata of the Département de l'Indre in France, says:[345] "The eggs,
larvae, and nymphs are the prey of several fishes, snakes, newts,
Coleoptera, aquatic Hemiptera, and of some diving birds. Sometimes the
destruction is on a considerable scale, and one may notice the dragon-flies
of some piece of water to diminish gradually in numbers, while the animals
that prey on them increase, so that a species may for a time entirely
disappear in a particular spot, owing to the attacks of some enemy that has
been specially prosperous, and also eager in their pursuit. De Selys found
that from a pond filled with carp, roach, perch, and eels, several of the
dragon-fly denizens disappeared directly the bream was introduced." On the
other hand, there can be little doubt that the nymphs are sometimes
injurious to fish; it has been recorded that in a piscicultural
establishment in Hungary 50,000 young fishes were put into a pond in
spring; in the following autumn only fifty-four fish could be found, but
there were present an enormous quantity of dragon-fly nymphs.
Odonata are among the few kinds of Insects that are known to form swarms
and migrate. Swarms of this kind have been frequently observed in Europe
and in North America; they usually consist of species of the genus
_Libellula_, but species of various other genera also swarm, and sometimes
a swarm may consist of more than one species. _L. quadrimaculata_ is the
species that perhaps most frequently forms these swarms in Europe; a large
migration of this species is said to occur every year in the Charente
inférieure from north to south.[346] It is needless to say that the
instincts and stimuli connected with these migrations are not understood.
The nymphs are capable, under certain circumstances, of accommodating
themselves to very peculiar conditions of life. The Sandwich Islands are
extremely poor in stagnant waters, and {426}yet there exist in this remote
archipelago several highly peculiar species of Agrioninae. Mr. R. C. L.
Perkins has recently discovered that the nymphs of some of these are
capable of maintaining their existence and completing their development in
the small collections of water that accumulate in the leaves of some lilies
growing on dry land. These nymphs (Fig. 271) have a shorter mask than
occurs, we believe, in any other Odonata, and one would suppose that they
must frequently wait long for a meal, as they must be dependent on stray
Insects becoming immersed in these tiny reservoirs. The cannibal habits of
the Odonata probably stand these lily-dwellers in good stead; Mr. Perkins
found that there were sometimes two or three nymphs of different sizes
together, and we may suspect that it sometimes goes hard with the smaller
fry. The extension in the length of the body of one of these
lily-frequenting Agrions when it leaves the water for its aerial existence
is truly extraordinary.
[Illustration: FIG. 271.—Under side of Agrionid nymph, with short mask,
living in water in lilies. Hawaiian Islands. × 3.]
The Odonata have no close relations with any other group of Insects. They
were associated by Latreille with the Ephemeridae, in a family called
Subulicornia. The members of the two groups have, in fact, a certain
resemblance in some of the features of their lives, especially in the
sudden change, without intermediate condition, from aquatic to aerial life;
but in all important points of structure, and in their dispositions,
dragon-flies and may-flies are totally dissimilar, and there is no
intermediate group to connect them. We have already, said that the Odonata
consist of two very distinct divisions—Anisopterides and Zygopterides. The
former group comprises the subfamilies Gomphinae, Cordulegasterinae,
Aeschninae, Corduliinae, and Libellulinae,—Insects having the hinder wings
slightly larger than the anterior pair; while the Zygopterides consist of
only two subfamilies—Calepteryginae and Agrioninae; they have the wings of
the two pairs equal in size, or the hinder a little the smaller. The two
groups Gomphinae and Calepteryginae are each, in several respects, of lower
development than the others, and authorities are divided {427}in opinion as
to which of the two should be considered the more primitive. It is
therefore of much interest to find that there exists an Insect that shares
the characters of the two primitive subfamilies in a striking manner. This
Insect, _Palaeophlebia superstes_ (Fig. 272), has recently been discovered
in Japan, and is perhaps the most interesting dragon-fly yet obtained. De
Selys Longchamps refers it to the subfamily Calepteryginae, on account of
the nature of its wings; were the Insect, however, deprived of these
organs, no one would think of referring _Palaeophlebia_ to the group in
question, for it has the form, colour, and appearance of a Gomphine
Odonate. Moreover, the two sexes differ in an important character,—the form
of the head and eyes. In this respect the female resembles a Gomphine of
inferior development; while the male, by the shape and large size of the
ocular organs, may be considered to combine the characters of Gomphinae and
Calepteryginae. The Insect is very remarkable in colour, the large eyes
being red in the dead examples. We do not, however, know what may be their
colour during life, as only one pair of the species is known, and there is
no record as to the life-history and habits. De Selys considers the nearest
ally of this Insect to be _Heterophlebia dislocata_, a fossil dragon-fly
found in the Lower Lias of England.
[Illustration: FIG. 272.—_Palaeophlebia superstes._ A, The Insect with
wings of one side and with two legs removed; B, front view of head of
female; C, of male. (After De Selys.)]
Numerous fossil dragon-flies are known; the group is well represented in
the Tertiary strata, and specimens have been found in amber. In strata of
the Secondary age these Insects {428}have been found as far back as the
Lower Lias; their remains are said to exist in considerable variety in the
strata of that epoch, and some of them to testify to the existence at that
period of dragon-flies as highly specialised as those now living. According
to Hagen[347] _Platephemera antiqua_ and _Gerephemera simplex_, two
Devonian fossils, may be considered as dragon-flies; the evidence as to
this appears inadequate, and Brongniart refers the latter Insect to the
family Platypterides, and considers Platephemera to be more allied to the
may-flies.
One of the most remarkable of the numerous discoveries lately made in
fossil entomology is the finding of remains of huge Insects, evidently
allied to dragon-flies, in the Carboniferous strata at Commentry.
Brongniart calls these Insects Protodonates,[348] and looks on them as the
precursors of our Odonata. _Meganeura monyi_ was the largest of these
Insects, and measured over two feet across the expanded wings. If M.
Brongniart be correct in his restoration of this giant of the Insect world,
it much resembled our existing dragon-flies, but had a simple structure of
the thoracic segments, and a simpler system of wing-nervures. On p. 276 we
figured _Titanophasma fayoli_, considered by Scudder and Brongniart as
allied to the family Phasmidae, and we pointed out that this supposed
alliance must at best have been very remote. This view is now taken by M.
Brongniart himself,[349] he having removed the Insect from the
Protophasmides to locate it in the Protodonates near Meganeura. There
appears to be some doubt whether the wings supposed to belong to this
specimen were really such, or belonged rather to some other species.
{429}CHAPTER XIX
AMPHIBIOUS NEUROPTERA _CONTINUED_—EPHEMERIDAE, MAY-FLIES
FAM. VII. EPHEMERIDAE—MAY-FLIES.
_Delicate Insects with atrophied mouth and small, short antennae; with
four membranous wings having much minute cross-veining; the hinder pair
very much smaller than the other pair, sometimes entirely absent: the
body terminated by three or two very elongate slender tails. The earlier
stages are passed through in water, and the individual then differs
greatly in appearance from the winged Insect; the passage between the two
forms is sudden; the creature in its first winged state is a subimago,
which by shedding a delicate skin reveals the final form of the
individual._
[Illustration: FIG. 273.—_Ephemera danica_, male, Britain.]
The may-flies are well known—in literature—as the types of a brief and
ineffective life. This supposed brevity relates solely to their existence
in the winged form. In the earlier stages the may-fly is so unlike its
subsequent self that it is not recognised as a may-fly by the uninitiated.
The total life of the individual is really quite as long as that of most
{430}other Insects. The earlier stages and life-histories of these Insects
are of great importance. The perfect Insects are so delicate and fragile
that they shrivel much in drying, and are very difficult to preserve in a
condition suitable for study.
The mouth of the imago is atrophied, the trophi scarcely existing as
separate parts. Packard says that in _Palingenia bilineata_ he could
discover no certain traces of any of the mouth-parts, but in _Leptophlebia
cupida_ he found, as he thought, the rudiments of the maxillae and labium,
though not of the mandibles. The antennae are always short, and consist of
one or two thick basal joints succeeded by a delicate needle-like segment,
which, though comparatively long, is not divided. The ocular organs are
remarkable for their large size and complex development; they are always
larger in the male than they are in the female. The compound eyes of the
former sex are in certain species, _e.g._ _Cloëon_ (Fig. 274), quite
divided, so that each eye becomes a pair of organs of a different
character; one part forms a pillar facetted at its summit, while the other
part remains as a true eye placed on the side of the head; in front of
these compound eyes there are three ocelli. Thus the Insect comes to have
three different kinds of eyes, together seven in number.
[Illustration: FIG. 274.—Front of head of _Cloëon_, male. _a_, Pillared
eye; _b_, sessile eye; _c_, ocellus.]
The prothorax is small, the pronotum being, however, quite distinct. The
mesothorax is very large; its notum forms by far the larger part of the
upper surface of the thoracic region, the metathorax being small and
different in structure, resembling in appearance a part of the abdomen, so
that the hind wings look as if they were attached to a first abdominal
segment. The mesosternum is also disproportionately large in comparison
with the homologous piece preceding it, and with that following it. The
pleural pieces are large, but their structure and disposition are only very
imperfectly understood. The coxae are small and are widely separated, the
anterior being, however, more elongate and approximate than the others. The
other parts of the legs are slender; the number of joints in the tarsi
varies from five to one. {431}The legs throughout the family exhibit a
considerable variety of structure, and the front pair in the males of some
species are remarkably long. The abdomen is usually slender, and consists
of ten segments; the terminal one bears three, or two, very long flexible
appendages. The first dorsal plate of the abdomen is either wanting or is
concealed to a considerable extent by the metanotum. The wings are
peculiar; the anterior pair vary a great deal in their width, but are never
very long in proportion to the width; the hind pair are always
disproportionately small, and sometimes are quite wanting. The venation
consists of a few, or of a moderate number, of delicate longitudinal veins
that do not pursue a tortuous course, but frequently are gracefully curved,
and form a system of approximately similar curves, most of the veins being
of considerable length; close to the anterior margin of the wing there are
two or three sub-parallel veins. Frequently there are very numerous fine,
short cross-veinlets, but these vary greatly and may be entirely wanting.
[Illustration: FIG. 275.—Wings of _Ephemera danica_. (After Eaton.)]
The earlier stages of the life of Ephemeridae are, it is believed, in the
case of all the species, aquatic. May-flies, indeed, during the period of
their post-embryonic development are more modified for an aquatic life than
any other Insects, and are provided with a complex apparatus of tracheal
gills. The eggs are committed to the waters without any care or foresight
on the part of the parent flies, thus the embryonic development is also
aquatic; little, however, is known of it. According to Joly[350] the
process in _Palingenia virgo_ is slow. The larva on emerging from the egg
has no respiratory system, neither could Joly detect any circulation or any
nervous system. The creature on emergence is very like _Campodea_ in form,
possessing long antennae and tails—caudal setae. Owing to the organisation
being inferior, the creature in its earlier stages is called a larvule; in
its later stages {432}it is usually spoken of as a nymph, but the term
larva is also frequently applied to it. Soon the gills begin to appear in
the form of small tubular caeca placed in the posterior and upper angles of
the abdominal rings; in fifteen days the gills begin to assume their
characteristic form, are penetrated by tracheae, and the circulation can be
seen. The amount of growth accomplished after hatching between March and
September is but small.
[Illustration: FIG. 276.—Nymph of _Cloëon dipterum_.[351] Wing-sheath of
left side, gills of right side, removed; _g_, tracheal gills. (After
Vayssière.)]
[Illustration: FIG. 277.—Larvule of _Cloëon dimidiatum_. (After Lubbock.)]
The metamorphosis of _Cloëon_ has been described by Sir John Lubbock; he
informs us that the young creature undergoes a constant and progressive
development, going through a series of more than twenty moults, each
accompanied by a slight change of form or structure. His observations were
made on captured {433}specimens, so that it is not certain that what he
calls[352] the first stage is really such. He found no tracheae in the
earliest stages; the small first rudiments of the gills became visible in
the third stage, when there were no tracheae; the fourth instar possessed
tracheae, and they could be seen in the gills. The wing rudiments could
first be detected in the ninth and tenth stages. The changes of skin during
the winter months are separated by longer intervals than those occurring at
other periods of the year.
[Illustration: FIG. 278.—Adult nymph of _Ephemera vulgata_. (After Eaton.)
Britain.]
The nymphs differ greatly in the structure and arrangement of their
tracheal gills, and display much variety in their general form and habits;
some of them are very curious creatures. Pictet[353] divides them in
accordance with their habits into four groups: (1) Fossorial larvae: these
live in the banks of streams and excavate burrows for shelter; they are of
cylindrical form, possess robust legs, abundant gills at the sides of the
body, and frequently processes projecting forwards from the head: examples,
_Ephemera_ (Fig. 278) and _Palingenia_. (2) Flat larvae: these live
attached to rocks, but run with rapidity when disturbed; they prefer rapid
streams, have the breathing organs attached to the sides of the body and
not reposing on the back; they are exclusively carnivorous, while the
fossorial forms are believed to obtain their nutriment by eating mud:
example, _Baëtis_. (3) Swimming larvae: elongate delicate creatures, with
feeble legs, and with strongly ciliated caudal setae: example, _Cloëon_
(Fig. 276). (4) Climbing larvae: these live in slowly-moving waters,
especially such as have much slimy mud in suspension, and they have a habit
of covering themselves with this mud sometimes to such an extent as to
become concealed by it: example, _Potamanthus_.
{434}[Illustration: FIG. 279.—Nymph of _Oligoneuria garumnica_, France.
_g_{2}_ and _g_{7}_, two of the dorsal tracheal gills. (After Vayssière.)]
The anatomy of the nymphs has been treated by Vayssière,[354] who arranges
them in five groups in accordance with the conditions of the tracheal
gills: (1) The gills are of large size, are exposed and furnished at the
sides with respiratory fringes: example, _Ephemera_ (Fig. 278). (2) The
branchiae are blade-like, not fringed, and are exposed at the sides of the
body: example, _Cloëon_ (Fig. 276). (3) The respiratory tubes are placed on
the under surface of plates whose upper surface is not respiratory:
example, _Oligoneuria garumnica_ (Fig. 279). (4) The anterior gill is
modified to form a plate that covers the others: example, _Tricorythus_
(Fig. 282, B). (5) The gills are concealed in a respiratory chamber:
example, _Prosopistoma_ (Fig. 280). The last of these nymphs is more
completely adapted for an aquatic life than any other Insect at present
known; it was for long supposed to be a Crustacean, but it has now been
shown to be the early stage of a may-fly, the sub-imago having been reared
from the nymph. The carapace by which the larger part of the body is
covered is formed by the union of the pro- and meso-thorax with the sheaths
of the anterior wings, which have an unusually extensive development; under
the carapace there is a respiratory chamber, the floor and sides of which
are formed by the posterior wing-sheaths, and by a large plate composed of
the united nota of the metathorax and the first six abdominal segments. In
this chamber there are placed five pairs of tracheal gills; entrance of
water to the chamber is effected by two laterally-placed orifices, and exit
by a single dorsal aperture. These nymphs use the body as a sucker, and so
adhere strongly to stones under water. When detached they swim rapidly by
means of their caudal setae; the form of these latter organs is different
from that {435}of other Ephemerid nymphs. This point and other details of
the anatomy of this creature have been described in detail by
Vayssière.[355] These nymphs have a very highly developed tracheal system;
they live in rapid watercourses attached to stones at a depth of three to
six inches or more under the water. Species of _Prosopistoma_ occur in
Europe, Madagascar, and West Africa.
[Illustration: FIG. 280.—_Prosopistoma punctifrons_, nymph. France. (After
Vayssière.) _o_, Orifice of exit from respiratory chamber.]
According to Eaton,[356] in the nymphs of some Ephemeridae the rectum
serves, to a certain extent, as a respiratory agent; he considers that
water is admitted to it and expelled after the manner we have described in
Odonata, p. 421.
[Illustration: FIG. 281.—A, Last three abdominal segments and bases of the
three caudal processes of _Cloëon dipterum_: _r_, dorsal vessel; _kl_,
ostia thereof; _k_, special terminal chamber of the dorsal vessel with its
entrance _a_; _b_, blood-vessel of the left caudal process; B, twenty-sixth
joint of the left caudal process from below; _b_, a portion of the
blood-vessel; _o_, orifice in the latter. (After Zimmermann.)]
The internal anatomy of the nymphs of Ephemeridae shows some points of
extreme interest. The long caudal setae are respiratory organs of a kind
that is almost if not quite without parallel in the other divisions of
Insecta. The dorsal vessel for the circulation of the blood is elongate,
and its chambers are arranged one to each segment of the body. It drives
the blood forwards in the usual manner, but the posterior chamber possesses
three blood-vessels, one of which is prolonged into each caudal seta. This
terminal chamber is so arranged as to drive the blood backwards into the
vessels of the setae; on the under surface of the vessels there are oval
orifices by which the blood escapes into the cavity of the seta so as to be
submitted to the action of the surrounding medium for some of the purposes
of respiration. This structure has been described by {436}Zimmermann,[357]
who agrees with Creutzberg[358] that the organ by which the blood is
propelled into the setae is a terminal chamber of the dorsal vessel;
Verlooren,[359] who first observed this accessory system of circulation,
thought the contractile chamber was quite separate from the heart. The
nature of the connexion between this terminal chamber that drives the blood
backwards and the other chambers that propel the fluid forwards appears
still to want elucidation.
[Illustration: FIG. 282.—A, Nymph of _Ephemerella ignita_ with gills of
left side removed; _g_, gills: B, nymph of _Tricorythus_ sp. with gill
cover of right side removed; _g.c_, gill cover; _g_, _g′_, gills. (After
Vayssière.)]
The nymphs of the Ephemeridae being creatures adapted for existence in
water, the details of their transformation into creatures having an
entirely aerial existence cannot but be of much interest. In the nymphs the
tracheal system is well developed, but differs from that of air-breathing
Insects in the total absence of any spiracles. Palmén has investigated this
subject,[360] and finds that the main longitudinal tracheal trunks of the
body of the nymph are not connected with the skin of the body by tracheae,
but are attached thereto by ten pairs of slender strings extending between
the chitinous integument and the tracheal trunks. When the skin is shed
these strings—or rather a chitinous axis in each one—are drawn out of the
body, and bring with them the chitinous linings of the tracheae. Thus
notwithstanding the absence of spiracles, the body wall is at each moult
pierced by openings that extend to the tracheae. After the ordinary moults
these orifices close immediately, but at the change to the winged state
they remain open and form the spiracles. At the same time the tracheal
gills are {437}completely shed, and the creature is thus transformed from a
water-breather to an Insect breathing air as usual. In addition to this
change there are others of great importance, such as the development of the
great eyes and the complete atrophy of the mouth-parts. The precise manner
of these changes is not known; they occur, however, within the nymph skin.
The sudden emergence of the winged Insect from the nymph is one of the most
remarkable facts in the life-history of the may-fly; it has been observed
by Sir John Lubbock,[361] who describes it as almost instantaneous. The
nymph floats on the water, the skin of the back opens, and the winged
Insect flies out, upwards and away; "from the moment when the skin first
cracks not ten seconds are over before the Insect has flown away." The
creature that thus escapes has not, however, quite completed its
transformation. It is still enveloped in a skin that compresses and
embarrasses it; this it therefore rapidly gets rid of, and thus becomes the
imago, or final instar of the life-cycle. The instar in which the creature
exists winged and active, though covered with a skin, is called the
sub-imago. The parts of the body in the sub-imago are as a whole smaller
than they are in the imago, and the colour is more dingy; the
appendages—wings, legs, and caudal setae—are generally considerably shorter
than they are in the imago, but attain their full length during the process
of extraction. The creatures being, according to Riley, very impatient and
eager to take to the wing, the completion of the shedding of the skin of
the sub-imago is sometimes performed while the Insect is flying in the air.
[Illustration: FIG. 283.—Lingua of _Heptagenia longicauda_, × 16. _m_,
Central; _l_, lateral pieces. (After Vayssière.)]
The food of young Ephemeridae is apparently of a varied and mixed nature.
Eaton says[362] that though sometimes the stronger larvae devour the
weaker, yet the diet is even in these cases partly vegetable. The
alimentary canal frequently contains much mud; very small organisms, such
as diatoms and confervae, are thought to form a large part of the bill of
fare of Ephemerid nymphs. Although {438}the mouth is atrophied in the
imago, yet it is highly developed in the nymphs. This is especially notable
in the case of the lingua or hypopharynx (Fig. 283); indeed Vayssière[363]
seems to incline to the opinion that this part of the mouth may be looked
on in these Insects as a pair of appendages of a head-segment (see p. 96
_ante_), like the labium or maxillae.
The life-history has not been fully ascertained in the case of any species
of may-fly; it is known, however, that the development of the nymph
sometimes occupies a considerable period, and it is thought that in the
case of some species this extends to as much as three years. It is rare to
find the post-embryonic development of an Insect occupying so long a
period, so that we are justified in saying that brief as may be the life of
the may-fly itself, the period of preparation for it is longer than usual.
Réaumur says, speaking of the winged fly, that its life is so short that
some species never see the sun. Their emergence from the nymph-skin taking
place at sunset, the duties of the generation have been, so far as these
individuals are concerned, completed before the morning, and they die
before sunrise. He thinks, indeed, that individuals living thus long are to
be looked on as Methuselahs among their fellows, most of whom, he says,
live only an hour or half an hour.[364] It is by no means clear to which
species these remarks of Réaumur refer; they are doubtless correct in
certain cases, but in others the life of the adult is not so very short,
and in some species may, in all probability, extend over three or four
days; indeed, if the weather undergo an unfavourable change so as to keep
them motionless, the life of the flies may be prolonged for a fortnight.
The life of the imago of the may-fly is as remarkable as it is brief; in
order to comprehend it we must refer to certain peculiarities of the
anatomy with which the vital phenomena are connected. The more important of
these are the large eyes of the males, the structure of the alimentary
canal, and that of the reproductive organs. We have already remarked that
the parts of the mouth in the imago are atrophied, yet the canal itself not
only exists but is even of greater capacity than usual; it appears to have
much the same general arrangement of parts as it had in the nymph. Its
coats are, however, of great tenuity, and according {439}to Palmén[365] the
divisions of the canal are separated by changes in the direction of certain
portions anterior to, and of others posterior to, its central and greater
part—the stomach—in such a manner that the portions with diverted positions
act as valves. The stomach, in fact, forms in the interior of the body a
delicate capacious sac; when movement tends to increase the capacity of the
body cavity then air enters into the stomachic sac by the mouth orifice,
but when muscular contractions result in pressure on the sac they close the
orifices of its extremities by the valve-like structures we have mentioned
above; the result is, that as complex movements of the body are made the
stomach becomes more and more distended by air. It was known even to the
old naturalists that the dancing may-fly is a sort of balloon, but they
were not acquainted with the exact mode of inflation. Palmén says that in
addition to the valve-like arrangements we have described, the entry to the
canal is controlled by a circular muscle, with which are connected
radiating muscles attached to the walls of the head. Palmén's views are
adopted, and to a certain extent confirmed, by Fritze,[366] who has
examined the alimentary canal of the may-fly, and considers that though the
normal parts of the canal exist, the function is changed in the imago, in
which the canal serves as a sort of balloon, and aids the function of the
reproductive organs. The change in the canal takes place in an anticipatory
manner during the nymph and sub-imago stages.
The sexual organs of Ephemeridae are remarkable for their simplicity; they
are destitute of the accessory glands and diverticula that, in some form or
other, are present in most other Insects. Still more remarkable is the fact
that the ducts by which they communicate with the exterior continue as a
pair to the extremity of the body, and do not, as in other Insects, unite
into a common duct. Thus in the female there is neither bursa copulatrix,
receptaculum seminis, nor uterine portion of oviduct, and there is no trace
of an ovipositor; the terminations of the ducts are placed at the hind
margin of the seventh ventral plate, just in front of which they are
connected by a fold of the integument. The ovary consists of a very large
number of small egg-tubes seated on one side of a sac, which forms their
calyx, and one of whose extremities is continued backwards as one of the
{440}pair of oviducts. The male has neither vesiculae seminales, accessory
glands, nor ductus ejaculatorius. The testes are elongate sacs, whose
extremities are prolonged backwards forming the vasa deferentia; these open
separately at the extremity of the body, each on a separate intromittent
projection of more or less complex character, the two organs being,
however, connected by means of the ninth ventral plate, of which they are,
according to Palmén, appendages. We should remark that this authority
considers _Heptagenia_ to form, to some extent, an exception as regards the
structures of the female; while _Polymitarcys_ is in the male sex strongly
aberrant, as the two vasa deferentia, instead of being approximately
straight, are bent inwards at right angles near their extremities so as to
meet, and form in the middle a common cavity, which then again becomes
double to pass into the pair of intromittent organs.
According to the views of Exner and others, the compound eyes of Insects
are chiefly organs for the perception of movement; if this view be correct,
movements such as those made during the dances of may-flies may, by the
number of the separate eyes, by their curved surfaces and innumerable
facets, be multiplied and correlated in a manner of which our own sense of
sight allows us to form no conception. We can see on a summer's evening how
beautifully and gracefully a crowd of may-flies dance, and we may well
believe that to the marvellous ocular organs of the flies themselves (Fig.
274) these movements form a veritable ballet. We have pointed out that by
this dancing the peculiarly formed alimentary canal becomes distended, and
may now add that Palmén and Fritze believe that the unique structure of the
reproductive organs is also correlated with the other anatomical
peculiarities, the contents of the sexual glands being driven along the
simple and direct ducts by the expansion of the balloon-like stomach.
During these dances the momentary conjugation of the sexes occurs, and
immediately thereafter the female, according to Eaton, resorts to the
waters appropriate for the deposition of her eggs. As regards this, Eaton
says:[367] "Some short-lived species discharge the contents of their
ovaries completely _en masse_, and the pair of fusiform or subcylindrical
egg-clusters laid upon the water rapidly disintegrate, so as to let the
eggs sink broadcast upon the river-bed. The less perishable species extrude
their eggs {441}gradually, part at a time, and deposit them in one or other
of the following manners: either the mother alights upon the water at
intervals to wash off the eggs that have issued from the mouths of the
oviducts during her flight, or else she creeps down into the water to lay
her eggs upon the under-side of stones, disposing them in rounded patches,
in a single layer evenly spread, and in mutual contiguity." The eggs are
very numerous, and it is thought may sometimes remain in the water as much
as six or seven months before they hatch.
The number of individuals produced by some kinds of may-flies is
remarkable. Swarms consisting of millions of individuals are occasionally
witnessed. D'Albertis observed _Palingenia papuana_ in countless myriads on
the Fly River in New Guinea: "For miles the surface of the river, from side
to side, was white with them as they hung over it on gauzy wings; at
certain moments, obeying some mysterious signal, they would rise in the
air, and then sink down anew like a fall of snow." He further states that
the two sexes were in very disproportionate numbers, and estimates that
there was but a single female to every five or six thousand males.
Ephemeridae in the perfect state are a favourite food of fishes, and it is
said that on some waters it is useless for the fly-fisher to try any other
lure when these flies are swarming. Most of the "duns" and "spinners" of
the angler are Ephemeridae; so are several of the "drakes," our large _E.
danica_ and _E. vulgata_ being known as the green drake and the gray drake.
Ronalds says[368] that the term "dun" refers to the pseud-imago condition,
"spinner" to the perfect Insect. _E. danica_ and _E. vulgata_ are perhaps
not distinguished by fishers; Eaton says that the former is abundant in
rapid, cool streams, while _E. vulgata_ prefers warmer and more tranquil
rivers.
These sensitive creatures are unable to resist the attractions of
artificial lights. Réaumur noticed this fact many years ago, and since the
introduction of the electric light, notes may frequently be seen in
journals recording that myriads of these Insects have been lured by it to
destruction. Their dances may frequently be observed to take place in
peculiar states of light and shade, in twilight, or where the sinking sun
has its light rendered broken by bushes or trees; possibly the broken
lights {442}are enhanced in effect by the ocular structures of the Insects.
It has recently been ascertained that a species of _Teleganodes_ is itself
luminous. Mr. Lewis,[369] who observed this Insect in Ceylon, states that
in life the whole of the abdomen was luminous, not brightly so, but
sufficient to serve as a guide for capturing the Insect on a dark night. It
has also been recorded that the male of _Caenis dimidiata_ gives a faint
blue light at night.
Nearly 300 species of Ephemeridae are known, but this may be only a
fragment of what actually exist, very little being known of may-flies of
other parts of the world than Europe and North America. One of the more
curious forms of the family is _Oniscigaster wakefieldi_; the body of the
imago is unusually rotund and furnished with lateral processes. In Britain
we have about forty species of may-fly. The family is treated as a distinct
Order by Brauer and Packard, and is called Plectoptera by the latter.
[Illustration: FIG. 284.—_Oniscigaster wakefieldi._ New Zealand. (After
M‘Lachlan.)]
That Insects so fragile, so highly organised, with a host of powerful
enemies, but themselves destitute of means of attack or defence, should
contrive to exist at all is remarkable; and it appears still more unlikely
that such delicate Insects as Ephemeridae should leave implanted in the
rocks their traces in such a manner that they can be recognised;
nevertheless, such is the case,—indeed, the may-fly palaeontological record
is both rich and remarkable. Several forms are preserved in amber. In the
Tertiary bed of the old lake at Florissant, Scudder has been able to
distinguish the remains of no less than six species; while in the Jurassic
layers of the Secondary epoch, in more than one locality, the remains of
several other species have been detected and described. Still more
remarkable is the fact that in the Devonian and Carboniferous layers of the
{443}Palaeozoic period, remains are found that appear to be akin to our
existing Ephemeridae. _Palingenia feistmantelii_ from the Carboniferous of
Bohemia is actually referred to a still existing genus; it is said to have
been of gigantic size for a may-fly.
The families Megasecopterides, Platypterides, and Stenodictyopterides of
the Carboniferous epoch (see p. 343) are all more or less closely allied to
the Ephemeridae, and in addition to these Brongniart has established the
family Protephemerides for some Insects that he considers to have been the
precursors in the Carboniferous epoch of our existing may-flies. These
ancient Insects differed in having the wings of another form from those of
existing Ephemeridae, and in having the hind wings equal in size to the
front pair. Besides this, these Insects had, as shown in Fig. 285,
prothoracic dorsal appendages; some had also projections from the abdominal
segments, considered by Brongniart to be of the nature of gills. Some doubt
must exist as to this point, for we find in the imago of one of our
existing Ephemeridae, _Oniscigaster wakefieldi_, Fig. 284, abdominal
processes that are not gills.
[Illustration: FIG. 285.—_Homaloneura bonnieri_; Carboniferous of
Commentry. (After Brongniart.)]
It is remarkable that may-flies, which now form a comparatively unimportant
part of the Insect tribe, should in far distant times have been represented
by so great a variety of allied forms. Our fragile, short-lived may-flies
appear to be, as Scudder says, the lingering fragments of an expiring
group.
{444}CHAPTER XX
NEUROPTERA PLANIPENNIA—SIALIDAE, ALDER-FLIES, SNAKE-FLIES—PANORPIDAE,
SCORPION-FLIES—HEMEROBIIDAE, ANT-LIONS, LACEWINGS, ETC.
FAM. VIII. SIALIDAE—ALDER-FLIES AND SNAKE-FLIES.
_Four wings of moderate size, meeting in repose over the back at an
angle; the hinder of the two pairs slightly the smaller; the anal area
small or nearly absent, not plicate. Nervures moderately numerous,
transverse veinlets moderately numerous, forming irregularly disposed
cells. The metamorphosis is great; there is a quiescent pupa. The larva
has the mandibles formed for biting, armed with strong teeth._
The Sialidae, though but a small family of only some six or eight genera,
comprise a considerable variety of forms and two sub-families—Sialides and
Raphidiides. The former group has larvae with aquatic habits possessed of
branchiae but no spiracles.
[Illustration: FIG. 286.—The alder-fly, _Sialis lutaria_. Britain. A, With
wings expanded; B, in profile.]
_Sialis lutaria_ is one of the commoner British Insects frequenting the
vegetation about the banks of tranquil streams; it is well known to
anglers, being used by them for a bait. According to Ronalds it is called
the alder or orl-fly, and in Wales the humpback.
{445}[Illustration: FIG. 287.—Portion of a row of eggs of _Sialis lutaria_.
(After Evans.)]
[Illustration: FIG. 288.—_Sialis lutaria_, larva.]
It is very unattractive in appearance, being of a blackish colour, with
wings of a yellow-brown tinge, and makes but a poor show when flying. The
female deposits patches of elongate eggs, placed on end and packed together
in a very clever manner (Fig. 287). These patches of eggs, of a stone-gray
colour, are common objects on rushes or stems of grass near water, and it
is stated that there may be no less than 2000 or 3000 eggs in one of them.
Our figure gives some idea of the mode in which the eggs are arranged, and
the curious narrow process that exists at the end of each. The eggs are
said to be sometimes placed at a considerable distance from water, so that
when the tiny larvae are hatched they must begin their lives by finding the
way to a suitable pool or stream. The larvae (Fig. 288) are objects of very
great interest owing to each of segments 1 to 7 of the hind body being
furnished on each side with a jointed filament, while the last segment ends
in a still longer, but unjointed process. These filaments are branchiae by
means of which the Insect obtains air, being, as we have said, destitute of
spiracles. It is an active creature and waves its filaments in a very
graceful manner; this process no doubt aids the branchiae in their
respiratory work. These larvae are well able to exist out of water if they
have a sufficiently damp environment. They live on animal matter, but their
life-history has not been followed in much detail and it is not known
{446}how many moults they make. The young larva has the head
disproportionately large and the branchial filaments longer. When the
growth is completed the larva returns to land, seeks a suitable situation
in the soil, and after an interval changes to a pupa, in which the
characters of the perfect Insect are plainly visible. Subsequently, without
becoming again active, it changes to the perfect Insect, and enjoys, for a
few days only, an aerial life.
The anatomy of the larva has been treated by Dufour.[370] The
supra-oesophageal ganglion is remarkably small; nothing is said as to the
existence of an infra-oesophageal ganglion; there are three thoracic and
eight abdominal ganglia; the first pair of these latter are nearer together
than the others, and this is also the case with the last three. The
alimentary canal in the adult is provided with a large paunch attached to
the crop by a narrow neck,[371] but Dufour could find no trace of this in
the larva. The structure of the branchiae has also been described by the
indefatigable French entomotomist. A tracheal tube sends a branch into one
of the appendages (Fig. 289); the branch gives off numerous smaller
tracheae, which at their extremities break up into branchlets close to the
integument. The tracheal tube that receives each main branchial trachea,
sends off from near the point of entry of the latter another trachea, that
distributes its branchlets on the alimentary canal. The margins of each
appendage are set with swimming hairs, so that the branchiae act as organs
of locomotion as well as of respiration, and by their activity in the
former capacity increase the efficiency of their primary function.
[Illustration: FIG. 289.—Structure of tracheal gill of _Sialis lutaria_.
(After Dufour.) _a_, Base of the gill; _b_, tracheal trunk with which it is
connected; _c_, trachea given off to alimentary canal.]
The genus _Sialis_ occurs in a few species only, throughout the {447}whole
of the Palaearctic and Nearctic regions, and reappears in Chili,[372]
though absent in all the intervening area. Several other genera of Insects
exhibit the same peculiarity of distribution.
[Illustration: FIG. 290.—_Corydalis crassicornis_, male, with greater
portions of the wings removed. Texas. (After M‘Lachlan.)]
[Illustration: FIG. 291.—_Raphidia notata_, female. Britain. (After
Curtis.)]
The genera _Corydalis_ and _Chauliodes_ form a group distinct from
_Sialis_, and are totally different in appearance, being gigantic Insects,
sometimes with the mandibles of the male enormously elongated (Fig. 290).
The species of _Corydalis_ are called in North America Hellgrammites;
Riley has described and figured the metamorphosis of _C. cornutus_,[373]
the life-history being very similar to that of our little _Sialis_. A mass
consisting of two or three thousand eggs is formed by the female, and the
young larva has long filaments at the sides of the body like _Sialis_.
These in the later larval life are comparatively shorter, but the Insect is
then provided with another set of gills in the form of spongy masses on the
under-side of the body. Riley, however, considers that these organs serve
the purpose of attachment rather than of respiration. The larvae are known
to the Mississippi fishermen as crawlers, and are greatly esteemed as bait.
The Raphidiides or snake-flies form the second tribe of Sialidae. There are
only two genera, _Raphidia_ and _Inocellia_, peculiar to the Palaearctic
and Nearctic regions. The perfect Insects are chiefly remarkable for the
elongation of the prothorax and back of the head to form a long neck, and
for the existence in the female of an elongate exserted ovipositor.
{448}The species are rather numerous, and have been recently monographed by
Albarda.[374] The three or four British species of the genus are all rare
Insects, and occur only in wooded regions.
The Raphidiides, like the Sialides, have a carnivorous larva, which,
however, is terrestrial in habits, feeding, it would appear, chiefly on
Insects that harbour in old timber. The snake-fly larvae (Fig. 292) are
very ingenious in their manner of escaping, which is done by an extremely
rapid wriggling backwards. They are capable of undergoing very prolonged
fasts, and then alter in form a good deal, becoming shorter and more
shrivelled; Fig. 292 is taken from a specimen that had been fasting for
several weeks. They are excessively voracious, and hunt after the fashion
of beasts of prey; their habits have been described by Stein,[375] who
states that he kept a larva from August to the end of May of the following
year without food; it then died in a shrivelled-up state. The larva of the
snake-fly changes to a pupa that is remarkably intermediate in form between
the perfect Insect and the larva; the eyes, legs, wing-pads, and ovipositor
being but little different from those of the imago, while the general form
is that of the larva, and the peculiar elongation of the neck of the imago
is absent. This pupa differs from that of _Sialis_ in the important
particular that before undergoing its final ecdysis it regains its activity
and is able to run about.
[Illustration: FIG. 292.—_Raphidia notata_, larva. New Forest.]
The internal anatomy of _Raphidia_ has been treated by Loew,[376] and is of
a very remarkable character; we can here only mention that the salivary
glands consist of a pair of extremely elongate tubes, that there is a very
definite paunch attached as an appendage to one side of the crop, and that
the most peculiar character consists of the fact that, according to Loew,
four of the six Malpighian tubes have not a free extremity, being attached
{449}at each end so as to form elongate loops; the mesenteron is very
complex in character.
A considerable number of fossil remains from both Tertiary and Mesozoic
strata are referred to Sialidae; and a larval form from the red sandstone
of Connecticut has been considered by Scudder to be a Sialid, and named
_Mormolucoides articulatus_, but the correctness of this determination is
very doubtful (Fig. 293). These fossils are, however, of special interest
as being the most ancient Insect larvae yet brought to light. A still older
fossil, from the Carboniferous strata of Illinois called _Miamia bronsoni_,
is considered by Scudder to have several points of resemblance to Sialidae.
[Illustration: FIG. 293.—_Mormolucoides articulatus_, larva. Trias of
Connecticut. (After Scudder.)]
FAM. IX. PANORPIDAE—SCORPION-FLIES.
_Head prolonged to form a deflexed beak, provided with palpi near its apex;
wings elongate and narrow, shining and destitute of hair, with numerous,
slightly divergent veins and moderately numerous transverse veinlets (in
one genus the wings are absent). Larvae provided with legs, and usually
with numerous prolegs like the saw-flies: habits carnivorous._
[Illustration: Fig. 294.—_Panorpa communis_, male. Cambridge.]
The majority of the members of this family are very readily distinguished
by the beak-like front of the head, this being chiefly due to enlargement
of parts of the head itself, and in a less degree to prolongation of the
mouth-parts. The upper (or front) face of the beak is formed entirely by
the clypeus, the labrum being scarcely {450}visible, though it may be
detected at the sides of the tip of the beak; the sutures between the
various parts of the head are nearly or quite obliterated, but it is
probable that the sides of the beak are formed by the genae and by the
stipites of the maxillae, and its under-surface chiefly by the submentum:
the mentum itself is but small, the ligula is small, bifid at the
extremity, and each branch bears a two-jointed palpus, the basal article
being of very peculiar structure in _Panorpa_. The mandibles are but small,
and are placed at the apex of the beak; they have each the form of an
oblong plate armed with two very sharp teeth, and they cross freely. The
maxillae are the only parts of the mouth-pieces that are very elongated;
each cardo is articulated at the base of the head, and the stipes extends
all the length of the side of the beak; each maxilla bears a five-jointed
palpus and two small but very densely ciliated lobes. The antennae are
long, very slender, and flexible, and are many-jointed; they are inserted
between the eyes in large foramina; there are three ocelli, or none, and
the compound eyes are moderately large. The prothorax is small, its notum
is quite small or moderate in size, and the prothoracic stigma is placed
behind it; the side-pieces are small, and there is no chitinous prosternum
except a small longitudinal strip placed in the membrane between the coxae;
these latter are of only moderate size, and are free and dependent. The
meso- and meta-thorax are large, their side-pieces are of considerable
dimensions and bear large, dependent coxae and supporting-pieces (Fig. 58);
there is a stigma placed between the meso- and meta-thorax at the hind
margin of the upper part of the meso-trochantin; both meso- and meta-notum
are transversely divided. The abdomen is elongate, slender,
conico-cylindrical, consisting of nine segments; the basal segment is
membranous and concealed; the terminal appendages are of variable nature
according to the species and sex. The legs are elongate and slender, the
tarsi five-jointed. The internal anatomy of _Panorpa communis_ has been
examined by Dufour[377] and Loew.[378] They agree in describing the
alimentary canal as being of peculiar structure: there is a short, slender
oesophagus leading to an organ in which there is seated a remarkable
arrangement of elongate hairs; this structure might be looked on as the
proventriculus, but Loew considers it to be rather a {451}division of the
true stomach. The particulars given by these two anatomists as to some
other parts of the internal anatomy are very discrepant.
The Panorpidae form a small family of only nine or ten genera, two or three
of these being exotic and only imperfectly known; the three genera found in
Europe are composed of very curious Insects. The scorpion-flies—_Panorpa_
proper—are very common Insects, and have received their vernacular name
from the fact that the males have the terminal segments elongate and
slender and very mobile, and carry them curved up somewhat after the
fashion of the scorpions (Fig. 294). It is said that Aristotle was
acquainted with these Insects, and considered them to be really winged
scorpions.
A second European genus, _Boreus_, is still more peculiar; it is destitute
of wings, and has the appearance of a minute wingless grasshopper; it is
found from late autumn to early spring in moss and under stones, and is
said to be sometimes found disporting itself on the surface of the snow:
the female of this Insect has an exserted ovipositor. The writer has found
this little creature in Scotland among moss in November, and under stones
early in March (Fig. 295). The third European genus, _Bittacus_, does not
occur in our islands, but is common on many parts of the Continent; the
perfect Insect has a great resemblance to a _Tipula_, or "daddy-long-legs"
fly, and attaches itself to the stems of grasses, and preys on flies;
according to Brauer it has the peculiar habit of using the hind pair of
legs as hands (Fig. 296), instead of the front pair, as is usual in
Insects. This remarkable genus is widely distributed, and species of it are
found even in the Antipodes. A species inhabiting caves has been mentioned
by M‘Lachlan.[379]
[Illustration: FIG. 295.—_Boreus hiemalis_, female. Dumfriesshire.]
The early stages of the Panorpidae were for long unknown, but have recently
been discovered by Brauer: he obtained eggs of _Panorpa_ by confining a
number of the perfect flies in a vessel containing some damp earth on which
was placed a piece of meat; when the young larvae were hatched they buried
themselves in the earth and nourished themselves with the meat or its
juices.
{452}[Illustration: FIG. 296.—_Bittacus tipularius_ holding a fly in its
hind legs. Austria. (After Brauer.)]
[Illustration: FIG. 297.—Young larva of _Panorpa communis_. (After
Brauer.)]
These larvae (Fig. 297) bear a great resemblance to those of the
Hymenopterous family Tenthredinidae; they have biting mandibles and
palp-bearing maxillae, and show no approach to the peculiar mouth structure
found in the Hemerobiidae; there are three pairs of feet placed on the
three thoracic segments, and there is also a pair of less perfect feet on
each of the first eight abdominal segments, those behind being the larger.
The upper surface of the body bears spines, which, however, disappear after
the first change of skin, with the exception of the larger processes on the
posterior segment, which persist throughout the life of the larva. The
larvae are active for about one month; after this they become quiescent,
but do not change to the pupa state for several weeks; when this happens
they change in form and cannot creep, although their limbs are not enclosed
in any pupa case. Brauer also discovered larvae of _Panorpa communis_ at
large in numbers in an old tree stump that was quite covered with moss, and
contained many ants in the mouldering wood. The ants appeared to be on
friendly terms with the _Panorpa_ larvae. The earlier stages of
{453}_Boreus_ and _Bittacus_ were also observed by Brauer; they are
essentially similar to those of _Panorpa_, but the larva in _Boreus_ is not
provided with abdominal prolegs. The Panorpidae have been separated from
the other Neuroptera by certain naturalists as a distinct Order, called
Panorpatae by Brauer, Mecaptera by Packard; but in their structure as well
as in their metamorphoses they are not so distinct from the Phryganeidae
and the Hemerobiidae as to justify this step.
Fossil forms of _Bittacus_ and of _Panorpa_ have been found in amber and in
the Tertiary strata, and Scudder has described some forms from Florissant
in which there are no cross-veinlets in the wings. Some remains from the
English Lias have been referred to Panorpidae by Westwood under the name
_Orthophlebia_, but it is by no means certain that they really belong to
the family.
FAM. X. HEMEROBIIDAE—ANT-LIONS, LACEWING-FLIES, ETC.
_Head vertical; maxillae free, with five-jointed palpi; labial palpi
three-jointed. Wings subequal in size, with much reticulation, without
anal area. Tarsi five-jointed. Metamorphosis great; the larvae with
mandibles and maxillae coadapted to form spear-like organs that are
suctorial in function. Pupa, similar in general form to the imago,
enclosed in a cocoon._
[Illustration: FIG. 298.—_Drepanepteryx phalaenoides._ Scotland.]
The Hemerobiidae are an extremely varied assemblage of Neuroptera; the
perfect Insects of the various sub-families are very different in
appearance, but the family as a whole is naturally defined by the very
peculiar structure of the mouth-organs of the larvae. These Insects have,
in fact, a suctorial {454}mouth in their early life, and one of the
ordinary biting type in adult life.
This is a very unusual condition, being the reverse of what we find in
Lepidoptera and some other of the large Orders, where the mouth is
mandibulate in the young and suctorial in the adult. The suctorial
condition is in Hemerobiidae chiefly due to modification of the mandibles;
but this is never the case in the Insects that have a suctorial mouth in
the imaginal instar. Nearly all the Hemerobiidae are terrestrial Insects in
all their stages; a small number of them are, to a certain extent,
amphibious in the larval life, while one or two genera possess truly
aquatic larvae. The metamorphosis is, so far as the changes of external
form are concerned, quite complete. There are no wingless forms in the
adult stage.
The classification given by Hagen[380] and generally adopted recognises
seven sub-families. These we shall mention seriatim.
SUB-FAM. 1. MYRMELEONIDES OR ANT-LIONS.—_Antennae short, clubbed, the
apical space of the wing with regular, oblong cellules._
[Illustration: FIG. 299.—_Tomateres citrinus._ S. E. Africa. (After
Hagen.)]
The ant-lions in their perfect state are usually unattractive Insects, and
many are nocturnal in their habits; the species of the genus _Palpares_ and
allies (Fig. 299) are, however, of more handsome appearance, and attain a
large expanse of wing. No member of the sub-family is an inhabitant of
Britain, though species of the typical genus _Myrmeleon_ are common in
Central and Northern Europe. The {455}remarkable habits of their larvae
attracted the attention of naturalists so long ago as two hundred years. We
owe to Réaumur an accurate and interesting account of _M. formicarius_, the
species found in the neighbourhood of Paris. The larvae are predaceous, and
secure their prey by means of pitfalls they excavate in the earth, and at
the bottom of which they bury themselves, leaving only their elongate jaws
projecting out of the sand at the bottom of the pit. They move only
backwards, and in forming their pit use their broad body as a plough, and
throw out the sand by placing it on the head and then sending it to a
distance with a sudden jerk. When about to construct its trap the larva
does not commence at the centre, but makes first a circular groove of the
full circumference of the future pit. Burying its abdomen in the surface of
the earth, the Insect collects on to its head, by means of the front leg,
the sand from the side which is nearest to the centre, and then jerks the
sand to a distance. By making a second circuit within the first one, and
then another, the soil is gradually removed, and a conical pit is formed,
at the bottom of which the ant-lion lurks, burying its body but leaving its
formidable mandibles widely extended and projecting from the sand. In this
position the young ant-lion waits patiently till some wandering Insect
trespasses on its domains. An ant or fly coming over the edge of the
pitfall finds the sand of the sloping sides yielding beneath its body, and
in its effort to secure itself probably dislodges some more of the sand,
which, descending to the bottom of the pit, brings the lurking lion into
activity. Availing himself of his power of throwing sand with his head, the
ant-lion jerks some in the neighbourhood of the trespasser, and continues
to do so until the victim is brought to the bottom of the pit and into the
very jaws of its destroyer; then there is no further hope of escape; the
mandibles close, empale their prey, and do not relax their hold till the
body of the victim is exhausted of its juices. The position chosen is in a
place that will keep dry, as the larva cannot carry on its operations when
the sand is wet or damp, hence the soil at the base of a high wall or a
rock frequently harbours these Insects.
{456}[Illustration: FIG. 300.—Larva of _Myrmeleon pallidipennis_. (After
Meinert.)]
The parts of the mouth of the _Myrmeleon_ are perfectly adapted for
enabling it to empty the victim without for a moment relaxing its hold.
There is no mouth-orifice of the usual character, and the contents of the
victim are brought into the buccal cavity by means of a groove extending
along the under side of each mandible; in this groove the elongate and
slender lobe that replaces the maxilla—there being no maxillary palpi—plays
backwards and forwards, probably raking or dragging backwards to the buccal
cavity at each movement a small quantity of the contents of the empaled
victim. The small lower lip is peculiar, consisting in greater part of the
two lobes that support the labial palpi. The pharynx is provided with a
complex set of muscles, and, together with the buccal cavity, functions as
an instrument of suction. After the prey has been sucked dry the carcass is
jerked away to a distance. When the ant-lion larva is full grown it forms a
globular cocoon by fastening together grains of sand with fine silk from a
slender spinneret placed at the posterior extremity of the body; in this
cocoon it changes to an imago of very elongate form, and does not emerge
until its metamorphosis is quite completed, the skin of the pupa being,
when the Insect emerges, left behind in the cocoon. The names by which the
European ant-lion has been known are very numerous. It was called Formicajo
and Formicario by Vallisneri about two hundred years ago; Réaumur called it
Formica-leo, and this was adopted by some modern authors as a generic name
for some other of the ant-lions. The French people call these Insects
Fourmilions, of which ant-lion is our English equivalent. The Latinised
form of the term ant-lion, Formicaleo, is not now applied to the common
ant-lion as a generic term, it having been proposed to replace it by
_Myrmecoleon_, _Myrmeleo_, or _Myrmeleon_; this latter name at present
seems likely to become generally adopted. There are several species of the
genus found in Europe, and their trivial names have been confounded by
various authors in such a way as to make it quite uncertain, without
reference to a synonymic list, what species is intended by any particular
writer. The species found in the neighbourhood of Paris, and to which it
may be presumed Réaumur's history refers, is now called {457}_Myrmeleon
formicarium_ by Hagen and others; M‘Lachlan renamed it _M. europaeus_, but
now considers it to be the _M. nostras_ of Fourcroy. The popular name
appears to be due to the fact that ants—Formica in Latin, Fourmi in
French—form a large part of the victims; while lion—the other part of the
name—is doubtless due to its prowess as a destroyer of animal life, though,
as Réaumur long ago remarked, it is a mistake to apply the term lion to an
Insect that captures its prey by strategy and by snares rather than by
rapidity and strength. The imago of _Myrmeleon_ is of shy disposition, and
is rarely seen even in localities where the larva is abundant. It is of
nocturnal habits, and is considered by Dufour to be carnivorous.
Considerable difference of opinion has existed as to the structure of the
mouth and of the alimentary canal in these larvae. Réaumur was of opinion
that there exists no posterior orifice to the alimentary canal, but Dufour
ridiculed this idea, and stated positively that such an orifice undoubtedly
exists. It is also usually said that the mouth is closed by a membrane.
Meinert has recently examined these points,[381] and he states that the
mouth is not closed by any membrane, but is merely compressed. He finds
that there is no posterior exit from the stomach; that there is a compact
mass without any cavity between the stomach and the point where the
Malpighian tubes connect with the small intestine. The portions of aliment
that are not assimilated by the larva collect in the stomach and are
expelled as a mass, but only after the Insect has become an imago. This
peculiar excrementitious mass consists externally of uric acid, and from
its form and appearance has been mistaken for an egg by several
naturalists. The posterior portions of the alimentary canal are, according
to Meinert, of a remarkable nature. The small intestine is elongate,
slender, and is coiled. There are eight very long and slender Malpighian
tubes; a pair of these have free extremities, but the other six in the
posterior part of their course are surrounded by a common membrane, and,
following the course of the intestine, form ultimately a dilated body
seated on a coecum. These six Malpighian tubes are considered to be
partially, if not entirely, organs for the secretion of silk for forming
the cocoon, the coecum being a reservoir. The canal terminates as a slender
tube, which acts as a spinneret and is surrounded by a sheath. A complex
set of muscles {458}completes this remarkable spinning apparatus. The
alimentary canal of the imago has been described and figured by
Dufour[382]; it is very different from that of the larva.
The ant-lion is capable of sustaining prolonged fasts. Dufour kept
specimens for six months without any food. These Insects are said to give
off a peculiar ant-like odour, due, it is thought, to their ant-eating
habits. Although no species inhabits Great Britain, yet one is found in
Southern Sweden. Introduced specimens get on very well in confinement in
our country,[383] and would probably flourish at large for some years if
they were liberated.
Although the number of known species and genera of Myrmeleonides is
considerable—that of the species being now upwards of 300—the members of
the small genus _Myrmeleon_ are the only forms that are known to make pits
of the kind we have described. Other larvae[384] are known similar in
general form to the common ant-lion, but they walk forwards in the normal
manner, and apparently hunt their prey by lurking in a hidden place and,
when a chance occurs, rushing on the victim with rapidity. Brauer has
observed this habit in the case of _Dendroleon pantherinus_ in the Prater
at Vienna.
[Illustration: FIG. 301.—Upper aspect of head and alimentary canal of
_Myrmeleon_: _a_, crop; _b_, stomach; _c_, free extremities of two
Malpighian tubes; _c′_, terminal common portion of other six tubes; _d_,
coecum; _e_, spinneret; _f_, _f_, muscles for protruding its sheath; _g_,
_g_, maxillary glands. (After Meinert.)]
The most remarkable forms of Myrmeleonides are contained in the genus
_Palpares_. We figure _Tomateres citrinus_ (Fig. 299), an allied genus
found in Eastern Africa as far south as Natal. These Insects have
conspicuous blotches and marks on their wings. The species of _Myrmeleon_
are similar in form, but are smaller, more feeble, and less ornate in
appearance.
{459}Pitfalls, formed in all probability by ant-lions, have been noticed in
the Galapagos islands and in Patagonia, though none of the Insects forming
them have been found.
SUB-FAM. 2. ASCALAPHIDES.—_Antennae elongate, with a knob at the tip; the
apical area of the wing with irregular cellules._
[Illustration: FIG. 302.—_Ascalaphus coccajus._ East Pyrenees.]
The sub-family Ascalaphides is not represented by any species in Britain,
though _Ascalaphus longicornis_ occurs as far north as Paris. In the
mountainous regions of Central and Southern Europe some species of the
group form a conspicuous part of the Insect fauna, owing to their bold and
active flight; they are predaceous in their habits, and fly about in a
hawking fashion somewhat like that of dragon-flies. Some of the larger of
the numerous exotic species of the group are very like dragon-flies, but
can be distinguished by a glance at the elongate antennae with a knob at
the end. The sub-family consists of two groups—Holophthalmi and
Schizophthalmi. M‘Lachlan says[385]: "The eyes in the Schizophthalmous
division are really double, the upper portion overlapping the under; if the
upper portion be separated the lower division looks like a small spherical
ordinary eye." There appears, however, to be considerable differences in
the genera in this respect.
{460}[Illustration: FIG. 303.—A, Eggs of _Ascalaphus macaronius_. B, Sketch
of position of the young larvae of _Helicomitus insimulans_ (?); C, outline
of natural size. (After Westwood.)]
When the weather is wet or cold the Ascalaphi repose on the stems of grass,
with their wings placed in a roof-like manner, with the head downwards, and
are then very successful in concealing themselves by the positions they
assume, and by sidling round the stems to escape from enemies. Some
information as to their metamorphosis has been obtained, though knowledge
of this point is far from complete even as regards our European species of
the typical genus _Ascalaphus_. For a long time it was supposed that a
larva mentioned by Bonnet in his writings was that of _Ascalaphus_, but
Brauer[386] is of opinion that such is not the case, and as he has
described the metamorphoses of _A. macaronius_ he is no doubt correct. The
eggs (Fig. 303, A), forty or fifty in number, are laid in two parallel rows
on the stems of grass. The larvae (Fig. 304, larva of _Helicomitus_ ?) are
in general appearance somewhat like those of _Myrmeleon_; they are
carnivorous in their habits, like the ant-lions, and have similar
extraordinarily developed mandibles. Efforts to rear the young larvae
failed, but they were kept alive for some time by supplying them with
Aphidides found on _Centaurea jacea_. The cocoon is globular, and the
change from the nymph state to the imago is made in the cocoon, the
structure of the mandibles of the pupa being peculiar, and specially
adapted to the purpose of opening the cocoon.[387] The larvae of
Ascalaphides, although so like the ant-lions in appearance, do not form
pitfalls for the capture of their prey, but lurk under leaves on the
ground, or under stones; they do not move backwards, but progress forwards
in an ordinary manner; the habit of backward movement that we noticed in
_Myrmeleon_ being probably correlative with the habit of forming pitfalls.
Hagen states[388] that the larvae of Ascalaphides and Myrmeleonides, in
addition to their peculiarities of form and mandibular structure, are
distinguished from those of other Hemerobiidae by the hind legs having the
tibia and tarsus united {461}without articulation. Westwood[389] has
recently given an account of the young larvae of a Ceylonese Ascalaphid of
doubtful species, but possibly _Helicomitus insimulans_; these were
observed by Mr. Staniforth Green to have the very peculiar habit of sitting
together in a long row on the stem of a plant, with the jaws widely
extended and the body of each one covered by the head of the individual
next it (Fig. 303, B). The little creatures waited patiently in this
position until a fly walked between the mandibles of one of them, then
these formidable weapons immediately closed, and did not relax their hold
until the fly was sucked dry. If Westwood is correct, the young larva of
this species differs much from the adult one, the back of the head being
broad and the setigerous processes of the body very much more developed.
Nearly thirty genera of Ascalaphides are known.[390] In the genus
_Haplogenius_ we find an exception to the usual rule that the wings in
repose are held in a roof-like manner, it having been noticed by Bates that
in the species in question the wings are held expanded as in the
dragon-flies.
[Illustration: FIG. 304.—Larva of _Helicomitus insimulans_ (?). (After
Westwood.)]
Guilding has described[391] a very peculiar mode of oviposition on the part
of _Ulula macleayana_ in the island of St. Vincent; the eggs are said to be
deposited by the female in circles on the extremity of a twig, and nearer
the base of this there is placed a kind of barrier to repel intruders. "The
female may be seen expelling from her ovary these natural barriers with as
much care as her real eggs." Guilding's description was accompanied by
drawings of the eggs, barriers and larvae, but unfortunately these were
never published, and no further information has been obtained on the
subject. Hagen[392] suggests that the barriers may {462}be somewhat similar
to the long stalks on which the eggs of _Chrysopa_ (Fig. 314) are placed.
SUB-FAM. 3. NEMOPTERIDES.—_Head more or less produced and beak-like. Hind
wings of peculiar form, being elongate and somewhat strap-like._
[Illustration: FIG. 305.—_Nemoptera ledereri._ Asia Minor. (After Selys.)
A, The imago; B, its head seen from in front and magnified.]
[Illustration: FIG. 306.—Presumed larva of _Nemoptera_ (_Necrophilus
arenarius_). After Roux. Pyramids of Egypt.]
The Nemopterides are a small group of delicate, graceful Insects. About
thirty species are known. Knowledge of the group is still very imperfect. A
larva has been found of a most remarkable nature that probably belongs to
it; it was described under the name of _Necrophilus arenarius_, and
considered to be a fully-developed Insect. This larva occurs in the tombs
and pyramids of Egypt where sand has accumulated. The perfect Insects of
the genus _Nemoptera_ are, however, found in open places amongst bushes,
and flit about in a very graceful manner. Several species are found in
Southern Europe and the Mediterranean region {463}(Fig. 305, _N.
ledereri_), but none come so far north as Central Europe. Formerly the
genus _Nemoptera_ was considered to be allied to _Panorpa_ on account of
the beak-like front of the head. The parts of the mouth are, however,
different from those of _Panorpa_, and it seems more probable that if the
Nemopterides have to be merged in any of the divisions of Hemerobiidae,
they will be placed in Chrysopides or Osmylides. The species of the
sub-family were for a long time believed to be peculiar to the continental
regions of the Old World, but a species has recently been discovered in
Northern Chili.[393]
SUB-FAM. 4. MANTISPIDES.—_Prothorax elongate; the raptorial front legs
inserted at its anterior part._
The members of this small group are readily recognised by the peculiar
structure of the front legs; these organs resembling those of the
Orthopterous family Mantidae, so that the earlier systematic entomologists,
deceived by this resemblance, placed the Mantispides in the Order referred
to.
[Illustration: FIG. 307.—_Mantispa areolaris._ Brazil. (After Westwood.)]
The Mantispides possess four membranous wings, either sub-equal in size or
the posterior pair smaller than the front pair and not folded; the veins of
these wings are rather numerous, as are also the cells they form; there is
considerable difference amongst the species in this latter respect, owing
to the transverse veinlets differing in their abundance. The antennae are
short, not in the least thickened at the tip. The head is not produced into
a beak. The anterior legs, placed quite at the front part of the thorax,
have the coxae very long; the femur is somewhat incrassate, and is armed on
one side with spines; the tibia is shaped and articulated so as to fold
closely on to the spines, and to thus constitute a formidable and perfect
prehensile organ, the tarsus being merely a small appendage.
{464}[Illustration: FIG. 308.—_Mantispa styriaca._ A, Larva newly hatched,
or first form; B, mature larva. (After Brauer.)]
Only a few species of _Mantispa_ are found in Southern Europe; but the
group has representatives in most of the warmer regions of the world, and
will probably prove to be rather numerous in species. The front legs are
used for the capture of prey in the same way as the somewhat similar front
legs of the Mantidae. The transformations have been observed by Brauer[394]
in the case of one of the European species, _M. styriaca_. The eggs are
numerous but very small, and are deposited in such a manner that each is
borne by a long slender stalk, as in the lacewing flies. The larvae are
hatched in autumn; they then hibernate and go for about seven months before
they take any food. In the spring, when the spiders of the genus _Lycosa_
have formed their bags of eggs, the minute _Mantispa_ larvae (Fig. 308, A)
find them out, tear a hole in the bag, and enter among the eggs; here they
wait until the eggs have attained a fitting stage of development before
they commence to feed. Brauer found that they ate the spiders when these
were quite young, and then changed their skin for the second time, the
first moult having taken place when they were hatched from the egg. At this
second moult the larva undergoes a considerable change of form; it becomes
unfit for locomotion, and the head loses the comparatively large size and
high development it previously possessed. The _Mantispa_ larva—only one of
which flourishes in one egg-bag of a spider—undergoes this change in the
midst of a mass of dead young spiders it has gathered together in a
peculiar manner. It undergoes no further change of skin, and is full fed in
a few days; after which it spins a cocoon in the interior of the egg-bag of
the spider, and changes to a nymph inside its larva-skin. {465}Finally the
nymph breaks through the barriers—larva-skin, cocoon, and egg-bag of the
spider—by which it is enclosed, and after creeping about for a little,
appears in its final form as a perfect _Mantispa_. Thus in this Insect
hypermetamorphosis occurs; the larval life consisting of two different
instars, one of which is specially adapted for obtaining access to the
creature it is to prey on. It should be noticed that though this Insect is
so destructive to the young spiders, the mother spider shows no hostility
to it, but allows the destroying larva to enter her bag of eggs without any
opposition; she appears, indeed, to be so unconscious of the havoc that is
going on amongst her young that in one case she continued to watch over and
protect the egg-bag in which the destruction was taking place during the
whole of the period of the larval development and half the period of
pupation of the _Mantispa_.
The larval history of a second species of the Mantispides, _Symphrasis
varia_, is partially known;[395] this Insect lives parasitically in the
nests of a South American wasp, and each larva when full fed spins a cocoon
in one of the cells of the Hymenopteron.
SUB-FAM. 5. HEMEROBIIDES.—_Wings in repose forming an angular roof over
the body; the antennae moniliform or pectinate, not clavate._
The Hemerobiides consist of several minor groups about whose number and
characters systematists are not very well agreed, and about some of which
very little is known. We merely mention the latter, giving details as to
some of the better known only.
1. The Dilarina are a small group found chiefly in the Old World, where,
however, they have a wide distribution. North and South America have each
one species. They are distinguished by their antennae, which, in the male,
are pectinate somewhat like those of many Lepidoptera, this character being
of extremely rare occurrence in the Neuroptera; the abdomen of the female
terminates in a long ovipositor. The metamorphoses are not known.
2. Nymphidina: Australian Insects resembling Myrmeleonides, but having
antennae without club. Metamorphoses not known.
{466}3. Osmylina: a group of delicate and elegant Insects of small or
moderate size, distinguished by the possession of three simple eyes placed
on the middle of the head just above the antennae. A species of this group,
_Osmylus chrysops_ (_maculatus_ of some authors), is an inhabitant of
Britain (Fig. 212); its larva is to some extent amphibious. The
metamorphoses have been observed by Dufour, Brauer, and Hagen;[396] it
lurks under stones in or close to the water, or in moss, or on the stems of
aquatic plants, and pierces and empties small Insects with its
sucking-spears, which are very elongate. The young are hatched from the egg
in the autumn and hibernate before becoming full grown; when this moment
arrives the larva spins a round cocoon of silk mixed with sand. The pupa,
or nymph, in general appearance somewhat resembles the perfect Insect,
except that it is shorter and has the short wing-pads clinging close to the
body. Dufour denied the existence of abdominal spiracles in either larva or
imago, but, according to Hagen, they are certainly present in both. It
would appear that in the larva the alimentary canal is not open beyond the
chylific ventricle, and that its terminal section is modified to form a
spinning apparatus.
[Illustration: FIG. 309.—_Osmylus chrysops._ A, Larva; B, side view of head
of larva (after Brauer); C, pupa (after Hagen).]
_Osmylus_ and its allies, including _Sisyra_, are now frequently treated as
a separate sub-family, Osmylides, equivalent to the Chrysopides. In it is
placed a very anomalous Insect—_Psectra dispar_—of great rarity. The male
has only two wings, the posterior pair being the merest rudiments, though
the female has the four wings normally developed. Individuals of the male
have been found[397] in widely separated localities in the Palaearctic
region—Somersetshire being one of them—and also in North America.
{467}The genus _Sisyra_ forms for some Neuropterists the type of a separate
group called Sisyrina, though by others it is placed, as we have said, with
the Osmylina, though it is destitute of ocelli. The larvae of at least one
species of this genus are aquatic, and have been found in abundance living
in _Spongilla_ (_Ephydatia_) _fluviatilis_, a fresh-water sponge; when
discovered their nature was not at first recognised, as they possess on
each ventral segment a pair of articulated appendages, looking like legs,
but which are considered to be more of the nature of gills. The
sucking-spears of this Insect are so long and slender as to look like
hairs; whether the little animal draws its nutriment from the sponge, or
merely uses this latter as a place of shelter, is not ascertained.
[Illustration: FIG. 310.—A, Larva of _Sisyra fuscata_, ventral aspect; B,
an abdominal appendage. (After Westwood.)]
[Illustration: FIG. 311.—Larva of _Hemerobius_ sp. from Kent. A, The larva
bare; B, the same, partially concealed by the remains of its victims, etc.;
a portion of the covering has been removed in order to show the head.]
4. Hemerobiina: a somewhat numerous group of small or more rarely
moderate-sized Insects, with moniliform antennae, no ocelli, a complex and
comparatively regular system of wing-nervures; the veinlets are especially
numerous at the margins, owing to the mode of forking of the nervures there
(Fig. 298, _Drepanepteryx phalaenoides_). The larvae of most of the species
of which the habits are known {468}live on Aphides, which they suck dry,
and at least one species, in all probability several, has the habit of
covering itself with the skins of the victims it has sucked; to these
remains it adds other small debris, and the whole mass completely covers
and conceals the Insect (Fig. 311, B). The larva is furnished at the sides
with projections which serve as pedicels to elongate divergent hairs, and
these help to keep the mass in place on the back of the Insect; some fine
threads are distributed through this curious mantle and serve to keep it
from disintegration, but whether they are fragments of spiders' webs or are
spun by the Insect itself is not quite clear.
[Illustration: FIG. 312.—Portions of wings of _Drepanepteryx phalaenoides_.
A, Under-face of basal parts of the two wings; _a_, base of front wing;
_b_, of hind wing. B, Portion of front wing, showing the apparent
interruption of nervures.]
The genus _Drepanepteryx_ consists of several species, and appears to be
best represented in the Antipodes; we have, however, one species in
Britain—_D. phalaenoides_ (Fig. 298)—an extremely interesting member of our
fauna. This Insect has, like several of its congeners, a moth-like
appearance, and it has a peculiar structure for bringing the hind and fore
wings into correlation, the costa at the base of the hind wing being
interrupted and prominent, furnished with setae (Fig. 312, A), and playing
in a cavity on the under-surface of the front wing. This character is of
great interest in connexion with analogous structures of a more perfect
nature existing in various moths. M‘Lachlan has described and figured[398]
a more primitive, though analogous, condition of the wings in _Megalomus
hirtus_, also a species of British Hemerobiina. Another very curious
feature of _D. phalaenoides_ is shown in Fig. 312, B, there being a narrow
space on the hind part of the front wing from which the colour is absent,
while the nervures appear to be interrupted; they are, however, really
present, though transparent; the nature of this peculiar mark is quite
unknown, but is of considerable interest in connexion with the small
transparent spaces that exist on the wings of some butterflies.
{469}SUB-FAM. 6. CHRYSOPIDES, LACEWING-FLIES.—_Fragile Insects with
elongate, setaceous antennae._
[Illustration: FIG. 313.—_Chrysopa flava._ Cambridge.]
[Illustration: FIG. 314.—Eggs of _Chrysopa_. A, Five eggs on a leaf; B, one
egg, more magnified. (After Schneider.)]
[Illustration: FIG. 315.—Larva of _Chrysopa_ sp. Cambridge. A, The Insect
magnified; B, foot more magnified; C, terminal apparatus of the claws,
highly magnified.]
The lacewing-flies—also called stink-flies and golden-eyes—are excessively
delicate Insects, of which we possess about 15 species in Britain. Their
antennae are more slender and less distinctly jointed than they are in
Hemerobiides, and the Chrysopides are more elongate Insects. The peculiar
metallic colour of their eyes is frequently very conspicuous, the eyes
looking, indeed, as if they were composed of shining metal; this fades very
much after death. Although not very frequently noticed, the Chrysopides are
really common Insects, and are of considerable importance owing to their
keeping "greenfly" in check.
{470}[Illustration: FIG. 316.—_Chrysopa_ (_Hypochrysa_) _pallida_, larva.
(After Brauer.)]
The eggs are very remarkable objects (Fig. 314), each one being supported
at the top of a stalk many times as long as itself; in some species (_C.
aspersa_) the eggs are laid in groups, those of each group being supported
on a common stalk. The larvae (Fig. 315) are of a very voracious
disposition, and destroy large quantities of plant-lice by piercing them
with sucking-spears, the bodies of the victims being afterwards quickly
exhausted of their contents by the action of the apparatus connected with
the spears. The larvae of two or three species of _Chrysopa_ cover
themselves with the skins of their victims after the manner of the larvae
of _Hemerobius_; but most of the larvae of _Chrysopa_ are unclothed, and
hunt their victims after the fashion of the larvae of Coccinellidae, to
which these _Chrysopa_ larvae bear a considerable general resemblance.
These larvae have a remarkable structure at the extremity of their feet,
but its use is quite unknown (Fig. 315, B, C). Some larvae of the genus
make use of various substances as a means of disguise or protection. Dewitz
noticed[399] that some specimens he denuded of their clothing and placed in
a glass, seized small pieces of paper with their mandibles and, bending the
head, placed the morsels on their backs; here the pieces remained in
consequence of the existence of hooked hairs on the skin. Green algae or
cryptogams are much used for clothing, and Dewitz supposes that the Insect
spins them together with webs to facilitate their retention. According to
Constant and Lucas[400] the larvae of _Chrysopa_ attack and kill the larvae
{471}of Lepidoptera and Phytophagous Hymenoptera. The curious form we
figure (Fig. 316) has been hatched from eggs found by Brauer on _Pinus
abies_ in Austria. The eggs were of the stalked kind we have described; the
young escaped from them in the autumn, twelve days after deposition, but
did not take any food till the following spring.
The Chrysopides are widely distributed over the earth's surface. They form
an important part of the fauna of the Hawaiian islands.
SUB-FAM. 7. CONIOPTERYGIDES.—_Minute Insects with very few transverse
nervules in the wings; having the body and wings covered by a powdery
efflorescence._
These little Insects are the smallest of the Order Neuroptera, and have the
appearance of winged Coccidae; their claim to be considered members of the
Neuroptera was formerly doubted, but their natural history is quite
concordant with that of the Hemerobiid groups, near which they are now
always placed. Löw has made us acquainted with the habits and structure of
an Austrian species, _Coniopteryx lutea_ Wallg., but for which he has
proposed the new generic name _Aleuropteryx_; the larvae are found on
_Pinus mughus_ at Vienna feeding on _Aspidiotus abietis_, which they pierce
with sucking-spears, after the fashion of the Hemerobiides; when full fed
they spin a cocoon formed of a double layer of silk, in which metamorphosis
takes place in a manner similar to that of other Hemerobiidae. The
better-known genus _Coniopteryx_ differs from _Aleuropteryx_ in having the
sucking-spears short and nearly concealed by the front of the head, which
is somewhat prolonged.
[Illustration: FIG. 317.—_Coniopteryx psociformis._ Cambridge. (After
Curtis.) A, The insect with wings expanded, magnified; B, with wings
closed, natural size.]
{472}We may conclude this sketch of the Hemerobiid groups by remarking that
fossil remains of specimens of most of them have been detected in the
Tertiary strata, and that in the Secondary strata these groups are
represented by only a small number of fossils, which are referred specially
to Hemerobiina, Nymphidina, and Chrysopides.
[Illustration: FIG. 318.—A, Larva of _Coniopteryx tineiformis_ (?). (After
Curtis.) B, Head and prothorax of larva of _Coniopteryx_ sp.; C, upper
surface of head of larva of _Coniopteryx_ (after Löw), much magnified.]
{473}CHAPTER XXI
NEUROPTERA _CONTINUED_—TRICHOPTERA, THE PHRYGANEIDAE OR CADDIS-FLIES
FAM. XI. PHRYGANEIDAE—CADDIS-FLIES.
(TRICHOPTERA OF MANY AUTHORS)
_Wings more or less clothed with hair, nervures dividing at very acute
angles, very few transverse nervules; hind pair larger than the front,
with an anal area which is frequently large and in repose plicately
folded. Antennae thread-like, porrect, of many indistinct joints.
Mandibles absent or obsolete. Coxae elongate and free but contiguous.
Metamorphosis great; larvae caterpillar-like, usually inhabiting cases of
their own construction. Pupa resembling the perfect Insect in general
form, becoming active previous to the last ecdysis. Wingless forms of the
imago excessively rare._
[Illustration: FIG. 319.—_Halesus guttatipennis._ Britain. (After
M‘Lachlan.)]
The caddis-flies are Insects of moth-like appearance, found in the
neighbourhood of water; their larvae live in this element, where they may
sometimes be found in abundance. Phryganeidae are not very attractive
Insects, and there are few of large size; Hence they have been much
neglected by entomologists, and very little is known about the exotic forms
of the family. The habitations constructed by the larvae are, many of them,
of a {474}curious nature, and usually attract more attention than do the
creatures they serve to protect.
The Phryganeidae form the division or series Trichoptera; the two terms are
therefore synonymous; those entomologists who consider these Insects to
form a distinct Order use the latter appellation for it.
[Illustration: FIG. 320.—_Hydroptila angustella_ ♀. Britain. (After
M‘Lachlan.)]
The perfect Insect, though the wings are usually ample, has but feeble
powers of flight, and rarely ventures far from the water it was reared in;
it has a moth-like appearance, and the wings in repose meet, at an angle,
in a roof-like manner over the back (Fig. 326, E). The head is small, with
the front inflexed; it has two large compound eyes, and usually three
ocelli; the antennae are slender, thread-like, and occasionally attain a
great length. The parts of the mouth are very peculiar, the labrum and the
palpi—especially the maxillary palps—being well developed, while the lobes
of the maxillae and labium are amalgamated and therefore indistinct. The
labrum is more or less elongate, and is more mobile than is usual in
mandibulate Insects; it is held closely applied to the maxillae. These
latter are small, have usually only a single small free lobe; they are
united to one another and to the labium by membrane in such a manner as to
form a channel along the middle of the mouth, the labrum forming the roof
of this channel. The palpi are in some cases (Sericostomatides) of a
remarkable nature; their joints vary in number from three to five, and
differ sometimes in the sexes of the same species. The lower lip appears as
a plate supporting the labial palpi, which are three-jointed and do not
exhibit any peculiarities of structure comparable with those we have
mentioned as so frequently existing in the maxillary palps. Difference of
opinion exists as to the mandibles, some entomologists declaring them to be
entirely absent, while others state that a small tubercular process that
may be seen in some species on each side of the labrum is their
representative. The prothorax is very small, the notum is the largest piece
but is quite short, the side-pieces are very small, and the sternum appears
to consist only of membrane. The mesothorax is much the largest segment of
the body; its sternum {475}is large, but is nearly perpendicular in
direction, and is much concealed by the elongate, free front coxae, which
repose against it. The metathorax is intermediate in size between the pro-
and meso-thorax; its side-pieces are rather large, but the sternum is
membranous, with a heart-shaped piece of more chitinous consistence in the
middle, entirely covered by the middle coxae. The side-pieces both of the
meso- and meta-thorax are large, and are closely connected; the middle and
posterior coxae are very large, elongate, and prominent, and the middle
pair slope backwards, so that their tips are in contact with the tips of
the hind pair. The abdomen is cylindric and rather slender; it looks as if
formed of eight segments in addition to the terminal segment; this latter
in the male usually bears remarkably modified appendages. The first ventral
plate is sometimes, if not always, entirely membranous; indeed the texture
of the segments is in general very delicate, so that they shrivel up to an
extent that renders their comprehension from dried specimens very
difficult. The legs are always elongate, the coxae attaining in some forms
a remarkable length, and the tibiae and tarsi are armed with many spines;
the tarsi are five-jointed, slender, frequently very elongate, terminated
by two large claws and an apparatus, placed between them, consisting of a
pair of hair-like processes with a membranous lobe.
[Illustration: FIG. 321.—Front view of head of _Anabolia furcata_ after
removal of labrum. _o_, Ocellus; _an_, base of antenna; _au_, eye; _cm_,
cardo; _st_, stipes; _l_, external lobe; _pt_, support of palpus; _pm_,
palpus of maxilla; _g_, condyle of articulation of the absent mandible;
_ha_, channel of haustellum; _h_, haustellum; _sp_, apex of channel of
haustellum (not explained by Lucas); _ch_, chitinous point of external lobe
of second maxilla; _pl_, labial palp. (After Lucas.)]
The structure of the mouth-parts of the Phryganeidae has given rise to much
difference of interpretation; it has recently been investigated by R.
Lucas[401] in connexion with _Anabolia furcata_ (Fig. 321). He agrees with
other observers that mandibles are present in the pupa, but states that no
rudiment of them exists in the imago. He calls the peculiar structure
formed by the combination of the maxillae and {476}labium a haustellum. He
looks on the Trichoptera as possessing a mouth intermediate between the
biting and sucking types of Insect-mouths. He considers that the
Phryganeidae take food of a solid, as well as of a liquid, nature by means
of the haustellum, but the solid matter must be in the form of small
particles, and then is probably sucked up by the help of saliva added to
it. Lucas says also that in the larvae certain parts of the salivary glands
serve the function of spinning organs, and it is from these that the
salivary glands of the imago are formed; those salivary glands of the larva
that are not spinning glands disappearing entirely.
[Illustration: FIG. 322.—_Anabolia nervosa._ A, Larva extracted from its
case; B, one of the dorsal spaces of the abdominal segments more strongly
magnified.]
The eggs are deposited in a singular manner; they are extruded in a mass
surrounded by jelly; there may be as many as one hundred eggs in such a
mass. This is sometimes carried about by the female after its extrusion
from the interior of the body, but is finally confided to a suitable place
in stream, spring, or pool. It is said that the female occasionally
descends into the water to affix the egg-mass to some object therein, but
this requires confirmation, and it is more probable that the egg-mass is
merely dropped in a suitable situation. As soon as the larvae are hatched
they begin to provide themselves with cases; they select small pieces of
such material as may be at hand in the water, and connect them together by
means of silk spun from the mouth. Particulars as to these tubes we will
defer till we have considered the larvae themselves. These have the general
appearance of caterpillars of moths; in order to move about they must put
their head and the three pairs of legs at the front of the body out of
their tube or case, and they then look very like case-bearing caterpillars.
The part of the body that usually remains under cover is different in
texture and colour, and frequently bears outstanding processes, or
filaments, containing tracheae for the purpose of extracting air from the
water. Some peculiar spaces of a {477}different texture may be seen on
certain larvae (Fig. 322, B); these may possibly be also connected with
respiration. On each side of the extremity of the body there is a rather
large hook by which the creature attaches its dwelling to its body, and
there are also frequently present three large bosses on the anterior
abdominal segment, which are supposed to assist towards the same end. The
hold it thus obtains is so firm that it cannot be dragged out by pulling
from the front; fishermen have, however, discovered a way of extracting it
by a strategic operation: the cases are, as a rule, partially open behind,
and by putting a blunt object in and annoying the larva it is induced to
relax the hold of its hooks and advance forwards in the case, or even to
leave it altogether. The firm hold of the larva is maintained in spite of
the fact that the body does not fill the case. It is necessary that water
should pass freely into and out of the case, and that there should be some
space for the respiratory filaments to move in. The mouth of the case is
open, and the posterior extremity is arranged by the larva in such manner
as to allow a passage for the water; various ingenious devices are adopted
by different species of larvae with the object of protecting the hind end
of the body, and at the same time of permitting water to pass through the
case.
The mode of changing the skin, or the frequency with which this occurs in
the larval state of the caddis flies has not been recorded. The duration of
life in this stage is usually considerable, extending over several months:
indeed in our climate many species pass the winter in this stage,
completing the metamorphosis in the following spring or summer; and as one
generation each year appears to be the rule, it may be assumed that the
larval condition in such cases lasts from seven to ten months. During this
stage the Insects are chiefly vegetable feeders, some being said to feed on
minute algae; animal diet is not, however, entirely avoided, and it is said
by Pictet that not only do some of the Phryganeidae eat other Insects, but
that they also sometimes devour their companions.
[Illustration: FIG. 323.—A, Pupa of _Phryganea pilosa_. (After Pictet.) B,
Mandibles of pupa of _Molanna angustata_.]
{478}At the end of the larval period of existence the creature closes its
case by a light web spun at each end, taking care not to prevent the
ingress and egress of the water; it sometimes adds a stone or piece of
stick, and having thus protected itself, changes to a nymph. During the
first part of this metamorphosis the creature is completely helpless, for
there is so great a difference between the external structures of the larva
and nymph as to make the latter a new being, so far as these organs are
concerned. The changes take place in the interior of the larval skin, and
as they are completed this latter is shed piecemeal. The resulting pupa or
nymph greatly resembles the perfect Insect, differing consequently very
much from the larva. Pictet, who paid special attention to the nymph
condition of these Insects, concludes, however, that many of the organs of
the nymph are actually formed within the corresponding parts of the larva,
and has given a figure that, if trustworthy, shows that the legs of the
nymph, notwithstanding the great difference between them as they exist in
the larva and in the perfect Insect, are actually formed within the legs of
the larva; each nymphal leg being rolled up in the skin of the
corresponding larval leg, in a spiral, compressed manner, and the only
articulations that can be detected in the leg being those of the tarsus.
The head of the nymph is armed in front with two curious projections that
are, in fact, enormously developed mandibles (Fig. 323, B); they serve as
cutting implements to enable the nymph to effect its escape from its
prison; they are cast off with the nymph-skin, the perfect Insect being
thus destitute of these organs. The abdomen of the nymph differs from that
of the perfect Insect in possessing external respiratory filaments; the
nymphs of some species have also the middle legs provided with
swimming-hairs, that do not exist in the imago.
As a rule the larvae bring the respiratory filaments into contact with the
water by moving the abdomen, but Fritz Müller found[402] that those of a
_Macronema_ move the gills themselves—after the manner of Ephemeridae—with
much rapidity. Many kinds of larvae of Phryganeids possess at the posterior
extremity of the body exsertile pouches in the form of finger-like, or even
branched, processes into which tracheae do not enter. Müller observed that
in the _Macronema_ alluded to these pouches were generally not
{479}exserted; when, however, the larva ceased to move the tracheal gills,
then these pouches were protruded. He is inclined to consider them
blood-gills. Similar structures are found in _Eristalis_ and some other
Dipterous larvae that have to breathe under difficulties.
The imagines of certain species possess filaments—or something of the
sort—on the abdomen. Palmén, who has examined these organs in
_Hydropsyche_, thinks that they are the remains of gills that existed in
the larva and pupa, and that they are functionless in the imaginal instar.
M‘Lachlan thinks that in _Diplectrona_, where the filaments are elongate,
they may be functionally active even in the imago.[403]
The skin of the nymph is at first very soft, but it soon hardens, and when
about fifteen or twenty days have elapsed the nymph opens its case by means
of the mandibular processes, and swims through the water with its back
downwards till it reaches some solid object by which it can ascend to the
air; the nymph skin then swells and splits, and the thorax of the imago
protrudes; this is soon followed by the disengagement of the head and other
parts, and the imago having thus escaped, the nymph skin remains a complete
model of the external structure of the nymph, and contains a considerable
number of tracheae. This sketch of the metamorphosis of a caddis-fly does
not apply in all its details to all the forms of caddis-flies, there being
exceptions, as we shall mention hereafter.
Dewitz has described[404] the first appearance and development of the wings
in larvae of Phryganeidae. Each one appears at first in the form of a small
thickening of the hypodermis, accompanied outwardly by a minute depression
of the chitin (Fig. 324, A). He compares the structure in the earliest
stage to the entothoracic projections into the interior of the body. The
rudiment grows as the larva increases in size, the chitinous portion being
duly shed at the ecdyses. When the rudiment is larger and more complex, a
mesoderm layer appears in it (Fig. 324, B); this is derived from a
nerve-sheath near the rudiment. During the resting state of the larva—after
its case has been closed, but before the pupal form has appeared—the wing
assumes the form and position shown in C, Fig. 324. Dewitz's description of
the process leaves much to be desired, and it is doubtful whether in {480}C
the position of the wing on the exterior of the body is due to the
stripping off of the chitinous integument, or to a process of eversion, or
to both.
[Illustration: FIG. 324.—Development of wings of Phryganeidae. (After
Dewitz.) A, Portion of body-wall of young larva of _Trichostegia_; _ch_,
chitin, forming at _r_ a projection into the hypodermis _m_; _r_ and _d_
forming thus the first rudiment of the wing. B, The parts in a largely
grown larva; _a_, _c_, _d_, _b_, the much grown hypodermis separated into
two parts by _r_, the penetrating extension of the chitin; _v_, mesoderm.
C, Wing-pad of another Phryganeid freed from its case at its change to the
pupa; _b_, _d_, outer layer of the hypodermis, _m_, of the body-wall; _v_,
inner layer without nuclei.]
[Illustration: FIG. 325.—Cases of British Trichoptera. A, Of _Odontocerum
albicorne_; A^1, its termination; B, quadrangular case of _Crunoecia
irrorata_; B^1, mouth of case.]
There are about 500 species of this family of Insects known as inhabiting
the European region, and about 150 of this number occur in Britain. These
are arranged by M‘Lachlan[405]—whose zealous and persevering work at this
neglected family of Insects is beyond praise—in eight sub-families, on a
system in which the structure of the maxillary palpi plays a principal
part; they are called Phryganeides, Limnophilides, Sericostomatides,
Leptocerides, Oestropsides, Hydropsychides, Rhyacophilides, Hydroptilides.
The first three of these form the division "Inaequipalpia."
PHRYGANEIDES.—This group includes the largest forms of the family, and
appears to be almost confined to the temperate regions of the northern
hemisphere, though a few species are already known from the corresponding
districts of the southern hemisphere. This feature in their geographical
{481}distribution is, however, by no means peculiar to them, for a similar
discontinuity of distribution exists in numerous other groups of Insects,
and even in other divisions of the Phryganeidae.
The Phryganeides almost without exception inhabit still waters, and it is
more specially to them that the brief sketch of metamorphosis given in the
preceding pages will be found to apply. The larva always has the
respiratory filaments simple and thread-like, though elongate, and lives in
a case that it carries about; this case is open at both ends, and the larva
is said to occasionally cut off the end having the least diameter and
increase the other end, thus accommodating the habitation to its own
growth.
LIMNOPHILIDES.—These Insects have only three, instead of four, joints in
the maxillary palpi, but in most other respects agree with the
Phryganeides. There is, however, greater variety in the habits of the
larvae, though all live in free cases. In the genus _Enoicyla_ (Fig. 326)
we meet with the anomaly of a Trichopterous Insect that lives amongst moss
and dead leaves, far away, it may be, from water. The cases of the
Limnophilides are constructed of a great variety of materials, and are
often decorated with shells containing living inmates.
In the genus _Apatania_ the phenomenon of parthenogenesis is thought to
occur, there being at least two species in which no male specimen has ever
been discovered, though M‘Lachlan has made special efforts to discover the
sex of _A. muliebris_. It should, however, be stated that these species
have not been extensively investigated; _A. arctica_ has been detected in
the Arctic regions, and _A. muliebris_ has occurred in several localities
in Europe, in Britain chiefly near Arundel in a lake of intensely cold
water.
[Illustration: FIG. 326.—Metamorphoses of _Enoicyla pusilla_. (After
Ritsema.) A, Case of full-grown larva; B, larva and case magnified; C,
larva extracted; D, wingless adult female; E, male.]
{482}SERICOSTOMATIDES, like the Limnophilides, is a group rich in species;
the larvae are chiefly found in streams. They form portable cases out of
sand and stones (Fig. 325, B, case of _Crunoecia irrorata_) in preference
to vegetable matter. It is here that the genus _Helicopsyche_, which for
long was an enigma to naturalists, is now placed. This genus consists of
Insects whose larvae form spiral cases, similar to small snail shells, of
sand or minute stones. These objects occur in various parts of the world.
Fritz Müller[406] has informed us that the larva inhabiting one of them,
when it withdraws entirely within its abode to repose, takes the precaution
of anchoring its snail-like habitation, fixing it to a rock or stone by
spinning some temporary silken threads. The respiratory filaments in this
group are filiform.
[Illustration: FIG. 327.—Cases of _Helicopsyche shuttleworthi_. (After von
Siebold.) A, Natural size; B, C, magnified.]
LEPTOCERIDES.—The first group of the division Aequipalpia; so that there
are five-jointed maxillary palpi in both sexes; these organs are frequently
developed in a remarkable manner. The antennae are usually extremely long
and slender. The case of the larva is portable (Fig. 325, A, case of
_Odontocerum_); the respiratory filaments are not very conspicuous; they
form short tufts placed on various parts of the abdomen. Müller[406] has
called attention to a species whose larva lives in Brazil between the
leaves of Bromeliae on trees.
The OESTROPSIDES is a small group, and has recently been reduced by
M‘Lachlan to the rank of an inferior division.
HYDROPSYCHIDES.—An extensive group, in which the larvae are believed to be
chiefly of carnivorous habits. They vary, according to species, as to the
nature of the respiratory filaments, and live in fixed abodes; these are
less tubular than is the rule with the portable cases, and are formed from
pieces of sand and stone spun together and fixed to larger stones under
water. Sometimes several larvae live together in loosely compacted
structures of this kind, and only form true cases when about to undergo
their metamorphosis. Müller describes[406] a Brazilian species of
_Rhyacophylax_ as forming a case in which the mouth-end has a {483}large
funnel-shaped verandah, covered by a beautiful silken net. This larva lives
in the rapids of various rivulets, and the entrance to the verandah is
invariably directed towards the upper part of the rivulet, so as to
intercept any edible material brought down by the water. Several of these
larvae, moreover, build their cases so that they form a transverse row on
the upper side of a stone; as many as thirty cases may be placed in one of
these rows, and sometimes several rows are placed parallel with one
another. This same larva has the habit of coming out of its case when
necessary, and suspending itself in the water—as some caterpillars do in
the air—by means of a silken thread. Other members of the Hydropsychides
form tubes or covered ways of silk, earth and mud attached to stones, and
in which they can move freely about. Some of the Hydropsychidae have been
ascertained with certainty to be carnivorous in the larval state. A species
of the genus _Hydropsyche_ has been found by Howard[407] to help itself in
the task of procuring food by spreading a net in the water in connexion
with the mouth of its case. This net is woven in wide meshes with extremely
strong silk, and supported at the sides and top by bits of twigs and small
portions of the stems of water-plants. Small larvae brought down by the
current are arrested by this net for the advantage of the larva that lurks
in the tube. The breathing organs of the larvae of Hydropsychides are
apparently of a varied character, and would well repay a careful study. Mr.
Morton informs the writer that some of our British species of
_Philopotamus_ and _Tinodes_ have no gills either in the larval or pupal
state, and probably respire by means of modified tracts in the integument.
In some of the allied genera, _e.g._ _Polycentropus_, the larvae are
destitute of gills, but the pupae possess them.
[Illustration: FIG. 328.—Case, with head of larva and snare of North
American Hydropsychid. (After Riley and Howard.)]
The RHYACOPHILIDES is another group in which the larval habitations are
fixed. Some of these larvae have no respiratory filaments, breathing only
by means of the stigmata, but others have tufts of filaments. These Insects
have a peculiarity in their {484}metamorphosis inasmuch as the larva,
instead of lying free, constructs a cocoon in its case or other habitation
in which to change to a nymph. In the larvae that do not make use of a
portable case the abdominal hooks are not essential, and are replaced by
other organs differing much in structure, being sometimes apparently of a
sensitive nature, in other forms possibly respiratory. Müller tells us of a
carnivorous larva of this group in which the anterior legs are armed with
powerful forceps for predatory purposes.
The HYDROPTILIDES comprise the most minute of the Phryganeidae, and their
species will probably prove to be very numerous in well-watered tropical
regions, though few have yet been described from there. The perfect Insects
(Fig. 320) bear an extreme resemblance to small moths of the group
Tineidae. The larvae (Fig. 329) are destitute of respiratory filaments, and
construct portable cases of a variety of forms, some resembling seeds.
Müller has given particulars of a curious nature as to the cases of some
Brazilian Hydroptilides; one species moors its dwelling to a stone by means
of a long silken cable, by this artifice combining safety with the power of
ranging over a considerable extent of water. In _Diaulus_ there is only a
narrow slit at each end of the case, but one side of it is provided with
two chimneys to permit the flow of water for respiratory purposes.
[Illustration: FIG. 329.—_Hydroptila maclachlani._ B, Case with larva
magnified; A, larva more magnified. (After Klapálek.)]
The larva of _Oxyethira_ (Fig. 330) is a curious form, possessing
comparatively long legs, and a head and thorax slender in comparison with
the distended hind body. The cases are fastened, for the purposes of
pupation, to a leaf of a water-lily.
Some very curious anomalies as regards the development of the wings exist
in the Phryganeidae; _Anomalopteryx_, for instance, has the wings quite
short and useless for flight in the male, while in the other sex they are
ample; in _Enoicyla_—the curious Insect figured on p. 481, in which the
larvae are of terrestrial habits—we find the females with only rudiments
{485}of wings, while in _Thamastes_ the posterior wings are absent in both
sexes. These anomalies are at present quite inexplicable; and we may here
mention that we are in complete ignorance as to the functional importance
of many of the peculiarities of the Phryganeidae. We do not know why the
mouth is reduced from the normal state, the maxillary palpi being, on the
other hand, extraordinarily developed; we do not know the importance of the
numerous spines and of the spurs on the legs, nor of the hairs on the
wings, although these are amongst the most characteristic of the special
features of this group of Insects.
[Illustration: FIG. 330.—_Oxyethira costalis._ A, Larva in case; B, cases
fastened to leaf for pupation. (After Klapálek.)]
FOSSILS.—Abundant remains of Phryganeidae belonging to the Tertiary epoch
have been discovered. They are common in amber, and it is a remarkable fact
that a larval case has been found in amber. This seems almost inexplicable,
except on the assumption that such larvae were of arboreal habits, a
condition that, at the present time, must be excessively rare, though the
terrestrial habits of _Enoicyla_ warrant us in believing it may occur. In
the Tertiary Lake Basin at Colorado the remains of Phryganeidae in the
imago state are extremely abundant, so that it is curious that but few such
remains have been found in Europe. In Auvergne the so-called indusial
limestone, which is two or three yards thick over a wide area, is
considered to be composed chiefly of the cases of larvae of this family.
In the Mesozoic epoch some wings found in the lower Purbeck strata are
considered to be those of Phryganeidae; similar wings have been found in
the Lias, but this is the only evidence of the existence of the family at
that period except a tube, supposed to be a larval case, detected in the
Cretaceous of Bohemia. Earlier than this nothing has been discovered that
can be connected with the family, so that at present the palaeontological
evidence appears unfavourable to the view held by some that the
Phryganeidae may be considered forms allied to the early {486}conditions of
the Lepidoptera. It should be noted that the head in Phryganeidae is the
most important part from a systematic point of view, and that fossils have
been chiefly identified from the wings; this is a much more doubtful
character, as the wings of the Phryganeidae have a simple system of
neuration, and in shape have nothing very characteristic.
EXTINCT ORDER PALAEODICTYOPTERA.
This seems to be the fittest place to notice the existence of some fossil
remains from the Palaeozoic rocks that cannot be fitly, or certainly,
assigned to any of our existing Orders, and to which the above name has
consequently been given. These remains consist chiefly of wings in a more
or less imperfect state of preservation, and it is therefore quite doubtful
whether the course of assigning them to a separate Order supposed to be
extinct be correct. This is all the more doubtful when we recollect that an
Insect fossil, _Eugereon bockingi_, having the head with mouth-parts of a
Hemipterous or Dipterous nature, has been found, the wings attached to it
being such as, had they been found separate, would have been considered to
be Neuropterous, or at any rate allied thereto. About forty-two forms of
Palaeodictyoptera are assigned by Scudder to a section called
Neuropteroidea, and may therefore be considered to have a special
resemblance to our Neuroptera. These Neuropteroidea comprise numerous
genera and no less than six families. Scudder's view is at the best
tentative, and is not very favourably received by some entomologists.
Brauer has, indeed, objected altogether to the formation of this Order
Palaeodictyoptera, and Brongniart has published a list of the Palaeozoic
Insects in which a system of arrangement different to that of Scudder is
adopted. In his most recent work[408] Brongniart assigns some of these
Neuropteroidea to the families Platypterides and Protodonates, which we
have previously discussed. The whole subject of these Palaeozoic Insect
remains is still in its infancy, and it would not be proper to accept any
view as final that has yet been stated, nor would it be fair to dismiss the
subject as unimportant because of the great divergence of opinion amongst
the authorities who have investigated it.
{487}CHAPTER XXII
HYMENOPTERA—HYMENOPTERA SESSILIVENTRES—CEPHIDAE—ORYSSIDAE—SIRICIDAE—
TENTHREDINIDAE OR SAWFLIES
ORDER IV. HYMENOPTERA.
_Wings four, membranous, without scales, usually transparent, never very
large, the posterior pair smaller than the anterior; the cells formed by
the nervures irregular in size and form, never very numerous (less than
twenty on the front, than fifteen on the hind, wing). Mandibles
conspicuous even when the other parts of the mouth form a proboscis. The
side-pieces of the prothorax are disconnected from the pronotum and
overlap the prosternum, usually entirely concealing it. The females are
furnished at the extremity of the body with either saw, sting, or
ovipositor; these parts may either be withdrawn into the body or be
permanently protruded. The metamorphosis is great and abrupt, the chief
changes being revealed in the pupa disclosed at the last moult of the
larva; this moult is frequently delayed till long after growth has been
completed. In the pupa the parts of the perfect Insect are seen nearly
free, each covered in a very delicate skin._
The term Hymenoptera includes ants, bees, wasps, sawflies, and the tribes
of innumerable Ichneumon-flies. The Order is of enormous extent, consisting
even at present of tens of thousands of described and named species, and
yet these are but few in comparison with those that remain unknown. It has
good claims to be considered the "highest" Order of Insects. Sir John
Lubbock says: "If we judge animals by their intelligence as evinced in
their actions, it is not the gorilla and the chimpanzee, but the bee, and
above all the ant, which approach nearest to {488}man."[409] The mechanical
perfection of the structures of the individuals, and the rapid and
efficient manner in which their functions are discharged, are very
remarkable. In many species of Hymenoptera the individuals have the habit
of living together in great societies, in which the efforts of the members
are combined for the support of the whole society and for the benefit of a
younger generation. To fit them for this social life the bodies of the
larger number of the individuals are more or less changed in structure, so
that they become workers. These workers are in all cases imperfect females;
besides carrying on the ordinary work of the society, they tend and feed
the young. The duty of reproduction is restricted to a single female,
called a queen, or to a small number of such individuals in each society.
The males occupy an unimportant position in the society, and are usually
much shorter-lived than the workers and queens. The social Hymenoptera do
not form a single zoological group, but are of three different kinds—wasps,
bees, and ants. There are numerous non-social, or solitary, wasps and bees.
[Illustration: FIG. 331.—_Bombus lucorum._ A, Adult larva; B, pupa; C,
imago, female. Britain.]
In the Order Hymenoptera—especially in the higher forms—the males and
females are often different in appearance and structure. In the ants, one
of the social groups, the workers, or imperfect females, are quite
wingless. There are numerous other groups in which species, not social, are
found, having the females wingless while the males have wings. In a few
species there is an apterous condition of the male, perhaps usually only as
a {489}dimorphic form. In the parasitic division there are species that are
apterous in both sexes. The structure of the outer skeleton, or external
part of the body, exhibits some peculiarities, the chief of which is the
detachment of the side-pieces of the prothorax and their great development.
Not less remarkable is the abstraction of a segment from the abdomen to
become, as it were, part of the thorax; while between the first and second
true segments of the abdomen there exists a joint, or articulation, of the
utmost mechanical perfection, enabling the operations of stinging and
piercing to be executed with an accuracy that cannot be surpassed.
As a result of the detachment of the thoracic side-pieces, the front legs
and the structures connected with them are disjoined from the notum, as
shown in Fig. 332, and act in connexion with the head, while the dorsal
portion of the segment remains attached to the great thoracic mass. The
head is quite free from the thorax and very mobile; the upper organs of the
mouth—the labrum and the mandibles—are not subject to modifications equal
to those exhibited by the maxillae and lower lip, which parts in the bees
are prolonged to form a suctorial apparatus that may exceed in length the
whole body of the Insect. The mandibles remain cutting or crushing
implements even when the maxillae and lower lip are modified to form a
suctorial apparatus of the kind we have mentioned; so that in the higher
forms—ants, bees, and wasps—the mouth-pieces are completely differentiated
for two sets of functions, one industrial, the other nutritive.
[Illustration: FIG. 332.—_Tenthredo_, with head fully extended: _a_,
pleuron; _b_, pronotum; _c_, membrane; _d_, mesonotum.]
Behind the head there is a large consolidated mass representing the thorax
of other Insects, but made up, as we have already indicated, in an unusual
manner, and which therefore may be called by a special name, the alitrunk
(Fig. 333). The pronotum forms the anterior part of the alitrunk, with
which it is usually very closely connected, being indeed frequently
immovably soldered {490}thereto. It exhibits, however, considerable
variety, and is seen in its simplest and least soldered state in _Cephus_.
In the higher bees the pronotum takes on a form not seen in any other
Insects, being one of the most beautiful sclerites to be found in the class
(Fig. 334, pronotum of _Xylocopa_). We have already remarked that in
Hymenoptera the lower portions of the prothoracic segment are detached from
the upper, so that the pronotum is not supported beneath by a sternum as
usual. In the bees in question the pronotum makes up for the removal of the
corresponding side-pieces and sternum, by becoming itself a complete ring,
its sides being prolonged and meeting in the middle line of the under
surface of the body. At the same time a large lobe is developed laterally
on each side, overlying and protecting the first breathing orifice. The
intermediate stages of this remarkable modification may be observed by
dissecting a small series of genera of bees.
[Illustration: FIG. 333.—Alitrunk of _Sphex chrysis_. A, Dorsal aspect:
_a_, pronotum; _b_, mesonotum; _c_, tegula; _d_, base of anterior, _e_, of
posterior, wing; _f_, _g_, divisions of metanotum; _h_, median (true first
abdominal) segment; _i_, its spiracle; _k_, second abdominal segment,
usually called the petiole or first abdominal segment. B, Posterior aspect
of the median segment: _a_, upper part; _b_, superior, _c_, inferior
abdominal foramen; _d_, ventral plate of median segment; _e_, coxa.]
[Illustration: FIG. 334.—Pronotum of a carpenter bee, _Xylocopa_ sp. East
India.]
Although the prosternum of a Hymenopterous Insect is not usually visible
owing to its being overwrapped by the side-pieces, it is really, as shown
in Fig. 335, B, of complicated form. In _Cimbex_ and some other sawflies
the side-pieces are not so large as usual, but the prosternum is larger and
is exposed. The prothoracic spiracle is rarely visible externally, but its
position is remarkably constant, and is usually indicated by a peculiar
lobe or angle of the pronotum projecting backwards just below {491}the
insertion of the front wing. This stigmatic lobe is frequently fringed with
short hairs.
The mesothorax is the largest of the three divisions of the thorax proper;
its notum is large, and usually divided into two parts by a transverse
suture. The side-pieces are so placed that the epimeron is rather behind
than below the episternum. The mesosternum forms the larger part of the
under-surface of the alitrunk. A very large phragma projects from the
mesothorax into the interior of the body. The mesothoracic spiracle is
usually not visible; its existence was unknown to the older entomotomists,
who were in consequence led to consider the spiracle of the median segment
as belonging to the thorax. The mesothoracic spiracle is, however, easily
seen in _Cimbex_, placed in the suture between the mesothoracic epimeron
and the metathoracic episternum, a little below the insertion of the front
wing; close to this spot the mesophragma, just spoken of, comes, in
_Cimbex_, to the surface. The mesothoracic spiracle is generally
conspicuous in the worker ant. The parts of the metathorax are usually
small, but so much variety prevails in this respect that no general
description can be given.
[Illustration: FIG. 335.—Articulation of front legs of the hornet (_Vespa
crabro_, ♀). A: _a_, side-piece of prothorax overlying the prosternum; _b_,
coxa; _c_, trochanter. B, prosternum proper, as seen from front when
extracted.]
The structure of the posterior part of the alitrunk has given rise to an
anatomical discussion that has extended over three-quarters of a
century,[410] with the result that it is now clear that the posterior part
of what appears to be thorax in Hymenoptera is composed of an abdominal
segment. This part has been called "Latreille's segment," the "median
segment," and the "propodeum." The latter term was proposed by Newman,
under the form of propodeon,[411] and appears to be on the whole the most
{492}suitable term for this part, which is of great importance in
systematic entomology, owing to the extreme variety of characters it
affords. Although it is clear that the propodeum is, in large part, an
abdominal segment, yet its morphology is still uncertain; what parts are
pleural, what tergal, and what may be chitinised spiracular area, or
portions of the metathorax, being undetermined. The ventral portion of the
propodeum affords a strong contrast to the dorsal part, being so small that
it has frequently been described as absent; it is, however, not difficult
to detect it in the position shown at _d_, Fig. 333, B.
Although the true first segment of the abdomen is detached from its normal
position and added to the thorax, yet the term abdomen is conventionally
restricted to the part that commences with the true second segment, which,
in counting the number of abdominal segments, is reckoned as being the
first. There are two modes of articulation of the Hymenopterous abdomen
with the alitrunk; in one (Fig. 336, A) the base of the abdomen remains of
the calibre usual in Insects, while in the other (Fig. 336, B) it is
greatly contracted, so that the two parts are connected only by a slender
stalk, the petiole. The petiole, besides articulating in a very perfect
manner with the propodeum by means of certain prominences and notches, is
also connected therewith by means of a slender ligament placed on its
dorsal aspect and called the funiculus, shown in Fig. 333, A, just at the
extremity of the pointing line _k_. This mode of articulation gives great
freedom of motion, so that in some Petiolata (_Ampulex_) the abdomen can be
doubled under the body and the sting brought to the head. It is worthy of
note that even in the Sessiliventres—as the sub-Order with broad-based
abdomen is called—some amount of movement exists at the corresponding spot;
while, as shown in Fig. 336, A, between _a_ and _b_, there exists an
exposed membrane, the homologue of the funiculus.
[Illustration: FIG. 336.—Articulation of abdomen and alitrunk of, A,
_Cimbex_, B, _Vespa_. _a_, Propodeum or median segment; _b_, dorsal plate
of first (second true) abdominal segment or petiole; _c_, spiracle of the
propodeum; _d_, hind coxa; _e_, ventral plate of first (second true)
abdominal segment.]
The number of abdominal segments that can be seen in the {493}perfect
Insect varies greatly. In Tenthredinidae nine can be distinguished, while
in some of the Chrysididae it is difficult to detect more than three behind
the petiole. These distinctions are, however, superficial or secondary,
being due to changes in the later life in connexion with the stings or
borers; in the larvae that have been examined thirteen segments behind the
head have usually been detected.
Nothing is more remarkable in the Hymenoptera than the great differences
that exist in the form of the petiole. This may be very short, as in the
bees, so that the abdomen when not deflexed does not appear to be separated
from the thorax (Fig. 331, C); in this condition it is said to be sessile,
a term which it would be well to replace by that of pseudosessile. In many
of the solitary wasps the petiole is very long. In ants it is replaced by
one or two curiously-shaped small segments called nodes (Fig. 60, B, 2, 3),
and in many ants these are provided with structures for the production of
sound. The abdomen is formed by a system of double imbrications; each
dorsal plate overlaps each ventral plate, and the hind margin of each
segment embraces the front part of the one following; thus this part of the
body has not only great mobility, but is also capable of much distension
and extension. The pleura are apparently absent, but each one has really
become a part of the dorsal plate of the segment to which it belongs. This
is shown to be the case by _Cimbex_, where the division between pleuron and
dorsal plate exists on each segment except the basal one. Owing to this
arrangement, the abdominal stigmata in Hymenoptera appear to be placed on
the dorsal plates.
The organs for mechanical purposes existing at the extremity of the body in
Hymenoptera exhibit a great diversity of form; they are saws, borers,
piercers, or stings. Notwithstanding their great differences they are all,
in their origin, essentially similar, and consist of six parts developed
from limb-like prolongations on the penultimate and antepenultimate
segments of the larva, as described by Packard and Dewitz.[412] These
processes have by some been thought to be not essentially different from
abdominal legs, and Cholodkovsky has recently advocated this opinion.[413]
{494}The legs of bees exhibit modifications for industrial purposes. In the
stinging Hymenoptera the trochanters are usually of a single piece, and
these Insects are called monotrochous; but in most of the other forms the
trochanters are more or less distinctly divided into two parts (Fig. 345,
_b_). The usual number of joints in the tarsus is five, but is subject to
diminution in many cases. In the bees and ants the first joint is altered
in form; in the bees to act as an instrument for gathering or carrying
pollen; in the ants to act, as it were, as a second tibia. Between the
claws there is a very perfect pad, already described and figured on p. 106.
The wings are remarkable for the beautiful manner in which the hinder one
is united to the anterior, so that the two act in flight as a single organ.
The hind wing is furnished with a series of hooks, and the hind margin of
the front wing is curled over so that the hooks catch on to it. In some of
the parasitic forms the wings are almost destitute of nervures, and have no
hooks. The powers of flight in these cases are probably but small, the
wings merely serving to float the Insect in the air. In some Hymenoptera,
especially in Pompilides and Xylocopa, the wings may be deeply pigmented or
even metallic; and in some forms of Tenthredinidae, Ichneumonidae, and
Braconidae the pigmentation assumes the form of definite patterns.
[Illustration: FIG. 337.—Wings of a carpenter bee. A, The pair of wings
separated; _a_, position of the hooks: B, the same wings when united by the
hooks. C, Portions of the two wings: _a_, the series of hooks; _b_,
marginal hairs; _c_, portion of edge of front wing, of which the other part
has been broken away in order to show the hooks.]
The studies of the internal anatomy of Hymenoptera are at present by no
means numerous or extensive. The alimentary canal (Fig. 69) possesses a
crop, gizzard, and chylific stomach in addition to the oesophagus and
intestine. The social Hymenoptera have the power of disgorging matter from
the alimentary canal for the purpose of supplying food for their young.
{495}[Illustration: FIG. 338.—Central nervous system (supra-oesophageal
ganglion and ventral chain) of a worker ant, _Camponotus ligniperdus_.
(After Forel.) _a_, Cerebral hemisphere; _b_, primordial cerebral lobe or
pedunculate body (depressed so as to show other parts); _c_, olfactory lobe
(raised from natural position); _d_, nerve to labrum; _e_, antennary nerve;
_f_, scape of antenna; _g_, eye; _h_, optic nerve; _i_, longitudinal
commissures connecting the hidden sub-oesophageal ganglion with _k_, the
prothoracic ganglion; _l_, mesothoracic, _m_, metathoracic ganglion; _s_,
ganglion of the petiole; _n_, nerve from petiole to other part of abdomen;
_r_, _q_, _o_, 2nd, 3rd, 4th abdominal ganglia; _p_, terminal nerve to
cloaca; _t_, bases of legs.]
The crop—which is situated in the anterior part of the abdomen—is the
reservoir that contains this matter. The mode of disgorgement is believed
to be pressure exerted on the crop by contraction of the abdomen. Salivary
glands are present in remarkable variety. The tracheal system possesses, in
the higher winged forms, large saccular dilatations situated at the side of
the abdomen. The nervous system is of peculiar interest on account of the
high intelligence of many of the members of this Order; and on this point
of the anatomy, Brandt[414] has made rather extensive investigations,
having examined it in the adult of seventy-eight species, and in the larva
of twenty-two. In the adult there are two cephalic—the supra- and the
sub-oesophageal—two or three thoracic, and from three to seven abdominal
ganglia. The bees, wasps, and some other of the Aculeata have only two
thoracic ganglia, while some ants have three. The supra-oesophageal
ganglion is very large. The most remarkable fact revealed by Brandt's
investigations is the great difference that exists between the sexes and
the worker caste in the same species. The {496}pedunculate bodies of the
supra-oesophageal ganglion are considered to be in their development
correlative with that of the intelligence or instinct. In the workers of
the social Hymenoptera these bodies are very large, while in the males and
females they are small. The workers and females of _Bombus_ have six
abdominal ganglia, while the males have only five; and the worker of the
honey-bee has five abdominal ganglia, while the male and the queen-bee have
but four. In the leaf-cutting bee (_Megachile_) the male has four abdominal
ganglia and the female five, and in the wasps the workers have five, the
males and females six. The nervous system in the larvae shows but little
difference between the ganglia, which are thirteen in number, eight being
abdominal. In the embryo of the bee Kowalewsky has observed seventeen
ganglia. The changes that take place from the embryonic to the imago
condition are therefore directed to the reduction in number of the ganglia,
which is accomplished by the fusion of some of them. In the adult
Hymenopterous Insect it would appear that the first abdominal ganglion is
always joined with the last thoracic.
SUB-ORDERS.—The distinction in the form of the abdominal articulation,
previously alluded to (p. 492, Fig. 336, A, B), divides the Hymenoptera
into two great sub-Orders, the members of which are very different in their
habits and life-histories. The Sessiliventres are plant-eaters; their
larvae (Fig. 343, A) are provided with legs, and are able to procure their
vegetable food for themselves. The larvae of the Petiolata are maggot-like
and helpless, and are dependent for food on supplies afforded them by their
parents or companions. It is said by Dewitz that although the larvae of the
Petiolata appear to be legless, there are thoracic legs within the body.
The metamorphosis, so far as it is known, and the early life-history of the
Sessiliventres are very similar to those of butterflies and moths, except
that the pupa is soft and has no hard external skin. A few of these
plant-eating Sessiliventres become carnivorous in the perfect state—a
change of habit that is most unusual in Insects, though the reverse
occurrence is common. The larvae of the Petiolata exhibit, in the cases
that have been examined, the peculiarity that the alimentary canal has not
any outlet posteriorly until the termination of the larval stage of
existence is approaching. In some cases there is no anal orifice; in others
this orifice exists, {497}but there is no communication between the stomach
and the posterior intestine.
Packard informs us[415] that in _Bombus_ the larva, after it is full fed,
passes into the pupa state (Fig. 331, A, B) by a series of transformations
accompanied by moultings of the skin. Packard's statements have been
confirmed by others, but details have not been fully given, so that the
number of the moults, their intervals and other particulars, are still
unknown. We have remarked that the pupal instar is very like the perfect
instar, except that it is colourless and soft, and that each of the members
is wrapped in a very delicate skin; the colour appears gradually. This
metamorphosis exhibits important differences from that of the Lepidoptera.
Packard calls the Insect, during the stages of transformation from the
full-fed larva to the pupa, the semi-pupa; the later stages of the pupa,
when the colouring has appeared, he terms the subimago. Altogether he
considers there is a series of at least ten moultings of the skin. His
ideas were apparently derived from examination of a series of specimens
after death rather than from observation of the development in living
individuals. The parasitic forms of Hymenoptera have apparently
extraordinary metamorphoses of very varied kinds.
PARTHENOGENESIS.—One of the most remarkable facts connected with this Order
is the prevalence of parthenogenesis in a considerable number of widely
separated species. In many of these Hymenoptera it is not a mere occasional
occurrence, but plays an important part in the continuity of the species;
indeed, it is believed that in some members of the Order the reproduction
is entirely parthenogenetic. We shall give particulars as to some of these
cases in subsequent chapters, and will here make some remarks on the
different forms of parthenogenesis existing in the Order. The three forms
of parthenogenesis mentioned on p. 141 all occur in Hymenoptera. In the
gall-making Cynipidae parthenogenesis is frequently accompanied with
alternation of generations, a generation consisting of the two sexes being
followed by another consisting entirely of females, which in its turn gives
origin to a bisexual generation. In this case deuterotokous parthenogenesis
is established as a part of the normal economy of the species. This same
form of parthenogenesis also occurs in other species of Cynipidae
unaccompanied by alternation {498}of generations. Thus in _Rhodites rosae_
the generations resemble one another, and the male is very rare, but is
still occasionally produced,[416] and the same condition exists in other
Cynipidae. According to the observations of Adler, we may assume that the
male, in the latter cases, is useless, the continuation of the species
being effected by virgin females although males exist. Deuterotokous
parthenogenesis also occurs in the sawflies, but as a comparatively rare
phenomenon.[417]
Thelyotokous parthenogenesis is common in sawflies, and it also occurs in
some Cynipidae. There are several species of this latter family in which no
males have ever been found.[418] The phenomena in _Rhodites rosae_ we have
mentioned, give rise to the idea that in that species deuterotokous
parthenogenesis occurs as an exception, the species being usually
thelyotokous. A most remarkable case of thelyotokous parthenogenesis is
said to exist in the case of the parasitic ant _Tomognathus_. This species
is said to be monomorphic, only the female existing, and reproducing by
uninterrupted parthenogenesis.
Arrhenotokous parthenogenesis—_i.e._ parthenogenesis in which the progeny
is entirely of the male sex—occurs in several species of sawflies. We find
it also occurring in the case of the social Hymenoptera; the workers of
ants, bees, and wasps occasionally produce eggs parthenogenetically, and
the progeny in these cases is always of the male sex. In the honey-bee the
queen sometimes produces eggs before she has been fertilised, and the
parthenogenetic young are then always of the male sex.
Some species of Hymenoptera exhibit two forms of parthenogenesis. In
_Nematus curtispina_ the parthenogenetic generation is generally of the
male sex, but a female is occasionally produced;[419] while in _Hemichroa
rufa_ parthenogenesis may result in either deuterotokous or thelyotokous
progeny. No case is yet known of a species exhibiting the three forms of
parthenogenesis. From this review we may conclude that parthenogenesis does
not favour the formation of one sex more than another; but it is clear that
it decidedly favours the production of a brood that is {499}entirely of one
sex, but which sex that is differs according to other circumstances.
PRODUCTION OF SEX.—It is believed that a very peculiar form of
parthenogenesis exists in the honey-bee, and it is confidently stated that
the drones, or males, of that species are always produced from unfertilised
eggs. These views are commonly called the Dzierzon theory, and are widely
accepted. They assume that the eggs are male till fertilised, and then
become female. After the queen-bee is fertilised most of the spermatozoa
soon find their way into a small chamber, the spermatheca, near the
posterior orifice of the body; it is believed that each egg may be
fertilised as it passes the door of this chamber, and that the eggs that
produce females (_i.e._ workers or queens) are so fertilised, but that the
eggs that produce drones are not fertilised. Hence it is supposed that the
sex is determined by this act of fertilisation, and Cheshire has described
what he calls an apparatus for differentiating the sexes. It is also
confidently stated that no male honey-bee ever has a father.
The facts we have stated as to the sexes resulting from parthenogenetic
reproduction in Hymenoptera generally, are extremely opposed to the
Dzierzon theory, in so far as this relates to the production of sex. There
have always been entomologists[420] who have considered this view
unsatisfactory, and the observations of several recent French
naturalists[421] are unfavourable to the idea that the sex of an egg is
determined by its fertilisation.
There can be no doubt that the queen honey-bee frequently produces males
parthenogenetically, and the error of the views we are alluding to consists
in taking the parthenogenesis to be the cause of the sex of the individual.
It must be recollected that the laying of an unfertilised egg by a
fertilised female may be different physiologically from the laying of an
egg by an unfertilised female; for, though both have as result an
unfertilised egg, it is possible that the fertilisation of the female may
initiate processes that modify the sex of the eggs produced by the ovaries,
so that though these may produce previous to fertilisation only male eggs,
yet after fertilisation they may produce eggs of the opposite sex or of
both sexes. In other {500}words, the act of fertilisation may initiate a
different condition of nutrition of the ovaries, and this may determine the
sex of the eggs produced.
POLYMORPHISM, OR CASTES.—The question of the causes of the modified
individuals forming the various castes of the social Hymenoptera has been
much discussed. These individuals are many of them very different in size
and structure from either of their parents, and are also different in their
habits and instincts. This difficult subject is far from being completely
elucidated. In the case of the honey-bee it is well established that an egg
of the female sex can, after deposition, be made either into a queen or a
worker-bee by the mode of nutrition—using that word in the largest sense.
On the other hand, Dewitz thought that in the case of the ant _Formica
rufa_, the caste—whether worker or winged female—is already determined in
the Insect before leaving the egg.[422] Weismann and others associate the
caste with some hypothetic rudiments they consider to exist at the very
earliest stage of the embryonic, or oogenetic process.
Herbert Spencer says:[423] "Among these social Insects the sex is
determined by degree of nutrition while the egg is being formed," and
"after an egg, predetermined as a female, has been laid, the character of
the produced Insect as a perfect female or imperfect female is determined
by the nutrition of the larva. _That is, one set of differences in
structure and instincts is determined by nutrition before the egg is laid,
and a further set of differences in structures and instincts is determined
by nutrition after the egg is laid._"
Spencer's generalisation is not inconsistent with the facts hitherto
brought to light, though it is possible that the progress of knowledge may
show some variety as to the periods of the development at which the
commencements of the modifications occur.
Fig. 339 represents the chief castes, or adult forms, existing in a
community of one of the most highly developed of the species of social
Hymenoptera, the leaf-cutting ant, _Atta cephalotes_. We shall, when
dealing with Formicidae, enter into some details as to these and other
cases of polymorphism.
{501}[Illustration: FIG. 339.—Adult forms of _Atta (Oecodoma) cephalotes_,
taken from a nest in Trinidad by Mr. J. H. Hart, 25th June 1895. A, male;
B, winged female; C-F, various forms unwinged; C, so-called soldier; D,
large worker; E, smaller worker; F, smallest worker or nurse. All equally
magnified (one and half times).]
{502}Our object at present is to bring to the eye of the reader the great
diversity of outer form that is believed, rightly or wrongly, to result
from the mode of treatment of the young. And we will also take this
opportunity of more fully illustrating the remark we made on p. 85 as to
the profound distinctions that exist between ants and white ants, or
Termites, notwithstanding the remarkable analogies that we shall find to
exist in many of their social arrangements.
The analogies we allude to, coupled with the fact that there is a certain
general resemblance in outer form between the workers of Termites and ants,
and even between the extraordinary castes called soldiers in the two
groups, have given rise to the idea that there is a zoological relationship
between the social forms of Neuroptera and Hymenoptera. The two are,
however, zoologically amongst the most different of Insects. The external
skeleton in Termites is remarkable for its imperfect development, the
sclerites being small and isolated, while the segmental differentiation of
the body is low (Fig. 225, etc.), so that there is no difficulty in
counting the segments. In ants the reverse is the case as regards both
these facts, the various segments being most unequal, so that their
homologies have only been detected after prolonged studies, while the
chitinisation and articulation of the various parts is so complete that the
ant may be described as cased in armour, fitting together so exactly that
it is difficult anywhere to introduce the point of a needle into its
chinks. The wings of the two kinds of Insects are also extremely different.
The differences between the modes of growth and development of the two sets
of Insects are as profound as the distinctions in their anatomy. Termitidae
belong to the division of Insects in which the wings are developed outside
the body; Hymenoptera to the division in which they are developed inside
the body. In Termites the growth of the individual is slow, and the final
form is reached gradually. In the ants the growth is carried on with great
rapidity, and during it the Insect is a helpless maggot absolutely
dependent on the attentions of its seniors, while the difference in form
and structure between the ant-larva and the ant are enormous. Both anatomy
and ontogeny are profoundly different in ants and Termites. To these
distinctions must be added, as of much importance, the fact that in
Hymenoptera only the female sex {503}is modified for the division of
labour, while in Termites both sexes undergo this change. Hence it is
impossible to suppose that the remarkable analogies that exist between the
societies of ants and those of Termites are due to any common origin. It is
probably to some similar physiological susceptibilities in the ancestors,
at an extremely remote epoch, of both groups that we must look for an
explanation of the interesting resemblances in the social lives of ants and
Termites.
The Hymenoptera are no doubt one of the largest Orders of Insects, the
species of the parasitic tribes being apparently innumerable. No doubt
250,000 species of the Order exist, and possibly the number may prove to be
very much larger. Up to the present time 25,000 or 30,000 have been
discovered. No remains of Insects of this Order, of older age than the
Lias, have been brought to light; it is indeed doubtful whether the fossils
considered to be Hymenopterous of the period referred to are really such.
The Order, as already mentioned, consists of two very distinct sub-Orders,
viz.:—
1. _Hymenoptera Sessiliventres._—Insects with the abdomen broad at the
base, its first segment not completely amalgamated with the thorax.
2. _Hymenoptera Petioliventres_ or _Petiolata_.—The abdomen connected
with what appears to be the thorax by a slender joint, the posterior part
of the apparent thorax consisting of an abdominal segment.
HYMENOPTERA SESSILIVENTRES.—This group has been variously called
_Hymenoptera phytophaga_, _H. securifera_, _H. sessiliventres_, _H.
serrifera_, _H. symphyta_. We prefer an old term, taken from a character
that enables us to recognise at a glance which group a species belongs to.
The division or sub-Order may be formally defined as follows:—
_Abdomen nearly continuous in outline with the thorax, the two parts
having a broad connexion instead of a small highly mobile articulation.
Anal lobe of hind wings usually of considerable size. Trochanters
ditrochous (transversely divided into two, Fig. 345). Extremity of body
of female furnished with saws or boring instruments, usually concealed,
in some cases visible in part. Larvae with complex mouth-parts; three
pairs of thoracic legs (imperfect in Cephidae and {504}Siricidae), and
frequently with numerous abdominal legs, which are destitute of hooks.
Food vegetable._
The Insects of this sub-Order never exhibit the highly specialised habits
and activity of the better known petiolate Hymenoptera. Though the food in
the larval stages is always vegetable, there is considerable variety in the
larvae and their habits; some feed in galls, some in the twigs of plants,
some in the hard wood of trees and shrubs. The majority, however, live on
the leaves of plants. Those that live in wood (Fig. 342, C) resemble in
appearance Coleopterous larvae that have similar habits, and those that
live on leaves (Fig. 343, A) resemble Lepidopterous larvae that do
likewise. There are four families included in the sub-Order, viz. Cephidae,
Oryssidae, Siricidae, Tenthredinidae.
The British Sessiliventres—under the name Phytophagous Hymenoptera—have
recently been monographed by Mr. Peter Cameron in a series of vols.
published by the Ray Society.[424] These contain many figures and many
details relating to natural history, in addition to the descriptions of
genera and species.
FAM. I. CEPHIDAE—STEM SAWFLIES.
_Slender Insects, with weak integument; free, more or less elongate
pronotum; one spine on the front tibia. Larvae living in the stems of
plants or in the tender shoots of trees and shrubs._
The obscure little Insects composing this family have slender antennae of
peculiar form, composed of eighteen to thirty joints, two of which are
short and stout; then come several long joints, with more or less power of
movement, the terminal portion consisting of an elongate club of many
joints with little power of movement. The pronotum is longer than is usual
in the Hymenoptera, and instead of being very closely connected with the
mesonotum, it is free and mobile, although its base overwraps the front of
the mesonotum. The median plate (_i.e._ the dorsal plate connecting the
thorax and abdomen) is divided to the base along the middle, the divisions
being separated by a membranous piece broader behind; the anal lobe of the
posterior {505}wings is small but distinct. The female bears a saw at the
extremity of the body, but it is covered by two flaps; these form a short,
terminal projection. Although too much neglected, the Cephidae are really
of great interest as being of more imperfect or primitive structure than
any of the other families of Hymenoptera. The larval history has been
traced in several species. _C. pygmaeus_ is sometimes very injurious to
corn crops on the continent of Europe, and even in our own country its
effects in this respect are considered to be occasionally serious. The egg
is laid in the stem of the corn plant; the larva soon hatches and eats its
way upwards in the stem. It is a soft grub, apparently footless, but really
possessing six small projections in place of thoracic legs. It occupies all
the summer in feeding, and when full fed and about to prepare for its
metamorphosis, it weakens the stem by a sort of girdling process below the
ear; it then descends in the stem to near the root, where it constructs a
transparent cocoon, in which it passes the winter as a larva, changing to a
chrysalis in the month of May, and completing its development by appearing
as a perfect Insect shortly thereafter. The girdling operation is very
injurious, and causes the corn stem, when ripe or nearly so, to break in
two under the influence of a strong wind, so that the ears fall to the
ground.
[Illustration: FIG. 340.—_Cephus pygmaeus._ Upper figure, larva; lower,
female imago. Britain. (After Curtis.)]
The history of _C. integer_ has been given by Riley. This Insect attacks
the young shoots of willows in North America. Riley states[425] that by a
wonderful instinct the female, after she has consigned her egg to the twig,
girdles the latter, preventing it from growing any further, and from
crushing the egg by so doing. The larva after hatching eats downwards,
sometimes destroying a length of two feet of the twig; when full grown it
fills the bottom of the burrow with frass, and then previous to making its
cocoon eats a passage through the side of the shoot about a quarter of an
inch above the spot where the cocoon will be placed, thus making it easy
for the perfect Insect to effect its {506}escape; it leaves the bark,
however, untouched, and is thus protected in its retreat. A delicate
transparent cocoon is then spun in which the larva passes the winter,
changing to a pupa in the following March, and emerging as a perfect Insect
about six weeks thereafter.
Somewhat less than 100 species of this family are at present known; the
great majority are found in the Mediterranean region, but there are several
in North America. As a single species is known from Mexico and another from
Japan, it is probable that the family may prove to have a wider
geographical extension than at present appears to be the case.
FAM. II. ORYSSIDAE.
_The median plate behind the metanotum entire, not divided in the middle;
antennae inserted below the eyes immediately above the mandibles, under a
sharp edge._
This family consists of the genus _Oryssus_, and includes only about twenty
species, but is nevertheless very widely distributed over the world. They
are very rare Insects, and little is known as to their habits; one species,
_O. abietinus_, was formerly found in England. Should any one be so
fortunate as to meet with it, he can scarcely fail to recognise it on
noticing the peculiar situation of the base of the antennae. In this
respect the Chrysididae somewhat resemble _Oryssus_, but in that group of
Hymenoptera the hind body or abdomen is remarkably mobile, so that the
Insects can coil themselves up by bending at this joint; whereas in
_Oryssus_ the hind body is very closely amalgamated with the thorax—more
so, in fact, than in any other Hymenopterous Insect—and has no power of
independent movement.
[Illustration: FIG. 341.—_Oryssus sayi._ North America. A, The female
Insect; B, head seen from the front.]
{507}_Oryssus abietinus_ very closely resembles _C. sayi_ (Fig. 341); it
has indeed been recently suggested by Mr. Harrington that the two supposed
species may really be identical.
FAM. III. SIRICIDAE OR UROCERIDAE.
_Pronotum closely connected with the mesonotum, perpendicular in front;
the anterior lobe of the latter not separated by the lateral lobes from
the posterior lobe: the median plate (behind the metathorax) is divided
longitudinally along the middle. The female is provided at the extremity
of the body with an elongate, cylindrical boring instrument. The larvae
live in the wood of trees._
[Illustration: FIG. 342.—_Tremex columba._ North America. A, Imago, female:
B, pupa, female, ventral aspect: C, larva; _a_, imperfect legs: D,
parasitic larva of _Thalessa_. (B and D after Riley.)]
The Insects of this family are usually of large size and of bright
conspicuous colours; these, however, frequently differ greatly in the sexes
of the same species, and may be very variable even in one sex. The antennae
are filiform and usually elongate; the head is usually contiguous with the
thorax, but in one division, Xyphidriides, it is exserted and separated
from the thorax by a well-marked neck. The pronotum is attached to the
mesonotum, and possesses very little, if any, freedom of movement; it
varies in its size, being sometimes conspicuous {508}from above; in the
Xyphidriides it is smaller, and in the middle is entirely vertical in its
direction. The mesonotum is moderate in size, and its divisions are
delimited by broad vague depressions. The prosternum appears to be entirely
membranous, but the prosternal plates (pleura) are large, and meet together
accurately in the middle, so as to protect the greater part of the
under-surface of the neck. The abdomen is cylindrical or somewhat flattened
above; it has seven dorsal plates in addition to the spine-bearing terminal
segment. The trochanters are double, the outer division being, however,
short; the anterior tibia has only one spur; the anal lobe of the posterior
wings is large. The "borer" or ovipositor of the female is a remarkable
organ; it is held projecting directly backwards from the extremity of the
body, and has the appearance of being a powerful sting. The apparatus is
much longer than it appears, for it proceeds not from the apex of the body,
but from the under-surface far forwards, so that the part exposed is only
about one-half of the total length; it consists of a pair of elongate
sheaths, which are easily separable though they wrap together, and enclose
a slender tube. This tube is rigid and quite straight; though appearing
solid, it is really composed of two very perfectly adjusted laminae and a
third arched piece or roof. The two lower laminae are called the spiculae;
they are serrated or grooved in a peculiar manner near the tip, and
although so closely adjusted to the borer or upper piece of the tube as to
appear to form one solid whole with it, they are said to be capable of
separate motion. In addition to these parts, the termination of the abdomen
bears above a shorter piece that projects in a parallel plane, and forms a
sort of thick spine above the ventral pieces we have described; this
process is very strong, and has in the middle of its under-face in _Sirex
gigas_ a membranous cavity, replaced in _S. juvencus_, according to
Westwood, by a pair of minute pilose styles. The Insect, by means of this
powerful apparatus, is enabled to deposit her eggs in the solid wood of
trees, in which the larva sometimes penetrates to the depth of eight
inches.
_Sirex gigas_ is one of the most remarkable of our British Insects, but is
little known except to entomologists, being usually rare. On the continent
of Europe it is, however, an abundant Insect, especially in the
neighbourhood of forests of fir-trees, and is a cause of considerable
terror. As the Insect is not {509}capable of inflicting much injury to the
person, it is probable that the peculiar ovipositor is believed to be a
sting. The eggs are laid—it is said to the number of 100—in the solid wood
of fir-trees, but not in perfectly healthy wood; the reason for this, it is
thought, being that in a healthy tree the great affluence of sap caused by
the burrows and presence of the Insect would be injurious to the latter.
The _Sirex_ will, however, attack a perfectly healthy tree immediately
after it has been felled. The larva, small at first, enlarges its burrows
as itself grows larger, and thus the wood of a tree may be rendered
completely useless for trade purposes, although there may be very little
outward indication of unsoundness. The larva (Fig. 342, C, larva of
_Tremex_) is a pallid, maggot-like creature, with six projections
representing thoracic legs; there are no other legs behind these, but some
slight protuberances take their place; the terminal segment is enlarged,
and bears a hard spine. There is a difference of opinion as to the duration
of the life of the larva, Kollar saying that in seven weeks after the
deposition of the egg the maggot is full fed, while others consider that it
takes two years to attain this condition; the latter statement is more
probably correct, it being the rule that the life of wood-feeding larvae is
more than usually prolonged. After becoming full fed, the Insect may still
pass a prolonged period in the wood before emerging as a perfect Insect. As
a result of this it not infrequently happens that the Insect emerges from
wood that has been carried to a distance, and used for buildings or for
furniture. A case is recorded in which large numbers of a species of
_Sirex_ emerged in a house in this country some years after it was built,
to the great terror of the inhabitants. The wood in this case was supposed
to have been brought from Canada.
Fabre has studied[426] the habits of the larva of _Sirex augur_, and finds
that it forms tortuous galleries in the direction of the longitudinal axis
of the tree or limb, and undergoes its metamorphosis in the interior,
leaving to the perfect Insect the task of finding its way out; this the
creature does, not by retracing its path along the gallery formed by the
larva, but by driving a fresh one at right angles to the previous course,
thus selecting the shortest way to freedom. By what perception or sense it
selects the road to the exterior is quite unknown. Fabre is not {510}able
to suggest any sort of perception that might enable the larva to pursue the
right course, and considers it must be accomplished by means of some
sensibility we do not possess. Fabre's observation is the opposite of what
has been recorded in the case of _S. gigas_, where the larva is said to
prepare the way for the exit of the perfect Insect.
Individuals of _Sirex_ are often found in dried and solid wood, encased by
metal. When the Insect finds itself so confined, it gnaws its way through
the metal, if this be lead, and escapes. The perseverance displayed by the
Insect in these circumstances seems to indicate a knowledge of the
direction in which liberty is to be found.
About 100 species of Siricidae are known. They form two sub-families:—
1. _Siricides_: back of head nearly or quite contiguous with the
pronotum.
2. _Xyphidriides_: back of head separated from the pronotum by an
elongate neck.
We are reputed to possess in Britain two species of each of these
sub-families, but it is doubtful whether more than one Siricid is truly
native. _Sirex gigas_ is frequently brought over in timber, and certainly
breeds at times freely in Britain. Mr. Leech has recorded the occurrence of
the larvae in abundance in fir-trees in the neighbourhood of Dublin. _Sirex
juvencus_ is more rarely met with. _Xyphidria camelus_ is doubtless a
native, though now apparently rare. It used to occur about old willows,
near London, in the New Forest, and, I believe, also in the neighbourhood
of Cambridge.
FAM. IV. TENTHREDINIDAE—SAWFLIES.
_Hymenoptera Sessiliventres, having the pronotum small, accurately
adapted to the mesonotum; the anterior lobe of the latter is widely
separated from the posterior; there are two spurs on the anterior tibiae.
The larvae usually live on leaves after the manner of caterpillars, but a
few inhabit galls._
The sawflies are an important family of Insects, their species being
numerous, while some of them are, in the larval state, very destructive to
vegetables and fruit. Being quiet creatures, rarely seen on the wing, they
are, though common Insects in this {511}country, but little known, and few
persons recognise a sawfly as such. They are usually of small or moderate
size, and the numerous species have a great family resemblance. This remark
requires some qualification in the case of the Cimbicides, they being
Insects of larger size—usually surpassing the honey-bee—of more robust
structure, and with greater powers of flight.
[Illustration: FIG. 343.—_Lophyrus pini._ Britain. A, Larva; B, ventral
aspect of pupa; C, imago, male. (After Vollenhoven.)]
The antennae are remarkably variable in form and structure. Cameron
considers that nine should be taken as the normal number of their joints;
but there are only three in _Hylotoma_, while in _Lyda_ there may be forty
or more. The head is usually held closely applied to the thorax, but is
really borne on a neck capable of much elongation (Fig. 332). The pronotum
forms a part of the alitrunk, but is not soldered thereto. Usually the
prosternum is more or less completely concealed by the side-pieces, but in
Cimbicides it is larger and conspicuous, the side-pieces being in this
group smaller than usual. The dorsal pieces of the mesothorax have their
relative proportions different to what we find them in the other families
of Sessiliventres, and even in most of the other Hymenoptera. There is
first an antero-median lobe of triangular shape projecting, like a wedge,
far backwards, into the great lateral lobes. These latter form the larger
part of the area of the mesonotum; they meet together in the middle line,
and behind are separated by a deep depression from the posterior lobe, or
scutellum of the mesothorax, which is frequently divided into two parts,
the anterior being the so-called scutum. The pieces of the metanotum are
short and obscure, owing to the great unevenness of their parts; on each
side of the middle there is a small membranous space of pallid colour. The
cenchri, as these spaces are called, are, in _Lyda_, {512}delicate,
membranous, depressed spaces, in front of each of which there stands up a
flap of membrane. The function of the cenchri is quite unknown. The median
plate is fastened to the hind margin of the metanotum, and looks quite like
one of the dorsal plates of the following abdominal segments, from which,
however, it is separated by a more or less conspicuous membrane. In the
majority of the Tenthredinidae the median plate is divided along the
middle, but in the Cimbicides this is not the case. The mesosternum is very
large, and the metasternum small, so that the middle and hinder pairs of
coxae are placed close together. The abdomen consists of nine segments,
there being eight dorsal plates in addition to the median plate, and seven
ventral plates besides the terminal armature. There is a pair of short
cerci, each of a single segment. The trochanters are divided; each tibia
bears two spurs at the extremity, and the tarsi are 5-jointed.
[Illustration: FIG. 344.—Saws of _Cimbex sylvarum_. A, The pair spread out
and placed in a horizontal position; _a_, the lower margin of the saw
proper; _b_, the upper margin of the support: B, two teeth of the saw more
highly magnified.]
The most characteristic and interesting of the structures with which the
Insects of this family are provided is the apparatus from which the name of
sawfly is derived. As long as two centuries ago these instruments excited
the admiration of Vallisnieri and of Réaumur, who described them at length;
and it is truly astonishing that any part of a living being should be
changed into tools so mechanically perfect as these saws are (Fig. 344).
They serve the purpose of assisting the female in depositing the eggs in a
suitable situation, the place selected being frequently the tender stems of
shrubs or other plants, or the interior of leaves. These organs are
therefore of course possessed only by the female. They are placed on the
{513}lower aspect of the hinder extremity of the body, where they are
enclosed and protected by a pair of sheaths, from which they can be made to
protrude by a little pressure exercised on the parts immediately in front
of them. Each female possesses a pair of these saws; they consist of thin
laminae of very hard consistence, and are not only toothed at their edge,
but in many cases each tooth is itself serrate; at the same time the outer
face of the saw is sculptured or plicate in a remarkable manner, so that
the saw in this way acts as a file or rasp. The Insect having selected a
suitable place, uses the saws by placing the extremity of the abdomen
against a twig or leaf, protruding the blades, which, moving with an
alternate motion, one being thrust forward while the other is retracted,
act on the plant so as to make an incision. Each saw is directed in its
movement by the support, the pair of supports being united at the base by
membrane as shown in Fig. 344. In the case of some species,—_Hylotoma
rosae_, the common sawfly of our rose-bushes, for instance—there is no
difficulty in observing the operation; indeed old Réaumur, when speaking of
the placid disposition of the sawflies, suggests that it was given them so
that we may easily observe their charming operations. We cannot but regret
that in these days we are unable to take so complacent a view of the
arrangements of nature. There is much variety in the details of the
structure of these saws; so much indeed that it is possible to identify
most of the species by means of the saw alone. According to certain
observers, the eggs are laid by some kinds on, not in, the leaves, so that
we may conclude that in these cases the saws are not used by their
possessors. An incision having been made, an egg is placed in it, and also
a drop of some liquid matter. The egg is at first small, but soon increases
till it becomes twice or three times its former size, and the development
of the embryo commences.
The larvae of the Tenthredinidae exhibit great variety, and are indeed in
this respect more interesting than the perfect Insects. The usual rule is
that the larvae much resembles those of Lepidopterous Insects, and feed
exposed on plants in the same way as Lepidopterous larvae do. But the
exceptions are numerous; sometimes the larva is covered with slime, and
thus protected from various enemies. In other cases it is very depressed, a
broad creature, of irregular outline, living closely {514}attached to the
leaf, somewhat after the fashion of a huge scale-Insect. Some larvae mine
between the layers of a leaf, others roll up leaves; a few live in the
stems of plants, and one or two inside fruits. Even this does not complete
the list of their habits, for a few species of _Nematus_ live in galls
caused by the deposition of the egg. A species of _Lyda_ forms for itself a
case out of bits of leaves, and carries this habitation about with it after
the fashion of the Phryganeidae. The number of legs in these larvae is
unusually great, varying from eighteen to twenty-two—that is, three pairs
of thoracic legs and eight of abdominal or pro-legs. This character offers
a ready means of distinguishing, in the majority of cases, these larvae
from those of the Lepidoptera in which the number of legs varies, but is
only from ten to sixteen; moreover, the pro-legs in sawflies are destitute
of the circles of hooklets that exist in Lepidoptera. This mode of
identifying the immature stages of the Tenthredinidae is not, however,
always satisfactory, as there are some of these larvae that have no
pro-legs at all, but only the three thoracic pairs. Another point of
distinction exists, inasmuch as the larvae of the sawflies have only one
ocellus on each side of the head, whereas in the Lepidopterous caterpillars
the rule is that there are several of these little eyes on each side. In
addition to this, we should mention that the Lepidopterous larva never has
any pro-legs on the fifth body-segment, whereas in the sawflies when
pro-legs are present there is always a pair on the segment in question.
These larvae are of various colours, but the patterns and markings they
exhibit are not quite like those of the Lepidoptera, though it would be
difficult to make any correct general statement as to the nature of the
differences. The variety of their postures is very remarkable; and in
respect of these also Tenthredinidae differ considerably from Lepidoptera.
Some of them hold the posterior part of the body erect, clasping the leaf
by their anterior legs; others keep the posterior part of the body curled
up (Fig. 343, A), and some combine these methods by curving the posterior
part of the body and holding it away from the food. These attitudes, like
the general form, are characteristic for each species. The _Nematus_ larvae
that inhabit galls possess all the characteristics of those that feed
externally. As a rule the skin of the larva is naked and free from hair,
but it is often minutely tuberculate, and in a few species it is armed
{515}with remarkable forked spines. These spines may exist during part of
the larval life, and completely disappear at one of the moults. The
creatures are as a rule very sluggish, and move about much less than
Lepidopterous larvae; many of them, when alarmed, have the power of exuding
a disagreeable liquid, either from the mouth or from pores in the skin; in
the latter case it may be sent as a sort of spray to some little distance
from the body. This operation is said to be very efficacious as a means of
protecting the larvae from the attacks of parasitic flies that are desirous
of laying eggs in their bodies. One peculiarity as to their colour has
attracted the attention of Réaumur and subsequent naturalists, namely, that
in the case of many species a great change takes place in the colour during
the life of the larva, and more especially at the period of the last moult.
The change to the pupal state usually takes place in a cocoon, and some
species have the peculiar habit of forming a double cocoon, the outer one
being hard and coarse, while the inner is beautifully delicate. The cocoon
is sometimes formed in the earth, and in that case it may be to a large
extent composed of earthy matter. The Insect frequently remains a long time
in its cocoon before emerging as a perfect Insect; however long this time
may be, it is nearly all of it passed in the larval state; when the Insect
does change to a pupa it speedily thereafter emerges as a perfect Insect.
In the pupa the parts of the imago may be seen enveloped in a very
delicate, transparent skin.
In Brazil _Dielocerus ellisii_, a sawfly allied to _Hylotoma_, constructs a
nest in which the cocoons of many specimens are crowded together, being
packed side by side like the cells in the comb of the bee, while the whole
mass is protected by a thick outer wall. It is not known in what manner
this communal work is carried out, but it is interesting to note that the
cocoons assume to a considerable extent the hexagonal form of the cells in
the comb of the bee. Some doubt was expressed as to the interpretation put
on this structure by Curtis, but his observations have been confirmed by
Smith and Peckholt.
Several species of sawflies are known to be very injurious to crops. One of
these—the sawfly of the turnip, _Athalia spinarum_ (_centifoliae_
Panz.)—sometimes commits excessive depredations on the turnip crops in this
country as well as on the continent of Europe; its life-history and anatomy
were described by Newport {516}in an essay published by the Entomological
Society in 1838. The eggs, it appears, are laid singly at the edges of the
leaves in the month of May, as many as 200 or 300 being deposited by one
female; as the parent flies are usually gregarious, appearing in large
numbers in fields of turnips, it is not difficult to form an idea of the
serious nature of their depredations. The egg grows very considerably; the
development of the embryo is rapid, occupying, even in unfavourable
weather, only seven or eight days, while in quite congenial circumstances
it is probable that the eggs may hatch about the fourth day after their
deposition. The young grub immediately begins to feed, and in about five
days changes its skin for the first time; it repeats this operation twice
at similar or slightly longer intervals, the third moult thus occurring
when the larva is three or four weeks old; it is then that the larva begins
to be most destructive. Sunshine and warm weather are very favourable to
it, and under their influence it grows so rapidly that in a few days a
field may be almost completely stripped of its foliage. This larva is of a
sooty black colour, and will live on other Cruciferous plants quite as well
as on the turnip. When full grown it buries itself to a slight depth under
the surface of the earth, and forms an oval cocoon of a firm texture, and
with many particles of earth closely adherent to it. The perfect fly
emerges towards the end of July, and a second brood will be produced in the
same season if circumstances are favourable; in that case the resulting
larvae enter the ground for the formation of their cocoons in September or
October, and pass the winter in their cocoons, but still in the larval
state; changing to pupae in the following spring, and appearing as perfect
Insects in May. From this account it appears not improbable that the
offspring of a single female existing in the April of one year may amount
by the following May—three generations having been passed through in the
interval—to as many as 27,000,000 larvae. Fortunately the creatures are, as
Frauenfeld observed, destroyed in very large numbers by a parasitic fungus
and by a Nematode (_Filaria_).
We have, earlier in the chapter, alluded to the fact that the phenomena of
parthenogenesis prevail somewhat extensively among sawflies. It is the rule
in the family that males are very much less numerous than females, and
there are some species of which no males have been discovered. This would
not be of {517}itself certain evidence of the occurrence of
parthenogenesis, but this has been placed beyond doubt by taking females
bred in confinement, obtaining unfertilised eggs from them, and rearing the
larvae produced from the eggs. This has been done by numerous observers
with curious results. In many cases the parthenogenetic progeny, or a
portion of it, dies without attaining full maturity. This may or may not be
due to constitutional weakness arising from the parthenogenetic state.
Cameron, who has made extensive observations on this subject, thinks that
the parthenogenesis does involve constitutional weakness, fewer of the
parthenogenetic young reaching maturity. This he suggests may be
compensated for—when the parthenogenetic progeny is all of the female
sex—by the fact that all those that grow up are producers of eggs. In many
cases the parthenogenetic young of Tenthredinidae are of the male sex, and
sometimes the abnormal progeny is of both sexes. In the case of one
species—the common currant sawfly, _Nematus ribesii_—the parthenogenetic
progeny is nearly, but not quite, always, entirely of the male sex; this
has been ascertained again and again, and it is impossible in these cases
to suggest any advantage to the species to compensate for constitutional
parthenogenetic weakness. On the whole, it appears most probable that the
parthenogenesis, and the special sex produced by it, whether male or
female, are due to physiological conditions of which we know little, and
that the species continue in spite of the parthenogenesis, rather than
profit by it. It is worthy of remark that one of the species in which
parthenogenesis with production of males occurs—_Nematus ribesii_—is
perhaps the most abundant of sawflies.
Although many kinds of Insects display the greatest solicitude and
ingenuity in providing proper receptacles for their eggs, and in storing
food for the young that will be produced, there are extremely few that
display any further interest in their descendants; probably, indeed, the
majority of Insects die before the eggs are hatched, one generation never
seeing the individuals of another. It is therefore interesting to find that
a fairly well authenticated case of maternal attachment, such as we have
previously alluded to as occurring in earwigs, has been recorded in _Perga
lewisii_, an Australian sawfly of the sub-family Cimbicides. The mother,
having deposited about eighty eggs on the leaf of a Eucalyptus, remains
with them until they hatch, {518}after which she sits over her brood with
outstretched legs, and with admirable perseverance protects them, so far as
she is able, from the attacks of parasites and other enemies; she quite
refuses to be driven away from her charges. Mr. Lewis, to whom we are
indebted for this account,[427] states that the sawfly does not recognise
her own special brood, but will give equal attention to another brood if
she be transferred thereto; and he adds that many of the batches of larvae
were destitute of any maternal guardian.
There are about 2000 species of sawflies known. A large majority of them
are found in the European and North American regions; still, a good many
are known to live in South America, and _Perga_—one of the genera of the
family containing many species of large size—is peculiar to the Australian
region. Although the family includes so many species, very few anomalies of
structure have been detected in it; one species, _Pompholyx dimorpha_
Freymuth, is described as being apterous in the female, and as having the
thorax curiously modified in its form. There are no very small Insects in
the family, and none over the middle size. Nearly 400 species have been
detected in Britain; this number could certainly be increased by
persevering researches. The palaeontological record has hitherto given only
a very meagre evidence about sawflies. Several species have been preserved
in amber, and three or four are known from Tertiary strata in Europe and
North America.
{519}CHAPTER XXIII
HYMENOPTERA PETIOLATA–PARASITIC HYMENOPTERA–CYNIPIDAE OR GALL-FLIES–
PROCTOTRYPIDAE–CHALCIDIDAE–ICHNEUMONIDAE–BRACONIDAE–STEPHANIDAE–
MEGALYRIDAE–EVANIIDAE–PELECINIDAE–TRIGONALIDAE.
We now pass to the consideration of the Hymenoptera of the sub-Order
Petiolata, or Apocrita, as they are styled by Brauer. We should make use of
the term Petioliventres, for it contrasts naturally by its termination with
Sessiliventres, were it not that the word is so uncouth that we think it
better to adopt the shorter and more euphonious expression, Petiolata.
The members of this sub-Order, without exception, have the hind body
connected with the thorax by means of a deep constriction, so that the base
of the abdomen (Fig. 336, B, _b_) is very narrow; the articulation between
the two parts is effected by means of a complex joint allowing great play,
and facilitating the operations of boring and stinging, processes that are
of extreme importance in the economy of the great majority of the species.
The petiole is sometimes extremely short, but it may be so long that it
appears like a stalk, at whose extremity is borne the remaining part of the
abdomen (Fig. 369). When the petiole is very short the abdomen reposes
close to the back of the thorax (Fig. 331, C), and in this case the abdomen
is usually described as sessile; while, when it is evidently stalked, it is
said to be petiolate. These terms are, however, unsuitable, as the words
sessile and petiolate should be reserved for the conditions characteristic
of the two sub-Orders. We shall therefore use the terms pseudo-sessile and
pedicellate for the two conditions of the Petiolata.
The Hymenoptera Petiolata comprises an enormous majority {520}of the Order.
Although it includes many of the most interesting and important of Insects,
its classification is but little advanced, for a great many of the forms
are still rare or unknown. Three series may be adopted for the purposes of
nomenclature.
1. _Parasitica._—Trochanters of two pieces, female with an ovipositor.
2. _Tubulifera._—Trochanters undivided; abdomen consisting of only three,
four, or five visible segments.
3. _Aculeata._—Trochanters undivided; abdomen consisting of six or seven
visible segments; female furnished with a retractile sting.
In the absence of any clear distinction between sting and ovipositor, these
groups are merely conventional. The character furnished by the trochanters
is unfortunately subject to some exceptions, there being a few parasitic
forms in which the trochanters are not divided, and a few aculeates in
which the reverse is more or less distinctly the case; moreover, the
division, when it exists, is in some cases obscure, and the two pieces are
of unequal size. Ratzeburg calls the upper division, which is frequently
much larger than the other, the trochanter, and the lower division the
apophysis. There is much reason for believing that the apophysis is really
merely a secondary division of the femur. The Tubulifera are a
comparatively small group, and will probably be merged in one of the other
two, when the anatomy and morphology of the abdomen have been more
thoroughly elucidated.
[Illustration: FIG. 345.—Divided (ditrochous) trochanter of an Ichneumon:
_a_, coxa; _b_, the two divisions of the trochanter; _c_, femur. (For
monotrochous trochanter see Fig. 335, A, _c_.)]
HYMENOPTERA PARASITICA OR TEREBRANTIA.
This is one of the most extensive divisions of the class Insecta. There can
be little doubt that it contains 200,000 species, and possibly the number
may be very much greater than this. It is, however, one of the most
neglected of the great groups of Insects, though it is perhaps of greater
economic importance to mankind than any other.
{521}Insects derive their sustenance primarily from the vegetable kingdom.
So great and rapid are the powers of assimilation of the Insect, so
prodigious its capacity for multiplication, that the Mammal would not be
able to compete with it were it not that the great horde of six-legged
creatures has divided itself into two armies, one of which destroys the
other. The parasitic Hymenoptera are chiefly occupied in destroying the
tribes of vegetarian Insects; the parasites do this by the simple and
efficient device of dwelling in the bodies of their hosts and appropriating
the nutriment the latter take in. The parasites do not, as a rule, eat the
structures of their host,—many of them, indeed, have no organs that would
enable them to do this,—but they absorb the vegetable juices that, in a
more or less altered state, form the lymph or so-called blood of the host.
The host could perhaps starve out his enemies by a judicious system of
abstention from food; instead, however, of doing this, he adopts the
suicidal policy of persistent eating, and as the result of his exertions,
furnishes sufficient food to his parasites, and then dies himself,
indirectly starved. Ratzeburg considers that the traditional view that the
larvae of parasitic Hymenoptera live by eating the fat-body of their host
is erroneous. They imbibe, he considers, the liquid that fills the body of
the parasitised Insect.[428]
The wide prevalence of Insect parasitism is appreciated only by
entomologists. The destructive winter moth—_Cheimatobia brumata_—is known
to be subject to the attacks of sixty-three species of Hymenopterous
parasites. So abundant are these latter that late in the autumn it is not
infrequently the case that the majority of caterpillars contain these
destroyers. Although Lepidoptera are very favourite objects with parasitic
Hymenoptera, yet other Insects are also pertinaciously attacked; there is
quite a host of Insect creatures that obtain their sustenance by living
inside the tiny Aphididae, or "green-flies," that so much annoy the
gardener. A still larger number of parasites attack eggs of Insects, one or
more individuals finding sufficient sustenance for growth and development
inside another Insect's egg. As Insects have attacked Insects, so have
parasites attacked parasites, and the phenomena called hyperparasitism have
been developed. These cases of secondary parasitism, in which another
{522}species attacks a primary parasite, are extremely numerous. It is also
pretty certain that tertiary parasitism occurs, and Riley is of opinion
that even quaternary destruction is not outside the range of probability.
The physiological problems connected with Insect parasitism are of great
interest to the entomologist; the modes of nutrition and respiration of
these encaged creatures could not fail to be most instructive were we fully
acquainted with them. It is obvious that when an Insect-egg is laid inside
another Insect's egg, and the parasite has to undergo the whole of its
growth therein, it is in the strangest condition as regards nutrition. It
is unnecessary for the intruded egg to have yolk of its own; moreover, the
embryonic mode of nutrition may be continued during what would, with other
Insects, be the larval period. And it seems to be the case that both these
conditions are actually met with in the lives of egg-parasites. The
embryology and post-embryonic development of parasitic Hymenoptera have
already been ascertained to be of the most extraordinary nature. Great
variety, however, will no doubt be found to exist, as will be readily
understood if we tabulate the conditions of the early life of various
parasitic Hymenoptera.
1. The egg may be laid outside a larva, and the embryonic and larval
developments may both be passed on the exterior.
2. The egg may be laid and the embryonic development passed through,
outside the host, but the parasite on hatching may enter the host, so that
the post-embryonic development is passed in the lymph of the host.
3. The egg may be laid inside the host, both embryonic and post-embryonic
developments being gone through in the fluids of the host.
4. The egg may be laid inside another egg, the embryonic and post-embryonic
developments being passed therein.
We shall find that all these conditions exist in the Insects we are about
to consider.
We shall treat the series as composed of ten families; but we must remind
the student that this great subject is still in a very unadvanced state;
the combined efforts of generations of naturalists will be required to
perfect it. Of the ten families five are comparatively insignificant in
number of species. Many of the Cynipidae are not parasitic in habits, but
live in galls. {523}After what we have said as to the mode of nutrition of
parasites it will be understood that the physiological conditions of life
may not be so different in a gall-dweller and a parasite as would at first
be supposed; and it is perhaps not a matter for much surprise that good
characters cannot be found to separate the gallicolous from the parasitic
forms.
FAM. I. CYNIPIDAE—GALL-FLIES.
_Wings with very few cells, with no dark patch (stigma) on the anterior
margin; pronotum fixed to the mesonotum, and at each side extending back
to the point of insertion of the front wing. Antennae not elbowed but
straight, composed of a moderate number (12-15) of joints. Early stages
passed either in galls or as parasites in the bodies of other Insects._
[Illustration: FIG. 346.—_Neuroterus lenticularis._ Britain.]
The Cynipidae are always small, frequently minute, Insects; usually black
or pitchy in colour. The simple structure of the antennae and the number of
their joints are of importance as an aid in identifying a Cynipid. The
mesonotum is usually remarkably convex, and has, behind, a prominent
scutellum, which more or less overhangs the small metanotum and the median
segment; these are perpendicular in their direction; the sculpture of these
posterior parts of the alitrunk is usually deep and remarkable. The abdomen
has usually only a short petiole, so as to be pseudo-sessile; but there are
some genera in which this part is rather long. The abdomen is generally so
very much changed in outer form that its structure is not easily
understood. The visible portion is frequently in larger part made up of the
greatly enlarged dorsal plate of the second or third segment, or of both.
These large plates are really chiefly composed of free flaps, and on
lifting them up the large ventral plates are disclosed, although these
appeared previously to be nearly or quite absent. In the female {524}there
is a very slender ovipositor, of which only a small part protrudes,
although the organ is really elongate; it is drawn into the abdomen by
means of a peculiar series of structures, the modified terminal segments to
which it is attached being folded over into the interior of the body in
such a way that the posterior part becomes situated anteriorly. In
conformity with this arrangement, the ovipositor is bent double on itself,
the anterior and the middle portions of the borer being carried into the
body, leaving only a small part projecting beyond the extremity. The
Cynipid ovipositor is an instrument of much delicacy, and is capable of a
great deal of movement; it is usually serrate just at the tip, and although
it looks so very different from the cutting apparatus of the sawflies (Fig.
344), it seems that it is really composed of pieces similar in their origin
to those of the Tenthredinidae.
[Illustration: FIG. 347.—Ovipositor of _Neuroterus laeviusculus_. (After
Adler.) _a_, _a_, The ovipositor partially coiled; _b_, extremity of
posterior plate; _c_, _c_, muscles.]
The wings frequently bear fine hairs; the paucity of nervures and the
absence of the "stigma" are of importance in the definition of the family.
The most important of the cells is one called the radial cell, situate just
beyond the middle of the front part of the wing.
We cannot enter into a consideration of the classification of the family,
as authorities are not agreed on the subject.[429] As regards their habits
Cynipidae are, however, of three different kinds: (1) the true gall-flies,
or Psenides, which lay an egg or eggs in the tissues of a growing plant, in
the interior of which the larva lives after it is hatched; this mode of
life may or may not, according to the species, be accompanied by formation
of a peculiar growth called a gall: (2) Inquilines,[430] or guest-flies;
{525}these lay their eggs in the galls formed by the gall-makers subsequent
to the growth of the galls, of which they obtain the benefit: (3)
Parasites; these live, like most Ichneumon-flies, in the interior of the
bodies of other living Insects; they prey on a considerable variety of
Insects, but chiefly, it is believed, on Aphididae, or on Dipterous larvae.
These parasitic flies belong to the sub-family Figitides.
A great deal of discussion has occurred relative to the nature and origin
of galls, and many points still remain obscure. Considerable light has been
thrown on the subject by the direct observations of modern naturalists.
Previous to Malpighi, who wrote on the subject two hundred years ago, it
was supposed that galls were entirely vegetable productions, and that the
maggots found in them were due to spontaneous generation, it having been an
article of belief in the Middle Ages that maggots in general arose from the
various organic substances in which they were found, by means of the
hypothetical process called, as we have said, spontaneous generation.
Malpighi was aware of the unsatisfactory nature of such a belief, and
having found by observation that galls arose from the punctures of Insects,
he came to the further conclusion that the growth of the gall was due to
the injection by the Insect into the plant of a fluid he termed Ichor,
which had, he considered, the effect of producing a swelling in the plant,
something in the same way as the sting of a bee or wasp produces a swelling
in an animal. Réaumur also made observations on the gall-Insects, and came
to the conclusion that the latter part of Malpighi's views was erroneous,
and that the swelling was not due to any fluid, but simply to irritation
caused by the prick; this irritation being kept up by the egg that was
deposited and by the subsequent development of the larva. Observations
since the time of Réaumur have shown that the matter is not quite so simple
as he supposed, for though in the case of some galls the development of the
gall commences immediately after the introduction of the egg, yet in other
cases, as in the Cynipidae, it does not occur till some time thereafter,
being delayed even until after the hatching of the egg and the commencement
of the development of the larva. Galls are originated {526}by a great
variety of Insects, as well as by mites, on many plants; and it must not be
concluded that a gall has been formed by Hymenoptera even when these
Insects are reared from one. Extremely curious galls are formed by
scale-Insects of the sub-family Brachyscelides on Eucalyptus trees in
Australia; they are much inhabited by parasitic Hymenoptera, and Froggatt
has obtained 100 specimens of a small black Chalcid from a single dead
Brachyscelid.[431] The exact manner in which many of these galls originate
is not yet sufficiently ascertained; but the subject of the galls resulting
from the actions of Cynipidae has received special attention, and we are
now able to form a conception of their nature. They are produced by the
meristematic or dividing tissue of plants, and frequently in the cambium
zone, which is caused to develop to an unusual extent, and in a more or
less abnormal manner, by the presence of the Insect. The exact way in which
a Cynipid affects the plant is perhaps not conclusively settled, and may be
found to differ in the cases of different Cynipidae, but the view advocated
by Adler and others, and recently stated by Riley,[432] seems satisfactory;
it is to the effect that the activity of the larva probably affects the
meristem, by means of a secretion exuded by the larva. The mere presence of
the egg does not suffice to give rise to the gall, for the egg may be
deposited months before the gall begins to form. It is for the same reason
improbable that a fluid injected by the parent fly determines the gall's
growth. It is true that the parent fly does exude a liquid during the act
of oviposition, but this is believed to be merely of a lubricant nature,
and not to influence the development. It is said that the gall begins to
form in some cases before the larva is actually hatched, but the eggs of
some Hymenoptera exhibit remarkable phenomena of growth, so that the egg,
even during development of the embryo in it, may in these cases, exert an
influence on the meristem. It is to reactions between the physiological
processes of the meristem and the growing Insect that the gall and its form
are due.
The investigations of several recent naturalists lend support to the view
that only the meristematic cells of the plant can give rise to a gall.
Riley says that the rate of growth of the gall is dependent on the activity
of the meristem, galls on {527}catkins developing the most quickly; those
forming on young leaves also grow with rapidity, while galls formed on bark
or roots may take months to attain their full size.
[Illustration: FIG. 348.—Bedeguar on rose, cut across to show the cells of
the larvae; in some of the cells larvae are seen.]
It is a curious fact that Cynipid galls are formed chiefly on oaks, this
kind of tree supplying a surprising number and variety of galls. The plants
that furnish Cynipid galls in Europe are not numerous. A list of them is
given by Cameron.[433] Several species, of the genus _Rhodites_, attack
rose-bushes. One of the best known of our British galls is the bedeguar,
found in various parts of the country on both wild and cultivated
rose-bushes (Fig. 348), and caused by _Rhodites rosae_ (Fig. 349). This
gall has the appearance of arising from a twig or stem, but it is really a
leaf gall. Pazlavsky[434] has described the mode of formation of the
bedeguar. The female _Rhodites_ in the spring selects a rose-bud—not a
flower-bud—that should produce a twig and leaves, and pricks this bud in a
systematic manner in three places. The three spots of the bud pricked by
the Insect are the three undeveloped leaves that correspond to a complete
cycle in the phyllotaxis of the plant. The three rudiments do not develop
into leaves, but by a changed mode of growth give rise to the bedeguar.
Usually this gall, as shown in our figure, is of large size, and contains
numerous cells; but abortive specimens are not infrequently met with;
sometimes a small one is seated on a rose-leaf, and it is thought that
these are due to a failure on the part of the Insect to complete the
pricking operation. {528}Cynipidae will not go through their gall-making
operations except under natural conditions. Giraud[435] attempted to obtain
oviposition, on gathered twigs of oak, from flies in confinement; but,
although he experimented with thousands of specimens, they on no occasion
laid their eggs in the fresh shoots placed at their disposal, but
discharged their eggs in little heaps, without attention to the twigs. The
same observer has also called attention to the fact that after being
deposited in a bud the eggs of certain species of _Cynips_ will remain
dormant without producing, so far as can be seen, any effect on the tree
for a period of fully ten months, but when the bud begins to develop and
the egg hatches then the gall grows.
[Illustration: FIG. 349.—_Rhodites rosae_, female. Cambridge.]
The exact mode in which the egg is brought to the requisite spot in the
plant is still uncertain. The path traversed by the ovipositor in the plant
is sometimes of considerable length, and far from straight; in some cases
before it actually pierces the tissues, the organ is thrust between scales
or through fissures, so that the terebra, or boring part of the ovipositor,
when it reaches the minute seam of cambium, is variously curved and flexed.
Now as the canal in its interior is of extreme tenuity, and frequently of
great length, it must be a very difficult matter for the egg to reach the
tissue where it should develop. The eggs of Cynipidae are very remarkable
bodies; they are very ductile, and consist of a head, and of a stalk that
in some cases is five or six times as long as the head, and is itself
somewhat enlarged at the opposite end. Some other Hymenoptera have also
stalked eggs of a similar kind (Fig. 357, A, egg of _Leucospis_). It has
been thought that this remarkable shape permits of the contents of the egg
being transferred for a time to the narrower parts, and thus allows the
broader portion of the egg to be temporarily compressed, and the whole
structure to be passed through a very narrow canal or orifice. It is,
however, very doubtful whether {529}the egg really passes along the canal
of the borer. Hartig thought that it did so, and Riley supports this view
to a limited extent. Adler, however, is of a different opinion, and
considers that the egg travels in larger part outside the terebra. It
should be remembered that the ovipositor is really composed of several
appendages that are developed from the outside of the body; thus the
external orifice of the body is morphologically at the base of the borer,
the several parts of which are in longitudinal apposition. Hence there is
nothing that would render the view of the egg leaving the ovipositor at the
base improbable, and Adler supposes that it actually does so, the thin end
being retained between the divisions of the terebra. Riley is of opinion
that the act of oviposition in these Insects follows no uniform system. He
has observed that in the case of _Callirhytis clavula_, ovipositing in the
buds of _Quercus alba_, the eggs are inserted by the egg-stalk into the
substance of the leaf, and that the egg-fluids are at first gathered in the
posterior end, which is not inserted. "The fluids are then gradually
absorbed from this exposed portion into the inserted portion of the egg,
and by the time the young leaves have formed the exposed [parts of the]
shells are empty, the thread-like stalk has disappeared, and the
egg-contents are all contained within the leaf tissue." He has also
observed that in _Biorhiza nigra_ the pedicel, or stalk, only is inserted
in the embryonic leaf-tissue, and that the enlarged portion or egg-body is
at first external. The same naturalist also records that in the case of a
small inquiline species, _Ceroptres politus_, the pedicel of the egg is
very short, and in this case the egg is thrust down into the puncture made
by the borer, so that the egg is entirely covered.
Some Cynipidae bore a large number of the channels for their eggs before
depositing any of the latter, and it would appear that it is the rule that
the boring of the channel is an act separate from that of actual
oviposition. Adler distinguishes three stages: (1) boring of the canal; (2)
the passage of the egg from the base of the ovipositor, where the egg-stalk
is pinched between the two spiculae and the egg is pushed along the
ovipositor; (3) after the point of the ovipositor is withdrawn, the
egg-body enters the pierced canal, and is pushed forward by the ovipositor
until it reaches the bottom.[436]
{530}About fifty years ago Hartig reared large numbers of certain species
of gall-flies from their galls, obtaining from 28,000 galls of _Cynips
disticha_ about 10,000 flies, and from galls of _C. folii_ 3000 or 4000
examples of this species; he found that all the individuals were females.
His observations were subsequently abundantly confirmed by other
naturalists, among whom we may mention Frederick Smith in our own country,
who made in vain repeated attempts to obtain males of the species of the
genus _Cynips_. On one occasion he collected in the South of England 4410
galls of _C. kollari_ (at that time called _C. lignicola_), and from these
he obtained 1562 flies, all of which were females. A second effort was
attended with similar results. Hartig, writing in 1843, after many years'
experience, stated that though he was acquainted with twenty-eight species
of the genus _Cynips_, he had not seen a male of any one of them. During
the course of these futile attempts it was, however, seen that a possible
source of fallacy existed in the fact that the Insects were reared from
collected galls; and these being similar to one another, it was possible
that the males might inhabit some different gall. Adler endeavoured to put
the questions thus raised to the test by means of rearing females from
galls, and then getting these females to produce, parthenogenetically,
galls on small oaks planted in pots, and thus completely under control. He
was quite successful in carrying out his project, and in doing so he made a
most extraordinary discovery, viz. that the galls produced by these
parthenogenetic females on his potted oaks, were quite different from the
galls from which the flies themselves were reared, and were, in fact, galls
that gave rise to a fly that had been previously considered a distinct
species; and of this form both sexes were produced. Adler's observations
have been confirmed by other naturalists, and thus the occurrence of
alternation of generations, one of the two generations being
parthenogenetic, has been thoroughly established in Cynipidae. We may
mention one case as illustrative. A gall-fly called _Chilaspis lowii_ is
produced from galls on oak-leaves at Vienna at the end of April, both sexes
occurring. The female thereafter lays eggs on the ribs of the leaves of the
same kind of oak, and thus produces a different gall from that which
nourished herself. These galls fall off with the leaves in the autumn, and
in July or August of the following year a gall-fly is produced from them.
It is a different creature from the {531}mother, and was previously known
to entomologists under the name of _Chilaspis nitida_. Only females of it
occur, and these parthenogenetic individuals lay their eggs in the young
buds of the oak that are already present in the autumn, and in the
following spring, when the buds open and the leaves develop, those that
have had an egg laid in them produce a gall from which _Chilaspis lowii_
emerges in April or May. In this case therefore the cycle of the two
generations extends over two years, the generation that takes the greater
part of the time for its production consisting only of females. Adler's
observations showed that, though in some species this alternation of
generations was accompanied by parthenogenesis in one part of the cycle,
yet in other species this was not the case. He found, for instance, that
some gall-flies of the genus _Aphilothrix_ produced a series of generations
the individuals of which were similar to one another, and were all females
and parthenogenetic. In some species of the old genus _Cynips_ no males are
even yet known to occur. A very curious observation was made by the
American, Walsh, viz. that of galls gathered by him quite similar to one
another, some produced speedily a number of both sexes of _Cynips
spongifica_, while much later on in the season the remainder of the galls
gave rise to females only of an Insect called _Cynips aciculata_. It is
believed that the galls gathered by Walsh[437] were really all one species;
so that parts of the same generation emerge at different times and in two
distinct forms, one of them parthenogenetic, the other consisting of two
sexes. It has, however, been suggested that _Cynips spongifica_ and _C.
aciculata_ may be two distinct species, producing quite similar galls.
Turning now to the questions connected with inquiline or guest-flies, we
may commence with drawing attention to the great practical difficulties
that surround the investigation of this subject. If we open a number of
specimens of any kind of gall it is probable that several kinds of larvae
will be found. In Fig. 350 we represent four kinds of larvae that were
taken out of a few bedeguar galls gathered on one day in a lane near
Cambridge. It is pretty certain that No. 1 in this figure represents the
larva of _Rhodites rosae_, and that Nos. 2 and 3 are larvae of inquilines,
possibly of _Synergus_, or of a parasite; while No. 4, which was engaged in
feeding on No. 3 in the position {532}shown, is possibly a Chalcid of the
genus _Monodontomerus_, or may be _Callimome bedeguaris_. It is clear that,
as we cannot ascertain what is inside a gall without opening it, and
thereby killing the tenants, it is a most difficult matter to identify the
larvae; the only safe method is that of observation of the act of
oviposition; this may be supplemented by rearing the flies from galls, so
as to ascertain what variety of flies are associated with each kind of
gall. This last point has been well attended to; but the number of cases in
which oviposition of inquiline gall-flies in the galls formed by the
Psenides has been ascertained by direct observation is still very small;
they are, however, sufficient to show that the inquilines deposit their
eggs only after the galls are formed.
[Illustration: FIG. 350.—Larvae inhabiting bedeguar gall at Cambridge. 1,
_Rhodites rosae_ in cell; 2 and 3, larvae of inquilines; 4, larva of a
parasitic Hymenopteron.]
Bassett recorded the first case of the kind in connexion with a North
American species, _Cynips_ (_Ceroptres_) _quercus-arbos_ Fitch. He says:
"On the first of June galls on _Quercus ilicifolia_ had reached their full
size, but were still tender, quite like the young shoots of which they
formed part. Examining them on that day, I discovered on them two
gall-flies, which I succeeded in taking. They were females, and the
ovipositor of each was inserted into the gall so deeply that they could not
readily free themselves, and they were removed by force."
The great resemblance of the inquiline gall-fly to the fly that makes the
gall both dwell in, has been several times noticed by Osten Sacken, who
says "one of the most curious circumstances connected with the history of
two North American blackberry galls is, that besides the _Diastrophus_,
which apparently is the genuine originator of the gall, they produce
another gall-fly, no doubt an inquiline, belonging to the genus _Aulax_,
and showing the most striking resemblance in size, colouring, and sculpture
to the _Diastrophus_, their companion. The one is the very counterpart
{533}of the other, hardly showing any differences, except the strictly
generic characters! This seems to be one of those curious instances, so
frequent in entomology, of the resemblance between parasites and their
hosts! By rearing a considerable number of galls of _D. nebulosus_ I
obtained this species as well as its parasite almost in equal numbers. By
cutting some of the galls open I ascertained that a single specimen of the
gall frequently contained both species, thus setting aside a possible doubt
whether these Insects are not produced by two different, although closely
similar galls."[438]
The substance of which galls are composed, or rather, perhaps, a juice they
afford, is apparently a most suitable pabulum for the support of Insect
life, and is eagerly sought after by a variety of Insects; hence by
collecting galls in large quantities many species of Insects may be reared
from them; indeed by this means as many as thirty different kinds of
Insects, and belonging to all, or nearly all, the Orders, have been
obtained from a single species of gall. Some galls are sought by birds,
which open them and extract their tenants, even in cases where it might be
supposed that the nauseous flavour of the galls would forbid such
proceedings.
Not more than 500 species of Psenides and Inquiline Cynipidae are known
from all parts of the world; and of described Parasitic Cynipidae there are
only about 150 species. The British forms have recently been treated by
Cameron in the work we have already several times referred to.[439]
A few Cynipidae have been found in amber; and remains of members of the
family, as well as some galls, are said by Scudder to have been found in
the Tertiary strata at Florissant.
FAM. II. PROCTOTRYPIDAE, OR OXYURA.
_Small Hymenoptera, with few, or even no, nervures in the wings: the
pronotum closely adherent to the mesothorax, and at the sides reaching
backwards to the points of insertion of the wings. The abdomen is
pointed, and the pointed apex is frequently deflexed; the ovipositor is
not coiled, but is retractile, and when extruded is of tubular form, and
{534}apparently a continuation of the tip of the body. The earlier stages
are passed in the bodies, or in the eggs, of other Arthropods._
[Illustration: FIG. 351.—_Helorus anomalipes_. Britain.]
The Proctotrypidae is one of the most difficult groups of Hymenoptera to
define; some of its members exhibit a great resemblance to Aculeate
Hymenoptera. This is the case with the Insect we figure (Fig. 351). It,
however, is an undoubted Proctotrypid, but there are other forms that
approach very closely in appearance to the Aculeata, or stinging
Hymenoptera; so that until a better comprehension is reached as to the
distinction between a sting and an ovipositor the separation between
Proctotrypidae and Aculeata must be considered somewhat arbitrary.
There is extreme variety in the family; the wings differ considerably in
shape and neuration; they are not infrequently altogether absent in one or
both sexes. The chief distinction of the family from other parasitic
Hymenoptera is the tubular form of the ovipositor; which part appears to be
a continuation of the tip of the body. This latter is more definitely
acuminate than usual, and has given rise to the term Oxyura, by which name
the Proctotrypidae are distinguished in many books. From the Chalcididae
they are distinguished also by the angles of the pronotum attaining the
tegulae. In this character they agree with the Cynipidae, but the
ovipositor and abdomen are very different in form in these two groups, and
the Proctotrypidae very frequently have a pigmented spot or stigma on the
front wings which is absent in Cynipidae. As if to add to the difficulties
the systematist meets with in dealing with this family, some of its members
have the trochanters undivided, as in the case of the stinging Hymenoptera.
The larvae of all that are known lead a completely parasitic life in the
bodies or eggs of other Insects or of Spiders. Sometimes half a dozen
specimens may find the means of subsistence during the whole of their
development in a single Insect's egg. Usually Proctotrypids pupate in
{535}the position in which they have fed up, enclosed each one in a more or
less distinct cocoon. In Fig. 352 we represent a very remarkable case of
Proctotrypid pupation; a larva of some beetle has nourished many specimens
of a species of the genus _Proctotrypes_, and the pupae thereof project
from the body of the host, a pair of the parasites issuing from each
segmental division in a remarkably symmetrical manner.
[Illustration: FIG. 352.—Pupation of _Proctotrypes_ sp. in body of a beetle
larva.]
Comparatively little is known as to the habits of the members of this
family, but such information as has been obtained leads to the conclusion
that great variety will be found to exist in this respect. We have already
mentioned that numerous species have been ascertained to feed inside the
eggs of Insects or of Spiders; others have been reared from larvae or from
galls of the minute Dipterous midges of the family Cecidomyiidae; others
have been obtained from Cynipid galls, a few from ants' nests and from
green-fly; some species are known to attack Coleoptera. The distinguished
Irish entomologist, Haliday, has written an account of the proceedings of a
species of _Bethylus_,[440] from which it has been supposed that this
Insect carries off living caterpillars, and stores them in a suitable
receptacle as food for its progeny, thus anticipating, as it were, the
habits of the fossorial division of the Aculeata, in which group this
instinct has, as we shall subsequently relate, attained an astonishing
degree of perfection. Haliday's observation was unfortunately incomplete
and has not been subsequently confirmed. The Bethylides are remarkable for
their great approach in structure to the Aculeates, so much so that
entomologists are not agreed as to whether certain Insects are
Proctotrypids or Aculeates. _Pristocera_, with a very wide distribution,
may be mentioned as illustrative of these doubtful forms; but other genera
of the Bethylides are in many respects very similar to the Aculeates, and
it is not matter for surprise that Haliday should have considered the
Bethylides to be a tribe of the stinging Hymenoptera. {536}The genus
_Scleroderma_ consists of small Insects much resembling ants, and, as well
as some of its allies, is of great interest from the remarkable phenomena
of polymorphism presented by certain species. The males in this genus are
winged, the females completely apterous; yet at times winged females are
produced—as exceptional individuals in a brood of wingless specimens—the
females in these cases being not only winged, but possessed of ocelli like
the females of other winged Hymenoptera. Particulars of a case of this kind
have been given by Sir Sidney Saunders,[441] and Ashmead also mentions[442]
the exceptional occurrence of these winged females. Westwood[443] was of
opinion that there are three forms of the female sex. This subject is of
importance in connexion with the production of the various castes in ants.
Although the presence of wings in these Insects is always accompanied by
the existence of ocelli (which, it will be remembered, are normally absent
from the wingless individuals), yet the converse is not always the case,
for a form of the female of _Cephalonomia formiciformis_, without any
wings, yet having ocelli, as well as eyes, well developed, is figured by
Westwood.[444]
[Illustration: FIG. 353.—_Cyclops_ form of larva of _Platygaster_ sp.
(After Ganin.) _a_, Mouth; _b_, antenna; _c_, claw-limb; _d_, lower lip
(the pointing line is a little too short); _e_, doubtful "zapfenförmig"
organ; _f_, wing-like lobe; _g_, branch of the tail.]
The development of some of the Proctotrypids has been partially described
by Ganin and others, and is of an extraordinary character. Ganin's
observations[445] were most complete in the case of a species of
_Platygaster_, which he found in the larva of a very minute Dipteron of the
genus _Cecidomyia_. The _Platygaster_ larva changes its form very much in
the course of its life, resembling at first a minute Crustacean rather than
an Insect-larva; it has a very large rounded anterior portion, while behind
it terminates in two, or more, tail-like processes. By a {537}very peculiar
kind of metamorphosis this _Cyclops_-like larva changes into an almost
unsegmented, oviform larva, destitute of appendages; by a second change
this creature assumes a third condition, in which it is similar to the
ordinary form of parasitic Hymenopterous larvae. Sometimes several of the
_Platygaster_ larvae are found in a single host, but only one of them
reaches this third stage. Afterwards the third larval instar passes into
the pupal stage, which lasts five or six days, and then the perfect Insect
appears. It is worthy of remark that the internal organs undergo quite as
remarkable a change as the outer form does. The metamorphoses of some other
Proctotrypidae have been examined by Ganin, and appear to be of an equally
interesting character.[446]
There is reason to suppose that these _Platygaster_ parasites are of great
economic importance as well as of scientific interest, for _Platygaster
herrickii_ is one of the enemies of the larva of the destructive Hessian
fly, _Cecidomyia destructor_.
The _Proctotrypidae_ are no doubt extremely numerous in species, but as yet
they have been very little studied; a good work on the British species is
much required. A valuable contribution has recently been made to the study
of the family by Ashmead, in the book we have already referred to. This
volume includes much information on the natural history of these Insects,
and the outline figures give some idea of the great variety of external
form.
[Illustration: FIG. 354.—_Alaptus excisus_, Westwood. Britain. (Probable
size about ½ millim.)]
Many entomologists include the Mymarides in Proctotrypidae, but Ashmead
considers that they should be treated as a separate family. _Alaptus
excisus_ Westw. (Fig. 354) has been frequently said to be the smallest
known Insect, the {538}measurement given for it by Westwood[447] being a
length of ⅙ of a millimetre—about 1/150 of an inch. Mr. Enock has recently
examined Westwood's type in the Museum at Oxford, and from his information
we may conclude that this Insect is probably the same as _Alaptus fusculus_
Hal., and that the measurement mentioned by Westwood is erroneous, the
Insect being really about half a millimetre long. The Mymarides are,
however, very minute, some of them not exceeding one-third of a millimetre
in length. Whether any of them are smaller than the beetles of the family
Trichopterygidae, some of which are only one-fourth of a millimetre long,
may be doubted.
The Mymarides are recognisable by their very minute size, and by their
peculiar wings. These are slender, destitute of nervures, fringed with
long, delicate hairs, and stalked at the base. Probably Mymarides may all
prove to be dwellers in eggs of other Insects. The group is remarkable from
the fact that it contains some of the very few Hymenoptera with aquatic
habits. Two species were discovered in their winged condition in the water
of a pond near London by Sir John Lubbock[448]; one of them—_Polynema
natans_ Lubbock—probably, according to Mr. Enock, the same as _Caraphractus
cinctus_ Hal., uses its wings freely for swimming under water, while the
other—_Prestwichia aquatica_—performs this operation by the aid of its
legs. This latter Insect seems to be very anomalous, and its position quite
doubtful. The embryogeny of _Polynema_ is very peculiar, and takes place in
the egg of a dragon-fly—_Calepteryx virgo_—under water. According to
Ganin,[449] in the earliest stages the developments of the embryos of the
_Calepteryx_ and of the _Polynema_ progress simultaneously, but that of the
dragon-fly does not proceed beyond the formation of the ventral plate. The
_Polynema_ appears to leave its own egg at an extremely early stage of the
embryonic development. It would appear, in fact, that there is no definite
distinction between embryonic and larval stages. The information given by
Ganin leads to the conclusion that a complete study of this remarkable mode
of development is necessary before forming any general ideas as to the
nature of Insect embryogeny and metamorphosis.
{539}FAM. III. CHALCIDIDAE.
_Pronotum with some freedom of movement, its angles not extending to the
insertion of the front wings. Antennae elbowed, consisting of from seven
to thirteen joints. Wings without a system of cells; with a single
definite nervure proceeding from the base near the front margin, or
costa; afterwards passing to the costa, and giving off a very short vein
more or less thickened at its termination. The species are, with few
exceptions, of parasitic habits._
[Illustration: FIG. 355.—_Eurytoma abrotani_, male. Britain. Hyper-parasite
through _Microgaster_ of _Liparis dispar_, and according to Cameron,
parasite of _Rhodites rosae_ and other gall-flies in Britain, × 10. (After
Ratzeburg.)]
The Insects of this family—the Pteromalini of Ratzeburg—are frequently of
brilliant colours and of remarkable form; the species are very numerous,
some 4000 or more having already been described. Of this number nearly 3000
are European, and as there is good reason for supposing that Chalcididae
are quite as numerous in the Tropics and in the New World as they are in
Europe, the family will probably prove to be one of the largest in the
class. About twenty sub-families have already been proposed for the
classification of the group; they are based chiefly on the number of joints
in the tarsi, and the details of the antennae and of the ovipositor. This
latter exhibits great variety in external appearance, due chiefly to the
modification in form of the basal, or of the following ventral abdominal
plates, one or more of which may be prolonged and altered in form or
direction, giving rise in this way to considerable diversity in the shape
of the abdomen. Correlative with this is a great variety in the mode of
parasitism of the larva. Many live in galls, feeding on the larvae of the
makers of the galls or on those of the inquilines; others attack
caterpillars, others pupae only; some flourish at the expense of bees or
other Hymenoptera, or of Coccidae {540}and Aphididae, and some deposit
their eggs in the egg-cases of Blattidae. The details of the life-history
are well known in only a few cases.
[Illustration: FIG. 356.—_Leucospis gigas_, female. Gibraltar.]
The career of _Leucospis gigas_ has been investigated by Fabre, and
exhibits a very remarkable form of hypermetamorphosis.[450] This Insect is
of comparatively large size and of vivid colours, wasp-like, black
contrasting with yellow, as in the case of the wasps; and like these it has
the wings folded or doubled. The female bears a long ovipositor, which by a
peculiar modification is packed in a groove on the back of the Insect. This
species lives in Southern Europe at the expense of _Chalicodoma muraria_, a
mason-bee that forms cells of a hard cement for its nest, the cells being
placed together in masses of considerable size; each cell contains, or
rather should contain, a larva of the bee, and is closed by masonry, in the
construction of which the bee displays much ability. It is the mission of
the _Leucospis_ to penetrate the masonry by means of its ovipositor, and to
deposit an egg in the cell of the bee. The period chosen for this predatory
attack is the end of July or the beginning of August, at which time the
bee-larva is in the torpid and powerless condition that precedes its
assumption of the pupal state. The _Leucospis_, walking about leisurely and
circumspectly on the masonry of the nest, tests it repeatedly by touching
with the tips of the antennae, for it is most important that a proper spot
should be selected. The bee's cell is placed in a mass of solid masonry, a
considerable part—but a part only—of whose area is occupied by the group of
cells; every cell is closed by hard mortar, making an uneven surface, and
the face of the masonry is rendered more even by a layer of hardened clay
outside the rougher material; it is the task of the _Leucospis_ to detect a
suitable spot, in the apparently uniform external covering, and there to
effect the penetration so as to introduce an egg into a cell. By what
sensations the fly may be guided is unknown. After a spot has been selected
and the ovipositor brought into play, the masonry is ultimately pierced
{541}by patient work; sometimes a quarter of an hour is sufficient for the
purpose, but in other cases three hours of uninterrupted effort are
required before the end is attained. Fabre expended much time in watching
this operation, and after the Insect had completed it, he marked with a
pencil the exact spot of the masonry that was penetrated, and the date on
which it was done, and he states that he afterwards found that without any
exception a proper spot had been selected, and a cell consequently
penetrated. Admirable as the instinct of the parasite appears from this
point of view, it is nevertheless accompanied by a remarkable deficiency in
two other respects. The first is that though the spot selected by the
_Leucospis_ invariably gives entrance to a cell, yet in the majority of the
cases the selected cell is not a suitable one; a large number of the cells
of the _Chalicodoma_ are not occupied by living larvae on the point of
pupation—though in that case only can the egg of the _Leucospis_ hatch and
successfully develop—but by dead and shrivelled larvae, or by mouldy or
dried-up food. And yet, in each case of penetration, Fabre believes that an
egg is deposited, even though it may be impossible that it can undergo a
successful development. Strange as this may appear, it is nevertheless
rendered less improbable by the second deficiency in the instinct of the
parasite. The Insect has no power of recognising a cell that has been
previously pierced either by itself or by another of its species. One bee
larva can only supply nourishment for a single larva of the parasite, and
yet it is a common occurrence for a cell to be revisited, pierced again and
another egg introduced; indeed Fabre, by means of the cells he had marked,
was able to assure himself that it is no uncommon thing for this to be done
four times; four eggs, in fact, are sometimes deposited in a cell that
cannot by any possibility supply food for more than one larva. The egg of
the _Leucospis_ is a curious object (Fig. 357, A), very elongate oval, with
one end drawn out and bent so as to form a hook; it is not placed at random
in the cell of the bee, but is suspended on the delicate cocoon with which
the _Chalicodoma_ larva is surrounded at the period of pupation.
{542}[Illustration: FIG. 357.—_Leucospis gigas._ A, Egg; B, primary, C,
secondary larva. (After Fabre.)]
Fabre allowed sufficient time to elapse for the hatching of the larvae from
the eggs, and then opened some cells where Leucospis eggs had been
deposited, in order to obtain the larvae; when doing this he was surprised
that he never found more than one _Leucospis_ larva in a cell. Even in
cells where he had observed more than one act of oviposition, and which he
had marked at the time, only one larva existed. This induced him to think
that it was possible that no egg was deposited by the _Leucospis_ at the
second penetration. He accordingly examined cells soon after the eggs were
laid, and thus discovered some that contained more than one egg,—indeed in
one cell he observed no less than five eggs suspended from the cocoon of
the _Chalicodoma_; he was also able to demonstrate that eggs were actually
deposited in some cells that contained no means of support for the larva.
How then could these two facts be reconciled—four or five eggs deposited in
a cell, only one larva present afterwards? It is of course impossible to
observe the operations of a larva shrouded in the obscurity of a cell
formed of masonry, so he transferred some bee larvae with their destructive
companions to glass tubes, in which he was able to note what took place. He
found that the egg deposited by the _Leucospis_ hatches and produces a very
peculiar larva, having little resemblance to the _Leucospis_ larva that he
had found eating the _Chalicodoma_ larva. The primary larva (Fig. 357, B)
of the _Leucospis_ is an arched worm, moderately deeply segmented, a
millimetre or a little more in length, with a remarkably large and
abruptly-defined head. The body bears erect setae, the most remarkable of
which are a pair on the ventral aspect of each of the segments, each of
these ventral setae being borne on a small conical prominence. These
prominences and setae serve as ambulatory organs, and are supplemented in
their function by a protuberance at the posterior extremity. The little
creature has considerable powers of locomotion; it moves, after the fashion
of many other larvae, by contracting and arching the body so as to bring
the posterior part nearer to the anterior; then fixing the hinder part, the
anterior is extended and fixed, the posterior being again brought nearer to
the front. The _Leucospis_ larva when hatched does not at once attack the
bee larva which is to be its future food, but every few hours makes
excursions over its surface, and even explores the walls of the cell;
returning, however, always to the cocoon for repose. The object of these
{543}excursions is, Fabre believes, to ascertain if another _Leucospis_ egg
has been laid in the cell, and in that case to destroy it. For the food, as
we have said, being only enough for one larva, and the mother _Leucospis_
frequently laying more than one egg in a cell, it is necessary that all the
eggs except one should be destroyed. Fabre did not actually observe the act
of destruction, but he found repeatedly in his glass tubes that the
supernumerary eggs were destroyed, being, in fact, wounded by the mandibles
of the first-hatched larva. After several days of this wandering life the
tiny destroyer undergoes a first moult, changing its skin and appearing as
a very different creature (Fig. 357, C); it is now completely destitute of
any means of locomotion, very deeply segmented, curved at one extremity,
with a very small head, bearing extremely minute, scarcely perceptible,
mandibles. The sole object of its existence in this state is to extract the
contents of the _Chalicodoma_ larva, and appropriate this material to the
purposes of its own organisation. This it accomplishes not by wounding,
tearing, or destroying the larva, for that apparently would not answer the
purpose; the contents must be conveyed while still in their vital state to
itself; and this it effects by applying its mouth to the extremely delicate
skin of the victim, the contents of whose body then gradually pass to the
destroyer, without any visible destruction of the continuity of the
integument. Thus the _Leucospis_ larva gradually grows, while the bee larva
shrinks and shrivels, without, however, actually suffering death. The
process of emptying the bee larva apparently does not occupy the
_Leucospis_ more than two or three weeks, being completed by about the
middle of the month of August; afterwards the larva remains in the cell by
the side of the shrivelled skin of its victim for ten or eleven months, at
the end of which time it assumes the pupal condition, and very shortly
thereafter appears as a perfect Insect.
_Monodontomerus cupreus_ is another member of the Chalcididae that lives
parasitically at the expense of bees of the genus _Chalicodoma_. Its habits
have been sketched by Fabre,[451] and exhibit considerable difference from
those of _Leucospis_. It is much less in size, and can accommodate itself
to a greater variety of food; it will, in fact, eat not only the larva of
_Chalicodoma_, but also that of another bee, of the genus _Stelis_, that is
frequently found {544}shut up in the cell of the _Chalicodoma_, at whose
expense the _Stelis_ also lives parasitically. The _Monodontomerus_ bores a
hole through the masonry of the bee and deposits its eggs in the cell after
the fashion of the _Leucospis_; one bee larva is, however, sufficient food
for several individuals of the young of this smaller parasite. There is no
hypermetamorphosis, the early larval condition resembling the later. This
Insect attacks not only _Chalicodoma_ and _Stelis_, as already mentioned,
but also other bees; and a single larva of some of the larger kinds will
afford sufficient food for fifty young of the _Monodontomerus_. They feed
on the bee larva, as the _Leucospis_ does, without wounding it. This fly
has the power of recognising what is suitable provender for its young by
the use of the antennae, even when the conditions are so changed that it is
clear the sense of sight has nothing to do with the recognition. Fabre
relates that he had extracted a number of the bee larvae from their cells
of masonry, and that as they were lying on his table enclosed in their
cocoons, the _Monodontomerus_ recognised the latter as containing the
desired provender for its young by examining them with its antennae; after
which, without hesitation, the _Monodontomerus_ pierced the cocoon with its
ovipositor and deposited the eggs in a suitable position. This observation,
together with those made on _Leucospis_, seem to indicate that it is
neither by sight nor smell that these Insects discover the desired object,
but by some sense we do not understand, though its seat is clearly in the
antennae of the Insect.
Newport discovered a _Monodontomerus_, which he described as _M.
nitidus_,[452] in the cells of the bee _Anthophora retusa_, and
demonstrated that the alimentary canal, as is usual in Petiolate
Hymenoptera, is closed behind until the Insect is about to enter the pupal
state, when it becomes perforated and faecal matters are for the first time
passed from it. "These matters were composed of the refuse of digestion and
of epithelial cells accumulated during the period of feeding, and retained
in the digestive sac until the period of its perforation. In this way the
food and abode of the Insects are maintained pure and uncontaminated, and
the digestive apparatus is completed, and the refuse of nutrition ejected
only when the whole of the food has been consumed."
{545}In the cells of the same bee Newport discovered another curious
parasitic Chalcid, _Anthophorabia retusa_.[453] The male has short wings,
and the compound eye is replaced by an ocellus on each side of the head,
the female having fully developed wings and eyes. A variation may occur in
the metamorphosis of this Insect, inasmuch as when the growth is completed
during the month of August, the Insect changes to a pupa, the imago appears
ten or twelve days thereafter, and the perfect Insect then hibernates for
seven or eight months; but should the completion of growth be deferred till
after the end of August, hibernation takes place in the larval condition. A
large and brilliant Chalcid _Eucharis myrmeciae_, has been described by
Cameron as preying on the formidable Australian ants of the genus
_Myrmecia_.
The development of _Smicra clavipes_ has been partially described by
Henneguy.[454] This Insect lives in the interior of the aquatic larva of
_Stratiomys strigosa_, a Dipterous Insect. As many as fifty eggs of the
parasite are found in one larva, but a large number of embryos die during
development, so that he has never found more than two or three well-grown
larvae in one _Stratiomys_ larva. It has been ascertained that the eggs of
many of these parasitic Insects are deficient in yolk, and the ovum of
_Smicra_ is said to obtain the nutritive materials necessary for the
development of the embryo from the blood of its host by endosmosis. For a
long time after the assumption of the larval condition, the larva appears
to nourish itself only at the expense of the blood of its host. The
segmentation of the ovum is total, and a single embryonic membrane appears
at an early period, before the formation of the embryo, by a process very
different from that giving origin to the amnion of the majority of Insects.
A very interesting sketch of the development of _Encyrtus fuscicollis_ has
been given by Bugnion.[455] This small parasite passes its earlier stages
in the interior of the larva of _Hyponomeuta cognatella_ or other
Lepidoptera. The female _Encyrtus_ deposits her eggs in the interior of a
caterpillar, in the form of a series of 50 to 100 or more eggs enclosed in
a sac; the origin {546}of the sac is obscure, but the embryonic development
and the early part of the larval life are passed in the sac, which contains
a supply of nutritive matter. The larvae of the _Encyrtus_ are at first
entirely confined to this sac, but when they have consumed all the
nutritive matter in it, they leave it and pass the remainder of their
larval and pupal existence in the body-cavity of the caterpillar. They live
at first on the lymph (blood) of the Insect, and apparently do it no harm;
nevertheless the strength of the caterpillar is so much enfeebled that it
fails to undergo the transformation to a pupa; the parasites then devour
its interior, and use the empty skin as a nidus for their own pupation;
they form cocoons which divide the area into compartments. Usually the
individuals disclosed from one _Hyponomeuta_ are all of one sex, which may
be either male or female. Unfortunately the most interesting points of this
development, viz. the history of the common sac for the larvae, the nature
of the eggs, the earlier embryonic stages, and the nutriment in the sac,
are still without elucidation. The account given by Bugnion raises a great
desire for information on these points.
We have in a previous page described the remarkable mode of oviposition of
_Mantis_. Captain Xambeu[456] has made a very curious observation to the
effect that a minute Chalcid, _Podagrion (Palmon) pachymerus_, shelters
itself under the wings of the _Mantis_ so as to be in a position to
oviposit in the eggs of the latter when it shall be forming its peculiar
ootheca.
The genus _Isosoma_ consists of Insects that differ in habits from their
congeners, being phytophagous instead of parasitic. _I. tritici_ and _I.
hordei_ live in the stalks of corn, and in North America, where they are
known to the agriculturist as joint-worms, are frequently very injurious to
crops. They are sometimes obtained in large numbers without any males
appearing, and a wingless as well as a winged form of the female occurs.
Owing to the fact that the allies of these Insects are parasitic, it has
been frequently maintained that this may also prove to be the case with
_Isosoma_, but the observations of Riley[457] and others leave no doubt
that the Insects of this genus are really plant-feeders.
{547}Riley has called attention[458] to some facts in connection with _I.
tritici_ and _I. grande_, that make it clear that these two supposed
species are really alternate generations, and that both generations are
probably in larger part, if not entirely, parthenogenetic. Some species of
the genus _Megastigmus_ are known to be of phytophagous habits.[459]
[Illustration: FIG. 358.—_Blastophaga grossorum._ A, Male, × 22; B, female,
× 15. (After Mayer, _Mitt. Stat. Neapel_, iii. 1882.)]
The most interesting of all the forms of Chalcididae are perhaps those
called fig-Insects. A considerable number of species are now known, and
amongst them we meet with the unusual phenomenon of species with wingless
males, the females possessing the organs of flight normally developed. The
wingless males exhibit the strangest forms, and bear no resemblance
whatever to their more legitimately formed partners (Fig. 358, A, B). Many
of the fig-Insects belong to a special group called Agaonides. Others
belong to the group Torymides, which contains likewise many Chalcididae of
an ordinary kind; possibly some of these may be parasitic on the Agaonides.
Some of these Torymid fig-Insects have winged males, as is normal in the
family, but in other cases winged and wingless forms of the male of one
species may be present.
The most notorious of these fig-Insects is the one known as _Blastophaga
grossorum_ (Fig. 358), this being the chief agent in the custom known as
caprification of the cultivated fig-tree. This process has been practised
from time immemorial, and is at the present day still carried on in Italy
and the Grecian archipelago. The Greek writers who describe it say that the
wild fig-tree, though it does not ripen its own fruit, is absolutely
essential for the perfection of the fruit of the cultivated fig. In
accordance with this view, branches from the wild fig {548}are still
gathered at certain seasons and suspended amongst the branches of the
cultivated fig-trees. The young fig is a very remarkable vegetable
production, consisting of a hollow, fleshy receptacle, in which are placed
the extremely numerous and minute flowers, the only admission to which is
by a small orifice at the blunt end of the young fig; this orifice is lined
with projecting scales, that more or less completely fill it up or close
it; nevertheless inside this fruit the _Blastophaga grossorum_ develops in
large numbers. The males are, as we have seen, wingless creatures, and do
not leave the fruit in which they were bred, but the females make their way
out of the wild fig, and some of them, it is believed, enter the young
fruit of the cultivated trees and lay their eggs, or attempt to do so,
therein; and it has been supposed by various writers that these proceedings
are essential to the satisfactory development of the edible fruit. It is a
curious fact that the _Blastophaga_ develops very freely in the wild fig—so
much so, indeed, as to be a means of preventing it from coming to maturity;
but yet the Insect cannot complete its development in the cultivated fruit.
This is due to the fact that the fly must lay its egg in a particular part
of the fig-ovule, so that when the egg hatches the larva may have a proper
supply of food. In the cultivated fig the structure of the flower differs
somewhat from that of the caprificus, as the wild fig is called, and so the
egg, if deposited at all, does not reach a proper nidus for its
development. Hence the _Blastophaga_ can never live exclusively on the
cultivated fig, and if it be really necessary for the development of the
latter, must be brought thereto by means of the caprifig. Whether the
_Blastophaga_ be really of use, as has been for so long supposed, is,
however, a matter for doubt. The reasons for this are (1) that those who
think caprification beneficial do not agree as to the mode in which they
suppose it to be so; (2) that there is but little reason for believing that
when introduced amongst the cultivated figs the _Blastophaga_ occupies
itself to any great extent therewith; and (3) that in some parts of the
world caprification is not performed, but the cultivated fig nevertheless
ripens its fruit there. Hence many writers on the subject—
Solms-Laubach,[460] Mayer,[461] and Saunders[462]—entertain considerable
doubt as to whether caprification is at present anything {549}more than an
old custom destitute of practical utility. On the other hand, Riley
states[463] "that the perfect Smyrna fig, the most esteemed of the edible
species, can be produced only by the intervention of the _Blastophaga
psenes_ [_grossorum_]."
Although the questions connected with the effect the _Blastophaga_ is
supposed to produce on the fruit are of a botanical rather than a
entomological nature, we may briefly say that two views have been held: (1)
that, as in the fruit of the cultivated fig, only female flowers are
produced, the _Blastophaga_ is necessary for their fertilisation and the
subsequent development of the fruit; (2) that the Insects stimulate the fig
by biting parts thereof or by burrowing in it, and so give rise to the
processes that have as their result the edible fruit. There seems to be
little doubt that the Insect agency is necessary to the fertilisation of
some species of figs. Cunningham, who has recently carried out an elaborate
investigation as to the fertilisation of _Ficus roxburghii_,[464] concludes
that in this fig, and probably also in other kinds, the perfect development
is dependent on the access of the fig-Insects to the interior of the
receptacular cavity. Should access fail to occur, both male and female
flowers abort, without the formation of pollen grains by the former or
seeds by the latter. The access of the _Blastophaga_ is thus as necessary
for the perfect evolution of the normal male and female flowers as it is
for that of the modified ♀ or gall-flowers, with their contained ova and
Insect-embryos. Whether the successful fertilisation of the flowers is
really essential to the production of the edible fig is not a question for
our discussion.
Fig-Insects are apparently more numerous in South America than they are in
any other part of the world; and Fritz-Müller has discovered[465] a number
of species there of a very extraordinary character, several of them
possessing two forms of the male, one winged like the female, the other
wingless and so different in character that they were considered to belong
to a different genus. The wingless male of a species found in Madagascar,
_Kradibia_ _cowani_, has the peculiarity of possessing only four legs, the
middle pair being represented merely by minute two-jointed rudiments. Some
of these Insects live in galls on the figs. The fig-Insects {550}were
formerly considered to belong to the Proctotrypidae or to the Cynipidae
(gall-makers), but there can be no doubt, notwithstanding they differ so
much in their habits from the parasitic Chalcididae, that they probably
belong to the same family. If treated as different from Chalcididae, they
should be separated as a distinct family rather than united with the
Cynipidae.[466]
It is impossible for us to do more than allude to the extraordinary shapes
exhibited by some Chalcididae. The genus _Thoracantha_ is specially
remarkable in this respect. _T. latreillei_ is said to resemble a beetle of
the family Mordellidae, and has the wings concealed by false
wing-cases—really projections from the thorax—so that from above the Insect
bears no resemblance to the other Insects of the Order it really belongs
to.
[Illustration: FIG. 359.—_Thoracantha latreillei._ Bahia. A, Upper, B,
lateral aspect. (After Waterhouse.)]
Howard has called attention to some peculiarities in the pupation of
Chalcididae.[467] Like the Cynipidae, they do not make a silken cocoon, but
some of them that change to pupae inside the victims on which they were
nourished have the power of forming oval cells in which to undergo their
transformation, and they thus cause a peculiar inflation of the skin of
their deceased victim, which after death still continues to serve as a
protection to the destroyers. The statement made by Haliday, and repeated
subsequently in various works, to the effect that Coryna spins a cocoon
under the _Aphis_ in which it has lived, is an error, the cocoon being
really formed by _Praon_, a Braconid that is a parasite of the _Aphis_, and
on which the Chalcid _Pachycrepis (Coryna)_ lives as a hyperparasite. The
pupae of some species differ from those of other Hymenoptera, in that the
integument is hard, and the limbs are soldered to the body as in
Lepidoptera. These forms pupate external to the victim.
Fritz Müller has recorded that the pupa of an unnamed species of Chalcid
that attacks a Brazilian ant (_Azteca instabilis_ Forel) is suspended on
the wall of the cell the ant lives in by its posterior extremity, just like
the chrysalis of a butterfly.
{551}Notwithstanding the small size of Chalcididae, their remains have been
detected in the tertiary strata of both Europe and North America.
FAM. IV. ICHNEUMONIDAE (ICHNEUMON-FLIES).
_Wings with a well-developed series of nervures and cells; the space on
the front wing separating the second posterior cell from the cubital
cells is divided into two cells by a transverse veinlet. The abdomen is
attached to the lower or posterior part of the median segment. Larvae
parasitic in habits._
[Illustration: FIG. 360.—_Lissonota setosa_, ♀. Britain. Parasite of the
goat-moth, etc. (After Ratzeburg.)]
The Ichneumonidae form a family of enormous extent, containing nearly 6000
described species. The study of the family is but little advanced, owing to
their parasitic habits and to this bewildering multiplicity in their
specific forms. Most of the species, in the larval state, live inside the
larvae of Lepidoptera, and they thus keep the myriads of caterpillars
within bounds, the number of these destroyed by Ichneumons being
prodigious. Some of the family are, however, external parasites, and some
are known to attack Spiders and Insects of other Orders than Lepidoptera.
Their antennae are not elbowed and are many-jointed, the joints being
closely compacted, especially towards the extremity. This character readily
distinguishes Ichneumonidae from the families we have previously
considered. The ocelli are well developed even in the apterous forms, and
are placed in a triangular position on the vertex. The pronotum is small in
front; and extends backwards at the sides to the points of insertion of the
front wings; it is fixed to the mesonotum. The wings (Fig. 367, A) have a
more complex neuration than those of most of the other parasitic
Hymenoptera, but are occasionally absent in one or both sexes of a species.
The metathorax is very small, and the middle and hind legs are placed close
together. The propodeum is very large, and is frequently covered with a
highly-developed sculpture.
{552}[Illustration: FIG. 361.—_Anomalon circumflexum_, larval development.
(After Ratzeburg.) A, First instar; B, second instar; C, the larva in the
third or encysted stage extracted from its cyst; D, the mature larva; E,
pupa.]
The hind body springs from the lower part of the propodeum; it is usually
of slender form, and its segmentation is very conspicuous. The females bear
an ovipositor, which differs greatly in length according to the species,
and is known in the case of one species to attain a length six times that
of the whole of the rest of the body.[468] The egg is deposited by some
species on the skin, by others within the body of the victim; it varies
much in form and colour, some eggs being stalked and of peculiar shape. The
larvae issuing from the eggs are legless maggots with a delicate integument
of pallid white or creamy colour. If the eggs are laid on the surface of
the body, the resulting larvae (except in the cases of the external
parasites) soon bore into the interior of their victim, and disappear
therein. The changes that take place in the lifetime of the larvae have
been studied in only a few cases; but if we can judge from Ratzeburg's
history[469] of the changes that take place in _Anomalon_, they are of
great interest. From observation of the differences existing amongst a
great number of larvae of _A. circumflexum_ he distinguished four stages.
It is of course impossible to follow directly the growth of one individual,
because it is concealed in the interior of the caterpillar in which it
lives, and to open this involves the death of both caterpillar and
Ichneumon-larva. The life history must therefore be constructed from a
great number of separate observations; and it is not ascertained that the
four instars described by Ratzeburg represent the number of moults of the
larva that actually take place. He, however, entertained no doubt that all
the forms he observed {553}were stages in the development of one species.
In the earliest stage, when only one millimetre in length and about as
thick as a horse-hair, the larva is free in the interior of the
caterpillar's body, and has a small head armed only with a pair of
mandibles. There are, in addition to the head, thirteen segments, and the
last of these is an elongate tail forming nearly one-half the length of the
creature. No trace of tracheae can be discovered. In the second stage the
larva is still free, an elongate tracheal tube exists, the tail has
diminished to half the length, the head has become much larger, and
rudimentary antennae of one joint are visible; possibly stigmata are
present at this stage, though they cannot afterwards be detected. In the
third stage (Fig. 361, C) the larva is encysted, the head is large, the
parts of the mouth are all developed, the tracheal system is extensive, and
the caudal termination of the body is quite short; notwithstanding the
extensive development of the tracheal system, no stigmata can be found. In
the fourth stage the larva is still encysted, the tail has disappeared, the
head and mouth parts are reduced in size and development, and the creature
has now the appearance of a normal larva. The changes to pupa and perfect
Insect take place within the body of the victim, in some cases, if not
usually, after it has undergone its metamorphosis into a chrysalis. Very
little information is extant as to the duration of the various stages, but
it appears to be the rule that only one generation appears annually, though
in some cases there are pretty certainly two.
It is very difficult to observe the act of oviposition; the Ichneumon-flies
usually decline to notice caterpillars with which they are placed in
confinement. Ratzeburg thinks they will only attack caterpillars that are
in a deficient state of health or vitality. Occasionally we may by a happy
chance observe the act in Insects at large, and from the records of
observers it may be deduced with tolerable certainty that the sense of
sight takes no part in the operation. Ratzeburg relates that he saw a
_Pimpla_ alight on a leaf of _Rhus_ and thrust its ovipositor through the
leaf. On looking to the under-side of the leaf he found that a cocoon of
_Bombyx neustria_ was concealed there in such a position that it could not
have been seen by the Ichneumon.
{554}[Illustration: FIG. 362.—_Thalessa lunator._ Oviposition. (After
Riley.)]
Among the most remarkable of the Ichneumon-flies are the Insects of the
genera _Rhyssa_ and _Thalessa_. These fine Insects have an ovipositor three
or four inches in length, and are parasitic on species of the family
Siricidae, which, as we have previously described, live in solid wood. In
order therefore to deposit the egg in a suitable place, the wood must be
pierced by the Ichneumon. The ovipositor is not only of extreme length, but
is also furnished with serrations on its apical part, so that it forms a
very effective boring apparatus. It is brought into use by being bent on
itself over the back of the Insect (Fig. 362), so as to bring the tip
vertically down on to the wood, through which it is then forced by a series
of efforts; the sheaths do not enter the wood. The egg is laid anywhere in
the burrow of the _Sirex_; the young larva seeks its prey, and lives on it
as an external parasite (Fig. 342, D). Erne, however, states[470] that the
young larva of _Rhyssa persuasoria_ enters its victim, and remains within
the latter till its death occurs. This happens when the young _Rhyssa_ is
two or three lines in length, and it then makes its exit from the interior
of the body and gradually eats it up. Should the larva it has attacked be
of large size, it of itself affords sufficient food for the completion of
the growth of the _Rhyssa_. Should the _Rhyssa_, however, have attacked a
small larva, this does not furnish it with sufficient food, and it
consequently dies without seeking another larva. Erne says, indeed, that it
will not eat another if offered to it, so that in order to rear the
_Rhyssa_ in captivity, the victim it has first attacked must always be
given to it. The same observer states that the _Rhyssa_ larva is sometimes
transported by the _Sirex_ deep into the wood, so that when it has
completed its metamorphoses the Ichneumon-fly may find itself buried in
solid wood to a depth of about two inches. In that case it excavates the
wood with its mandibles, and should it fail to gain the exterior after
{555}three days of work, it dies. In the case of _Thalessa_ it is stated
that it sometimes bores into wood where there are no larvae, but Riley
thinks this erroneous; it is, on the other hand, certain that the Insect
after penetrating the wood is frequently unable to withdraw the ovipositor,
and consequently dies.
Packard has recorded,[471] without mentioning the species, the oviposition
of an Ichneumon of which the egg is deposited externally. It was placed on
the head of the caterpillar, and speedily hatched; the young larva at once
bored through the prothoracic segment of the victim, the head of the latter
then became swollen, and covered the opening into the prothorax, made by
the parasite.
[Illustration: FIG. 363.—Young larva of _Paniscus_ in position of feeding
on the skin of _Mamestra_. (After Newport.) _a_, The egg-shell.]
The history of an Ichneumon larva that feeds as an external parasite has
been sketched by De Geer and Newport. The observations of the latter[472]
refer to _Paniscus virgatus_; he found small, shining, black bodies
attached to the skin of the larva of a moth, _Mamestra pisi_; these were
the eggs of the Ichneumon. They are furnished with a short peduncle, which
is implanted in the skin of the victim; the egg, according to De Geer,
being retained more firmly by the peduncle subsequently swelling, so as to
form two knobs. The hatching takes place by the egg-shell splitting
longitudinally, while from the split protrudes the little head of the
destroying larva. This becomes fixed to the caterpillar, from which the
nutriment is to be drawn; the _Paniscus_ larva does not, however, leave the
egg-shell, but, on the contrary, becomes adherent to it, so that the
parasite is in this manner fixed by the two ends to its victim. In fifteen
days the parasite was full-grown, and had become half an inch in length. At
first no tracheae were to be seen, but these were detected after the second
day. Moulting took place three times, and in a peculiar manner, very
different from that described by Ratzeburg as occurring in the internal
parasites (which, he states, change their very delicate skin by detaching
it in almost imperceptible fragments). In the external parasite the
{556}skin remains entire, and is shuffled down to the extremity of the
body, but cannot be completely detached owing to the anchoring of the
posterior part of the body to the caterpillar; the cast skins thus remain
as envelopes to the posterior part of the body. Newport states that if the
mouth of the parasite be detached, it usually cannot again seize hold of
the victim, and consequently perishes. It is a curious fact that more eggs
than one caterpillar can support are habitually placed on it, and some of
the resulting larvae of necessity perish during the period of growth.
Poulton, who has recently made some additional observations on the
development of _Paniscus_,[473] says that if three larvae are close
together, it is the middle one that perishes, and suggests that this is due
to some simple physical condition. From Newport's account it may be
gathered that the _Mamestra_ retains sufficient vitality to form its
cocoon, and that the _Paniscus_ larvae likewise construct their own cocoons
within that of the _Mamestra_. In the case of _Paniscus cephalotes_ feeding
on _Dicranura vinula_, Poulton relates that the latter died after the
twelfth day of attack. The parasites, having relaxed their hold on the
victim just previous to this event, then thrust their heads into the dead
body, and devoured the larva, leaving only a dried and empty integument.
These larvae span a loose sort of web in which to undergo their
metamorphosis. In a natural state, however, they form cocoons inside the
cocoon of the _Dicranura_. The period passed in the pupal condition was
about four weeks. This parasite only attacks the Lepidopterous larva during
the last stage of its existence as a larva, but the eggs may be laid on the
victim in an earlier stage; and in such case De Geer has stated, and
Poulton has confirmed the observation, that though the larva sheds its skin
it does not get rid of the eggs.
The little Ichneumons of the genus _Pezomachus_ are quite destitute of
wings and somewhat resemble ants; they are common Insects in Britain. Only
the female sex is known, and it is believed that the winged Ichneumons
assigned to the genus _Hemiteles_—of which no females are known—are the
males of _Pezomachus_. Repeated efforts have been made to place this beyond
doubt, but they have usually failed, for when a brood of these parasites is
reared, the individuals generally prove to be {557}either all _Hemiteles_
or all _Pezomachus_. It is to be hoped that this interesting case will be
fully elucidated.
Although the Ichneumonidae are perhaps the most purely carnivorous of all
the great families of Hymenoptera, there is nevertheless reason for
supposing that some of them can be nourished with vegetable substances
during a part at any rate of the larval existence, Giraud and Cameron[474]
having recorded observations that lead to the conclusion that some species
of the genus _Pimpla_ may inhabit galls and live on the substance, or
juices thereof.
[Illustration: FIG. 364.—_Agriotypus armatus_, female. Britain. (After
Curtis.)]
Over 1200 species of Ichneumonidae are known to inhabit Britain, and there
can be no doubt that this number will be increased as a result of further
observation. Unfortunately no general work has yet been published on this
department of our fauna, and the literature is very scattered.[475] The
species of North America have not received so much investigation as those
of Europe, and the Ichneumon fauna of the tropics remains almost
uninvestigated. Six sub-families are recognised: Agriotypides,
Ichneumonides, Cryptides, Tryphonides, Pimplides, Ophionides. Of these the
first is the most remarkable, as it consists of an Insect having aquatic
habits. It has for long been known that the unique species _Agriotypus
armatus_, a rare Insect in our islands, is in the habit of going under
water and remaining there for a considerable period, and it has now been
satisfactorily ascertained that it does this for the purpose of laying its
eggs in the larvae of Trichoptera.[476] The resultant larva lives inside
the cases of species of _Silo_, _Goëra_, etc. It undergoes a sort of
hypermetamorphosis, as its shape before assuming the pupal condition
{558}is very different to what it was previously. It changes to a pupa
inside the case of the Trichopteron in a cocoon attached to the walls of
the case. Previous to making this, however, the _Agriotypus_ forms a
curious, elongate, string-like process attached to the anterior extremity
of its cocoon. The use of this is unknown. Full information as to the
life-history of this aquatic Hymenopterous larva, especially as to its
respiratory functions, would be of great interest. The affinities of this
remarkable Insect are still doubtful. It may probably prove to be between
Proctotrypidae and Ichneumonidae.
[Illustration: FIG. 365.—Metamorphosis of _Agriotypus_. (After Klapálek.)
A, Larva; B, sub-nymph; C, case of the _Silo_ with the string of attachment
formed by _Agriotypus_; D, section of the case: _v_^1, operculum of case;
_v_^2, cocoon; _ag_, pupa of _Agriotypus_; _e_, exuvia of _Agriotypus_;
_w_^2, wall of cocoon; _s_, remains of _Silo_; _w_^1, closure of case.]
Remains of Insects that may be referred with more or less certainty to
Ichneumonidae have been found in some abundance in various tertiary strata
both in Europe and North America, but nothing indicative of the existence
of the family has yet been found in the older rocks.
FAM. V. BRACONIDAE—SUPPLEMENTARY ICHNEUMON-FLIES.
_Antennae with many (nearly always more than fifteen) joints, not
geniculate. Wings with a moderate number of cells, which on the anal part
of the front wing are more or less imperfect, the anal (i.e. the second
posterior) cell being separated from the cubital cells by a large space
in which there is no cross-nervure. Abdomen with but little mobility
between the segments; the suture between the second and third usually
{559}absent, or obsolete. Larvae living parasitically in—possibly
exceptionally outside—the bodies of larvae or pupae of Insects._
[Illustration: FIG. 366.—_Bracon palpebrator_, female. Europe. (After
Ratzeburg.)]
[Illustration: FIG. 367.—Diagram of wing of Ichneumonid (A) and of Braconid
(B). 1, 2, 3, 4, series of cells extending across the wing; _a_, _b_,
divided cell of the Ichneumonid wing, corresponding with _a_, the undivided
cell of the Braconid wing.]
The Braconidae are the Ichneumones, or Ichneumonides, adsciti of the older
Hymenopterists. They are extremely similar to the Ichneumonidae, but the
hind body has a much less degree of mobility of its segments, and there are
some constant distinctions in the wings. Although there is a great deal of
difference in the various forms of each of the two families, yet there are
two points of distinction easily appreciated; the series of cells running
across the wing (Fig. 367) being only three in the Ichneumonides (Fig. 367,
A), but four in the Braconids (Fig. 367, B); besides this the space _a_ of
the Braconid wing is divided into two (_a_, _b_) in the Ichneumonid wing. A
glance at these characters enables us at once to separate correctly the
thousands of species of the two families.
The habits of the Braconidae are similar to those of Ichneumonidae, it
being believed that all are parasites. Usually they attack larvae, but they
are bred in great numbers from pupae, and even from imagos of other
Insects. _Elasmosoma_ is one of the few parasites known to attack ants. As
many as 1200 specimens of _Microgaster_ have been reared from a single
Lepidopterous larva. Although such parasitism raises a feeling of
repulsion, yet there is reason for supposing that there may be {560}little
or no cruelty or acute suffering connected with this mode of life. The
victim attacked is not eaten, the parasites in the interior taking in the
lymph of the caterpillar either by the mouth or by endosmosis, but not
biting their host. The latter displays no sign of sickness, but eats
voraciously, so that it serves merely as a sort of intermediary between the
juices of the plant and the larvae inside itself. It is only when the
metamorphosis is at hand that the host sickens, but this does not always
happen: parasitised larvae frequently change to pupae, and they may
occasionally even become perfect Insects. Cases are known in which imagos
have appeared with some of the small parasites embedded in some of the
outer parts of their bodies. These cases are, however, very rare; in the
enormous majority of instances the host is destroyed either when it is in
the larval stage or before the pupa has advanced to any great extent on its
metamorphosis to an imago. Particulars as to various species will be found
in the valuable work of Ratzeburg we have already referred to.[477]
Reference may also be made to Goureau's account of _Microgaster
globatus_,[478] this latter including some suggestions by Dr. Boisduval on
some of the difficult physiological questions involved in the lives of
these parasites.
[Illustration: FIG. 368.—Stalked cocoon of _Apanteles formosus_. (After
Marshall.)]
The metamorphosis of _Microgaster fulvipes_ has been studied by Ratzeburg,
and an epitome of his observations is given by Marshall.[479] The larva
goes through a series of changes somewhat similar to those we have already
sketched in _Anomalon circumflexum_. Usually these Insects after emerging
from the body of their host spin a mass of cocoons more or less loosely
connected together. A most curious case has, however, been recorded by
Marshall[479] of a stalked cocoon (Fig. 368) being formed as an exceptional
act by _Apanteles formosus_. Mr. Marshall has recently received other
specimens of this cocoon as well as the Insects reared therefrom in France,
and inclines to the opinion that the stalked cocoon may be the usual form,
and is sometimes departed from by the Insect for unknown reasons.
{561}This family is of enormous extent; we have several hundred species of
it in Britain,[480] and there are no doubt many thousands of undescribed
exotic forms. To _Apanteles glomeratus_ we are indebted for keeping our
cabbages and kindred vegetables from destruction by the caterpillars of the
white butterflies. The larvae of the various species of _Pieris_, as well
as those of other Lepidoptera, are attacked by this little Insect, the
masses of whose cocoons may frequently be found in numbers in and near
cabbage gardens. The tropical species of Braconidae are greatly neglected,
but many large and remarkable forms—some of brilliant colours—have been
brought from there, so that we are justified in believing that Insects of
this family will prove to be very numerous. There are but few apterous
Braconidae. Both sexes of _Chasmodon apterus_ are destitute of wings; the
females of one species of _Spathius_, and also those of _Pambolus_ and
_Chasmodon_ are apterous; in a small number of species of various genera
the wings are so minute as to be incapable of serving as organs of flight.
In the genus _Alloea_ the wings of the male are shorter than those of the
female.
[Illustration: FIG. 369.—_Stenophasmus ruficeps_, female. Aru Islands.
(After Westwood.)]
FAM. VI. STEPHANIDAE.
_Antennae composed of many (thirty to seventy) joints; hind body attached
to the lower and posterior part of the median dorsal {562}plate. Wings
with a distinct costal cellule; head globose, posterior femora frequently
toothed._
This is a doubtful family, consisting of a few anomalous Insects.
Schletterer assigns to it only two genera, _Stephanus_ and
_Stenophasmus_;[481] both have a wide distribution over the world, though
we have no species in Britain. Nothing is known of their habits, and they
are apparently all very scarce Insects. The definition is compiled from
those of Cameron and Schletterer. There seems very little to distinguish
these Insects from Braconidae.
FAM. VII. MEGALYRIDAE.
_Hymenoptera with short broad hind body, which is not separated by a
pedicel from the thorax. The female has a very long bristle-like
ovipositor. Antennae with fourteen joints._
This family is constituted by the Australian genus _Megalyra_,[482] one of
the most interesting of the numerous extraordinary Insect-forms found in
that region; the species appear to be very rare and not numerous.
Apparently nothing is known as to their habits. It is quite possible that
these Insects will prove to be anomalous Braconidae.
FAM. VIII. EVANIIDAE.
_Petiole of the abdomen attached to the upper part of the median dorsal
plate; antennae not elbowed, of thirteen or fourteen joints. Wings with a
moderate number of nervures. Larva of parasitic habits._
This family is composed of only three genera—_Evania_, _Gasteruption_, and
_Aulacus_, each possessing a considerable number of species; they agree in
the characters mentioned above, and may be readily recognised by the
peculiar insertion of the hind body. This character occurs outside the
limits of the Evaniidae only in one or two genera of Chalcididae and
Braconidae; it is to this latter family that the Evaniidae must be
considered most closely allied.
The species of the genus _Evania_ are believed to live at {563}the expense
of cockroaches (Blattidae), and to deposit their eggs in the egg-capsules
of those Insects. The species of _Gasteruption_ live, in the larval state,
on the larvae of other Hymenoptera, more especially of such as form nests
in wood. Very little is known as to the habits of the species of _Aulacus_,
but it is believed that they are parasitic on members of the Hymenopterous
families, Siricidae and Oryssidae. Only the most meagre details as to the
life history of any of the Evaniidae have been recorded. The species of
_Evania_ are met with most freely where cockroaches abound, and are said,
hence, to be frequently observed on board ship. Two or three species of
each of the two genera _Evania_ and _Gasteruption_ occur in Britain. The
latter genus is more widely known under the name of _Foenus_.[483]
FAM. IX. PELECINIDAE.
_Sexes very different; the female without exserted ovipositor, but with
extremely long abdomen. Articulation between the femur and trochanter
oblique and elongate, but without division of the trochanter._
[Illustration: FIG. 370.—_Pelecinus polyturator_, ♀. Mexico.]
This family at present comprises, according to Schletterer,[484] only the
three genera _Pelecinus_, _Ophionellus_, and _Monomachus_. The systematic
position of the Insects is very doubtful, and their habits are but little
known. _Pelecinus polyturator_ (Fig. 370) appears, however, in the female
sex, to be a common Insect over a large part of the warmer regions {564}of
the New World; it is in all probability parasitic in its habits, the
elongate ovipositor of the female Ichneumon being in this Insect replaced
by an extraordinary linear extension of the abdomen itself. Doubleday has
recorded that he saw twenty or thirty specimens of this species that had
perished with their elongated hind bodies inserted into the stem of a tree,
from which they could not extricate themselves. On the other hand, Patton
thinks they are parasitic on locusts.[485]
The male in _Pelecinus_ has the proportions of the parts of the body
normal, there being no elongation of the abdomen; it thus differs very much
in appearance from the female. There seems to be very little to distinguish
_Pelecinus_ from Proctotrypidae. The undivided trochanters have led to
these Insects being placed, by some, among the Aculeate Hymenoptera. This
character, as we have already shown, occurs also in Proctotrypidae.
FAM. X. TRIGONALIDAE.
_Abdomen ovate, not separated by a pedicel from the thorax. Antennae
twenty-five-jointed. Trochanters imperfectly two-jointed. Both the
anterior and posterior wings provided with a well-developed neuration.
Abdomen composed of only five apparent segments. Larva (in some cases)
parasitic on Aculeate Hymenoptera._
[Illustration: FIG. 371.—_Trigonalys maculifrons_ Cam. _i.l._ Mexico.]
This family is chiefly constituted by the very rare Insects contained in
the genus _Trigonalys_, of which we have one species in Britain. Although,
so far as appearance goes, they have little in common with the parasitic
Hymenoptera, and look quite like members of the Aculeata, yet the late F.
Smith found a species in the cells of _Polistes lanio_, thereby showing it
to be of parasitic habits. Although some Aculeate Hymenoptera are also of
parasitic habits, yet the characters of _Trigonalys_ perhaps agree, on the
whole, better with the Hymenoptera parasitica. The British species is very
{565}rare. The South American genus, _Nomadina_, looks still more like a
bee, and the trochanters are even more imperfectly divided than they are in
some of the Aculeate group, Nyssonides, the outer portion being merely a
small piece imperfectly separated from the base of the femur.
----
_Note._—The citation of Saint Augustine on p. 85 is made in the words
used by Wasmann in _Der Trichterwickler, eine naturwissenschaftliche
Studie über den Thierinstinkt_, 1884.
The authenticity of the passage we have adopted as the motto for this
volume is somewhat doubtful. It is explained in an "admonitio ad
lectorem" of the soliloquy, that this work is probably a compilation by a
later writer, from two, or more, works of Saint Augustine. Father Wasmann
has been so kind as to inform the writer that the idea of the passage
quoted occurs frequently in the undoubted works of the Saint, as, for
instance, de Civitate Dei, lib. xi. cap. 22; Serm. ccxiii. in traditione
symboli II. cap. i.; contra Faustum, lib. xxi. cap. v. etc. The passage
quoted is, however, the only one in which "angeli" and "vermiculi" are
associated.
{567}INDEX
Every reference is to the page: words in italics are names of genera or
species; figures in italics indicate that the reference relates to
systematic position; figures in thick type refer to an illustration; f. =
and in following page or pages.
Abdomen, 109;
of Hymenoptera, 492 f.
Abdominal appendages, 188, 189, 190
_Acantherpestes_, 74, _76_
Accessory glands, 392, 404
_Acheta_, 330, 338
_Achorutes murorum_, 194
Acini, 126
Acoustic orifice, 317
Acridiidae, _201_, 279-310, _309_
Acridiides, _310_
_Acridium peregrinum_, 298;
growth, 156;
at sea, 297
—see also _Schistocerca_
Acrophyllides, _278_
Aculeata, _520_
Aculeates and Proctotrypids, 535, 564
Adler, on alternation of generations, 530;
on galls, 526 f.;
on useless males, 498
_Aeschna cyanea_, 412;
_A. grandis_, labium, 411;
nymph, 420, 421
Aeschninae, 416, _426_
Agaonides, _547_
_Agathemera_, 274, 276
Agrion nymph, 426
_Agrion pulchellum_, 412
Agrioninae, 412, _426_
Agriotypides, _557_
_Agriotypus armatus_, 557
Air sacs, 128, 282, 283, 294, 495
_Alaptus excisus_, 537;
_A. fusculus_, 538
Alar organs, of earwigs, 206;
of Blattidae, 225;
of Mantidae, 245;
of Phasmidae, 269;
of Acridiidae, 281;
development of, in earwigs, 212;
in Mantidae, 248
—see also Tegmina, Wings, Elytra
Alary muscles, 134
Albarda on Raphidiides, _448_
Alder flies, 444
_Aleuropteryx_, _471_
Alimentary canal, 123-127, 403, 446;
of may-flies, 438 f.;
of _Panorpa_, 450;
closed, 457, 466, 496, 544
Alitrunk, 489 f., 490, 492
_Alloea_, _561_
Alternation of generations, 497, 530
Amber, Myriapods in, 74, 76, 77;
Insects, 179;
Aptera, 196;
Blattidae, 239;
Mantidae, 258;
Phasmidae, 276;
Psocidae, 397;
Perlidae, 407;
Phryganeidae, 485;
Tenthredinidae, 518;
Cynipidae, 533
Ambua, 40
_Ameles_, 245
Ametabola, 158, 174
Amnion, 148, 545
Amnios, 291
Amorphoscelides, 251, _259_
_Amorphoscelis annulicornis_, 251
Amphibiotica, _342_
_Amphientomum paradoxum_, 397
_Ampulex_, abdomen, 492
Ampulla, 290
_Amylispes_, _76_
_Anabolia furcata_, mouth-parts, 475;
_A. nervosa_, larva, 476
_Anabrus purpurascens_, 321
_Anaplecta azteca_, folded wing, 227
Anaplectinae, _240_
Anatomy—see External Structure and Internal Anatomy
_Anax formosus_, 410, 414
Anderson, Dr. J., on _Gongylus_, 254
_Anechura scabriuscula_, 208
_Anisolabis maritima_, 205;
_A. moesto_, 205;
_A. tasmanica_, 216
_Anisomorpha pardalina_, 274
Anisomorphides, _278_
Anisopterides, 412, _414_, _426_;
nymphs, 421
_Anomalon_, metamorphosis, 552
_Anomalopteryx_, 484
_Anostostoma australasiae_, 326
_Anoura_, 190
Ant, brain, 119; {568}
nervous system, 495;
castes, 500
Ant destroyer, 545, 559
Ante-clypeus, 93
Antennae, 97;
growth of, 212
_Anthophora retusa_, parasites of, 544, 545
_Anthophorabia retusa_, 545
Ant-lions, 453, 454
_Anurida maritima_, 194, 195
Aorta, 133, 134
_Apanteles glomeratus_, 561
_Apatania_, 481;
_A. arctica_, _A. muliebris_, 481
Apex, 112
_Aphilothrix_, 531
Apocrita, 519
Apodeme, 103
Apophysis, 103, 520
Appendages, 91, 188, 189, 190
Aptera, 172, _180_-189
Apterous Insects, 205, 216, 217, 220, 234, 235, 252, 261, 262, 264, 269,
272, 274, 277, 299, 302, 303, 307, 321, 322, 323, 324, 325, 326, 329,
518, 556, 561
—see also Wingless Insects
Apterygogenea, 175, 196
Aquatic Acridiidae, 301, 303;
Aq. Hymenoptera, 538, 557;
Aq. Phasmids, 272
Arachnides antennistes, 77
Archidesmidae, _76_
_Archidesmus_, _76_
Archijulidae, _76_
Archipolypoda, 74, _76_
Arolium, 105, 223
Arrhenotoky, 141, 498
Arthromeres, 87
_Arumatia ferula_, anatomy, 262
Ascalaphides, _459_ f.
_Ascalaphus coccajus_, 459;
_A. longicornis_, 459;
_A. macaronius_, 460;
eggs, 460
_Aschipasma catadromus_, 263, 266
Aschipasmides, _278_
Ashmead, on Mymarides, 537;
on Proctotrypids, 537;
on _Scleroderma_, 536
_Astroma_, 300
Asymmetry, 216
_Athalia_ (_centifoliae_) _spinarum_, 515
Atropinae, 394 f.
_Atropos divinatoria_, 394 f., 396
_Atta_ (_Oecodoma_) _cephalotes_, 501
Attitude, 248, 250, 256, 268, 514
Attraction of light, 230
Auditory organ, 400;
of _Calotermes_, 358
—see also Ear
Audouin on thorax, 100, 101
_Aulacus_, _562_
_Aulax_, 532
Avicenna, 41
Axes of body, 113
BACILLIDES, _278_
_Bacillus patellifer_, 263
_Bacteria_, _276_
Bacteriides, _277_
Bacunculides, _277_
_Baëtis_, 433
_Ballostoma_, 196
Ballowitz on spermatozoa, 140
Barber, Mrs., on S. African locust, 294
_Barbitistes yersini_, 321
Barnston on Perlidae, 402, 405
Barriers with eggs, 461
Base, 112
Basement membrane, 162
Bassett on oviposition of inquilines, 532
Bataillon, on metamorphosis, 131, 168;
on reversed circulation, 135
Bates, on singing grasshopper, 319;
on Termites, 375
Bateson, on forceps of earwig, 209;
on antennae of same, 212
_Batrachotettix whiti_, 305
Bedeguar, 527, 531
Bees killed by _Locusta_, 321
Belt on domestic cockroaches, 231
Bermuda, 33
Bertkau, on _Psocus_, 391;
on micropterous Psocidae, 394
_Bethylus_ habits, 535
Bherwa, 326
Bird eaten by _Mantis_, 250
Bird-lice, 345, 351
Biting-lice, 345, 351
_Bittacus_, 451, 453;
_B. tipularius_, 452
_Blabera_, 235;
wings, 237;
_B. gigantea_, 222
Blaberides, _241_
Black beetle, 221
Blanjulidae, _44_
_Blanjulus_, 44
Blastoderm, 147
_Blastophaga grossorum_, 547 f.
_Blatta_, 240
Blattidae, _201_, 220-241, _240_;
parasites of, 563
Blattinae, _240_
Blind Insects, 217, 233
Blood, 132
Blood-gills, 479
Blowfly, egg, 145;
metamorphosis, 163
Bolivar on eyes of _Machilis_, 185
_Bombus_, dorsal vessel of, 133;
metamorphosis, 497;
_B. lucorum_, 488
Bombyliidae, 291
Bonnet and Finot on _Eugaster_, 324
Book-lice, 390 f.
_Boreus hiemalis_, 451;
larva, 453
Boutan on concealment of leaf-like Insects, 323
Brachyscelides, 526
_Brachystola magna_, 308
_Brachytrypes megacephalus_, 332
_Bracon palpebrator_, 559
Braconidae, _558_ f.
Bradford Cave, Myriapods in, 34 {569}
Brain, 118, 120;
of ant, 119;
of Perlidae, 404
Branchiae, 401, 421
—see also Gills
Brandt on nervous system, 119, 495
Brauer, on classification, 175;
on median segment, 491;
on hypermetamorphosis, 160;
on Menorhyncha, etc., 161;
on _Ascalaphus_ larva, 460;
on development of _Mantispa_, 464;
on Palaeodictyoptera, 486;
on _Panorpa_ larva, 452;
on tegmina of _Phyllium_, 270
Breitenbach on Proscopiides, 299
Bridgman on British Ichneumonidae, 557
Brindley on growth of cockroach, 229
British, Myriapods, 36;
Orthoptera, 201;
earwigs, 215;
grasshoppers and locusts, 308;
crickets, 339;
Psocidae, 395;
Perlidae, 406;
Odonata, 424;
Sialidae, 444, 448;
Chrysopides, 469;
Trichoptera, 480;
Phytophagous Hymenoptera, 504;
Siricidae, 510;
Cynipidae, 533;
Ichneumonidae, 557;
Braconidae, 561
Brongniart, on fossil Insects, 428;
on fossil Neuroptera, 343;
on Neuropteroidea, 486;
on post-embryonic development of locust, 287;
on young _Mantis_, 247 f.
Brongniart and Becquerel on chlorophyll in _Phyllium_, 268
Bruner on variation of Orthoptera, 304
Brunner, on Hypertely, 322;
on classification of Orthoptera, 202;
of Blattidae, 240;
of Mantidae, 259;
of Phasmidae, 277;
of Acridiidae, 309;
of Locustidae, 328;
on variation of Oedipoda, 304
_Bryodema tuberculata_, 281
Bugnion on histolysis, 166;
on _Encyrtus_, 545
Buller on Weta-punga, 326
Burchell on _Mantis_, 249
Burgess on _Psocus_, 391 f.
Burmeister on Mantidae, 250
Bursa copulatrix, 139
Caddis-flies, 473 f.
Caecum, 125
_Caenis dimidiata_, 442
Calcares, 104
Calepteryginae, 422, _426_
_Calepteryx_, _417_, 420, 422;
its eggs' parasite, 538
Callimenides, 318, _329_
_Callimome bedeguaris_, 532
_Caloptenus spretus_, 288 f., 289, 298, 303;
development, 289
_Calotermes flavicollis_, 362, 363, 371, 376;
_C. nodulosus_, 359;
_C. rugosus_, 358, 382, 383
Calvert on Odonata, 412
_Calvisia atrosignata_, 266, 273
Calyx, 283, 439
Cameron, on ant-parasite, 545;
on gall-producing plants, 527;
on parthenogenesis, 498, 499, 517;
on _Pimpla_ larva, 557
Camerano on earwig, 211, 213
_Campodea_, 61;
_C. staphylinus_, 182, 183, 197
Campodeidae, _183_
_Camponotus_, nerves, 495
Cannibalism, 425, 477
Cantharidae, 291
_Capnia vernalis_, 405
Caprification, 547 f.
Capsule of eggs, 201
—see also Egg-capsule
_Caraphractus cinctus_, 538
Carboniferous, Myriapods, 75, 76;
Insects, 196, 238 f., 259, 276, 408, 428, 442 f., 449
_Cardiophorus_ larva, 90
Cardo, 95
Carnivorous and vegetarian, 250
Carpenter bee wings, 494
Carruthers on locust swarm, 292
Case, Hymenopterous, 514
Cases, caddis-fly, 476 f., 480, 481, 482, 483, 484, 485
Castes, 500, 501
Caudal branchiae, 423
Cave, Myriapods, 34, 37;
Insects, 197, 451;
Locustidae, 321;
cockroach, 232, 233
_Cecidomyia_, parasites of, 536, 537
Cenchri, 511
Centipedes, 30, 36, 40
_Cephalocoema lineata_, 299
_Cephalonomia formiciformis_, 536
Cephidae, 504 f.
_Cephus integer_, 505;
_C. pygmaeus_, 505
Cerci, 110, 183, 216, 257, 337, 400;
of Blattidae, 224, 238
_Cermatia_, 35
Cermatiidae, _46_
_Ceroys saevissima_, 264
Cervical sclerites, 99, 99, 409
Chalcididae, _539_
_Chalicodoma muraria_, nest, parasites, 540 f.
Changing colour, 288, 253, 267, 268
_Chasmodon apterus_, 561
Chatin on labrum, 93;
on mandibles, 95
_Chauliodes_, _447_
Cheeks, 94
_Cheimatobia brumata_, parasites, 521
_Chelidura dilatata_, 205
Cheshire on fertilisation of bee, 499
_Chilaspis lowii_, 530;
_C. nitida_, 531
Chilian Insects, 447, 463
Chilognatha, 30, _43_, 47, _76_;
development of, 63-72;
structure of, 52-56, 53;
double segments, 53, 70
Chilopoda, 30, 33, _44_, 47, 52, 74, _75_;
structure of, 56-59;
development of, 70-72
Chitin, 162 {570}
Chitinogenous cells, 162
Chlorophyll in tegmina, 269
_Choeradodis cancellata_, 252
Cholodkovsky, on head, 87;
on styles of cockroach, 224;
on embryology of _Phyllodromia_, 237;
on morphology of sting, 493
_Chordeuma_, 31
Chordeumidae, _44_
Chordotonal organs, 121
Chorion, 144
_Chorisoneura_, _240_
Chromosomes, 146
_Chrysopa_ eggs, 469;
larva, 469;
_C. aspersa_, 470;
_C. flava_, 469;
_C. pallida_ larva, 470
Chrysopides, _469_ f., 472
Chun on rectal gills, 422
Chyle, 133
Chylific ventricle, 125, 228
_Cimbex_ abdomen, 493;
abdominal articulation, 492;
dorsal vessel, 134;
_C. sylvarum_, saws, 512
Cimbicides, 511, 517
Cinura, 182
Circulation, 132 f.;
in caudal setae, 435
Cladomorphides, _278_
_Cladonotus humbertianus_, 301
Classification, 171 f.;
of Blattidae, _240_;
of Mautidae, _259_;
of Phasmidae, _277_;
of Acridiidae, _309_;
of Locustidae, _328_;
of Gryllidae, _340_
Claws, 105, 106, 469
Clitumnides, _278_
_Cloëon_, eyes, 430;
_C. dimidiatum_, larvule, 432;
_C. dipterum_, nymph, 432;
respiration of nymph, 435
_Clothilla_, 395;
_C. pulsatoria_, 395, 396;
anatomy, 392
Clypeus, 92, 93
Cockroaches, 220
Cocoons of sawfly, 515
Coeloblast, 149
Coleoptera, _173_
Collembola, _182_, _189_ f.
Collophore, 193
Colour, 200
Commissures, 116
Common cocoons, 515
Compass Termite, 386
Complementary Termites, 361
Compound eyes, 97, 430;
(=facetted eyes) in Myriapods, 36
Concealment by movement and position, 268;
by selection of place, 308
Coniopterygides, _471_
_Coniopteryx lutea_, 471;
_C. psociformis_, 471;
_C. tineiformis_, 472
Conocephalides, 313, 327, 328
_Copiophora cornuta_, 313
_Cordulegaster_, 415;
_C. annulatus_, 415
Cordulegasterinae, _426_
Corduliinae, _426_
Correlative variation, 536
Corrodentia, _175_, 389
Corrosion by Termites, 360
_Corydalis_, _447_;
_C. crassicornis_, 447
_Corydaloides scudderi_, 344
_Corydia_, 221;
_C. petiveriana_, 233
Corydiides, _241_
_Coryna_, 550
_Corynothrix borealis_, 191
Costa, 108
Cotes on Indian locusts, 298
_Cotylosoma dipneusticum_, 272
Coxa, 88, 104
_Craspedosoma_, _76_
Crawlers, 447
Creepers, 407
Cretaceous Myriapods, 75;
Insects, 485
Creutzberg on circulation, 436
Cricket, 330, 338
_Crioceris asparagi_, legs of larvae, 106
Crop, 114, 124, 495
_Crunoecia irrorata_, case of, 480
Cryptides, _557_
_Cryptocerus_, abdomen of, 109
_Cryptops_, 36, 41
Crystalline cone, 98
_Cuculligera flexuosa_, 304
Cunningham on fig fertilisation, 549
Cursoria (Orthoptera), _201_
Cuvier, 77
Cyclops form, 536
_Cylindrodes campbellii_, 336;
_C. kochi_, 336
Cynipidae, _523_
_Cynips aciculata_, 531;
_C. disticha_, 530;
_C. folii_, 530;
_C. kollari_, 530;
_C. lignicola_, 530;
_C. spongifica_, 531
_Cyphocrania aestuans_, 266
Cyprus, 32
_Cyrtophyllus concavus_, 320;
_C. crepitans_, 311
Dahl and Ockler on feet, 105
D'Albertis on may-flies, 441
Damsel-flies, 417
Dancing may-flies, 439 f.
_Dasyleptus lucasii_, 196
Death-watch, 395 f.
Decaux on cannibalism of mole-cricket, 336
Deception, 250, 265
Decoys, 257
Decticides, _329_
De Geer on earwigs, 214
Degeeriidae, _190_
_Deinacrida heteracantha_, 326
Demoiselles, 417
_Dendroleon pantherinus_, 458
Denny on _Mantis_ in England, 258
Derham on death-watches, 396, 397
Dermaptera, 202, 216
Dermatoptera, 202
_Derocalymma_, 235 {571}
_Deroplatys sarawaca_, 243
De Saussure, on Orthoptera, 202;
on wings of Blattidae, 226 f.;
on classification of Gryllidae, 340;
on _Hemimerus_, 217;
on nomenclature of Blattidae, 240;
on oceans as barriers to migration, 297
Desert Insects, 253, 304
Deuterotoky, 141, 497 f.
Deuto-cerebron, 118
Development, of alar organs of _Platycleis_, 312;
of crickets, 332
—see also Embryology and Metamorphosis
Devonian, 428, 442
Dewitz on caste, 500;
on ovipositor of _Locusta_, 314;
on morphology of sting, 493;
on internal legs, 496;
on development of wings of Phryganeidae, 479, 480;
on dragon-fly nymphs, 423;
on _Chrysopa_ larva, 470
_Diaphana fieberi_, 226
_Diapheromera femorata_, 263, 264, 265, 267
_Diastrophus_, 532
_Diaulus_, 484
_Dicranota_, larva, glands of, 142
_Dictyoneura_, 277, 344
_Dictyopteryx microcephala_, 406;
_D. signata_, 401
_Dielocerus ellisii_, 515
Digestion, 127
Dilarina, _465_
Dilke, Sir Charles, on Orchis-like _Mantis_, 254
Dimorphic cocoons, 560;
males, 547, 549
_Diplectrona_, 479
Diploglossata, 217
Diplopoda, _43_, 53, 74
_Diploptera silpha_ folded wing, 227
Diptera, _173_
Disgorgement, 495
Distant on S. African locust, 298
Ditrochous, 494, 520
Divided eyes, 409
_Docophorus fuscicollis_ anatomy, 348;
_D. icterodes_, _D. cygni_, 349
Dog, biting-louse of, 349
Dohrn on tracheal system of _Gryllotalpa_, 132;
on embryology of _Gryllotalpa_, 336
_Dolichopoda palpata_, 322
Dorsal vessel, 133, 134;
reversed action, 435
Dorsum, 100
Dragon-flies, 409
Drakes, 441
_Drepanepteryx phalaenoides_, 453, 468;
wings, 468
Drones, 499
Drummers, 237
Dubois on decapitated _Mantis_, 250
Duchamp on egg-capsule of cockroach, 228
Ductus ejaculatorius, 140
Dudley and Beaumont on Termites, 372, 387
Dufour, on alimentary canal, 124;
on tracheal system, 129;
on air sacs of Acridiidae, 283;
on sexual organs, 138, 139;
on testes, 140;
on phonation, 286;
on _Tridactylus_, 338;
on Mantidae, 246;
on earwigs, 210;
on anatomy of cockroach, 228;
on anatomy of _Gryllotalpa_, 335;
on anatomy of Termites, 360;
on anatomy of _Panorpa_, 450;
on larva of _Sialis_, 446;
on _Myrmeleon_ larva, 458
Duns, 441
Dust-lice, 390 f.
Dwellings of Termites, 385 f.
_Dytiscus_, mesothorax, 101;
egg-tube, 138, 139
Dzierzon theory, 499
Ear, 101, 121;
of Acridiidae, 285 f., 285;
of Locustidae, 316 f., 316, 317;
of crickets, 332;
of _Gryllotalpa_, 333, 334
Earliest Insect, 238
Earwig, 202 f., 211, 213, 214;
forceps, 208 f., 209;
wing, 206;
the name, 214
Eaton, on nymph, 157;
on Ephemeridae, 435, 437, 440
Ecdysis, 156, 162;
nature of, 169
_Ectobia_, 236;
_E. lapponica_, egg-capsule, 229
Ectobiides, _240_
Ectoblast, 149
Ectoderm, 148;
of _Peripatus_, 20 f., 22
Ectognathi, 189
Ectotrophi, 189
Eggs, 143-145;
of _Peripatus_, 19;
of Myriapods, 38, 39, 64;
of _Ascalaphus_, 460;
growing, 513;
of parasites, 552;
of egg-parasites, 545;
of _Corydalis_, 447;
of Cynipidae, 528;
of _Limacodes_, 153;
of Mallophaga, 348;
of _Microcentrum_, 314;
of Phasmidae, 265, 270 f., 270;
of _Perla_, 404;
of _Sialis_, 445;
of Trichoptera, 476
Egg-capsule, 265, 290;
of _Phyllium_, histology, 271
Egg-parasites, 522, 536, 538
Egg-tubes, 137, 139, 392
—see also Ovaries
_Eileticus_, _76_
Eisig on chitinous excretion, 130, 163
Ejaculatory duct, 392, 414
Ejection of fluid, 264, 324, 399, 515
_Elasmosoma_, 559
_Elater_ larva, 29
_Elipsocus brevistylus_, 393
Elytra, 108
_Embia_, 352, 353
_Embidopsocus_, 395
Embiidae, 351, 395
Embryology, 145-153;
of _Peripatus_, 19 f.;
of Myriapods, 63 f.;
of parasites, 522;
of earwig, 216;
of Blattidae, 237;
of _Encyrtus_, 546;
of _Gryllotalpa_, 336; {572}
of _Polynema_, 538;
of _Smicra_, 545;
of Proctotrypidae, 536 f.
Emergence from egg, 263, 264, 290, 291, 313
Empodium, 105
_Empusa pauperata_, 245, 257
Empusides, _259_
_Encyrtus fuscicollis_ development, 545
Endoblast, 149
Endoderm, 148;
of _Peripatus_, 20 f., 22
Endolabium, 97
Endo-skeleton, 399
Eneopterides, _340_
Enock on _Alaptus_ and _Caraphractus_, 538
_Enoicyla pusilla_, 481
Entognathi, 189
Entomology, 86
Entothorax, 103, 114, 116
Entotrophi, 189
Eocene, 407
_Ephemera_, 434;
_E. danica_, 429, 441;
wing, 431;
_E. vulgata_, 441;
nymph, 433
Ephemeridae, _429_-443
_Ephippigera_ Malpighian tubes, 335;
_E. rugosicollis_, 323
Ephippigerides, 318, _329_
Epiblast, 65, 149
Epicranium, 92, 93, 93
Epidemes, 107
Epilamprides, _240_
Epimeron, 100, 101, 104
Episternum, 88, 100, 101, 104
Epistome, 92
Epithelium of stomach, 126
_Eremiaphila_, 243, 253;
_E. turcica_, 253
Eremobiens, 304
_Erianthus_, 301
Erichson on Neuroptera, 342
Erne on _Rhyssa_, 554
_Etoblattina manebachensis_, 238, 239
_Eucharis myrmeciae_, 545
_Euchroma_, head and neck, 99
_Eucorybas_, 37
_Eugaster guyoni_, 324
_Eugereon bockingi_, 486
_Eumegalodon blanchardi_, 327
Eumegalodonidae, 327
Euorthoptera, 216
_Euphaea_, 422
_Euphoberia_, _76_
Euphoberiidae, 73, _76_
_Euprepocnemis plorans_, 303
_Eurycantha australis_, 274
_Eurytoma abrotani_, 539
_Eusthenia spectabilis_, 407
_Eutermes_, 374;
_E. ripperti_, 388
_Euthyrhapha_, 226
_Evania_, _562_
Evaniidae, _562_
Exner on sight, 416
Exodus, locust of the book of, 298
Exsertile blood-sacs, 132
External parasite, 555
External structure, 87;
diagram, 88;
of earwigs, 203 f.;
of cockroaches, 221;
of Mantidae, 242 f.;
of Phasmidae, 260 f.;
of Acridiidae, 280 f.;
of Odonata, 409 f.;
of Ephemeridae, 430 f.;
of _Panorpa_, 450;
of Phryganeidae, 474;
of Hymenoptera, 489 f.;
of Tenthredinidae, 511
Eyes, 97
—see also Compound Eyes and Ocelli
Fabre on _Leucospis_, 540;
on _Monodontomerus_, 543;
on _Sirex_, 509
Facetted eyes—see Compound Eyes
Family, 177
Fasting, 448, 458
Fat-body, 136
Feeding, by Termites, 376;
young, 495
Femur, 88, 104
Fenestra, 221
Fenestrate membrane, of eye, 98;
of pericardium, 134
Fertilisation, 499;
of fig, 549
Field-cricket, 332
Fields of wings, 206
Fig-Insects, 547 f.
Figitides, _525_
Finot on _Japyx_, 196
Fire-brats, 186
Fischer on instars, 158
Fish destroyed, 425
Fletcher on parthenogenesis, 498
Flight, 416
Floral simulators, 254 f.
Flying-machine, model for, 417
_Foenus_, _563_
Foetus of _Hemimerus_, 218
Foramen, occipital, 92, 94
Forbes on Blattid, 235
Forceps of earwigs, 208, 209
Forel on nervous system of ant, 495
_Forficula auricularia_, 202 f., 204, 209, 211;
_F. gigantea_, _210_
Forficulidae, _201_, 202
Formica-leo, 456
Formicajo, 456
Formicario, 456
Fossil, Insects, 178, 472, 485, 486;
Acridiidae, 308;
Blattidae, 238;
cricket, 340;
dragon-flies, 427;
earwigs, 216;
Locustidae, 328;
Mantidae, 258;
may-flies, 442, 443;
Phasmidae, 276;
Panorpidae, 453;
Perlidae, 407;
Sialidae, 449;
Termites, 389;
Thysanura, 196;
Myriapods, 72 f.;
Palaeozoic Neuroptera, 343
Founding communities, 381
Fourmilions, 456
Fowl, biting-louse of, 350
Fritze on Ephemerid alimentary canal, 439 {573}
Frons, 94
Front wings absent, 260 f.
Fungus chambers, 387
Fungus-growing Termites, 385, 387
Funiculus, 492
Furca, 103
Furcal orifices, 399, 402
Galapagos Islands, 459
Galea, 95
Gall-flies, 523 f.
Galls, 514 f.;
nature of, 525 f., 533
Ganglia, 116
Ganin, on metamorphosis, 162;
on embryology, 536 f., 538
_Gasteruption_, _562_
Gena, 94
Geophilidae, _46_, 58, 75
_Geophilus_, 33, 36, 39, 46;
marine, 30;
phosphorescent, 34
Geoscapheusides, _241_
_Gerephemera simplex_, 428
Gerstaecker, on Neuroptera, 343;
on mouth of Odonata, 411
Giebel on Mallophaga, 347
Gigantic Insects, 276, 306, 428
Gilbert White, on mole-cricket, 333;
on field-cricket, 339
Gills, 132, 400, 421, 432 f., 478;
jointed, 445, 446, 467;
filamentous, 476;
spongy, 447;
prothoracic, 443;
of pupa, 483;
on imago, 401, 479;
blood-gills, 479
Giraud on Cynipid oviposition, 528
Gizzard, 124, 125
Glacier water, 405
Glande sébifique, 139
Glands, 139, 142;
conglobate, 229;
maxillary, 458;
mushroom, 228
—see also Salivary Glands
_Glandulae odoriferae_, 31, 36, 54
Glomeridae, _43_, 76
_Glomeris_, 33, 43, 52
Gnathites, 94, 97
Golden-eyes, 469
Göldi on eggs of Phasmidae, 265
Gomphinae, _426_
_Gomphocerus_, 308
_Gomphus_, 415
Gonapophysis, 110
_Gongylus gongylodes_, 254 f., 255
Gosch on median segment, 491
Goureau on _Microgaster_, 560
Graber, on dorsal vessel, 134;
on blood cells, 137;
on embryology, 148-151;
on ears, 286;
on ears of Locustidae, 316, 317;
on chordotonal organs, 121;
on blood, 133;
on phonation of _Stenobothrus_, 284;
on _Platycleis_, 312
Grassi, on Myriapoda, 47;
on _Campodea_, 163;
on _Embia_, 353;
on Termitidae, 361 f.
Grassi and Rovelli on Thysanura, 182
Green grasshoppers, 311
Green, Mr. Staniforth, on _Helicomitus_ larva, 461
_Gromphadorhina portentosa_, 235
Grosse on Mallophaga, 346
Growth of wings, 393;
of Mantidae, 248
Gryllacrides, _329_
Gryllidae, _201_, 330-340, _340_
Gryllides, _340_
_Gryllotalpa_, 332;
dorsal vessel, 134;
Malpighian tubes, 127;
tracheal system, 132
Gryllotalpides, _340_
_Gryllus_, head, 93;
_G. campestris_, 332, 339;
_G. domesticus_, 330, 338
Guilding on _Ulula_, 461
Gula, 88, 93
Gyri cerebrales, 119
_Gyropus_, 350
Haase on abdominal appendages, 189, 192
Haemocoele, 22, 23
Hagen, on segments, 88;
on wing-rudiments, 395;
on respiration of immature dragon-fly, 423 f.;
on larvae of Ascalaphides, 460;
on amber Psocidae, 397;
on _Platephemera_, 428;
on Perlidae, 401;
on Psocidae, 393 f.;
on Termites, 360 f.
_Haldmanella_, 308
_Halesus guttatipennis_, 473
Haliday on _Bethylus_, 535
_Halobates_, 83
Halteres, 108
Hansen on _Hemimerus_, 217
_Haplogenius_, 461
_Haplophlebium_, 345
_Haplopus grayi_, egg, 265
Harpagides, _259_
_Harpalus caliginosus_, head, 92
_Harpax ocellata_, 253;
_H. variegatus_, 244
Harrington on _Oryssus_, 507
Harris on Katydids' music, 320
Hart on forms of _Atta_, 501
Hartig on gall-flies, 530
Harvesting Termites, 383
Harvey on metamorphosis, 168
Hatchett Jackson on ecdysis, 162;
on oviduct of Lepidoptera, 139
Haustellata, 94
Haustellum, 476
Haviland on Termites, 368, 373, 384
Hawaiian Islands, 354, 395, 425, 471
Head, 92-94
Heart, 133
Heat, 131
_Helicomitus insimulans_, 460, 461
_Helicopsyche shuttleworthi_, cases of, 482
Hellgrammites, 447 {574}
_Helorus anomalipes_, 534
Hemerobiidae, _453_ f.
Hemerobiides, _465_ f.
Hemerobiina, _467_, 472
_Hemerobius_ larva, 467
_Hemichroa rufa_, 498
Hemimeridae, _201_, 217
_Hemimerus hanseni_, 217;
foetus of, 218;
_H. talpoides_, 218
Hemimetabola, 158
Hemiptera, _173_
_Hemiteles_, 556
Henking on embryology, 146
Henneguy on egg-capsule of _Phyllium_, 271;
on embryology of _Smicra_, 545
_Heptagenia_, 440;
_H. longicauda_, 437
Hessian-fly, parasites, 537
_Heterogamia_, 222;
_H. aegyptiaca_, 220;
egg-capsule, 229
Heterometabola, 158
Heteromorpha, 158
_Heterophlebia dislocata_, 427
_Heteropteryx grayi_, 262
Hetrodides, _329_
Hexapoda, 86
Heymons on earwig embryology, 216
Hind body, 109
Hind wings absent, 429
Histoblasts, 167
Histogenesis, 165
Histolysis, 165, 166
_Hodotermes japonicus_, 383;
_H. havilandi_, 384;
_H. mossambicus_, 356;
_H. brunneicornis_, 359;
_H. quadricollis_, 371
Hoffbauer on elytra, 108
_Holocampsa_, misprint—see _Holocompsa_
_Holocompsa_, 226, 235
Holometabola, 158
Holophthalmi, _459_
Homomorpha, 158
Hooks for wings, 494
_Hoplolopha_, 303
Hose, 393
Howard, on pupation of Chalcididae, 550;
on _Hydropsyche_, 483
Hubbard and Hagen on Termites, 388
Humboldt, 31
Humpback, 445
Huxley, on head, 87;
on cervical sclerites, 99
_Hydropsyche_, 479
Hydropsychides, _482_;
larva, 483
_Hydroptila angustella_, 474;
_H. maclachlani_, larva, 484
Hydroptilides, _484_
_Hylotoma rosae_, 513
Hymenoptera, _173_, _487_-565
_Hymenoptera phytophaga_, _503_ f.
_Hymenopus bicornis_, 253
_Hyperetes_, 395, 397
Hypermetamorphosis, 158, 159, 465, 540, 552, 557
Hyperparasitism, 521
Hypertely, 323
_Hypnorna amoena_, 234
Hypoblast, 65, 149
_Hypocephalus_, 99
_Hypochrysa_, 470
Hypodermis, 162, 480
Hypoglottis, 96
_Hyponomeuta cognatella_, parasite of, 545
Hypopharynx, 96
—see also Lingua
_ICHNEUMONES ADSCITI_, _559_
Ichneumon-flies, 265, _551_;
uninjurious, 264;
supplementary, _558_
Ichneumonidae, _551_-558
Ichneumonides, _557_
_Ictinus_, 419
Imaginal, discs, 165, 166;
folds, 165
Imago, 157
Imbrications, 493
Imhof on _Perla_, 403 f.
Inaequipalpia, _480_
Indusial limestone, 485
Infra-oesophageal ganglion, 117
Inner margin of wing, 108
_Inocellia_, _447_
Inquilines, 373, 524, 531, 533
Insecta, definition, 86
Instar, 155, 158
Instinct of _Leucospis_, 541
Integument, 162
Internal anatomy, 186 f.;
of Acridiidae, 282 f.;
of earwigs, 210;
of _Gryllotalpa_, 335;
of Hymenoptera, 494;
of _Libellula_, 414;
of Mantidae, 246;
of _Myrmeleon_ larva, 457, 458;
of Odonata, 414;
of _Stilopyga orientalis_, 228;
of Phasmidae, 262;
of _Raphidia_, 448;
of _Sialis_ larva, 446;
of Thysanura, 187 f.
Intestine, 114, 124
Involucrum alarum, 206
_Iris oratoria_, 248
_Isogenus nubecula_, 405, 406
_Isopteryx_, 400
_Isosoma_, 546
_Isotoma_, 190
JAMAICA, 388
Japygidae, _184_
_Japyx_, abdomen of, 109;
_J. solifugus_, 184, 196
Jhering, Von, on Termites, 387
Joint, 105
Joint-worms, 546
Joly, on Ephemeridae, 431;
on anatomy of _Phyllium_, 262
Julidae, 34, _43_, 71, 73, 77
_Julopsis_, 74
_Julus_, 36-39, 52;
_J. nemorensis_, 43;
_J. terrestris_, 37, 70, 77;
breeding, 37;
development, 66-69; {575}
heart, 50;
ovum, 63, 64;
eye, 69
Jurassic, 216, 259, 407, 442
Jurine on pieces at base of wing, 102
_KAMPECARIS_, _76_
_Karabidion_, 274
Katydids, 319, 320
King, 361, 378
Klapálek, on Trichopterous larvae, 484 f.;
on _Agriotypus_, 557
Knee, 104
Koch, 42
Koestler on stomatogastric nerves, 120
Kolbe, on entothorax, 103;
on wings of Psocidae, 394
Kollar on _Sirex_, 509
Korotneff on embryology of _Gryllotalpa_, 336
Korschelt on egg-tubes, 138
Korschelt and Heider on regenerative tissue, 167
Kowalevsky, on phagocytes, 166;
on regenerative tissue, 167;
on bee embryo, 496
_Kradibia cowani_, 549
Krancher on stigmata, 111
Krawkow on chitin, 162
Kulagin, on embryology, 537;
of _Encyrtus_, 545
Künckel d'Herculais, on histoblasts, 167;
on emergence of _Stauronotus_, 290
_Labia minor_, 214
_Labidura riparia_, 210, 211, 214, 215
Labium, 95;
of Odonata, 410, 411;
of O. larva, 420
Laboulbène, on _Anurida maritima_, 194;
on _Perla_, 399
Labrum, 93, 93
Lacewing flies, 453, 469
_Lachesilla_, 395
Lacinia, 95
_Laemobothrium_, 347
Lamarck, 77
Lamina, subgenitalis, 224;
supra-analis, 224
Landois on stigmata, 111
Languette, 96
Lankester, 40
Larva, 157;
(resting-larva), 164;
oldest, 449
Larvule, 431, 432
Latreille, 30
Latreille's segment, 491
Latzel, 42, 77
Leach, 30, 77
Lead, eating, 510
Leaf-Insects, 260
Legs, 104;
internal, 496;
four only, 549;
of larvae, 106, 110
Lendenfeld, on dragon-flies, 416, 417;
on muscles of dragon-fly, 115
Lens, 98
Lepidoptera, _173_
_Lepisma_, 185, 196;
_L. saccharina_, 186;
_L. niveo-fasciata_, 195
Lepismidae, _185_
Leptocerides, _482_
_Leptophlebia cupida_, 430
Lespès on _Calotermes_, 364
Leuckart on micropyle apparatus, 145
Leucocytes, 137
_Leucospis gigas_, 540;
larva, egg, 542;
habits, 540 f.
Lewis, Geo., on luminous may-fly, 442
Lewis on _Perga_, 518
Leydig, on brain, 119, 120;
on Malpighian tubes of _Gryllotalpa_, 335;
on ovaries, 137, 142;
on glands, 142
Lias, 216, 239, 340, 427, 428, 453, 485, 503
_Libellago caligata_, 413
_Libellula quadrimaculata_, 411, 425
Libellulidae, _409_
Libellulinae, 416, _426_
Lichens, resemblance to, 253
Liénard on oesophageal ring, 118
Light, attraction of, 441
Ligula, 96
Lilies and dragon-flies, 426
_Limacodes_ egg, 153
Limnophilides, _481_
Lingua, 95, 96, 391, 411, 420, 437
Linnaeus quoted, 84
Liotheides, 346, _350_
_Lipeurus heterographus_, 346;
_L. bacillus_, 347;
_L. ternatus_, 349
_Lipura burmeisteri_, 190;
_L. maritima_, 194
Lipuridae, _190_
Liquid emitted, 264, 324, 399, 515
_Lissonota setosa_, 551
Lithobiidae, _45_, 70, 75
_Lithobius_, 32, 36-39, 41, 45, 58;
breeding, 38;
structure, 48, 49, 57
_Lithomantis_, 259;
_L. carbonaria_, 344
_Locusta_, ovipositor, development and structure, 315;
_L. viridissima_, 318, 319, 321, 324, 327
Locustidae, _201_, _311_-329, _328_
Locustides, _329_
Locusts, 291 f.;
of the Bible, 298;
in England, 299;
swarms, 292-299;
eggs, 292
Loew on anatomy of _Panorpa_, 450;
of _Raphidia_, 448
_Lonchodes duivenbodi_, egg, 265;
_L. nematodes_, 260, 261
Lonchodides, _277_
Longevity, 377, 429, 438;
of cockroach, 229
_Lopaphus cocophagus_, 264
_Lophyrus pini_, 511
Löw on _Coniopteryx_, 471, 472
Löw, F., on snow Insects, 194
Lowne, on embryonic segments, 151; {576}
on integument, 162;
on stigmata, 111;
on respiration, 130
Lubbock, Sir John, on _Pauropus_, 62;
on aquatic Hymenoptera, 538;
on auditory organs, 121;
on sense organs, 123;
on respiration, 130;
on stadia, 165;
on _Cloëon_, 432, 437;
on Collembola, 192;
on Insect intelligence, 487
Lucas on mouth-parts of Trichoptera, 475
Luminous may-flies, 412
Lycaenidae, eggs, 144
Lyonnet on muscles, 115
Lysiopetalidae, _76_
MACHILIDAE, _184_
_Machilis maritima_, 185;
_M. polypoda_, 184
_Macronema_, 478
Malacopoda, 77
Mallophaga, _342_, _345_-350
Malpighi on galls, 525
Malpighian tubes, 114, 124, 127, 187, 353, 360, 392, 403, 414, 421, 448,
457, 458;
of _Gryllotalpa_, 335;
of _Ephippigera_, 335;
of _Mantis_, 246;
of Myriapods, 48
Malta, Myriapods at, 35
Mandibles, 94, 95;
absent, 474, 475
Mandibulata, 94
_Manticora_, 304
Mantidae, _201_, _242_-259, _259_
Mantides, _259_
_Mantis_, immature tegmina, 248;
parasite, 546;
_M. religiosa_, 246, 247, 258
_Mantispa areolaris_, 463;
_M. styriaca_ larva, 464
Mantispides, _463_ f.
_Mantoida luteola_, 251
Marchal on Malpighian tubes, 127
Marine Myriapods, 30
Marshall, on _Apanteles_ cocoons, 560;
on Braconidae, 561
Mask, 420
Mastacides, 301, _309_
_Mastax guttatus_, 301
Maternal care, 214, 336, 517
Maxilla, 95, 96;
of Odonata, 411;
absent, 190
May-flies, 429;
number of, 442
Mayer, on Apterygogenea, 196;
on caprification, 547, 548
Mazon Creek, Myriapods at, 75
M‘Coy on variation of ocelli, 267
M‘Lachlan, on Ascalaphides, 459;
on _Oligotoma_, 354;
on Psocidae, 395;
on Trichoptera, 480 f.
Mecaptera, _174_, 453
Mechanism of flight, 416
_Mecistogaster_, 412
_Meconema varium_, 321
Meconemides, _328_
_Mecopoda_, 319
Mecopodides, _328_
_Mecostethus grossus_, 285, 299, 308
Median plate, 504, 506, 507, 512
Median segment, 109, 490, 491
_Megachile_, nervous system, 496
_Megaloblatta rufipes_, 235
_Megalomus hirtus_, 468
_Megalyra_, _562_
_Megalyridae_, _562_
_Meganeura monyi_, 428
Megasecopterides, 344
_Megastigmus_, 547
Meinert, on earwigs, 210, 211, 212;
on _Myrmeleon_ larva, 457;
on stink-glands, 210
_Melittobia_, 545
Melliss on Termite of St. Helena, 389
Melnikow on eggs of Mallophaga, 348
Membranule, 413
Menognatha, 161
_Menopon leucostomum_, 348;
_M. pallidum_, 350
Menorhyncha, 161
Mentum, 95, 96, 96
Mesoblast, 20, 65, 149
Mesoderm, 20, 149
Mesonotum, 88
_Mesopsocus unipunctatus_, _394_
Mesothoracic spiracle, 491
Mesothorax, 101
Mesozoic, 309, 449, 485
Metabola, 158, 174
Metagnatha, 161
Metamorphosis, 153-170;
of Hymenoptera, 497;
of nervous system, 495 f.
Metanotum, 88
Metapodeon, 491
_Methone_, 200;
_M. anderssoni_, 305, 306
Miall, on imaginal discs, 165, 167;
on unicellular glands, 142
Miall and Denny, on pericardial tissue, 135;
on epithelium of stomach, 126;
on spermatheca of cockroach, 228;
on stigmata, 111;
on stomato-gastric nerves, 120
_Miamia bronsoni_, 449
_Microcentrum retinerve_, 313, 314, 320
_Microgaster_, 559;
_M. fulvipes_, 560;
_M. globatus_, 560
Micropterism, 339, 394, 405 f., 484
Micropyle, 145;
apparatus, 404
Migration, 293, 425
Migratory locusts, 292, 297
Millepieds, 41
Millipedes, 30, 40, 41
Miocene, 216, 258, 407
_Molanna angustata_, mandibles of pupa, 477
Mole-cricket, 333;
leg, 333
Moniez on _Anurida maritima_, 194
_Monodontomerus_, 532;
_M. cupreus_, 543;
_M. nitidus_, 544
_Monomachus_, 563 {577}
Monomorphic ant, 498
Monotrochous trochanters, 494, 520, 564, 565
_Mordella_ eye, 98
_Mormolucoides articulatus_, 449
Morton, on gills of Trichoptera, 483;
on Perlidae, 406
Moult, 156
Moulting, 437;
of external parasite, 556
Mouth-parts, of dragon-fly, 411;
of dragon-fly nymph, 420;
atrophied, 430
Müller, Fritz, on caddis-flies, 482 f.;
on fig-Insects, 549;
on Termites, 358, 360, 374, 381, 382
Müller, J., on anatomy of Phasmidae, 262
Murray, on _Phyllium scythe_, 263; on
post-embryonic development of Orthoptera, 265
_Musca_, metamorphosis, 163, 167
Muscles, 115
Music, of _Locusta_, 318;
of Tananá, 319;
of Katydids, 319
—see also Phonation
Mylacridae, 239
Mymarides, _537_, 538
Myoblast, 149
Myriapoda, 27, _42_, _74_;
definition, 29;
as food, 31;
habits, distribution, and breeding, 29-40;
locomotion, 40;
names for, 41;
classification, _42-47_;
structure, 47-63;
embryology, 63-72;
fossil, 72-77;
affinities, 78
_Myrmecoleon_, 456
_Myrmecophana fallax_, 323
Myrmecophilides, _340_
_Myrmeleo_, 456
_Myrmeleon_, 456;
_M. europaeus_, 457;
_M. formicarius_, 455, 457;
_M. nostras_, 457;
_M. pallidipennis_, 456
Myrmeleonides, _454_ f.
NASUTI, 370
_Necrophilus arenarius_, 462
Necroscides, _278_
Needham on locusts at sea, 297
_Nematus_, 514;
_N. curtispina_, 498
_Nemobius sylvestris_, 339
_Nemoptera ledereri_, 462;
_N._ larva, 462
Nemopterides, _462_
_Nemoura_, 401;
_N. glacialis_, 405
Neoteinic Termites, 362, 380
Nervous system, 116
Nervures, 107, 108, 206;
of Psocidae, 393;
of Embiidae, 352;
of Termitidae, 359
Neuroptera, _172_, _341_-485;
N. amphibiotica, _342_;
N. planipennia, _342_
Neuropteroidea, 486
_Neuroterus lenticularis_, 523
Neuters, 137
Newman on abdomen, 491
Newport on _Anthophorabia_, 545;
on _Monodontomerus_, 544;
on _Paniscus_, 555;
on _Pteronarcys_, 399 f.;
on turnip sawfly, 515
Nicolet on Smynthuridae, 191
Nietner on Psocidae, 395
_Nirmus_, 346 f.
Nitzsch, on Mallophaga, 346 f.;
on Psocidae, 392
_Nocticola simoni_, 232
Nodes, 493
Nodus, 413
_Nomadina_, _565_
Notophilidae, _45_
_Notophilus_, 45
Notum, 91, 100
Number of species, of Insects, 83, 171, 178;
of Cephidae, 506;
of Chalcididae, 539;
of gall-flies, 533;
of Hymenoptera, 503;
of Parasitica, 520;
of Ichneumonidae, 551;
of Odonata, 424;
of Orthoptera, 201;
of earwigs, 215;
of cockroaches, 236;
of Mantidae, 258;
of Phasmidae, 272;
of migratory locusts, 297;
of Perlidae, 407;
of Psocidae, 395;
of sawflies, 518
Nurseries of Termites, 387
Nusbaum on embryology, 149, 152
Nyctiborides, _240_
Nymph, 157;
of dragon-fly, 418, 419, 420, 422, 426;
of Ephemeridae, 432 f., 432, 433, 434, 435, 436
Nymphidina, 465, 472
Nyssonides, 565
OAK-GALLS, 527
Occiput, 94
Ocelli, 97, 282, 313, 400, 409, 430;
variation in, 267, 536
Odonata, _409_ f.
_Odontocerum albicorne_, case of, 480
_Odontura serricauda_, 316
Oecanthides, _340_
_Oecanthus_, 339
_Oecodoma_—see _Atta_
Oedipodides, 304, _309_
Oenocytes, 137
Oesophageal "bone," 391
Oesophageal nervous ring, 118, 121
Oesophagus, 114, 124, 403
Oestropsides, _482_
Oligonephria, 175
_Oligoneuria garumnica_, nymph, 434
_Oligotoma michaeli_, 351, 354;
_O. saundersi_, 352;
_O. insularis_, 354
Ommatidium, 98
_Oniscigaster wakefieldi_, 442
Ontogeny, 153
Oolemm, 144
Oolitic, 239
Ootheca of _Mantis_, 246, 247
_Ophionellus_, _563_
Ophionides, _557_
_Opisthocosmia cervipyga_, 215
Orders, 172 {578}
Orientation, 112
Origin of wings, 206
Orl-fly, 445
Ormerod, Miss, on importation of locusts, 299
Ornament, 200, 215, 233 f., 243, 244, 282, 302, 313, 339
_Orphania denticauda_, 321
_Orthodera ministralis_, 249
Orthoderides, 251, _259_
_Orthophlebia_, 453
Orthoptera, _172_, 198-340, 407
Oryssidae, _506_
_Oryssus abietinus_, 506;
_O. sayi_, 506
Osborn on _Menopon_, 350
Osmylides, _466_
Osmylina, _466_
_Osmylus chrysops_, 341;
larva, 466;
_O. maculatus_, 466
Osten Sacken on similar gall-flies, 532
Ostia, 48 f., 133, 435
Oudemans on Thysanura, 182
Oustalet on Odonata, 422, 423
Outer margin of wing, 108
Ovaries, 137, 138;
of earwigs, 211;
of _Oedipoda_, 283, 284;
of _Perla_, 404;
of Thysanura, 188
Oviduct, 139, 392
Oviposition, 229, 246, 265, 290, 291, 440;
of _Agriotypus_, 557;
of Cynipidae, 527 f., Adler on, 529;
of _Encyrtus_, 545;
of Ichneumon, 555;
of inquiline gall-flies, 532;
of _Meconema_, 321;
of _Pelecinus_, 564;
of _Pimpla_, 553;
of _Podagrion_, 546;
of sawflies, 513;
of _Sirex_, 509;
of _Xiphidium_, 321
Ovipositor, 110, 552, 554;
Cynipid, 524;
of _Locusta_, development, 314, 315
Owen, Ch., 40, 78
_Oxyethira_, 484;
_O. costalis_, larva, 485
Oxyhaloides, 234, _241_
Oxyura, _533_, 534
_PACHYCREPIS_, 550
_Pachytylus cinerascens_, 293, 297, 298, 299, 308;
_P. marmoratus_, 298;
_P. migratorioides_, 298;
_P. migratorius_, 298, 299, 308;
_P. nigrofasciatus_, 285, 298
Packard, on cave-Myriapods, 34;
on air sacs of locusts, 283, 294;
on classification, 173;
on development of _Diplax_, 419;
on may-flies, 430;
on metamorphosis of _Bombus_, 497;
on scales, 397;
on spiral fibre, 129
Pad, 105
Paedogenesis, 142
Pagenstecher on development of _Mantis_, 247
Palaeacrididae, 309
Palaeoblattariae, 239
_Palaeoblattina douvillei_, 238 f.
_Palaeocampa_, 73
Palaeodictyoptera, 486
Palaeomantidae, 259
Palaeontology, 178
_Palaeophlebia superstes_, 427
Palaeozoic, Myriapods, 76;
Insects, 343, 486
_Palingenia bilineata_, 430;
_P. feistmantelii_, 443;
_P. papuana_, 441;
_P. virgo_, 431
Palmén, on dragon-fly nymphs, 423;
on Ephemeridae inflation, 439;
on gills of Perlidae, 402;
on rectal gills, 422;
on tracheal system of immature Ephemeridae, 436
_Palmon_, 546
Palmula, 105
_Palophus centaurus_, 275
_Palpares_, 454
Palpiger, 95
Palpus, 95;
of _Pieris brassicae_, 122
_Pambolus_, 561
Pamphagides, 303, _310_
_Panchlora viridis_, 229
Panchlorides, _241_
Panesthiides, _241_
_Paniscus virgatus_ larva, 555 f.
_Panorpa_, 450, 453;
leg, 104;
_P. communis_, 449;
larva, 452
Panorpatae, _175_, 453
Panorpidae, _449_, 451
Pantel on phonation of _Cuculligera_, 304
Papiriidae, _191_
Paraderm, 164
Paraglossa, 95, 96, 96
Parapteron, 100, 101, 102
Parasites, 540 f., 543;
external, 555
Parasitica, _520_, _521_
Parasitism, 521 f., 535, 559, 560
Parthenogenesis, 141, 481, 497, 516 f. 530 f., 547;
utility, 517
Passalidae, mandibles, 95
Patagia, 102, 103
Patagonia, 459
Paunch, 348, 360, 446, 448
Paurometabola, 158, 199
Pauropidae, 33, 42, _47_
Pauropoda, _47_, 57, 77, 79;
structure, 62
_Pauropus_, 47
Pazlavsky on bedeguar, 527
Pedicellate, 519
Pedunculate body, 495
Pelecinidae, _563_
_Pelecinus polyturator_, 563
_Pelopaeus spinolae_ foot, 105, 106
Perez on Termes, 366, 382
_Perga lewisii_, 517
Periblast, 149
Pericardial septum, 134;
sinus, 134;
tissue, 135
_Peringueyella jocosa_, 325
_Peripatus_, 1, 6, 23, 77, 79;
tracheae, 3, 14, 15;
affinities, 4;
external features, 5;
head, 6; {579}
tail, 6;
colour, 6;
jaws, 7;
legs, 8;
habits, food, 9;
breeding, 10, 19;
alimentary canal, 11;
nervous system, 12, 22;
body-wall, 13;
muscles, vascular system, 15;
haemocoele, 22, 23;
body-cavity, 16, 22;
nephridia, 16, 17, 22;
reproductive organs, 18;
development, 10, 19, 20, 22;
species, _23_;
distribution, 24-26
_Periplaneta americana_, 236;
_P. australasiae_, 221, 236, 239
Periplanetides, _241_
Perisphaeriides, _241_
_Perla_, anatomy, 403 f.;
nymph, 400;
_P. cephalotes_, 406;
_P. maxima_, 400, 406;
_P. parisina_, 399
Perlidae, _398_ f.
Perris on _Termes_, 366, 374
_Petasia_, 303
Petiolata, 496, 503, _519_
Petiolate, 519
Petiole, 492, 493, 519
Petioliventres, 503, 519
Peyrou on atmosphere in bodies, 131
Peytoureau on styles of cockroach, 224
_Pezomachus_, 556
Phagocytes, 137, 165
Phaneropterides, 323, _328_
Pharynx, 114, 124
Phasgonuridea, 311
_Phasma_, 276
Phasmidae, _201_, 407, _260_-278, _277_
Phasmides, _278_
_Phasmodes ranatriformis_, 324
_Philopotamus_, 483
Philopterides, 346, 350
Phonation, 200, 257, 302, 306;
of Acridiidae, 284, 304;
of Locustidae, 318, 319, 320, 324, 327;
of Gryllidae, 331 f;
of _Gryllotalpa_, 334;
of _Brachytrypes_, 332
Phosphorescent Myriapods, 34;
may-flies, 442
Phragma, 103, 491
_Phryganea grandis_, 422;
_P. pilosa_, pupa, 477
Phryganeidae, 398, _473_ f.
Phryganeides, _480_
Phylliides, 267, _278_
_Phyllium_, 262, 263, 267 f.;
_P. crurifolium_, 269 f.;
egg-capsule, structure, 271;
_P. scythe_, 267, 268;
egg, 270;
_P. siccifolium_, egg, 265
_Phyllodromia germanica_, 229, 236;
egg-capsule, 229
Phyllodromiides, _240_
_Phymateus_, 303
Phytophagous Parasitica, 522, 546, 547, 557
Pick, of death-watch, 391
Pictet on nymphs of Ephemeridae, 433
_Pieris_, palpus, 122;
instars, 156;
parasites, 561
Pigment, of iris, 98;
retinal, 98
Pillared eyes, 430
_Pimpla_, 553, 557
Pimplides, _557_
Pitfalls of ant-lions, 455, 459
_Planipennia_, _342_
Plantula, 105
Plateau, on marine Myriapods, 30;
on digestion, 127;
on sight, 416
_Platephemera antiqua_, _428_
_Platyblemmus lusitanicus_, 339
_Platycleis grisea_, 312
_Platycnemis_, 413;
_P. pennipes_, 413, 417
_Platycrania edulis_, egg, 265
_Platygaster_, embryology, 536
Platyptera, _174_
Platypterides, 259, 344, 428
Plecoptera, _175_, 407
Plectoptera, _174_, 442
Plectopterinae, _241_
Pleura, abdominal, 493
Pleuron, 88, 91, 100
Plica of earwig, 209
_Pneumora scutellaris_, 302
Pneumorides, 299, 302, _309_
Pocock on W. Indian Myriapods, 33
_Podacanthus wilkinsoni_, 272
_Podagrion_, parasitism of, 546
Podeon, 491
_Podura_, 194;
_P. aquatica_, 194
Poduridae, _190_
_Poecilimon affinis_, 200
Poisers, 108
Poison-claws, 36, 58, 60
Poletajewa, Olga, on dorsal vessel, 133;
on Odonata, 414
_Polistes lanio_, parasite of, 564
_Polycentropus_, 483
Polydesmidae, 34, 36, _44_, 76
_Polydesmus_, 36, 39, 44
_Polymitarcys_, 440
Polymorphism, 500, 536
_Polynema natans_, 538
Polynephria, 175
Polyxenidae, _43_, 53, 59, 77
_Polyxenus_, 33, 37, 48, 55, 72;
transverse section, 56;
sense-organ, 51
Polyzoniidae, _44_, 53
_Polyzonium_, 44, 48
_Pompholyx dimorpha_, _518_
Pompilides, 494
_Porthetis_, 280, 282
Post-clypeus, 93
Post-embryonic development, 154
Post-scutellum, 100, 101
_Potamanthus_, 433
Potts on _Mantis_, 249
Poulton on _Paniscus_, 556
Praescutum, 100, 101
_Praon_, 550
Pratt, on imaginal discs, 167 {580}
Praying Insects, 242
_Prestwichia aquatica_, 538
Primary larva, 542
Primary segmentation, 150
_Prisopus_, 272
Procephalic lobes, 97, 150
Prochilides, _328_
_Prochilus australis_, 324
Proctodaeum, 123, 151;
in _Musca_, 124
Proctotrypidae, _533_-538
Production of sex, 499
Pro-legs, 514
Pronotal wing-rudiments, 344, 395
Pronotum, 88, 100;
of _Xylocopa_, 490
Pronymph, 164
Propleuron, 100, 489
Propodeon, 491
Propodeum, 491, 492
Proscopiides, 299, _309_, 325
_Prosopistoma punctifrons_, 435
Prostemmatic organ, 195
Prosternum, 88, 100;
of _Vespa crabro_, 491
Protection, 513, 515
Protephemerides, 443
Prothoracic dorsal appendages, 443
Prothorax, 102
Protoblast, 149
Proto-cerebron, 118
Protocranium, 92, 93
Protodonates, 428
Protoperlidae, 408
Protosyngnatha, _75_
Prototracheata, ix, 4
Proventriculus, 114, 124, 125, 450
_Psalis americana_, 215
_Psectra dispar_, 466
Psenides, 524, 533
_Pseudoglomeris fornicata_, 235
Pseudoneuroptera, _342_
Pseudonychium, 105
Pseudophyllides, _328_
Pseudo-sessile, 493
_Pseudotremia_, 34, 35
_Psilocnemis dilatipes_, 413
Psocidae, _390_ f.
_Psocus fasciatus_, 390;
_P. heteromorphus_, 391
Pteromalini, _539_
_Pteronarcys frigida_, 398;
_P. regalis_, 402
_Pteroplistus_, 331
Pterygogenea, 175, 196
Pulvillus, 105
Pupa, 157, 169;
active, 448, 465, 473, 479
Pupation, of Chalcididae, 550;
of _Encyrtus_, 546;
of Proctotrypids, 534, 535
Pupipara, 143
_Pygidicrana hugeli_, 202
Pygidium, 205
Pylorus, 127
Pyramids of Egypt, 462
_Pyrgomantis singularis_, 252
_Pyrgomorpha grylloides_, 303
Pyrgomorphides, 303, _309_
Queen, 144, 361, 378
Radial cell, 524
_Raphidia_, _447_;
_R. notata_, 447;
larva, 448
Raphidiides, _444_, _447_
Raptorial legs, 242 f., 257, 463, 484
Ratzeburg, on _Anomalon_, 553;
on trochanter, 520
Ravages of Termites, 388
Réaumur, on ant-lions, 455;
on circulation of silkworm, 135;
on galls, 525;
on may-flies, 438, 441;
on sawflies, 512, 513;
on spheroidal condition, 164
Receptaculum seminis, 139, 404
Rectal, gills, 421 f.;
respiration, 435
Rectum, 125
Redtenbacher, on migratory locust, 297;
on wing, of _Oligotoma_, 353;
of _Termes_, 359
Reduviid egg, 145
Reflex action, 250
Reproduction of lost parts, 213, 265, 266
Reproductive organs of Ephemeridae, 439
Resemblance, of eggs to seeds, 265, 270, 271;
of one part to another, 208, 266;
of parasite to host, 532;
histological, 271;
of Trichoptera to moths, 484;
to bark, 251;
to flowers, 254, 255, 256;
to inorganic things, 253, 304, 307;
to leaves, 255, 267, 268, 322 f., 323;
to lichens, 253;
to other creatures, 235;
to other Insects, 197, 215, 235, 251, 274, 300, 301, 323, 324, 504,
513, 550;
to vegetation, 200, 260, 274
Respiration [and respiratory organs], 128-132, 431;
by integument, 483;
by setae, 435;
of nymphs of Odonata, 420 f.;
of Perlidae, 401 f.
Respiratory chamber, 434
Retinula, 98
Reuter on ventral tube, 192
Rhabdom, 98
_Rhipipteryx_, 337, 338
_Rhizotrogus_ egg-tubes, 138
_Rhodites rosae_, 498, 527, 528, 531;
larva, 532;
parasite, 539
Rhyacophilides, _483_
_Rhyacophylax_, 482
Rhynchota, _175_
_Rhyparobia maderae_, 237
_Rhyssa persuasoria_, 554
Riley, on caprification, 549;
on _Cephus_, 505;
on development of _Caloptenus_, 288, 289;
on galls, 526 f.;
on Katydids, 320;
on locust swarms, 293;
on _Microcentrum_, 313;
on ovipositing of locust, 290; {581}
on subimago, 437;
on _Thalessa_, 554
Ritsema on _Enoicyla_, 481
Ronalds on anglers' flies, 441
Roux on _Necrophilus_, 462
Royal pairs, 377
Rühl on earwig, 213
SACS—see Air Sacs
Sagides, _328_
Salivary glands, 124, 126, 187, 210, 228, 246, 283, 335, 348, 353, 403,
414, 495;
of _Peripatus_, 11;
of Myriapods, 48, 49
Salivary receptacle, or reservoir, 126, 228, 246, 335, 348, 360
Saltatoria (Orthoptera), _201_
Sandwich Islands—see Hawaiian Islands
Saunders, Sir Sydney, on _Scleroderma_, 536;
on caprification, 548
Saussure, H. de—see De Saussure
Savage on Termites, 368
Saw, 493, 512
Sawflies—see Tenthredinidae
Scales, 185, 189, 397
_Scapteriscus_, 334
_Scelimena_, 301
Schindler on Malpighian tubes, 246;
of _Gryllotalpa_, 335
_Schistocerca peregrina_, 298;
development, 287;
_S. americana_, 298, 308
_Schizodactylus monstrosus_, 325
Schizophthalmi, 459
Schizotarsia, 35, _46_, 57, 58, 70, 75;
structure, 59
Schletterer on parasitic Hymenoptera, _562_, _563_
Sclerite, 91
_Scleroderma_, 536
_Scolia_, ovaries, 138
_Scolopendra_, 30, 31, 32, 41, 78
_Scolopendrella_, 47, 61
Scolopendrellidae, 33, 42, _46_
Scolopendridae, 31, 33, 39, _45_, 75;
spermatophores, 39
Scorpion-flies, 449 f.
Scudder, on grasshopper music, 287;
on Katydids' music, 320;
on locusts at sea, 297;
on reproduction of lost limbs, 265;
on fossil Insects, 486;
on fossil earwigs, 216;
on fossil may-flies, 443;
on fossil Sialidae, 449;
on Tertiary Insects, 179
Scutellum, 100, 101
_Scutigera_, 35, 36, 48;
sense organ, 51
Scutigeridae, 35, 36, 40, _46_, 50
Scutum, 100, 101
Secondary, 427, 472;
larva, 542
Securifera, 503
Segmentation, 149, 237;
of ovum of _Smicra_, 545
Segments, 88, 90;
number of, 87
Selys, De, on dragon-flies, 425, 427
Semi-pupa, 497
Sense organs, 121-123
Senses, 541, 544, 553
Sericostomatides, _474_, _482_
Series, 177, 201
Serosa, 148
Serrifera, 503
Sessile abdomen, 493
Sessiliventres, 492, 496, _503_
Sex, 498, 499, 500
Sexes, 137
Sexual organs, external, 141
Shaw on Orthoptera, 201
Sialidae, 407, _444_
Sialides, _444_
_Sialis lutaria_, 444;
eggs, 445;
larva, 445;
tracheal gill, 446
Silk, 127
_Silo_, parasite of, 558
Silurian Insect, 238
Silver fish, 186
Simple eyes, 97, 184
—see also Ocelli
Siphonaptera, _174_, _175_
_Sirex_, habits of its parasite, 554;
_S. augur_, 509;
_S. gigas_, 508, 510;
_S. juvencus_, 508
Siricidae, _507_;
parasites of, 563
Siricides, _510_
_Sisyra_ 467;
_S. fuscata_ larva, 467
Sisyrina, _467_
_Sitaris humeralis_, early stages, 159
Sloane, Sir Hans, on locusts at sea, 297
Smallest Insect, 537
Smeathman on Termites, 366 f., 381, 383, 387
_Smicra clavipes_ embryology, 545
Smith, F., on _Cynips_, 530;
on _Trigonalys_, 564
Smynthuridae, _191_
_Smynthurus variegatus_, 191;
_S. fuscus_, 192
Snow-Insects, 194
Social, Insects, 85, 361, 369;
Hymenoptera, 488, 500 f.
Soldiers, 370, 371, 372
Somites, 87
Sommer on _Macrotoma_, 163, 195
Soothsayers, 242
Sound production, 358
—see also Phonation
_Spathius_, 561
Species, number of—see Number
Spencer, Herbert, on caste and sex, 500
Spermatheca, 139, 228, 499
Spermatophores, 39
Spermatozoa, 140
_Sphaeropsocus kunowii_, 397
Sphaerotheriidae, _43_
_Sphaerotherium_, 43
_Sphex chrysis_, 490
Spiders eaten, 464, 465 {582}
Spinneret, 458
Spinners, 441
Spiracles, 89, 111, 128;
number of, 186;
of dragon-fly nymph, 423;
absent, 436
—see also Stigmata
Spiral fibre, 128
_Spongilla fluviatilis_, larva in, 467
Spontaneous generation, 525
Spring of Collembola, 191
Spurs, 104
Stadium, 155, 158
Stalked, cocoons, 560;
eggs, 469
St. Augustine quoted, 85, 565
Stein on _Raphidia_ larva, 448
_Stelis_, parasitic, 544;
parasitised, 543
Stem sawflies, 504
_Stenobothrus_, 308;
sound-instruments, 284
Stenodictyopterides, _344_
Stenopelmatides, 321, _329_
_Stenophasmus ruficeps_, 561
_Stenophylla cornigera_, 257, 258
Stephanidae, _561_
_Stephanus_, 562
Sternum, 91, 100
St. Helena, 389
Stick-Insects, 260
Stigma of wing, 524, 534
Stigmata, 88, 89, 111, 204;
position, 493;
on head, 193;
S. repugnatoria, 36
—see also Spiracles
_Stilopyga orientalis_, 223, 228, 231, 236
Sting, 493;
and ovipositor, 534
Stink-flies, 469
Stink-glands, 31, 125, 210, 264, 335
Stipes, 95
Stoll on spectres, etc., 254
Stomach, 114, 124, 125
Stomato-gastric nerves, 120, 121
Stomodaeum, 123, 151
Stone-flies, 407
_Stratiomys strigosa_ parasite, 545
Stridulation, 304
—see also Phonation
Stummer-Traunfels on Thysanura and Collembola, 189
St. Vincent, island of, 461
Styles, 224, 238
Sub-imago, 429, 437
Sub-Order, 177
Subulicornia, _426_
Sucking spears, 466, 467, 470, 471
Suctorial mandibles, 453, 456
Super-Orders, 177
Supplementary Ichneumon-flies, _558_
Supra-oesophageal ganglion, 117
Sutures, 92
Swarms: of locusts, 292-299;
of may-flies, 441;
of Termites, 362
Sympathetic nervous system, 120;
absent, 353
_Symphrasis varia_, 465
Symphyla, 42, _46_, 77, 79;
structure, 61
Symphyta, 503
_Sympycna fusca_, 415
Synaptera, _175_
_Synergus_, 531
Syngnatha, _44_
Tananá, 319
_Tarachodes lucubrans_, 249
Tarsus, 88, 104, 106
Taschenberg on parthenogenesis, 141
Tausendfüsse, 41
Teeth, 95
Tegmina, 108;
leaf-like, of _Pterochroza_, 322;
of crickets, 331;
of earwigs, 205, 212;
of _Phyllium_, 269;
of _Schizodactylus_, 325
Tegula, 103, 108
_Teleganodes_, 442
Telson, 205
Temples, 94
Templeton on _Lepisma_, 195
Tendons, 116
Tenthredinidae, _510_-518
_Tenthredo_ sp., 489;
testes, 140
Tentorium, 99
Tepper on fossorial Blattid, 241
Terebrantia, _520_
Tergum, 91, 100
_Termes_ sp., 378;
_T. lucifugus_, 359, 360, 364, 365, 373, 374;
_T. mossambicus_, 356;
_T. bellicosus_, 366, 371;
trophi, 357;
cell of, 367;
_T. occidentis_, 371;
_T. armiger_, 371;
_T. tenuis_, 389;
_T. cingulatus_, 371;
_T. dirus_, 371;
_T. debilis_, 371;
_T. viarum_, 383
Termitarium, 386, 387
Termites, 357 f.;
distinctions from ants, 502;
wings, 359;
anatomy, 360
Termitidae, _356_;
number of species, 389
Tertiary, 196, 216, 239, 276, 309, 340, 398, 427, 442, 449, 453, 472,
485, 533, 551, 558
Testes, 18, 49, 140, 404, 440;
of Psocidae, 392;
of _Stilopyga orientalis_, 228
_Tetrophthalmus chilensis_, 346
Tettigides, 299, 300, _309_
_Tettix bipunctatus_, 300
_Thalessa_ larva, 507;
oviposition, 554
_Thamastes_, 485
_Thamnotrizon apterus_, 316
_Thecla_ egg, 145
Thelyotoky, 141, 498
_Thermobia furnorum_, 186
_Thliboscelus camellifolius_, 319
_Thoracantha latreillei_, 550
Thorax, 99-103, 101, 103
_Thorax porcellana_ wing, 227
_Thyrsophorus_, 395
Thysanoptera, _173_
Thysanura, _182_ f.; {583}
distinctions from Symphyla, 61, 77, 79
Tibia, 88, 104
_Tillus elongatus_ larva, 90
_Tinodes_, 483
_Titanophasma fayoli_, 276, 428
_Tomateres citrinus_, 454, 458
_Tomognathus_, 498
Tongue, 96
—see also Lingua
Torymides, _547_
_Toxodera_, 253;
_T. denticulata_ 254
Trabeculae, 345
Tracheae, 128;
absent, 553, 555
Tracheal gills, 400 f., 401
—see also Branchiae
_Tremex columba_, 507
Trias, 449
Triassic, 239
_Trichijulus_, _76_
_Trichodectes_, 350;
_T. latus_, 349
Trichoptera, _342_, _473_ f.
_Trichostegia_, 480
_Tricorythus_, 434, 436
Tridactylides, _340_
_Tridactylus variegatus_, 337
Trigonalidae, _564_
_Trigonalys maculifrons_, 564
Trigonidiides, _340_
Trimen on _Trachypetra bufo_, 304
Trinidad, 501
_Trinoton luridum_, 345, 347
Trito-cerebron, 118
Trochanter, 88, 104, 491, 494, 520
Trochantin, 104;
of cockroach, 222
Trophi, 91, 94
Tryphonides, _557_
Tryxalides, 303, _309_, 325
_Tryxalis nasuta_, 279
Tubulifera, _520_
Tympanophorides, _328_
Tympanum, 285 f.
Tyndall on grasshopper music, 286
Ulloa, 33
Uroceridae, _507_
Useless wings, 199, 394, 484, 561
Uterus, 18, 392
Vagus nervous system, 120
Van Rees on metamorphosis, 162, 164
Variation, 536;
of colour, 252, 288, 304, 308;
in desert Insects, 305;
in ocelli, 267, 395, 536
Vatides, _259_
Vas deferens, 18, 140, 187, 392
Vayssière, on nymphs of Ephemeridae, 434;
on lingua, 438
Veins, 206
Ventral chain, 116, 187, 414;
of Perlidae, 404
Ventral plate, 148;
tube, 191, 192
Verhoeff, 38
Verloef [misprint for Verhoeff]
Verlooren on circulation, 436
Vertex, 94
Vesicula seminalis, 140, 392;
absent, 404, 414
_Vespa crabro_ prosternum, _491_
Vestibule, 112
Viallanes, on head, 87;
on brain, 118, 119;
on metamorphosis, 162
Visceral nervous system, 120
Vitellophags, 147, 152, 168
Viviparous Insects, 217, 229, 143, 218
Voetgangers, 295 f.
Vom Rath on sense organs, 122
Voracity, 250, 258
Vosseler on stink-glands, 210
Walker, J. J., on Australian Termites, 386
Walking-leaves, 267
Walking on perpendicular and smooth surfaces, 106
Walsh on galls, 531
Wasmann on St. Augustine's works, 565
Wattenwyl, Brunner von—see Brunner
Weismann, on caste, 500;
on metamorphosis, 162, 166;
on imaginal discs, 167
Westwood, on _Forficula_, 204;
on _Helicomitus_ larva, 460, 461;
on _Lachesilla_, 395;
on _Scleroderma_, 536
Weta-punga, 326
Wheeler, on Malpighian tubes, 127;
on embryology of Orthoptera, 199;
on embryology of _Xiphidium_, 321;
on vitellophags, 147, 152, 168;
on segmentation, 150
White ants, 356
—see Termites
Wielowiejski on blood-tissue, 133, 137
Will on brain of Aphididae, 118
Wingless: caddis-fly, 481;
earwigs, 205;
Insects, 345, 352, 356, 451, 488, 536, 547;
wingless Psocidae, 394 f.
—see also Apterous
Wings, 107;
origin and function, 394;
of Blattidae, 225 f., 227;
development of, in locust, 288;
in Trichoptera, 479, 480;
of dragon-fly, 413;
of earwigs, 206;
of _Ephemera_, 431;
growth of, 418;
of Ichneumon and _Bracon_, 559;
posterior absent, 466, 485;
wing-hooks, 494;
veins, 107
—see also Tegmina and Alar Organs
"Wire-worm," 29, 36
Wistinghausen on tracheae, 129
Wood-Mason on _Cotylosoma_, 272;
on mandibles, 95;
on Mantidae, 251, 253;
on _Oligotoma_, 352;
on phonation of Mantidae, 258
Woodworth on embryology, 146, 153
Workers, 361, 374, 488, 495
Wyandotte Caves, Myriapods in, 34
Xambeu on _Palmon_, 546 {584}
_Xerophyllum simile_, 301
_Xiphidium ensiferum_, 321
_Xiphocera asina_, 303
_Xylobius_, 73, _76_
_Xylocopa_, 494;
metamorphosis, 170;
pronotum, 490
Xyphidriides, 507 f., _510_
Yolala, 298
Yolk, 19, 64, 145, 152, 545
Zimmermann on caudal respiration, 435
Zittel, figure from, 276
_Zygaena_ embryo, 151
Zygopterides, _417_, _426_;
nymphs, 422
END OF VOL. V
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NOTES
[1] L. Guilding, "_Mollusca caribbaeana_: an Account of a New Genus of
Mollusca," _Zool. Journ._ vol. ii. 1826, p. 443, pl. 14; reprinted in
_Isis_, vol. xxi. 1828, p. 158, pl. ii.
[2] H. N. Moseley, "On the Structure and Development of _Peripatus
capensis_," _Phil. Trans._ clxiv. pls. lxxii.-lxxv. pp. 757-782; and
_Proc. R. S._ xxii. pp. 344-350, 1874.
[3] A. Sedgwick, "A Monograph of the Genus _Peripatus_," _Quart. Journ.
of Mic. Science_, vol. xxviii., and in _Studies from the
Morphological Laboratory of the University of Cambridge_, vol. iv.
[4] A. Sedgwick, "A Monograph of the Development of _Peripatus
capensis_," _Studies from the Morphological Laboratory of the
University of Cambridge_, vol. iv.
[5] F. M. Balfour, "The Anatomy and Development of _Peripatus capensis_,"
edited by Professor H. N. Moseley and A. Sedgwick, _Quart. Journ.
Mic. Sci._ xxiii. pp. 213-259, pls. xiii.-xx. 1883.
[6] See Whitman, _Journal of Morphology_, vol. i.
[7] There are now, I am told by Professor Jeffrey Bell, specimens from
Natal (I believe undescribed) at the British Museum with twenty-three
and twenty-four pairs of legs.
[8] This name was first applied by Blanchard to a species from Cayenne.
The description, however, is very imperfect, and it is by no means
clear that the Cayenne species is identical with the species here
named _Edwardsii_.
[9] The existence of this species is very doubtful. The description of it
was taken from a single specimen. The evidence that this specimen was
actually found in Sumatra is not conclusive.
[10] Not to be confused with the larva of _Elater lineatus_, also known as
"wire-worm."
[11] See L. Jenyns' _Observations in Nat. Hist._ London, 1846, p. 296.
[12] "A Revision of the Lysiopetalidae, a family of the Chilognath
Myriapoda, with a notice of the genus _Cambala_," by A. S. Packard,
junior, _Proc. Amer. Phil. Soc._ xxi. 1884, p. 187.
[13] C. L. Koch, _System der Myriapoden_. Regensburg, 1847.
[14] C. L. Koch, _Die Myriapoden_. Halle, 1863.
[15] Latzel, _Die Myriapoden der Œsterreichisch-Ungarischen Monarchie_.
Wien, 1880.
[16] Tres muscae consumunt cadaver equi, aeque cito ac leo. _Syst. Nat._,
ed. xii. ref. I. pt. 2, p. 990.
[17] _Ann. Sci. Nat._ (7) iv. 1887, p. 111.
[18] _Stettin. Ent. Zeit._ l. 1889, p. 165.
[19] The wings, by many morphologists, are not included in the category of
"appendages"; they apparently, however, differ but little in their
nature from legs, both being outgrowths of the integument; the wings
are, however, always post-embryonic in actual appearance, even when
their rudiments can be detected in the larva. No insect is hatched
from the egg in the wing-bearing form.
[20] See on this subject, p. 217.
[21] _Ann. Sci. Nat._ I. 1824, p. 97, etc.
[22] See also Fig. 47 (p. 88).
[23] In entomological language the piece between each two joints of an
appendage is itself called a joint, though segment is doubtless a
better term.
[24] _Arch. f. Naturgeschichte_, lvi. 1890, p. 221.
[25] _Zeitschr. wiss. Zool._ liv. 1892, p. 579.
[26] _Mem. Acc. Lincei Rom._ (4) iv. 1888, p. 554.
[27] _Zeitschr. wiss. Zool._ xvii. 1867, p. 187.
[28] _Zool. Anz._ iii. 1880, p. 584.
[29] _The Cockroach_, 1886, p. 151.
[30] _Anatomy of the Blowfly_, 1893, p. 362.
[31] Lyonnet, _Traité anatomique de la Chenille qui ronge le bois de
Saule_. La Haye, 1762. On p. 188 he says that he found 1647 muscles,
without counting those of the head and internal organs of the body.
He puts the number found in the human body at 529.
[32] _SB. Ak. Wien_, Abth. 1, lxxxiii. 1881, pp. 289-376.
[33] _Mem. Acc. Torino_ (2), xliii. 1893, p. 229.
[34] _Bull. Soc. Philom._ Paris (7), xi. 1887, p. 119, etc., and _C. R._
civ. 1887, p. 444.
[35] _Zool. Jahrbuch. Anat._ iii. 1888, p. 276.
[36] Kolbe, _Einführung_, 1893, p. 411.
[37] _Arch. de Biol._ i. 1880, p. 381.
[38] _Ann. Sci. Nat. Zool._ (7) ii. 1887, and iv. 1887.
[39] _Zool. Anz._ iv. 1881, p. 452.
[40] _Zeitschr. wiss. Zool._ xlvi. 1888, pl. xxxi.
[41] _On the Senses, Instincts, and Intelligence of Animals, with special
reference to Insects._ Vol. LXV. International Scientific Series,
1888.
[42] _Bijd. Dierkunde_, 16, 1888, p. 192.
[43] For a review of their number see Wheeler, _Psyche_, vi. 1893, pp.
457, etc.
[44] _Ann. Soc. Ent. France_, lxi. 1892, Bull. p. cclvi.
[45] _Mem. Ac. Belgique_ (2), xli. 1875, and _Bull. Ac. Belgique_ (2),
xliv. 1877, p. 710.
[46] _American Naturalist_, xx. 1886, pp. 438 and 558.
[47] _Zeitschr. wiss. Zool._, xlix. 1890, p. 565.
[48] See Miall and Denny, _Cockroach_, p. 158.
[49] Eisig, _Mon. Capitelliden_, 1887, p. 781.
[50] _Tr. Linn. Soc. London Zool._ xxiii. 1860, p. 29.
[51] _Blowfly, etc._ p. 376.
[52] _C. R. Ac. Sci._, cxv. 1892, p. 61, and _Bull. Sci. France Belgique_,
xxv. 1893, p. 18.
[53] _Compt. rend. Ac. Paris_, cii. 1886, p. 1339.
[54] See Newport, _Phil. Trans._ 1837, and Lubbock _Linn. Trans._ xxiii.
1860, p. 29, etc.
[55] _Zeitschr. wiss. Zool._ xxvi. 1876, p. 137.
[56] _Zeitschr. wiss. Zool._ xliii. 1886, p. 512.
[57] _Zool. Anz._ ix. 1886, p. 13.
[58] _Cockroach_, p. 140.
[59] _Bull. Sci. France Belgique_, xxv. 1893, p. 22.
[60] _Biol. Centralbl._ xi. 1891, p. 212.
[61] _Acta. Ac. German._ xxxiii. 1867, No. 2.
[62] _Linnaea entomologica_, xii. 1858, p. 313.
[63] _Zeitschr. wiss. Zool._ 1886, xliii. p. 539.
[64] _Tr. Linn. Soc. London_, 2nd ser.; _Zool._ v. 1890, p. 173.
[65] _Zeitschr. wiss. Zool._ l. 1890, p. 317.
[66] _Abh. Ges. Halle_, xvii. 1892, p. 365.
[67] _Tr. Ent. Soc. London_, 1893, p. 241.
[68] _Arch. Anat. Phys._ 1855 and 1859.
[69] _Acta. Ac. German._ xxxiii. 1867, No. 2, p. 81.
[70] _Müller's Arch. Anat. Phys._ 1855, p. 90.
[71] _Zeitschr. wiss. Zool._ xxvi. 1876, p. 115.
[72] Scudder, _Butterflies of New England_, i. 1889, p. 99.
[73] _J. Morphol._ viii. 1893, p. 81; see also Graber's table on p. 149.
[74] _Denk. Ak. Wien_, lv. 1888, p. 109, etc.
[75] _Morph. Jahrb._ xiv. 1888, p. 347.
[76] In Miall and Denny, _Cockroach_, p. 188.
[77] _Morph. Jahrb._ xiv. 1888, p. 345.
[78] _J. Morphol._ viii. 1893, p. 1.
[79] _J. Morphol._ viii. 1893, pp. 64, 65, and 81.
[80] _Trans. Linn. Soc._, 2nd Series, "Zool." 1888, iii. p. 12.
[81] _Orthoptera europaea_, 1853, p. 37.
[82] _Ann. Sci. Nat. Zool._ Ser. iv. vol. vii. 1857, pl. 17.
[83] Nature Series, 1874.
[84] See _Proctotrupidae_ subsequently.
[85] _Verh. Zool.-bot. Ges. Wien_, xix. 1869, p. 839.
[86] "Syst. Zool. Stud." _SB. Ak. Wien_, Abth. 1, xci. 1885, p. 291.
[87] _Zeitschr. wiss. Zool._ xiv. 1864, p. 187.
[88] Viallanes, _Ann. Sci. Nat._, Series 6, "Zool." xiv. 1882.
[89] Unfortunately in the Russian language.
[90] _Zool. Jahrb._ Abth. Anat. iii. 1888, p. 1.
[91] _Zeitschr. Biol._, xxix. 1892, p. 177.
[92] _Trans. Linn. Soc. London_, "Zoology," 2nd series, v. 1890, p. 174.
[93] _Trans. Linn. Soc._ xxv. 1866, p. 491.
[94] _Zeitschr. wiss. Zool._ xli. 1885, p. 712.
[95] "Fauna und Flora d. Golfes von Neapel," _Die Capitelliden_, 1887, p.
781.
[96] _Trans. Linn. Soc._ xxiv. 1863, p. 65.
[97] _Trans. Linn. Soc._ "Zool." v. 1892, p. 267.
[98] _Ann. Sci. Nat._, Series 6, "Zool." xiv. 1882, p. 150.
[99] _Zool. Anz._ viii. 1885, p. 125.
[100] _Mitt. Schweiz. ent. Ges._ viii. 1893, p. 403.
[101] _Recherches Org. des Volucelles_, 1875, p. 143.
[102] _Zeitschr. wiss. Zool._ xlv. 1887, p. 587.
[103] _Lehrbuch Entwicklungsgeschichte_, Spec. Theil. 1890, p. 875.
[104] _Zeitschr. wiss. Zool._ xiv. 1864, p. 187.
[105] _Arch. f. Naturges._ lix. 1893, 1, p. 168.
[106] Wheeler, in _J. Morphol._ viii. 1893, p. 81.
[107] _Syst. Nat. Ed._ 12, ref. i. pars ii. p. 536 (by error, 356).
[108] It must not be supposed that all wingless Insects fall within the
limits of this Order.
[109] _American Naturalist_, xx. 1886, p. 808.
[110] "Syst. Zool. Studien." _S.B. Ak. Wien_, xci. 1885, Abth. I. p. 374.
[111] The term natural is here employed in the empirical sense described by
Brunner von Wattenwyl, _Nouv. Syst. Blattaires_, 1865, p. vii.
[112] Lord Walsingham, _Proc. Ent. Soc. London_, 1889, p. lxxx.
[113] We may mention that fossil Insects are chiefly determined from their
wing-remains, which are often surprisingly perfect. This is one of
the reasons that have induced us to prefer a classification of
Insects in which the nature of the wings is considered of great
value. It would be impossible to refer fossil Insects to groups that
are established on account of the metamorphosis or of the internal
structure of their components, for there is not yet any evidence on
either of these points in the fossil remains preserved for us by the
rocks.
[114] _Bull. U.S. Geol. Survey_, No. 31, 1886, p. 109.
[115] _Mem. Acc. Lincei Roma_ (4), iv. 1888, p. 543, etc., and other
preceding memoirs mentioned therein.
[116] _Bijdr. Dierkunde_, xvi. 1888, pp. 147-227.
[117] _Natural. Sicil._, ix. 1889, pp. 25, etc.
[118] _Ann. Soc. ent. France_, 1892, p. 34.
[119] _Morph. Jahrb._ xv. 1889, p. 363.
[120] _SB. Ak. Wien_, c. 1891, Abth. I. p. 216.
[121] _Ent. Tidskr._ i. 1880, p. 159.
[122] _Morphol. Jahrb._ xv. 1888, p. 361.
[123] _Verh. zool.-bot. Ges. Wien_, viii. 1858, p. 564.
[124] _Ann. Soc. ent. France_, 4th ser. iv. 1864, p. 705.
[125] _Rev. biol. Nord France_, ii. 1890, p. 347.
[126] _J. Morphol._ viii. 1893, p. 64.
[127] _Ent. Mo. Mag._ xxv. 1889, and xxvi. 1890.
[128] _Ann. Mus. Genova_, xxxiii. (1892).
[129] _Orthoptera Europaea_, 1853, pl. vi. f. 4, p. 434.
[130] _Morph. Bedeut. Seg. Orthopt._ 1876, p. 14; and _Prod. Orthopt.
Europ._ 1882, p. 3.
[131] _Proc. Zool. Soc. London_, 1892, p. 586.
[132] _Naturhistorisk Tidsskrift_, 3rd ser. ii. 1863, p. 475.
[133] _Arch. mikr. Anat._ xxxvi. 1890, p. 565.
[134] _Ann. Sci. Nat._ xiii. 1828, p. 337.
[135] _Naturhistorisk Tidsskrift_, 3rd ser. ii. 1863, p. 475.
[136] Some writers are of opinion that there are only two thoracic
spiracles in Insects, considering the third as belonging really to
the abdomen. Looking on the point as at present chiefly one of
nomenclature, we make use of the more usual mode of expression.
[137] As on last page, and also _op. cit._ v. 1868, p. 278.
[138] _Bull. Ent. Ital._ xii. 1880, p. 46.
[139] It may be worth while to repeat that "joint" means a piece, and is
the equivalent of "link" in a chain.
[140] _Materials for the Study of Variation_, 1894, p. 413.
[141] _Naturhist. Tidsskrift_, 3rd ser. ii. 1863, p. 474.
[142] _Mt. Schweiz. ent. Ges._ vii. 1887, p. 310.
[143] _Mem. hist. Insectes_, iii. 1773, p. 548.
[144] _SB. Ges. naturf. Fr. Berlin_, 1893, p. 127.
[145] _Ent. Tidskr._ 1894, p. 65.
[146] This enigmatic structure is similar in position to the aural orifice
of Locustidae (see Fig. 101); but it is closed by a transparent
membrane, whereas the ear orifice of Locustidae is, as we shall
subsequently see, quite open.
[147] _Rev. biol. Nord France_, vii. 1894, p. 111.
[148] _Ann. Nat. Hist._ Decr. 6th, ser. x. 1892, p. 433.
[149] _Prod. Orth. europ._ 1882, p. 27, and _Rev. Syst. Orthopt._ 1892, p.
15. Unfortunately de Saussure adopts a different nomenclature; we
have preferred Brunner's as being more simple.
[150] _Ann. Sci. Nat. Zool._ ser. 5, x. 1868, p. 161.
[151] _Nouv. Syst. Blattaires_, 1865, p. 265.
[152] _The Cockroach_, p. 170.
[153] Cf. Duchamp, _Rev. Sci. Nat. Montpellier_, vii. [?1879], p. 423.
[154] Huxley, _Manual Anat. Invert. Animals_, 1877, p. 416.
[155] Riley, _Insect Life_, iii. 1891, p. 443, and iv. 1891, p. 119.
[156] _Essais entomologiques_, St. Petersburg, 1821.
[157] _Beiträge zur näheren Kenntniss von Periplaneta orientalis_,
Elberfeld, 1853.
[158] _Nouv. Syst. Blattares_, 1865, p. 16, etc.
[159] _Naturalist in Nicaragua_, 1874, p. 110.
[160] See Bolivar, _Ann. Soc. ent. France_, 1892, p. 29.
[161] _P. ent. Soc. London_, 1881, p. 1.
[162] _Biol. Centr. Amer. Orthopt._ 1893, p. 57.
[163] Schäff, _Zool. Anz._ xvi. 1893, p. 17.
[164] Westwood, _Modern Class. Insects_, i. 1839, p. 418.
[165] _Zeitschr. wiss. Zool._ xlviii. 1889, p. 89; and _Mem. Ac. St.
Petersb._ xxxviii. No. 5, 1891.
[166] _Ann. Hofmus. Wien._, i. 1886, p. 104.
[167] Zittel, _Handb. Palaeont._ I Abth. ii. 1885, p. 753.
[168] _Biol. Centr.-Amer. Orthoptera_, 1893.
[169] Although the genus _Chorisoneura_ has unarmed femora, it must be
placed in this division.
[170] The "black beetle," _Stilopyga orientalis_, belongs to this tribe, as
does also _Periplaneta americana_.
[171] _Tr. R. Soc. S. Austral._ xvii. 1893, p. 68.
[172] _Zeitschr. wiss. Zool._ xxx. 1878, p. 609, pl. xxxviii. fig. 7.
[173] _Arch. f. Naturgesch._ xxx. Band 1, 1864, p. 7.
[174] _Biol. Centr. Amer. Orthopt._ 1894, p. 160.
[175] Our figures do not exhibit this attitude; if portrayed in their
natural position in a drawing the front legs would be to a large
extent obscured.
[176] The name of the species is not given (_Tr. N. Z. Inst._ xvi. 1883, p.
114), but it is probably _Orthodera ministralis_ Fab., an Australian
Insect perhaps taken to New Zealand by miners. Cf. Wood-Mason, _Cat.
Mantodea_, i. 1889, p. 20.
[177] _Berlin. ent. Zeitschr._ viii. 1864, p. 234.
[178] _Ann. Soc. Linn. Lyon_, xi. 1893, p. 205.
[179] _Proc. ent. Soc. London_, 1867, p. cv.
[180] _Cat. Mantodea_, i. 1889, p. 4.
[181] _Ann. Soc. ent. France_, 1835, p. 457.
[182] _P. ent. Soc. London_, 1877, p. xxix.
[183] _Afbeeldingen der Spoken en wandelende Bladen_, etc., Amsterdam,
1813.
[184] _P. Asiat. Soc. Bengal_, 1877, p. 193.
[185] _Tr. ent. Soc. London_, 1878, p. 263.
[186] _Ann. Nat. Hist._ 3rd ser. xix. 1867, p. 144.
[187] _Bull. Soc. Philomat._ (8) ii. 1890, p. 154.
[188] _Insectes fossiles des temps primaires_, 1894, p. 353.
[189] _Acta Ac. German._ xii. 1825, pp. 555-672, pls. l.-liv.
[190] _Mem. Ac. Sci. Toulouse_, series 7, iii. pp. 1-30.
[191] _Edinburgh Philosoph. Journ._ January 1856.
[192] _Zool. Jahrb. Syst._ i. 1886, p. 724.
[193] _P. Boston Soc._ xii. 1869, p. 99.
[194] _Prod. Zool. Victoria_, Decade vii. 1882, p. 34.
[195] See de Borre, _CR. Soc. ent. Belgique_, xxvii. 1883, p. cxliii.
[196] See Murray, _Edinburgh New Philosophical Journal_, January 1856.
[197] _CR. Ac. Paris_, cxviii. 1894, No. 24, p. 1299.
[198] _SB. Ak. Wien_, xci. 1885, p. 361. The nomenclature applied to the
nervures by these authors is not the same as that of Brunner;
according to their view the wing of _Phyllium_, female, differs more
from the wing of _Blatta_ than it does according to a comparison made
with the nomenclature we adopt.
[199] _Bull. Soc. Philomathique_ (8), ii. p. 18.
[200] Laboulbène, _Bull. Soc. ent. France_, 1857, p. cxxxvi., and Henneguy
as above.
[201] _Ann. Nat. Hist._ (5) i. 1878, p. 101.
[202] The antennae in the specimen represented were no doubt mutilated,
though Westwood did not say so.
[203] _CR. Ac. Paris_, xcviii. 1884, p. 832.
[204] In his recent _Insectes fossiles des temps primaires_, pp. 373 and
396, M. Brongniart has himself removed this Insect to Protodonates.
We shall again mention it when discussing that group.
[205] _Bactridium_, though placed in this tribe, has only short antennae,
of 20 joints.
[206] _Bostra_ and _Clonistria_, belonging to Bacunculides, have the median
segment almost as long as the metanotum.
[207] The American genera _Pterinoxylus_, _Haplopus_, and _Candaules_, as
well as the African _Palophus_, possess winged females.
[208] The African and Australian genera _Orobia_ and _Paraorobia_, although
they have a short median segment, are placed in the tribe Phasmides
of this division.
[209] This character is evidently erroneous as regards the males of the
genus Phyllium.—D. S.
[210] _Ann. Hofmus. Wien_, i. 1886, p. 175.
[211] Newport, _Tr. Linn. Soc._ xx. 1851, p. 419.
[212] _Mem. Ac. Sci. Étrang._ vii. 1834, p. 274.
[213] _First Ann. Rep. U.S. Ent. Comm._ 1878, p. 271.
[214] _Rep. U.S. Ent. Comm._ ii. 1880, p. 223.
[215] _Ann. Sci. Nat._ (7) iv. _Zool._ 1887.
[216] _Verh. zool-bot. Ges. Wien_, xxi. 1871, p. 1097.
[217] _Verh. zool.-bot. Ges. Wien_, xxiv. 1874, p. 286.
[218] _Denk. Ak. Wien_, xxxvi. 1875; _Arch. mikr. Anat._ xx. and xxi.,
1882.
[219] _Mem. Ac. Sci. Étrang._ vii. 1834, p. 306.
[220] _Bull. Soc. Philomath._ (8) v. 1893, p. 5.
[221] _First Ann. Rep. U.S. Ent. Comm._ 1878, p. 279.
[222] _Rep. Ins. Missouri_, ix. 1877, p. 86.
[223] _Bull. Soc. ent. France_ (6), x. 1890, p. xxxvii., and _CR. Ac.
Paris_, ex. 1890, p. 657.
[224] Carruthers in _Nature_, xli. 1889, p. 153.
[225] _Blue-book, C_, 4960, 1887; and _P. ent. Soc. London_, 1881, p.
xxxviii.
[226] _Rep. Entomologist_, 1885, p. 229.
[227] _Tr. S. Afr. Phil. Soc._ i. 1880, p. 193. The species is thought to
be _Pachytylus sulcicollis_ Stål.
[228] _CR. Soc. ent. Belgique_, xxi. 1878, p. 5.
[229] _Addit. ad Prodromum Oedipodiorum_, 1888, p. 12.
[230] See Redtenbacher, _Über Wanderheuschrecken_, in _Jahresber.
Realschule Budweis_, 1893.
[231] _J. Bombay N. H. Soc._ viii. 1893, p. 120.
[232] _P. ent. Soc. London_, 1893, p. xxi.
[233] _Rep. injurious Insects_, xvii. 1893, p. 47.
[234] _Ent. Nachricht._ viii. 1882, p. 160.
[235] Monograph by Bolivar, _Ann. Soc. Esp._ xiii. 1884, p. 1, etc.
[236] Monograph, de Saussure, _Spicilegia entomologica Genavensia_, pt. 2,
Geneva, 1887.
[237] Monograph, de Saussure, _Mem. Soc. Phys. Genève_, xxviii. 1884, No.
9; and xxx. 1888, No. 1.
[238] _Prod. Eur. Orthopt._ 1882, p. 160.
[239] _Science_, xxi. p. 133.
[240] _An. Soc. Espan._ xv. 1886, p. 273.
[241] _Nature_, iv. 1871, p. 333.
[242] _Bull. Soc. Rouen_, 1885, and _Insectes fossiles_, etc. 1894, p. 439.
[243] A few species of Proscopiides and Oedipodides, though placed in the
next division, are destitute of any claw-pad.
[244] This applies specially to the males.—D. S.
[245] _Ann. Rep. Insects Missouri_, vi. 1874, p. 155.
[246] _Zeitschr. wiss. Zool._ xxv. 1875, pp. 174-200, pl. xii.
[247] _Arch. f. mikr. Anat._ xx. 1882, and xxi. See also von Adelung,
_Zeitschr. wiss. Zool._ liv. 1892, p. 316.
[248] The small space above _lm_ left free from dots is, we presume, due to
an omission on the part of Graber's artist, but we have not thought
it right to interfere with his diagram.
[249] _Ann. Rep. Insects Missouri_, vi. 1874, p. 159.
[250] Wheeler, _J. Morphol._ viii. 1893.
[251] _Verh. zool.-bot. Ges. Wien_, xxxiii. 1883, p. 248.
[252] Bonnet and Finot, _Rev. Sci. Nat._ (3) iv. p. 345. The word we have
translated as humming is "bruissement."
[253] De Saussure, _Ann. Soc. ent. France_, 1888, p. 151, pl. v. fig. 1.
[254] _Indian Mus. Notes_, ii. 1893, p. 172.
[255] _Zoologist_, 1867, p. 489.
[256] This diagnosis is an attempt to express in something approaching an
exact manner the distinction of the flattened from the arched or
convex head.
[257] Scrobes are the depressions in which the antennae are inserted.
[258] There are unfortunately a few exceptions in the case of this
character.
[259] See Pungur, _Termes. Füzetek_, 1877, p. 223.
[260] Brunner, _Verh. zool.-bot. Ges. Wien_, xxiv. 1874, p. 288.
[261] _Natural History of Selborne_, Letter xc.
[262] Müller's _Arch._ 1859, p. 159.
[263] _Bull. Soc. ent. France_, 1893, p. cccxli.
[264] _Zeitschr. wiss. Zool._ xxiii. 1876, p. 122.
[265] _Ibid._ xli. 1885, p. 570.
[266] _Morph. Jahrb._ xv. 1889, p. 400.
[267] _Mem. Soc. phys. Genève_, xxv. 1877, and _Biol. Centr. Amer.
Orthoptera_, 1894, p. 198.
[268] The genus _Myrmecophila_, being exceptional in several respects, is
treated separately.
[269] _Insectes fossiles des temps primaires_, 1893, vol. i. and atlas.
[270] Giebel and Nitzsch, _Insecta epizoica_, folio, 1874.
[271] _Zeitschr. wiss. Zool._ xlii. 1885, p. 537.
[272] _Zeitschr. wiss. Zool._ xlii. 1885, pl. xviii. f. 15.
[273] _Arch. f. Naturg._ xxxv. i. 1869, p. 154, pls. x. xi.
[274] _Op. cit._ pp. vii.-xiv. For classification, etc., see also Piaget,
_Les Pédiculines_. Leyden, 1880.
[275] _Zeitschr. wiss. Zool._ xlii. 1885, p. 532.
[276] _P. ent. Soc. London_, 1890, p. xxx.
[277] _Bull. Soc. Philom._ (7) ix. p. 33.
[278] _P. Zool. Soc. London_, 1883, p. 628.
[279] _Ann. Hofmus. Wien_, i. 1886, p. 171.
[280] _Atti Acc. Gioenia_, vii. 1893.
[281] _J. Linn. Soc. Zool._ xiii. 1878, pl. xxi. f. 2.
[282] _Canadian Entomologist_, xvii. 1885, throughout.
[283] _Jena. Zeitschr. Naturw._ ix. 1875, pl. xii. See also Stokes in
_Science_, xxii. 1893, p. 273.
[284] _Ann. Hofmus. Wien_, i. 1886, p. 183.
[285] _Jena. Zeitschr. Naturw._ ix. 1875, p. 257.
[286] Bidie, in _Nature_, xxvi. 1882, p. 549.
[287] _Linnaea Entomologica_, xii. 1858, p. 305.
[288] _P. Boston Soc._ xx. 1878, p. 118.
[289] _Atti Acc. Gioen._ vi. and vii. 1893 and 1894.
[290] _Ann. Sci. Nat. Zool._ (4) v. 1856, p. 227.
[291] _Ann. Soc. ent. France_ (5), vi. 1876, p. 201.
[292] _Phil. Trans._ lxxi. 1781, pp. 139-192.
[293] _Ann. Nat. Hist._ (2) v. 1850, p. 92.
[294] Dr. G. D. Haviland informs the writer that he thinks it probable this
so-called peristaltic movement is merely the result of alarm; he has
not, however, had any opportunity of observing _T. bellicosus_.
[295] _Tr. N. York Ac._ viii. 1889, pp. 85-114; and ix. 1890, pp. 157-180.
[296] Camerano, _Bull. Soc. ent. Ital._ xvii. 1885, p. 89; and Kollmann,
_Verh. Ges. Basel_, vii. 1883, p. 391.
[297] _Jena. Zeitschr. Naturw._ vii. 1873, p. 458.
[298] _CR. Ac. Paris_, cxix. 1894, p. 804.
[299] _Congr. internat. Zool._ ii. 1892, pt. i. p. 249.
[300] _P. Boston Soc._ xi. 1868, p. 399.
[301] Kolbe, _Ent. Nachr._ xiii. 1887, p. 70.
[302] _Trans. N. York Ac._ viii. 1889, p. 91.
[303] _Congr. internat. Zool._ ii. 1892, p. 249.
[304] _P. Boston Soc._ xix. 1878, p. 267; and xx. 1881, p. 121.
[305] According to Melliss, it is thought that the Insect may have been
carried to the island in a captured slave-ship. Melliss, _St.
Helena_, 1875, p. 171.
[306] In some exotic species there is a dense network on a part of the
anterior wing.
[307] _P. Boston Soc._ xix. 1878, p. 292.
[308] Germar, _Mag. Entomol._ iv. 1821, p. 276, pl. ii.
[309] _Psyche_, iii. 1881, p. 196.
[310] Kolbe, _Stettin, ent. Zeit._ xli. 1880, p. 179.
[311] _Op. cit._ p. 209, etc.
[312] _Arch. f. Naturg._ xlix. i. 1883, p. 99.
[313] _Verh. Ver. Rheinland_, xxxix. 1882, Corr.-bl. p. 128.
[314] _Berlin ent. Zeit._ xxviii. 1884, p. 36.
[315] _Stettin. ent. Zeit._ xliv. 1883, pp. 299, 305.
[316] For the British species, see M‘Lachlan, _Ent. Month. Mag._ iii. 1867,
p. 177.
[317] The genera _Atropos_ and _Clothilla_ were named after the two fates
Atropos and Clotho. Westwood attempted some years ago to complete the
trio by establishing a genus _Lachesilla_. This proved a failure, the
genus being a misconception. As the name Lachesis is in use in
various branches of zoology, the desired circle of Psocid fates is
likely to remain always incomplete.
[318] _Phil. Trans._ xxii. 1701, pp. 832-834; and xxiv. 1704, pp.
1586-1594, Plate 291, Figs. 4, 5 (pp. 1565 to 1604 occur twice in
this volume).
[319] _Stettin. ent. Zeit._ xliii. 1882, p. 265.
[320] _P. Boston Soc._ xiii. 1871, p. 407.
[321] _Tr. Linn. Soc._ xx. 1851, p. 433.
[322] _Bull. Soc. ent. France_ (4), viii. 1868, p. xxxvii.
[323] _Zool. Anz._ iii. 1880, p. 304.
[324] _Stettin. ent. Zeit._ xxxviii. 1877, p. 487.
[325] _Morphologie des Tracheensystems_, Helsingfors, 1877, p. 21.
[326] _Beitr. Anat. Perla maxima._ Inaug.-Diss. Aarau, 1881.
[327] _Entom. Month. Mag._ xxix. 1893, p. 249.
[328] No satisfactory systematic work of a general character on British
Perlidae exists. References to the scattered descriptions and notes
will be found in the Catalogue of British Neuroptera published by
Entom. Soc. London, 1870.
[329] _Mem. Ac. Pétersb._ (7) xxxvi. No. 15, 1889.
[330] _Insectes fossiles_, etc., p. 407, 1893.
[331] _Festschrift Ges. naturf. Freunde Berlin_, 1873.
[332] Reference may be made to Calvert's recent paper introductory to the
study of Odonata, in _Tr. Amer. ent. Soc._ xx. 1893, pp. 159-161.
[333] _Horae Soc. ent. Ross._ xvi. 1881, p. 3.
[334] _Physiol. facett._ _Aug._ 1891, p. 115.
[335] _Bull. Ac. Belgique_ (3), xvi. 1888, No. 11, p. 31.
[336] _SB. Ak. Wien_, lxxxiii. 1881, pp. 289-376, pls. i.-vii.
[337] _Rev. Sci. Nat. Montpellier_ (3), ii. p. 470.
[338] _Abh. Senckenb. Ges._ x. 1875, p. 13, pl. iii.
[339] _Zool. Anz._ iii. 1880, p. 160.
[340] _CR. Soc. ent. Belgique_, xxiii. 1880, p. lxvii.
[341] _Ann. Sci. Nat._ (5) xi. Zool. 1869, p. 377.
[342] _Zur Morphologie des Tracheensystems_, Helsingfors, 1877, p. 38.
[343] _Zool. Anz._ xiii. 1890, p. 500.
[344] The following works convey the best information: Evans's _British
Libellulinae or Dragon-flies_, illustrated in a series of
lithographic drawings, 1845. Hagen, "A Synopsis of the British
Dragon-flies," in _Entomologists' Annual_, 1857. M‘Lachlan,
_Catalogue of the British Neuroptera_, published by the Entomological
Society of London in 1870; and "The British Dragon-flies annotated,"
_Entom. Month. Mag._ xx. 1884, pp. 251-256.
[345] _Rev. d'Entomol._ v. 1886, p. 232.
[346] Riveau, _Feuille Nat._ xii. 1882, p. 123.
[347] _Bull. Mus. Harvard_, viii. 1880-81, p. 276.
[348] _Insectes fossiles_, p. 394.
[349] _Insectes fossiles_, p. 396.
[350] _Mem. Ac. Sci. Toulouse_ (7), iii. 1871, p. 379.
[351] In reference to a doubt as to the name of this nymph cf. Eaton, _Tr.
Linn. Soc. Zool._ (2) iii. p. 20.
[352] _Tr. Linn. Soc._ xxiv. 1863, p. 62, and xxv. 1866, p. 477.
[353] _Hist. Nat. Neuropt. Ephémérines_, 1843, p. 24.
[354] _Ann. Sci. Nat. Zool._ (6) xiii. 1882, pp. 1-137, pls. 2-11.
[355] _Ann. Sci. Nat. Zool._ (7) ix. 1890, pp. 19-87, pls. 2-5.
[356] _Ann. Nat. Hist._ (3) xviii. 1866, p. 145.
[357] _Zeitschr. wiss. Zool._ xxxiv. 1880, p. 404.
[358] _Ann. Nat. Hist._ (5) xv. 1885, p. 494.
[359] _Mem. Cour. Ac. Belg._ 4to, xix. 1847, p. 1.
[360] _Zur Morphologie des Tracheensystems_, Helsingfors, 1877, pp. 1-20.
[361] _Tr. Linn. Soc._ xxv. 1866, p. 483.
[362] _Ann. Nat. Hist._ (3) xviii. 1866, p. 145.
[363] _Ann. Sci. Nat. Zool._ (6) xiii. 1882, p. 113.
[364] Réaumur, _Mem._ vi. 1742, p. 457.
[365] _Über vaarige Ausführsgänge_, etc., Helsingfors, 1884, p. 53.
[366] _Ber. Ges. Freiburg_, iv. p. 5; cf. _J. R. Micr. Soc._ 1889, p. 206.
[367] _Tr. Linn. Soc._ 2nd ser. _Zool._ iii. 1883, p. 11.
[368] _Fly-Fisher's Entomology_, 4th ed. 1849, p. 49.
[369] _P. ent. Soc. London_, 1882, p. xiii.
[370] _Ann. Sci. Nat._ series 3, ix. _Zool._ 1848, p. 91, pl. 1.
[371] Newport, _Tr. Linn. Soc._ xx. 1851, pl. 21, fig. 13. Loew, however,
who also describes and figures the anatomy of _S. lutaria_, states
that there is no paunch. _Linnaea entomologica_, iii. 1848, p. 354.
[372] M‘Lachlan, _Ent. Month. Mag._ vii. 1870, p. 145.
[373] _Rep. Ins. Missouri_, ix. 1877, p. 125.
[374] _Tijdschr. Ent._ vol. xxxiv. 1891.
[375] _Arch. f. Naturg._ iv. i. 1838, p. 315.
[376] _Linnaea entomologica_, iii. p. 1848, 346, pl. i.
[377] _Mem. Ac. Sci. étrang._ vii. 1841, p. 582.
[378] _Linnaea entom._ iii. 1848, p. 363.
[379] _Ent. Month. Mag._ 1894, p. 39.
[380] _Stettin. ent. Zeit._ xxvii. 1866, p. 369; this author has also
sketched a classification of the larvae in _P. Boston Soc._ xv. 1873,
p. 243.
[381] _Ov. Danske Selsk._ 1889, p. 43.
[382] _Ann. Sci. étrang._ vii. 1834, pl. 12.
[383] M‘Lachlan, _Ent. Month. Mag._ ii. 1865, p. 73.
[384] Redtenbacher, _Denk. Ak. Wien_, xlviii. 1884, p. 335.
[385] _J. Linn. Soc. Zool._ xi. 1873, p. 227.
[386] _Verh. zool.-bot. Ges. Wien_, iv. 1854, p. 471.
[387] Westwood, _l.c._ p. 12.
[388] _P. Boston Soc._ xv. 1873, p. 244.
[389] _Tr. Entom. Soc. London_, 1888, p. 1, pls. 1, 2.
[390] Cf. M‘Lachlan, _J. Linn. Soc. Zool._ ii. 1873, p. 219.
[391] _Tr. Linn. Soc._ xiv. 1825, p. 140, and xv. 1827, p. 509.
[392] _P. Boston Soc._ xv. 1873, p. 245.
[393] M‘Lachlan, _Tr. Ent. Soc. London_, 1885, p. 375.
[394] _Verh. zool.-bot. Ges. Wien_, xix. 1869, p. 831.
[395] Brauer, _Zool. Anz._ x. 1887, pp. 212 and 218.
[396] _Linnaea entomologica_, vii. 1852, p. 368, with plates.
[397] See Albarda in _Tijdschr. Ent._ xvii. 1874, p. xvi.
[398] _Tr. ent. Soc. London_, 1868, p. 189.
[399] _Biol. Centralbl._ iv. 1885, p. 722.
[400] _Bull. Soc. ent. France_ (6), i. 1881, pp. xxi. and xxxi.
[401] _Arch. Naturges._ lix. 1893, Band I. p 285.
[402] _Ent. Nachr._ xiv. 1888, p. 274.
[403] _Trichoptera europ._ 1878, p. 356, note.
[404] _Berl. ent. Zeitschr._ xxv. 1881, p. 54.
[405] Monograph of the British Trichoptera in _Tr. ent. Soc. London_, third
series, vol. v. 1865; and Monographic Revision of the European
Trichoptera, 1874-1880.
[406] _Zeitschr. wiss. Zool._ xxxv. 1881, Pl. IV. fig. 6.
[407] _Rep. of the Entomologist_, 1886, p. 510, Washington.
[408] _Insectes fossiles des temps primaires_, 1893, p. 38.
[409] _P. ent. Soc. London_, 1866, p. lxv.
[410] For a history of this complex question, see Gosch, _Naturhist.
Tidskr._ (Rk. 3) vol. xiii. 1881; and also Brauer, _Sitzb. Ak. Wien_,
lxxxv. 1882.
[411] _Introd. hist. Insects_, 1841, p. 143. The names proposed by Newman
may be adopted when it is specially requisite to use terms that are
morphologically correct. According to his nomenclature the true whole
abdomen of petiolate Hymenoptera consists of three anatomical parts:
1, the petiole or podeon; 2, the propodeon or part in front of the
petiole; 3, the metapodeon or part behind the petiole.
[412] _Zeitschr. wiss. Zool._ xxv. 1874, p. 184.
[413] _Ann. Mag. Nat. Hist._ (6) x. 1892, p. 442.
[414] _CR. Ac. Paris_, lxxxiii. 1876, p. 613, and _Ann. Mag. Nat. Hist._
(4) xviii. 1876, p. 504; also _Horae Soc. Ross._ xv. 1880, pp. 20 and
31.
[415] _P. Boston Soc._ x. 1866, p. 279.
[416] Adler, _Deutsche ent. Zeitschr._ xxi. 1877, p. 209.
[417] Cameron, _Brit. Phyt. Hym._ Ray Society, i. 1882, p. 29, and ii.
1885, p. 218.
[418] Cameron, _op. cit._ iv. 1893, p. 9.
[419] _Brit. Phyt. Hym._ i. p. 27. Fletcher's record, referred to by
Cameron, mentions _N. miliaris_, but this name was probably
erroneous.
[420] See Perez and Cameron, _Tr. Nat. Hist. Soc. Glasgow_, n.s. ii. 1889,
p. 194.
[421] Fabre, Marchal, Nicolas.
[422] _Zeitschr. wiss. Zool._ xxx. Supp. 1878, p. 103.
[423] Rejoinder to Professor Weismann, p. 11. Reprint from _Contemporary
Review_, December 1893.
[424] _Mon. Brit. Phyt. Hym._ 4 vols. 1882 to 1893.
[425] _Insect Life_, i. 1888, p. 8.
[426] _Souvenirs entomologiques_: quatrième série, 1891, p. 308.
[427] _Tr. ent. Soc. London_, i. 1836, p. 232.
[428] _Ichneumonen der Forstinsecten_, i. 1844, p. 86.
[429] See Cameron, _Brit. Phyt. Hym._ iii. Ray Soc. 1890, p. 152.
[430] The term inquiline is applied in entomology to a great variety of
conditions covered by the Latin word "inquilinus" (incolinus),
signifying a tenant or dweller in another's property. The term
parasite is used in a still wider and vaguer sense, being in fact
applied to a large number of cases, in many of which we do not at
present understand the exact relations between the two parties
concerned. This subject is no doubt destined to become a most
interesting department of entomology. See Riley, _P. ent. Soc.
Washington_, ii. 1893, p. 397; and Wasmann, _Zusammengesetzten
Nester_, etc., 1891.
[431] _P. Linn. Soc. N. S. Wales_ (2), vii. 1892, p. 357.
[432] _Science_ (n.s.), i. 1895, p. 457.
[433] _Ray Soc._ vol. iv. 1893, p. 24.
[434] _Term. Füzetek_, v. 1882, p. 198, and _Biol. Centralbl._ ii. 1882, p.
617.
[435] _Ann. Soc. ent. France_ (4), vi. 1866, p. 198.
[436] Adler and Straton, _Alternating Generations_, 1894, p. 119.
[437] _P. entom. Soc. Philadelphia_, ii. 1864, pp. 447, etc.
[438] _P. ent. Soc. Philad._ ii. 1863, p. 34.
[439] _Brit. Phyt. Hym._ vols. iii. and iv. Ray Soc. 1891 and 1893.
[440] _Entom. Mag._ ii. 1835, p. 219.
[441] _Tr. ent. Soc. London_, 1881, p. 109.
[442] _Bull. U. S. Museum_, No. 45, 1893, p. 28.
[443] _Tr. ent. Soc. London_, 1881, p. 117.
[444] _Tr. ent. Soc. London_, 1881, pt. vi. f. 3; pp. 120, 126.
[445] _Zeitschr. wiss. Zool._ xix. 1869; Ganin's observations are described
by Lubbock, _Origin and Metamorphoses of Insects_, 1874, p. 34.
[446] See also Kulagin, _Zool. Anz._ xiii. 1890, p. 418; xv. 1892, p. 85;
and _Congr. internat. Zool._ ii. 1892, pt. i. p. 258.
[447] _Tr. Linn. Soc._ (2) _Zool._ i. 1878, p. 587.
[448] _Tr. Linn. Soc._ xxiv. 1863, p. 135.
[449] _Zeitschr. wiss. Zool._ xix. 1869, p. 417.
[450] _Souvenirs entomologiques._ Troisième série, 1886, p. 155.
[451] _Souvenirs entomologiques._ Troisième série, 1886, p. 179.
[452] _Tr. Linn. Soc._ xxi. 1855, p. 67.
[453] According to Ashmead, _P. ent. Soc. Washington_, ii. 1893, p. 228,
this genus should take the name of _Melittobia_.
[454] _Ann. Nat. Hist._ (6) x. 1892, p. 271.
[455] _Rec. Zool. Suisse_, v. 1891, pp. 435-534. Cf. Koulaguine, _Congr.
internat. Zool._ ii. 1892, pt. i. p. 265.
[456] _Bull. Soc. Ent. France_ (5) vii. 1877, p. lxix.; also André,
_Feuille Natural._ vii. 1877, p. 136, and Riley and Howard, _Insect
Life_, iv. 1892, p. 242.
[457] _Insect Life_, i. 1888, p. 121.
[458] _Report of the Entomologist, Dep. Agriculture, Washington_, 1886, p.
542.
[459] Wachtl, _Wien. ent. Zeit._ xii. 1893, p. 24, and Howard, _P.U.S. Nat.
Mus._ xiv. 1892, p. 586.
[460] _Abh. Ges. Göttingen_, xxviii. 1882.
[461] _Mitt. Stat. Neapel_, iii. 1882, p. 55.
[462] _Tr. ent. Soc. London_, 1883. p. 389.
[463] _P. biol. Soc. Washington_, vii. 1892, p. 99.
[464] _Ann. Botan. Garden, Calcutta_, i. 1889, Appendix L.
[465] _P. ent. Soc. London_, 1886, p. x.
[466] For a systematic memoir refer to Mayr, _Verh. zool.-bot. Ges. Wien_,
xxxv. 1885, p. 147, etc.
[467] _Insect Life_, iv. 1891, p. 193.
[468] Tosquinet, _Ann. Soc. ent. Belgique_, xxxviii. 1894, p. 694.
[469] _Ichneum. Forst. Ins._ 1844, p. 81.
[470] _Mitt. schweizer. ent. Ges._ iv. 1876, p. 518.
[471] _Fifth Rep. U. S. Ent. Comm._ 1890, p. 15.
[472] _Tr. Linn. Soc._ xxi. 1852, p. 71.
[473] _Tr. ent. Soc. London_, 1886, p. 162, and 1887, p. 303.
[474] _Ent. Month. Mag._ xiii. 1877, p. 200.
[475] A catalogue, with references, of the British Ichneumonidae was
published by the Entomological Society of London in 1872. Since then
many additional species have been detected and recorded, by Mr.
Bridgman and others, in the _Transactions_ of the same Society.
[476] Klapálek, _Ent. Month. Mag._ xxv. 1889, p. 339, and _Arch.
Landesdurchforschung Böhmen_, viii. No. 6, 1893, p. 53.
[477] _Ichneum. Forst. Ins._ 1844.
[478] _Ann. Soc. ent. France_ (2), iii. 1845, p. 355.
[479] _Tr. ent. Soc. London_, 1885, pp. 224, 219.
[480] A monograph of the British Braconidae was commenced by the Rev. T. A.
Marshall in 1885, and is still in progress, in the _Transactions of
the Entomological Society of London_; cf. _op. cit._ 1885, 1887,
1889, 1891, 1894.
[481] _Berlin entom. Zeitschr._ xxxiii. 1889, p. 197.
[482] _Ibid._
[483] Monograph, Schletterer, _Verh. zool.-bot. Ges. Wien_, xxxv. 1885, p.
267, etc.; xxxvi. 1886, p. 1, etc.; and _Ann. Hofmus. Wien_, iv. pp.
107, etc.
[484] _Berlin. entom. Zeitschr._ xxxiii. 1889, p. 197.
[485] _Amer. Nat._ xxviii. 1894, p. 895.
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