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Title: Beginners' zoology
Author: Walter M. Coleman
Release date: April 5, 2024 [eBook #73338]
Language: English
Original publication: Toronto: Macmillan, 1921
Credits: Richard Tonsing, 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 BEGINNERS' ZOOLOGY ***
BEGINNERS’ ZOOLOGY
BY
WALTER M. COLEMAN
[Illustration: [Logo]]
_AUTHORIZED BY THE MINISTER OF EDUCATION FOR ONTARIO_
TORONTO
THE MACMILLAN CO. OF CANADA, LIMITED
1921
Copyright, Canada, 1921
BY THE MACMILLAN COMPANY
OF CANADA, LIMITED
CONTENTS
CHAPTER PAGE
I. INTRODUCTION 1
II. PROTOZOANS 10
III. SPONGES 17
IV. POLYPS 22
V. ECHINODERMS 34
VI. WORMS 42
VII. CRUSTACEANS 51
VIII. INSECTS 63
IX. MOLLUSCS 97
X. FISHES 109
XI. BATRACHIANS 126
XII. REPTILES 139
XIII. BIRDS 150
XIV. MAMMALS 184
BEGINNERS’ ZOOLOGY
CHAPTER I
THE PRINCIPLES OF BIOLOGY
Biology (Greek, _bios_, life; _logos_, discourse) means the science of
life. It treats of animals and plants. That branch of biology which
treats of animals is called _zoology_ (Gr. _zoon_, animal; _logos_,
discourse). The biological science of _botany_ (Gr. _botane_, plant or
herb) treats of plants.
Living things are distinguished from the not living by a series of
processes, or changes (feeding, growth, development, multiplication,
etc.), which together constitute what is called life. These processes
are called _functions_. Both plants and animals have certain parts
called _organs_ which have each a definite work, or function; hence
animals and plants are said to be organized. For example, men and most
other animals have a certain organ (the mouth) for taking in
nourishment; another (the food tube), for its digestion.
Because of its _organization_, each animal or plant is said to be an
_organism_. Living things constitute the _organic kingdom_. Things
without life and not formed by life constitute the _inorganic_, or
_mineral_, _kingdom_. Mark I for inorganic and O for organic after the
proper words in this list: granite, sugar, lumber, gold, shellac, sand,
coal, paper, glass, starch, copper, gelatine, cloth, air, potatoes,
alcohol, oil, clay. Which of these things are used for food by animals?
Conclusion?
=Energy in the Organic World.=—We see animals exerting energy; that is,
we see them moving about and doing work. Plants are never seen acting
that way; yet they need energy in order to form their tissues, grow, and
raise themselves in the air.
=Source of Plant Energy.=—We notice that green plants thrive only in the
light, while animal growth is largely independent of light. In fact, in
the salt mines of Poland there are churches and villages below the
ground, and children are born, become adults, and live all their lives
below ground, without seeing the sun. (That these people are not very
strong is doubtless due more to want of fresh air and other causes than
to want of sunlight.)
[Illustration:
FIG. 1.—SURFACES OF A LEAF, magnified.
]
[Illustration:
FIG. 2.—A LEAF STORING ENERGY IN SUNLIGHT.
]
_The need of plants for sunlight shows that they must obtain something
from the sun._ This has been found to be _energy_. This enables them to
_lift_ their _stems_ in growth, and _form_ the various structures called
_tissues_ which make up their stems and leaves. It is noticed that they
take in food and water from the soil through their roots. Experiments
also show that green plants take in through pores (Fig. 1), on the
surface of their leaves, a gas composed of carbon and oxygen, and called
_carbon dioxide_. The _energy in the sunlight_ enables the plant _to
separate out the carbon, of the carbon dioxide_ and to build mineral and
water and carbon into organic substances. The oxygen of the carbon
dioxide is set free and returns to the air (Fig. 2). Starch, sugar, oil,
and woody fibre are examples of substances thus formed. Can you think of
any fuel not due to plants?
=How Animals obtain Energy.=—You have noticed that starch, oil, etc.,
will _burn_, or _oxidize_, that is, _unite with the oxygen of the air_;
thus the sun’s energy, stored in these substances, is changed back to
heat and motion. The oxidation of oil or sugar may occur in a furnace;
it may also occur in the living substance of the active animal.
[Illustration:
FIG. 3.—COLOURLESS plants, as A GREEN LEAF, even after it is cut,
MUSHROOMS, give off no oxygen. gives off oxygen (O) if kept in the
sun.
]
Fortunately for the animals, the plants oxidize very little of the
substances built up by them, since they do not move about nor need to
keep themselves warm. We notice that animals are constantly using plant
substances for food, and constantly drawing the air into their bodies.
If the sunlight had not enabled the green plant to store up these
substances and to set free the oxygen (Fig. 3), animals would have no
food to eat nor air to breathe; hence we may say that the sunlight is
indirectly the source of the life and energy of animals. Mushrooms and
other plants without green matter cannot set oxygen free (Fig. 3).
=Experiment to show the Cause of Burning, or Oxidation.=—Obtain a large
glass bottle (a pickle jar), a short candle, and some matches. Light the
candle and put it on a table near the edge, and cover it with the glass
jar. The flame slowly smothers and goes out. Why is this? Is the air now
in the jar different from that which was in it before the candle was
lighted? Some change must have taken place or the candle would continue
to burn. To try whether the candle will burn again under the jar without
changing the air, slide the jar to the edge of the table and let the
candle drop out. Light the candle and slip it up into the jar again, the
jar being held with its mouth a little over the edge of the table to
receive the candle (Fig. 5). The flame goes out at once. Evidently the
air in the jar is not the same as the air outside. Take up the jar and
wave it to and fro a few times, so as to remove the old air and admit
fresh air. The candle now burns in it with as bright a flame as at
first. So we conclude that the candle will not continue to burn unless
there is a constant supply of fresh air. The gas formed by the burning
is carbon dioxide. It is the gas from which plants extract carbon.
(Beginners’ Botany, Chap. XIII.) One test for the presence of this gas
is that it forms a white, chalky cloud in lime water; another is that it
smothers a fire.
=Experiment to show that Animals give off Carbon Dioxide.=—Place a
cardboard over the mouth of a bottle containing pure air. Take a long
straw, the hollow stem of a weed, a glass tube, or a sheet of stiff
paper rolled into a tube, and pass the tube into the bottle through a
hole in the cardboard. Without drawing in a deep breath, send one long
breath into the bottle through the tube, emptying the lungs by the
breath as nearly as possible (Fig. 4). Next, invert the bottle on the
table as in the former experiment, afterward withdrawing the cardboard.
Move the bottle to the edge of the table and pass the lighted candle up
into it (Fig. 5). Does the flame go out as quickly as in the former
experiment?
If you breathe through a tube into clear lime water, the water turns
milky. The effect of the breath on the candle and on the lime water
shows that carbon dioxide is continually leaving our bodies in the
breath.
[Illustration:
FIG. 4.—Breathing into a bottle.
]
[Illustration:
FIG. 5.—Testing the air in the bottle.
]
=Oxidation and Deoxidation.=—The union of oxygen with carbon and other
substances, which occurs in fires and in the bodies of animals, is
called _oxidation_. The separation of the oxygen from carbon such as
occurs in the leaves of plants is called _deoxidation_. _The first
process sets energy free, the other process stores it up._ Animals give
off carbon dioxide from their lungs or gills, and plants give off oxygen
from their leaves. But plants need some energy in growing, so oxidation
also occurs in plants, but to a far less extent than in animals. At
night, because of the absence of sunlight, no deoxidation is taking
place in the plant, but oxidation and growth continue; _so at night the
plant actually breathes out some carbon dioxide_. The deepest part of
the lungs contains the most carbon dioxide. Why was it necessary to
empty the lungs as nearly as possible in the experiment with the candle?
Why would first drawing a deep breath interfere with the experiment? Why
does closing the draught of a stove, thus shutting off part of the air,
lessen the burning? Why does a “firefly” shine brighter at each breath?
Why is the pulse and breathing faster in a fever? Very slow in a trance?
=The key for understanding any animal= is to find _how it gets food and
oxygen_, and how it uses the energy thus obtained to grow, move, avoid
its enemies, and get more food. Because it moves, it needs senses to
guide it.
=The key for understanding a plant= is to find _how it gets food and
sunlight_ for its growth. It makes little provision against enemies; its
food is in reach, so it needs no senses to guide it. The plant is built
on the plan of having the nutritive activities _near the surface_
(_e.g._ absorption by roots; gas exchange in leaves). The animal is
built on the plan of having its nutritive activities _on the inside_
(_e.g._ digestion; breathing).
=Cell and Protoplasm.=—Both plants and animals are composed of small
parts called _cells_. Cells are usually microscopic in size. They have
various shapes, as spherical, flat, cylindrical, fibre-like,
star-shaped. The living substance of cells is called _protoplasm_. It is
a stiff, gluey fluid, _albuminous_ in its nature. Every cell has a
denser spot or kernel called a _nucleus_, and in the nucleus is a still
smaller speck called a _nucleolus_. Most cells are denser and tougher on
the outside, and are said to have a _cell wall_, but many cells are
naked, or without a wall. Hence the indispensable part of a cell is not
the wall but the nucleus, and a _cell may be defined as a bit of
protoplasm containing a nucleus_. This definition includes naked cells
as well as cells with walls.
=One-celled Animals.=—There are countless millions of animals and plants
the existence of which was not suspected until the invention of the
microscope several centuries ago. They are one-celled, and hence
microscopic in size. It is believed that the large animals and plants
are descended from one-celled animals and plants. In fact, each
individual plant or animal begins life as a single cell, called an egg
cell, and forms its organs by the subdivision of the egg cell into many
cells. An egg cell is shown in Fig. 6, and the first stages in the
development of an egg cell are shown in Fig. 7.
[Illustration:
FIG. 6.—Egg cell of mammal with yolk.
]
[Illustration:
FIG. 7.—Egg cell subdivides into many cells forming a sphere (morula)
containing a liquid. A dimple forms and deepens to form the next
stage (gastrula).
]
The animals to be studied in the first chapter are _one-celled animals_.
To understand them we must learn how they eat, breathe, feel, and move.
They are called _Protozoans_ (Greek _protos_, first, and _zoon_). All
other animals are composed of many cells and are called _Metazoans_
(Greek _meta_, beyond or after). The cells composing the mucous membrane
in man are shown in Fig. 8. The cellular structure of the leaf of a
many-celled plant is illustrated in Fig. 1.
=Method of Classifying Animals.=—The various animals display differences
more or less marked. The question arises, are not some of them more
closely related than others? We conclude that they are, since the
difference between some animals is very slight, while the difference
between others is quite marked.
[Illustration:
FIG. 8.—MUCOUS MEMBRANE formed of one layer of cells. A few cells
secrete mucus.
]
To show _the different steps in classifying_ an animal, we will take an
example,—the cow. Even little children learn to recognize a cow,
although individual cows differ somewhat in form, size, colour, etc. The
varieties of cows, such as short-horn, Jersey, etc., all form one
_species_ of animals, having the scientific name _taurus_. Let us
include in a larger group the animals closest akin to a cow. We see a
cat, a bison, and a dog; rejecting the cat and the dog, we see that the
bison has horns, hoofs, and other similarities. We include it with the
cow in a _genus_ called _Bos_, calling the cow Bos taurus, and the
bison, Bos bison. The sacred cow of India (Bos indicus) is so like the
cow and the buffalo as also to belong to the genus Bos. Why is not the
camel, which, like Bos bison, has a hump, placed in the genus Bos?
The Old World buffaloes,—most abundant in Africa and India,—the
antelopes, sheep, goats, and several other genera are placed with the
genus Bos in a _family_ called the _hollow-horned animals_.
This family, because of its even number of toes and the habit of chewing
the cud, resembles the camel family, the deer family, and several other
families. These are all placed together in the next higher systematic
unit called an _order_, in this case, the order of _ruminants_.
The ruminants, because they are covered with hair and nourish the young
with milk, are in every essential respect related to the one-toed
horses, the beasts of prey, the apes, etc. Hence they are all placed in
a more inclusive division of animals, the _class_ called _mammals_.
All mammals have the skeleton, or support of the body, on the inside,
the axis of which is called the vertebral column. This feature also
belongs to the classes of reptiles, amphibians, and fishes. It is
therefore consistent to unite these classes by a general idea or
conception into a great _branch_ of animals called the _vertebrates_.
Returning from the general to the particular by successive steps, state
the branch, class, order, family, genus, and species to which the cow
belongs.
=The Eight Branches or Sub-kingdoms.=—The simplest classification
divides the whole animal kingdom into eight branches, named and
characterized as follows, beginning with the lowest: I. PROTOZOANS.
One-celled. II. SPONGES. Many openings. III. POLYPS. Circular; cuplike;
having only one opening which is both mouth and vent. IV. ECHINODERMS.
Circular; rough-skinned; two openings. V. MOLLUSCS. No skeleton; usually
with external shell. VI. VERMES. Elongate body, no jointed legs. VII.
ARTHROPODS. External jointed skeleton; jointed legs. VIII. VERTEBRATES.
Internal jointed skeleton with axis or backbone.[1]
Footnote 1:
This is the briefest classification. Animals have also been divided
into twelve branches. The naming of animals is somewhat chaotic at
present, but an attempt to come to an agreement is now being made by
zoologists of all nations.
CHAPTER II
PROTOZOA (One-celled Animals)
THE AMŒBA
SUGGESTIONS.—Amœbas live in the slime found on submerged stems and
leaves in standing water, or in the ooze at the bottom. Water plants
may be crowded into a glass dish and allowed to decay, and after about
two weeks the amœba may be found in the brown slime scraped from the
plants. An amœba culture sometimes lasts only three days. The most
abundant supply ever used by the writer was from a bottle of water
where some oats were germinating. Use ⅕ or ⅙ inch objective, and cover
with a thin cover glass. Teachers who object to the use of the
compound microscope in a first course should require a most careful
study of the figures.
[Illustration:
FIG. 9.—AMŒBA PROTEUS, much enlarged.
]
[Illustration:
FIG. 10.—AMŒBA.
_cv_, contractile vacuole; _ec_, ectoplasm; _en_, endoplasm; _n_,
nucleus; _ps_, pseudopod; _ps_, pseudopod forming; ectoplasm
protrudes and endoplasm flows into it.
]
=Form and Structure.=—The amœba looks so much like a clear drop of jelly
that a beginner cannot be certain that he has found one until it moves.
It is a speck of protoplasm (Fig. 9), with a clear outer layer, the
_ectoplasm_; and a granular, internal part, the _endoplasm_. Is there a
distinct line between them? (Fig. 10.)
Note the central portion and the slender prolongations or _pseudopods_
(Greek, false feet). Does the endoplasm extend into the pseudopods?
(Fig. 10.) Are the pseudopods arranged with any regularity?
Sometimes it is possible to see a denser appearing portion, called the
_nucleus_; also a clear space, the _contractile vacuole_ (Fig. 10).
[Illustration:
FIG. 11.—The same amœba seen at different times.
]
=Movements.=—Sometimes while the pseudopods are being extended and
contracted, the central portion remains in the same place (this is
_motion_). Usually only one pseudopod is extended, and the body flows
into it; this is _locomotion_ (Fig. 11). There is a new foot made for
each step.
=Feeding.=—If the amœba crawls near a food particle, the _pseudopod is
pressed against it_, or a depression occurs (Fig. 12), and the particle
is soon embedded in the endoplasm. Often a clear space called a _food
vacuole_ is noticed around the food particle. This is the water that is
taken in with the particle (Fig. 12). The water and the particle are
soon absorbed and assimilated by the endoplasm.
[Illustration:
FIG. 12.—THE AMŒBA taking food.
]
=Excretion.=—If a particle of sand or other indigestible matter is taken
in, _it is left behind_ as the amœba moves on. There is a clear space
called the _contractile vacuole_, which slowly contracts and disappears,
then reappears and expands (Figs. 9 and 10). This possibly aids in
excreting oxidized or useless material.
=Circulation= in the amœba consists of the movement of its protoplasmic
particles. It lacks special organs of circulation.
=Feeling.=—_Jarring_ the glass slide seems to be felt, for it causes the
activity of the amœba to vary. It does not take in for food every
particle that it touches. This may be the beginning of _taste, based
upon mere chemical affinity_. The pseudopods aid in feeling.
=Reproduction.=—Sometimes an amœba is seen dividing into two parts. A
_narrowing_ takes place in the middle; the _nucleus also divides_, a
part going to each portion (Fig. 13). The mother amœba finally divides
into two daughter amœbas. Sex is wanting.
[Illustration:
FIG. 13.—AMŒBA, Dividing.
]
=Source of the Amœba’s Energy.=—We thus see that the amœba moves without
feet, eats without a mouth, digests without a stomach, feels without
nerves, and, it should also be stated, breathes without lungs, for
_oxygen is absorbed_ from the water _by its whole surface_. Its
_movements require energy_; this, as in all animals, is furnished by the
_uniting of oxygen with the food_. Carbon dioxide and other waste
products are formed by the union; these pass off at the surface of the
amœba and taint the water with impurities.
=Questions.=—Why will the amœba die in a very small quantity of water,
even though the water contains enough food? Why will it die still
quicker if air is excluded from contact with the drop of water?
The amœba never dies of old age. Can it be said to be immortal?
According to the definition of a cell (_Chapter I_), is the amœba a
unicellular or multicellular animal?
=Cysts.=—If the water inhabited by a protozoan dries up, it encysts,
that is, it forms a tough skin called a cyst. Upon return of better
conditions it breaks the cyst and comes out. Encysted protozoans may be
blown through the air: this explains their appearance in vessels of
water containing suitable food but previously free from protozoans.
THE SLIPPER ANIMALCULE OR PARAMECIUM
SUGGESTIONS.—Stagnant water often contains the paramecium as well as
the amœba; or they may be found in a dish of water containing hay or
finely cut clover, after the dish has been allowed to stand in the sun
for several days. A white film forming on the surface is a sign of
their presence. They may even be seen with the unaided eye as tiny
white particles by looking through the side of the dish or jar. Use at
first a ⅓ or ¼ in. objective. Restrict their movements by placing
cotton fibres beneath the cover glass; then examine with ⅕ or ⅙
objective. Otherwise, study figures.
=Shape and Structure.=—The paramecium’s whole body, like the amœba’s, is
only one cell. It resembles a slipper in _shape_, but the pointed end is
the hind end, the _front end_ being rounded (Fig. 14). The paramecium is
propelled by the rapid beating of numerous fine, threadlike appendages
on its surface, called _cilia_ (Latin, eyelashes) (Figs.). The cilia,
like the pseudopods of the amœba, are merely prolongations of the cell
protoplasm, but they are permanent. The separation between the outer
_ectoplasm_ and the interior granular _endoplasm_ is more marked than in
the amœba (Fig. 14).
[Illustration:
FIG. 14.—PARAMECIUM, showing cilia, _c_.
Two contractile vacuoles, _cv_; the macronucleus, _mg_; two
micronuclei, _mi_; the gullet (_Œ_), a food ball forming and ten
food balls in their course from gullet to vent, _a_.
]
[Illustration:
FIG. 15.
]
=Nucleus and Vacuoles.=—There is a large nucleus called the
macronucleus, and beside it a smaller one called the micronucleus. They
are hard to see. About one third of the way from each end is a clear,
pulsating space (bb. Fig. 15) called the pulsating vacuole. These spaces
contract until they disappear, and then reappear, gradually expanding.
Tubes lead from the vacuoles which probably serve to keep the contents
of the cell in circulation.
[Illustration:
FIG. 16.—TWO PARAMECIA exchanging parts of their nuclei.
]
=Feeding.=—A depression, or _groove_, is seen on one side; this serves
as a mouth (Figs.). A _tube_ which serves as a gullet leads from the
mouth-groove to the interior of the cell. The mouth-groove is lined with
cilia which sweep food particles inward. The particles accumulate in a
mass at the inner end of the gullet, become separated from it as a _food
ball_ (Fig. 14), and sink into the soft protoplasm of the body. The food
balls follow a circular course through the endoplasm, keeping near the
ectoplasm.
[Illustration:
FIG. 17.—VORTICELLA (or bell animalcule), two extended, one withdrawn.
]
=Reproduction.=—This, as in the amœba, is by division, the constriction
being in the middle, and part of the nucleus going to each half.
Sometimes two individuals come together with their mouth-grooves
touching and exchange parts of their nuclei (Fig. 16). They then
separate and each divides to form two new individuals.
[Illustration:
FIG. 18.—Euglena.
]
We thus see that the paramecium, though of only one cell, _is a much
more complex and advanced animal than the amœba_. The tiny paddles, or
cilia, the mouth-groove, etc., have their special duties similar to the
specialized organs of the many-celled animals to be studied later.
[Illustration:
FIG. 19.—SHELL OF A RADIOLARIAN.
]
If time and circumstances allow a prolonged study, several additional
facts may be observed by the pupil, _e.g._ Does the paramecium swim with
the same end always foremost, and same side uppermost? Can it move
backwards? Avoid obstacles? Change shape in a narrow passage? Does
refuse matter leave the body at any particular place? Trace movement of
the food particles.
Draw the paramecium.
Which has more permanent parts, the _amœba_ or _paramecium_? Name two
anatomical similarities and three differences; four functional
similarities and three differences.
The amœba belongs in the class of protozoans called _Rhizopoda_ “root
footed.”
=Other classes of Protozoans= are the _Infusorians_ (in the broad sense
of the term), which have many waving cilia (Fig. 17) or one whiplike
flagellum (Fig. 18), and the _Foraminifers_, which possess a calcareous
shell pierced with holes (Fig. 19). Much chalky limestone has been
formed of their shells. To which class does the paramecium belong?
Protozoans furnish a large amount of food to the higher animals.
CHAPTER III
SPONGES
SUGGESTIONS.—In many parts of North America, fresh-water sponges may,
by careful searching, be found growing on rocks and logs in clear
water. They are brown, creamy, or greenish in colour, and resemble
more a cushion-like plant than an animal. They have a characteristic
gritty feel. They soon die after removal to an aquarium.
[Illustration:
FIG. 21.—FRESH-WATER SPONGE.
]
A number of common small bath sponges may be bought and kept for use
in studying the skeleton of an ocean sponge. These sponges should not
have large holes in the bottom; if so, too much of the sponge has been
cut away. A piece of marine sponge preserved in alcohol or formalin
may be used for showing the sponge with its flesh in place.
Microscopic slides may be used for showing the spicules.
[Illustration:
FIG. 22.—SECTION of fresh-water sponge (enlarged).
]
The =small fresh-water sponge= (Fig. 21) lacks the more or less vaselike
form typical of sponges. It is a rounded mass growing upon a rock or a
log. As indicated by the Arrows, where does _water enter_ the sponge?
This may be tested by putting colouring matter in the water near the
living sponge. Where does the _water come out_? (Fig. 22.) Does it pass
through _ciliated chambers_ in its course? Is the _surface_ of the
sponge rough or smooth? Do any of the skeletal _spicules_ show on the
surface? (Fig. 21.) Does the sponge thin out near its edge?
[Illustration:
FIG. 23.—EGGS and SPICULES of fresh-water sponge (enlarged).
]
The _egg_ of this sponge is shown in Fig. 23. It escapes from the parent
sponge through the _osculum_, or large outlet. As in most sponges, the
first stage after the egg is ciliated and free-swimming.
=Marine Sponges.=—The _grantia_ (Fig. 24) is one of the simplest of
marine sponges. What is the _shape_ of grantia? What is its length and
diameter? How does the free end differ from the fixed end? Are the
_spicules_ projecting from its body few or many?
[Illustration:
FIG. 24.—Grantia.
]
Where is the _osculum_, or large outlet? With what is this surrounded?
The osculum opens from a central cavity called the cloaca. The canals
from the pores lead to the _cloaca_.
_Buds_ are sometimes seen growing out from the sponge near its base.
These are young sponges formed asexually. Later they become detached
from the parent sponge.
[Illustration:
FIG. 25.—Plan of a sponge.
]
=Commercial “Sponge.”=—What part of the complete animal remains in the
bath sponge? _Slow growing sponges_ grow more at the top and form tall,
simple, tubular or vaselike animals. _Fast growing sponges_ grow on all
sides at once and form a complicated system of canals, pores, and
oscula. Which of these habits of growth do you think belonged to the
bath sponge? Is there a large hole in the base of your specimen? If so,
this is because the cloaca was reached in trimming the lower part where
it was attached to a rock. Test the _elasticity_ of the sponge when dry
and when wet by squeezing it. Is it softer when wet or dry? Is it more
elastic when wet or dry? How many _oscula_ does your specimen have? How
many _inhalent pores_ to a square inch? Using a probe (a wire with knob
at end, or small hat pin), try to trace the _canals_ from the pores to
the cavities inside.
[Illustration:
FIG. 26.—Bath Sponge.
]
Do the _fibres_ of the sponge appear to interlace, or join, according to
any system? Do you see any fringe-like growths on the surface which show
that new tubes are beginning to form? Was the sponge growing faster at
the top, on the sides, or near the bottom?
[Illustration:
FIG. 27.—Bath Sponge.
]
[Illustration:
FIG. 28.—Bath Sponge.
]
Burn a bit of the sponge; from the odor, what would you judge of its
composition? Is the inner cavity more conspicuous in a simple sponge or
in a compound sponge like the bath sponge? Is the bath sponge branched
or lobed? Compare a number of specimens (Figs. 26, 27, 28) and decide
whether the common sponge has a typical shape. What features do their
forms possess in common?
[Illustration:
FIG 29.—Skeleton of a glass sponge.
]
Sponges are divided into _three classes_, according as their skeletons
are flinty (silicious), limy (calcareous), or horny.
Some of the _silicious sponges_ have skeletons that resemble spun glass
in their delicacy. Flint is chemically nearly the same as glass. The
skeleton shown in Fig. 29 is that of a glass sponge which lives near the
Philippine Islands.
The _horny sponges_ do not have spicules in their skeletons, as the
flinty and limy sponges have, but the skeleton is composed of
interweaving fibres of _spongin_, a durable substance of the same
chemical nature as silk (Figs. 30 and 31).
The _limy sponges_ have skeletons made of numerous spicules of lime. The
three-rayed spicule is the commonest form.
[Illustration:
FIG. 30.—A horny sponge.
]
[Illustration:
FIG. 31.—Section of horny sponge.
]
The commercial sponge, seen _as it grows in the ocean_, appears as a
roundish mass with a smooth, dark exterior, and having about the
consistency of beef liver. Several large openings (oscula), from which
the water flows, are visible on the upper surface. Smaller holes
(inhalent pores—many of them so small as to be indistinguishable) are on
the sides. If the sponge is disturbed, the smaller holes, and perhaps
the larger ones, will close.
The outer layer of cells serves as a sort of skin. Since so much of the
sponge is in contact with water, most of the cells do their own
breathing, or absorption of oxygen and giving off of carbon dioxide.
_Nutriment_ is passed on from the surface cells to nourish the rest of
the body.
=Reproduction.=—Egg cells and sperm-cells are produced by certain cells
along the canals. The egg cell, after it is fertilized by the sperm
cell, begins to divide and form new cells, some of which possess cilia.
The embryo sponge passes out at an osculum. By the vibration of the
cilia, it swims about for a while. It afterwards settles down with the
one end attached to the ocean floor and remains fixed for the rest of
its life. The other end develops oscula. Some of the cilia continue to
vibrate and create currents which bring food and oxygen.
The _cilia_ in many species are found only in cavities called ciliated
chambers. (Figs. 22, 32.) There are no _distinct organs_ in the sponge
and there is very little _specialization_ of cells. The ciliated cells
and the reproductive cells are the only specialized cells. The sponges
were for a long time considered as colonies of separate one-celled
animals classed as protozoans. They are, without doubt, many-celled
animals. If a living sponge is cut into pieces, each piece will grow and
form a complete sponge.
[Illustration:
FIG. 32.—Microscopic plan of ciliated chamber. Each cell lining the
chamber has a nucleus, a whip-lash, and a collar around base of
whip-lash. _Question_: State two uses of whip-lash.
]
=That the sponge is not a colony of one-celled animals=, each like an
amœba, but is a many-celled animal, will be realized by examining Fig.
32, which shows a bit of sponge highly magnified. A sponge may be
conceived as having developed from a one-celled animal as follows:
Several one-celled animals happened to live side by side; each possessed
a threadlike flagellum (E, Fig. 32) or whip-lash for striking the water.
By lashing the water, they caused a stronger current (Fig. 25) than
protozoans living singly could cause. Thus they obtained more food and
multiplied more rapidly than those living alone. The habit of working
together left its impress on the cells and was transmitted by
inheritance.
Cell joined to cell formed a ring; ring joined to ring formed a tube
which was still more effective than a ring in lashing the water into a
current and bringing fresh food (particles of dead plants and animals)
and oxygen.
=Few animals eat sponges=; possibly because spicules, or fibres, are
found throughout the flesh, or because the taste and the odour are
unpleasant enough to protect them. Small animals sometimes crawl into
sponges to hide. One sponge grows upon shells inhabited by hermit crabs.
Moving of the shell from place to place is an advantage to the sponge,
while the sponge conceals and thus protects the crab.
=Special Report=: _Sponge “Fisheries.”_ (Localities; how sponges are
taken, cleaned, dried, shipped, and sold.)
CHAPTER IV
POLYPS (CUPLIKE ANIMALS)
THE HYDRA, OR FRESH-WATER POLYP
[Illustration:
FIG. 33.—A HYDRA.
]
SUGGESTIONS.—Except in the drier regions of North America the hydra can
usually be found by careful search in fresh-water ponds not too
stagnant. It is found attached to stones, sticks, or leaves, and has a
slender, cylindrical body from a quarter to half an inch long, varying
in thickness from that of a fine needle to that of a common pin. The
green hydra and the brown hydra, both very small, are common species,
though hydras are often white or colourless. They should be kept in a
large glass dish filled with water. They may be distinguished by the
naked eye but are not studied satisfactorily without a magnifying glass
or microscope. Place a living specimen attached to a bit of wood in a
watch crystal filled with water, or on a hollowed slip, or on a slip
with a bit of weed to support the cover glass, and examine with hand
lens or lowest power of microscope. Prepared microscopical sections,
both transverse and longitudinal, may be bought of dealers in
microscopic supplies. One is shown in Fig. 39.
[Illustration:
FIG. 34.—Forms assumed by Hydra.
]
Is the hydra’s =body= round or two-sided? (Fig. 35.) What is its
_general shape_? Does one individual keep the same shape? (Fig. 34.) How
does the length of the threadlike _tentacles_ compare with the length of
the hydra’s body? About how many tentacles are on a hydra’s body? Do all
have the same number of tentacles? Are the tentacles knotty or smooth?
(Fig. 35.) The hydra is usually extended and slender; sometimes it is
contracted and rounded. In which of these conditions is the base (the
foot) larger around than the rest of the body? (Fig. 34.) Smaller? How
many _openings_ into the body are visible? Is there a depression or an
eminence at the base of the tentacles? For what is the _opening_ on top
of the body probably used? Why are the tentacles placed at the top of
the hydra’s body? Does the _mouth_ have the most convenient location
possible?
[Illustration:
FIG. 35.—HYDRA (much enlarged).
]
The conical projection bearing the _mouth_ is called _hypostome_ (Fig.
34). The mouth opens into the _digestive cavity_. Is this the same as
the general body cavity, or does the stomach have a wall distinct from
the _body cavity_? How far down does the body cavity extend? Does it
extend up into the tentacles? (Fig. 39.)
If a _tentacle is touched_, what happens? Is the body ever bent? Which
is more sensitive, the columnar body or the tentacles? In searching
for hydras would you be more likely to find the tentacles extended or
drawn in? Is the hypostome ever extended or drawn in? (Fig. 34.)
=Locomotion.=—The round surface, or disk, by which the hydra is
attached, is called its foot. Can you move on one foot without hopping?
The hydra moves by alternately elongating and rounding the foot. Can you
discover other ways by which it moves? Does the hydra always stand upon
its foot?
[Illustration:
FIG. 36.—NETTLING CELL. II. discharged, and I. not discharged.
]
=Lasso Cells.=—Upon the tentacles (Fig. 35) are numerous cells provided
each with a threadlike process (Fig. 36) which lies coiled within the
cell, but which may be thrown out upon a water flea, or other minute
animal that comes in reach. The touch of the lasso paralyzes the prey
(Fig. 37). These cells are variously called lasso cells, nettling cells,
or thread cells. The thread is hollow and is pushed out by the pressure
of liquid within. When the pressure is withdrawn the thread goes back as
the finger of a glove may be turned back into the glove by turning the
finger outside in. When a minute animal, or other particle of food comes
in contact with a tentacle, how does the tentacle get the food to the
mouth? By bending and bringing the end to the mouth, or by shortening
and changing its form, or in both ways? (Fig. 34, _C_.) Do the
neighbouring tentacles seem to bend over to assist a tentacle in
securing prey? (Fig. 34, _C_.)
[Illustration:
FIG. 37.—HYDRA capturing a water flea.
]
=Digestion.=—The food particles break up before remaining long in the
stomach, and the nutritive part is absorbed by the lining cells, or
endoderm (Fig. 39). The indigestible remnants go out through the mouth.
The hydra is not provided with a special vent. Why could the vent not be
situated at the end opposite the mouth?
[Illustration:
FIG. 38.—HYDRAS on the under surface of pondweed.
]
=Circulation and Respiration.=—Does water have free access to the body
cavity? Does the hydra have few or nearly all of its cells exposed to
the water in which it lives? From its structure, decide whether it can
breathe like a sponge or whether special respiratory cells are necessary
to supply it with oxygen and give off carbon dioxide. Blood vessels are
unnecessary for transferring oxygen and food from cell to cell.
=Reproduction.=—Do you see any swellings upon the side of the hydra?
(Fig. 34, A.) If the swelling is near the tentacles, it is a _spermary_;
if near the base, it is an _ovary_. A sperm coalesces with or fertilizes
the ovum after the ovum is exposed by the breaking of the ovary wall.
Sometimes the sperm from one hydra unites with the ovum of another
hydra. This is called _cross-fertilization_. The same term is applied to
the process in plants when the male element, developed in the pollen of
the flower, unites with the female element of the ovule of the flower on
another plant. The hydra, like most plants and some other animals, is
hermaphrodite, that is to say, both sperms and ova are produced by one
individual. In the autumn, eggs are produced with hard shells to
withstand the cold until spring. Sexual reproduction takes place when
food is scarce. Asexual generation (by budding) is common with the hydra
when food supply is abundant. After the bud grows to a certain size, the
outer layer of cells at the base of the bud constricts and the young
hydra is detached.
[Illustration:
FIG. 39.—Longitudinal section of hydra (microscopic and diagrammatic).
]
=Compare the sponge and the hydra= in the following respects:—many
celled, or one-celled; obtaining food; breathing; tubes and cavities;
openings; reproduction; locomotion. Which ranks higher among the
metazoa? The metazoa, or many-celled animals, include all animals except
which branch?
Figure 39 is a _microscopic view_ of a vertical section of a hydra to
show the =structure of the body wall=. There is an outer layer called
the _ectoderm_, and an inner layer called the _endoderm_. There is
also a thin supporting layer (black in the figure) called the
_mesoglea_. The mesoglea is the thinnest layer. Are the cells larger
in the endoderm or the ectoderm? Do both layers of cells assist in
forming the reproductive bud? The ectoderm cells end on the inside in
contractile tails which form a thin line and have the effect of muscle
fibres. They serve the hydra for its remarkable changes of shape. When
the hydra is cut in pieces, each piece makes a complete hydra,
provided it contains both endoderm and ectoderm.
In what ways does the hydra show “=division of labour=”? Answer this
by explaining the classes of cells specialized to serve a different
purpose. Which cells of the hydra are least specialized? In what
particulars is the plan of the hydra different from that of a simple
sponge? An ingenious naturalist living more than a century ago,
asserted that it made no difference to the hydra whether the ectoderm
or the endoderm layer were outside or inside,—that it could digest
equally well with either layer. He allowed a hydra to swallow a worm
attached to a thread, and then by gently pulling in the thread, turned
the hydra inside out. More recently a Japanese naturalist showed that
the hydra could easily be turned inside out, but he also found that
when left to itself it soon reversed matters and returned to its
natural condition, that the =cells are really specialized= and each
layer can do its own work and no other.
=Habits.=—The hydra’s whole body is a hollow bag, the cavity extending
even into the tentacles. The tentacles may increase in number as the
hydra grows but seldom exceed eight. The hydra has more active motion
than locomotion. It seldom moves from its place, but its tentacles are
constantly bending, straightening, contracting, and expanding. The body
is also usually in motion, bending from one side to another. When the
tentacles approach the mouth with captured prey, the mouth (invisible
without a hand lens) opens widely, showing five lobes or lips, and the
booty is soon tucked within. A hydra can swallow an animal larger in
diameter than itself.
The =endoderm= cells have _amœboid motion_, that is, they extend
pseudopods. They also resemble amœbas in the power of _intra-cellular
digestion_; that is, they absorb the harder particles of food and digest
them afterwards, rejecting the indigestible portions. Some of these
cells have _flagella_ (see Fig. 39) which keep the fluid of the cavity
in constant motion.
Sometimes the =hydra moves= after the manner of a small caterpillar
called a “measuring worm,” that is, it takes hold first by the foot,
then by the tentacles, looping its body at each step. Sometimes the body
goes end over end in slow somersaults.
[Illustration:
FIG. 40.—HYDROID COLONY, with nutritive (_P_) reproductive (_M_) and
defensive (_S_) hydranths.
]
The _length_ of the extended hydra may reach one half inch. When
touched, both tentacles and body contract until it looks to the unaided
eye like a round speck of jelly. This shows _sensibility_, and a few
small star-shaped cells are believed to be _nerve cells_, but the hydra
has not a nervous _system_. Hydras show their liking for light by moving
to the side of the vessel or aquarium whence the light comes.
[Illustration:
FIG. 41.—“PORTUGUESE MAN-O’-WAR” (compare with Fig. 40). A floating
hydroid colony with long, stinging (and sensory) streamers.
Troublesome to bathers in Gulf of Mexico. Notice balloon-like float.
]
=The Branch Polyps= (sometimes called _Cœlenterata_).—The hydra is the
chief _fresh-water representative_ of this great branch of the animal
kingdom. This branch is characterized by its members having only one
opening to the body. The polyps also include the salt water animals
called _hydroids_, _jellyfishes_, and _coral polyps._
=Hydroids.=—Figure 40 shows a _hydroid_, or group of hydra-like growths,
one of which eats and digests for the group, another defends by nettling
cells, another produces eggs. Each hydra-like part of a hydroid is
called a _hydranth_. Sometimes the buds on the hydra remain attached so
long that a bud forms upon the first bud. Thus three generations are
represented in one organism. Such growths show us that it is not always
easy to tell what constitutes an individual animal.
[Illustration:
FIG. 42.—The formation of many free-swimming jellyfishes from one
fixed hydra-like form. The saucer-like parts (_h_) turn over after
they separate and become like Fig. 43 or 44. Letters show sequence
of diagrams.
]
_Hydroids_ may be conceived _to have been developed_ by the failure of
budding hydras to separate from the parent, and by the gradual formation
of the habit of living together and assisting one another. When each
hydranth of the hydroid devoted itself to a special function of
digestion, defence, or reproduction, this group lived longer and
prospered; more eggs were formed, and the habits of the group were
transmitted to a more numerous progeny than were the habits of a group
where members worked more independently of one another.
As the _sponge_ is a simple example of the devotion of _special cells to
special purposes_, the hydroid is a primitive and simple example of the
occurrence of _organs_, that is of _special parts of the body set aside
for a special work_.
[Illustration:
FIG. 43.—A JELLYFISH.
]
How many mature hydranths are seen in the hydroid shown in Fig. 40? Why
are the defensive hydranths on the outside of the colony? Which
hydranths have no tentacles? Why not?
[Illustration:
FIG. 44.—A JELLYFISH (medusa).
]
=Jellyfish.—Alternation of Generations.—Medusa.=—With some species of
hydroids, a very curious thing happens.—The _hydranth that is to produce
the eggs falls off_ and becomes independent of the colony. More
surprising still, its appearance changes entirely and instead of being
hydra-like, it becomes the large and complex creature called _jellyfish_
(Fig. 43). But the _egg of the jellyfish_ produces a small _hydra-like
animal_ which gives rise by budding to a _hydroid_, and the cycle is
complete.
The bud (or reproductive hydranth) of the hydroid does not produce a
hydroid, but a jellyfish; the egg of the jellyfish does not produce a
jellyfish, but a hydroid. This is called by zoologists, _alternation of
generations_. A _complete individual_ is the life from the germination
of one egg to the production of another. So that an “individual”
consists of a hydroid colony fixed in one place together with all the
jellyfish produced from its buds, which may now be floating miles away
from it in the ocean. Bathers in the surf are sometimes touched and
stung by the long, streamer-like tentacles of the jellyfish. These, like
the tentacles of the hydra, have nettling cells (Fig. 41).
[Illustration:
FIG. 45.—CORAL POLYPS (tentacles, a multiple of _six_). Notice
hypostome.
]
The umbrella-shaped free-swimming jellyfish is called a _medusa_ (Fig.
44).
=Coral Polyps.=—Some of the salt water relatives of the hydra produce
buds which remain attached to the parent without, however, becoming
different from the parent in any way. The _coral polyps_ and
_corallines_ are examples of _colonies_ of this kind, possessing a
common stalk which is formed as the process of multiplication goes on.
In the case of coral polyps, the separate animals and the flesh
connecting them secrete within themselves a hard, _limy, supporting
structure known as coral_. In some species, the coral, or stony part, is
so developed that the polyp seems to be inserted in the coral, into
which it withdraws itself for partial protection (Fig. 45).
The _corallines_ secrete a smooth stalk which affords no protection, but
they also secrete a coating or sheath which incloses both themselves and
the stalk. The coating has apertures through which the polyps protrude
in order to feed when no danger is near (Fig. 46). The red “corals” used
for jewelry are bits of stalks of corallines. The corallines (Figs. 47,
48) are not so abundant nor so important as the coral polyps (Figs. 45,
49).
[Illustration:
FIG. 46.—RED CORALLINE with crust and polyps (_eight_ tentacles).
]
[Illustration:
FIG. 47.—SEA FAN (a coralline).
]
[Illustration:
FIG. 48.—ORGAN PIPE “Coral” (a coralline).
]
Colonies of coral polyps grow in countless numbers in the tropical seas.
The coral formed by successive colonies of polyps accumulates and builds
up many islands and important additions to continents. The Florida
“keys,” or islands, and the southern part of the mainland of Florida
were so formed.
[Illustration:
FIG. 49.—UPRIGHT CUT through coral polyp × 4.
_ms_, mouth; _mr_, gullet; _ls_, _ls_, fleshy partitions (mesenteries)
extending from outer body wall to gullet (to increase absorbing
surface); _s_, _s_, shorter partitions; _mb_, _fb_, stony support
(of lime, called coral); _t_, tentacles.
]
[Illustration:
FIG. 50.—SEA ANEMONE.
]
The =Sea Anemone=, like the coral polyp, lives in the sea, but like the
fresh-water hydra, it _deposits no limy support for its body_. The
anemone is much larger than the hydra and most coral polyps, many
species attaining a height of several inches. It _does not form
colonies_. When its arms are drawn in, it looks like a large knob of
shiny but opaque jelly. Polyps used to be called _zoophytes_
(_plant-animals_), because of their flower-like appearance (Figs. 50,
51).
[Illustration:
FIG. 51.—SEA ANEMONES.
]
CHAPTER V
ECHINODERMS (SPINY ANIMALS)
THE STARFISH
[Illustration:
FIG. 52.—Starfish on a rocky shore.
]
SUGGESTIONS. Since the echinoderms are aberrant though interesting
forms not in the regular line of development of animals, this chapter
may be omitted if it is desired to shorten the course.—The common
starfish occurs along the Atlantic coast. It is captured by wading
along the shore when the tide is out. It is killed by immersion in
warm, fresh water. Specimens are usually preserved in 4 per cent
formalin. Dried starfish and sea urchins are also useful. A living
starfish kept in a pail of salt water will be instructive.
[Illustration:
FIG. 53.—PLAN of starfish; III, madreporite.
]
=External Features.=—Starfish are usually brown or yellow. Why? (See
Fig. 52.) Has it a head or a tail? Right and left sides? What is the
shape of the _disk_, or part which bears the five arms or _rays_? (Fig.
53.) Does the body as a whole have symmetry on two sides of a line
(bilateral symmetry), or around a point (radial symmetry)? Do the
separate rays have bilateral symmetry? The _skeleton_ consists of limy
plates embedded in the tough skin (Fig. 54). Is the _skin_ rough or
smooth? Hard or soft? Are the projections (or _spines_) in the skin long
or short? The skin is hardened by the limy plates, except around the
_mouth_, which is at the centre of the lower side and surrounded by a
membrane. Which is rougher, the mouth side, (_oral_ side) or the
opposite (_aboral_ side)? Which side is more nearly flat? The _vent_ is
at or near the centre of the disk on the aboral surface. It is usually
very small and sometimes absent. Why a vent is not of much use will be
understood after learning how the starfish takes food.
[Illustration:
FIG. 54.—LIMY PLATES in portion of a ray.
]
[Illustration:
FIG. 55.—Starfish (showing MADREPORITE).
]
[Illustration:
FIG. 56.—WATER tube SYSTEM of starfish.
_m_, madreporite; _stc_, stone canal; _ap_, ampulla.
]
An organ peculiar to animals of this branch, and called the _madreporic
plate_, or _madreporite_, is found on the aboral surface between the
bases of two rays (Fig. 55). It is wartlike, and usually white or red.
This plate is a _sieve_; the small openings keep out sand but allow
water to filter through.
=Movements: the Water-tube System.=—The water, which is filtered through
the perforated madreporite, is needed to supply a _system of canals_
(Fig. 56). The madreporite opens into a canal called the _stone canal_,
the wall of which is hardened by the same kind of material as that found
in the skin. The stone canal leads to the _ring canal_ which surrounds
the mouth (Fig. 56). The ring canal sends _radial canals_ into each ray
to supply the double row of _tube feet_ found in the groove at the lower
side of each ray (Fig. 57). Because of their arrangement in rows, the
feet are also called _ambulacral_ feet (Latin _ambulacra_, “forest
walks”). There is a water holder (_ampulla_), or muscular water bulb at
the base of each tube foot (Fig. 58). These contract and force the water
into the tube feet and extend them. The cuplike ends of the tubes cling
to the ground by suction. The feet contain delicate muscles by which
they contract and shorten. Thus the animal pulls itself slowly along,
hundreds of feet acting together. The tube feet, for their own
protection, may contract and retire into the groove, the water which
extended them being sent back into the ampulla. This system of water
vessels (or water-vascular system) of the echinodermata is
characteristic of them; _i.e._ is not found elsewhere in the animal
kingdom. The grooves and the plates on each side of them occupy the
_ambulacral areas_. The rows of spines on each side of the grooves are
freely movable. (What advantage?) The spines on the aboral surface are
not freely movable.
[Illustration:
FIG. 57.—Starfish, from below; tube feet extended.
]
[Illustration:
FIG. 58.—SECTION OF ONE RAY and central portion of starfish.
_f_{1}_, _f_{2}_, _f_{3}_, tube feet more or less extended; _au_, eye
spot; _k_, gills; _da_, stomach; _m_, madreporite; _st_, stone
canal; _p_, ampulla; _ei_, ovary.
]
=Respiration.=—The _system of water vessels serves the additional
purpose_ of bringing water containing oxygen into contact with various
parts of the body, and the starfish was formerly thought to have no
special respiratory organs. However, there are holes in the aboral wall
through which the folds of the delicate lining membrane protrude. These
are now supposed to be _gills_ (_k_, Fig. 58).
[Illustration:
FIG. 59.—Starfish eating a sea snail.
_b_, stomach everted.
]
=The nervous system= is so close to the aboral surface that much of it
is visible without dissection. Its chief parts are a _nerve ring_ around
the mouth, which sends off a _branch_ along each ray. These branches may
be seen by separating the rows of tube feet. They end in a pigmented
cell at the end of each ray called the _eye-spot._
=The food= of starfish consists of such animals as crabs, snails, and
oysters. When the prey is too large to be taken into the mouth, the
starfish _turns its stomach inside out_ over the prey (Fig. 59). After
the shells separate, the stomach is applied to the soft digestible
parts. After the animal is eaten, the stomach is retracted. This odd way
of eating is very economical to its digestive powers, for _only that
part of the food which can be digested and absorbed is taken into the
body_. Only the lower part of the stomach is wide and extensible. The
upper portion (next to the aboral surface) is not so wide. This portion
receives the secretion from five pairs of digestive glands, a pair of
which is situated in each ray. Jaws and teeth are absent. (Why?) The
vent is sometimes wanting. Why?
=Reproduction.=—There is a pair of ovaries at the base of each ray of
the female starfish (Fig. 58). The spermaries of the male have the same
position and form as the ovaries, but they are of a lighter colour,
usually white.[2]
Footnote 2:
The sperm cells and egg cells are poured out into the water by the
adults, and the sperm cell, which, like nearly all sperm cells, has a
vibratory, taillike flagellum to propel it, reaches and fertilizes the
egg cell.
=Regeneration after Mutilation.=—If a starfish loses one or more rays,
they are replaced by growth. Only a very ignorant oysterman, angry at
the depredations of starfish upon his oyster beds, would chop starfish
to pieces, as this only serves to multiply them. This power simulates
multiplication by division in the simplest animals.
[Illustration:
FIG. 60.—Young starfish crawling upon their mother. (Challenger
Reports.)
]
=Steps in Advance of Lower Branches.=—The starfish and other
echinodermata have a more developed nervous system, sensory organs, and
digestion, than forms previously studied; most distinctive of all, they
have a body cavity distinct from the food cavity. The digestive glands,
reproductive glands, and the fluid which serves imperfectly for blood,
are in the body cavity. There is no heart or blood vessels. The motions
of the stomach and the bending of the rays give motion to this fluid in
the body cavity. It cannot be called blood, but it contains white blood
corpuscles.
The starfish when first hatched is an actively swimming bilateral
animal, but it soon becomes starlike (Fig. 60). The limy plates of the
starfish belong neither to the outer nor to the inner layer (endoderm
and ectoderm) of the body wall, but to a third or middle layer
(mesoderm); for echinoderms, like the polyps, belong to the
three-layered animals. In this its skeleton differs from the shell of a
crawfish, which is formed by the hardening of the skin itself.
=Protective Coloration.=—Many starfish are brown or yellow. This makes
them inconspicuous on the brown rocks or yellow sand. Brightly coloured
species are usually chosen for aquaria.
THE SEA URCHIN
=External Features.=—What is the _shape_ of the body? What kind of
_symmetry_ has it? Do you find the oral (or mouth) surface? The aboral
surface? Where is the body flattened? What is the shape of the spines?
What is their use? How are the tube feet arranged? Where do the rows
begin and end? Would you think that a sea urchin placed upside down in
water, could right itself less or more readily than a starfish? What
advantage in turning would each have that the other would not have? The
name sea urchin has no reference to a mischievous boy, but means sea
hedgehog (French _oursin_, hedgehog), the name being suggested by its
spines.
[Illustration:
FIG. 61.—A SEA URCHIN crawling up the glass front wall of an aquarium
(showing mouth spines and tube feet).
]
=Comparison of Starfish and Sea Urchin.=—The water system of the sea
urchin, consisting of madreporite, tubes, and water bulbs, or ampullæ,
is similar to that of the starfish. The tube feet and locomotion are
alike. There is no need for well-developed respiratory organs in either
animal, as the whole body, inside and out, is bathed in water. The
method of reproduction is the same.
[Illustration:
FIG. 62.—A SEA URCHIN with spines removed, the limy plates showing the
knobs on which the spines grew.
]
[Illustration:
FIG. 63.—SECTION OF SEA URCHIN with soft parts removed, showing the
jaws which bear the teeth protruding in Fig. 62.
]
The starfish eats soft animal food. The food of the sea urchin is mainly
vegetable, and it needs teeth (Fig. 62, 63); its food tube is longer
than that of a starfish, just as the food tube of a sheep, whose food
digests slowly, is much longer than that of a dog.
[Illustration:
FIG. 64.—THE SEA OTTER, an urchin with mouth (_o_) and vent (_A_) on
same side of body.
]
The largest species of sea urchins are almost as big as a child’s head,
but such size is unusual. The spines are mounted on knobs, and the joint
resembles a ball-and-socket joint, and allows a wide range of movement.
Some sea urchins live on sandy shores, other species live upon the
rocks. The sand dollars are of a lighter colour. (Why)? They are usually
flatter and have lighter, thinner walls than the other species. The
five-holed sand cake or sand dollar has its weight still further
diminished by the holes, which also allow it to rise more easily through
the water.
Both starfish and sea urchin rest on the flattened lower surface of the
body, while the tube feet are stretching forward for another step.
OTHER ECHINODERMS
[Illustration:
FIG. 65.—SEA CUCUMBERS.
]
The =sea cucumbers=, or =holothurians=, resemble the sea urchin in many
respects, but their bodies are elongated, and the limy plates are absent
or very minute. The mouth is surrounded by tentacles (Fig. 65).
[Illustration:
FIG. 66.—A BRITTLE STAR.
]
The =brittle stars= resemble the starfish in form, but their rays are
very slender, more distinct from the disk, and the tube feet are on the
edges of the rays, not under them (Fig. 66).
[Illustration:
FIG. 67.—CRINOID, arms closed.
]
[Illustration:
FIG. 68.—DISK OF CRINOID from above, showing mouth in centre and vent
near it, at right (arms removed).
]
The =crinoids= are the most ancient of the echinoderms. (Figs. 67, 68.)
Their fossils are very abundant in the rocks. They inhabited the
geological seas, and it is believed that some of the other echinoderms
descended from them. A few now inhabit the deep seas. Some species are
fixed by stems when young, and later break away and become
free-swimming, others remain fixed throughout life.
The four classes of the branch echinoderms are Starfish (_asteroids_),
Sea urchins (_echinoids_), Sea cucumbers (_holothurians_), and Sea
lilies (_crinoids_).
Comparative Review
Make a table like this as large as the page of the notebook will allow,
and fill in without guessing.
══════════════════════════╤════════╤════════╤════════╤════════╤════════
│ AMŒBA │ SPONGE │ HYDRA │ CORAL │STARFISH
│ │ │ │ POLYP │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
Is body round, two-sided, │ │ │ │ │
or irregular │ │ │ │ │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
What organs of sense │ │ │ │ │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
Openings into body │ │ │ │ │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
Hard or supporting │ │ │ │ │
parts of body │ │ │ │ │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
How food is taken │ │ │ │ │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
How move │ │ │ │ │
──────────────────────────┼────────┼────────┼────────┼────────┼────────
How breathe │ │ │ │ │
══════════════════════════╧════════╧════════╧════════╧════════╧════════
CHAPTER VI
WORMS
SUGGESTIONS:—Earthworms may be found in the daytime after a heavy rain,
or by digging or turning over planks, logs, etc., in damp places. They
may be found on the surface at night by searching with a lantern. Live
specimens may be kept in the laboratory in a box packed with damp (not
wet) loam and dead leaves. They may be fed on bits of fat meat, cabbage,
onion, etc., dropped on the surface. When studying live worms, they
should be allowed to crawl on damp paper or wood. An earthworm placed in
a glass tube with rich, damp soil, may be watched from day to day.
[Illustration:
FIG. 69.—AN EARTHWORM.
]
=External Features.=—Is the body _bilateral_? Is there a _dorsal_ and a
_ventral_ surface? Can you show this by a test with live worm? Do you
know of an animal with dorsal and ventral surface, but not bilateral?
Can you make out a head? A head end? A neck? Touch the head and test
whether it can be made to crawl backwards. Which end is more tapering?
Is the mouth at the tip of the head end or on the upper or lower
surface? How is the _vent_ situated? Its shape? As the worm lies on a
horizontal surface, is the body anywhere flattened? Are there any very
distinct divisions in the body? Do you see any _eyes_?
=Experiment= to find whether the worm is sensitive (1) to _touch_, (2)
to _light_, (3) to strong _odours_, (4) to irritating liquids. Does it
show a sense of _taste_? The experiments should show whether it avoids
or seeks a bright light, as of a window; also whether any parts of the
body are especially sensitive to touch, or all equally sensitive. What
effect when a bright light is brought suddenly near it at night?
Is _red blood_ visible through the skin? Can you notice any _pulsations_
in a vessel along the back? Do all earthworms have the same number of
_divisions_ or rings? Compare the size of the rings or segments. Can it
crawl faster on glass or on paper?
[Illustration:
FIG. 70.—MOUTH AND SETÆ.
]
A magnifying glass will show on most species tiny bristle-like
projections called _setæ_. How are the setæ arranged? (_d_, Fig. 70.)
How many on one ring of the worm? How do they point? Does the worm feel
smoother when it is pulled forward or backward between the fingers? Why?
Are setæ on the lower surface? Upper surface? The sides? What is the use
of the setæ? Are they useful below ground? Does the worm move at a
uniform rate? What change in form occurs as the front part of the body
is pushed forward? As the hinder part is pulled onward? How far does it
go at each movement? At certain seasons a broad band, or ring, appears,
covering several segments and making them seem enlarged (Fig. 71). This
is the _clitellum_, or _reproductive girdle_. Is this girdle nearer the
mouth or the tail?
[Illustration:
FIG. 71.—EARTHWORM, mouth end above.
]
=Draw= the exterior of an earthworm.
=Dorsal and Ventral Surfaces.=—The earthworm always crawls with the same
surface to the ground; this is called the _ventral_ surface, the
opposite surface is the _dorsal_ surface. This is the first animal
studied to which these terms are applicable. What are the ventral and
dorsal surfaces of a fish, a frog, a bird, a horse, a man?
[Illustration:
FIG. 72.—FOOD TUBE of earthworm. (Top view.)
]
=The name “worm”= is often carelessly applied to various crawling things
in general. It is properly applied, however, only to _segmented animals
without jointed appendages_. Although a caterpillar crawls, it is not a
worm for several reasons. It has six jointed legs, and it is not a
developed animal, but only an early stage in the life of a moth or a
butterfly. A “grubworm” also has jointed legs (Fig. 167). It does not
remain a grub, but in the adult stage is a beetle. A worm never develops
into another animal in the latter part of its life; its setæ are not
jointed.
[Illustration:
FIG. 73.—FOOD TUBE AND BLOOD VESSELS of earthworm showing the ringlike
hearts. (Side view.)
]
=The Food Tube.=—The earthworm has no teeth, and the food tube, as might
be inferred from the form of the body, is simple and straight. Its
parts, recognizable because of slight differences in size and structure,
are named the pharynx (muscular), gullet, crop, gizzard (muscular), and
stomach-intestine. The last extends through three fourths of the length
of the body (Fig. 72). The functions of the parts of the food tube are
indicated by their names.
[Illustration:
FIG. 74.
]
=Circulation.=—There is a _large dorsal_ blood vessel above the food
tube (Fig. 73). From the front portion of this tube arise several large
tubular rings or “hearts” which are contractile and serve to keep the
blood circulating. They lead to a _ventral vessel_ below the food tube
(Fig. 74). The blood is red, but the _colouring matter_ is in the
liquid, not in the blood cells.
[Illustration:
FIG. 75.—GANGLIA NEAR MOUTH and part of nerve chain of earthworm.
]
=Nervous System.=—Between the ventral blood vessels is a _nerve cord_
composed of two strands (see Fig. 75). There is a slight swelling, or
_ganglion_, on each strand, in each segment (Fig. 75). The strands
separate near the front end of the worm, and a branch goes up each side
of the gullet and enters the two pear-shaped _cerebral ganglia_, or
“brain” (Fig. 75).
=Food.=—The earthworm eats earth containing organic matter, the
inorganic part passing through the vent in the form of circular casts;
these are found in the morning at the top of the earthworm’s burrow.
The earthworm has no teeth. It excretes through the mouth an _alkaline
fluid_ which softens and partly digests the food before it is eaten.
When this fluid is poured out upon a green leaf, the leaf at once turns
brown. The starch in the leaf is also acted upon. The snout aids in
pushing the food into the mouth.
=Kidneys.=—Since oxidation is occurring in its tissues, and impurities
are forming, there must be some way of _removing impurities from the
tissues_. The earthworm does not possess one-pair organs like the
kidneys of higher animals to serve this purpose, but it has numerous
pairs of small tubular organs called _nephridia_ which serve the
purpose. Each one is simply a tube with several coils. There is a pair
on the floor of each segment. Each nephridium has an inner open end
within the body cavity, and its outer end opens by a pore on the surface
between the setæ. The nephridia absorb waste from the liquid in the
_celom_, or body cavity surrounding the food tube, and convey it to the
outside.
[Illustration:
FIG. 76.—TWO PAIRS OF NEPHRIDIA in a worm (diagram).
]
=Respiration.=—The skin of the earthworm is moist, and the blood
capillaries approach so near to the surface of the body that the oxygen
is constantly passing in from the air, and carbon dioxide passing out;
hence it is constantly breathing through all parts of its skin. _It
needs no lungs_ nor special respiratory organs of any kind.
[Illustration:
FIG. 77.—Sperm (_sp_) and egg glands (_es_) of worm.
]
=Reproduction.=—When one individual animal produces both sperm cells
and egg cells, it is said to be hermaphrodite. This is true of the
earthworm. The egg cell is always fertilized, however, not by the
sperm cells of the same worm, but by sperm cells formed by another
worm. The openings of these _ovaries_ consist of two pairs of small
pores found in most species on the ventral surface of the fourteenth
segment (see Fig. 77). There are also two pairs of small _receptacles_
for temporarily holding the _foreign sperm cells_. One pair of the
openings from these receptacles is found (with difficulty) in the
wrinkle behind the ninth segment (Fig. 77), and the other pair behind
the tenth segment. The _spermaries_ are in front of the ovaries (Fig.
77), but the _sperm ducts_ are longer than the _oviducts_, and open
behind them on the fifteenth segment (Figs. 77, 78). The worms
exchange sperm cells, but not egg cells. The reproductive girdle, or
_clitellum_, already spoken of, forms the case which is to hold the
eggs (see Fig. 71). When the sperm cells have been exchanged, and the
ova are ready for fertilization, the worm draws itself backward from
the collar-like case or clitellum so that this slips over the head. As
it passes the fourteenth segment, it collects the ova, and as it
passes the ninth and tenth segments, it collects the sperm cells
previously received from another worm. The elastic, collar-like
clitellum closes at the ends after it has slipped over the worm’s
head, forming a _capsule_. The ova are _fertilized in this capsule_,
and some of them hatch into worms in a few days. These devour the eggs
which do not hatch. The eggs develop into complete but very small
worms before escaping from the capsule.
[Illustration:
FIG. 78.—Side view, showing setæ, nephridia pores, and reproductive
openings.
]
=Habits.=—The earthworm is _omnivorous_. It will eat bits of meat as
well as leaves and other vegetation. It has also the advantage, when
digging its hole, of _eating the earth_ which must be excavated. Every
one has noticed the fresh “casts” piled up at the holes in the morning.
As the holes are partly filled by rains, the casts are most abundant
after rains. The chief _enemies_ of the earthworm are moles and birds.
The worms _work at night_ and retire so early in the morning that the
very early bird has the advantage in catching worms. Perhaps the nearest
to an intelligent act the earthworm accomplishes is to _conceal the
mouth of its hole_ by plugging it with a pebble or a bit of leaf. Worms
_hibernate_, going below danger of frost in winter. In dry weather they
burrow several feet deep.
=The muscular coat= of the body wall is much thicker than the skin. It
consists of two layers: an outer _layer of fibres which run around the
body_ just beneath the skin, and an inner, thicker _layer of fibres
which run lengthwise_. The worm crawls by shortening the longitudinal
muscles. As the bristles (_setæ_) point backward, they prevent the front
part of the body from slipping back, so the hinder part is drawn
forward. Next, the circular muscles contract, and the bristles
preventing the hind part from slipping back, the fore portion is pushed
forward. Is the worm thicker when the hinder part is being pulled up or
when the fore part is being thrust forward? Does the earthworm pull or
push itself along, or does it do both? Occasionally it travels backward,
_e.g._ it sometimes goes backward into its hole. Then the bristles are
directed forward.
The right and left halves of the body are counterparts of each other,
hence the earthworm is _bilaterally symmetrical_. The lungs and the
gills of animals must always be kept moist. The worm _cannot live long
in dry air_, for respiration in the skin ceases when it cannot be kept
moist, and the worm smothers. Long immersion in water is injurious to
it, perhaps because there is far less oxygen in water than in the air.
Darwin wrote a book called “Vegetable Mould and Earthworms.” He
estimated that there were fifty thousand earthworms to the acre on farm
land in England, and that they bring up eighteen tons of soil in an acre
each year. As the acids of the food tube act upon the mineral grains
that pass through it, the earthworm renders _great aid in forming soil_.
By burrowing it makes the soil more _porous_ and brings up the subsoil.
Although without eyes, the worm is sensitive to light falling upon its
anterior segments. When the light of a lantern suddenly strikes it at
night, it crawls quickly to its burrow. Its sense of touch is so keen
that it can detect a light puff of breath. Which of the foods kept in a
box of damp earth disappeared first? What is indicated as to a sense of
taste?
[Illustration:
FIG. 79.—SAND WORM × ⅔ (Nereis).
]
Why is the bilateral type of structure better adapted for development
and higher organization than the radiate type of the starfish? The
earthworm’s body is a double tube; the hydra’s body is a single tube;
which plan is more advantageous, and why? Would any other colour do just
as well for an earthworm? Why, or why not?
The _sandworm_ (Nereis) lives in the sand of the seashore, and swims
in the sea at night (Fig. 79). It is more advanced in structure than
the earthworm, as it has a distinct head (Fig. 80), eyes, two teeth,
two lips, and several pairs of antennæ, and two rows of muscular
projections which serve as feet. It is much used by fishermen for
bait. If more easily obtained, it may be studied instead of the
earthworm.
[Illustration:
FIG. 80.—HEAD OF SANDWORM (enlarged).
]
=There are four classes in the branch Vermes=: 1) the _worms_, including
sandworms and leeches; 2) the _roundworms_, including trichina,
hairworms, and vinegar eels; 3) _flatworms_, including tapeworm and
liver fluke; 4) _rotifers_, which are microscopic aquatic forms.
The =tapeworm= is a flatworm which has lost most of its organs on
account of its parasitic life. Its egg is picked up by an herbivorous
animal when grazing. The embryo undergoes only partial development in
the body of the herbivorous animal, _e.g._ an ox. The next stage will
not develop until the beef is eaten by a carnivorous animal, to whose
food canal it attaches itself and soon develops a long chain of segments
called a “tape.” Each segment absorbs fluid food through its body wall.
As the segments at the older end mature, each becomes full of eggs, and
the segments become detached and pass out of the canal, to be dropped
and perhaps picked up by an herbivorous animal and the life cycle is
repeated.
The =trichina= is more dangerous to human life than is the tapeworm. It
gets into the food canal in uncooked pork (bologna sausage, for
example), multiplies there, migrates into the muscles, causing great
pain, and encysts there, remaining until the death of the host. It is
believed to get into the bodies of hogs again when they eat rats, which
in turn have obtained the cysts from carcasses.
=Summary of the Biological Process.=—An earthworm is _a living machine
which does work_ (digging and crawling; seizing, swallowing, and
digesting food; pumping blood; growing and reproducing). To do the work
it must have a continual _supply of energy_. The energy for its work is
set free by the protoplasm (in its microscopic cells) undergoing a
destructive chemical change (_oxidation_). The waste products from the
breaking down of the protoplasm must be continually removed
(_excretion_). The broken-down protoplasm must be continually replaced
if life is to continue (the income must exceed the outgo if the animal
is still growing). The microscopic cells construct more protoplasm out
of food and oxygen (_assimilation_) supplied them by the processes of
nutrition (eating, digesting, breathing, circulating). This protoplasm
in turn oxidizes and releases more energy to do work, and thus the cycle
of life proceeds.
CHAPTER VII
CRUSTACEANS
CRAWFISH
SUGGESTIONS.—In regions where crayfish are not found, a live crab may
be used. Locomotion and behaviour may be studied by providing a tub of
water, or better, a large glass jar such as a broad candy jar. For
suggestions on study of internal structure, see p. 58.
=Habitat.=—Do you often see crawfish, or crayfish, moving about, even in
water where they are known to be abundant? What does your answer suggest
as to the time when they are probably most active?
Why do you never see one building its chimney, even where crayfish holes
are abundant? Is the chimney always of the same colour as the surface
soil? Are the crayfish holes only of use for protection? In what kind of
spots are crayfish always dug; Why? What becomes of crayfish when the
pond or the creek dries up? How deep are the holes? How large are the
lumps of mud of which the chimney is built? How does it get them out of
the hole? Why is the mud built into a chimney instead of thrown away?
(What would happen to a well with its mouth no higher than the ground?)
Why are crayfish scarce in rocky regions?
How does the colour of the crayfish compare with its surroundings? Is
its colour suited to live in clear or muddy water? Define protective
colouration.
=Habits.=—Does the crayfish walk better in water or out of it? Why? Does
it use the legs with the large claws to assist in walking? Do the
swimmerets (under the abdomen) move fast or slow? (Observe it from below
in a large jar of clear water.) What propels it backward? Forward? Does
the crayfish move at a more uniform rate when swimming backward or
forward? Why? In which way can it swim more rapidly? Do the big legs
with claws offer more resistance to the water while it is swimming
backward or forward? How does it hold the tail after the stroke, while
it is darting backward through the water? Hold a crayfish with its tail
submerged and its head up. Can the tail strike the water with much
force? Allow it to grasp a pencil: can it sustain its own weight by its
grip?
=Feeding.=—Offer several kinds of food to a crayfish that has not been
alarmed or teased. Does it prefer bread, meat, or vegetables? How does
it get the food to its mouth? Does it eat rapidly or slowly? Does it
tear the food with the big pincers? Can it gnaw with the small
appendages near the mouth?
=Breathing.=—Does the crayfish breathe with gills or lungs? Place a few
drops of ink near the base of the hind legs of a crayfish resting
quietly in shallow water. Where is the ink drawn in? Where does it come
out? To explain the cause and the purpose of this motion, place a
crayfish in a large glass jar containing water, and see the vibratory
motion of the parts under the front portion of the body. There is under
the shell on each side of the body a gill paddle, or gill bailer, that
moves at the same rate.
=Senses.=—Crayfish are best caught with a piece of meat or beef’s liver
tied to a string. Do they always lose hold as soon as they are lifted
above the water? What do you conclude as to the alertness of their
senses? Does the covering of their bodies suggest the possession of a
delicate or a dull sense of touch?
Of what motions are the _eyes_ capable? Touch one of the eyes. The
result? Can a crayfish see in all directions? To test this, place a
crayfish on a table and try whether you can move to a place where you
can see the crayfish without seeing its eyes. What are the advantages
and disadvantages of having the eyes on stalks?
[Illustration:
FIG. 81.—CRAWFISH (dorsal surface).
]
[Illustration:
FIG. 82.
]
Touch the body and the several appendages of the crayfish. Where does it
seem most sensitive to _touch_? Which can reach farther, the antennæ or
the big claws? Why are short feelers needed as well as long ones?
Make a loud and sudden noise without jarring the crayfish. Is it
affected by _sound_?
=External Anatomy= (Figs. 81, 82, 83, 84).—Is the body of the crayfish
rounded out (convex) everywhere, or is any part of its surface either
flat or rounded in (concave)? What _colour_ has the crayfish? Is this
colour of any use to the crawfish?
[Illustration:
FIG. 83.—LATERAL VIEW OF CRAWFISH.
]
Make out the two distinct regions or _divisions of the body_ (Fig. 81).
The anterior (front) region is called the head chest or cephalothorax,
and the posterior (rear) region is called the tail. Which region is
larger? Why? Which is flexible? Why?
Is the _covering_ of the body hard or soft? What is the advantage of
such a covering? What are its disadvantages? How is the covering
modified at the joints to permit motion?
[Illustration:
FIG. 84.—FOURTH ABDOMINAL SEGMENT OF CRAWFISH with swimmeret.
]
=Tail.=—How many joints, or segments, of the tail? (Figs. 81, 83.) Does
the hard covering of each segment slip under or over the segment behind
it when the tail is straight? Does this lessen friction while swimming
forward?
Is there a pair of _swimmerets_ to each segment of the tail? (Figs. 82,
86.) Notice that each swimmeret has a main stalk (protopod), an outer
branch (exopod), and an inner branch (endopod) (Fig. 84). Are the stalk
and the branches each in one piece or jointed? The middle part of the
tail fin is called the telson. By finding the position of the vent,
decide whether the food tube goes into the telson (Fig. 82). Should it
be called an abdominal segment. Are the side pieces of the tail fin
attached to the telson or to the sixth segment? Do these side pieces
correspond to swimmerets? Do they likewise have the Y-shaped structure?
(Fig. 86.)
[Illustration:
FIG. 85.—1, mandible; 2,3, maxillæ; 4,5,6, maxillipeds.
]
If the swimmerets on the first abdominal segment are large, the specimen
is a male. If they are small, it is a female. Which sex is shown in Fig.
82? Fig. 86?
[Illustration:
FIG. 86.—CRAYFISH (ventral surface).
]
=Carapace.=—The covering of the head chest (cephalothorax) is called the
carapace. Has it free edges? The _gills_ are on the sides of the body
and are covered by the carapace (Fig. 87). The projection in front is
called the _rostrum_, meaning beak. Does the rostrum project beyond the
eyes? There is a transverse groove across the carapace which may be said
to divide the head from the abdomen. Where does this groove end at the
sides?
=Legs.=—How many legs has the crayfish? How many are provided with large
claws? Small claws? Is the outer claw hinged in each of the large
grasping pincers? The inner claw?
=Appendages for Taking Food.=—If possible to watch a living crayfish
eating, notice whether it places the food directly into the mouth with
the large claws. Bend the large claws under and see if they will reach
the mouth.
Attached just in front of the legs the crayfish has three pairs of
finger-like appendages, called foot jaws (maxillipeds), with which it
passes the food from the large pincers to its mouth (Figs. 85, 86). They
are in form and in use more like fingers than feet. In front of the foot
jaws are two pairs of thin jaws (maxillæ) and in front of the thin jaws
are a pair of stout jaws (mandibles) (Fig. 85). Do the jaws move
sidewise or up and down? Which of the jaws has a jointed finger (palp)
attached to it? Do all the appendages for taking food have both exopod
and endopod branches on a basal stalk or protopod? Which of the
appendages have a scalloped edge? How would you know from looking at the
crayfish that it is not merely a scavenger? Why are there no pincers on
the hind feet?
[Illustration:
FIG. 87.—Gill cover removed and gills exposed.
_Mp_, gill bailer.
]
=Sense Organs.=—Find the _antennæ_, or long feelers (Figs. 82, 90). Are
the antennæ attached above or below the eyes? (Fig. 87.)
[Illustration:
FIG. 88.—LENGTHWISE SECTION OF MALE CRAWFISH.
_c_, heart; _Ac_, artery to head; _Aa_, artery to abdomen; _Km_,
stomach; _D_, intestine; _L_, liver; _T_, spermary; _Go_, opening of
sperm duct; _G_, brain; _N_, nerve chain.
]
Find the pair of _antennules_, or small feelers. Are their divisions
like or unlike each other? Compare the length of the antennules and the
antennæ. Compare the flexibility of the antennæ with that of the other
appendages.
Observe the position of the _eyes_ (Figs. 81, 88). How long are the
eyestalks? Is the stalk flexible or stiff? Touch the eye. Where is the
joint which enables the stalk to move? Is the outer covering of the eye
hard or soft? A mounted preparation of the transparent covering (cornea)
of the eye, seen with lower power of microscope, reveals that the cornea
is made up of many divisions, called facets. Each facet is the front of
a very small eye, hundreds of which make up the whole eye, which is
therefore called a compound eye. The elongated openings to the _ear
sacs_ are located each on the upper side of the base of a small feeler
just below the eye.
=Respiratory System.=—The respiratory organs are gills located on each
side of the thorax in a space between the carapace and the body (Fig.
87). The gills are white, curved, and feathery. Is the front gill the
largest or the smallest? The gills overlap each other; which is the
outermost gill? On the second maxilla is a thin, doubly curved plate
called a gill bailer (Fig. 85). The second maxilla is so placed that the
gill bailer comes at the front end of the gill chamber. The bailer
paddles continually, bringing the water forward out of the gill. The
gills are attached below at the base of the legs. Are the gills thick or
thin? How far upward do they go? Does the backward motion in swimming
aid or hinder the passage of the water through the gills? Does a
crayfish, when at rest on the bottom of a stream, have its head up or
down stream? Why?
=Openings.=—The slitlike _vent_ is on the under side of the telson
(Figs. 82, 88). The _mouth_ is on the under side of the thorax behind
the mandibles. At the base of the long antennæ are the openings from the
_green glands_, two glands in the head which serve as kidneys (Fig. 89).
The openings of the _reproductive organs_ are on the third pair of legs
in the female, and the fifth pair of legs in the male (Fig. 88). The
eggs are carried on the swimmerets.
[Illustration:
FIG. 89.—Level lengthwise section showing _h_, heart. _d_, green
gland. _le_, liver. _kie_, gills. _kh_, gill cavity. _ma_, stomach.
(After Huxley.)
]
=Internal Structure.=—SUGGESTIONS. If studied by dissection, it will
be necessary to have several crayfish for each pupil, one for gaining
general knowledge, and others for studying the systems in detail.
Specimens should have lain in alcohol for several days.
[Illustration:
FIG. 90.—SECTION OF CRAYFISH showing—stomach _s_, liver _li_, and vent
_a_.
]
=The Food Tube.=—Is the stomach in the head portion of the
cephalothorax or in the thoracic portion? (Figs. 88,89). Is the
stomach large or small? What is its general shape? Does the gullet
lead upward or backward? Is it long or short? (Fig. 88.) The mid tube,
which is the next portion of the food tube, is smaller than the
stomach. On each side of it are openings from the bile ducts which
bring the secretion from the digestive gland, sometimes called the
liver. Does this gland extend the whole length of the thorax? Is it
near the floor or the top of the cavity? The third and last portion of
the food tube is the intestine. It extends from the thorax to the
vent. Is it large or small? Straight or curved? The powerful flexor
muscles of the tail lie in the abdomen below the intestines. Compare
the size of these muscles with the extensor muscle above the intestine
(Fig. 90). Why this difference? Does the food tube extend into the
telson? Locate the vent (Fig. 90).
[Illustration:
FIG. 91.—Showing heart and main blood vessels.
]
=The Circulation.=—The blood is a liquid containing _white
corpuscles_. It lacks red corpuscles and is colourless. The heart is
in the upper part of the thorax. It is surrounded by a large, thin
bag, and thus it is in a chamber (called the _pericardial sinus_). The
blood from the pulmonary veins enters this sinus before it enters the
heart. The origin of this pericardial sinus by the fusing of veins is
shown in Fig. 130. Does one artery, or do several arteries, leave the
heart? There is a larger dorsal artery lying on the intestine and
passing back to the telson; there are three arteries passing forward
close to the dorsal surface (Figs. 89, 91). One large artery (the
sternal) passes directly downward (Figs. 88, 91), and sends a branch
forward and another backward near the ventral surface. The openings
into the heart from the sinus have valvular lips which prevent a
backward flow of blood into the sinus. Hence, when the heart
contracts, the blood is sent out into the several arteries. The
arteries take a supply of fresh blood to the eyes, stomach, muscles,
liver, and the various organs. After it has given oxygen to the
several organs and taken up carbon dioxide, it returns by veins to
pass through the gills on each side, where it gives out the useless
gas and takes up oxygen from the water. It is then led upward by veins
into the pericardial sinus again.
[Illustration:
FIG. 92.
]
The central nervous system consists of a _double chain_ of ganglia
(Fig. 92). This main nerve chain lies along the ventral surface below
the food tube (Fig. 90), except one pair of ganglia which lie above
the œsophagus or gullet (Fig. 88), and are called the supra-œsophageal
ganglia, or brain.
=Crustacea.=—The crayfish and its kindred are placed in the class called
_Crustacea_.
[Illustration:
FIG. 93.—CRAB FROM BELOW.
]
[Illustration:
FIG. 94.—HERMIT CRAB, using shell of sea snail for a house.
]
=Decapods.=—All crustacea which have ten feet belong in the order called
decap´oda (ten-footed). This order includes the crabs, lobsters, shrimp,
etc. The crabs and the lobsters are of considerable importance because
of use as food. Small boys sometimes catch crayfish, and in some
instances are known to cook and eat them for amusement, the only part
cooked being the muscular tail. The crab’s tail is small and flat and
held under the body (Fig. 93).
[Illustration:
FIG. 95.—DEVELOPMENT OF A CRAB.
_a_, nauplius just after hatching; _b_, _c_, _d_, zoëa; _e_, megalops;
_f_, adult.
=Question=: Which stage is most like a crayfish? Compare with
metamorphoses of insects.
]
Since the limy covering to serve the purpose of protection is not soft
enough to be alive and growing, it is evident that the crustacea are
hampered in their growth by their crusty covering. During the first year
the crayfish sheds its covering, or =moults= three times, and once each
year thereafter. It grows very fast for a few days just after moulting,
while the covering is soft and extensible. Since it is at the mercy of
birds, fish, and other enemies while in this soft and defenceless
condition, it stays hidden until the covering hardens. Hence it cannot
eat much, but probably by the absorption of water the tissues grow; that
is, enlarge. In the intervening periods, when growth is impossible, it
develops; that is, the tissues and organs change in structure and become
stronger. “Soft-shelled crab” is a popular dish, but there is no species
by that name, this being only a crab just after moulting which has been
found by fishermen in spite of its hiding.
=General Questions.=—How do crayfish choose their food? How long can
they live out of water? Why do their gills remain moist out of water
longer than a fish? How do they breathe out of water? Are they
courageous or cowardly animals? When they lose appendages in fighting
or moulting these are readily reproduced, but an organ moults several
times in regaining its size. Have you seen crayfish with one claw
smaller than the other? Compare the crayfish and crab (Figs. 81, 93,
and 95) in the following particulars: shape, body, eyes, legs,
abdomen, habitat, movement.
KEY TO THE FOUR CLASSES IN BRANCH ARTHROPODS
1. INSECTS 3 body divisions, 6 legs
2. ARACHNIDS 2 body divisions, 8 legs
3. MYRIAPODS many body divisions, many legs
4. CRUSTACEANS gill breathers, skeleton (external) limy
By the aid of the key and of figures 96–105, classify the following
Arthropods: tick, thousand-leg centipede, king crab, pill bug, spider,
scorpion, beetle.
[Illustration:
FIG. 96.—PILL BUG.
]
[Illustration:
FIG. 97.—LADY BEETLE.
]
[Illustration:
FIG. 98.—SCORPION.
]
[Illustration:
FIG. 99.—TICK before and after feeding.
]
[Illustration:
FIG. 100.—CENTIPEDE.
]
[Illustration:
FIG. 101.—ONE SEGMENT OF CENTIPEDE with one pair of legs.
]
[Illustration:
FIG. 102.—ONE SEGMENT OF THOUSAND LEGS with two pairs of legs.
]
[Illustration:
FIG. 103.—THOUSAND LEGS.
]
[Illustration:
FIG. 104.—A SPIDER.
]
[Illustration:
FIG. 105.—KING CRAB.
]
=Illustrated Study.= CLASSIFICATION OF ARTHROPODS. Key on p. 61.
CHAPTER VIII
INSECTS
THE GRASSHOPPER
SUGGESTIONS.—Collect grasshoppers, both young and full-grown, and keep
alive in broad bottles or tumblers and feed on fresh grass or lettuce.
When handling a live grasshopper, never hold it by its legs, as the
joints are weak. To keep them for some time and observe their moults,
place sod in the bottom of a box and cover the box with mosquito
netting or wire gauze.
[Illustration:
FIG. 106.—A GRASSHOPPER.
]
What is the =general shape= of its body? (Fig. 106.) Where is the body
thickest? Is it bilaterally symmetrical, that is, are the two sides of
the body alike? Is the _skeleton_, or hard part of the body, internal or
external? Is the skeleton as stiff and thick as that of a crayfish? What
is the length of your specimen? Its colour? Why does it have this
coloration? In what ways does the grasshopper resemble the crayfish?
Differ from it?
=The Three Regions of the Body.=—The body of the grasshopper is divided
into three regions—the _head_, the _thorax_, and the _abdomen_. Which of
these three divisions has no distinct subdivisions? The body of the
grasshopper, like that of the earth worm, is made of _ringlike
segments_. Are the segments most distinct in the head, the thorax, or
the abdomen? Which region is longest? Shortest? Strongest? Why? Which
region bears the chief sense organs? The appendages for taking food? The
locomotory appendages? Which division of the body is most active in
breathing?
=The Abdomen.=—About how many segments or rings in the abdomen? Do all
grasshoppers have the same number of rings? (Answer for different
species and different individuals of the same species.) The first
segment and the last two are incomplete rings. Does the flexibility of
the abdomen reside in the rings or in the joints between the rings? Is
there merely a thin, soft line between the rings, or is there a fold of
the covering? Does one ring slip into the ring before it or behind it
when the abdomen is bent?
[Illustration:
FIG. 107.—A GRASSHOPPER DISSECTED.
]
As the grasshopper =breathes=, does each ring enlarge and diminish in
size? Each _ring is divided into two parts_ by folds. Does the upper
half-ring overlap the lower half-ring, or the reverse? With magnifying
glass, find a small slit, called a _spiracle_, or breathing hole, on
each side of each ring just above the side groove (Fig. 106). A tube
leads from each spiracle. While the air is being taken in, do the two
portions of the rings move farther apart? When they are brought together
again, what must be the effect? In pumping the air, the abdomen may be
said to work like a bellows. Bellows usually have folds to allow motion.
Is the comparison correct?
How many times in a minute does the grasshopper take in air? If it is
made to hop vigorously around the room and the breathing is again timed,
is there any change?
Find the =ears= on the front wall of the _first abdominal ring_ (Fig.
107). They may be seen by slightly pressing the abdomen so as to widen
the chink between it and the thorax. The ears are merely glistening,
transparent _membranes_, oval in form. A _nerve_ leads from the inner
surface of each membrane. State any advantage or disadvantage in having
the ears located where they are.
[Illustration:
FIG. 108.—GRASSHOPPER LAYING EGGS. (Riley.)
]
=Ovipositor.=—If the specimen is a female, it has an egg-placer or
ovipositor, consisting of _four blunt projections_ at the end of the
abdomen (Fig. 107). If it is a male, there are two appendages above the
end of the abdomen, and smaller than the parts of the ovipositor.
Females are larger and more abundant than males. In laying the eggs, the
four blunt points are brought tightly together and then forced into the
ground and opened (Fig. 108). By repeating this, the grasshopper makes a
pit almost as deep as the abdomen is long. The eggs are laid in the
bottom of the pit.
=Draw= a side view of the grasshopper.
=Thorax.=—This, the middle portion of the body, consists of _three
segments_ or rings (Fig. 107). Is the division between the rings most
apparent above or below? Which two of the three rings are more closely
united?
The front ring of the thorax is called _prothorax_. Is it larger above
or below? Does it look more like a collar or a cape? (Fig. 106.) A
spiracle is found on the second ring (_mesothorax_, or middle thorax)
just above the second pair of legs. There is another in the soft skin
between the prothorax and the mesothorax just under the large cape or
collar. The last ring of the thorax is called the _metathorax_ (rear
thorax).
How many =legs= are attached to each ring of the thorax? Can a
grasshopper walk? Run? Climb? Jump? Fly? Do any of the legs set forward?
(See Fig. 106.) Outward? Backward? Can you give reasons for the position
of each pair? (Suggestion: What is the use of each pair?) If an organ is
modified so that it is suited to serve some particular purpose or
function, it is said to be _specialized_. Are any of the legs
specialized so that they serve for a purpose different from that of the
other legs?
[Illustration:
FIG. 109.—HOW A GRASSHOPPER WALKS.
]
[Illustration:
FIG. 110.—HOW A SPIDER WALKS.
]
The leg of a grasshopper (as of all insects) is said to have _five
parts_, all the small parts after the first four parts being counted as
one part and called the foot. Are all the legs similar, that is, do the
short and the long joints in all come in the same order? Numbered in
order from the body, which joint of the leg is the largest,—the first,
second, third, or fourth? Which joint is the shortest? The slenderest?
Which joint has a number of sharp points or spines on it? Find by
experiment whether these spines are of use in walking (Fig. 106).
Jumping? Climbing? In what order are the legs used in walking? How many
legs support the body at each step?
All animals that have ears have ways of communicating by =sounds=. Why
would it be impossible for the grasshopper to have a _voice_, even if it
had vocal cords in its throat? The male grasshoppers of many species
make a =chirping=, or stridulation, by rubbing the wing against the leg.
Look on the inner side (why not outer side?) of the largest joint of the
hind leg for a _row of small spines_ visible with the aid of a hand lens
(Fig. 111). The sound is produced by the outer wings rubbing against the
spines. Have you noticed whether the sound is produced while the insect
is still or in motion? Why? The male grasshoppers of some species,
instead of having spines, rub the under side of the front wing on the
upper side of the hind wing.
[Illustration:
FIG. 111.—_A_, ROW OF SPINES, _z_, used in chirping.
_B_, the same more enlarged.
]
=Wings.=—To what is the first pair of wings attached? The second pair?
Why are the wings not attached to the prothorax? Why are the wings
attached so near the dorsal line of the body? Why are the second and
third rings of the thorax more solidly joined than the first and second
rings?
[Illustration:
FIG. 112.—GRASSHOPPER IN FLIGHT.
]
Compare the first and second pairs of wings in shape, size, colour,
thickness and use (Fig. 112). How are the second wings folded so as to
go under the first wings? About how many folds in each?
=Draw= a hind wing opened out.
=Head.= What is the shape of the head viewed from the front, the side,
and above? _Make sketches._ What can you say of the neck? Is the head
movable in all directions?
What is the position of the large =eyes=? Like the eyes of the crayfish,
they are _compound, with many facets_. But the grasshopper has also
_three simple eyes_, situated one in the middle of the forehead and one
just above each antenna. They are too small to be seen without a hand
lens. How does the grasshopper’s range of vision compare with that of
the crayfish?
[Illustration:
FIG. 113.
]
Are the =antennæ= flexible? What is their shape? Position? Are they
segmented? Touch an antenna, a wing, a leg, and the abdomen in
succession. Which seems to be the most sensitive to touch? The antennæ
are for feeling. In some species of insects they also are organs of
hearing and smelling.
The =mouth parts= of a grasshopper should be compared with the mouth
parts of a beetle shown in Fig. 113, since they correspond closely. If
the grasshopper is fed with a blade of fresh grass, the function of each
organ may be plainly seen. It is almost impossible to understand these
functions by studying a dead specimen, but a fresh specimen is much
better than a dry one.
[Illustration:
FIG. 114.—_a_, FOOD TUBE OF BEETLE. _b_, gizzard; _d_, intestine; _c_,
biliary vessels. See Fig. 127.
]
The upper lip, or _labrum_, is seen in front. Is it tapering or
expanded? In what direction is it movable? The dark pointed biting jaws
(_mandibles_) are next. Are they curved or straight? Sharp or blunt
pointed? Notched or smooth? Do they work up and down, or sideways? The
holding jaws (_maxillæ_), each with two jaw fingers (_maxillary palpi_),
are behind the chewing jaws. Why? The lower lip (_labium_) has a pair of
lip fingers (_labial palpi_) upon it. The brown tongue, usually bathed
in saliva, is seen in the lower part of the mouth. Since the grasshopper
has no lips, or any way of producing suction, it must lap the dew in
drinking. Does it merely break off bits of a grass blade, or does it
chew?
The heart, circulation, nervous system, digestive and respiratory organs
of the grasshopper agree mainly with the general description of the
organs of insects given in the next section.
[Illustration:
FIG. 115.—EGG AND MOULTS OF A GRASSHOPPER.
]
=Microscopic Objects.=—These may be bought ready mounted, or may be
examined fresh. A portion of the covering of the large eye may be cut
off and the dark layer on the inside of the covering scraped off to make
it transparent. What is the shape of the facets? Can you make any
estimate of their number? A portion of the transparent hind wing may be
used, and the “veins” in it studied. A thin bit of an abdominal segment
containing a spiracle will show the structure of these important organs.
=Growth of the Grasshopper.=—Some species hibernate in sheltered places
and lay eggs in the spring, but adult species are scarce at that season.
Most species lay the eggs in the fall; these withstand the cold and
hatch out in the spring. Those hatched from one set of eggs sometimes
stay together for a few days. They eat voraciously, and as they grow,
the soft skin becomes hardened by the deposit of horny substance called
chitin. This retards further growth until the insect moults, the skin
first splitting above the prothorax. After hatching, there are five
successive periods of growth. At which moult do the very short wings
first appear? (Fig. 115.) After the last moult the animal is complete,
and changes no more in size for the rest of its life. There has been an
attempt among writers to restrict the term grasshopper to the
long-winged, slender family, and to call the shorter winged, stouter
family locusts, according to old English usage.
[Illustration:
FIG. 116.—COCKROACH.
]
[Illustration:
FIG. 117.—PRAYING MANTIS, or devil’s horse.
]
[Illustration:
FIG. 118.—CRICKET.
]
[Illustration:
FIG. 119.—MOLE CRICKET.
]
[Illustration:
FIG. 120.—FRONT LEG OF MOLE CRICKET. × 3.
]
=Economic Importance of Grasshoppers.=—Great injury is often done to
vegetation by grasshoppers; however, the millions of tiny but ravenous
eaters hatched in early spring are usually soon thinned out by the
birds. The migratory locusts constitute a plague when they appear, and
they have done so since ancient times. The Rocky Mountain locusts flying
eastward have darkened the sky, and where they settled to the earth ate
almost every green thing. In 1874–5 they produced almost a famine in
Kansas, Nebraska, and other Western states. The young hatched away from
the mountains were not healthy, and died prematurely, and their
devastations came to an end. Of course the migrations may occur again.
Packard calculates that the farmers of the West lost $200,000,000
because of grasshopper ravages in 1874–5.
The _cockroaches_ (Fig. 116), =kindred of the grasshoppers=, are
household pests that have migrated almost everywhere that ships go. The
_praying mantis_ (Fig. 117), or _devil’s horse_, also belongs to this
order. It is beneficial, since it destroys noxious insects. Which of its
legs are specialized? The _walking stick_ (Fig. 121) and the _cricket_
(Fig. 118), like most members of the order, are vegetarian.
[Illustration:
FIG. 121.—FOUR WALKING STICK INSECTS.
]
Are grasshoppers more common in fields and meadows, or in wooded places?
How many different colours have you seen on grasshoppers? Which colours
are most common?
Grasshoppers are very scarce in Europe as they love dry, warm countries.
Why do locusts migrate? Give an instance in ancient times.
How long do most grasshoppers live? Does a grasshopper spread its wings
before it flies? Does it jump and fly together? Can it select the place
for alighting?
NOTE TO TEACHER.—=Field work in Zoology= should be systematic. Every
trip has a definite region and definite line of study in view, but
every animal seen should be noted. The habitat, adaptation by
structure and habits to the environment, relations to other animals,
classification of animals seen, should be some of the ideas guiding
the study. The excursions may be divided somewhat as follows,
according as opportunities offer: Upland woods, lowland woods, upland
pastures, fields, swamps, a fresh-water lake, a pond, lower sea beach,
higher sea beach, sand hills along shore, roadside, garden, haunts of
birds, insect visits to flowers, ground insects, insects in logs.
=Collecting Insects.=—In cities and towns insects, varying with the
season, are attracted by electric lights. Beetles and bugs will be found
under the lights, moths on posts near the lights, grasshoppers and
crickets and other insects in the grass near by. A lamp placed by a
window brings many specimens. In the woods and in rocky places insects
are found under logs and stones, and under the bark of dead trees. In
open places, prairies, meadows, and old fields with grass and flowers,
it will be easy to find grasshoppers, butterflies, and some beetles.
Ponds and streams are usually rich in animal forms, such as bugs and
beetles, which swim on or under the surface, and larvæ of dragon flies
crawling on the bottom. Dragon flies and other insects that lay eggs on
the water are found flying in the air above. (In the spring, newly
hatched crayfish, tadpoles, and the eggs of frogs and toads should also
be collected, if found.) Moths may be caught at night by daubing
molasses or syrup made from brown sugar upon the trunks of several
trees, and visiting the trees at intervals with a lantern.
An insect net for catching butterflies and for dredging ponds may be
made by bending a stout wire into a circle one foot in diameter, leaving
enough straight wire to fasten with staples on an old broomstick. To the
frame is fastened a flour sack, or cone made of a piece of mosquito
netting.
Butterflies and moths should be promptly killed, or they will beat their
wings to pieces. The quickest method is by dropping several drops of
gasoline upon the ventral (under) side of the thorax and abdomen.
(Caution: Gasoline should never be used near an open fire, or lamp, as
explosions and deaths result from the flame being led through the
gasoline-saturated air to the vessel containing it.)
A cigar box and a bottle with a notched cork may be used for holding
specimens. Cigar boxes may be used for holding collections of dried
insects. Cork or ribbed packing paper may be fixed in the bottom for
supporting the insect pins. Moth balls or tobacco may be placed in each
box to keep out the insect pests which infest collections.
Captured insects which, in either the larval or the perfect stage, are
injurious to vegetation, should always be killed after studying their
actions and external features, even if the internal structure is not to
be studied. Beneficial insects, such as ladybugs, ichneumon flies, bees,
mantis (devil’s horse), dragon flies, etc., should be set free
uninjured.
ANATOMY AND GENERAL CHARACTERISTICS OF THE CLASS INSECTA
The =body= of an insect is divided by means of two marked narrowings
into three parts: the head, the chest, and the abdomen.
[Illustration:
FIG. 122.—YELLOW FEVER MOSQUITO, showing head, thorax, abdomen.
]
The =head= is a freely movable capsule bearing four pairs of appendages.
Hence it is regarded as having been formed by the union of four rings,
since the _ancestor of the insects_ is believed to have consisted of
similar rings, each ring bearing a pair of unspecialized legs.
The typical =mouth parts= of an insect (Fig. 123) named in order from
above, are (1) an upper lip (labrum, _ol_), (2) a pair of biting jaws
(mandibles, _ok_), (3) a pair of grasping jaws (maxillæ, _A_, _B_), and
(4) a lower lip (labium, _m_, _a_, _b_). The grasping jaws bear two
pairs of jointed jaw fingers (maxillary palpi, _D_, _C_), and the lower
lip bears a pair of similar lip fingers (labial palpi, _d_). The biting
jaws move sideways; they usually have several pointed notches which
serve as teeth. Why should the grasping jaws be beneath the chewing
jaws? Why is it better for the lower lip to have fingers than the upper
lip? Why are the fingers (or palpi) jointed? (Watch a grasshopper or
beetle eating.) Why does an insect need grasping jaws?
[Illustration:
FIG. 123.—MOUTH PARTS OF BEETLE.
]
[Illustration:
FIG. 124.—EXTERNAL PARTS OF A BEETLE.
]
The chest, or =thorax=, consists of three rings (Fig. 124) called the
front thorax (prothorax), middle thorax (mesothorax) and hind thorax
(metathorax), or first, second, and third rings. The first ring bears
the first pair of legs, the second ring bears the second pair of legs
and the upper or front wings, and the third ring bears the third pair of
legs and the under or hind wings.
[Illustration:
FIG. 125.—LEG OF INSECT.
]
The =six feet= of insects are characteristic of them, since no other
adult animals have that number, the spider having eight, the crayfish
and crabs having ten, the centipedes still more, while birds and beasts
have less than six. Hence the insects are sometimes called the
Six-Footed class (_Hexapoda_). The insects are the only animals that
have the =body= in =three divisions=. Man, beasts, and birds have only
two divisions (head and trunk). Worms are not divided.
=Define= the class _insecta_ by the two facts characteristic of them
(_i.e._ possessed by them alone), viz.: Insects are animals with ————
and ————. Why would it be ambiguous to include “hard outer skeleton” in
this definition? To include “bilateral symmetry”? “Segmented body”? The
definition of a class must _include_ all the individuals of the class,
and _exclude_ all the animals that do not belong to the class.
[Illustration:
FIG. 126.—FOOT OF FLY, with climbing pads.
]
The leg of an insect (Fig. 125) has five joints (two short joints, two
long, and the foot). Named in order from above, they are (1) the hip
(coxa), (2) thigh ring (trochanter), (3) thigh (femur), (4) the shin
(tibia), (5) the foot, which has five parts. Which of the five joints
of a wasp’s leg (Fig. 161) is thickest? Slenderest? Shortest? One
joint (which?) of the foot (Fig. 161) is about as long as the other
four joints of the foot combined. Is the relative length of the joints
of the leg the same in grasshoppers, beetles, etc., as in the wasp
(Figs.)? Figure 125 is a diagram of an insect’s leg cut lengthwise.
The leg consists of thick-walled tubes (_o_, _n_) with their ends held
together by thin, easy-wrinkling membranes which serve as joints. Thus
motion is provided for at the expense of strength. When handling live
insects they should never be held by the legs, as the legs come off
very easily. Does the joint motion of insects most resemble the motion
of hinge joints or ball-and-socket joints? Answer by tests of living
insects. There are no muscles in the foot of an insect. The claw is
moved by a muscle (_m_) in the thigh with which it is connected by the
long tendon (_z_, _s_, _t_, _v_). In which part are the breathing
muscles? As the wings are developed from folds of the dorsal skin, the
wing has two layers, an upper and a lower layer. These inclose the
so-called “nerves” or ribs of the wing, each of which consists of a
blood tube inclosed in an air tube.
The =abdomen= in various species consists of from five to eleven
overlapping rings with their fold-like joints between them. Does each
ring overlap the ring in front or the one behind it?
[Illustration:
FIG. 127.—VISCERA OF GRASSHOPPER. Key in text. Compare with Fig. 114.
]
[Illustration:
FIG. 128.—AIR TUBES OF INSECT.
]
The =food tube= (Fig. 127) begins at the mouth, which usually bears
salivary glands (4, Fig. 127, which represents internal organs of the
grasshopper). The food tube expands first into a _croplike_ enlargement;
next to this is an organ (6, Fig. 127), which resembles the gizzard in
birds, as its inner wall is furnished with chitinous teeth (_b_, Fig.
114). These reduce the food fragments that were imperfectly broken up by
the biting jaws before swallowing. _Glands_ comparable to the liver of
higher animals open into the food tube where the stomach joins the small
intestine. At the junction of the small and the large intestine (9) are
a number of _fine tubes_ (8) which correspond to _kidneys_ and empty
their secretion into the large intestine.
The =breathing organs= of the insects are peculiar to them (see Fig.
128). They consist of tubes which are kept open by having in their walls
continuous spirals of horny material called _chitin_. Most noticeable
are the two large membranous tubes filled with air and situated on each
side of the body. Do these tubes extend through the thorax? (Fig. 128.)
The air reaches these two main tubes by a number of pairs of short
windpipes, or _tracheas_, which begin at openings (_spiracles_). In
which division are the spiracles most numerous? (Fig. 128.) Which
division is without spiracles? Could an insect be drowned, _i.e._
smothered, by holding its body under water? Could it be drowned by
immersing all of it but its head? The motion of the air through the
breathing tubes is caused by a bellowslike _motion of the abdomen_. This
is readily observed in grasshoppers, beetles, and wasps. As each ring
slips into the ring in front of it, the abdomen is shortened, and the
impure air, laden with carbon dioxide, is forced out. As the rings slip
out, the abdomen is extended and the fresh air comes in, bringing
oxygen.
[Illustration:
FIG. 129.—INSECT’S HEART (plan).
]
[Illustration:
FIG. 130.—DIAGRAMS OF EVOLUTION OF PERICARDIAL SAC around insect’s
heart from a number of veins (Lankester).
]
[Illustration:
FIG. 131.—POSITION OF INSECT’S HEART, food tube, and nerve chain.
]
=The Circulation.=—Near the dorsal surface of the abdomen (Fig. 131)
extends the long, slender _heart_ (Fig. 129). The heart has divisions
separated by valvelike partitions. The blood comes into each of the
heart compartments through a pair of openings. The heart contracts from
the rear toward the front, driving the blood forward. The blood contains
bodies corresponding to the _white corpuscles_ of human blood, but lacks
the red corpuscles and the red colour. The blood is sent even to the
wings. The veins in the wings consist of horny tubes inclosing air tubes
surrounded by blood spaces, and the purification of the blood takes
place throughout the course of the circulation. Hence the imperfect
circulation is no disadvantage. The perfect provision for supplying
oxygen explains the remarkable activity of which insects are capable and
their great strength, which, considering their size, is unequalled by
any other animals.
[Illustration:
FIG. 132.—NERVOUS SYSTEM OF BEE.
]
[Illustration:
FIG. 133.—FEELER of a beetle.
]
=The Nervous System.=—The heart in backboned animals, _e.g._ man, is
ventral and the chief nerve trunk is dorsal. As already stated, the
heart of an insect is dorsal; its chief nerve chain, consisting of a
_double row of ganglia_, is near the ventral surface (Fig. 131). All the
ganglia are below the food tube except the first pair in the head, which
are above the gullet. This pair may be said to correspond somewhat to
the brain of backboned animals; the nerves from the eyes and the feelers
lead to it. With social insects, as bees and ants, it is large and
complex (Fig. 132). In a typical insect they are the largest ganglia.
=The Senses.=—The sense of _smell_ of most insects is believed to be
located in the feelers. The organ of _hearing_ is variously located in
different insects. Where is it in the grasshopper? The organs of _sight_
are highly developed, and consist of two compound eyes on the side of
the head and three simple eyes on the top or front of the head between
the compound eyes. The simple eye has nerve cells, pigments, and a lens
resembling the lens in the eyes of vertebrates (Fig. 134). The compound
eye (Fig. 135) has thousands of facets, usually hexagonal, on its
surface, the facets being the outer ends of cones which have their inner
ends directed toward the centre of the eye. It is probable that the
large, or compound, eyes of insects only serve to distinguish bright
objects from dark objects. The simple eyes afford distinct images of
objects within a few inches of the eye. In general, the sight of
insects, contrary to what its complex sight organs would lead us to
expect, is not at all keen. Yet an insect can fly through a forest
without striking a twig or branch. Is it better for the eyes that are
immovable in the head to be large or small? Which has comparatively
larger eyes, an insect or a beast?
[Illustration:
FIG. 134.—Diagram of simple eye of insect.
_L_, lens; _N_, optic nerve.
]
[Illustration:
FIG. 135.—COMPOUND EYE OF INSECT.
1, hexagonal facets of crystalline cones. 6, blood vessel in optic
nerve.
]
=Inherited Habit, or Instinct.=—Insects and other animals inherit from
their parents their particular form of body and of organs which perform
the different functions. For example, they inherit a nervous system with
a structure similar to that of their parents, and hence with a tendency
to repeat similar impulses and acts. Repeated acts constitute a habit,
and _an inherited habit is called an instinct_. Moths, for example, are
used to finding nectar in the night-blooming flowers, most of which are
white. The habit of going to white flowers is transmitted in the
structure of the nervous system; so we say that moths have an instinct
to go to white objects; it is sometimes more obscurely expressed by
saying they are attracted or drawn thereby.
=Instincts are not Infallible.=—They are trustworthy in only one narrow
set of conditions. Now that man makes many fires and lights at night,
the instinct just mentioned often causes the death of the moth. The
instinct to provide for offspring is necessary to the perpetuation of
all but the simplest animals. The dirt dauber, or mud wasp, because of
inherited habit, or instinct, makes the cell of the right size, lays the
egg, and provides food for offspring that the mother will never see. It
seals stung and semiparalyzed spiders in the cell with the egg. If you
try the experiment of removing the food before the cell is closed, the
insect will bring more spiders; if they are removed again, a third
supply will be brought; but if taken out the third time, the mud wasp
will usually close the cell without food, and when the egg hatches the
grub will starve.
=The Development of Insects.=—The growth and the moulting of the
grasshopper from egg to adult has been studied. All insects do not
develop exactly by this plan. Some hatch from the egg in a condition
markedly different from the adult. The butterfly’s egg produces a
wormlike caterpillar which has no resemblance to the butterfly. After it
grows it forms an inclosing case in which it spends a quiet period of
development and comes out a butterfly. This change from caterpillar to
butterfly is called the _metamorphosis_. The life of an insect is
divided into four stages: (1) _egg_, (2) _larva_, (3) _pupa_, and (4)
_imago_, or perfect insect (Figs. 136, 137, 138).
[Illustration:
FIG. 136.—Measuring worm, the larva of a moth.
]
[Illustration:
FIG. 137.—Pupa of a mosquito.
]
The egg stage is one of development, no nourishment being absorbed. The
larval stage is one of voracious feeding and rapid growth. In the pupa
stage no food is taken and there is no growth in size, but rapid
development takes place. In the perfect stage food is eaten, but no
growth in size takes place. In this stage the eggs are produced. When
there is very little resemblance between the larva and the imago, and no
pupal stage, the metamorphosis, or change, is said to be _complete_.
When, as with the grasshopper, no very marked change takes place between
the larva and the imago, there being no pupal stage, the metamorphosis
is said to be incomplete. By studying the illustrations and specimens,
and by thinking of your past observations of insects, determine which of
the insects in the following list have a complete metamorphosis: beetle,
house fly, grasshopper, butterfly, cricket, wasp.
[Illustration:
FIG. 138.—THE FOUR STAGES OF A BOTFLY, all enlarged.
_a_, egg on hair of horse (bitten off and swallowed); _b_, larva; _c_,
larva with hooks for holding to lining of stomach; _d_, pupal stage,
passed in the earth; _e_, adult horse fly.
]
RECOGNITION-CHARACTERS FOR THE PRINCIPAL ORDERS OF ADULT WINGED INSECTS
(All are wingless when young, and wingless adult forms occur in all the
orders: order APTERA lacks wing-bearing thoracic structures.)
A single pair of wings is characteristic of the order DIPTERA.
A jointed beak, that is sheath-like, inclosing the other mouth parts, is
characteristic of the order HEMIPTERA.
A coiled sucking proboscis and a wing covering of dust-like microscopic
scales are characteristic of the order LEPIDOPTERA.
Horny sheath-like fore wings, covering the hind wings and meeting in a
straight line down the middle of the back, will distinguish the order
COLEOPTERA.
Hind wings folded like a fan beneath the thickened and overlapping fore
wings, will distinguish most members of the order ORTHOPTERA.
The possession of a sting (in females) and of two pairs of thin
membranous wings—the small hind wing hooked to the rear margin of the
fore wing—will distinguish the common HYMENOPTERA.
Besides these, there remain a number of groups most of which have in the
past been included under the order NEUROPTERA, among which the Mayflies
will be readily recognized by the lack of mouth parts and by the
possession of two or three long tails; the dragon flies by the two pairs
of large wings, enormous eyes, and minute bristle-like antennæ; the
scorpion flies, by the possession of a rigid beak, with the mouth parts
at its tip; the caddis flies, by their hairy wings and lack of jaws; the
lace wings, by the exquisite regularity of the series of cross veins
about the margin of their wings, etc.
[Illustration:
FIG. 139.—MAY FLY. What order (see table)?
]
[Illustration:
FIG. 140.—SILVER SCALE. (Order?)
]
=Exercise in the Use of the Table or Key.=—Write the name of the order
after each of the following names of insects:—
Wasp (Fig. 122)
Weevil (Fig. 163)
Squash bug (Fig. 184)
Ant lion (Fig. 170)
Dragon fly (Fig. 177)
Ichneumon fly (Fig. 159)
House fly (Fig. 172)
Flea (Fig. 173)
Silver scale or earwig (Fig. 140)
Codling moth (Fig. 141)
Botfly (Fig. 138)
=Moths and Butterflies.=—Order ____? Why ____ (p. 82)?
The presence of scales on the wings is a never-failing test of a moth or
a butterfly. The wings do not fold at all. They are so large and the
legs so weak and delicate that the butterfly keeps its balance with
difficulty when walking in the wind.
The maxillæ are developed to form the long sucking proboscis. How do
they fit together to form a tube? (See Fig. 147.) The proboscis varies
from a fraction of an inch in the “miller” to five inches in some
tropical moths, which use it to extract nectar from long tubular
flowers. When not in use, it is held coiled like a watch spring under
the head (Fig. 148). The upper lip (labrum), under lip (labium), and lip
fingers (labial palpi) are very small, and the mandibles small or
wanting (Fig. 146).
The metamorphosis is complete, the contrast between the caterpillar or
larva of the moth and the butterfly and the adult form being very great.
The caterpillar has the three pairs of jointed legs typical of insects;
these are found near the head (Fig. 141). It has also from three to five
pairs of fleshy unjointed prolegs, one pair of which is always on the
last segment. How many pairs of prolegs has the silkworm caterpillar?
(Fig. 143.) The measuring worm, or looper? (Fig. 136.) The pupa has a
thin shell. Can you see external signs of the antennæ, wings, and legs
in this stage? (Fig. 143.) The pupa is concealed by protective
coloration and is sometimes inclosed in a silken cocoon which was spun
by the caterpillar before the last moult. Hairy caterpillars are
uncomfortable for birds to eat. The naked and brightly marked ones
(examples of warning coloration) often contain an acrid and distasteful
fluid. The injuries from lepidoptera are done in the caterpillar stage.
The codling moth (Fig. 141) destroys apples to the estimated value of
$6,000,000 annually. The clothes moth (Fig. 171) is a household pest.
The tent caterpillar denudes trees of their leaves. The only useful
caterpillar is the silkworm (Fig. 143). In Italy and Japan many of the
country dwellings have silk rooms where thousands of these caterpillars
are fed and tended by women and children. Why is the cabbage butterfly
so called? Why can it not eat cabbage? Why does sealing clothes in a
paper bag prevent the ravages of the clothes moth?
=Flight of Lepidoptera.=—Which appears to use more exertion to keep
afloat, a bird or a butterfly? Explain why. Of all flying insects which
would more probably be found highest up mountains? How does the
butterfly suddenly change direction of flight? Does it usually fly in a
straight or a zigzag course? Advantage of this? Bright colours are
protective, as lepidoptera are in greatest danger when at rest on
flowers. Are the brightest colours on upper or under side of wings of
butterfly? Why? (Think of the colours in a flower.) Why is it better for
moths to hold their wings flat out when at rest? Where are moths during
the day? How can you test whether the colour of the wings is given by
the scales?
State =how moths and butterflies differ= in respect to: body, wings,
feelers, habits.
=Insects and Flowers.=—Perhaps we are indebted to insects for the bright
colours and sweet honey of flowers. Flowers need insects to carry their
pollen to other flowers, as cross-fertilization produces the best seeds.
The insects need the nectar of the flowers for food, and the bright
colours and sweet odours are the advertisements of the flowers to
attract insects. Flowers of brightest hues are the ones that receive the
visits of insects. Moths, butterflies, and bees carry most pollen (see
Beginners’ Botany, Chap. VI).
=Comparative Study.=—Make a table like this, occupying entire page of
notebook, leaving no margins, and fill in accurately:—
═════════════════╤═══════════╤═════════╤═══════╤═══════╤═══════╤═══════
│GRASSHOPPER│BUTTERFLY│FLY pp.│DRAGON │BEETLE │BEE pp.
│ │ │92, 93 │FLY p. │pp. 90,│88, 89
│ │ │ │ 93 │ 91 │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Number and kind │ │ │ │ │ │
of wings │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Description of │ │ │ │ │ │
legs │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Antennæ (length, │ │ │ │ │ │
shape, joints) │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Biting or sucking│ │ │ │ │ │
mouth parts │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Complete or │ │ │ │ │ │
incomplete │ │ │ │ │ │
metamorphosis. │ │ │ │ │ │
═════════════════╧═══════════╧═════════╧═══════╧═══════╧═══════╧═══════
[Illustration:
FIG. 141.—CODLING MOTH, from egg to adult. (See Farmers’ Bulletin, p.
95.)
]
[Illustration:
FIG. 142.—CABBAGE BUTTERFLY, male and female, larva and pupa.
]
[Illustration:
FIG. 143.—LIFE HISTORY OF SILKWORM.
]
[Illustration:
FIG. 144.—SCALES FROM BUTTERFLIES’ WINGS, as seen under microscope.
]
[Illustration:
FIG. 145.—SCALES ON MOTH’S WING.
]
TO THE TEACHER: _These illustrated studies require slower and more
careful study than the text. One, or at most two, studies will suffice
for a lesson. The questions can be answered by studying the figures._
FIGS. 141–148. =Illustrated Study of Lepidoptera.=—Study the stages in
the development of _codling moth_, _silkworm moth_, and _cabbage
butterfly_.
Where does each lay its eggs? What does the larva of each feed upon?
Describe the pupa of each. Describe the adult forms. Find the
_spiracles_ and _prolegs_ on the silkworm. Compare _antennæ_ of moth
and butterfly. Which has larger body compared to size of wings?
[Illustration:
FIG. 146.—HEAD OF BUTTERFLY.
]
Describe the _scales_ from a butterfly’s wings as seen under
microscope (144). How are the scales arranged on moth’s wing (145)? By
what part is scale attached to wing? Do the scales overlap?
Study butterfly’s head and _proboscis_ (Figs. 146–148). What shape is
compound eye? Are the antennæ jointed? Is the proboscis jointed? Why
not call it a tongue? (See text.)
Which mouth parts have almost disappeared? What is the shape of cut
ends of halves of proboscis? How are the halves joined to form a tube?
If you saw a butterfly on a flower, for what purpose would you think
it was there? What, if you saw it on a leaf? How many spots on fore
wing of female cabbage butterfly? (Fig. 124, above.)
Does the silkworm chrysalis fill its cocoon?
[Illustration:
FIG. 148.—HEAD OF BUTTERFLY (side view).
]
[Illustration:
FIG. 147.—SECTION OF PROBOSCIS of butterfly showing lapping joint and
dovetail joint.
]
[Illustration:
FIG. 149.
]
[Illustration:
FIG. 150.
]
[Illustration:
FIG. 151.
]
[Illustration:
FIG. 152.
]
[Illustration:
FIG. 153.
]
[Illustration:
FIG. 154.
]
[Illustration:
FIG. 155.
]
[Illustration:
FIG. 156.
]
[Illustration:
FIG. 157.
]
[Illustration:
FIG. 158.—Anatomy of bee.
]
FIGS. 149–161. =Illustrated Study of Bees and their Kindred.=—Head of
worker (Fig. 149): _o_, upper lip; _ok_, chewing jaws; _uk_, grasping
jaws; _kt_, jaw finger; _lt_, lip finger; _z_, tongue.
How do heads of drone (150) and queen (151) differ as to mouth, size
of the two compound eyes, size and position of the three simple eyes?
Is the head of a worker more like head of drone or head of queen?
Judging by the head, which is the queen, drone, and worker in Figs.
154–156? Which of the three is largest? Smallest? Broadest?
Figure 152 shows hind leg of worker. What surrounds the hollow, _us_,
which serves as pollen basket? The point, _fh_, is a tool for removing
wax which is secreted (_c_, Fig. 157) between rings on abdomen. In
Fig. 158, find relative positions of heart, _v_, food tube, and nerve
chain. Is crop, _J_, in thorax or abdomen? In this nectar is changed
to honey, that it may not spoil. Compare nerve chain in Fig. 132.
[Illustration:
FIG. 159.—Ichneumon fly.
]
Compare the cells of _bumble bee_ (Fig. 153) with those of hive bee.
They differ not only in shape but in material, being made of web
instead of wax, and they usually contain larvæ instead of honey. Only
a few of the queens among bumble bees and wasps survive the winter.
How do ants and honey bees provide for the workers also to survive the
winter? Name all the social insects that you can think of. Do they all
belong to the same order?
[Illustration:
FIG. 160.
]
The ichneumon fly shown enlarged in Fig. 159 lays its eggs under a
caterpillar’s skin. What becomes of the eggs? The true size of the
insect is shown by the cross lines at _a_. The eggs are almost
microscopic in size. The pupæ shown (true size) on caterpillar are
sometimes mistaken for eggs. The same mistake is made about the pupa
cases of ants. Ichneumon flies also use tree-borers as “hosts” for
their eggs and larva. Is this insect a friend of man?
[Illustration:
FIG. 161.—Wasp using pebble.
From Peckham’s “Solitary Wasps,” Houghton, Mifflin & Co.
]
The _digging wasp_ (Figs. 160 and 161) supplies its larva with
caterpillars and closes the hole, sometimes using a stone as pounding
tool. Among the few other uses of tools among lower animals are the
elephant’s use of a branch for a fly brush, and the ape’s use of a
walking stick. This wasp digs with fore feet like a dog and kicks the
dirt out of the way with its hind feet.
Are the wings of bees and wasps more closely or less closely veined
than the wings of dragon flies? (Fig. 177.)
=Illustrated Study of Beetles.=
[Illustration:
FIG. 162.—Diving beetle (_Dytiscus_), with larva, _a_.
]
[Illustration:
FIG. 163.—Weevil.
]
[Illustration:
FIG. 164.
]
[Illustration:
FIG. 165.
]
[Illustration:
FIG. 166.—Click beetle.
]
[Illustration:
FIG. 167.—MAY BEETLE.
]
[Illustration:
FIG. 168.
]
[Illustration:
FIG. 169.—Colorado beetle (potato bug).
]
=Illustrated Study of Beetles= (Figs. 162–169).—Write the life history
of the _Colorado beetle_, or potato bug (Fig. 169), stating where the
eggs are laid and describing the form and activities of each stage
(the pupal stage, _b_, is passed in the ground).
Do the same for the _May beetle_ (Figs. 167–168). (It is a larva—the
white grub—for three years; hogs root them up.) Beetles, like moths,
may be trapped with a lantern set above a tub of water.
Where does a _Scarab_ (or sacred beetle of the Egyptians), also called
tumble bug (Fig. 164), lay its eggs (Fig. 165)? Why?
How does the _click beetle_, or jack snapper (Fig. 166), throw itself
into the air? For what purpose?
The large proboscis of the _weevil_ (Fig. 163) is used for piercing a
hole in which an egg is laid in grain of corn, boll of cotton, acorn,
chestnut, plum, etc.
How are the legs and body of the _diving beetle_ suited for swimming
(Fig. 162)? Describe its larva.
What is the shape of the lady bug (Fig. 97)? It feeds upon plant lice
(Fig. 185). Is any beetle of benefit to man?
[Illustration:
FIG. 170.—Life history of ant lion.
]
=Illustrated Study of Ant Lion, or Doodle Bug= (Fig. 170).—Find the
pitfall (what shape?); the larva (describe it); the pupa case (ball
covered with web and sand); the imago. Compare imago with dragon fly
(Fig. 177).
How does ant lion prevent ant from climbing out of pitfall (see Fig.
170)? What is on edge of nearest pitfall? Explain.
Ant lions may be kept in a box half filled with sand and fed on ants.
How is the pitfall dug? What part of ant is eaten? How is unused food
removed?
How long is it in the larval state? Pupal state? Keep net over box to
prevent adult from flying away when it emerges.
[Illustration:
FIG. 171.
]
[Illustration:
FIG. 172.—Metamorphosis of house fly (enlarged).
]
[Illustration:
FIG. 173.—Metamorphosis of flea.
]
[Illustration:
FIG. 174.—Louse and its eggs attached to a hair. Natural size and
magnified.
]
[Illustration:
FIG. 175.—Bed bug. × 5.
]
[Illustration:
FIG. 176.—Life history of mosquito.
]
=Illustrated Study of Insect Pests= (Figs. 171–176).—Why does the
_clothes moth_ (171) lay its eggs upon woollen clothing? How does the
larva conceal itself? The larva can cut through paper and cotton, yet
sealing clothes in bags of paper or cotton protects them. Explain.
The _house fly_ eats liquid sweets. It lays its eggs in horse dung.
Describe its larval and pupal forms. Banishing horses from city would
have what beneficial effect?
Describe the _louse_ and its eggs, which are shown attached to a hair,
natural size and enlarged.
Describe the _bed bug_. Benzine poured in cracks kills bed bugs. Do
bed bugs bite or suck? Why are they wingless?
Describe the larva, _f_, pupa, _g_, and the adult _flea_, all shown
enlarged. Its mandibles, _b_, _b_, are used for piercing. To kill
fleas lather dog or cat completely and let lather remain on five
minutes before washing. Eggs are laid and first stages passed in the
ground.
How does the _mosquito_ lay its eggs in the water without drowning
(176)? Why are the eggs always laid in still water? Which part of the
larva (wiggletail) is held to the surface in breathing? What part of
the pupa (called tumbler, or bull head) is held to the surface in
breathing? Give differences in larva and pupa. Where does pupa change
to perfect insect? Describe mouth parts of male mosquito (at left) and
female (at right). Only female mosquitoes suck blood. Males suck juice
of plants. Malarial mosquito alights with hind end of body raised at
an angle. Why does killing fish and frogs increase mosquitoes? 1 oz.
of kerosene for 15 ft. of surface of water, renewed monthly, prevents
mosquitoes.
What is the use to the squash bug (Fig. 184) of having so bad an
odour?
[Illustration:
FIG. 177. =Illustrated Study of Dragon Fly.=—3 shows dragon fly laying
its eggs in water while poised on wing. Describe the larval form
(water tiger). The extensible tongs are the maxillæ enlarged. The
pupa (1) is active and lives in water. Where does transformation to
adult take place (5)? Why are eyes of adult large? its legs small?
Compare front and hind wings.
Do the eyes touch each other? Why is a long abdomen useful in flight?
Why would long feelers be useless? What is the time of greatest
danger in the development of the dragon fly? What other appropriate
name has this insect? Why should we never kill a dragon fly?
]
[Illustration:
FIG. 178.—The tarantula.
]
[Illustration:
FIG. 179.—Trap-door spider.
]
[Illustration:
FIG. 180.
]
[Illustration:
FIG. 181.—Anatomy of spider.
]
[Illustration:
FIG. 182.—Laying egg.
]
[Illustration:
FIG. 183.—Foot of spider.
]
=Illustrated Study of Spiders= (Figs. 178–183).—The tarantula, like
most spiders, has eight simple eyes (none compound). Find them (Fig.
178). How do spiders and insects differ in body? Number of legs? Which
have more joints to legs? Does trap-door spider hold the door closed
(Fig. 179)? How many pairs of spinnerets for spinning web has a spider
(_Spw_, 180)? Foot of spider has how many claws? How many combs on
claws for holding web? Spiders spin a cocoon for holding eggs. From
what part of abdomen are eggs laid (_E_, 182; 2, 181)? Find spider’s
air sacs, _lu_, Fig. 181; spinning organs, _sp_; fang, _kf_; poison
gland, _g_; palpi, _kt_; eyes, _au_; nerve ganglia, _og_, _ug_;
sucking tube, _sr_; stomach, _d_; intestine, _ma_; liver, _le_; heart,
_h_, (black); vent, _a_. Give two reasons why a spider is not an
insect. How does it place its feet at each step (Fig. 110)? Does the
size of its nerve ganglia indicate great or little intelligence? Why
do you think first part of body corresponds to both head and thorax of
insects?
The following Farmer’s Bulletins, (revised to 1921) are available for
distribution to those interested, by the United States Department of
Agriculture, Washington, D.C.—
Farmer’s Bulletin No. 47, Insects Affecting the Cotton Plant; No. 447,
Bee Keeping; No. 440, The Peach Twig Borer; No. 120, The Principal
Insects Affecting the Tobacco Plant; No. 856, Important Insecticides;
No. 835, The Principal Insect Enemies of Growing Wheat; No. 799, Carbon
Bisulphide as an Insecticide; No. 243, Insecticides and Fungicides; No.
152 (revised) Mange in Cattle; No. 155, How Insects Affect Health in
Rural Districts; No. 492, The Control of the Codling Moth; No. 172,
Scale Insects and Mites on Citrus Trees; No. 196, Usefulness of the
Toad; No. 209, Controlling the Boll Weevil in Cotton Seed and at
Ginneries; No. 211, The Use of Paris Green in Controlling the Cotton
Boll Weevil; No. 872, The Cotton Bollworm; No. 848, The Control of the
Boll Weevil; No. 223, Miscellaneous Cotton Insects in Texas; No. 908,
The Control of the Codling Moth and Apple Scab.
Bulletins of the Bureau of Entomology may be obtained from the same
source, while the supply lasts, as follows:
Destructive Locusts; The Honey Bee; The San José Scale; The Principal
Household Insects of the United States; The Gypsy Moth in America; The
Periodical Cicada; The Chinch Bug; The Hessian Fly; Insects Injurious to
Vegetables; Notes on Mosquitoes; Some Insects Attacking the Stems of
Growing Wheat, Rye, Barley, and Oats.
Bulletins on Similar Topics, Published by the Department of Agriculture,
Ontario—
(Write to the Publications Branch)
Bulletin No. 187—The Codling Moth
Bulletin No. 195—The Insecticides and Fungicides
Bulletin No. 198—Lime Sulphur Wash
Bulletin No. 219—The San José and Oyster-shell Scales
Bulletin No. 241—Peach Growing in Ontario
Bulletin No. 250—Insects Attacking Fruit Trees
Bulletin No. 251—Insects Affecting Vegetables
Bulletin No. 256—The Wintering of Bees
Bulletin No. 257—The More Important Fruit Tree Diseases in Ontario
Bulletin No. 258—The More Important Fungus and Bacterial Diseases of
Vegetables in Ontario
Bulletin No. 271—The Apple Maggot
Bulletin No. 276—Bee Diseases in Ontario
Bulletins Published by the Department of Agriculture, Ottawa—
(Write to the Publications Branch)
Bulletin No. 9—The Army Worm
Bulletin No. 10—Cutworms and their Control
Bulletin No. 26—Bees and How to Keep Them
Circular No. 9—1921—Common Garden Insects and their Control
[Illustration:
Pearl divers.
]
CHAPTER IX
_MOLLUSCS_
THE FRESH-WATER MUSSEL
SUGGESTIONS.—The mussel is usually easy to procure from streams and
lakes by raking or dredging. In cities the hard-shelled clam, or
quahog, is for sale at the markets, and the following descriptions
apply to the anodon, unio, or quahog, with slight changes in regard to
the siphons. Mussels can be kept alive for a long time in a tub with
sand in the bottom. Pairs of shells should be at hand for study.
=External Features.=—The shell is an elongated oval, broader and blunter
at one end (Fig. 188). Why does the animal close its shell? Does it open
the shell? Why? Does it thrust the foot forward and pull up to it, or
thrust the foot back and push? (Mussels and clams have no bones.) Does
it go with the blunt end or the more tapering end of the shell forward?
(Fig. 188.) Can a mussel swim? Why, or why not?
[Illustration:
FIG. 188.—ANODON, or fresh-water mussel.
]
Lay the shells, fitted together, in your hand with _the hinge side away
from you and the blunt end to the left_ (Fig. 188). Is the right or the
left shell uppermost? Which is the top, or dorsal, side? Which is the
front, or anterior, end? Is the straight edge at the top or at the
bottom? Our word “valve” is derived from a word meaning shell, because
the Romans used shells for valves in pumps. Is the mussel a univalve or
a bivalve? Which kind is the oyster? The snail?
Does the mussel have _bilateral symmetry_? Can you find a _horny
covering_, or epidermis, over the limy shell of a fresh specimen? Why is
it necessary? Does water dissolve lime? Horn? Find a bare spot. Does any
of the shell appear to be missing there?
[Illustration:
FIG. 189.—DIAGRAM OF SHELL open and closed, showing muscle, _m_, and
ligament, _b_.
]
The bare projection on each shell is called the _umbo_. Is the umbo near
the ventral or the dorsal line? The posterior or anterior end? Is the
surface of the umbones worn? Do the umbones rub against the sand as the
mussel ploughs its way along? How are the shells held together? Where is
the _ligament_ attached? (Fig. 189.) Is it opposite the umbones or more
to the front or to the rear? (Fig. 189.) Is the ligament of the same
material as the shell? Is the ligament in a compressed condition when
the shell is open or when it is closed? (Fig. 189.) When is the muscle
relaxed?
[Illustration:
FIG. 190.—MUSSEL crawling in sand.
]
Notice the _lines_ on the outside of the shell (Figs. 188 and 190). What
point do they surround? They are _lines of growth_. Was each line once
the margin of the shell? If the shell should increase in size, what
would the present margin become? (Fig. 191.) Does growth take place on
the margin only? Did the shell grow thicker as it grew larger? Where is
it thinnest?
=Draw= the outside of the shell from the side. Draw a dorsal view. Near
the drawings write the names of the margins of the shell (p. 98) and of
other parts learned, using lines to indicate the location of the parts.
Study the surface of the shell inside and out. The inside is called
_mother-of-pearl_. Is it of lime? Is the deeper layer of the shell of
lime? (When weak hydrochloric acid or strong vinegar is dropped on limy
substances, a gas, carbon dioxide, bubbles up.) Compare the thickness of
the _epidermal layer_, the middle _chalky layer_, and the inner, _pearly
layer_.
[Illustration:
FIG. 191.—DIAGRAM.
Change of points of attachment of muscles as mussel enlarges.
(Morgan.)
]
=Anatomy of the Mussel.=—What parts protrude at any time beyond the edge
of the shell? (Fig. 190.) The shell is secreted by two folds of the
outer layer of the soft body of the mussel. These large, flaplike folds
hang down on each side, and are called the mantle. The two great flaps
of the _mantle_ hang down lower than the rest of the body and line the
shell which it secretes (Fig. 192). The epidermis of the mantle secretes
the shell just as the epidermis of the crayfish secretes its crust. Can
you find the pallial line, or the line to which the mantle extended on
each shell when the animal was alive? A free portion of the mantle
extended like a fringe below the pallial line.
[Illustration:
FIG. 192.—CROSS SECTION OF MUSSEL. (Diagram, after Parker.)
]
The shells were held together by two large _adductor muscles_. The
anterior adductor (Fig. 193) is near the front end, above the foot. The
posterior adductor is toward the rear end, but not so near the end as
the anterior. Can you find both _muscle scars_ in the shells? Are they
nearer the ventral or the dorsal surface? The points of attachment
travelled downward and farther apart as the animal grew (see Fig. 191).
Higher than the larger scars are small scars, or impressions, where the
protractor and retractor muscles that extend and draw in the foot were
attached.
[Illustration:
FIG. 193.—ANATOMY OF MUSSEL. (Beddard.)
]
The muscular _foot_ extends downward in the middle, halfway between the
shells (Fig. 193). On each side of the foot and behind it hang down the
two pairs of =gills=, the outer pair and the inner pair (Fig. 192). They
may be compared to four V-shaped troughs with their sides full of holes.
The water enters the troughs through the holes and overflows above. Is
there a marked difference in the size of the two pairs of gills? A kind
of chamber for the gills is made by the joining of the mantle flaps
below, along the ventral line. The mantle edges are separated at two
places, leaving openings called _exhalent_ and _inhalent siphons_.
[Illustration:
FIG. 194.—MUSSEL.
_A_, left shell and mantle flap removed.
_B_, section through body.
=Question=: Guided by other figures, identify the parts to which lines
are drawn.
]
Fresh water with its oxygen, propelled by _cilia_ at the opening and on
the gills, enters through the lower or inhalent siphon, passes between
the gills, and goes to an upper passage, leaving the gill chamber by a
slit which separates the gills from the foot. For this passage, see
arrow (Fig. 194). The movement of the water is opposite to the way the
arrow points. After going upward and backward, the water emerges by the
exhalent siphon. The gills originally consisted of a great number of
filaments. These are now united, but not completely so, and the gills
still have a perforated or lattice structure. Thus they present a large
surface for absorbing oxygen from the water.
The =mouth= is in front of the foot, between it and the anterior
adductor muscle (Fig. 194). On each side of the mouth are the _labial
palps_, which are lateral lips (Fig. 195). They have cilia which convey
the food to the mouth after the inhalent siphon has sent food beyond the
gill chamber and near to the mouth. Thus both food and oxygen enter at
the inhalent siphon. The foot is in the position of a lower lip, and if
regarded as a greatly extended lower lip, the animal may be said to have
what is to us the absurd habit of using its lower lip as a foot. The
foot is sometimes said to be hatchet-shaped (Fig. 195). Do you see any
resemblance? Does the foot penetrate deep or shallow into the sand?
(Fig. 190.) Why, or why not?
[Illustration:
FIG. 195.—MUSSEL. From below. Level cut across both shells.
_Se_, palp; _P_, foot; _O_, mouth; _G_, liver; _Gg_, _Vg_, _Pg_,
ganglia.
]
The =food tube= of the mussel is comparatively simple. Behind the
mouth it enlarges into a swelling called the _stomach_ (Fig. 193). The
bile ducts of the neighbouring liver empty into the stomach. The
_intestine_ makes several turns in the substance of the upper part of
the foot and then passing upward, it runs approximately straight to
the vent (or anus), which is in the wall of the exhalent siphon. The
intestine not only runs through the _pericardial cavity_ (celome)
surrounding the heart, but through the ventricle of the heart itself
(Fig. 196).
[Illustration:
FIG. 196.—HEART OF MUSSEL, with intestine passing through it.
]
The =kidneys= consist of tubes which open into the pericardial chamber
above and into the gill chamber below (_Neph._, Fig. 193). The tubes
are surrounded by numerous blood vessels (Fig. 198) and carry off the
waste matter from the blood.
[Illustration:
FIG. 197.
]
The =nervous system= consists of _three pairs of ganglia_ and nerves
(Fig. 197). The ganglia are distinguishable because of their orange
colour. The pedal ganglia on the front of the foot are easily seen
also; the visceral ganglia on the posterior adductor muscle may be
seen without removing the mussel from the shell (Fig. 193). The
reproductive organs open into the rear portion of the gill cavity
(Fig. 193). The sperms, having been set free in the water, are drawn
into the ova by the same current that brings the food. The eggs are
hatched in the gills. After a while the young mussels go out through
the siphon.
=Summary.=—In the gills (Fig. 198) the blood gains what? Loses what?
From the digestive tube the blood absorbs nourishment. In the kidneys
the blood is partly purified by the loss of nitrogenous waste.
[Illustration:
FIG. 198.—DIAGRAM OF MUSSEL CUT ACROSS, showing mantle, _ma_; gills,
_kie_; foot, _f_; heart, _h_; intestine, _ed_.
]
The cilia of the fringes on the inhalent, or lower, siphon, vibrate
continually and drive water and food particles into the mouth cavity.
Food particles that are brought near the labial palps are conveyed by
them to the mouth. As the water passes along the perforated gills, its
oxygen is absorbed; the mantle also absorbs oxygen from the water as it
passes. The water, as stated before, goes next through a passage between
the foot and the palp into the cavity above the gills and on out through
the exhalent siphon. By stirring the water, or placing a drop of ink
near the siphons of a mussel kept in a tub, the direction of its flow
may be seen. The pulsations of the heart are plainly visible in a living
mollusc.
=Habits of the Mussel.=—Is it abundant in clear or in muddy water;
swift, still, or slightly moving water? Describe its track or furrow.
What is its rate of travel? Can you distinguish the spots where the foot
was attached to the ground? How long is one “step” compared to the
length of the shell? The animal usually has the valves opened that it
may breathe and eat. The hinge ligament acts like the case spring of a
watch, and holds the valves open unless the adductor muscles draw them
together (Fig. 189).
[Illustration:
FIG. 199.—OYSTER.
_C_, mouth; _a_, vent; _g_, _g′_, ganglia; _mt_, mantle; _b_, gill.
]
When the mussel first hatches from the egg, it has a triangular shell.
It soon attaches itself to some fish and thus travels about. After two
months it drops to the bottom again.
[Illustration:
FIG. 200.—TROCHUS.
]
=Other Mollusca.=—The _oyster’s_ shells are not an exact pair, the shell
which lies upon the bottom being hollowed out to contain the body, and
the upper shell being flat. Can you tell by examining an oyster shell
which was the lower valve? Does it show signs of having been attached to
the bottom? The young oyster, like the young mussel, is free-swimming.
Like the arthropoda, most molluscs undergo a metamorphosis to reach the
adult stage (Fig. 199).
[Illustration:
FIG. 201.—CYPRÆA. (Univalve, with a long opening to shell.)
]
Examine the shells of clams, snails, scallops, and cockles. Make
drawings of their shells. The slug is very similar to the snail except
that it has no shell. If the shell of the snail shown in Fig. 202 were
removed, there would be left a very good representation of a slug.
=Economic Importance of Mollusca.=—Several species of clams are eaten.
One of them is the _hardshell clam_ (quahog) found on the Atlantic coast
from Cape Cod to Texas. Its shell is white. It often burrows slightly
beneath the surface. The _softshell clam_ is better liked as food. It
lives along the shores of all northern seas. It burrows a foot beneath
the surface and extends its siphons through the burrow to the surface
when the tide is in, and draws into its shell the water containing
animalcules and oxygen.
_Oysters_ to the value of many millions of dollars are gathered and sold
every year. The most valuable oyster fisheries of North America are in
Chesapeake Bay. The young oysters, or “spat,” after they attach
themselves to the bottom in shallow water, are transplanted. New oyster
beds are formed in this way. The beds are sometimes strewn with pieces
of rock, broken pottery, etc., to encourage the oysters to attach
themselves. The dark spot in the fleshy body of the oyster is the
digestive gland, or liver. The cut ends of the tough adductor muscles
are noticeable in raw oysters. The starfish is very destructive in
oyster beds.
[Illustration:
FIG. 202.—A SNAIL.
_l_, mouth; _vf_, _hf_, feelers; _e_, opening of egg duct; _f_, foot;
_ma_, mantle; _lu_, opening to lung; _a_, vent.
]
_Pearls_ are deposited by bivalves around some irritating particle that
gets between the shell and the mantle. The pearl oyster furnishes most
of the pearls; sometimes pearls of great value are obtained from
fresh-water mussels. Name articles that are made partly or wholly of
mother-of-pearl.
=Study of a Live Snail or Slug.=—Is its body dry or moist? Do land
snails and slugs have lungs or gills? Why? How many pairs of tentacles
have they? What is their relative length and position? The eyes are
dark spots at bases of tentacles of snail and at the tips of the rear
tentacles of slug. Touch the tentacles. What happens? Do the tentacles
simply stretch, or do they turn inside out as they are extended? Is
the respiratory opening on the right or the left side of the body? On
the mantle fold or on the body? (Figs. 202–3–4.) How often does the
aperture open and close?
[Illustration:
FIG. 203.—A SLUG.
]
Place the snail in a moist tumbler. Does the whole under surface seem
to be used in creeping? Does the creeping surface change shape as the
snail creeps? Do any folds or wrinkles seem to move either toward the
front or the rear of its body? Is enough mucus left to mark the path
travelled? The fold moves to the front, adheres, and smooths out as
the slug or snail is pulled forward.
[Illustration:
FIG. 204.—CIRCULATION AND RESPIRATION IN SNAIL.
_a_, mouth; _b_, _b_, foot; _c_, vent; _d_, _d_, lung; _h_, heart.
Blood vessels are black. (Perrier.)
]
=Cephalopods.=—The highest and best developed molluscs are the
=cephalopods=, or “head-footed” molluscs. Surrounding the mouth are
eight or ten appendages which serve both as feet and as arms. These
appendages have two rows of sucking disks by which the animal attaches
itself to the sea bottom, or seizes fish or other prey with a firm
grip. The commonest examples are the _squid_, with a long body and ten
arms, and the _octopus_, or devilfish, with a short body and eight
arms. Cephalopods have strong biting mouth parts and complex eyes
somewhat resembling the eyes of backboned, or vertebrate, animals. The
large and staring eyes add to the uncanny, terrifying appearance.
[Illustration:
FIG. 205.—A SQUID.
]
The sepia or “ink” discharged through the siphon of the squid makes a
dark cloud in the water and favours its escape from enemies almost as
much as does its swiftness (Fig. 205). The squid sometimes approaches
a fish with motion so slow as to be imperceptible, and then suddenly
seizes it, and quickly kills it by biting it on the back behind the
head.
[Illustration:
FIG. 206.—PEARLY NAUTILUS. (Shell sawed through to show chambers used
when it was smaller, and siphuncle, _S_, connecting them. Tentacles,
_T_.)
]
The octopus is more sluggish than the squid. Large species called
devilfish sometimes have a spread of arms of twenty-five feet. The
_pearly nautilus_ (Fig. 206) and the _female of the paper argonaut_
(Fig. 207) are examples of cephalopods that have shells. The
_cuttlefish_ is closely related to the squid.
[Illustration:
FIG. 207.—PAPER ARGONAUT (female). × ⅓ (_i.e._ the animal is three
times as long and broad as figure).
]
[Illustration:
FIG. 208.—PAPER ARGONAUT (male). × ½.
]
=General Questions.=—The living parts of the mussel are very soft, the
name mollusca being derived from the Latin word _mollis_, soft. Why is
it that the softest animals, the molluscs, have the hardest coverings?
To which class of molluscs is the name acephala (headless) appropriate?
Lamellibranchiata (platelike gills)?
Why is a smooth shell suited to a clam and a rough shell suited to an
oyster? Why are the turns of a snail’s shell so small near the centre?
Why does the mussel have no use for head, eyes, or projecting feelers?
In what position of the valves of a mussel is the hinge ligament in a
stretched condition? How does the shape of the mussel’s gills insure
that the water current and the blood current are brought in close
contact?
The three main classes of molluscs are: the pelecypoda (hatchet-footed);
gastropoda (stomach-footed); and cephalopoda (head-footed). Give an
example of each class.
Comparison of Mollusks
═════════════════╤═════════════════╤═════════════════╤═════════════════
│ MUSSEL │ SNAIL │ SQUID
─────────────────┼─────────────────┼─────────────────┼─────────────────
Shell │ │ │
─────────────────┼─────────────────┼─────────────────┼─────────────────
Head │ │ │
─────────────────┼─────────────────┼─────────────────┼─────────────────
Body │ │ │
─────────────────┼─────────────────┼─────────────────┼─────────────────
Foot │ │ │
─────────────────┼─────────────────┼─────────────────┼─────────────────
Gills │ │ │
─────────────────┼─────────────────┼─────────────────┼─────────────────
Eyes │ │ │
═════════════════╧═════════════════╧═════════════════╧═════════════════
=Comparative Review.=—(To occupy an entire page in notebook.)
════════════════════╤═══════════╤═════════╤═════════╤═════════╤════════
│GRASSHOPPER│ SPIDER │CRAYFISH │CENTIPEDE│ MUSSEL
────────────────────┼───────────┼─────────┼─────────┼─────────┼────────
Bilateral or radiate│ │ │ │ │
────────────────────┼───────────┼─────────┼─────────┼─────────┼────────
Appendages for │ │ │ │ │
locomotion │ │ │ │ │
────────────────────┼───────────┼─────────┼─────────┼─────────┼────────
Names of divisions │ │ │ │ │
of body │ │ │ │ │
────────────────────┼───────────┼─────────┼─────────┼─────────┼────────
Organs and method of│ │ │ │ │
breathing │ │ │ │ │
────────────────────┼───────────┼─────────┼─────────┼─────────┼────────
Locomotion │ │ │ │ │
════════════════════╧═══════════╧═════════╧═════════╧═════════╧════════
CHAPTER X
FISHES
[Illustration]
SUGGESTIONS.—The behaviour of a live fish in clear water, preferably
in a glass vessel or an aquarium, should be studied. A skeleton may be
prepared by placing a fish in the reach of ants. Skeletons of animals
placed on ant beds are cleaned very thoroughly. The study of the
perch, that follows, will apply to almost any other common fish.
=Movements and External Features.=—What is the _general shape of the
body_ of a fish? How does the dorsal, or upper, region differ in form
from the ventral? Is there a narrow part or neck where the head joins
the trunk? Where is the body thickest? What is the ratio between the
length and the height? (Fig. 209.) Are the right and the left sides
alike? Is the symmetry of the fish bilateral or radial?
The _body of the fish may be divided_ into three regions—the head, the
trunk, and the tail. The trunk begins with the foremost scales; the tail
is said to begin at the vent, or anus. Which regions bear appendages? Is
the head movable independently of the trunk, or do they move together?
State the advantage or the disadvantage in this. Is the body depressed
(flattened vertically) or compressed (flattened laterally)? Do both
forms occur among fishes? (See figures on pages 123, 124.)
How is the _shape of the body advantageous for movement_? Can a fish
turn more readily from side to side, or up and down? Why? Is the head
wedge-shaped or conical? Are the jaws flattened laterally or vertically?
The fish swims in the water, the bird swims in the air. Account for the
differences in the shape of their bodies.
[Illustration:
FIG. 209.—WHITE PERCH (_Morone Americana_).
]
Is the _covering of the body_ like the covering of any animal yet
studied? The scales are attached in little pockets, or folds, in the
skin. Observe the shape and size of scales on different parts of the
body. What parts of the fish are without scales? Examine a single scale;
what is its shape? Do you see concentric lines of growth on a scale?
Sketch a few of the scales to show their arrangement. What is the use of
scales? Why are no scales needed on the head? How much of each scale is
hidden? Is there a film over the scale? Are the colours in the scale or
on it?
=The Fins.=—Are the movements of the fish active or sluggish? Can it
remain stationary without using its fins? Can it move backward? How are
the fins set in motion? What is the colour of the flesh, or muscles, of
a fish? Count the fins. How many are in pairs? (Fig. 209.) How many are
vertical? How many are on the side? How many are on the middle line? Are
the paired or the unpaired fins more effective in balancing the fish? In
turning it from side to side? In raising and lowering the fish? In
propelling it forward? How are some of the fins useful to the fish
besides for balancing and swimming?
The hard _spines_ supporting the fins are called the fin rays. The fin
on the dorsal line of the fish is called the _dorsal_ fin. Are its rays
larger or smaller than the rays of the other fins? The perch is
sometimes said to have two dorsal fins, since it is divided into two
parts. The fin forming the tail is called the tail fin, or _caudal_ fin.
Are its upper and its lower corners alike in all fishes? (Fig. 228.) On
the ventral side, just behind the vent, is the ventral fin, also called
the anal fin. The three fins mentioned are unpaired fins. Of the
four-paired fins, the pair higher on the sides (and usually nearer the
front) are the _pectoral_ fins. The pair nearer the ventral line are the
_pelvic_ fins. They are close together, and in many fish are joined
across the ventral line. The ventral fins are compared to the legs, and
the pectoral fins to the arms, of higher vertebrates. (Fig. 244.)
Compare fins of fish, pages 123, 124.
Make a =drawing= of the fish seen from the side, omitting the scales
unless your drawing is very large.
Are the =eyes= on the top or on the sides of the head, or on both? Can a
fish shut its eyes? Why, or why not? Is the eyeball bare, or covered by
a membrane? Is the covering of the eyeball continuous with the skin of
the head? Is there a fold or wrinkle in this membrane or the surrounding
skin? Has the eye a pupil? An iris? Is the eye of the fish immovable,
slightly movable, or freely movable? Can it look with both eyes at the
same object? Is the _range of vision_ more upward or downward? To the
front or the side? In what direction is vision impossible? Can a fish
close its eyes in sleep? Does the eyeball appear spherical or flattened
in front? The ball is really spherical, the lens is very convex, and
fish are nearsighted. Far sight would be useless in a dense medium like
water. In what direction from the eyes are the =nostrils= (Fig. 211.)
There are two pair of nostrils, but there is only one pair of nasal
cavities, with two nostrils opening into each. There are no nasal
passages to the mouth, as the test with a probe shows that the cavities
do not open into the mouth. What two functions has the nose in man? What
function has it in the fish?
[Illustration:
FIG. 210.—BLACKBOARD OUTLINE OF FISH.
]
There are _no external_ =ears=. The ear sacs are embedded in the bones
of the skull. Is hearing acute or dull? When you are fishing, is it more
necessary not to talk or to step lightly, so as not to jar the boat or
bank?
[Illustration:
FIG. 211.—HEAD OF CARP.
]
What is the use of the large openings found at the back of the head on
each side? (Fig. 211.) Under the skin at the sides of the head are thin
membrane bones formed from the skin; they aid the skin in protection.
Just under these membrane bones are the gill covers, of true bone. Which
consists of more parts, the membranous layer, or the true bony layer in
the gill cover? (Figs. 211 and 212.)
Is the =mouth= large or small? Are the _teeth_ blunt or pointed? Near
the outer edge, or far in the mouth? (Fig. 212.) Does the fish have
lips? Are the teeth in one continuous row in either jaw? In the upper
jaw there are also teeth on the premaxillary bones. These bones are in
front of the maxillary bones, which are without teeth. Teeth are also
found in the roof of the mouth, and the tongue bears horny appendages
similar to teeth. Are the teeth of the fish better suited for chewing or
for grasping? Why are teeth on the tongue useful? Watch a fish eating:
does it chew its food? Can a fish taste? Test by placing bits of brown
paper and food in a vessel or jar containing a live fish. Is the throat,
or gullet, of the fish large or small?
[Illustration:
FIG. 212.—SKELETON OF PERCH.
]
The =skeleton= of a fish is simpler than the skeleton of other backboned
animals. Study Fig. 212 or a prepared skeleton. At first glance, the
skeleton appears to have two vertebral columns. Why? What bones does the
fish have that correspond to bones in the human skeleton? Are the
projections (processes) from the vertebræ long or short? The _ribs_ are
attached to the vertebræ of the trunk, the last rib being above the
vent. The tail begins at the vent. Are there more tail vertebræ or trunk
vertebræ? Are there any neck (cervical) vertebræ (_i.e._ in front of
those that bear ribs)? The first few ribs (how many?) are attached to
the central body of the vertebræ. The remaining ribs are loosely
attached to processes on the vertebræ. The ribs of bony fishes are not
homologous with the ribs of the higher vertebrates. In most fishes there
are bones called intermuscular bones attached to the first ribs (how
many in the perch?) which are possibly homologous to true ribs; that is,
true ribs in the higher vertebrates may have been developed from such
beginnings.
[Illustration:
FIG. 213.
]
[Illustration:
FIG. 214.—SOFT-RAYED AND SPINY-RAYED FINS.
]
Which, if any, of the _fin skeletons_ (Fig. 214) are not attached to the
general skeleton? Which fin is composed chiefly of tapering, pointed
rays? Which fins consist of rays which subdivide and widen toward the
end? Which kind are stiff, and which are flexible? Which of the fin rays
are segmented, or in two portions? The outer segment is called the
radial, the inner the basal segment. Which segments are longer? There is
one basal segment that lacks a radial segment. Find it (Fig. 212).
[Illustration:
FIG. 215.—CARP, with right gill cover removed to show gills.
]
What is the advantage of the backbone plan of structure over the
armour-plate plan? You have seen the spool-like body of the vertebra in
canned salmon. Is it concave, flat, or convex at the ends?
[Illustration:
FIG. 216.—SKELETON AROUND THROAT OF FISH.
]
The =gills= are at the sides of the head (Fig. 215) under the opercula,
or gill covers. What is the colour of the gills? Do the blood vessels
appear to be very near the surface of the gills, or away from the
surface? What advantage in this? Are the gills smooth or wrinkled? (Fig.
215.) What advantage? The bony supports of the gills, called the gill
arches, are shown in Fig. 216 (_k_{1}_ to _k_{4}_). How many arches on
each side? The gill arches have projections on their front sides, called
gill rakers, to prevent food from being washed through the clefts
between the arches. The fringes on the rear of the gill arches are
called the gill filaments (_a_, Fig. 216). These filaments support the
thin and much-wrinkled borders of the gills, for the gills are
constructed on the plan of exposing the greatest possible surface to the
water. Compare the plan of the gills and that of the human lungs. The
gill opening on each side is guarded by seven rays (_kh_, Fig. 216)
along the hinder border of the gill cover. These rays grow from the
tongue bone. (_Zu_, Fig. 216. This is a rear view.)
[Illustration:
FIG. 217.—CIRCULATION IN GILLS.
]
[Illustration:
FIG. 218.—NOSTRILS, MOUTH, AND GILL OPENINGS OF STING-RAY.
]
Watch a live fish and determine how the water is forced between the
gills. Is the mouth opened and closed in the act of breathing? Are the
openings behind the gill covers opened and closed? How many times per
minute does fresh water reach the gills? Do the mouth and the gill
covers open at the same time? Why must the water in contact with the
gills be changed constantly? Why does a fish usually rest with its head
up stream? How may a fish be kept alive for a time after it is removed
from the water? Why does drying of the gills prevent breathing? If the
mouth of a fish were propped open, and the fish returned to the water,
would it suffocate? Why, or why not?
[Illustration:
FIG. 219.—GILL OPENINGS OF EEL.
]
=Food Tube.=—The gullet is short and wide. The stomach is elongated
(Fig. 220). There is a slight constriction, or narrowing, where it
joins the intestine. Is the intestine straight, or does it lie in few
or in many loops? (Fig. 220.) The liver has a gall bladder and empties
into the intestine through a bile duct. Is the liver large or small?
Simple or lobed? The spleen (_mi_, Fig. 220) lies in a loop of the
intestine. The last part of the intestine is straight and is called
the rectum. Is it of the same size as the other portions of the
intestine? The fish does not possess a pancreas, the most important
digestive gland of higher vertebrates.
[Illustration:
FIG. 220.—ANATOMY OF CARP. (See also coloured figure 4.)
_bf_, barbels on head (for feeling); _h_, ventricle of heart; _as_,
aortic bulb for regulating flow to gills; _vk_, venous sinus; _ao_,
dorsal aorta; _ma_, stomach; _l_, liver; _gb_, gall cyst; _mi_,
spleen; _d_, small intestine; _md_, large intestine; _a_, vent; _s_,
_s_, swim bladder; _ni_, _ni_, kidney; _hl_, ureter; _hb_, bladder;
_ro_, eggs (roe); _mhe_, opening of ducts from kidney and ovary.
=Questions=: Are the kidneys dorsal or ventral? The swim bladder? Why?
Why is the swim bladder double? Does blood enter gills above or
below?
]
The _ovary_ lies between the intestine and the air bladder. In Fig.
220 it is shown enlarged and filled with egg masses called roe. It
opens by a pore behind the vent. The silver lining of the body cavity
is called the peritoneum.
Is the _air bladder_ in the perch simple or partly divided? In the
carp? (Fig. 220.) Is it above or below the centre of the body? Why?
The air bladder makes the body of the fish about as light as water
that it may rise and sink with little effort. When a fish dies, the
gases of decomposition distend the bladder and the abdomen, and the
fish turns over. Why?
Where are the _kidneys_? (Fig. 220.) Their ends unite close under the
spinal column. The ureters, or tubes, leading from them, unite, and
after passing a small urinary bladder, lead to a tiny urinary pore
just behind the opening from the ovary. (Coloured figure 4.)
=The Circulation.=—The fish, unlike other vertebrates, has its
breathing organs and its heart in its head. The gills have already
been described. The heart of an air-breathing vertebrate is near its
lungs. Why? The _heart_ of a fish is near its gills for the same
reason. The heart has one auricle and one ventricle. (Coloured figure
1.)
[Illustration:
FIG. 221.—PLAN OF CIRCULATION.
_Ab_, arteries to gills; _Ba_, aortic bulb; _V_, ventricle.
]
Blood returning to the heart comes through several veins into a
_sinus_, or antechamber, whence it passes down through a valve into
the _auricle_; from the auricle it goes forward into the _ventricle_.
The ventricle sends it into an _artery_, not directly, but through a
_bulb_ (_as_, Fig. 220), which serves to maintain a steady flow,
without pulse beats, into the large artery (_aorta_) leading to the
gills. The arteries leading from the gills join to form a _dorsal
aorta_ (_Ao_, Fig. 221), which passes backward, inclosed by the lower
processes of the spinal column. After going through the _capillaries_
of the various organs, the blood returns to the heart through veins.
[Illustration:
FIG. 222.—BRAIN OF PERCH, from above.
_n_, end of nerve of smell; _au_, eye; _v_, _z_, _m_, fore, mid, and
hind brain; _h_, spinal bulb; _r_, spinal cord.
]
The _colour of the blood_ is given by red corpuscles. These are
nucleated, oval, and larger than the blood corpuscles of other
vertebrates. The blood of the fish is slightly above the temperature
of the water it inhabits.
Notice the general shape of the brain (Fig. 222). Are its subdivisions
distinct or indistinct? Are the lobes in pairs? The middle portion of
the brain is the widest, and consists of the two _optic lobes_. From
these lobes the optic nerves pass beneath the brain to the eyes (_Sn_,
Fig. 223). In front of the optic lobes lie the two cerebral lobes, or
the _cerebrum_. The small _olfactory lobes_ are seen (Fig. 224) in
front of the cerebrum. The olfactory nerves may be traced to the
nostrils. Behind the optic lobes (mid brain) is the cerebellum (hind
brain) and behind it is the _medulla oblongata_ or beginning of the
spinal cord.
[Illustration:
FIG. 223.—BRAIN OF PERCH, side view.
]
[Illustration:
FIG. 224.—BRAIN OF PERCH, from above.
]
If you take the eyeball for comparison, is the whole brain as large as
one eyeball? (Fig. 222.) If you judge from the size of the parts of
the brain, which is more important with the fish, thinking or
perception? Which is the most important sense?
The scales along a certain line on each side of the fish, called the
lateral line, are perforated over a series of lateral line sense
organs, supposed to be the chief organs of _touch_ (see Fig. 209).
[Illustration:
FIG. 225.—THE STICKLEBACK. Instead of depositing the eggs on the
bottom, it makes a nest of water plants—the only fish that does
so—and bravely defends it.
]
=Questions.=—Which of the fins of the fish have a use which corresponds
to the keel of a boat? The rudder? A paddle for sculling? An oar? State
several reasons why the head of the fish must be very large, although
the brain is very small. Does all the blood go to the gills just after
leaving the heart?
[Illustration:
FIG. 226.—ARTIFICIAL FECUNDATION. The egg cells and sperm-cells are
pressed out into a pan of water.
]
Make a list of the different species of fish found in the waters of your
neighbourhood; in the markets of your town.
[Illustration:
FIG. 227.—NEWLY HATCHED TROUT, with yolk-sac adhering, eyes large, and
fins mere folds of the skin. (Enlarged.)
]
=Reproduction.=—The female fish deposits the unfertilized eggs, or ova,
in a secluded spot on the bottom. Afterward the male fish deposits the
sperms in the same place (see Fig. 225). The eggs, thus unprotected, and
newly hatched fish as well, are used for food by fish of the same and
other species. To compensate for this great destruction, most fish lay
(spawn) many thousands of eggs, very few of which reach maturity. Higher
vertebrates (_e.g._ birds) have, by their superior intelligence, risen
above this wasteful method of reproduction. Some kinds of marine fish,
notably cod, herring, and salmon, go many miles up fresh rivers to
spawn. It is possible that this is because they were originally
fresh-water species; yet they die if placed in fresh water except during
the spawning season. They go because of _instinct_, which is simply an
inherited habit. Rivers may be safer than the ocean for their young.
They are worn and exhausted by the journey, and never survive to lay
eggs the second time.
[Illustration:
FIG. 228.—A SHARK (_Acanthias vulgaris_).
]
The _air bladder is developed from the food tube_ in the embryo fish,
and is homologous with lungs in the higher vertebrates. Are their
functions the same?
Fish that _feed on flesh have a short intestine_. Those that eat plants
have a long intestine. Which kind of food is more quickly digested?
There are _mucous glands in the skin_ of a fish which supply a secretion
to facilitate movement through the water; hence a freshly caught fish,
before the secretion has dried, feels very slippery.
The air bladder, although homologous to lungs, is not a breathing organ
in common fishes. It is filled by the formation of gases from the blood,
and can be made smaller by the contraction of muscles along the sides of
the body; this causes the fish to sink. In the gar and other ganoids,
the air bladder contains blood vessels, is connected with the gullet,
and is used in breathing. Organs _serving the same purpose_ in different
animals are said to be _analogous_. To what in man are the gills of the
fish analogous? Organs having _a like position and origin_ are said to
be _homologous_. The air bladders of a fish are homologous with the
lungs of man; but since they have not the same use they are not
analogous.
How does the tail of a shark or a gar differ from the tail of common
fishes? (Fig. 228.) Do you know of fish destitute of scales? Do you know
of fish with whiplike feelers on the head? (Figs.) Why are most fishes
white on the under side?
=Comparative Review.=—(Copy table on one page or two facing pages of
notebook.)
═══════════╤═══════════╤═══════════╤═══════════╤════════════╤══════════
│IS THERE A │ METHOD OF │ DIGESTIVE │REPRODUCTION│ SENSES
│ HEAD? A │ FEEDING │ORGANS AND │ │
│ NECK? │ │ DIGESTION │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Amœba │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Sponge │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Hydra │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Starfish │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Earthworm │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Wasp │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Mussel │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼────────────┼──────────
Fish │ │ │ │ │
═══════════╧═══════════╧═══════════╧═══════════╧════════════╧══════════
[Illustration:
FIG. 229.—DRAWING THE SEINE.
]
[Illustration:
FIG. 230.—SUNFISH.
]
[Illustration:
FIG. 231.—TUNNY.
]
[Illustration:
FIG. 232.—SWORDFISH.
]
[Illustration:
FIG. 233.—SWELLFISH.
]
[Illustration:
FIG. 234.—TURBOT.
]
[Illustration:
FIG. 235.—CARP.
]
[Illustration:
FIG. 236.—HERRING.
]
[Illustration:
FIG. 237.—SPECKLED TROUT.
]
[Illustration:
FIG. 238.—PERCH.
]
[Illustration:
FIG. 239.—SALMON.
]
=Seven Food Fish. Three Curious Fish.=
SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)
[Illustration:
FIG. 240.—SEA HORSE (_Hippocampus_), with incubating pouch, _Brt_.
]
[Illustration:
FIG. 241.—BAND FISH.
]
[Illustration:
FIG. 242.—TORPEDO. Electrical organs at right and left of brain.
]
[Illustration:
FIG. 243.—LANTERN FISH (_Linophryne lucifer_). (After Collett.)
]
[Illustration:
FIG. 244.—LUNG FISH of Australia (_Ceratodus miolepis_).
]
[Illustration:
FIG. 245.—TRUNK FISH.
]
[Illustration:
FIG. 246.—SEAWEED FISH. × ⅕ (_Phyllopteryx eques_).
]
=Remarkable Fish.= SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)
RECOGNITION GROUP CHARACTERS
The commoner members of the several branches may be recognized by the
following characters:—
1. The =Protozoans= are the only one-celled animals.
2. The =Sponges= are the only animals having pores all over the body for
the inflow of water.
3. The =Polyps= are the only many-celled animals having a single opening
into the body, serving for both mouth and vent. They are radiate in
structure, and usually possess tentacles.
4. The =Echinoderms= are marine animals of more or less radiate
appearance, having a food tube in the body separate from the body wall.
The following groups are plainly bilateral: that is, dorsal and ventral
surfaces, front and hind ends are different.
5. The =Vermes= have usually a segmented body but lack jointed legs.
6. The =Arthropods=[3] have an external skeleton and jointed legs.
Footnote 3:
Insects and crustaceans.
7. The =Molluscs= have soft bodies, no legs, no skeleton, but usually a
limy shell.
8. The =Vertebrates= have an internal skeleton of bones, and usually two
pairs of legs.
[Illustration:
FIG. 247.—A SNAIL. (Which branch? Why?)
]
CHAPTER XI
BATRACHIA
The theory of evolution teaches that animal life began in a very simple
form in the sea, and that afterward the higher sea animals lost their
gills and developed lungs and legs and came out to live upon the land;
truly a marvellous procedure, and incredible to many, although the
process is repeated every spring in countless instances in pond and
brook.
In popular language, every cold-blooded vertebrate breathing with lungs
is called a reptile. The name reptile is properly applied only to
lizards, snakes, turtles, and alligators. The common mistake of speaking
of frogs and salamanders as reptiles arises from considering them only
in their adult condition. Reptiles hatch from the egg as tiny reptiles
resembling the adult forms; frogs and salamanders, as every one knows,
leave the egg in the form of tadpoles (Fig. 248). The fact that frogs
and salamanders begin active life as fishes, breathing by gills, serves
to distinguish them from other cold-blooded animals, and causes
naturalists to place them in a separate class, called batrachia (twice
breather) or amphibia (double life).
TADPOLES
SUGGESTIONS.—Tadpoles may be studied by placing a number of frog’s
eggs in a jar of water, care being taken not to place a large number
of eggs in a small amount of water. When they hatch, water plants
(_e.g._ green algæ) should be added for food. The behaviour of frogs
may be best studied in a tub of water. A toad in captivity should be
given a cool, moist place, and fed well. A piece of meat placed near a
toad may attract flies, and the toad may be observed while catching
them, but the motion is so swift as to be almost imperceptible. Live
flies may be put into a glass jar with a toad. Toads do not move about
until twilight, except in cloudy, wet weather. They return to ponds
and brooks in spring at the time for laying eggs. This time for both
frogs and toads is shown by trilling. All frogs, except tree frogs,
remain in or near the water all the year.
[Illustration:
FIG. 248.—METAMORPHOSES OF THE FROG, numbered in order.
]
Do =eggs hatch= and tadpoles grow more rapidly in a jar of water kept in
a warm place or in a cold place? In pond water or in drinking water? Can
the tadpoles be seen to move in the eggs before hatching? When do the
external gills show? (Fig. 248.)
[Illustration:
FIG. 249.—TADPOLE, from below, showing intestine and internal gills.
(Enlarged.)
]
What =parts= may be described in a tadpole? What is the shape of the
tail? _Compare the tadpole with the fish_ as to (1) general shape, (2)
covering, (3) fins, (4) tail, (5) gills.
Do the external =gills= disappear before or after any rudiments of limbs
appear? (6, 7, Fig. 248.) Can you locate the gills after they become
internal? (Fig. 249.)
In what state of growth are the _legs_ when the tadpole first goes to
the surface to breathe? Which legs appear first? Of what advantage is
this? What becomes of the tail? Is the tail entirely gone before the
frog first leaves the water? Are tadpoles habitually in motion or at
rest?
Is the =intestine= visible through the skin? (Fig. 249.) Is it straight
or coiled? Remembering why some fish have larger intestines than others,
and that a cow has a long intestine and a cat a short one, state why a
tadpole has a relatively longer intestine than a frog.
=Compare= the mouth, jaws, eyes, skin, body, and habits of _tadpole and
frog_.
FROGS
Prove that frogs and toads are _beneficial to man_. Did you ever know of
a frog or a toad destroying anything useful, or harming any one, or
causing warts? How many pupils in class ever had warts? Had they handled
frogs before the warts came? Frogs are interesting, gentle, timid
animals. Why are they repulsive to some people?
=Environment=.—_Where are frogs found_ in greatest numbers? What occurs
when danger threatens them? What _enemies_ do they have? What colour, or
tint, is most prominent on a frog? Does the colour “mimic” or _imitate_
its surroundings? What is the colour of the under side of the body?
(Fig. 250.) Why is there greater safety in that colour? What enemies
would see water frogs from below? Do tree frogs mimic the bark? The
leaves?
Can a _frog stay under water_ for an indefinite time? Why, or why not?
What part of a frog is above the surface when it floats or swims in a
tub of water? Why? Do frogs croak in the water or on the bank? Why do
they croak after a rain? Do toads croak?
Are the _eggs_ laid in still or in flowing water? In a clear place or
among sticks and stems? Singly, or in strings or in masses? (Fig. 248.)
Describe an egg. Why do frogs dig into the mud in autumn in cold
climates? Why do they not dig in mud at the bottom of a pond?
[Illustration:
FIG. 250.—PAINTED FROG (_Chorophilus ornatus_), of Mexico.
]
Describe the =position= of the frog when still (Fig. 250). Of what
advantage in this position? Does the frog use its fore legs in swimming
or jumping? Its hind legs? How is the frog fitted for jumping? Compare
it in this respect with a jumping insect; a jumping mammal. How is it
fitted for swimming? Is the general build of its body better fitted for
swimming or for jumping? How far can a frog jump?
=External Features.=—The frog may be said to have two _regions in its
body_, the head and the trunk. A neck hardly exists, as there is only
one vertebra in front of the shoulders (Fig. 252), while mammals have
seven neck (cervical) vertebræ. There are no tail (caudal) vertebræ,
even in the tadpole state of frogs and toads.
The _head_ appears triangular in shape when viewed from what direction?
The head of a frog is more pointed than the head of a toad. Is the skull
a closed case of broad bones or an open structure of narrow bones? (Fig.
252.)
[Illustration:
FIG. 251.—HEAD OF FROG.
]
Describe the _mouth._ Observe the extent of the mouth opening (Fig.
251). Are _teeth_ present in the upper jaw? The lower jaw? Are the teeth
sharp or dull? Does the frog chew its food? Is the _tongue_ slender or
thick? (Fig. 251.) Is it attached to the front or the back of the mouth?
In what direction does the free end extend when the tongue lies flat? Is
the end pointed or lobed? How far out will the tongue stretch? For what
is it used? Why is it better for the teeth to be in the upper jaw rather
than in the lower jaw? That the teeth are of little service is shown by
the fact that the toad with similar habits of eating has no teeth. Will
a toad catch and swallow a bullet or a pebble rolled before it? The toad
is accustomed to living food, hence it prefers a moving insect to a
still one.
=The Senses.=—Compare the _eyes_ with the eyes of a fish in respect to
position and parts. Are the eyes protruding or deep-set? Touch the eye
of a live frog. Can it be retracted? What is the shape of the pupil? The
colour of the iris? Is the eye bright or dull? What probably gave rise
to the superstition that a toad had a jewel in its head? Is there a
third eyelid? Are the upper and lower eyelids of the same thickness?
With which lid does it wink? Close its eye?
Observe the large oval _ear_ drum or tympanum. What is its direction
from the eye? (Fig. 251.) The mouth? Is there a projecting ear? Does the
frog hear well? What reason for your answer? As in the human ear, a tube
(the Eustachian tube) leads from the mouth to the inner side of the
tympanum.
How many _nostrils_? (Fig. 251.) Are they near together or separated?
Large or small? A bristle passed into the nostril comes into the mouth
not far back in the roof. Why must it differ from a fish in this?
[Illustration:
FIG. 252.—SKELETON OF FROG.
]
How do the _fore and hind legs_ differ? How many toes on the fore foot
or hand? On the hind foot? On which foot is one of the toes rudimentary?
Why is the fore limb of no assistance in propelling the body in jumping?
Do the toes turn in or out? (Fig. 250.) How does the frog give direction
to the jump? What would be the disadvantage of always jumping straight
forward when fleeing? Which legs are more useful in alighting?
=Divisions of the Limbs=.—Distinguish the upper arm, forearm, and hand
in the fore limb (Figs. 252 and 253). _Compare with skeleton of man_
(Fig. 399). Do the arms of a man and a frog both have one bone in the
_upper arm_ and two in the _forearm_? Both have several closely joined
bones in the _wrist_ and five separate bones in the _palm_. Do any of
the frog’s fingers have three joints? _Compare also the leg of man_ and
the hind leg of the frog (Figs. 253 and 399). Does the _thigh_ have one
bone in each? The shank of man has two bones, shin and splint bone. Do
you see a groove near the end in the shank bone of a frog (Fig. 252),
indicating that it was formed by the union of a shin and a splint bone?
The first two of the five bones of the ankle are elongated, giving the
hind leg the appearance of having an extra joint (Fig. 253). The foot
consists of six digits, one of which, like the thumb on the fore limb,
is rudimentary. The five developed toes give the five digits of the
typical vertebrate foot. Besides the five bones corresponding to the
instep, the toes have two, three, or four bones each. How is the hind
foot specialized for swimming? Which joint of the leg contains most
muscle? (Fig. 254.) Find other bones of the frog analogous in position
and similar in form to bones in the human skeleton.
[Illustration:
FIG. 253.—SKELETON OF FROG.
]
[Illustration:
FIG. 254.—LEG MUSCLES OF FROG.
]
Is the =skin= of a frog tight or loose? Does it have any appendages
corresponding to scales, feathers, or hair of other vertebrates? Is the
skin rough or smooth? The toad is furnished with glands in the skin
which are sometimes swollen; they form a bitter secretion, and may be,
to some extent, a protection. Yet birds and snakes do not hesitate to
swallow toads whole. Show how both upper and under surfaces of frog
illustrate protective colouration.
[Illustration:
FIG. 255.—DIGESTIVE CANAL OF FROG.
_Mh_, mouth; _Z_, tongue pulled outward; _S_, opening to larynx; _Oe_,
gullet; _M_, stomach; _D_, intestine; _P_, pancreas; _L_, liver;
_G_, gall bladder; _R_, rectum; _Hb_, bladder; _Cl_, cloaca; _A_,
vent.
]
All batrachians have large and _numerous blood vessels in the skin_ by
which gases are exchanged with the air, the skin being almost equal to
_a third lung_. That the skin may function in this way, it must not
become dry. Using this fact, account for certain habits of toads as well
as frogs.
If a frog is kept in the dark or on a dark surface, _its skin will
become darker_ than if kept in the light or on a white dish. Try this
experiment, comparing two frogs. This power of changing colour is
believed to be due to the diminution in size of certain pigment cells by
contraction, and enlargement from relaxation. This power is possessed to
a certain degree not only by batrachians but also by many fishes and
reptiles. The chameleon, or green lizard, surpasses all other animals in
this respect (Fig. 280). What advantage from this power?
=Digestive System.=—The large mouth cavity is connected by a short
throat with the gullet, or œsophagus (Fig. 255). A slit called the
glottis opens from the throat into the lungs (Fig. 255). Is the gullet
long or short? Broad or narrow? Is the stomach short or elongated? Is
the division distinct between stomach and gullet, and stomach and
intestine? Is the liver large or small? Is it simple or lobed? The
pancreas lies between the stomach and the first bend of the intestines
(Fig. 255). What is its shape? A bile duct connects the liver with the
small intestine (_Dc_, Fig. 255). It passes through the pancreas, from
which it receives several pancreatic ducts. After many turns, the small
intestine joins the large intestine. The last part of the large
intestine is called the rectum (Latin, straight). The last part of the
rectum is called the cloaca (Latin, a drain), and into it the ducts from
the kidneys and the reproductive glands also open. The kidneys are
large, elongated, and flat. They lie under the dorsal wall. The urinary
bladder is also large. Does the salamander have a similar digestive
system? (Fig. 256) Why are the liver and the lungs (Fig. 256) longer in
a salamander than in a frog?
[Illustration:
FIG. 256.—ANATOMY OF SALAMANDER.
_1a_, heart; _2_, lungs; _3a_, stomach; _3b_, intestine; _3c_, large
intestine; _4_, liver; _8_, egg masses; _10_, bladder; _11_, vent.
]
=Respiration.=—How many _lungs_? Are they simple or lobed? (Fig. 256.) A
lung cut open is seen to be baglike, with numerous ridges on its inner
surface. This increases the surface with which the air may come in
contact. In the walls of the lungs are numerous capillaries. Does the
frog _breathe with mouth open or closed_? Does the frog have any ribs
for expanding the chest? What part of the head expands and contracts? Is
this motion repeated at a slow or a rapid rate? Regularly or
irregularly? There are valves in the nostrils for opening and closing
them. Is there any indication of opening and closing as the throat
expands and contracts? The mouth and throat (pharynx) are filled with
air each time the throat swells, and the exchange of gases (which
gases?) takes place continually through their walls and the walls of the
lungs. At intervals the air is forced through the glottis into the
lungs. After a short time it is expelled from the lungs by the muscular
abdominal walls, which press upon the abdominal organs, and so upon the
lungs. Immediately the air is forced back into the lungs, so that they
are kept filled. In some species the lungs regularly expand at every
second contraction of the throat. This is shown by a slight outward
motion at the sides. Does the motion of the throat cease when the frog
is under water? Why would the frog be unable to breathe (except through
the skin) if its mouth were propped open? Why does the fact that the
breathing is so slow as almost to cease during hibernation, aid the frog
in going through the winter without starving? (Chap. I.) Why must frogs
and toads keep their skins moist? Which looks more like a clod? Why?
=The Heart and Circulation.=—What is the shape of the heart? (Fig.
257.) Observe the two auricles in front and the conical ventricle
behind them. The great arterial trunk from the ventricle passes
forward beyond the auricles; it divides into two branches which turn
to the right and the left (Fig. 257). Each branch immediately
subdivides into three arteries (Fig. 257), one going to the head, one
to the lungs and skin, and a third, the largest, passes backward in
the trunk, where it is united again to its fellow.
[Illustration:
FIG. 257.—PLAN OF FROG’S CIRCULATION.
Venous system is black; the arterial, white. _AU_, auricles; _V_,
ventricle; _L_, lung; _LIV_, liver. Aorta has one branch to right,
another to left, which reunite below. Right branch only persists in
birds, left branch in beasts and man.
]
Both the pulmonary veins, returning to the heart with pure blood from
the lungs, empty into the left auricle. Veins with the impure blood
from the body empty into the right auricle. Both the auricles empty
into the ventricles, but the pure and the impure blood are prevented
from thoroughly mixing by ridges on the inside of the ventricle. Only
in an animal with a four-chambered heart does pure blood from the
lungs pass unmixed and pure to all parts of the body, and only such
animals are warm-blooded. The purer (_i.e._ the more oxygenated) the
blood, the greater the oxidation and warmth.
[Illustration:
FIG. 258.—FROG’S BLOOD (magnified 2500 areas). Red cells oval,
nucleated, and larger than human blood cells. Nuclei of two white
cells visible near centre. (Peabody.)
]
The red corpuscles in a frog’s _blood_ are oval and larger than those
of man. Are all of them nucleated? (Fig. 258.) The flow of _blood_ in
the web of a frog’s foot is a striking and interesting sight. It may
be easily shown by wrapping a small frog in a wet cloth and laying it
with one foot extended upon a glass slip on the stage of a microscope.
[Illustration:
FIG. 259.—BRAIN OF FROG.
]
[Illustration:
FIG. 260.—NERVOUS SYSTEM OF FROG.
]
The =brain= of the frog (Fig. 259) is much like that of a fish (Fig.
224). The _olfactory_, _cerebral_, and _optic lobes_, _cerebellum_ and
_medulla_ are in the same relative position, although their relative
sizes are not the same. Compared with the other parts, are the olfactory
lobes more or less developed than in a fish? The cerebral hemispheres?
The optic lobes? The cerebellum? There is a cavity in the brain. It is
readily exposed on the under surface of the medulla by cutting the
membrane, which is there its only covering (Fig. 259).
[Illustration:
FIG. 261.—Position of legs in tailless (_A_) and tailed (_B_)
amphibian.
]
=Frogs and toads are beneficial= (why?) and do not the slightest injury
to any interest of man. If =toads= are encouraged to take up their abode
in a garden, they will aid in ridding it of insects. A house may be made
in a shady corner with four bricks, or better still, a hole a foot deep
may be dug to furnish them protection from the heat of the day. A toad’s
muzzle is not so tapering as a frog’s (why?), its feet are not so fully
webbed (why?), and its skin is not so smooth (why?). In case of doubt,
open the mouth and rub the finger along the upper jaw; a frog has sharp
teeth, a toad none at all. The tadpoles of frogs, toads, and salamanders
are much alike. In toad’s spawn the eggs lie in strings inclosed in
jelly; frogs spawn is in masses (Fig. 248).
Any batrachian may easily be passed around the class after placing it
in a tumbler with gauze or net tied over top. It should be kept in a
box with two inches of moist earth on the bottom. If no live insects
are obtainable for feeding a toad, bits of moist meat may be dangled
from the end of a string. If tadpoles are placed in a pool or a tub in
a garden, the toads hatched will soon make destructive garden insects
become a rarity.
Does a frog or a =salamander= have the more primitive form of body? Why
do you think so? Salamanders are sometimes called mud puppies. The
absurd belief that salamanders are poisonous is to be classed with the
belief that toads cause warts. The belief among the ancients that
salamanders ate fire arose perhaps from seeing them coming away from
fires that had been built over their holes on river banks by travellers.
Their moist skin protected them until the fire became very hot.
Describe the “mud puppy” shown in Fig. 262. The pouched gopher, or rat
(Fig. 371), is sometimes absurdly called a salamander.
[Illustration:
FIG. 262.—BLIND SALAMANDER (_Proteus anguinus_). × ½. Found in caves
and underground streams in Balkans. Gills external, tail finlike,
legs small.
]
CHAPTER XII
REPTILIA (REPTILES)
This =class= is divided into _four orders_ which have such marked
differences of external form that there is no difficulty in
distinguishing them. These orders are represented by _Lizards_,
_Snakes_, _Turtles_, and _Alligators_. Of these, only the forms of
lizards and alligators have similar proportions, but there is a marked
difference in their size, lizards being, in general, the smallest, and
alligators the largest of the reptiles.
[Illustration:
FIG. 263.—A SALAMANDER.
]
[Illustration:
FIG. 264.—A LIZARD.
]
=Comparison of Lizards and Salamanders.=—To make clear the difference
between reptiles and batrachians, it will be well to compare the orders
in the two classes which resemble each other in size and shape; namely,
lizards and salamanders (Figs. 263 and 264). State in a tabular form
their differences in _skin_, _toe_, _manner of breathing_, _development
from egg_, _shape of tail_, _habitat_, _habits_. Each has an elongated
body, two pairs of limbs, and a long tail, yet they are easily
distinguished. Are the differences suggested above valid for the other
batrachians (frogs) and other reptiles (_e.g._ turtles)? Trace the same
differences between the toad or frog (Fig. 250) and the “horned toad,”
which is a lizard (Fig. 265).
[Illustration:
FIG. 265.—“HORNED TOAD” LIZARD, of the Southwest (_Phrynosoma
cornita_). × ⅔.
]
STUDY OF A TURTLE OR A TORTOISE
SUGGESTIONS.—Because of the ease with which a tortoise or a turtle may
be caught and their movements and habits studied, it is suggested that
one of these be studied as an example of reptiles. Besides a live
specimen, a skeleton of one species and the shells of several species
should be available.
[Illustration:
FIG. 266.—EUROPEAN POND TURTLE (_Emys lutaria_). (After Brehms.)
]
The =body (of a turtle or a tortoise) is divided= distinctly into
_regions_ (Fig. 266). Is there a head? Neck? Trunk? =Tail=? The trunk is
inclosed by the _so-called shell_, which consists of an upper portion,
the _carapace_, and a lower portion, the _plastron_. How are the other
regions covered? What is the shape of the head? Is the mouth at the
front, or on the under side? Where are the _nostrils_? Are the motions
of breathing visible? Is there a beak or snout? Do the jaws contain
_teeth_?
Do the =eyes= project? Which is thinner and more movable, the upper or
the lower lid? Identify the third eyelid (_nictitating membrane_). It is
translucent and comes from, and is drawn into, the inner corner of the
eye. It cleanses the eyeball. Frogs and birds have a similar membrane.
The circular =ear= drum is in a depression back of the angle of the
mouth. What other animal studied has an external ear drum?
The tortoise has a longer, more flexible =neck= than any other reptile.
Why does it have the greatest need for such a neck? Is the skin over the
neck tight or loose? Why?
Do the =legs= have the three joints or parts found on the limbs of most
vertebrates? How is the skin of the legs covered? Do the toes have
_claws_? Compare the front and the hind feet. Does the tortoise slide
its body or lift it when walking on hard ground? Lay the animal on its
back on a chair or a table at one side of the room in view of the class.
Watch its attempts to right itself. Are the motions suited to accomplish
the object? Does the tortoise succeed?
What are the prevailing =colours= of turtles? How does their colouration
correspond to their surroundings?
What parts of the tortoise extend at times beyond the shell? Are any of
these parts visible when the _shell is closed_? What movements of the
shell take place as it is closed? Is the carapace rigid throughout? Is
the plastron?
[Illustration:
FIG. 267.—SKELETON OF EUROPEAN TORTOISE.
_C_, rib plates; _M_, marginal plates; _B_, plastron; _H_, humerus
bone; _R_, radius; _U_, ulna; _Fe_, femur.
]
=The Skeleton= (Fig. 267).—The _carapace_ is covered with thin
_epidermal plates_ which belong to the skin. The bony nature of the
carapace is seen when the plates are removed, or if its inner surface is
viewed (Fig. 267). It is seen to consist largely of wide _ribs_ (how
many?) much flattened and grown together at their edges. The ribs are
seen to be rigidly attached to the vertebræ. The rear projections of the
vertebræ are flattened into a series of bony plates which take the place
of the sharp ridge found along the backs of most vertebrates. Show that
the shell of a turtle is not homologous with the shells of mollusks.
Does the turtle have shoulder blades and collarbones? Hipbones? Thigh
bones? Shin bone (fibia) and splint bone (fibula)? (Fig. 267.)
[Illustration:
FIG. 268.—THREE-CHAMBERED HEART OF A REPTILE (tortoise).
_a_, veins; _b_, _f_, right and left auricles; _cg_, ventricle; _d_,
arteries to lungs; _e_, veins from lungs; _i_, _n_, two branches of
aorta. Compare with Fig. 269 and coloured Fig. 2.
]
Do the plates formed by the ribs extend to the edge of the carapace? See
Fig. 267. About how many bony plates form the carapace? The plastron? Do
the horny plates outside correspond to the bony plates of the shell? How
many axial plates? How many costal (rib) plates? How many border plates?
Which plates are largest? Smallest? Do the horny plates overlap like
shingles, or meet edge to edge? Is there any mark where they meet on the
bony shell? Basing it upon foregoing facts, give a connected and
complete description of the structure of the carapace. Compare the
skeleton of the turtle with that of the snake, and correlate the
differences in structure with differences in habits.
[Illustration:
FIG. 269.—PLAN OF REPTILIAN CIRCULATION. See arrows.
]
=Draw= the tortoise seen from the side or above, with its shell closed,
showing the arrangement of the plates.
[Illustration:
FIG. 270.—REPTILIAN VISCERA (lizard).
_lr_, windpipe; _h_, heart; _lu_, lungs; _lr_, liver; _ma_, stomach;
_dd_, _md_, intestines; _hb_, bladder.
]
Place soft or tender vegetable =food=, lettuce, mushroom, roots,
berries, and water, also meat, in reach of the turtle. What does it
prefer? How does it eat? It has no lips; how does it drink?
Study the =movements= of its eyeballs and eyelids, and the respiratory
and other movements already mentioned. State a reason for thinking that
no species of land animals exists that lacks the simple power of
righting itself when turned on its back.
=Tortoise, Turtle, Terrapin.=—The turtles belong to the order of
reptiles called _chelonians_. No one can have any difficulty in knowing
a member of this order. The subdivision of the order into families is
not so easy, however, and the popular attempts to classify chelonians as
turtles, tortoises, and terrapins have not been entirely successful.
Species with a vaulted shell and imperfectly webbed toes and _strictly
terrestrial_ habits are called _tortoises_. Species with flattened
shells and _strictly aquatic_ habits should be called _terrapins_
(_e.g._ mud terrapin). They have three instead of two joints in the
middle toe of each foot. The term _turtle_ may be applied to species
which are _partly terrestrial and partly aquatic_ (_e.g._ snapping
turtle (Fig. 271)). Usage, however, is by no means uniform.
[Illustration:
FIG. 271.—SNAPPING TURTLE (_Chelydra serpentina_).
]
Most reptiles eat animal food; green terrapins and some land tortoises
eat vegetable food. Would you judge that carnivorous chelonians catch
very active prey?
The fierce _snapping turtle_, found in ponds and streams, sometimes has
a body three feet long. Its head and tail are very large and cannot be
withdrawn into the shell. It is carnivorous and has great strength of
jaw. It has been known to snap a large stick in two. The _box tortoise_
is yellowish brown with blotches of yellow, and like its close kinsman,
the pond turtle of Europe (Fig. 266), withdraws itself and closes its
shell completely. Both lids of the plastron are movable, a peculiarity
belonging to these two species. The _giant tortoise_ of the Galapagos
Islands, according to Lyddeker, can trot cheerfully along with three
full-grown men on its back. “Tortoise shell” used for combs and other
articles is obtained from the overlapping scales of the _hawkbill
turtle_, common in the West Indies. The _diamond-back terrapin_, found
along the Atlantic Coast from Massachusetts to Texas, is prized for
making soup.
[Illustration:
FIG. 272.—A RATTLESNAKE.
]
[Illustration:
FIG. 273 _a_.—HEAD OF VIPER, showing typical triangular shape of head
of venomous snake.
]
[Illustration:
FIG. 273 _b_.—SIDE VIEW, showing poison fangs; also tongue (forked,
harmless).
]
[Illustration:
FIG. 274.—VIPER’S HEAD, showing poison sac at base of fangs.
]
[Illustration:
FIG. 275.—SKULL, showing teeth, fangs, and quadrate bone to which
lower jaw is joined. See Fig. 284.
]
=Venomous snakes= named in order of virulence: 1. Coral snakes, _Elaps_,
about seventeen red bands bordered with yellow and black (coloured
figure 6) (fatal). 2. Rattlesnakes (very deadly). 3. Copperhead (may
kill a small animal of the size of a dog). 4. Water moccasin (never
fatal). 5. Ground rattler.—_Effects_: Pulse fast, breathing slow, blood
tubes dilated, blood becomes stored in abdominal blood tubes,
stupefaction and death from blood being withdrawn from brain. Always two
punctures, the closer together the smaller the snake. _Remedies_:
Ligature between wound and heart, lance wound and suck; inject into
wound three drops of 1 per cent solution of chromic acid or potassium
permanganate. Give strychnine, hypodermically, until strychnine symptoms
(twitchings) appear. No one but a physician should give strychnine.
Digitalin or caffein acts like strychnine; alcohol has opposite effect.
[Illustration:
FIG. 276.—“GLASS SNAKE,” a lizard without legs.
]
[Illustration:
FIG. 277.—SKULL OF ELAPS. See colored Fig. 5.
]
[Illustration:
FIG. 278.—SKULL OF LAMPROPELTIS.
]
=Protective Coloration and Mimicry.=—When an animal imitates the colour
or form of its _inanimate surroundings_ it is said to be _protectively
coloured_ or formed. Give an instance of _protective Coloration_ or
_form_ among lizards; butterflies; grasshoppers; amphibians;
echinoderms. When an animal imitates the colour or the form of _another
animal_ it is said to _mimic_ the animal. Mimicry usually enables an
animal to deceive enemies into mistaking it for an animal which for some
reason they avoid. The milkweed butterfly has a taste that is repulsive
to birds. The viceroy butterfly is palatable to birds, but it is left
untouched because of its close resemblance to the repulsive milkweed
butterfly. The harlequin snake (_Elaps_) of the Gulf states is the most
deadly snake of North America (Figs. 277, 278). It is very strikingly
coloured with rings of scarlet, yellow, and black. This is an example of
_warning_ coloration. The scarlet snake (_Lampropeltis_) has bands of
scarlet, yellow, and black (coloured Fig. 6) of the same tints, and it
is hardly distinguishable from the harlequin. The scarlet snake is said
to _mimic_ the harlequin snake. It also imitates the quiet inoffensive
habits of the harlequin snake, which fortunately does not strike except
under the greatest provocation. The rattles of the less poisonous but
deadly rattlesnake (Fig. 272) may be classed as an example of _warning
sound_ which most animals are quick to heed and thus avoid encounters
which might be destructive to either the snake or its enemy.
[Illustration:
COLOURED FIGURES 1, 2, 3.—CIRCULATION IN FISH, REPTILE, MAMMAL.
In which is blood from heart all impure? Mixed? Both pure and impure?
]
[Illustration:
FIG. 4.—ANATOMY OF CARP. For description see Fig. 220, page 117.
]
THE DEADLY HARLEQUIN SNAKE IS MIMICKED BY THE HARMLESS SCARLET SNAKE.
[Illustration:
FIG. 5.—HARLEQUIN SNAKE (_Elaps_).
]
[Illustration:
FIG. 6.—SCARLET SNAKE (_Lampropeltis_).
]
[Illustration:
FIG. 279.—GILA MONSTER (_Heloderma suspectum_), of Arizona. If
poisonous, it is the only instance among lizards. It is heavy-built,
orange and black mottled, and about 16 inches long. Compare it with
the green lizard (Fig. 280).
]
[Illustration:
FIG. 280.—CHAMELEON (_Anolis_), or green lizard of southern U.S. Far
excels European chameleon (Fig. 281) and all known animals in power
of changing colour (green, gray, yellow, bronze, and black).
]
=Survival of the Fittest.=—The two facts of most far-reaching
importance in the history of animals and plants are: (1) _Heredity_;
animals inherit the characteristics of their parents. (2) _Variation_;
animals are not exactly like their parents. The first fact gives
stability, the second makes evolution possible. The climate of the
world is slowly changing, and animals must change to adapt themselves
to it. A more sudden change of environment (surroundings) of animals
occurs because of migration or isolation; these in turn are caused by
the crowding of other animals or by the formation or disappearance of
geographical barriers, such as deserts, water, mountain chains.
[Illustration:
FIG. 281.—CHAMELEON OF SOUTHERN EUROPE.
]
The young vary in many ways from their parents. Some have a more
protective colour or form, sharper claws, swifter movements, etc. The
individuals possessing such beneficial variations live longer and
leave more offspring, and because of heredity transmit the desirable
qualities to some of their young. Variations which are disadvantageous
for getting food, defence, etc., cause shorter life and fewer
offspring. Thus the _fittest survive_, the unfit perish; an automatic
_natural selection_ occurs.
[Illustration:
FIG. 282.—EMBRYO OF A TURTLE, showing four gill slits. (Challenger
Report.)
]
Darwin taught that variations are infinitesimal and gradual. Recent
experiments and observations seem to show that many variations are by
sudden jumps, somewhat resembling so-called “freaks of nature.” As to
whether these “sports,” or individuals with new peculiarities,
survive, depends upon their fitness for their environment. “Survival
of the fittest” results from this natural selection, but the selection
occurs between animals of marked, not infinitesimal, differences, as
Darwin taught. Darwin’s theory is probably true for species in the
usual state of nature; the new theory (of De Vries) is probably true
for animals and plants under domestication and during rapid
geographical changes.
=Table for Review= (for notebooks or blackboards).
═══════════╤═══════════╤═══════════╤═══════════╤═══════════╤═══════════
│ FISH │ TADPOLE │ FROG │ TURTLE │ LIZARD
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Limbs, kind│ │ │ │ │
and │ │ │ │ │
number │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Are claws │ │ │ │ │
present? │ │ │ │ │
How many?│ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Covering of│ │ │ │ │
body │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Teeth, kind│ │ │ │ │
of, if │ │ │ │ │
present │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Which bones│ │ │ │ │
found in │ │ │ │ │
man are │ │ │ │ │
lacking? │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Chambers of│ │ │ │ │
heart │ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Respiration│ │ │ │ │
───────────┼───────────┼───────────┼───────────┼───────────┼───────────
Movements │ │ │ │ │
═══════════╧═══════════╧═══════════╧═══════════╧═══════════╧═══════════
[Illustration:
FIG. 283.—BIG-HEADED TURTLE (_Platysternum megalocephalum_). × ⅓.
China.
This and Fig. 282 suggest descent of turtles from a lizardlike form.
Figure 282 shows earlier ancestors to have been gill breathers.
]
CHAPTER XIII
BIRDS
SUGGESTIONS.—The domestic pigeon, the fowl, and the English sparrow
are most commonly within the reach of students. The last bird has
become a pest and is almost the only bird whose destruction is
desirable. The female is somewhat uniformly mottled with gray and
brown in fine markings. The male has a black throat with the other
markings of black, brown, and white, in stronger contrast than the
marking of the female. As the different species of birds are
essentially alike in structural features, the directions and questions
may be used with any bird at hand. When studying feathers, one or more
should be provided for each pupil in the class. The feet and the bills
of birds should be kept for study.
[Illustration]
Does the =body of the bird= like the toad and the turtle, have a head, a
trunk, a tail, and two pairs of limbs? Do the fore and hind limbs differ
from each other more or less than the limbs of other backboned animals?
Does any other vertebrate use them for purposes as widely different?
=Eye.=—Does the _eyeball_ have parts corresponding to the eyeball of a
fish or a frog; viz., cornea, iris, pupil? Which is more movable, the
upper or the lower _eyelid_? _Are_ there any lashes? The bird (like what
other animal?) has a third eyelid, or nictitating membrane. Compare its
thickness with that of the other lids. Is it drawn over the eyeball from
the inner or the outer corner of the eye? Can you see in the human eye
any wrinkle or growth which might be regarded as remains, or vestige, of
such a membrane?
How many =nostrils=? In which mandible are they located? Are they nearer
the tip or the base of the mandible? (Fig. 284.) What is their shape? Do
the nasal passages go directly down through the mandible or do they go
backward? Is the inner nasal opening into the mouth or into the throat?
[Illustration:
FIG. 284.—SKULL OF DOMESTIC FOWL.
_q_, quadrate (“four-sided”) bone by which lower jaw is attached to
skull (wanting in beasts, present in reptiles; see Fig. 277).
]
The beak or =bill= consists of the upper and lower mandibles. The
outside of the beak seems to be of what kind of material? Examine the
decapitated head of a fowl or of a dissected bird, and find if there is
a covering on the bill which can be cut or scraped off. Is the mass of
the bill of bony or horny material? With what part of the human head are
the mandibles homologous? (Fig. 284.)
=Ears.=—Do birds have external ears? Is there an _external opening_
leading to the ear? In searching for it, blow or push forward the
feathers. If found, notice its location, size, shape, and what surrounds
the opening. There is an owl spoken of as the long-eared owl. Are its
ears long?
The =leg= has three divisions: the uppermost is the _thigh_ (called the
“second joint” in a fowl); the middle division is the _shank_ (or
“drumstick”); and the lowest, which is the slender bone covered with
scales, is formed by the union of the _ankle_ and the _instep_. (The
bones of the three divisions are named femur, tibiotarsus, and
tarsometatarsus.) The _foot_ consists entirely of toes, the bones of
which are called phalanges. Is there a bone in each claw? (See Fig.
285.) Supply the numerals in this sentence: The pigeon has ____ toes,
the hind toe having ____ joints; of the three front toes, the inner has
____ joints (count the claw as one joint), the middle has ____ joints,
and the outer toe has ____ joints (Fig. 285). Is the thigh of a bird
bare or feathered? The shin? The ankle? Where is the ankle joint of a
bird? Do you see the remains of another bone (the splint bone, or
fibula) on the shin bone of the shank? (Fig. 285 or 286.) Why would
several joints in the ankle be a disadvantage to a bird?
[Illustration:
FIG. 285.—LEG BONES OF BIRD.
]
[Illustration:
FIG. 286.—SKELETON OF BIRD.
_Rh_, vertebræ; _Cl_, clavicle; _Co_, coracoid; _Sc_, scapula; _St_,
sternum; _H_, humerus; _R_, radius; _U_, ulna; _P_, thumb; _Fe_,
femur; _T_, tibia. See Fig. 394.
=Questions=: Which is the stiffest portion of the vertebral column?
How are the ribs braced against each other? Which is longer, thigh
bone or shin? Compare shoulder blade with man’s (Fig. 399). Which is
the extra shoulder bone? Compare tail vertebræ with those of extinct
bird, Fig. 290.
]
The _thigh_ hardly projects beyond the skin of the trunk, as may be
noticed in a plucked fowl. The thigh extends forward from the hip joint
(Figs. 286, 299) in order to bring the point of support forward under
the centre of weight. Why are long front toes more necessary than long
hind toes? As the bird must often bring its head to the ground, the hip
joints are near the dorsal surface and the body swings between the two
points of support somewhat like a silver ice pitcher on its two pivots.
Hence stooping, which makes a man so unsteady, does not cause a bird to
lose steadiness.
[Illustration:
FIG. 287.—HAND AND WRIST OF FOWL (after Parker).
_DG._ 1–3, digits; _MC._ 1–3, metacarpals; _CC._ 3, wrist.
]
The =wing= has three divisions which correspond to the upper arm, the
forearm, and the hand of man (Fig. 286). When the wing is folded, the
three divisions lie close alongside one another. Fold your arm in the
same manner. The similarity of the bones of the first and second
divisions to the bones of our upper _arm_ and _forearm_ is very obvious
(Fig. 286). Explain. The _hand_ of a bird is furnished with only three
digits (Fig. 287). The three palm bones (metacarpals) are firmly united
(Fig. 287). This gives firmness to the stroke in flying.
[Illustration:
FIG. 288.—HAND, WRIST (_c_), FOREARM, AND ELBOW OF YOUNG CHICK (after
Parker).
]
That the bird is _descended from animals_ which had the fingers and palm
bones less firmly united is shown by comparing the hands of a _chick_
and of an _adult_ fowl (Figs. 287, 288). The wrist also solidifies with
age, the five carpals of the chick being reduced to two in the fowl
(Figs. 287, 288). The thumb or first digit has a covering of skin
separate from that of the other digits, as may be seen in a plucked
bird. The degenerate hand of the fowl is of course useless as a hand
(what serves in its place?) but it is well fitted for firm support of
the feathers in flying. The two bones of the forearm are also firmly
joined. There are eighteen movable joints in our arm and hand. The bird
has only the three joints which enable it to fold its wing. The wrist
joint is the joint in the forward angle of the wing.
[Illustration:
FIG. 289.—BREASTBONE AND SHOULDER BONES OF CASSOWARY.
]
[Illustration:
FIG. 290.—A FOSSIL BIRD (_archæopteryx_) found in the rocks of a
former geological epoch.
=Question=: Find two resemblances to reptiles in this extinct bird
absent from skeletons of extant birds.
]
Since the fore limbs are taken up with locomotion, the =grasping
function= has been assumed by the _jaws_. How does their shape adapt
them to this use? For the same reason the _neck_ of a bird surpasses the
necks of all other animals in what respect? Is the trunk of a bird
flexible or inflexible? There is thus a _correlation_ between structure
of neck and trunk. Explain. The same correlation is found in which of
the reptiles? (Why does rigidity of trunk require flexibility of neck?)
Why does the length of neck in birds correlate with the length of legs?
Examples? (See Figs. 314, 315, 332.) Exceptions? (Fig. 324.) Why does a
swan or a goose have a long neck, though its legs are short?
[Illustration:
FIG. 291.—QUILL FEATHER.
_D_, downy portion.
]
To make a firm support for the wings the vertebræ of the back are
immovably joined, also there are three bones in each shoulder, the
collar bone, the shoulder blade, and the coracoid bone (Fig. 286). The
collar bones are united (why?) and form the “wishbone” or “pulling
bone.” To furnish surface for the attachment of the large flying muscles
there is a prominent ridge or keel on the breastbone (Fig. 286). It is
lacking in most birds which do not fly (Fig. 289).
The =feathers= are perhaps the most characteristic feature of birds. The
large feathers of the wings and tail are called _quill feathers_. A
quill feather (Fig. 291) is seen to consist of two parts, the _shaft_,
or supporting axis, and the broad _vane_ or web. What part of the shaft
is round? Hollow? Solid? Is the shaft straight? Are the sides of the
vane usually equal in width? Can you tell by looking at a quill whether
it belongs to the wing or the tail, and which wing or which side of the
tail it comes from? Do the quills overlap with the wide side of the vane
above or beneath the next feather? Can you cause two parts of the vane
to unite again by pressing together the two sides of a split in the
vane? Does the web separate at the same place when pulled until it
splits again?
[Illustration:
FIG. 292.—I, CONTOUR FEATHER. II, III, PARTS OF QUILL FEATHER,
enlarged.
]
The hollow part of the shaft of a quill feather is called the _quill_.
The part of the shaft bearing the vane is called the _rachis_ (rā-kis).
The vane consists of slender _barbs_ which are branches of the shaft
(II, Fig. 292). As the name indicates (see dictionary), a barb resembles
a hair. The barbs in turn bear secondary branches called _barbules_, and
these again have shorter branches called _barbicels_ (III, Fig. 292).
These are sometimes bent in the form of hooklets (Fig. 292, III), and
the hooklets of neighbouring barbules interlock, giving firmness to the
vane. When two barbules are split apart, and then reunited by stroking
the vane between the thumb and the finger, the union may be so strong
that a pull upon the vane will cause it to split in a new place next
time.
[Illustration:
FIG. 293.—A DOWN FEATHER, enlarged.
]
There are =four kinds= of feathers, (1) the _quill_ feathers, just
studied; (2) the _contour_ feathers (I, Fig. 292), which form the
general surface of the body and give it its outlines; (3) the _downy_
feathers (Fig. 293), abundant on nestlings and found among the contour
feathers of the adult but not showing on the surface; (4) the _pin_
feathers, which are hair-like, and which are removed from a plucked bird
by singeing. The contour feathers are similar in structure to the quill
feathers. They protect the body from blows, overlap so as to shed the
rain, and, with the aid of the downy feathers, retain the heat, thus
accounting for the high temperature of the bird. The downy feathers are
soft and fluffy, as they possess few or no barbicels; sometimes they
lack the rachis (Fig. 293). The pin feathers are delicate horny shafts,
greatly resembling hairs, but they may have a tuft of barbs at the ends.
[Illustration:
FIG. 294.—DORSAL AND VENTRAL VIEW OF PLUCKED BIRD, showing regions
where feathers grow.
]
A =feather grows= from a small projection (or papilla) found at the
bottom of a depression of the skin. The quill is formed by being moulded
around the papilla. Do you see any opening at the tip of the quill for
blood vessels to enter and nourish the feather? What is in the quill?
(Fig. 291.) The rachis? A young contour or quill feather is inclosed in
a delicate sheath which is cast off when the feather has been formed.
Have you seen the sheath incasing a young feather in a moulting bird?
There are considerable =areas= or tracts on a bird’s skin =without
contour feathers=. Such bare tracts are found along the ridge of the
breast and on the sides of the neck. However, the contour feathers lie
so as to overlap and cover the whole body perfectly (Fig. 294).
[Illustration:
FIG. 295.—WING OF BIRD.
_1_, false quills (on thumb); _2_, primaries; _3_, secondaries;
tertiaries (dark) are one above another at right; _a_, _b_, coverts.
]
The shedding of the feathers is called =moulting=. Feathers, like the
leaves of trees, are delicate structures and lose perfect condition with
age. Hence the annual renewal of the feathers is an advantage. Most
birds shed twice a year, and with many the summer plumage is brighter
coloured than the winter plumage. When a feather is shed on one side,
the corresponding feather on the other side is always shed with it.
(What need for this?) A large _oil gland_ is easily found on the dorsal
side of the tail. How does the bird apply the oil to the feathers?
[Illustration:
FIG. 296.
_A_, point dividing primaries from secondaries; _B_, coverts.
]
[Illustration:
FIG. 297.—CEDAR WAXWING, with regions of body marked.
_S_, forehead; _Sc_, crown (with crest); _Hh_, nape; _K_, throat;
_Br_, breast; _Ba_, lower parts; _R_, back; _Rt_, tail; _B_, tail
coverts; _P_, shoulder feathers (scapulars); _T_, wing coverts;
_HS_, primaries; _AS_, secondaries; _Al_, thumb feathers.
]
In describing and classifying birds, it is necessary to know the names
of the various external =regions= of the body and plumage. These may be
learned by studying Figs. 295, 296, 297, 298. The quills on the hand are
called primaries, those on the forearm are the secondaries, those on the
upper arm are the tertiaries. Those on the tail are called the _tail
quills_. The feathers at the base of the quills are called the
_coverts_. The thumb bears one or more quills called the spurious
quills. Is the wing concave on the lower or the upper side? Of what
advantage is this when the bird is at rest? When it is flying?
[Illustration:
FIG. 298.—PLAN OF BIRD.
_s_, centre of gravity.
]
[Illustration:
FIG. 299.—POSITION OF LIMBS OF PIGEON.
]
=Control of Flight.=—Did you ever see a bird sitting on a swinging limb?
What was its chief means of balancing itself? When flying, what does a
bird do to direct its course upward? Downward? Is the body level when it
turns to either side? Birds with long, pointed wings excel in what
respect? Examples? Birds with great wing surface excel in what kind of
flight? Examples. Name a common bird with short wings which has a
laboured, whirring flight. Is its tail large or small? Does it avoid
obstacles and direct its flight well? Why or why not? When a boat is to
be turned to the right, must the rudder be pulled to the right or to the
left? (The rudder drags in the water and thus pulls the boat around.)
When the bird wishes to go upward, must its tail be turned up or down?
How when it wishes to go down? When a buzzard soars for an hour without
flapping its wings, does it move at a uniform rate? For what does it use
the momentum gained when going with the wind?
[Illustration:
FIG. 300.
_a_, clambering foot of chimney sweep; _b_, climbing foot of
woodpecker; _c_, perching foot of thrush; _d_, seizing foot of hawk;
_e_, scratching foot of pheasant; _f_, stalking foot of kingfisher;
_g_, running foot of ostrich; _h_, wading foot of heron; _i_,
paddling foot of gull; _k_, swimming foot of duck; _l_, steering
foot of cormorant; _m_, diving foot of grebe; _n_, skimming foot of
coot. =Question=: Does any bird use its foot as a hand? (Fig. 320.)
]
=Flying.=—When studying the quill feathers of the wing, you saw that the
wider side of the vane is beneath the feather next behind it. During the
downward stroke of the wing this side of the vane is pressed by the air
against the feather above it and the air cannot pass through the wing.
As the wing is raised the vanes separate and the air passes through. The
convex upper surface of the wing also prevents the wing from catching
air as it is raised. Spread a wing and blow strongly against its lower
surface; its upper surface. What effects are noticed?
Study the =scales= on the leg of a bird (Fig. 300). Why is the leg scaly
rather than feathered from the ankle downward? Which scales are largest?
(Fig. 300.) How do the scales on the front and the back differ? What can
you say of the scales at the bottom of the foot; at the joints of the
toes? Explain. How does the covering of the nails and the bill compare
in colour, texture, hardness, and firmness of attachment with the scales
of the leg?
[Illustration:
FIG. 301.—AN ALTRICAL BIRD, _i.e._ poorly developed at hatching. Young
pigeon, naked, beak too weak for eating.
]
=Draw= an outline of the bird seen from the side. Make drawings of the
head and the feet more detailed and on a larger scale.
[Illustration:
FIG. 302.—A PRECOCIAL BIRD (well developed at hatching). Feathered,
able to run and to pick up food. Precocity is a sign of instinctive
life and low intelligence. A baby is not precocious.
=Question=: Is pigeon or fowl exposed to more dangers in infancy?
]
Why does a goose have more feathers suitable for making pillows than has
a fowl? In what country did the domestic fowl originate? (Encyclopædia.)
Why does a cock crow for dawn? (Consider animal life in jungle.)
=Activities of a Bird.=—Observe a bird _eating_. Does it seem to chew or
break its food before swallowing? Does it have to lift its head in order
to swallow food? To swallow drink? Why is there a difference? After
feeding the bird, can you feel the food in the crop, or enlargement of
the gullet at the base of the neck? (Fig. 304.)
Feel and look for any movements in _breathing_. Can you find how often
it breathes per minute? Place hand under the bird’s wing. What do you
think of its _temperature_; or better, what temperature is shown by a
thermometer held under its wing? Do you see any connection between the
breathing rate and the temperature? Test (as with the crayfish) whether
a bird can _see_ behind its head. Notice the movements of the
nictitating membrane. Does it appear to be transparent?
Watch a bird _fly_ around a closed room and review the questions on
Control of Flight.
_Bend_ a bird’s leg and see if it has any effect upon its toes. Notice a
bird (especially a large fowl) walk, to see if it bends its toes as the
foot is lifted. Pull the rear tendon in a foot cut from a fowl for the
kitchen. Does the bird have to use muscular exertion to _grasp_ a stick
upon which it sits? Why, or why not? When is this bending of the toes by
bending the legs of special advantage to a hawk? To a duck? To a wading
bird? Why is a fowl safe from a hawk if it stands close to a tree?
[Illustration:
FIG 303.—HEAD OF WOODPECKER.
_c_, tongue; _a_, _b_, _d_, hyoid bone; _e_, _q_, windpipe; _f_,
salivary gland.
]
Do you see any signs of teeth in the bird’s jaws? Why are duck’s “teeth”
(so called by children) not teeth? Can the tongue of a bird be pulled
forward? (Fig. 303.) What is its shape? If there is opportunity, dissect
and study the slender, bony (hyoid) apparatus to which the base of the
tongue is attached (Fig. 303), the opening of the windpipe, or trachea,
the slitlike opening of windpipe, which is so narrow as to prevent food
falling into the windpipe.
[Illustration:
FIG. 304.—ANATOMY OF DOVE × ½.
_bk_, keel of breastbone; _G_, _g_, brain; _lr_, windpipe; _lu_, lung;
_h_, heart; _sr_, gullet; _k_, crop; _dr_, glandular stomach; _mm_,
gizzard; _d_, intestine; _n_, kidney; _hl_, ureter; _eil_, openings
of ureter and egg duct into cloaca, _kl_.
]
[Illustration:
FIG. 305.—FOOD TUBE OF BIRD.
_P_, pancreas; _C_, cæca.
=Question=: Identify each part by means of Fig. 304.
]
=The Internal Organs, or Viscera= (Figs. 304 and 305).—The viscera
(vis’se-ra), as in most vertebrates, _include_ the food tube and its
glands; the lungs, the heart, and the larger blood vessels; the kidneys
and bladder and the reproductive organs. The lower part, or gullet, is
enlarged into a _crop_. It is largest in grain-eating birds. It is found
in the V-shaped depression at the angle of the wishbone, just before the
food tube enters the thorax. The food is stored and softened in the
crop. From the crop the food passes at intervals into the glandular
stomach. Close to this is the muscular stomach, or gizzard. Are the
places of entrance and exit on opposite sides of the gizzard, or near
together? (Fig. 304.) Is the lining of the gizzard rough or smooth? Why?
Is the gizzard tough or weak? Why are small stones in the gizzard? Why
do not hawks and other birds of prey need a muscular gizzard? The liver
and pancreas empty their secretions into the intestines by several ducts
a little way beyond the gizzard. Beyond the mouths of two cæca (Fig.
305) the many-coiled intestine empties into the straight rectum, which
terminates in a widened part called the cloaca. Not only the intestine,
but the two ureters of the urinary system and the two genital ducts of
the reproductive system all empty into the cloaca (Figs. 304, 305).
[Illustration:
FIG. 306.—POSITION OF LUNGS AND AIR SACS (Pigeon).
_Tr_, windpipe; _P_, lungs; _Lm_, sac under clavicle with prolongation
(_Lh_) into humerus; _La_, sacs in abdomen.
]
The =lungs= have their rear surfaces attached to the spinal column and
ribs (_lu_, Fig. 304). They are connected with thin-walled, transparent
_air sacs_ which aid in purifying the blood. When inflated with warm
air, they probably make the body of the bird more buoyant. For the
names, location, and shape of several pairs of air sacs, see Fig. 306.
The connection of the air sacs with hollows in the humerus bones is also
shown in the figure. Many of the _bones are hollow_; this adds to the
buoyancy of the bird. The pulmonary artery, as in man, takes dark blood
to the lungs to exchange its carbon dioxide for oxygen. Of two animals
of the same weight, which expends more energy, the one that flies, or
the one that runs the same distance? Does a bird require more oxygen or
less, in proportion to its weight, than an animal that lives on the
ground? Are the vocal chords of a bird higher or lower in the windpipe
than those of a man? (Fig. 307.)
[Illustration:
FIG. 307.—POSITION OF VOCAL CORDS (_str_) OF MAMMAL AND BIRD.
=Question=: Does a fowl ever croak after its head and part of its neck
are cut off? Explain.
]
The heart of a bird, like a man’s heart, has four chambers; hence it
keeps the purified blood separate from the impure blood. Since pure
blood reaches the organs of a bird, oxidation is more perfect than in
the body of any animals yet studied. Birds have higher temperature than
any other class of animals whatsoever. Tell how the jaws, the tail, and
the wings of the fossil bird Archæopteryx differed from living birds
(Fig. 290).
SUGGESTIONS.—In the field work, besides seeking the answers to
definite questions, pupils may be required to hand in a record of the
places and the times of seeing a certain number of birds (20–40) with
the actions and features which made each distinguishable. Also, and
more important, each pupil should hand in a record of a careful and
thorough outdoor study of one common species (see below) as regards
habits, nesting, relation to environment, etc.
FIELD STUDY OF A COMMON SPECIES.—(_For written report._) Name of
species. _Haunts._ Method of locomotion when not flying. _Flying_
(rate, sailing, accompanying sound if any, soaring).
What is the _food_? How obtained? _Association_ with birds of its own
species. _Relation_ to birds of other species.
Where does it build its _nest_? Why is such a situation selected? Of
what is the nest built? How is the material carried, and how built
into the nest? Does the bird’s body fill the nest?
Describe the _eggs_. Does the male bird ever sit or otherwise assist
female before hatching? Does it assist after hatching? How long is
taken to lay a sitting of eggs? How long before the birds are hatched?
_When hatched_ are they helpless? Blind? Feathered? (Figs. 301, 302.)
Do the nestlings require much food? How many times in an hour is food
brought? How distributed? Even if the old birds sometimes eat fruit do
they take fruit to the young? What do they feed to the young? How long
before they leave the nest? Do the parents try to teach them to fly?
Do the parents care for them after the nest is left? What songs or
calls has the bird?
[Illustration:
FIG. 308.—EUROPEAN TOMTIT’S NEST.
What are the advantages of its shape?
]
[Illustration:
FIG. 309.—TAILOR BIRD’S NEST (India).
Instinct for nest building highly perfected.
]
=General Field Study.=—(_For written report._) Name the best and poorest
flyers you know; birds that fly most of the time; birds that seldom fly.
Observe birds that pair; live in flocks. Does their sociability vary
with the season? Do you ever see birds quarrelling? Fighting? What birds
do you observe whipping or driving birds larger than themselves? Which
parent do young birds most resemble? Name the purposes for which birds
sing. Which senses are very acute? Why? Dull? Why? Can you test your
statements by experiment? A partridge usually sits with 18 to 24 eggs in
nest. About how long after laying first egg before sitting begins? Do
several partridge hens lay in the same nest?
[Illustration:
FIG. 310.—HOUSE WREN.
]
_Haunts._—Name some birds that are found most often in the following
localities: about our homes, in gardens and orchards, fields and
meadows, in bushes, in the woods, in secluded woods, around streams of
water, in thickets, in pine woods.
_Size._—Name birds as large as a robin or larger, nearly as large, half
as large, much smaller.
_Colours._—Which sex is more brilliant? Of what advantage are bright
colours to one sex? Of what advantage are dull colours to the other sex?
Which have yellow breasts, red patch on heads, red or chestnut breasts,
blue backs, black all over?
_Habits._—Name the birds that walk, jump, swim, live in flocks, sing
while flying, fly in undulations, in circles, have laboured flight.
=Economic Importance of Birds.=—Farmers find their most valuable allies
in the class _aves_, as birds are the deadliest enemies of insects and
gnawing animals. To the innumerable robbers which devastate our fields
and gardens, nature opposes the army of birds. They are less numerous
than insects and other robbers, it is true, but they are skilful and
zealous in pursuit, keen of eye, quick, active, and remarkably
voracious. The purely insectivorous birds are the most useful, but the
omnivorous and graminivorous birds do not disdain insects. _The perchers
and the woodpeckers should be protected most carefully._ The night birds
of prey (and those of the day to a less degree) are very destructive to
field mice, rabbits, and other gnawing animals. Some ignorant farmers
complain continually about the harm done by birds. To destroy them is as
unwise as it would be to destroy the skin which protects the human body
because it has a spot upon it! It cannot be repeated too plainly that to
hunt useful birds is a wrong and mischievous act, and it is stupid and
barbarous to destroy their nests.
[Illustration:
FIG. 311.—SCREECH OWL (_Megascops asio_).
=Question=: Compare posture of body, position of eyes, and size of
eyes, with other birds.
]
[Illustration:
FIG. 312.—GOSHAWK, or chicken hawk.
]
Injurious birds are few. Of course birds which are the enemies of other
birds are enemies of mankind, but examples are scarce (some owls and
hawks). Many birds of prey are classed thus by mistake. Sparrow-hawks,
for instance, do not eat birds except in rare instances; they feed
chiefly upon insects. A sparrow hawk often keeps watch over a field
where grasshoppers are plentiful and destroys great numbers of them.
When a bird is killed because it is supposed to be injurious, the crop
should always be examined, and its contents will often surprise those
who are sure it is a harmful bird. The writer once found two frogs,
three grasshoppers, and five beetles that had been swallowed by a
“chicken hawk” killed by an irate farmer, but no sign of birds having
been used for food. Fowls should not be raised in open places, but among
trees and bushes, where hawks cannot swoop. Birds which live exclusively
upon fish are, of course, opposed to human interests. Pigeons are
destructive to grain; eagles feed chiefly upon other birds.
[Illustration:
FIG. 313.—ROAD RUNNER, or chaparral bird (Tex. to Cal.). What order?
(Key, p. 177.)
]
If the birds eat the grapes, do not kill the birds, but plant more
grapes. People with two or three fruit trees or a small garden are the
only ones that lose a noticeable amount of food. We cut down the forests
from which the birds obtain part of their food. We destroy insect pests
at great cost of spraying, etc. The commission the birds charge for such
work is very small indeed. (See pages 177–183.)
[Illustration:
FIG. 314.—WOOD DUCK, male (_Aix sponsa_). Nests in hollow trees
throughout North America. Also called summer duck in South. Why?
]
The =English sparrow= is one bird of which no good word may be said.
Among birds, it holds the place held by rats among beasts. It is crafty,
quarrelsome, thieving, and a nuisance. It was imported in 1852 to eat
moths. The results show how ignorant we are of animal life, and how slow
we should be to tamper with the arrangements of nature. In Southern
cities it produces five or six broods each year with four to six young
in each brood. (Notice what it feeds its young.) It fights, competes
with and drives away our native useful birds. It also eats grain and
preys upon gardens. They have multiplied more in Australia and in North
America than in Europe, because they left behind them their native
enemies and their new enemies (crows, jays, shrikes, etc.) have not yet
developed, to a sufficient extent, the habit of preying upon them.
Nature will, perhaps, after a long time, restore the equilibrium
destroyed by presumptuous man.
=Protection of Birds.=—1. Leave as many trees and bushes standing as
possible. Plant trees, encourage bushes.
2. Do not keep a cat. A mouse trap is more useful than a cat. A tax
should be imposed upon owners of cats.
3. Make a bird house and place it on a pole; remove bark from pole that
cats may not climb it; or put a broad band of tin around the pole.
4. Scatter food in winter. In dry regions and in hot weather keep a
shallow tin vessel containing water on the roof of an outhouse, or in an
out-of-the-way place, for shy birds.
5. Do not wear feathers obtained by the killing of birds. What feathers
are not so obtained?
6. Report all violators of laws for protection of birds.
7. Destroy English sparrows.
[Illustration:
FIG. 315.—GREAT BLUE HERON. In flight, balancing with legs.
]
=Migration.=—Many birds, in fact most birds, migrate to warmer climates
to spend the winter. Naturalists were once content to speak of the
migration of birds as a wonderful instinct, and made no attempt to
explain it. As birds have the warmest covering of all animals, the
winter migration is not for the purpose of escaping the cold; it is
probably to escape starvation, because in cold countries food is largely
hidden by snow in winter. On the other hand, if the birds remained in
the warm countries in summer, the food found in northern countries in
summer would be unused, while they would have to compete with the
numerous tropical birds for food, and they and their eggs would be in
danger from snakes, wild cats, and other beasts of prey so numerous in
warm climates. These are the best reasons so far given for migration.
[Illustration:
FIG. 316.—EUROPEAN SWALLOWS (_Hirundo urbica_), assembling for autumn
flight to South.
]
The =manner= and =methods of migration= have been studied more carefully
in Europe than in America. Migration is not a blind, infallible
instinct, but the route is learned and taught by the old birds to the
young ones; they go in flocks to keep from losing the way (Fig. 316);
the oldest and strongest birds guide the flocks (Fig. 317). The birds
which lose their way are young ones of the last brood, or mothers that
turn aside to look for their strayed young. The adult males seldom lose
their way unless scattered by a storm. Birds are sometimes caught in
storms or join flocks of another species and arrive in countries
unsuited for them, and perish. For example, a sea or marsh bird would
die of hunger on arriving in a very dry country.
The =landmarks of the route= are mountains, rivers, valleys, and coast
lines. This knowledge is handed down from one generation to another. It
includes the location of certain places on the route where food is
plentiful and the birds can rest in security. Siebohm and others have
studied the routes of migration in the Old World. The route from the
nesting places in northern Europe to Africa follows the Rhine, the Lake
of Geneva, the Rhone, whence some species follow the Italian and others
the Spanish coast line to Africa. Birds choose the lowest mountain
passes. The Old World martin travels every year from the North Cape to
the Cape of Good Hope and back again! Another route has been traced from
Egypt along the coast of Asia Minor, the Black Sea and Ural Mts. to
Siberia.
[Illustration:
FIG. 317.—CRANES MIGRATING, with leader at point of V-shaped line.
]
=Field Study of Migration.=—Three columns may be filled on the
blackboard in an unused corner, several months in spring or fall being
taken for the work. _First_ column, birds that stay all the year.
_Second_ column, birds that come from the south and are seen in summer
only. _Third_ column, birds that come from the north and are seen in
winter only. Exact dates of arrival and departure and flight overhead
should be recorded in notebooks. Many such records will enable American
zoologists to trace the migration routes of our birds.
[Illustration:
FIG. 318.—APTERYX, of New Zealand. Size of a hen, wings and tail
rudimentary, feathers hair-like.
]
=Moulting.=—How do birds arrange their feathers after they have been
ruffled? Do they ever bathe in water? In dust? Dust helps to remove old
oil. At what season have birds the brightest feathers? Why? Have you
ever seen evidence of the moulting of birds? Describe the moulting
process (page 120).
[Illustration:
FIG. 319.—GOLDEN, SILVER, AND NOBLE PHEASANTS, males. Order? (Key, p.
177.) Ornaments of males, brightest in season of courtship, are due
to sexual selection (Figs. 321–7–9, 333).
]
[Illustration:
FIG. 320. COCKATOO.
]
[Illustration:
FIG. 321.—BIRD OF PARADISE (Asia).
]
=Adaptations for Flying.=—Flight is the most difficult and
energy-consuming method of moving found among animals, and careful
adjustment is necessary. For balancing, the heaviest muscles are placed
at the lower and central portion of the body. These are the flying
muscles, and in some birds (humming birds) they make half of the entire
weight. Teeth are the densest of animal structures; teeth and the strong
chewing muscles required would make the head heavy and balancing
difficult; hence the chewing apparatus is transferred to the heavy
gizzard near the centre of gravity of the body. The bird’s neck is long
and excels all other necks in flexibility, but it is very slender
(although apparently heavy), being inclosed in a loose, feathered skin.
A cone is the best shape to enable the body to penetrate the air, and a
small neck would destroy the conical form. The internal organs are
compactly arranged and rest in the cavity of the breast bone. The
bellowslike air sacs filled with warm air lighten the bird’s weight. The
bones are hollow and very thin. The large tail quills are used by the
bird only in guiding its flight up and down, or balancing on a limb. The
feet also aid a flying bird in balancing. The wing is so constructed as
to present to the air a remarkably large surface compared with the small
bony support in the wing skeleton. Are tubes ever resorted to by human
architects when lightness combined with strength is desired? Which
quills in the wing serve to lengthen it? (Fig. 296.) To broaden it? Is
flight more difficult for a bird or for a butterfly? Which of them do
the flying machines more closely resemble? Can any bird fly for a long
time without flapping its wings?
[Illustration:
FIG. 322.—HERRING GULL. (Order?)
]
=Exercise in the Use of the Key.=—Copy this list and write the name of
the order to which each of the birds belongs. (Key, page 177.)
Cockatoo (Fig. 320)
Sacred Ibis (Fig. 328)
Screech Owl (Fig. 311)
Nightingale (Fig. 325)
Top-knot Quail (Fig. 329)
Wren (Fig. 310)
Apteryx (Fig. 318)
Lyre bird (Fig. 327)
Road Runner (Fig. 313)
Ostrich (Fig. 332)
Penguin (Fig. 330)
Pheasant (Fig. 319)
Wood Duck (Fig. 314)
Jacana (Fig. 324)
Sea Gull (Fig. 322)
Heron (Fig. 315)
Hawk (Fig. 312)
KEY, OR TABLE, FOR CLASSIFYING BIRDS (_Class Aves_) INTO ORDERS
ORDERS
A_{1} =Wings not suited for flight=, 2 or 3 toes RUNNERS
A_{2} =Wings suited for flight= (except the penguin)
B_{1} _Toes united by a web for swimming, legs short_
C_{1} Feet placed far back; wings short, tip not DIVERS
reaching to base of tail (Fig. 300)
C_{2} Bill flattened, horny plates under margin of BILL-STRAINERS
upper bill (Fig. 323)
C_{3} Wings long and pointed, bill slender SEA-FLIERS
C_{4} All four toes webbed, bare sac under GORGERS
throat
B_{2} _Toes not united by web for swimming_
C_{1} Three front toes, neck and legs long, tibia WADERS
(shin, or “drumstick”) partly bare
C_{2} Three front toes, neck and legs not long
D_{1} Claws short and blunt (e, Fig. 300)
E_{1} Feet and beak stout, young feathered, base SCRATCHERS
of hind toe elevated
E_{2} Feet and beak weak, young naked MESSENGERS
D_{2} Claws long, curved and sharp, bill hooked and ROBBERS
sharp
D_{3} Claws long, slightly curved, bill nearly PERCHERS
straight
C_{3} Two front and two hind toes (Fig. 300)
D_{1} Bill straight, feet used for climbing FOOT-CLIMBERS
D^1 Bill hooked, both bill and feet used for BILL-CLIMBERS
climbing
=The Food of Birds.=—Extracts from Bulletin No. 54 (United States Dept.
of Agriculture), by F. E. L. Beal.
[Illustration:
FIG. 323.—HEAD OF DUCK.
]
The practical value of birds in controlling insect pests should be
more generally recognized. It may be an easy matter to exterminate the
birds in an orchard or grain field, but it is an extremely difficult
one to control the insect pests. It is certain, too, that the value of
our native sparrows as weed destroyers is not appreciated. Weed seed
forms an important item of the winter food of many of these birds, and
it is impossible to estimate the immense numbers of noxious weeds
which are thus annually destroyed. If crows or blackbirds are seen in
numbers about cornfields, or if woodpeckers are noticed at work in an
orchard, it is perhaps not surprising that they are accused of doing
harm. Careful investigation, however, often shows that they are
actually destroying noxious insects; and also that even those which do
harm at one season may compensate for it by eating insect pests at
another. Insects are eaten at all times by the majority of land birds.
During the breeding season most kinds subsist largely on this food,
and rear their young exclusively upon it.
[Illustration:
FIG. 324.—JACANA. (Mexico, Southwest Texas, and Florida.)
=Questions=: What appears to be the use of such long toes? What
peculiarity of wing? head?
]
=Partridges.=—Speaking of 13 birds which he shot, Dr. Judd says: These
13 had taken weed seed to the extent of 63 per cent of their food.
Thirty-eight per cent was ragweed, 2 per cent tick trefoil, partridge
pea, and locust seeds, and 23 per cent seeds of miscellaneous weeds.
About 14 per cent of the quail’s food for the year consists of animal
matter (insects and their allies). Prominent among these are the
Colorado potato beetle, the striped squash beetle, the
cottonboll-weevil, grasshoppers. As a weed destroyer the quail has
few, if any, superiors. Moreover, its habits are such that it is
almost constantly on the ground, where it is brought in close contact
with both weed seeds and ground-living insects. It is a good ranger,
and, if undisturbed, will patrol every day all the fields in its
vicinity as it searches for food.
[Illustration:
FIG. 325.—NIGHTINGALE, × ⅓.
]
[Illustration:
FIG. 326.—SKYLARK, × ⅓.
]
Two celebrated European songsters.
=Doves=.—The food of the dove consists of seeds of weeds, together
with some grain. The examination of the contents of 237 stomachs shows
that over 99 per cent of the food consists wholly of vegetable matter.
=Cuckoos.=—An examination of the stomachs of 46 black-billed cuckoos,
taken during the summer months, showed the remains of 906
caterpillars, 44 beetles, 96 grasshoppers, 100 sawflies, 30 stink
bugs, and 15 spiders. Of the yellow-billed cuckoos, or “rain-crow,”
109 stomachs collected from May to October, inclusive, were examined.
The contents consisted of 1,865 caterpillars, 93 beetles, 242
grasshoppers, 37 sawflies, 69 bugs, 6 flies, and 86 spiders.
[Illustration:
FIG. 327.—LYRE BIRD, male.
]
=Woodpeckers.=—Careful observers have noticed that, excepting a single
species, these birds rarely leave any conspicuous mark on a healthy
tree, except when it is affected by wood-boring larvæ, which are
accurately located, dislodged, and devoured by the woodpecker. Of the
flickers’ or yellow-hammers’ stomachs examined, three were completely
filled with ants. Two of the birds each contained more than 3,000
ants, while the third bird contained fully 5,000. These ants belong to
species which live in the ground. It is these insects for which the
flicker is reaching when it runs about in the grass. The
yellow-bellied woodpecker or sapsucker (_Sphyrapicus varius_) was
shown to be guilty of pecking holes in the bark of various forest
trees, and sometimes in that of apple trees, and of drinking the sap
when the pits became filled. It has been proved, however, that besides
taking the sap the bird captures large numbers of insects which are
attracted by the sweet fluid, and that these form a very considerable
portion of its diet. The woodpeckers seem the only agents which can
successfully cope with certain insect enemies of the forests, and, to
some extent, with those of fruit trees also. For this reason, if for
no other, they should be protected in every possible way.
[Illustration:
FIG. 328.—SACRED IBIS. (Order?)
]
=The night hawk, or “bull bat,”= may be seen most often soaring high
in air in the afternoon or early evening. It nests upon rocks or bare
knolls and flat city roofs. Its food consists of insects taken on the
wing; and so greedy is the bird that when food is plentiful, it fills
its stomach almost to bursting. Ants (except workers) have wings and
fly as they are preparing to propagate. In destroying ants night hawks
rank next to, or even with, the woodpeckers, the acknowledged
ant-eaters among birds.
[Illustration:
FIG. 329.—TOP-KNOT QUAIL, or California Partridge. (West Texas to
California.)
]
=The kingbird, or martin=, is largely insectivorous. In an examination
of 62 stomachs of this bird, great care was taken to identify every
insect or fragment that had any resemblance to a honeybee; as a
result, 30 honeybees were identified, of which 29 were males or drones
and 1 was a worker.
=Blue Jay.=—In an investigation of the food of the blue jay 300
stomachs were examined, which showed that animal matter comprised 24
per cent and vegetable matter 76 per cent of the bird’s diet. The
jay’s favourite food is mast (_i.e._ acorns, chestnuts, chinquapins,
etc.), which was found in 200 of the 300 stomachs, and amounted to
more than 42 per cent of the whole food.
[Illustration:
FIG. 330.—PENGUIN OF PATAGONIA. Wings used as flippers for swimming.
]
=Crow.=—That he does pull up sprouting corn, destroy chickens, and rob
the nests of small birds has been repeatedly proved. Nor are these all
of his sins. He is known to eat frogs, toads, salamanders, and some
small snakes, all harmless creatures that do some good by eating
insects. Experience has shown that they may be prevented from pulling
up young corn by tarring the seed, which not only saves the corn but
forces them to turn their attention to insects. May beetles,
“dorbugs,” or June bugs, and others of the same family constitute the
principal food during spring and early summer, and are fed to the
young in immense quantities.
=Ricebird.=—The annual loss to rice growers on account of bobolinks
has been estimated at $2,000,000.
[Illustration:
FIG. 331.—Umbrella holding the nests of social weaver bird of Africa;
polygamous.
]
=Meadow Lark.=—Next to grasshoppers, beetles make up the most
important item of the meadow lark’s food, amounting to nearly 21 per
cent. May is the month when the dreaded cut-worm begins its deadly
career, and then the lark does some of its best work. Most of these
caterpillars are ground feeders, and are overlooked by birds which
habitually frequent trees, but the meadow lark finds and devours them
by thousands.
=Sparrows.=—Examination of many stomachs shows that in winter the tree
sparrow feeds entirely upon seeds of weeds. Probably each bird
consumes about one fourth of an ounce a day. Farther south the tree
sparrow is replaced in winter by the white-throated sparrow, the
white-crowned sparrow, the fox sparrow, the song sparrow, the field
sparrow, and several others; so that all over the land a vast number
of these seed eaters are at work during the colder months reducing
next year’s crop of worse than useless plants.
[Illustration:
FIG. 332.—AFRICAN OSTRICH, × ¹⁄₂₀. (order?)
]
=Robin.=—An examination of 500 stomachs shows that over 42 per cent of
its food is animal matter, principally insects, while the remainder is
made up largely of small fruits or berries. Vegetable food forms
nearly 58 per cent of the stomach contents, over 47 per cent being
wild fruits, and only a little more than 4 per cent being possibly
cultivated varieties. Cultivated fruit amounting to about 25 per cent
was found in the stomachs in June and July, but only a trifle in
August. Wild fruit, on the contrary, is eaten in every month, and
constitutes during half the year a staple food.
=Questions.=—Which of these birds are common in your neighbourhood?
Which of them according to the foregoing report are plainly injurious?
Clearly beneficial? Doubtful? Which are great destroyers of weed
seeds? Wood-borers? Ants? Grain? Why is the destruction of an ant by a
night hawk of greater benefit than the destruction of an ant by a
woodpecker? Name the only woodpecker that injures trees. If a bird
eats two ounces of grain and one ounce of insects, has it probably
done more good or more evil?
CHAPTER XIV
MAMMALS
SUGGESTIONS.—A tame rabbit, a house cat, or a pet squirrel may be
taken to the school and observed by the class. Domestic animals may be
observed at home and on the street. A study of the teeth will give a
key to the life of the animal, and the teacher should collect a few
mammalian skulls as opportunities offer. The pupils should be required
to identify them by means of the chart of skulls (p. 194). If some
enthusiastic students fond of anatomy should dissect small mammals,
the specimens should be killed with chloroform, and the directions for
dissection usual in laboratory works on this subject may be followed.
There is a brief guide on page 223. The following outline for the
study of a live mammal will apply almost as well to the rabbit or the
squirrel as to the cat.
=The Cat.=—The house cat (_Felis domestica_) is probably descended from
the Nubian cat (_Felis maniculata_, Fig. 333) found in Africa. The wild
species is about half as large again as the domestic cat, grayish brown
with darker stripes; the tail has dark rings. The lynx, or wild cat of
America (_Lynx rufus_), is quite different. Compare the figures (333,
335) and state three obvious differences. To which American species is
the house cat closer akin, the lynx (Fig. 335) or the ocelot (Fig. 334)?
The domestic cat is found among all nations of the world. What is
concluded, as to its nearest relatives, from the fact that the Indians
had no cats when America was discovered? It was considered sacred by the
ancient Egyptians, and after death its body was embalmed.
The =body of the cat= is very flexible. It may be divided into five
regions, head, neck, trunk, tail, and limbs. Its eyes have the same
parts as the eyes of other mammals. Which part of its eye is most
peculiar? (Fig. 333.) What part is lacking that is present in birds? How
are the eyes especially adapted for seeing at night? Does the pupil in
the light extend up or down or across the iris? Does it ever become
round?
[Illustration:
FIG. 333.—WILD CAT OF AFRICA (_Felis maniculata_), × ⅛.
]
What is the shape and the position of the _ears_? Are they large or
small compared with those of most mammals? They are fitted best for
catching sound from what direction? What is thus indicated in regard to
the cat’s habits? (Compare with ears of rabbit.) Touch the _whiskers_ of
the cat. What result? Was it voluntary or involuntary motion? Are the
_nostrils_ relatively large or small compared with those of a cow? Of
man?
Is the _neck_ long or short? Animals that have long fore legs usually
have what kind of neck? Those with short legs? Why? How many _toes_ on a
fore foot? Hind foot? Why is this arrangement better than the reverse?
Some mammals are sole walkers (_plantigrade_), some are toe walkers
(_digitigrade_). To which kind does the cat belong? Does it walk on the
ends of the toes? Does it walk with all the joints of the toes on the
ground? Where is the _heel_ of the cat? (Fig. 334.) The _wrist_? To make
sure of the location of the wrist, begin above: find the shoulder blade,
the upper arm (one or two bones?), the lower arm (one or two bones?),
the wrist, the palm, and the fingers (Fig. 337). Is the heel bone
prominent or small?
[Illustration:
FIG. 334.—OCELOT (_Felis pardalis_), of Texas and Mexico. × ⅑.
]
In what direction does the _knee_ of the cat point? The heel? The elbow?
The wrist? Compare the front and the hind _leg_ in length; straightness;
heaviness; number and position of toes; sharpness of the _claws_. What
makes the _dog’s claws_ duller than a cat’s? What differences in habit
go with this? Judging from the toe that has become useless on the fore
foot of the cat, which toe is lacking in the hind foot? Is it the cat’s
thumb or little finger that does not touch the ground? (Fig. 337.)
Locate on your own hand the parts corresponding to the pads on the
forefoot of a cat. Of what use are soft pads on a cat’s foot?
Some animals have short, soft =fur= and long, coarse over hair. Does the
cat have both? Is the cat’s fur soft or coarse? Does the fur have a
colour near the skin different from that at the tip? Why is hair better
suited as a covering for the cat than feathers would be? Scales? Where
are long, stiff bristles found on the cat? Their length suggests that
they would be of what use to a cat in going through narrow places? Why
is it necessary for a cat to be noiseless in its movements?
[Illustration:
FIG. 335.—LYNX (_Lynx rufus_). The “Bob-tailed cat” (North America).
]
Observe the =movements of the cat=.—Why cannot a cat come down a tall
tree head foremost? Did you ever see a cat catch a bird? How does a cat
approach its prey? Name a jumping insect that has long hind legs; an
amphibian; several mammals (Figs. 362, 374). Does a cat ever trot?
Gallop? Does a cat chase its prey? When does the cat move with its heel
on the ground? The claws of a cat are withdrawn by means of a tendon
(see Fig. 338). Does a cat seize its prey with its mouth or with its
feet.?
How does a cat make the purring sound? (Do the lips move? The sides?)
How does a cat drink? Do a cat and dog drink exactly the same way? Is
the cat’s tongue rough or smooth? How is the tongue used in getting the
flesh off close to the bone? Can a cat clean a bone entirely of meat?
[Illustration:
FIG. 336.—JAGUAR, of tropical America.
]
In what state of development is a newly born kitten? With what does the
cat _nourish its young_? Name ten animals of various kinds whose young
are similarly nourished. What is this class of animals called? Why does
a cat bend its back when it is frightened or angry? Does _a cat or a dog
eat_ a greater variety of food? Which refuses to eat an animal found
dead? Will either bury food for future use? Which is sometimes
troublesome on account of digging holes in the garden? Explain this
instinct. Which lived a solitary life when wild? Which had a definite
haunt, or home? Why are dogs more sociable than cats? A dog is more
devoted to his master. Why? A cat is more devoted to its home, and will
return if carried away. Why? Why does a dog turn around before lying
down? (Consider its original environment.)
[Illustration:
FIG. 337.—SKELETON OF CAT.
]
=The Skeleton= (Fig. 337).—Compare the _spinal column_ of a cat in form
and flexibility with the spinal column of a fish, a snake, and a bird.
The _skull_ is joined to the spinal column by two knobs (or _condyls_),
which fit into sockets in the first vertebra. Compare the jaws with
those of a bird and a reptile. There is a prominent ridge in the temple
to which the powerful chewing muscles are attached. There is also a
ridge at the back of the head where the muscles which support the head
are attached (Fig. 348).
[Illustration:
FIG. 338.—CLAW OF CAT (1) retracted by ligament, and (2) drawn down by
muscle attached to lower tendon.
]
Count the _ribs_. Are there more or fewer than in man? The breastbone is
in a number of parts, joined, like the vertebræ, by cartilages. Compare
it with a bird’s sternum; why the difference? The shoulder girdle, by
which the front legs are attached to the trunk, is hardly to be called a
girdle, as the collar bones (clavicles) are rudimentary. (They often
escape notice during dissection, being hidden by muscles.) The shoulder
blades, the other bones of this girdle, are large, but relatively not so
broad toward the dorsal edge as human shoulder blades. The clavicles are
tiny because they are useless. Why does the cat not need as movable a
shoulder as a man? The pelvic, or hip girdle, to which the hind legs are
attached, is a rigid girdle, completed above by the spinal column, to
which it is immovably joined. Thus the powerful hind legs are joined to
the most rigid portion of the trunk.
=Mammals.=—The cat belongs to the _class Mammalia_ or mammals. The
characteristics of the class are that the young are not hatched from
eggs, but _are born alive, and nourished with milk_ (hence have lips),
and the _skin is covered with hair_. The milk glands are situated
ventrally. The position of the class in the animal kingdom was shown
when the cow was classified (p. 9). Their care for the young, their
intelligence, and their ability to survive when in competition with
other animals, causes the mammals to be considered the highest class in
the animal kingdom.
According to these tests, what class of vertebrates should _rank next to
mammals_? Compare the heart, the lungs, the blood, and the parental
devotion of these two highest classes of animals.
[Illustration:
FIG. 339.—SKELETON OF LION (cat family).
]
=The first mammals=, which were somewhat like small opossums, appeared
millions of years ago, when the world was inhabited by giant reptiles.
These reptiles occupied the water, the land, and the air, and their
great strength and ferocity would have prevented the mammals from
multiplying (for at first they were small and weak), but the mammals
carried their young in a pouch until able to care for themselves, while
the reptiles laid eggs and left them uncared for. The first mammals used
reptilian eggs for food, though they could not contend with the great
reptiles. Because birds and mammals are better parents than reptiles,
they have conquered the earth, and the reptiles have been forced into
subordination, and have become smaller and timid.
[Illustration:
FIG. 340.—WALRUS (_Trichechus rosmarus_).
]
=Classification of Mammals=.—Which two have the closest _resemblances_
in the following lists: Horse, cow, deer. Why? Cat, cow, bear. Why?
Monkey, man, sheep. Why? Rat, monkey, squirrel. Why? Giraffe, leopard,
camel. Why? Walrus, cat, cow. Why? Check the five mammals in the
following lists that form a group _resembling one another most closely_:
Lion, bear, pig, dog, squirrel, cat, camel, tiger, man. State your
reasons. Giraffe, leopard, deer, cow, rat, camel, hyena, horse, monkey.
State reasons.
[Illustration:
FIG. 341.—WEASEL, in summer; in Canada in winter it is all white but
tip of tail.
]
[Illustration:
FIG. 342.—FOOT OF BEAR (_Plantigrade_).
]
=Teeth and toes= are the basis for subdividing the class mammalia into
orders. Although the breathing, the circulation, and the internal organs
and processes are similar in all mammals, the external organs vary
greatly because of the varying environments of different species. The
internal structure enables us to place animals together which are
essentially alike; _e.g._ the whale and man are both mammals, since they
resemble in breathing, circulation, and multiplication of young. The
external organs guide us in separating the class into orders. The teeth
vary according to the food eaten. The feet vary according to use in
obtaining food or escaping from enemies. This will explain the
difference in the length of legs of lion and horse, and of the forms of
the teeth in cat and cow. Make a careful study of the teeth and the
limbs as shown in the figures and in all specimens accessible. Write out
the dental formulas as indicated at the top of page 194. The numerals
above the line show the number of upper teeth, those below the line show
the number of lower teeth, in one half of the jaw. They are designated
as follows: _I_, incisors; _C_, canine; _M_, molars. Multiplying by two
gives the total number. Which skulls in the chart have the largest
canines? Why? The smallest, or none at all? Why? Compare the molars of
the cow, the hog, and the dog. Explain their differences. In which
skulls are some of the molars lacking? Rudimentary? Why are the teeth
that do not touch usually much smaller than those that do?
[Illustration:
FIG. 343.—POLAR BEAR (_Ursus maritimus_).
]
KEY, OR TABLE,
FOR CLASSIFYING
MAMMALS (_class
Mammalia_) INTO
ORDERS
│ ORDERS │
=A_{1} Imperfect Mammals=, young hatched │
or prematurely born │
│B_{1} Jaws a birdlike beak, _Mon’otremes_
│ egg-laying
│B_{2} Jaws not beaklike, young _Marsu’pials_
│ carried in pouch
=A_{2} Perfect Mammals=, young not │
hatched, nor prematurely born │
B_{1} │C_{1} Front part of both jaws _Eden’tates_
_Digits │ lack teeth
with │
claws_ │
│C_{2} Teeth with sharp points _Insect’ivors_
„ │ for piercing shells of
│ insects
│C_{3} Canines very long, _Car’nivors_
„ │ molars suited for
│ tearing
„ │C_{4} Canines lacking, _Rodents_
│ incisors very large
B_{2} │C_{1} Head large; carnivorous _Ceta’ceans_
_Digits │
not │
distinct_│
„ │C_{2} Head small; herbivorous _Sire’neans_
B_{3} │C_{1} Five toes, nose _Proboscid’eans_
_Digits │ prolonged into a snout
with │
nails or │
hoofs_ │
„ │C_{2} Toes odd number, less _E’quines_ │_Ungulates_
│ than five │
│C_{3} Toes even number, upper _Ru’minants_ │
„ │ front teeth lacking, │ „
│ chew the cud │
│C_{4} Toes even number, upper _Swine_ │
„ │ front teeth present, │ „
│ not cud-chewers │
„ │C_{5} All limbs having hands _Quad’rumans_
„ │C_{6} Two limbs having hands _Bi’mans_
=Exercise in Classification=.—Copy the following list, and by
reference to figures write the name of its order after each mammal:—
Ape (Figs. 405, 406)
Rabbit (Fig. 345)
Dog (Figs. 356, 408)
Hog (Figs. 357, 393)
Bat (Figs. 347, 370)
Cat (Figs. 337, 348)
Armadillo (Figs. 349, 365)
Cow (Figs. 344, 386)
Walrus (Fig. 340)
Monkey (Figs. 352, 401)
Horse (Figs. 355, 395)
Ant-eater (Figs. 354, 364)
Antelope (Fig. 391)
Mole (Figs. 367, 368)
Beaver (Figs. 372, 373)
Duckbill (Fig. 359)
Tapir (Fig. 384)
Dolphin (Figs. 379, 397)
Use chart of skulls and Figs. 381, 382, 395–400 in working out this
exercise.
Man’s dental formula is (_M_ ⁵⁄₅, _C_ ¹⁄₁, _I_ ²⁄₂)^2 = 32.
In like manner fill out formulas below:—
Cow (_M_—_C_—_I_—)^2 = 32
Rabbit (_M_—_C_—_I_—)^2 = 28
Walrus (_M_—_C_—_I_—)^2 = 34
Bat (_M_—_C_—_I_—)^2 = 34
Cat (_M_—_C_—_I_—)^2 = 30
Armadillo (_M_—_C_—_I_—)^2 = 28
Horse (_M_—_C_—_I_—)^2 = 40
Whale (_M_—_C_—_I_—)^2 = 0
Am. Monkey (_M_—_C_—_I_—)^2 = 36
Sloth (_M_—_C_—_I_—)^2 = 18
Ant-eater (_M_—_C_—_I_—)^2 = 0
Dog (_M_—_C_—_I_—)^2 = 42
Hog (_M_—_C_—_I_—)^2 = 44
Sheep (_M_—_C_—_I_—)^2 = 32
[Illustration:
FIG. 344.—Skull and front of lower jaw of COW.
]
[Illustration:
FIG. 345.—RABBIT. _A_, _B_, incisors; _C_, molars
]
[Illustration:
FIG. 346.—WALRUS (see Fig. 341).
]
[Illustration:
FIG. 347.—BAT.
]
[Illustration:
FIG. 348.—CAT.
]
[Illustration:
FIG. 349.—ARMADILLO.
]
[Illustration:
FIG. 350.—HORSE (front of jaw).
]
[Illustration:
FIG. 351.—GREENLAND WHALE.
]
[Illustration:
FIG. 352.—AMERICAN MONKEY.
]
[Illustration:
FIG. 353.—SLOTH (Fig. 363).
]
[Illustration:
FIG. 354.—ANT-EATER (Fig. 364).
]
[Illustration:
FIG. 355.—HORSE.
]
[Illustration:
FIG. 356.—DOG. Upper (_A_) and lower (_B_) jaw.
]
[Illustration:
FIG. 357.—HOG.
]
[Illustration:
FIG. 358.—SHEEP.
]
[Illustration:
FIG. 359.—DUCKBILL (_Ornithorhynchus paradoxus_).
]
The =lowest order of mammals= contains only two species, the duckbill
and the porcupine ant-eater, both living in the Australian region. Do
you judge that the _duckbill_ of Tasmania (Fig. 359) lives chiefly in
water or on land? Why? Is it probably active or slow in movement? It
dabbles in mud and slime for worms and mussels, etc. How is it fitted
for doing this? Which feet are markedly webbed? How far does the web
extend? The web can be folded back when not in use. It lays two eggs in
a nest of grass at the end of a burrow. Trace resemblances and
differences between this animal and birds.
[Illustration:
FIG. 360.—SPINY ANT-EATER (_Echidna aculeata_). View of under surface
to show pouch. (After Haacke.)
]
The _porcupine ant-eater_ has numerous quill-like spines (Fig. 360)
interspersed with its hairs. (Use?) Describe its claws. It has a long
prehensile tongue. It rolls into a ball when attacked. Compare its jaws
with a bird’s bill. It lays one egg, which is carried in a fold of the
skin until hatched. Since it is pouched it could be classed with the
pouched mammals (next order), but it is egg-laying. Suppose the two
animals in this order did not nourish their young with milk after
hatching, would they most resemble mammals, birds, or reptiles?
Write the name of this _order_. —— (See Table, p. 193.) _Why_ do you
place them in this order (——)? (See p. 193.) The name of the order comes
from two Greek words meaning “one opening,” because the ducts from the
bladder and egg glands unite with the large intestine and form a cloaca.
What other classes of vertebrates are similar in this?
[Illustration:
FIG. 361.—OPOSSUM (_Didelphys Virginianus_).
]
=Pouched Mammals.=—These animals, like the last, are numerous in the
Australian region, but are also found in South America, thus indicating
that a bridge of land once connected the two regions. The _opossum_ is
the only species which has penetrated to North America (Fig. 361). Are
its jaws slender or short? What kinship is thus suggested? As shown by
its grinning, its lips are not well developed. Does this mean a low or a
well-developed mammal? Where does it have a thumb? (Fig. 361.) Does the
thumb have a nail? Is the tail hairy or bare? Why? Do you think it
prefers the ground or the trees? State two reasons for your answer. It
hides in a cave or bank or hollow tree all day, and seeks food at night.
Can it run fast on the ground? It feigns death when captured, and
watches for a chance for stealthy escape.
[Illustration:
FIG. 362.—GIANT KANGAROO.
]
The _kangaroo_ (Fig. 362), like the opossum, gives birth to imperfectly
developed young. (Kinship with what classes is thus indicated?) After
birth, the young (about three fourths of an inch long) are carried in a
ventral pouch and suckled for seven or eight months. They begin to reach
down and nibble grass before leaving the pouch. Compare fore legs with
hind legs, front half of body with hind half. Describe tail. What is it
used for when kangaroo is at rest? In jumping, would it be useful for
propelling and also for balancing the body? Describe hind and fore feet.
_Order_ ——. _Why?_ ________. See key, page 193.
=Imperfectly Toothed Mammals.=—These animals live chiefly in South
America (sloth, armadillo, giant ant-eater) and Africa (pangolin). The
sloth (Fig. 363) eats leaves. Its movements are remarkably slow, and a
vegetable growth resembling moss often gives its hair a green colour.
(What advantage?) How many toes has it? How are its nails suited to its
manner of living? Does it save exertion by hanging from the branches of
trees instead of walking upon them?
[Illustration:
FIG. 363.—SLOTH of South America.
]
[Illustration:
FIG. 364.—GIANT ANT-EATER of South America. (See Fig. 354.) Find
evidences that the edentates are a degenerate order. Describe
another ant-eater (Fig. 360).
]
[Illustration:
FIG. 365.—NINE-BANDED ARMADILLO of Texas and Mexico. (_Dasypus
novemcinctus._) It is increasing in numbers; it is very useful, as
it digs up and destroys insects. (See Fig. 347.)
]
Judging from the figures (363, 364, 365), are the members of this order
better suited for attack, active resistance, passive resistance, or
concealment when contending with other animals? The ant-eater’s claws
(Fig. 364) on the fore feet seem to be a hindrance in walking; for what
are they useful? Why are its jaws so slender? What is probably the use
of the enormous bushy tail? The nine-banded armadillo (Fig. 365) lives
in Mexico and Texas. It is omnivorous. To escape its enemies, it burrows
into the ground with surprising rapidity. If unable to escape when
pursued, its hard, stout tail and head are turned under to protect the
lower side of the body where there are no scales. The three-banded
species (Fig. 366) lives in Argentina. Compare the ears and tail of the
two species; give reasons for differences. Why are the eyes so small?
The claws so large? _Order_______. _Why?_ ______.
[Illustration:
FIG. 366.—THREE-BANDED ARMADILLO (_Tolypeutes tricinctus_).
]
=Insect Eaters.=—The soft interior and crusty covering of insects makes
it unnecessary for animals that prey upon them to have flat-topped teeth
for grinding them to powder, or long cusps for tearing them to pieces.
The teeth of insect eaters, even the molars (Fig. 368), have many sharp
tubercles, or points, for holding insects and piercing the crusty outer
skeleton and reducing it to bits. As most insects dig in the ground or
fly in the air, we are not surprised to learn that some insect-eating
mammals (the bats) fly and others (the moles) burrow. Are the members of
this order friends or competitors of man?
[Illustration:
FIG. 367.—THE MOLE.
]
[Illustration:
FIG. 368.—SKELETON OF MOLE. (Shoulder blade is turned upward.)
]
Why does _the mole_ have very small eyes? Small ears? Compare the shape
of the body of a mole and a rat. What difference? Why? Compare the front
and the hind legs of a mole. Why are the hind legs so small and weak?
Bearing in mind that the body must be arranged for digging and using
narrow tunnels, study the skeleton (Fig. 368) in respect to the
following: Bones of arm (length and shape), fingers, claws, shoulder
bones, breastbone (why with ridge like a bird?), vertebræ (why are the
first two so large?), skull (shape). There are no eye sockets, but there
is a snout gristle; for the long, sensitive snout must serve in place of
the small and almost useless eyes hidden deep in the fur. Is the fur
sleek or rough? Why? Close or thin? It serves to keep the mole clean.
The muscles of neck, breast, and shoulders are very strong. Why? The
mole eats earthworms as well as insects. It injures plants by breaking
and drying out their roots. Experiments show that the Western mole will
eat moist grain, though it prefers insects. If a mole is caught, repeat
the experiment, making a careful record of the food placed within its
reach.
[Illustration:
FIG. 369.—SKELETON OF BAT.
]
As with the mole, the skeletal adaptations of _the bat_ are most
remarkable in the hand. How many fingers? (Fig. 369.) How many nails on
the hand? Use of nail when at rest? When creeping? (Fig. 369.) Instead
of feathers, the flying organs are made of a pair of extended folds of
the skin supported by elongated bones, which form a framework like the
ribs of an umbrella or a fan. How many digits are prolonged? Does the
fold of the skin extend to the hind legs? The tail? Are the finger bones
or the palm bones more prolonged to form the wing skeleton?
[Illustration:
FIG. 370.—VAMPIRE (_Phyllostoma spectrum_) of South America. × ⅙.
]
The skin of the wing is rich in blood vessels and nerves, and serves, by
its sensitiveness to the slightest current of air, to guide the bat in
the thickest darkness. Would you judge that the bat has sharp sight?
Acute hearing?
The moles do not _hibernate_; the bats do. Give the reason for the
difference. If bats are aroused out of a trance-like condition in
winter, they may die of starvation. Why? The mother bat carries the
young about with her, since, unlike birds, she has no nest. How are the
young nourished? _Order_ ________. _Why?_ ________. (Key, p. 193.)
[Illustration:
FIG. 371.—POUCHED GOPHER (_Geomys bursarius_) × ¼, a large, burrowing
field rat, with cheek pouches for carrying grain.
]
[Illustration:
FIG. 372.—Hind foot _a_, fore foot _b_, tail _c_, of BEAVER.
]
[Illustration:
FIG. 373.—BEAVER.
]
=The Gnawing Mammals.=—These animals form the most numerous order of
mammals. They _lack canine_ teeth. Inference? The incisors are four in
number in all species except the rabbits, which have six (see Fig. 345).
They are readily recognized by their _large incisors_. These teeth grow
throughout life, and if they are not constantly worn away by gnawing
upon hard food, they become inconveniently long, and may prevent closing
of the mouth and cause starvation. The hard enamel is all on the front
surface, the dentine in the rear being softer; hence the incisors
sharpen themselves by use to a chisel-like edge. The molars are set
close together and have their upper surfaces level with each other. The
ridges on them run crosswise so as to form a continuous filelike surface
for reducing the food still finer after it has been gnawed off (Fig.
345). The lower jaw fits into grooves in place of sockets. This allows
the jaw to work back and forth instead of sidewise. The rabbits and some
squirrels have a hare lip; _i.e._ the upper lip is split. What advantage
is this in eating? In England the species that burrow are called
rabbits; those that do not are called hares.
[Illustration:
FIG. 374.—POSITION OF LIMBS IN RABBIT.
]
Name six enemies of rabbits. Why does a rabbit usually sit motionless
unless approached very close? Do you usually see one before it dashes
off? A rabbit has from three to five litters of from three to six young
each year. Squirrels have fewer and smaller litters. Why must the rabbit
multiply more rapidly than the squirrel in order to survive? English
rabbits have increased in Australia until they are a plague. Sheep
raising is interfered with by the loss of grass. The Australians now
ship them to England in cold storage for food. Rabbits and most rodents
lead a watchful, timid, and alert life. An exception is the porcupine,
which, because of the defence of its barbed quills, is dull and
sluggish.
The common rodents are:—
squirrels
rabbits
rats
mice
beavers
muskrats
porcupines
guinea pig
pouched gopher
prairie dog
prairie squirrel
chipmunk
ground hog
field mouse
Which of the above rodents are commercially important? Which are
injurious to an important degree? Which have long tails? Why? Short
tails? Why? Long ears? Why? Short ears? Why? Which are aquatic? Which
dig or burrow? Which are largely nocturnal in habits? Which are
arboreal? Which are protected by coloration? Which escape by running? By
seeking holes?
[Illustration:
FIG. 375.—FLYING SQUIRREL (_Pteromys volucella_). × ¼.
]
=Economic Importance.=—Rabbits and squirrels destroy the eggs and young
of birds. Are rabbits useful? Do they destroy useful food? The use of
beaver and muskrat skins as furs will probably soon lead to their
extinction. Millions of rabbits’ skins are used annually, the hair being
made into felt hats. There are also millions of squirrel skins used in
the fur trade. The hairs of the tail are made into fine paint brushes.
The skins of common rats are used for the thumbs of kid gloves. _Order_
________. _Why?_ ________.
=Elephants.=—Elephants, strange to say, have several noteworthy
resemblances to rodents. Like them, elephants have no canine teeth;
their molar teeth are few, and marked by transverse ridges and the
incisors present are prominently developed (Figs. 376, 377). Instead of
four incisors, however, they have only two, the enormous tusks, for
there are no incisors in the lower jaw. Elephants and rodents both
subsist upon plant food. Both have peaceful dispositions, but one order
has found safety and ability to survive by attaining enormous size and
strength; the other (_e.g._ rats, squirrels) has found safety in small
size. Explain.
[Illustration:
FIG. 376.—HEAD OF AFRICAN ELEPHANT.
]
Suppose you were to observe an elephant for the first time, without
knowing any of its habits. How would you know that it does not eat meat?
That it does eat plant food? That it can defend itself? Why would you
make the mistake of thinking that it is very clumsy and stupid? Why is
its skin naked? Thick? Why must its legs be so straight? Why must it
have either a very long neck or a substitute for one? (Fig. 376.) Are
the eyes large or small? The ears? The brain cavity? What anatomical
feature correlates with the long proboscis? Is the proboscis a new organ
not found in other animals, or is it a specialization of one or more old
ones? Reasons? What senses are especially active in the proboscis? How
is it used in drinking? In grasping? What evidence that it is a
development of the nose? The upper lip?
[Illustration:
FIG. 377.—MOLAR TOOTH OF AFRICAN ELEPHANT.
]
The tusks are of use in uprooting trees for their foliage and in digging
soft roots for food. Can the elephant graze? Why, or why not? There is a
finger-like projection on the end of the snout which is useful in
delicate manipulations. The feet have pads to prevent jarring; the nails
are short and hardly touch the ground. _Order_ ________. _Why?_
________. Key, page 193.
=Whales, Porpoises, Dolphins.=—As the absurd mistake is sometimes made
of confusing _whales_ with fish, the pupil may compare them in the
following respects: eggs, nourishment of young, fins, skin, eyes, size,
breathing, temperature, skeleton (Figs. 209, 379, and 397).
[Illustration:
FIG. 378.—HARPOONING GREENLAND WHALE (see Fig. 351).
]
_Porpoises and dolphins_, which are smaller species of whales, live near
the shore and eat fish. Explain the expression “blow like a porpoise.”
They do not exceed five or eight feet in length, while the deep-sea
whales are from thirty to seventy-five feet in length, being by far the
largest animals in the world. The size of the elephant is limited by the
weight that the bones and muscles support and move. The whale’s size is
not so limited.
The _whale_ bears one young (rarely twins) at a time. The mother
carefully attends the young for a long time. The _blubber_, or thick
layer of fat beneath the skin, serves to retain heat and to keep the
body up to the usual temperature of mammals in spite of the cold water.
It also serves, along with the _immense lungs_, to give lightness to the
body. Why does a whale need large lungs? The _tail of a whale_ is
horizontal instead of vertical, that it may steer upward rapidly from
the depths when needing to breathe. The _teeth_ of some whales do not
cut the gum, but are reabsorbed and are replaced by horny plates of
“whalebone,” which act as strainers. Give evidence from the flippers,
lungs, and other organs, that the whale is descended from a land mammal
(Fig. 397). Compare the whale with a typical land mammal, as the dog,
and enumerate the specializations of the whale for living in water. What
change took place in the general form of the body? It is believed that
on account of scarcity of food the land ancestors of the whale, hundreds
of thousands of years ago, took to living upon fish, etc., and,
gradually becoming swimmers and divers, lost the power of locomotion on
land. _Order_____. _Why?_____.
[Illustration:
FIG. 379.—DOLPHIN.
]
Elephants are rapidly becoming extinct because of the value of their
ivory tusks. Whales also furnish valuable products, but they will
probably exist much longer. Why?
[Illustration:
FIG. 380.—MANATEE, or sea cow; it lives near the shore and eats
seaweed. (Florida to Brazil.)
]
The =manatees and dugongs= (sea cows) are a closely related order living
upon water plants, and hence living close to shore and in the mouths of
rivers. _Order_____. _Why?_ ____.
=Hoofed Mammals.=—All the animals in this order walk on the tips of
their toes, which have been adapted to this use by the claws having
developed into _hoofs_. The order is subdivided into the _odd-toed_
(such as the horse with one toe and the rhinoceros with three) and the
_even-toed_ (as the ox with two toes and the pig with four). All the
even-toed forms except the pig and hippopotamus chew the cud and are
given the name of _ruminants_.
[Illustration:
FIG. 381.—Left leg of man, left hind leg of dog and horse; homologous
parts lettered alike.
]
=Horse and Man Compared.=—To which finger and toe on man’s hand and foot
does a horse’s foot correspond? (Figs. 381, 383, 399.) Has the horse
kneecaps? Is its heel bone large or small? Is the fetlock on toe,
instep, or ankle? Does the part of a horse’s hind leg that is most
elongated correspond to the thigh, calf, or foot in man? On the fore
leg, is the elongated part the upper arm, forearm, or hand? (Figs. 395,
399.) Does the most elongated part of the fore foot correspond to the
finger, the palm, or the wrist? (Fig. 382.) On the hind foot is it toe,
instep, or ankle? Is the fore fetlock on the finger, the palm, or the
wrist? (Figs. 382, 385, 399.) Is the hock at the toe, the instep, the
heel, or the knee?
=Specializations of the Mammals.=—The early mammals, of which the
present marsupials are believed to be typical, had five toes provided
with claws. They were not very rapid in motion nor dangerous in fight,
and probably ate both animal and vegetable food.
[Illustration:
FIG. 382.—SKELETONS OF FEET OF MAMMALS.
_P_, horse; _D_, dolphin; _E_, elephant; _A_, monkey; _T_, tiger; _O_,
aurochs;
_F_, sloth; _M_, mole.
=Question=: Explain how each is adapted to its specialized function.
]
[Illustration:
FIG. 383.—Feet of the ancestors of the horse.
]
According to the usual rule, they tended to increase faster than the
food supply, and there were continual contests for food. Those whose
claws and teeth were sharper drove the others from the food, or preyed
upon them. Thus the specialization into the bold flesh eating beasts of
prey and the timid vegetable feeders began. Which of the flesh eaters
has already been studied at length? The insectivora escaped their
enemies and found food by learning to burrow or fly. The rodents
accomplished the same result either by acquiring great agility in
climbing, or by living in holes, or by running. The proboscidians
acquired enormous size and strength. The hoofed animals found safety in
flight.
[Illustration:
FIG. 384.—TAPIR OF SOUTH AMERICA (_Tapirus americanus_). × ¹⁄₂₅.
=Questions=: How does it resemble an elephant? (Fig. 376.) A horse?
(p. 210.)
]
[Illustration:
FIG. 385.—HORSE, descended from a small wild species still found in
Western Asia.
]
=Ungulates=, as the horse, need no other protection than their great
speed, which is due to lengthening the bones of the legs and rising upon
the very tip of the largest toe, which, to support the weight, developed
an enormous toe-nail called a hoof. The cattle, not having developed
such speed as the horse, usually have horns for defence. If a calf or
cow bellows with distress, all the cattle in the neighbourhood rush to
the rescue. This unselfish instinct to help others was an aid to the
survival of wild cattle living in regions infested with beasts of prey.
Which of Æsop’s fables is based upon this instinct? The habit of rapid
grazing and the correlated habit of chewing the cud were also of great
value, as it enabled cattle to obtain grass hurriedly and to retire to a
safe place to chew it. Rudiments of the upper incisors are present in
the jaw of the calf, showing the descent from animals which had a
complete set of teeth. The rudiments are absorbed and the upper jaw of
the cow lacks incisors entirely, as they would be useless because of the
cow’s habit of seizing the grass with her rough tongue and cutting it
with the lower incisors as the head is jerked forward. This is a more
rapid way of eating than by biting. Which leaves the grass shorter after
grazing, a cow or a horse? Why? Grass is very slow of digestion, and the
ungulates have an alimentary canal twenty to thirty times the length of
the body. Thorough chewing is necessary for such coarse food, and the
ungulates which chew the cud (ruminants) are able, by leisurely and
thorough chewing, to make the best use of the woody fibre (cellulose)
which is the chief substance in their food.
[Illustration:
FIG. 386.—SKELETON OF COW. Compare with horse (Fig. 395) as to legs,
toes, tail, mane, dewlap, ears, body.
]
=Ruminants= have four divisions to the stomach. Their food is first
swallowed into the roomy _paunch_ in which, as in the crop of a bird,
the bulky food is temporarily stored. It is not digested at all in the
paunch, but after being moistened, portions of it pass successively into
the _honeycomb_, which forms it into balls to be belched up and ground
by the large molars as the animal lies with eyes half closed under the
shade of a tree. It is then swallowed a second time and is acted upon in
the third division (or _manyplies_) and the fourth division (or _reed_).
Next it passes into the intestine. Why is the paunch the largest
compartment? In the figure do you recognize the paunch by its size? The
honeycomb by its lining? Why is it round? The last two of the four
divisions may be known by their direct connection with the intestine.
[Illustration:
FIG. 387.—Food traced through stomachs of cow. (Follow arrows.)
]
[Illustration:
FIG. 388.—Section of cow’s stomachs. Identify each. (See text.)
]
[Illustration:
FIG. 389.—OKAPI. This will probably prove to be the last large mammal
to be discovered by civilized man. It was found in the forests of
the Kongo in 1900.
=Questions=: It shows affinities (find them) with giraffe, deer, and
zebra. It is a ruminant ungulate (explain meaning—see text).
]
The true _gastric juice_ is secreted only in the fourth stomach. Since
the cud or unchewed food is belched up in balls from the round
“honeycomb,” and since a ball of hair is sometimes found in the stomach
of ruminants, some ignorant people make the absurd mistake of calling
the ball of hair the cud. This ball accumulates in the paunch because of
the friendly custom cows have of combing each other’s hair with their
rough tongues, the hair sometimes being swallowed. Explain the saying
that if a cow stops chewing the cud she will die.
[Illustration:
FIG. 390.—AFRICAN CAMEL (_Camelus dromedarius_).
]
[Illustration:
FIG. 391.—PRONG-HORNED ANTELOPE (_Antelocarpa Americana_).
]
Does a cow’s lower jaw move sidewise or back and forth? Do the ridges on
the molars run sidewise or lengthwise? Is a cow’s horn hollow? Does it
have a bony core? (Fig. 344.)
The permanent hollow horns of the cow and the solid deciduous horns of
the deer are typical of the two kinds of horns possessed by ruminants.
The prong-horned antelope (Fig. 391) of the United States, however, is
an intermediate form, as its horns are hollow, but are shed each year.
The hollow horns are a modification of hair. Do solid or hollow horns
branch? Which are possessed by both sexes? Which are pointed? Which are
better suited for fighting? Why would the deer have less need to fight
than the cattle? Deer are polygamous, and the males use their horns
mostly for fighting one another. The sharp hoofs of deer are also
dangerous weapons. The white-tail deer (probably the same species as the
Virginian red deer) is the most widely distributed of the American deer.
It keeps to the lowlands, while the black-tailed deer prefers a hilly
country. The moose, like the deer, browses on twigs and leaves. The elk,
like cattle, eats grass.
[Illustration:
FIG. 392.—ROCKY MOUNTAIN SHEEP (_Ovis montana_). × ¹⁄₂₄.
]
The native sheep of America is the big horn, or Rocky Mountain sheep
(Fig. 392). The belief is false that they alight upon their horns when
jumping down precipices. They post sentinels and are very wary. There is
also a native goat, a white species, living high on the Rocky Mountains
near the snow. They are rather stupid animals. The bison once roamed in
herds of countless thousands, but, with the exception of a few protected
in parks, it is now extinct. Its shaggy hide was useful to man in
winter, so it has been well-nigh destroyed. For gain man is led to
exterminate elephants, seals, rodents, armadillos, whales, birds, deer,
mussels, lobsters, forests, etc.
[Illustration:
FIG. 393.—PECCARY (_Dicotyles torquatus_) of Texas and Mexico. × ¹⁄₁₂.
]
Our only native hog is the peccary, found in Texas (Fig. 393). In
contrast with the heavy domestic hog, it is slender and active. It is
fearless, and its great tusks are dangerous weapons. The swine are the
only ungulates that are not strictly vegetable feeders. The habit of
fattening in summer was useful to wild hogs, since snow hid most of
their food in winter. The habit has been preserved under domestication.
Are the small toes of the hog useless? Are the “dew claws” of cattle
useless? Will they probably become larger or smaller? _Order?_
[Illustration:
FIG. 394.—BIRD.
]
[Illustration:
FIG. 395.—HORSE.
]
[Illustration:
FIG. 396.—OX.
]
[Illustration:
FIG. 397.—DOLPHIN.
]
[Illustration:
FIG. 398.—FISH.
]
[Illustration:
FIG. 399.—MAN.
]
[Illustration:
FIG. 400.—CHIMPANZEE. (See Fig. 406.)
]
=Illustrated Study of Vertebrate Skeletons=: Taking man’s skeleton as
complete, which of these seven skeletons is most incomplete?
Regarding the fish skeleton as the original vertebrate skeleton, how
has it been modified for (1) walking, (2) walking on two legs, (3)
flying?
Which skeleton is probably a degenerate reversion to original type?
(p. 209.)
How is the horse specialized for speed?
Do all have tail vertebræ, or vertebræ beyond the hip bones? Does each
have shoulder blades?
Compare (1) fore limbs, (2) hind limbs, (3) jaws of the seven
skeletons. Which has relatively the shortest jaws? Why? What seems to
be the typical number of ribs? limbs? digits?
Does flipper of a dolphin have same bones as arm of a man?
How many thumbs has a chimpanzee? Which is more specialized, the foot
of a man or that of a chimpanzee? Is the foot of a man or that of a
chimpanzee better suited for supporting weight? How does its
construction fit it for this?
Which has a better hand, a man or a chimpanzee? What is the difference
in their arms? Does difference in structure correspond to difference
in use?
Which of the seven skeletons bears the most complex breastbone?
Which skeleton bears no neck (or cervical) vertebræ? Which bears only
one?
Are all the classes of vertebrates represented in this chart? (p.
125.)
[Illustration:
FIG. 401.—SACRED MONKEY OF INDIA (_Semnopithecus entellus_). × ¹⁄₁₂.
]
[Illustration:
FIG. 402.—LEMUR (_Lemur Mongoz_). × ⅒. Which digit bears a claw?
]
=Monkeys, Apes, and Man.=—Study the figures (399, 400); compare apes and
man and explain each of the differences in the following list: (1) feet,
three differences; (2) arms; (3) brain case; (4) jaws; (5) canine teeth;
(6) backbone; (7) distance between the eyes.
_A hand_, unlike a foot, has one of the digits, called a thumb, placed
opposite the other four digits that it may be used in grasping.
Two-handed man and four-handed apes and monkeys are usually placed in
one order, the _Primates_, or in two orders (see table, page 193). The
lowest members of this order are the _lemurs_ of the old world. Because
of their hands and feet being true grasping organs, they are placed
among the primates, notwithstanding the long muzzle and expressionless,
foxlike face. (Fig. 402.) Next in order are the _tailed monkeys_, while
the _tailless apes_ are the highest next to man.
[Illustration:
FIG. 403.—BROAD-NOSED MONKEY. × ⅒. America.
]
[Illustration:
FIG. 404.—NARROW-NOSED MONKEY. × ¹⁄₁₂. Old World.
]
[Illustration:
FIG. 405.—GORILLA. (Size of a man.)
]
The _primates of the New World_ are all monkeys with long tails and
broad noses. They are found from Paraguay to Mexico. The _monkeys and
apes of the Old World_ have a _thin partition_ between the nostrils, and
are thus distinguished from the monkeys of the New World, which have a
_thicker partition_ and have a broader nose. (Figs. 403, 404.) The
monkeys of America all have _six molar teeth_ in each half jaw (Fig.
352); the monkeys and apes of the Old World have thirty-two teeth, which
agree both in number and arrangement with those of man.
[Illustration:
FIG. 406.—CHIMPANZEE.
]
Which of the primates figured in this book appear to have the arm longer
than the leg? Which have the eyes directed forward instead of sideways,
as with cats or dogs?
Nearly all the primates are _forest dwellers_, and inhabit warm
countries, where the boughs of trees are never covered with ice or snow.
Their _ability in climbing_ serves greatly to protect them from beasts
of prey. Many apes and monkeys are able to assume the upright position
in walking, but they touch the ground with their knuckles every few
steps to aid in preserving the balance.
The _Simians_ are the highest family of primates below man, and include
the gorilla, chimpanzee, orang, and gibbon. Some of the simians weave
together branches in the treetops to form a rude nest, and all are very
affectionate and devoted to their young. How are apes most readily
distinguished from monkeys? (Figs. 401, 406.)
[Illustration:
FIG. 407.—ANATOMY OF RABBIT.
]
_a_, incisor teeth;
_b_, _b′_, _b″_, salivary glands;
_k_, larynx;
_l_, windpipe;
_c_, gullet;
_d_, diaphragm (possessed only by mammals);
_e_, stomach;
_g_, small intestine;
_h_, _h′_, large intestine;
_f_, junction of small and large intestine;
_g_, _g′_, cæcum, or blind sac from _f_ (corresponds to the shrunken
rudimentary vermiform appendix in man);
_m_, carotid arteries;
_n_, heart;
_o_, aorta;
_p_, lungs;
_q_, end of sternum;
_r_, spleen;
_s_, kidney;
_t_, ureters (from kidney to bladder _v_).
2. brain of rabbit:
_a_, olfactory nerves;
_b_, cerebrum;
_c_, midbrain;
_d_, cerebellum.
Table for Review
══════════════════════╤══════╤══════╤══════╤══════╤══════╤══════╤══════
│ FISH │ FROG │TURTLE│ BIRD │ CAT │HORSE │ MAN
──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────
Names of limbs │ │ │ │ │ │ │
──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────
Acutest sense │ │ │ │ │ │ │
──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────
Digits on fore and │ │ │ │ │ │ │
hind limb │ │ │ │ │ │ │
──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────
Locomotion │ │ │ │ │ │ │
──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────
Kind of food │ │ │ │ │ │ │
──────────────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────
Care of young │ │ │ │ │ │ │
══════════════════════╧══════╧══════╧══════╧══════╧══════╧══════╧══════
[Illustration]
St. Bernard German Pointer Newfoundland
mastiff
Eskimo English Bulldog Shepherd
bloodhound
Poodle Greyhound Spitz
Dachshund
FIG. 408.—ARTIFICIAL SELECTION. Its effects in
causing varieties in one species. Which of
the dogs is specialized for speed? Driving
cattle? Stopping cattle? Trailing by scent?
Finding game? Drawing vehicles? Going into
holes? House pet? Cold weather? In Mexico
there is a hairless dog specialized for hot
climates. The widely differing environments
under various forms of domestication cause
“sports” which breeders are quick to take
advantage of when wishing to develop new
varieties. Professor De Vries by cultivating
American evening primroses in Europe has
shown that a sudden change of environment
may cause not only varieties but new species
to arise.
INDEX
Aboral surface, 35.
Acephala, 107.
Adaptation to environment, 148, 185, 201, 205, 207.
Ambulacral, 36.
Amœba, 10.
Anodon, 98.
Antelope, 215.
Antennæ, 68, 87.
Ant-eater, giant, 199;
spiny, 196.
Ant lion, 91.
Ape, 220.
Aptera, 82.
Apteryx, 174.
Aquarium, 17.
Argonaut, paper, 107.
Armadillo, 200.
Arthropoda, 9, 125.
Bat, 202.
Batrachia, 126.
Beaver, 204.
Bedbug, 92, 93.
Bee, bumble, 89;
honey, 88.
Beetle, 90, 91.
Big-headed turtle, 149.
Bilateral, 34, 49, 98.
Bill of bird, 151.
Biology defined, 1.
Birds, 150.
Blood, of insects, 78.
Boll weevil, 95, 96.
Boll worm, 95, 96.
Brain, of fish, 118.
Breathing, of bird, 161;
of insect, 76.
Bureau of entomology, 95.
Butterfly, 83.
Cabbage butterfly, 84, 86, 87.
Camel, 214.
Candle, 5.
Carbon dioxide, 24.
Carp, 112, 117, 123.
Cat, 184.
Caterpillar, tent, 84.
Cell, 6, 7.
Celom, 46.
Cephalopod, 106.
Chelonia, 143.
Chimpanzee, 219, 221.
Chirping, 66.
Chitin, 77.
Cilia, 14, 20, 101, 103.
Ciliated chamber, 17.
Circulation, in amœba, 12;
in insect, 77;
in fish, 117.
Clam, hardshell, 104;
softshell, 104.
Class, 9.
Classification, of animals, 8, 125;
of birds, 177;
insects, 82;
mammals, 193.
Click beetle, 91.
Clitellum, 43, 47.
Cloaca, 18.
Clothes moth, 84, 92, 93.
Cockroach, 71.
Cocoon, 84.
Codling moth, 84, 86, 87, 95.
Cœlenterata, 28.
Coleoptera, 82.
Collecting insects, 72.
Colorado beetle, 90, 91.
Coloration, warning, 84, 146;
protective, 34, 37, 49.
Colours of flowers, 85.
Comparative study, 85, 108, 122, 223;
moth and butterfly, 85.
Copper head, 145.
Coral, 31.
Coralline, 31.
Coral snake, 145, 146.
Cricket, 71.
Cross-fertilization, 25.
Cuckoo, 179.
Cuttlefish, 107.
Cypræa, 104.
Cysts, 13.
Darwin, 48, 148.
Devil’s horse, 71.
De Vries, 148, 224.
Digits, 222.
Diptera, 82.
Division of labour, 27, 29.
Dog, 224.
Dolphin, 209.
Doodle bug, 91.
Dorsal, 43.
Dove, 179.
Dragon fly, 93.
Duckbill, 196.
Ear, of bird, 151;
of frog, 131;
of fish, 112.
Earthworm, 42.
Echinoderms, 9, 34, 125.
Economic importance of birds, 167;
insects, 93;
molluscs, 105;
rodents, 206.
Ectoderm, 26, 87.
Ectoplasm, 11, 14.
Egg, of insect, 81.
Endoderm, 26, 27, 37.
Endoplasm, 11, 14.
Energy, in amœba, 12;
organic, 2, 3;
plant, 2, 3, 5.
Environment, 148.
Epidermis, of mussel, 98.
Excretion, 12.
Eye, of bird, 150;
of frog, 30;
of grasshopper, 67, 79;
of fish, 111.
Family, 8.
Fangs, venomous, 145.
Farmers’ bulletins, 95.
Feather, 155.
Fertilization, cross, 85.
Field study, 10, 22, 42, 71, 72, 97, 127, 165, 166, 167, 184.
Fins, 110, 113.
Flagellum, 21, 27.
Flatworm, 49.
Flea, 92, 93.
Flight, of bird, 157, 175;
of moth, 84.
Fly, horse, 81;
house, 92, 93.
Food, of birds, 177.
Food tube, of bird, 163;
of fish, 116;
of insect, 76;
of mussel, 102.
Foraminifera, 15, 18.
Frog, 128.
Function, 1.
Ganglion, 45.
Gasteropod, 108.
Gastrula, 7.
Genus, 8.
Geographical barriers, 148.
Gila monster, 147.
Gills, of mussel, 100;
of fish, 115.
Gnawing mammals, 203.
Gopher, pouched, 204.
Gorilla, 221.
Grantia, 18.
Grasshopper, 70.
Gypsy moth, 95.
Hands, defined, 220.
Heart, insect, 77.
Hemiptera, 82.
Heredity, 147, 153.
Hessian fly, 95.
Horned toad, 140.
House fly, 92, 93.
Human species, 220.
Hydra, 22.
Hydranth, 29.
Hydroid, 28, 29, 30.
Hymenoptera, 82.
Hypostome, 23.
Ichneumon fly, 89.
Imago, 81.
Infusoria, 16.
Inorganic, 1.
Insecticides, 95.
Insects, 73, 75;
biting, 82;
classified, 82;
sucking, 82.
Instinct, 80, 121.
Jacana, Mexican, 178.
Jay, blue, 181.
Jelly fish, 29, 30.
Kangaroo, 198.
Kidneys, of fish, 117;
of insects, 76;
of mussel, 102;
of worm, 45.
Labial palpi, 68, 74, 101.
Labium, 68, 74.
Labrum, 68, 74.
Lady bug, 91.
Lamellibranch, 107.
Lark, meadow, 182;
sky, 179.
Larva, 81.
Lasso cell, 34.
Leg, of bird, 152;
of horse, 210;
of insect, 74.
Lemur, 220.
Lepidoptera, 82, 87.
Louse, 92, 93.
Lungs, of bird, 165.
Madreporite, 35.
Mammal, 184;
classified, 193;
defined, 189.
Manatee, 209.
Mandibles, 68, 74.
Mantis, praying, 3.
Mantle, 99.
Maxillæ, 68, 74.
Maxillary palpi, 68, 74.
May beetle, 90, 91.
May fly, 83.
Measuring worm, 81, 84.
Medusa, 31.
Mesoglea, 26.
Metamorphosis of insect, 80, 81, 82.
Metazoan, 1.
Migration of birds, 171, 173.
Mimicry, 146.
Moccasin, 145.
Mole, 201.
Mollusc, 9, 97, 125.
Moulting, 69, 174.
Monkey, 220.
Morula, 7.
Mosquito, 92, 93, 96.
Moth, 83.
Mother-of-pearl, 99.
Mussel, 96, 103.
Nautilus, chambered, 107.
Nectar, 8.
Nephridium, 45.
Nervous system, of bee, 78;
of mussel, 102.
Nest building, 166, 182.
Neuroptera, 82.
Nostril, of bird, 151;
of fish, 112.
Nucleolus, 6.
Nucleus, 6, 11, 14.
Octopus, 106.
Okapi, 214.
Omnivorous, 47.
One-celled animals, 7.
Opossum, 197.
Oral surface, 35.
Orang, 227.
Order, 9.
Organ, 1.
Organism, 1.
Orthoptera, 82.
Osculum, 18.
Ovary, 25, 37, 117.
Oviduct, 46.
Oxidation, 3, 4, 5.
Oxygen, 4, 5.
Oyster, 104.
Paramecium, 13.
Parasites, 49, 93.
Partridge, 178.
Pearls, 105.
Peccary, 217.
Perch, 109, 110, 123.
Pests, insect, 93.
Pheasant, 174.
Plastron, 141.
Pollen, 85.
Pollen basket, 88.
Polyp, 9, 22, 125.
Portuguese man-o’-war, 28.
Potato bug, 90.
Primates, 220.
Proboscis, of butterfly, 83, 87;
elephant, 207.
Prolegs, 84, 87.
Protection of birds, 171.
Protective resemblance, 34, 146.
Protoplasm, 6, 11.
Protozoa, 7, 9, 11, 125.
Pseudoneuroptera, 82.
Pseudopod, 11.
Quill, 156.
Rabbit, 205, 223.
Radial symmetry, 34, 125.
Rattlesnake, 145.
Rectum, 134.
Regeneration of lost parts, 37.
Reproduction, 12, 15, 20, 25, 37, 46, 120.
Reptiles, 139.
Rhizopoda, 16.
Road runner, 169.
Robin, 183.
Rotifer, 49.
Round worm, 49.
Ruminant, 213.
Salamander, 134, 138, 139.
Sandworm, 49.
San José scale, 95.
Scab in sheep, 95.
Scales, of bird, 161;
fish, 110;
moth, 89.
Scallops, 104.
Scarab, 90, 91.
Sea anemone, 33.
Sea fan, 32.
Sea horse, 124.
Sea urchin, 38.
Senses of insects, 76.
Setæ, 43, 48.
Sexual selection, 174.
Shark, 121.
Silkworm, 84, 86, 95.
Silver scale, 83.
Siphon, 101.
Siphonoptera, 82.
Skeleton, of bird, 152;
cat, 188;
frog, 131;
of fish, 113;
chart of, 218.
Skull, mammalian, 194.
Slipper animalcule, 13.
Sloth, 199.
Slug, 105.
Snail, 105.
Soil, 48.
Sparrow, 182;
English, 170.
Specialization, 20, 27, 66, 210.
Species, 8.
Spermary, 25, 27.
Spicule, 18.
Spider, 94.
Spiracle, 77, 87.
Sponges, 17, 125;
glass, 19;
horny, 19;
limy, 19.
Sports, 148, 224.
Squash bug, 93, 95.
Squid, 106.
Stickleback, 119.
Struggle to live, 147.
Study, comparative, 82, 149, 223.
Sun energy, 2.
Sunlight, 2.
Survival of fittest, 147.
Tadpole, 126, 134.
Tapeworm, 49.
Tarantula, 94.
Teeth, of frog, 130.
Terrapin, 143, 144.
Toad, 137.
Tortoise, 140, 143, 144.
Trap-door spider, 94.
Tube feet, 35.
Tumble bug, 90, 91.
Turtle, 140, 143, 144.
Umbo, 98.
Ungulate, 212.
Vacuole, 11, 12, 14.
Vampire, 203.
Variation, 147.
Variety, 8.
Venomous snakes, 143.
Vent, 42.
Ventral, 43.
Vermes, 9, 125.
Vertebrates, 9, 125.
Vertebrate skeletons, 218.
Viscera, of bird, 163.
Warning sound, 147.
Wasps, digging, 89.
Weevil, 90, 91, 96.
Whale, 208.
Wings, of grasshopper, 67;
of bird, 153, 158.
Woodpecker, 180.
Worms, 42.
Zoology defined, 1.
Zoophytes, 33.
------------------------------------------------------------------------
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