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Title: A first book in organic evolution
Author: D. Kerfoot Shute
Release date: June 15, 2024 [eBook #73834]
Language: English
Original publication: Chicago: The Open Court Publishing Company, 1899
Credits: Charlene Taylor 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 A FIRST BOOK IN ORGANIC EVOLUTION ***
[Illustration: PLATE I.—Illustrating the results of Artificial Selection.
Within historic times the small Wild Rock Pigeon has been evolved into
the large Pouter. The figure illustrates the plasticity of a living
organism.]
A FIRST BOOK
IN
ORGANIC EVOLUTION
BY
D. KERFOOT SHUTE, A.B., M.D.
OPHTHALMIC SURGEON TO THE UNIVERSITY HOSPITAL (COLUMBIAN)
PROFESSOR OF ANATOMY IN THE COLUMBIAN UNIVERSITY
[Illustration]
CHICAGO
THE OPEN COURT PUBLISHING COMPANY
LONDON: KEGAN PAUL, TRENCH, TRÜBNER & CO., LTD.
PATERNOSTER HOUSE, CHARING CROSS ROAD
1899
COPYRIGHT BY
THE OPEN COURT PUBLISHING CO.
CHICAGO, U. S. A.
1899
_All rights reserved._
THIS LITTLE BOOK IS INSCRIBED TO
DR. THEODORE GILL,
NOT ONLY IN ADMIRATION FOR HIS HIGH SCHOLARSHIP
AND EMINENT SCIENTIFIC ATTAINMENTS, BUT
ALSO IN APPRECIATION OF MANY
ACTS OF COURTESY AND
KINDNESS TO THE
AUTHOR.
PREFACE.
This little book has been written chiefly for the use of students in the
Medical Department of the Columbian University. It is designed to serve
only as an _introduction_ to the study of the Development Theory, and the
subject has been presented, it is hoped, in a manner that will render it
interesting and easily intelligible to the general reader.
The doctrine of Evolution itself enters so largely into all those
departments of knowledge that especially concern the human race, and
it has so profoundly modified our ideas with regard to the origin and
destiny of man, that it has attained a commanding interest and become an
almost necessary ingredient in what is called a liberal education.
An overwhelming majority of Anthropologists, Zoölogists, and Botanists,
and a goodly number—constantly increasing—of Christian clergymen and
laymen, have been almost compelled to believe in the truth of the
Evolution Theory, whether they would or not, and they cannot but realize
how very widely the theory extends into almost every department of human
knowledge. No one, therefore, who aspires even to a moderate degree of
intellectual culture, can well afford to exclude a clear understanding of
what this Doctrine of Evolution really is. It is hoped this little work
will render such a conception easily attainable.
The author makes no claim for originality, unless it be in the _manner_
of presenting the subject. He has utilized the facts collated by other
observers, and sometimes quoted the exact language and expressions of
well-known writers on Evolution, and has endeavored to put them together
in a way that may be helpful to those who are beginning the study of the
Evolution Theory.
No attempt has been made to prove the truth of the theory: this is
assumed. The arguments in support of it are coextensive with our
knowledge of Comparative Anatomy, Embryology, Physiology, Psychology, and
many other sciences.
In the preparation of the book the author is especially indebted to his
friend Prof. Theodore Gill, the eminent ichthyologist, for many valuable
suggestions, and more particularly for his aid in constructing the
Diagram of Development. He also desires to thank his friend Dr. A. F.
A. King for his kindly assistance in preparing the manuscript for the
press; and also his friend Dr. L. O. Howard, Chief of the U. S. Bureau of
Entomology, for much valuable information and assistance.
D. K. SHUTE.
August 1, 1899, 1318 L Street, N. W., Washington, D. C.
CONTENTS.
PAGE
INTRODUCTION xiii
System of Classification xiv
Definition of Evolution xv
SECTION I.
ORGANIC CELLS: THE VISIBLE UNITS OF LIFE 3
Structure and Composition of Cells 4
Activities of Cells 7
Examples of Unicellular Animals and Plants 10
Mitosis 25
Maturation of the Human Ovum 29
Fertilization of the Human Ovum 29, 42
Segmentation of the Oösperm 31
Gastrulation 32
SECTION II.
HEREDITY WITH VARIATION 39
Examples of Variations 39
Illustrations of Heredity 40
Nucleus in Heredity 41
Heritages 47
Pseudo-Heredity 53
Environment and Variations 55
Acquired Characters 65
Pangenesis 66
Continuity of Germ-Cells 67
Modified Pangenesis 68
Heredity Stronger than Environment 75
SECTION III.
UNSTABLE ENVIRONMENT 81
Development of North America 85
Archæan Era 85
Palæozoic Era 86
Silurian Period 87
Devonian Period 87
Carboniferous Period 87
Jurassic Period 88
Cretaceous Period 88
Tertiary Period 89
Quaternary Period 89
SECTION IV.
TRANSMUTATIONS OF LIVING FORMS 93
Archæan Era 94
Table of Stratified Rocks and the Successive
Appearance of Typical Life-Forms 95
Cambrian Period 96
Lower Silurian Period 96
Upper Silurian Period 98
Devonian Period 100
Carboniferous Period 102
Permian Period 104
Triassic Period 105
Jurassic Period 106
Cretaceous Period 108
Tertiary Period 110
Quaternary Period 113
SECTION V.
NATURAL SELECTION 119
Artificial Selection 120
Multiplication of Animals 122
Elimination of the Unfit 125
The Coloration of Animals and Environment 127
Protective Coloration 128
Protective Resemblance 138
Alluring Coloration 141
Warning Coloration 144
Mimicry 147
Recognition Marks 150
Sexual Selection 152
Insect Selection 160
Isolation of Varieties 166
SECTION VI.
EVOLUTION OF MAN 173
Development of the Frog 173
Development of Man 180
Useless Scaffolding in Man 191
Development of the Brain 199
The Brain and Psychic Phenomena 206
Evolution and Social Problems 222
SECTION VII.
CLASSIFICATION OF ANIMALS AND PLANTS 227
Protozoa 229
Porifera 230
Cœlenterata 230
Echinodermata 231
Vermes 232
Arthropoda 233
Mollusca 233
Vertebrata 234
Tunicata 234
Leptocardii 235
Marsipobranchii 235
Pisces 236
Amphibia 237
Reptilia 238
Aves 238
Mammalia 239
Primates 239
Lemuroidea 240
Anthropoidea 241
Hapalidæ 242
Cebidæ 242
Cercopithecidæ 242
Simiidæ 243
Hominidæ 243
Flowerless Plants 244
Flowering Plants 244
SECTION VIII.
WORKS OF REFERENCE 247
SECTION IX.
GLOSSARY 255
SECTION X.
INDEX 277
ILLUSTRATIONS.
FIG. PAGE
1. Diagram of a Cell. (_Drawn by Mr. E. P. Copeland from a
sketch by the Author._) 5
2. Stylonychia. (_Drawn by Mr. E. P. Copeland._) 9
3. Amœba. (_Drawn by Mr. E. P. Copeland._) 11
4. Rotalia. (_Drawn by Dr. A. L. Lawrence._) 12
5. Difflugia. (_Drawn by Dr. A. L. Lawrence._) 17
6. Noctiluca. (_Drawn by Dr. A. L. Lawrence._) 18
7. Gromia. (_Drawn by Dr. A. L. Lawrence._) 21
8. Diagram Illustrating Mitosis. (_Drawn by Mr. E. P. Copeland
from a sketch by the Author._) 26
9. Diagram Illustrating the Maturation and Fertilization of
the Ovum. (_Drawn by Mr. E. P. Copeland from a sketch
by the Author._) 30
10. Diagram Illustrating Segmentation and Gastrulation. (_Drawn
by Mr. E. P. Copeland from a sketch by the Author._) 34
11. Archæan North America. (_From a drawing in Shaler’s “First
Book in Geology.”_) 84
12. Cretaceous North America. (_From a drawing in Shaler’s
“First Book in Geology.”_) 86
13. Tertiary North America. (_From a drawing in Shaler’s “First
Book in Geology.”_) 89
14. Genesis of Horse’s Feet. (_Drawn by Mr. E. P. Copeland._) 112
15. Bipes, Cheirotes, and Snake. (_From a drawing in Shaler’s
“First Book in Geology.”_) 114
16. Domesticated Pig and Wild Boar. (_From Romanes’ “Darwin
and After Darwin.”_) 121
17. Tadpoles and Frog. (_Drawn by Dr. A. L. Lawrence._) 175
18. Diagram of Development. (_Drawn by Mr. B. H. Esterly from
a sketch by the Author._) 183
19. Brain of Fish. (_Drawn by Mr. B. H. Esterly from specimens
of the Author._) 198
20. Brain of Reptile. (_Drawn by Mr. B. H. Esterly from
specimens of the Author._) 199
21. Brain of a Marsupial. (_Drawn by Mr. B. H. Esterly from
specimens of the Author._) 200
22. Brain of a Lemur. (_Modified by Mr. B. H. Esterly from
Flower._) 201
23. Ideal Sections of Brains. (_Modified from Le Conte. Drawn
by Dr. A. L. Lawrence from a sketch by the Author._) 202
24. Brain of Human Fœtus—Fish Phase. (_Drawn by Mr. B. H.
Esterly from specimens of the Author._) 204
25. Brain of Human Fœtus—Reptile Phase. (_Drawn by Mr. B. H.
Esterly from specimens of the Author._) 204
26. Brain of Human Fœtus—Marsupial Phase. Side View. (_Drawn
by Mr. B. H. Esterly from specimens of the Author._) 204
27. Brain of Human Fœtus—Marsupial Phase. Dorsal View. (_Drawn
by Mr. B. H. Esterly from specimens of the Author._) 205
COLORED PLATES
PLATE FACING PAGE
I. Wild Rock Pigeon and Pouter. (_Drawn by Mr. J. L. Ridgway
from specimens in the Smithsonian Institution._) Frontispiece
II. Butterflies. (_Drawn by Miss L. Sullivan from specimens
in the United States Bureau of Entomology._) 138
III. Caterpillar of Geometer Moth. (_Drawn by Miss L. Sullivan
from specimens in the United States Bureau of Entomology._) 142
V. Spider on Flower. (_Drawn by Miss L. Sullivan from a plate
in McCook’s “American Spiders.”_) 144
VI. Elaps and Erythrolamprus. (_Modified by Mr. J. L. Ridgway
from a figure in Romanes’ “Darwin and After Darwin.”_) 146
VII. Salamandra maculosa. (_Drawn by Mr. J. L. Ridgway from
specimens in the United States National Museum._) 148
VIII. Paradise Birds. (_Drawn by Mr. J. L. Ridgway from specimens
in the Smithsonian Institution._) 152
IX. Primrose Flowers. (_Drawn by Miss L. Sullivan from
specimens._) 162
X. Bee Fertilizing Flower. (_Drawn by Miss L. Sullivan from
specimens in the United States Bureau of Entomology._) 164
PLATES ENGRAVED IN BLACK AND WHITE
IV. Leaf-hoppers. (_Drawn by Miss L. Sullivan from drawings
collected by Dr. L. O. Howard._) 140
XI. Babies’ Grasping Power. (_From a Photograph taken by Dr.
Louis Robinson._) 192
XII. Brain of Man. (_From Carus’ “The Soul of Man.”_) 202
INTRODUCTION.
It is extremely difficult to realize the variety, wealth, and grandeur
of animal and plant life as they exist on the globe to-day. Even if we
endeavor to recall, in imagination, all that we have seen in streams and
woodland, in ponds and rivers, in meadows, and in the air; even when
we call to mind the multifarious specimens we have beheld in all the
museums of natural history we have visited, and remember the most vivid
descriptions that we have ever read of the wealth of tropical life;—even
then we have only the faintest conception of the multitude and variety of
_living forms_, not to mention the _vanished hosts of bygone ages_.
It has always been the endeavor of students of nature to reduce this
great host of living creatures to order by some system of classification.
First one system of classification was adopted, and then another, with
the progress of Botany and Zoölogy, until eventually, before the theory
of evolution was entertained by scientific men, that system was adopted
which naturalists likened to a tree. In this system, those lowest
organisms which cannot properly be called either animals or plants, may
be represented by a short trunk. Soon this short trunk divides into two
large trunks, one of which represents the animal kingdom and the other
the vegetable kingdom. Each of these trunks then sends off large branches
representing classes, from which smaller and more numerous branches,
representing orders, are given off. From these, other branches and
sub-branches are separated, representing families and genera, and finally
the terminal twigs or leaves represent species.
In this tree, while there is a general advance in organization from
below upwards, there are many deviations in this respect. Some leaves
may be growing on different branches at the same level, which means
that species belonging to widely divergent classes or orders may still
possess an equal grade of organization. On the same branch there may be
growing leaves at different levels. This means that one species may be
more highly organized than another belonging to the same class. Not only
may all living species be classified in the form of a family tree, but
all the extinct hosts of species that lived in the ages of the past may
be similarly classified. _If all the animals that have ever lived on the
globe should be represented by a tree, those existing on the earth to-day
would be indicated by the topmost twigs and leaves, while the extinct
forms would be represented by the trunk and main branches._ (Vid. Diagram
of Development.)
The detecting of this tree-like arrangement of species in nature is
the progressive work of naturalists for centuries past. At about the
commencement of the present century, when it was finally detected,
naturalists were unable to understand the significance of it. They did
not perceive the underlying principle that accounts for the fact that
groups of living forms have such natural affinities that they are
arranged like a family tree.
When Darwin came upon the scene and found that his predecessors had
already empirically worked out the tree-like system of classification, he
convinced naturalists that the great underlying principle of this system
was =Heredity=; and that, therefore, the grouping of living and extinct
organisms in a family tree according to their natural affinities is a
grouping based upon genetic affinities; and further that the ultimate
meaning of classification is the tracing of lines of pedigree. This
signifies that all the creatures living on the globe to-day, and all
the hosts that lived in the ages of the past, are blood relations in
greater or less degree, and that they have all been evolved from simple
microscopic creatures that appeared on the globe at the dawn of life. All
organisms, then, have undergone an evolution.
The factors of fundamental importance in the study of the theory of
=Evolution=, or the doctrine of the Transmutations of Organisms, are
=Cells=, =Heredity= and =Variation=, =Environment=, =Natural Selection=,
and =Isolation=.
_The evolution of an organism means its descent from preceding organisms
with continuous adaptation to its Environment. Its adaptation occurs
chiefly, if not entirely, through the Natural Selection of its useful
Variations, and the tending of these variations to be transmitted to the
offspring by the forces of Heredity. The summation of the variations, by
Heredity and Isolation, leads ultimately to specific, generic, ordinal,
and other differences in the descendants; leads, in other words, to the
transmutations of organisms._
An organism consists of two great groups of _structural units_ called
_cells_,—=Germ-Cells= and =Body-Cells=,—harmoniously associated together.
As far as Evolution is concerned, the most fundamental parts of an
organism are the Germ-Cells.
In order that the reader may have a working knowledge of the wonderful
powers of Germ-Cells and their progeny, it is vitally important that some
concrete illustrations of the activities of different kinds of cells
should be given.
SECTION I.
ORGANIC CELLS: THE VISIBLE UNITS OF LIFE.
ORGANIC CELLS: THE VISIBLE UNITS OF LIFE.
In the sanctuary of S. Vitale at Ravenna, in Italy, is a very interesting
representation, in mosaic pictures, and over life-size, of the Emperor
Justinian and his Empress Theodora, attended by a numerous suite of
ladies and courtiers. The mosaics are small bits of glass, of varying
pattern and color, cemented together so nicely as to form beautiful
delineations of the Emperor and his attendants.
The bits of glass or mosaics that form the figures may very appropriately
be called _structural units_.
The body of man, a bird, a lizard, an oak tree, and many other animals
and plants, may usefully be compared to such mosaic figures; for, just
as the mosaic figure has its structural unit, the little bit of glass
or stone, called the mosaic; so the bodies of men, birds, and other
creatures may be looked upon as infinitely complex figures formed of
minute mosaics called _cells_.
The groups of minute mosaics or _cells_ that make up the bodies of
animals and plants differ profoundly from the mosaics that form the
figures of the dead Emperor and his companions, inasmuch as each
mosaic or cell of the animal or plant body is so small as to require
the microscope to reveal it; also each mosaic of the living animal or
plant is a living mosaic or cell, in that it can absorb food, digest
it, assimilate it, grow, and multiply in numbers. Cells, then, are the
_morphological or structural units_ which compose the bodies of all
living creatures.
All animals and plants begin life as _single_ cells, which, in the vast
majority of cases, are microscopic in size. Those that remain single
cells, and dissociated throughout life, are called _Unicellular_ Animals
(Protozoa) and Plants (Protophyta), and are to be seen mostly by the
microscope alone; but those which, by multiplication and growth, form
large numbers of cells that remain associated together as in the body of
a bird or lizard, are called _Multicellular_ Animals (Metazoa) or Plants
(Metaphyta).
A cell (Fig. 1) is a _nucleated lump of protoplasm_, or cytoplasm, and
most often of microscopic size and more or less covered on its exterior
by, and holding in its interior, various products and formations
resulting from its activity, which are called _metaplasm_. Since the
protoplasm of a cell, under the microscope, presents a superficial
resemblance to a minute speck of that jelly-like substance (albumen)
which forms the white of an egg, it is often called an albumenoid
substance. But it is very misleading to use such an expression, for
protoplasm is not a single chemical substance of great complexity; but it
is rather composed of a large number of different chemical substances of
great complexity. Many of these substances, it is true, are albumenoid
in character. The same is true as to the chemical complexity of the
nucleus, which is a physically and chemically differentiated part of the
protoplasm.
The protoplasm contains certain globulins, and also albumins and
peptones; it also contains large quantities of nucleo-albumins, with
other substances. The nucleus not only contains these same substances,
but also nuclein and nucleo-proteids. It is important to state that
nuclein consists of an albumin and nucleic acid.
[Illustration: FIG. 1.—Diagram of a Cell, highly magnified.]
The protoplasm, structurally, is made up of threads forming a complex,
sponge-like substance, or reticulum, called _spongioplasm_; and in the
meshes of the spongioplasm is a more or less fluid-like substance known
as _hyaloplasm_: suspended in the hyaloplasm are various kinds of living
bodies known as _plastids_, besides various products resulting from the
activity of the protoplasm and which are designated _metaplasm_.
In many cells the protoplasm has formed on its periphery a layer of
metaplasm which is frequently called a cell-wall. This cell-wall prevents
amœboid movements of the protoplasm, and a cell possessing it is said to
be _encysted_.
In many cells, especially vegetable ones, will also be observed clear
spaces termed _vacuoles_. These vacuoles contain water with various
chemical substances held in solution, which serve the purpose chiefly of
food-reservoirs.
The nucleus also is formed of threads called _nuclear or chromatin
threads_ (_chromosomes_), the interstices of which are filled with
hyaloplasm or _achromatin_. In the nucleus can also be observed the
nucleolus.
The protoplasmic and nuclear threads show various structural
modifications in different regions and under different physiological
states of the cell.
As will be observed later on, the nuclear threads are of special interest
to the student of heredity. They may in one phase of cell-activity look
like one thread forming an inextricable network, while in other phases
they may look like thick, short, distinct rods.
The _centrosome_ (Fig. 1), with its enveloping attraction-sphere,
constitutes another fundamentally important part of the cell. It
is especially concerned with the phenomena of cell division and
multiplication.
Just as the living body consists of an infinitely complex figure of
living mosaics termed cells, so the cell itself consists of an infinitely
complex figure of still smaller living mosaics called, by Spencer,
_Physiological Units_. These units have been given different names by
various writers, viz.: by Darwin, _gemmæ_ (gemmules); by de Vries,
_pangennæ_; by Hertwig, _idioblasts_; by Weismann, _biophors_, etc., etc.
Like the atom of the chemist and the molecule of the physicist, the
physiological unit of the biologist is merely at present an intellectual
conception, yet it is, at the same time, an intellectual necessity and
plays a very important part as the theoretical component of many vital
questions. Just as the cells are the _visible_ units of life, so the
physiological units are the _invisible_ units.
The physiological activities of cells are those that pertain to their
_nutrition_ and _reproduction_.
The nutrition of cells includes all processes that are subservient
to their life and well-being, such as irritability, contractility,
absorption of food, its digestion and assimilation, secretion, etc.
In consequence of the wonderful _nutritive_ activities of cells, we may
well speak of them as marvelous magicians. Hertwig, following Haeckel,
speaks of many cells as being _builders_. In the same spirit, we can
say that multitudes of cells are expert chemists, artists, sculptors,
mathematicians, and so on, in that they make all the myriad chemical
products of organic nature, such as spices, pigments, sugars, starches,
acids, perfumes, and numerous other substances; they paint in colors
that rival the hues of the rainbow; they construct all of the beautiful
forms in the animal and plant worlds; and they draw lines as straight and
curves as graceful as the most expert mathematician.
One of the most important _reproductive_ activities of a cell is
_mitosis_ (see below). Mitosis essentially consists of a series of
processes by which each _nuclear thread_ of the nucleus _splits
longitudinally into two equal parts_, and then these equivalent parts
separate from each other, so that from the one nucleus we get two smaller
nuclei. Then each of these smaller nuclei appropriates its share of the
enveloping protoplasm, finally splitting it into two parts. Thus from the
larger cell (nucleated piece of protoplasm) we get two smaller cells
(two smaller nucleated pieces of protoplasm). In technical language,
we say that the larger cell is the _mother cell_, and the two smaller
cells that it has divided into are the _daughter cells_. In consequence
of the method of mitosis, the two daughter cells very frequently are
exactly like the mother cell, except in size. But by the absorption of
nutriment, and through digestion and assimilation, they grow and finally
become exactly like the mother cell. This is the simplest illustration of
_heredity_. The reproductive process may be repeated very many times, so
that from one cell we may get millions of cells.[1]
It is necessary to assume that the nutritive and reproductive activities
of _cells_ are based upon and controlled by the nutritive and
reproductive activities of the _physiological units_, inasmuch as these
are the ultimate living units.
In the activities of a cell the nucleus and protoplasm are intimately
correlated with one another.
The nucleus is looked upon by the majority of cytologists as the
_formative center_ of the cell in a chemical, and also, consequently, in
a morphological, sense. Active exchanges of material take place between
the nucleus and the protoplasm during the nutritive processes of the
cell. Possibly this may be altogether a chemical process, or possibly it
may be due, as Hertwig suggests, to the migrations of the _physiological
units_ as carriers and elaborators.
In these exchanges, and in the upbuilding chemical activities (anabolism)
of the cell, the nucleic acid plays a leading part. Here the nucleic
acid in the physiological units of the nuclear threads, combines with
albumins from the protoplasm, forming nuclein. Much of this nuclein,
undergoing further elaboration, is passed into the protoplasm as one of
its finished products (metaplasm). The more purely nutritive the activity
of a cell, the more nuclein its nuclear threads contain; on the other
hand, when the cell is in the phase of reproductive activity, the nucleus
contains little nuclein, and is almost entirely composed of pure nucleic
acid.
[Illustration: FIG. 2.—Stylonychia: c, an entire animal, showing planes
of section; the middle piece of c contains two nuclei and can regenerate
a perfect animal; a, and b, contain no nuclei,—they live and swim about
for a while and then die.]
That the nucleus is the formative center of the cell is indicated
by the following, among many facts: If a unicellular animal, such
as =Stylonychia= (Fig. 2), for instance, be broken up into several
fragments, it will be observed that some of the fragments are nucleated
and others non-nucleated. The nucleated fragments have the power of
quickly healing the wounds on them, regenerating the missing parts,
and thus restoring the mutilated fragments to perfect individuals.
These nucleated fragments have the power to perform all the activities
of the perfect animal. The non-nucleated portions, on the other hand,
cannot undergo regeneration. They cannot digest food, or grow or secrete
substances as the nucleated fragments can. They can simply live for
awhile, responding to stimuli and moving about. They finally perish.
Having mentioned in a general way some of the wonderful powers of cells,
it will be well now to describe briefly a few of the _unicellular plants
and animals_ that can be so easily obtained and studied in warm weather,
and which may thus serve as illustrations of the powers of nucleated
pieces of protoplasm or cells. Many unicellular plants and animals
can be obtained in summer from the superficial ooze on the bottom of
slow-running streams and also on the under surfaces of the leaves of
water plants, a study of which will be of the greatest value and interest.
=Amœba proteus= (Fig. 3). This little unicellular animal, which belongs
to the Rhizopod type, is very common in ponds and streams in warm
weather. In the resting state it is spherical in form, but when active
its form is as changeable as the fabled =Proteus=, hence its name, _Amœba
proteus_. This little creature is a naked piece of protoplasm, with its
outer layer differentiated into a firmer and pellucid part called the
_ectoplasm_ (Fig. 3, ec); its interior, the _endoplasm_ (en), is quite
granular and much more fluid, the granular particles moving quite freely
upon one another when the animal changes its shape. The superficial
portion of the endoplasm is firmer than its more central parts, and
graduates insensibly into the more consistent ectoplasm.
[Illustration: FIG. 3.—Amœba proteus: n, nucleus; cv, contractile
vesicle; ec, ectoplasm; en, endoplasm; p, pseudopodia.]
In the periphery of the granular endoplasm, and adherent to the inner
surface of the ectoplasm, is a clearly defined _nucleus_ (n). When
most distinctly seen, it presents the appearance of a clear vesicle
surrounding a solid and more or less spherical nucleolus. A _contractile
vacuole_ (cv) is also uniformly present, located in the endoplasm. The
creature has the power of putting out projections (p) from the surface
called false feet (_pseudopodia_). Sometimes the protrusion consists
of ectoplasm alone, but more commonly endoplasm extends into it, when
a current of granules will be observed moving from the more central
portions of the Amœba into its protrusion, whilst from some other
protrusion that is being withdrawn a similar current may set towards the
center of the body, and thus the animal moves, in a creeping manner,
from place to place. While moving about in this way the little animal
comes across other one-celled creatures, such as _Desmids_ and _Diatoms_,
seizing them and forcing them through its ectoplasm into the endoplasm,
where the nutritious parts are digested and assimilated. After the animal
has taken its prey through its ectoplasm, no break in the continuity
of the ectoplasm remains, but the parts immediately come together in a
perfect manner. After it has abstracted all the nutriment from its prey,
the Amœba casts away from it the parts that are indigestible.
[Illustration: FIG. 4.—Rotalia Freyeri: a many-shelled Foraminifer, or a
colony of many single-shelled Foraminifera, with pseudopodia extended.]
=Foraminifera.= These are little protoplasmic unicellular animals
that have the power of secreting for themselves more or less complex
envelopes composed of _limestone_. They may be single, as in _Lagena_,
or composed of a number of individuals with the shells cemented together
as in Globigerina or _Rotalia_ (Fig. 4). They have played a part of vast
importance in the geological development of the world. Their myriads of
shells remaining at the bottom of seas millions of years after the little
protoplasmic bodies have perished, they have been consolidated into vast
expanses of limestone rocks, and finally uplifted into such formations as
the huge chalk cliffs of England.
=Osteoblasts and Osteoclasts.= These cells are naked pieces of
protoplasm, the latter much the larger and having many nuclei. They are
concerned in some of the most interesting phenomena of many growing
animals. Just as the Foraminifera have the power of forming complex
aggregations of limestone shells, so the Osteoblasts have the power to
construct the bones of animals. And when a bone is broken as the result
of accident, these little cells do the mending. While the Osteoblasts are
_bone-formers_, the Osteoclasts are _bone-destroyers_. It is very curious
that little specks of living jelly, like these Osteoclasts, should have
the power of destroying hard tissue like bone, but such is the fact.
These Osteoclasts can, by their wonderful chemical processes, liquefy
and absorb, and by these means destroy, ivory pegs that are driven into
living bone. They are the agents by which the roots of children’s milk
teeth are destroyed, so that the crowns of the teeth are shed and the way
paved for the appearance of the permanent teeth. The wonderful activity
of these little Osteoblasts and Osteoclasts is well exemplified in the
growth and shedding of the antlers of deer. While these antlers are
growing in the spring, they are covered with a delicate skin, technically
called “velvet.” This velvet is very sensitive and quite warm from the
nutrient blood circulating through it. In it are hundreds and thousands
of busy, living Osteoblasts that work together under some mysterious,
directing or coördinating agency, to build up the splendid beams, tynes
and snags that constitute the antlers, which in many deer of the Rocky
Mountains reach such a size that a man may walk under the archway made by
setting the shed antlers up on their points. No hive of bees is busier
or more replete with active life than the antler of a stag as it grows
beneath the warm, soft velvet, through the agency of the Osteoblasts.
The building of the antlers by these little agents continues through the
spring and summer. In the autumn the Osteoblasts cease their activity
and die; the delicate, sensitive velvet dries and peels off, leaving the
dead, hard, bony substance exposed, and they now become weapons adapted
for fighting. This is the season when the stags challenge one another to
single combat, the hinds standing timidly by to be taken by the victor
as his mates. When the loves and battles of the autumn are over and the
mating is completed, the antlers no longer serve a useful purpose, and
they are shed. The shedding is accomplished through the agency of the
bone-destroyers, the little jelly-like cells called Osteoclasts.
=Bacteria= are exceedingly minute specks of naked protoplasm. They are
unicellular plants. Some of them are harmless to mankind; some are very
useful to him, and others are his deadly enemies. Many of them are
concerned in the production of the infectious diseases. They do so by
elaborating various chemical products that are virulent poisons, hence
these products are called toxines; when taken up by the blood, they are
carried to various parts of the body. In this manner they cause the
particular symptoms that are characteristic of a special infectious
disease. Why is it that some persons, on exposure to an infectious
disease, contract the malady while others similarly exposed do not? In
other words, what gives immunity to disease? The explanation is probably
as follows: Just as the invading bacteria have the power of secreting
_toxines_, so the cells of the body, normally, have the power of
elaborating chemical products that are antidotes to the toxines, and are
appropriately called _antitoxines_. Infectious diseases and immunity from
them, are the result of a contest between the invading bacteria and the
protecting cells of the body. If the bacteria secrete toxines in greater
quantities than can be neutralized by the cells of the body, we have
disease; if the reverse occur, we have immunity.
The =white blood-corpuscles= (cells) also take part in this warfare. They
have the power of traveling, in virtue of their amœboid movements, from
the blood to the part invaded by the bacteria. Here a contest takes place
between them, the corpuscle takes the bacteria into its interior, and
either kills them or is itself killed. The result of this contest helps
to produce either immunity or infection.
=Tetanus bacillus= is a cell shaped like a slender rod. It has the power
of secreting a poison which, when introduced into the body, produces
convulsions and other symptoms of lockjaw. These much resemble those
induced by strychnine poisoning.
=Bacillus diphtheriæ= is an exceedingly small unicellular plant, and has
the power of producing a poison called _toxalbumin_, which is analogous
to the poison of certain venomous serpents. It is the speck of protoplasm
through whose activity diphtheria is caused.
Many useful bacteria have the power of so acting on dead organic bodies
as to decompose them, the three most conspicuous end-products of this
decomposition being water, carbonic oxide and ammonia. When the dead
bodies are decomposed in the soil there are other bacteria, in addition,
that have the power of further acting on the ammonia, causing its
oxidation and producing nitrous and nitric acids and their salts. The
unicellular plants that bring about these changes are the _nitrifying
bacteria_. Conspicuous illustrations of the functional activity of these
little naked pieces of protoplasm are seen in the immense saltpeter
beds of Peru and Chili, where, from the enormous fecal accumulations of
sea-fowls, the immense quantities of nitrates are produced that supply
the commercial world.
[Illustration: FIG. 5.—Difflugia Pyriformis.]
=Arcella=, of which there are many species, is a unicellular animal whose
protoplasmic body has secreted from its surface an enclosing “test” that
is composed of a _horny membrane_, resembling very much in constitution
the chitin which gives firmness to the integuments of insects. This
creature is commonly discoidal in shape, with one face arched and the
other flat, an aperture being situated in the center of the flat side
through which the creature may thrust its pseudopodia or withdraw them.
The surface of the testaceous covering is often marked with a regular
but minute and attractive pattern. In =Difflugia= (Fig. 5), the test
is somewhat pitcher-shaped, and is mostly made up (by the constructive
activity of the protoplasm) of exceedingly small particles of shell and
gravel cemented together. Many testaceous amœbans form tests of singular
beauty and remarkable regularity. In some of the animals the minute
plates of which the tests are formed have been picked up from the surface
over which the animals crawl, and are cemented into various charming
patterns; and in other cases they are formed by secretion from their own
bodies. In =Quadrula symmetrica= the protoplasmic body has constructed
a pear-shaped testaceous covering, of complete transparence-like glass,
composed of a great number of square plates touching each other by
their edges. The protoplasmic body of the animal does not entirely
fill the test, the intervening space being occupied by a clear liquid
and traversed by bands of protoplasm. A clear, large spherical nucleus
is seen in the part farthest from the pseudopodia. It contains a dark
and well-defined nucleolus. In front of the nucleus two contractile
vesicles are to be observed. The pseudopodia in these creatures, it
must be remembered, are not appendages, but lobate protrusions of the
protoplasmic body, are few in number, rounded, short and broad.
=Diatoms= are unicellular plants, isolated or aggregated together, that
have the power of constructing flint coverings, often of great complexity
and charming pattern. The tracings on many of these flint coverings are
so constant and small, that they are frequently employed for the purpose
of testing the power of modern compound microscopes. In various parts
of the world vast deposits of Diatoms have been discovered. The most
remarkable of these for extent, as well as for the beauty and number of
the species contained in it, is that on which the city of Richmond, in
Virginia, is built, which is over thirty feet deep and extends for many
miles.
[Illustration: FIG. 6.—Noctiluca miliaris. A, dorsal view; B, side view;
n, nucleus; f, flagellum; a, entrance to atrium; b, atrium; o, œsophagus;
r, superficial ridge.]
=Noctiluca miliaris= (Fig. 6) is a very large unicellular, flagellate
animal. It is spheroidal in form, and has an average diameter of not
quite one-half a millimeter. It is just large enough to be observed
by the unaided eye when the water in which the animal may be swimming
is contained in a glass jar held up to the light. It has a tail-like
appendage (flagellum) by which the animal moves about. Along one side
of the cell is a meridional groove resembling that of a peach, and
leading into a deep depression of the surface termed the atrium (Fig.
6, B, b). It is from the shallow commencement of this depression that
the flagellum (Fig. 6, f) originates. At the base of the flagellum the
depression sinks down to the mouth (o). A slightly elevated ridge (r)
extends along the opposite meridian and commences with a bifurcation at
that end of the atrium farthest from the flagellum. The mouth opens into
a short œsophagus, which leads down directly to the central protoplasmic
mass. The central protoplasmic mass sends off branching prolongations
of its substance in all directions, the ramifications of which freely
inosculate. The farther these ramifications extend out to the periphery,
the thinner they become, until finally a protoplasmic network of extreme
tenuity is formed immediately under the enveloping membrane of the cell.
In addition to these ramifying prolongations, the central protoplasmic
mass sends off a thin, broad, irregular extension to the superficial
ridge and coalesces with it. Near the central protoplasmic mass is seen
the nucleus (n).
The flagellum is a flattened, whip-like filament, having a striated
appearance, and gradually tapers from the base to its extremity. It
slowly bends over five or six times a minute to the mouth, and then,
more slowly still, bends away again. It is through the movements of the
flagellum that particles of food are driven into the mouth and down
the œsophagus into the central protoplasmic mass. In this mass and its
extensions the food is digested and assimilated.
This little one-celled animal has the power, through its special chemical
activities, of manufacturing and emitting light. It is through the agency
of myriads of these little creatures that the diffused luminosity of some
seas is produced and can be observed at night. The Noctiluca is very
transparent, and for this reason it is a particularly favorable subject
for the study of its luminosity or phosphorescence. They can be obtained
by the tow-net in unlimited quantities from the sea and transferred into
a jar of sea water. Here they soon rise to the surface, forming a thick
layer. If the jar be placed in the dark and agitated in the slightest
degree, there is an instantaneous display of light, which is of a
beautiful greenish tint. The light emitted by the Noctiluca is so vivid
that it can even be observed in ordinary lamp-light. This phosphorescence
is only of an instant’s duration, and a short rest is necessary for its
renewal. The special locality for the formation of the phosphorescence
is in the very fine protoplasmic network, which lines the external
structureless membrane or cell wall. These wonderful little Noctilucæ may
well be figuratively called the fire-flies of the ocean.
[Illustration: FIG. 7.—Gromia oviformis with protoplasmic threads
(pseudopodia) extended and forming an elaborate network in which a
captured unicellular organism is seen; d, diatom captured; p, protoplasm
containing captured diatoms; s, shell.]
=Gromia oviformis= (Fig. 7) is often found in fresh water adhering to
confervæ and other plants of running streams. The protoplasmic body of
this animal is enveloped in a chitinous covering that is egg-shaped and
of a brownish-yellow color. It is about two millimeters in diameter.
When the animal is quiet, no one would suspect its real nature, so much
does it look like the seed of an aquatic plant. The testaceous envelope
has a single round orifice at its more pointed end. The animal, when in
an active state, pushes out the protoplasmic substance, which speedily
gives off ramifying extensions, and these by further ramification and
inosculation form a complicated network. The protoplasm of the animal
also extends itself in such a way as to form a continuous layer on the
external surface of the test. From this layer numerous protoplasmic
threads may extend out, forming more or less complicated networks. By
the alternate contraction and extension of its protoplasmic threads and
networks, minute one-celled plants and animals are entrapped like flies
in a spider’s web (d). When caught they are carried, by retraction of the
protoplasmic thread-like pseudopodia, into the endoplasm in the test.
Here the nutritious parts of the entrapped creatures are abstracted and
assimilated. In transparent species, the indigestible parts, such as the
silicious valves of diatoms, may be distinguished in the midst of the
endoplasm, from which they are ultimately extruded.
When gromia oviformis reproduces by mitosis it gives off a bud (small
cell), which finally separates from the parent form and constitutes a
distinct individual. This process may be repeated many times, so that a
great number of separate individuals may be formed, all of which lead
detached and independent lives.
Most of the protozoa, which are produced by fission (cell division by
mitosis), separate entirely from each other, as in Gromia; but in many of
these unicellular animals, the new creatures produced by fission do not
separate from one another, but remain more or less closely connected, and
thus form _colonies_ of Protozoans. These colonies are of the greatest
interest, for they represent a lower stage of the _cell colonies_ of the
Metazoa (multicellular animals). They reproduce, in many cases, in a way
which is strongly suggestive of reproduction in the Metazoa.
=Microgromia socialis= is a little unicellular animal, having a thin,
nearly globular, calcareous shell that it secretes upon its surface. It
multiplies by fission, and forms a number of distinct individuals which
have the curious habit of fusing their pseudopodia and uniting into
a more or less closely associated colony. The individuals sometimes
remain at a distance from one another, but sometimes associate themselves
together into a compact colony. These individuals are all alike,
performing the same functions. There is no division of labor among the
units, but they live practically an independent life. If the individual
animals were detached from one another, they would live and build new
colonies.
=Codosiga umbellata= is another unicellular animal—a flagellate
Protozoan. It has a collar-like extension of its ectoplasm from the
anterior extremity of its body, forming a sort of funnel from the bottom
of which the thread-like structure (flagellum) arises. The vibrations of
this flagellum cause a current of the surrounding fluid to set into the
funnel so that particles of food reach the soft protoplasmic substance
which serves as a mouth. The nucleus is seen near the base of the collar.
Near the posterior extremity of the body two contractile vesicles are to
be observed. This posterior extremity of the animal has a cylindrical
extension of its ectoplasm by which it attaches itself to an object. This
protozoan multiplies by longitudinal fission. In some species the animals
separate completely from one another and lead entirely independent lives.
But in _Codosiga umbellata_ the fission does not extend through the
cylindrical extension, so that a group of animals are associated in a
colony.
=Rotalia or Globigerina.= The shelled amœba (_Lagena_) gives off a bud
(unseparated cell) which grows to the full size, secretes its calcareous
shell and remains connected with the parent form. This process may be
repeated a number of times until a colony of shelled amœbæ, of varying
pattern in different species, may be formed and permanently associated
together (Fig. 4). The individual amœbæ are all alike and perform the
same functions. There is no division of labor, no specialization, among
them. If the individual animals could be separated from one another they
would live and build new colonies.
=Pandorina morum= forms a small colony of sixteen cells (solid sphere) of
mulberry-like shape and enclosed in a common gelatinous envelope. Each
cell in the mulberry mass bears two flagella on its peripheral end. These
project out beyond the surface of the gelatinous envelope, and are agents
for locomotion of the colony. The cells in the colony are all alike.
There is no division of labor among them. They all act alike. The cells
(flagellate protozoans) of the colony may reproduce in two ways. Each
animal in the colony may subdivide into sixteen smaller units, each of
which by growth and multiplication may form a new mulberry mass, a new
colony, each unit of which acquires two flagella. Or two of the small
units may amalgamate (conjugate), and then develop (by fission) into a
new colony. The conjugating units are nearly of the same size and look
very much alike.
=Volvox globator= is a spheroidal shaped colony (hollow sphere) of
unicellular flagellate animals, about one-half a millimeter in size.
It was formerly supposed to be a fresh-water _Alga_. It is now known
to be a colony of _Protozoans_. All the animals in this colony are not
alike. There is a division of labor among the cells, for some are merely
vegetative, serving purposes of nutrition, and having no reproductive
powers; while other members of the colony are purely reproductive
animals. Furthermore, there is quite a marked specialization of the
reproductive cells. Those reproductive cells that may be spoken of as
the female cells are large and non-motile encysted cells. The male cells
are small and actively motile, in that they have two flagella developed
on them. A small flagellate male cell penetrates the large encysted
female cell, and as the result of this conjugation, fission takes place
repeatedly, and a new colony of flagellate protozoans (volvox) is formed.
Volvox approaches very suggestively towards the type of animals known as
Metazoan.
In order to comprehend, in some measure, the transition from _Colonial
Protozoa_ to _Metazoa_, it will be well for the reader to study a
typical sponge. For a long time the Porifera (Sponges) were looked upon
as compound Protozoa (colonial Protozoa), but while they are nearer the
Protozoa than any of the other types of Metazoa, their position in the
animal series is unquestionably among the Metazoa. The Sponge, like the
rest of the Metazoa, develops from a fertilized egg by a process of cell
multiplication, differentiation, gastrulation, etc.
CELL REPRODUCTION BY MITOSIS.
The multiplication of cells plays a part of such fundamental importance
in Evolution, and therefore in Embryology and studies in Heredity,
that it is necessary to study the subject somewhat in detail. It is a
wonderful process, and is worthy of very careful attention.
[Illustration: FIG. 8.—Diagram illustrating Mitosis. A, the cell
commencing activity; B, C, D, phases in the formation of the spindle and
the chromatin loops or V’s, also showing that the mother V’s have split
into daughter V’s; D, the chromatin loops forming the equatorial plate,
_chr_; E, F, G, separation of the daughter loops (daughter chromosomes)
and their passage towards the poles of the spindle, thus forming daughter
nuclei; H, I, division of the protoplasm so as to form two daughter
cells; at, attraction sphere enclosing a centrosome; n m, nuclear
membrane; chr., chromatin threads; p, protoplasm; c w, cell wall; sp,
spindle.]
The process by which one cell (a mother cell) divides into two
cells (daughter cells) is called _mitosis_, and is inaugurated by the
_centrosome_ (Fig. 8, A, _at_). The centrosome divides into _two_
centrosomes, which at first remain close together (Fig. 8, B, _sp_),
and then gradually separate from one another. Each centrosome becomes
the center of a system of fine achromatin fibers arranged round it in
a radiating manner and forming what is called the _attraction sphere_;
also, at the same time, a spindle-shaped bundle of achromatin fibers,
called the _spindle_ (Fig. 8, B, sp), extends between the centrosomes.
In the meantime, important changes have been taking place in the
chromosomes (hereditary threads) of the nucleus. The chromosomes, which
at first are arranged in an apparently inextricable tangle or network,
frequently assume U-shaped or V-shaped forms (Fig. 8, C, _chr_), and
the nuclear membrane disappears. Sooner or later each chromosome splits
longitudinally into two daughter chromosomes, with which the achromatin
fibers of the spindle become connected (Fig. 8, D). In this phase of
mitosis the split V-shaped chromosomes form a single group called the
_equatorial plate_ (chr), and extend across the axis of the spindle.
It is to be observed from the diagrams in the figure, that one of the
centrosomes has traveled to the opposite pole of the nucleus, thus
causing the achromatin fibers of the spindle to extend across the
original site of the nucleus. The equatorial plate of split V-shaped
mother chromosomes (hereditary threads) thus divides the fibers of the
spindle into two parts, one half extending from one centrosome to one
group of daughter chromosomes, while the remaining half extend from the
other centrosome to the other group of daughter chromosomes. Soon the
achromatin fibers of the spindle contract, and in this way separate the
two groups of daughter chromosomes, so that one group is drawn towards
one centrosome, and the other group to the other centrosome (Fig. 8, E,
F, G, H). After the two groups of daughter chromosomes have been drawn to
their respective centrosomes, each group assumes the tangle or network
phase like the nucleus of the mother cell, and an investing nuclear
membrane reappears for each (Fig. 8, I). Thus from the mother nucleus of
the mother cell we get two daughter nuclei (I). In a further phase of
the mitotic process, a furrow appears on the surface of the protoplasm
and surrounds it in the form of a ring. This furrow is in a plane at
right angles to the long axis of the spindle, and gradually deepens until
the protoplasm is divided into two parts, each segment of protoplasm
containing its own nucleus and centrosome; in short, the mother cell has
divided into two daughter cells (I).
It will thus be observed that the centrosomes and their achromatin fibers
are a beautiful mechanism by which the heredity threads (chromosomes) are
exactly divided into two equivalent halves.
There are some cells (_Amœba proteus_, for instance,) which divide in a
much simpler manner than by mitosis; in these there is no complicated
rearrangement of the chromosomes and no disappearance of the nuclear
membrane, the nucleus simply becoming separated into two parts
(_Amitosis_).
=The Human Ovum.= The human ovum is a typical cell about one-fifth
of a millimeter in size and spherical in shape. It is a nucleated
piece of protoplasm possessing an enveloping cell-wall (metaplasm).
The protoplasm contains nutrient material or yolk (metaplasm). The
_maturation_ of the ovum essentially consists in throwing out half of its
chromosomes. In doing this the nucleus (mother) approaches the surface of
the protoplasm (Fig. 9, A), and divides, by mitosis, into two daughter
nuclei; then the unripe ovum divides into two cells, but of very unequal
size. This process is repeated a second time. Thus two small cells are
formed which are known as the _polar bodies_ (Fig. 9, A, B, pol. b). The
large cell remaining after the formation of the two polar bodies is the
_mature ovum_ (B). Its nucleus, which recedes towards the center of the
protoplasm, is called the female _pronucleus_ (Fig. 9, B, f. pr.). The
pronuclei of mature ova differ from the nuclei of all the other cells of
the body in that they only contain half as many chromosomes (hereditary
threads).
The ripe _spermatozoid_ (a flagellate sexual cell of the male)
corresponds to the ovum of the female. It also contains a pronucleus
having only half the number of chromosomes that the other cells of the
adult body possess.
=Fertilization.= The male sexual cell (_spermatozoid_) is vastly smaller
than the female sexual cell (ovum). Having a _flagellum_ (Fig. 9, B,
s), it moves about, like a tadpole in water, and seeks the ovum. When
it comes in contact with the ovum it penetrates into its interior
(usually only one doing so), as indicated at (Fig. 9, B, s). The tail or
_flagellum_ of the spermatozoid fuses with the protoplasm of the ovum,
and disappears from view. Its _pronucleus_ (C, m. pr.), accompanied
by its _centrosome_ (C, m. c.), approaches the _female pronucleus_
(f. pr.) of the ovum (Fig. 9, C, D). Finally the male and female
pronuclei coalesce to form a single nucleus (Fig. 9, E, n. os.). The
centrosome of the ovum persists for awhile and then disappears; that of
the spermatozoid remains in the ovum, and is the agency by which cell
multiplication, through _mitosis_, takes place.
[Illustration: FIG. 9.—Diagram illustrating the maturation and
fertilization of the human ovum. A, one polar body is formed and a
second is in process of formation; B, both polar bodies are formed and
a spermatozoid is penetrating the ovum; C and D represent the approach
of the male pronucleus towards the female pronucleus; E indicates the
amalgamation of the two pronuclei to form the nucleus of the oösperm
(segmentation nucleus); pol. b, polar bodies; pol. c, centrosome of the
polar body; chr. p, chromatin of the polar body; f pr, female pronucleus;
p, protoplasm; p p, peripheral protoplasm (but _not_ cell wall); f c,
female centrosome; m c, male centrosome; m pr, male pronucleus; n, os,
nucleus of the oösperm (first stage of a human being).]
The cell resulting from the coalescence of the male pronucleus with the
pronucleus of the ovum, and which is only one fifth of a millimeter in
size, is the first stage in the existence of a human being. Man thus
starts his career as a Protozoan-like creature,—as a unicellular animal.
The fertilized ovum is called the sperm-egg (_oösperm_), and contains now
the normal number of _hereditary threads_ (chromosomes); for those of the
male have been added to those of the female.
=Segmentation of the Oösperm.= The fertilization of the ovum imparts
to it a wonderful stimulus, so that the oösperm divides, by mitosis,
into two cells, these two into four, the four into eight, the eight
into sixteen, these into thirty-two, and so on repeatedly, until a
large number of comparatively small cells are formed (Fig. 10). This
mass of cells is spherical in shape, and the little round cells towards
the surface project in such a way as to give to the mass an appearance
somewhat similar to the fruit of the mulberry, whence it is termed the
mulberry body or _morula_ (Fig. 10, 4). In the morula stage of his
existence man resembles the solid colony of protozoans represented by
_Pandorina_. The cells of the morula next become arranged regularly in a
single layer at the circumference, by which the embryo assumes the form
of a hollow sphere, and is known as the _blastula_ (Fig. 10, 5). This
phase of man’s existence is quite suggestive of _Volvox_.
Soon one side of the blastula is invaginated or pushed in, as one
would push in one side of a hollow india-rubber ball. The result of
this invagination (called _gastrulation_ technically) is the formation
of a sort of cup. This is the _gastrula_ (Fig. 10, 6) phase of man’s
existence. It is a higher and fundamentally different phase of existence
than either the morula or the blastula. It corresponds, not to a
Protozoan, but to the higher Metazoan. It possesses the fundamental
anatomical qualities of a low Cœlenterate (Polyp).
The mode of gastrulation is different in man from that just described,
and varies in different animals, but the essential point common to all
is the formation of a double cellular-membrane; the outer membrane being
called _epiblast_ or ectoderm, and the inner one _hypoblast_ or endoderm,
the enclosed cavity being the primitive digestive cavity. These two
layers are the primary germinal layers. A third layer is subsequently
formed between them, by the agency of one or both of them, and is called
the _mesoblast_. From these three simple membranes, which are composed
exclusively of cells, are formed all the complex tissues and organs of
the adult man. The _epiblast_ develops into the nervous system (brain,
spinal cord, and nerves), and the cuticle, hair, etc. The _hypoblast_
develops into the cellular parts of the digestive canal, the liver,
lungs, etc. The _mesoblast_ develops into the muscles, bones, ligaments,
blood-vessels, etc. To trace the details of this evolution of a human
being from the microscopic _oösperm_ is a fascinating and instructive
study, but is beyond the limits and purpose of this little book. It will
well repay further careful study by the reader.
A careful study of the life-histories of the few unicellular animals and
plants mentioned in the preceding pages will help to let one realize the
wonderful powers of nucleated pieces of protoplasm (cells). If isolated
pieces of protoplasm can accomplish so much, one will not be astonished
to learn that many diverse cells associated together in intimate
correlations, as occurs in the higher animals, may accomplish results
that are profoundly interesting and marvelous. As far as anatomy and
physiology alone can reveal, it is the result of millions of cells acting
together that makes possible the existence of such a living, sentient,
thinking creature as man or the highly intelligent elephant or any other
multicellular animal. It is due to the mysterious powers of protoplasm
that one little microscopic cell, like the fertilized ovum of a woman, is
able to hold all the heritages of the race, and gradually unfold them as
it builds up the body into myriads of diverse cells intimately associated
together.
All of the wonderful results of Embryology are accomplished through
cell-multiplications, cell-differentiations, cell-associations,
invagination and evaginations of cell-groups (tissues or organs), and
unequal growth of parts (cells or groups of cells).
[Illustration: FIG. 10.—Segmentation of the fertilized ovum and
Gastrulation: 4, morula; 5, section through blastula showing hollow
sphere; 6, gastrula showing outer layer of cells (epiblast) and inner
layer (hypoblast); the 6 is at the mouth of the cavity (enteron) of the
gastrula.]
In concluding this brief but, we hope, useful study of a few selected
cells, we may say that an eminent English physiologist has made the
statement that a student who has not looked through the microscope and
observed the circulation of the blood in the web of a frog’s foot is not
fit to study medicine. However beautiful, fascinating and instructive the
sight of this circulation may be, we are tempted to make the assertion
that the student who has not looked through the microscope at some of
the superficial ooze from the bottom of any slow-running stream, in
summer, and observed the structure and actions of that wonderful little
unicellular animal, the Amœba proteus, is still less prepared to study
medicine. In this little speck of protoplasm the problems of life are
reduced to their simplest forms, for all higher plants and animals may be
regarded as groups of more or less modified amœbæ peculiarly associated
together. In our studies of the amœba we will be forcibly reminded
of a very clever trick which is practiced in India and is called the
mango-trick. In this trick a seed is put into the ground and covered up,
and after divers incantations a full-blown mango-bush appears within five
minutes. We have never met any one who knew how this thing was done, nor
have we ever seen a person who believed it to be anything else than a
conjuring trick. So it is with the _amœba_, a beautiful and fascinating
trickster of nature. We understand some of its activities, interesting
and exceedingly instructive, but there are many others beyond our ken. We
see the commencement and ending of many of its chemical activities, but
there are numerous other intermediary processes that take place in the
hidden recesses of the protoplasm, and concerning which we know nothing.
It may fall to the lot of some reader of this little book, as a patient
and keen observer, to unravel some of these mango-like tricks of the
amœba or other unicellular creature.
SECTION II.
HEREDITY WITH VARIATION.
HEREDITY WITH VARIATION.
That an offspring always inherits from its parents many of their
characteristics is well known; that it always varies, more or less, from
them is also equally well known. Heredity and variation are twin forces
that play upon every creature, holding it rigidly true to the parental
type or compelling more or less divergence therefrom, according to
the strength of the one or other power; so that every creature is the
resultant of the activities of these two great parallel forces. Variation
is coextensive with heredity, and every living creature gives evidence of
the existence of variations.
=Examples of Variations.= No two leaves on a plant are exactly alike;
no two children of the same parents give a perfect resemblance; no two
individuals of the same species are molded in precisely the same pattern;
of the thousands and thousands of faces that we observe in a city in the
course of a year, each has some distinctive peculiarity.
The trained eye of the gardener recognizes each hyacinth among hundreds
of bulbs; of the shepherd, each sheep in his flock; of the Laplander,
each reindeer crowded in his herd like ants on the anthill. In a flock of
1,000 sheep each mother can even recognize a variation in the _voice_ of
her own lamb, all alike to _us_.
Every part of an animal is subject to variations, not only in bodily
structure, but also in habits and instincts, and these variations are
large in amount, numerous and diverse in character. Many observations,
experiments and measurements that have been made at various times attest
the truth of this assertion. Not only do variations take place in animals
and plants under domestication, but also in the wild state.
=Illustrations of Heredity.= _Mental heredity_ can be illustrated by
studying the genealogies of such persons as Aristotle, Goethe, Darwin,
Coleridge, Milton, etc. Probably the Bach family, of Germany, supply one
of the best illustrations of the inheritance of intellectual character
that we know of. The record of this family begins in 1550, lasting
through eight generations to 1800. For about two centuries it gave to the
world musicians and singers of high rank. The founder was Weit Bach, a
baker of Presburg, who sought recreation from his routine work in song
and music. For nearly two hundred years his descendants, who were very
numerous in Franconia, Thuringia, and Saxony, retained a musical talent,
being all church singers and organists.
When the members of the family had become very numerous and widely
separated from one another, they decided to meet at a stated place once a
year. Often more than a hundred persons—men, women and children—bearing
the name of Bach were thus brought together. This family reunion
continued until nearly the middle of the eighteenth century. In this
family of musicians twenty-nine became eminent.
_Inheritance of moral character_ is well established. Heredity, in its
relation to crime and pauperism, has been thoroughly investigated by Mr.
Dugdale in his most instructive little work entitled _The Jukes_. In
this work the descendants of _one_ vicious and neglected girl are traced
through a large number of generations. It reveals that a large proportion
of the descendants of this woman became licentious, for, in the course of
six generations, fifty-two per cent. of the females became harlots and
twenty-three per cent. of the children were illegitimate. It shows also
that there were seven times more paupers among the women than among the
average women of the State, and nine times more paupers among the male
descendants than among the average men of the State.
The inheritance of _physical peculiarities_ is so obvious as to need
no illustration. Among the ancients the Romans stereotyped its truth
by the use of such expressions as the _labiones_, or thick-lipped;
the _nasones_, or big-nosed; the _capitones_, or big-headed; and the
_buccones_, or swollen-cheeked, etc. In more recent times we read of the
Austrian lip and the Bourbon nose.
Questions of heredity and variation are cytological ones—that is,
questions of the anatomy, physiology, physiological chemistry, and
pathology of cells. The most important part of a cell, as far as these
questions are concerned, is the =nucleus=. The nucleus is the physical
basis of all the heritages of an organism, from the simplest to the most
complex. The nuclear threads may, therefore, very appropriately be termed
the _hereditary threads_, or, collectively, the hereditary mass; and
the physiological units in them the _hereditary units_. The nucleus is
of fundamental importance in the reproduction or multiplication of both
unicellular and multicellular animals and plants.
In unicellular creatures multiplication may take place by fission and by
conjugation. Both of these processes can be studied by observation of
the infusorians. Maupas’s beautiful investigations on these unicellular
animals have demonstrated that multiplication by fission may proceed to
a prodigious extent for many generations, but that a time comes when
the process fails, and the species will become exhausted and die out
unless there is a rejuvenation of it by conjugation of individuals. In
conjugation two individual infusoria come in apposition with each other,
the nucleus in each undergoes subdivision. They reciprocally exchange
part of their nuclear contents so that each infusorian comes to contain
hereditary threads of two distinct individuals. From these rejuvenated
(or fertilized) individuals multitudes of others may be derived by
fission until exhaustion again takes place.
Multiplication in multicellular creatures may be accomplished by budding
(which is allied to fission), and is exemplified in the plant, hydra,
the queen bee (parthenogenesis), etc., and by fertilization (which is
allied to conjugation). A knowledge of the phenomena of fertilization of
the ovum by the spermatozoid is essential to any understanding of the
problems of heredity and variation in mankind. The nuclear threads of
the ovum are its hereditary threads—the _groups of maternal hereditary
units_; likewise, the nucleus of the spermatozoid contains the _paternal
groups of hereditary units_.
=Fertilization.= In fertilization, the spermatozoid (a nucleated
flagellate cell) penetrates the ovum (a nucleated, encysted cell), its
protoplasm mixes with that of the ovum, and its nuclear threads come into
relation with the nuclear threads of the ovum; so that the fertilized
ovum (a new creature, a veritable microcosm) is still a nucleated cell,
but one in which the nucleus is compound, is _hermaphroditic_, in that
it contains maternal and paternal threads—that is, maternal and paternal
hereditary units which constitute its hereditary mass.
It will be convenient to speak of the maternal and paternal hereditary
units in the fertilized ovum as _ancestral hereditary units_.
This hermaphroditic cell passes through complex phases, illustrated by
embryology, to the adult. In doing so this hermaphroditic cell (mother
cell) first divides into two smaller cells (daughter cells). The mother
cell divides in such a way (by mitosis) that one-half of its nucleus
and part of its protoplasm goes to one daughter cell and the other half
of the nucleus, with the remainder of the protoplasm, goes to the other
daughter cell. It is an interesting fact that although the amount of
protoplasm which goes from the mother cell to the two daughter cells may
be unequal at times, yet the amount of the nucleus in one daughter cell
is always exactly equal[2] to that in the other; _so that each daughter
cell contains maternal and paternal hereditary masses of equal quantity
and quality_, being in fact one-half that of the fertilized ovum. In
consequence of the fact that each hereditary unit in the nucleus of the
daughter cell can absorb nutriment and grow, it comes about that the
nucleus of each daughter cell attains to the size of that of the mother
cell. The enveloping protoplasm of the nuclei also grows to a greater or
less extent, so that the cells as a whole grow. These two daughter cells
go through the same process and form other daughter cells, and so on
through all the mitoses of development, until all the myriads of cells
of a living organism are produced, _each of which contains maternal and
paternal hereditary masses of equal quality and quantity, and also of
the same character as that of the fertilized ovum whence they are all
derived_.
Apart from their activity in absorbing nutriment and growing, the great
majority of the hereditary units in the nuclei of the forming cells
remain latent. But some of the hereditary units in each cell produced are
active. They multiply, grow and migrate out of the nucleus, and get among
the units of the enveloping protoplasm. During this activity they undergo
physical and chemical changes and effect corresponding differentiations
in the protoplasm of the cell. Thus, through many mitoses and many
differentiations of the protoplasm of cells, we finally derive from the
fertilized ovum all the cells that constitute the adult body, such as
muscle cells, glandular cells (as liver cells, kidney cells, etc.), nerve
cells, skeletal cells (as bone, cartilage, and connective-tissue cells),
and the ova and spermatozoids. According to this theory, the _nucleus_ of
each cell in the adult animal or plant is _pure hereditary mass_, exactly
like that in the nucleus of the fertilized ovum; but the _protoplasm_
of each adult cell that envelopes the nucleus may differ greatly in
different cell groups, as in muscle, nerve, cartilage, and the like. Of
course, the protoplasm of those cells that develop into the ova and the
spermatozoids has differentiated along such lines as to become like that
of the ovum and spermatozoid, the junction of which formed the fertilized
ovum. These statements hold true for plants and the lower animal
organisms, although they cannot be verified for the higher animals. More
than likely the pure hereditary masses are present in the body (somatic)
cells of the higher organism in latent conditions, but are unable ever to
be developed owing to the greater specialization of these cells. It is
thus seen that all the cells of many animals and plants can perform their
own special functions and at the same time contain all of the hereditary
units of the complex organism in a state ready to develop under favoring
conditions.
Since the ova and spermatozoids are cells specially differentiated for
the purpose of propagating the species by sexual generation, and since
their conjugation produces the germ of a new creature, they may very
appropriately be spoken of as =germ cells=. Since all the other cells of
the adult form the great bulk of the body that envelopes and protects the
germ cells, they may be termed the =body cells=, or =somatic cells=.
Suppose that ova, containing maternal and paternal groups of hereditary
units, are fertilized by similarly complex spermatozoids, and the process
is repeated generation after generation. There will come a time when the
fertilized ovum will have a highly complex nucleus composed of _many
different ancestral groups of hereditary units_.
One often hears the expression that a child is a chip of the old block;
but this is only a very partial truth, for a child is preëminently a
composite chip of many old blocks.
The complex nucleus of the fertilized ovum may be compared to a modern
Italian building which has been constructed of material—a column here, a
cornice there, a lintel yonder—gathered from different classic buildings
of varying antiquity. In view of the increasing number of ancestral
groups of hereditary units that must have accumulated in the nuclei
of ova in the course of time, there must necessarily, for mechanical
reasons, have arrived a period when these nuclei could receive no more
of them by fertilization, unless natural selection should develop some
saving device; hence we have, possibly, an explanation of the phenomena
of maturation in ova (the _reducing process_ of Weismann and Hertwig).
Here the ovum, prior to fertilization, undergoes mitosis twice in
succession, by which the polar bodies are formed and the hereditary mass
is diminished by one-half (the mature germ cells having only one-half
the number of nuclear threads that the body cells possess). A homologous
process takes place in the maturation of spermatozoids. Fertilization
increases the amount of the hereditary mass in the ovum to the original
quantity, and thus restores the number of nuclear threads to the specific
number. All the body cells derived from the fertilized ovum possess,
also, the specific number of threads.
This union of two distinct hereditary masses is called _amphimixis_ as
well as _fertilization_.
Maturation and amphimixis or fertilization are _the source of many
variations in the body_, good and bad, beautiful and ugly, geniuses and
monstrosities; because, in the commingling of distinct hereditary masses,
there is a struggle for existence between the hereditary units and a
survival of the fittest.
In this struggle some of the hereditary units are strengthened so that
heritages may be augmented; some mix so that there may be a blending
of characteristics; some are mutually exclusive; some are prepotent;
some are neutralized; some are destroyed; some lie dormant (latent) for
varying lengths of time, and some are so altered as to produce much
modified forms; and thus the possibilities of combination, reactions
and modifications of the hereditary units, and therefore heritages, are
almost endless.
The _augmentation of heritages_ in the fertilized ovum is well displayed,
for instance, where fleet horses are bred with fleet ones, until, by
careful selection, generation after generation, a progeny may be secured
much more swift than the original stock from whence they were derived. In
the same way good milch cows have been produced.
The mixing of hereditary units and _blending of heritages_ is shown in
the color of the skin, as where a mulatto child is born to a negress by
a white father; _mutually exclusive heritages_ are well illustrated in
the color of the eyes, as where a child has either the blue eyes of one
parent or the black of the other, but never any blending of the colors;
this may also be illustrated where the white game bird and black one
are crossed, the young being either white or black, but never blended.
_Prepotency_ is illustrated where the silky variety of fan-tailed pigeon
is mated with any other small-sized variety of pigeon, for the silkiness
is invariably transmitted. A most interesting case of prepotency in
mankind, mentioned by Ribot, is that of Lislet-Geoffrey, an engineer in
Mauritius. He was the son of a very stupid negress and an educated white
man. In physical constitution he was as much a negro as his mother; he
had the woolly hair, the features, the complexion, and the peculiar odor
of his race. He was so thoroughly a white man as regards intellectual
development that he succeeded in vanquishing the prejudices of race,
so strong in the French colonies, and in being admitted into the most
aristocratic houses. At the time of his death he was Corresponding Member
of the Academy of Sciences.
In this, it will be observed, we have prepotency in the mother’s physical
constitution, and in the father’s intellectual characteristics.
The struggle of heritages in the impregnated ovum may lead to such
structural changes of the nucleus, and therefore of the cell, as to
develop the most marked variations—such variations as the biologists call
_sports_.
In the latter part of the eighteenth century the farmers of Massachusetts
had flocks of ordinary sheep on their farms. These sheep were continually
jumping fences and getting on neighboring farms. They were the source of
many disputes and much irritation between neighboring farmers. Finally,
one of the sheep had a lamb which, when grown, displayed well-marked
peculiarities (a sport). It had a longer body than the ordinary sheep
and shorter legs, which were bowed. It was noticed that this sheep could
not get over the fences. The cute Yankee farmer, noticing this valuable
peculiarity, carefully preserved this peculiar sheep, and from it was
ultimately derived, by careful selective breeding, a special variety
known as the Ancon sheep.
The germinal variations resulting from the mixing of two separate
hereditary masses by impregnation find their expression in the most
varied qualities of the minds and bodies of developing children. If the
variations are not especially marked, they are looked upon as normal and
attract no special attention.
But if the variations are so pronounced as to compel attention, and at
the same time it is known that they are useful, they are spoken of as
talents, or, on the other hand, if they are harmful or useless, they are
designated as pathological or monstrosities.
These are truly what the biologists call sports; and to those classes of
sports that occur as specially gifted in human culture, in the varied
fields of science, art, or literature, we assign such a person as
Shakespeare, and call the remarkable variations embodied in him genius.
On the other hand, such variations as lead to certain forms of pigmentary
degeneration of the retina, and to Daltonism, to dyschromatopsia and
achromatopsia, to certain supernumerary glands, polydactylism, and such
like, which are either useless or harmful, we designate as pathological
cases or monstrosities.
Hereditary units (the carriers of heritages) may be _latent_—that is,
they may appear late in life, or in the offspring, or, still again, in
remote descendants; in the latter cases the heritages are spoken of as
reversional or _atavistic_. Latent hereditary units may very usefully be
compared to dormant seeds buried in the ground. It is stated that buried
seeds may lie dormant for many years, so that when a plot of ground is
plowed deeply and upturned, plants that have not been seen there within
the memory of one will often make their appearance and flourish. The
hereditary units are veritable _living seeds_, that, under certain and
often unknown stimuli, grow and unfold their heritages as do the buried
seeds.
Latent heritages are well illustrated by a study of secondary sexual
characters as developed at puberty.
Among our barnyard fowls, the hens often, when they have atrophy
or degeneration of the ovaries, although up to this time they have
laid eggs for years, stop this function, put aside the plumage and
appearance proper to their sex, and don more or less completely the
garments of the rooster. Thus females have latent in them many secondary
sexual characters of the male. For similar reasons the male develops,
occasionally, female characters.
This latency is illustrated again in deer. In most species of the
deer tribe the males alone possess antlers, yet it is a well-known
circumstance that in females with degenerations of the ovaries
rudimentary horns that are never shed appear. A study of congenital
color-blindness illustrates beautifully latent heritages, showing how the
females of one generation may be free from the malady and the males of
the next afflicted.
A study of the _regeneration of lost parts_ in various animals and plants
illustrates well the latency of many hereditary units. A cutting made
from the willow and planted sends out roots and finally reaches the
dimensions of the adult tree. Here the body cells of the stem evidently
contained, in a latent condition, many hereditary units in their nuclei,
which became active through the special stimulus of being planted as
a cutting. Adult plants can be raised from the cuttings of many other
plants.
If the garden worm is cut in two, the head-part will reproduce the
tail-portion. If the little fresh-water polyp, Hydra, be cut into a
number of pieces, each segment will reproduce a perfect animal. Many
lizards, after losing their tails by violence, manufacture new tails
through the agency of the latent hereditary units contained in the body
cells of the stump left. If the tentacle or “horn” of a snail, which
contains an eye with a perfect lens and retina, be cut off, the animal
can reproduce another one with a perfect eye, and this can be repeated a
number of times. Often newts, when fighting with one another, or lobsters
when fighting, lose a leg or a claw. These highly organized animals
have the power of creating new limbs, making bones, ligaments, muscles,
nerves, cuticle, and so on. All of this is done _through the hereditary
masses in the nuclei of the body cells_ at the site of the injury.
A study of the phenomena of polymorphism in hydroids and insects will
beautifully and most interestingly illustrate latent hereditary units.
Much that is speculative and fanciful is included under the subject
of atavism, and the safest plan for pathologists and biologists, in
considering any abnormality, is to remember a golden rule of Gegenbaur,
that only those structures are reversional which are taxonomically not
far distant or phylogenetically not very old. Embryology is also a very
important check in considering such subjects.
In mankind supernumerary limbs and digits, microcephalia and
micrencephalia, have been looked upon as reversions to the simian type.
Lombroso, in contrasting the criminal with normal man, looks upon his
_homo delinquens_ as an illustration of atavism, contrasting with _homo
sapiens_. But, as Ziegler, in his _Pathology_, well observes, many
writers have gone too far in this respect, and have characterized as
atavistic formations various acquired pathological formations and fresh
variations of germ cells.
I think one can safely say that supernumerary ribs and those
supernumerary nipples and mammary glands along the line of the deep
epigastric and internal mammary arteries are truly atavistic structures;
also certain muscles normally belonging to those mammalia which come near
to man in the scale of relationship, and which appear in man as muscular
variations, are reversional.
Children are often born with pigmented hairy patches on their bodies
known as moles; sometimes these hairy moles are only of the size of a
split pea, in other cases they are several square inches in area, while
in rare cases almost all of the trunk may be thus covered. Although many
similar pathological cases are often but marked variations called sports,
yet the illustrations mentioned are undoubtedly reversional. Of the
multitudinous illustrations of atavism that could be mentioned I wish to
refer to but one more case.
The conjunctiva is a modification of skin, and frequently proclaims its
ancestry by reverting to its original form. It is by no means a very
rare event to see a patient having a patch of hair-covered skin growing
upon the ocular conjunctiva. While a clinical assistant at the Royal
Ophthalmic Hospital in London, we saw one such case, and Dr. Treacher
Collins, the pathologist of that eye hospital, has stated that about
twelve cases are seen there annually of this pathological condition,
which is atavistic, according to Sutton, although it seemingly violates
Gegenbaur’s rule about phylogenetic remoteness, and may be looked upon by
some as a pathological illustration of a sport.
In speaking of inheritance, we should carefully discriminate between
_heredity_ and _pseudo-heredity_. Physicians constantly write of
tuberculosis, lepra, smallpox, and syphilis as hereditary; but it is
incorrect and misleading to do so. When a person has syphilis, say, from
the earliest existence—that is, from the fertilized ovum by transmission
of a syphilitic microbe through the germ cells of the parents—this should
be designated by its proper name as _congenital bacterial infection_.
This is totally different from the hereditary qualities that flow from
the structural equilibrium following the commingling and struggle for
existence of multitudes of hereditary units.
The one set of hereditary qualities is _purely germinal_, while the
other is germinal _profoundly modified by the presence of an infecting
microbe_. Of course, to the extent that any toxines that are secreted by
the bacteria may cause permanent structural changes in the germ-cells, to
that extent may the germinal characteristics be transmitted and become
hereditary.
Many instances of infection of the child _in utero_ have been reported
in cases of endocarditis, scarlet fever, and smallpox; and there can
no longer be any doubt, from experimental investigation and recent
observation, that pneumococci, typhoid bacilli, anthrax bacilli, and
pus cocci are able to pass to the fœtus through the placenta. But the
diseases that develop in this way can be called hereditary with even less
semblance of correctness than in the case of the fertilized ovum that is
invaded with a microbe.
All of these cases are illustrations of pseudo-hereditary transmission,
and should, for the sake of clearness and accuracy, be spoken of as
_prenatal_ infections.
So far as the problems of heredity and variation are concerned, we may
say that the life cycle begins and ends with the germ cell. Insects lay
their eggs in old age; among plants the annuals flower but to die; in
higher creatures the cessation of the procreative power often marks the
beginning of bodily decline.
Bearing in mind that the human body consists of two great classes of
cells, germ cells and somatic cells, the following scheme will be found
very useful in discussing heredity with variation—viz.:
{ Stable
{ (Heredity) { Temperature. }
{ { Chemical }
{ { substances in }
{ { solution in the }
Germ-Cell { { Blastogenetic { fluids that }
{ { { bathe the }
{ { { germ-cells, as }
{ { { food, drugs, }
{ Unstable { { poisons, etc. }
{ (Variation) { } Environment
{ { Habitat }
{ { Temperature }
{ { Climate }
{ { Air }
{ Somatogenetic { Food }
{ Soil }
{ Water }
{ “Use” }
{ “Disuse” }
Just in proportion as fertilized germ cells during the mitoses of
ontogeny give origin, among the somatic cells, to other germ cells that
are structurally, and therefore physiologically, like themselves, just to
that extent do we have heredity; on the other hand, just to the degree
that the new germ cells which are produced are unstable, to that degree
also do we meet with variations.
ENVIRONMENT.
In zoölogy the environment of an organism means the sum-total of the
conditions of life that surround and affect it, such as food, air, water,
climate, etc.
We have already stated that as far as evolution is concerned the
structures of fundamental importance in an organism are the Germ-Cells;
therefore, for our purposes, we will define _environment to be the
sum-total of the conditions that directly or indirectly influence in any
way the germ-cells_, by which variations in them may be produced, or
through which stability may be maintained.
There are two great classes of environmental factors that bring about
variations in the germ-cells. One of these classes acts directly on
the germ-cells, and is therefore called _blastogenetic_; the other
acts indirectly through the body cells, and is therefore designated
_somatogenetic_. Many of the blastogenetic factors bringing about
structural changes in the delicate mechanism of germ-cells are entirely
unknown, and are therefore designated as fortuitous. Many other causes,
such as poisons in solution in the fluids that bathe them, can readily
enough be appreciated.
=Blastogenetic Factors.= It has been demonstrated that various _chemical
substances_, such as chloroform, morphia, chloral, etc., _have a
pronounced influence upon the vital activities of cells_. It is well
known that microscopic unicellular plants constitute the essential part
of yeast. These little cells have the power of causing fermentation in
solutions of grape sugar by which alcohol and carbon dioxide are formed,
the latter being a gas and escaping as bubbles. If chloroform or ether be
added to the solution of sugar, before adding the yeast, no fermentation
takes place, for the yeast-cells are paralyzed. But when the yeast is
separated from the chloroform solution and rinsed with distilled water,
it soon regains the power of causing fermentation in pure solutions of
sugar.
_Ova and Spermatozoids_ are subject to the action of drugs in a similar
manner. If actively motile spermatozoids of a sea-urchin be placed
in a one-half of one per cent. solution of chloral in sea water, it
will be found that after five minutes their action will be completely
arrested. These motions can soon be restored if the chloral solution be
sufficiently diluted with pure sea water. These temporarily paralyzed
spermatozoids, when completely recovered, will unite as quickly with ova
as fresh spermatozoids. When spermatozoids are kept for half an hour in
the chloral solution, a more decided paralysis will be observed, which
persists for some time after the removal of the poisonous agent. A few
minutes elapse before some of the spermatozoids exhibit feeble movements
which finally become active. Even when placed near ova, it is some time
before they fertilize them, although several may attach themselves to
the egg’s surface. But, finally, fertilization does take place by the
penetration of one spermatozoid, and the egg normally develops.
In like manner, if ova are subjected to chloral solution of varying
strength, they also are influenced in a marked degree; for, when
fertilized, they develop in an abnormal manner. Ordinarily, normal ova
are fertilized by one spermatozoid. If fertilized by two or more, they
become diseased, and develop pathologically. The chloral solution favors
this fertilization by several spermatozoids. The stronger the solution
of chloral, the larger the number of spermatozoids that fertilize the
ovum. Experiment and observation show that the behavior of the nuclear
hereditary mass is modified, during mitosis, by the chloral and other
solutions. It is thus seen that _the germ-cells of the lower animals can
be profoundly modified by various substances_.
Equally true is it that the man or woman who makes use of such drugs
as alcohol, opium, chloral, and such like, in an intemperate manner,
contains these poisons in solution in the blood, circulating to every
part of the body, and thus bathing and profoundly influencing the
germ-cells. In consequence of this fact an acquired and habitual
intemperance will seldom fail to leave its impress upon one or more of
the offspring, either like the original vice or one very closely allied
to it. Intemperate people not only profoundly impair the health, the
intelligence, and the morals of their offspring, by poisoning these
delicate germ-cells, but they also transmit the fatal tendency to crave
for the very substances that have acted as poisons on these germ-cells
before and after fertilization. And one of the saddest features of this
great medical truth is that the hereditary units which are concerned
in transmitting these grave abnormal tendencies may lie dormant in the
germs of one generation, to become active in those of the next; so that
children of intemperate parents may lead honorable and temperate lives,
and take every pains to rear, in turn, their own children in a wholesome
and refining atmosphere, and yet these children of good environment may
become intemperate through heredity, so that the sins of the grandparents
may be visited, not on the children, but on the grandchildren.
These profound truths should lead all, and especially law-makers, to
remember that “the man who inherits from his parents an impulsive or
easily tempted nature and an inert will and judgment, and commits a crime
under the influence of strong emotion, can no more be placed in the same
category of responsibility with a man of more favorable constitution
and temperament than can a man who steals a loaf under the pangs of
starvation with a merchant who commits a forgery to afford him the means
of prolonging a guilty career.”[3]
Not only do certain known poisons circulating in the blood, or other
fluid that may bathe the germ-cells of living creatures, profoundly
affect the germ-cells, but many other substances probably have great
influence upon them. Certainly, the _amount and character of the food_
have a very decided influence on them, as will be understood from the
following facts.
According to Yung, who has experimented very extensively upon tadpoles,
all tadpoles pass through a bisexual (hermaphroditic) stage, as is the
case probably with most animals. During this tadpole phase external
influences, and, more particularly, food, determine their fate as regards
sex. In Yung’s experiments it was found that when tadpoles were left to
themselves, the percentage of females was in the majority, the average
being probably about 57 per cent. females and 43 per cent. males. In
experimenting with three broods, those fed on beef gave 78 per cent.
females; those fed on fish gave 80 per cent. females; and those fed on
the highly nutritious flesh of frogs gave 92 per cent. females.
In Mrs. Treat’s interesting experiments on moths and butterflies, it
was observed that if caterpillars were confined and starved before they
entered the chrysalis state, the resultant moths or butterflies were
males, but others of the same brood that had been highly nourished came
out females.
The study of bees illustrates the same conclusions. It is well known that
in a beehive there are three kinds of inmates, as the queen, the drones,
and the workers,—the last-mentioned being females whose reproductive
organs are imperfectly developed. It is believed that the eggs that
give rise to queens and workers are fertilized and developed normally.
But it is a very curious fact that the eggs which develop into drones
do so without fertilization (_parthenogenesis_). What factor or factors
decide the destiny of the two former, determining whether a given ovum
will develop into a queen, and thus be the possible mother of a new
generation, or stay at the lower grade of a working, non-fertile female?
These factors are the quality and quantity of the food. An abundance of
what is called royal food causes the development of the larva in such a
way that the queen with her reproductive organs is formed. If a larva
on the road to develop into a worker (non-fertile female) “receive by
chance some crumbs from the royal superfluity,” it is found that the
reproductive organs may develop to such an extent that workers partially
fertile may be formed. A worker larva may, by this royal food, be
intentionally reared into a queen bee.
It is thus seen how profoundly the germ-cells, in their growth, may be
affected and made to vary by such a blastogenetic factor as food.
=Somatogenetic Factors.= As to somatogenetic factors—granting that
structural changes in the body (body-cells) of an animal or plant can
profoundly influence in some way the germ-cells, and that, therefore,
acquired characters can be transmitted—they are many and well defined.
Some of them are the habitat of an animal or plant, the temperature,
climate, air, food, soil, water, _structures in use or disuse_ (so-called
“Use” and “Disuse”), etc.
The following brief descriptions will enable the reader to understand
that change in the surroundings (environment) of a living creature may
cause its body (body-cells) to vary.
A certain species of snail was introduced into Lexington, Virginia, a
few years ago from Europe. In its new _habitat_ it varied very much. One
hundred and twenty-five varieties have been discovered there, sixty-seven
of which are new and unknown in Europe, the native home of the species.
The common ringed snake, when living in its natural habitat, deposits
eggs in the sand, which are hatched by the heat of the sun; but when
this snake is confined in a cage in which no sand is strewn, it gives
birth to little living snakes.
In experimenting on moths it has been found that the _variations of
temperature_ to which the pupæ, and probably also the larvæ, are
subjected, tend to bring about very pronounced differences in the moths.
Cold has a tendency to develop a darker hue in the perfect insect.
English dogs when taken to hot climates, like that of India, are known to
degenerate in a few generations. It is well known how climate affects the
hairiness of animals. When greyhounds are taken to the uplands of Mexico
they are unable to course on account of the rarity of the air.
In 1870 a number of pupæ of a certain species of moth (Saturnia) were
taken from Texas to Switzerland. After passing the winter there, the pupæ
emerged from their cocoons as moths, and resembled the Texan species
entirely. The young of these moths were fed on the leaves of a plant
different from that the moths in Texas feed on, and they developed into
moths so different in form and color-pattern from their parents that
entomologists classified them as a distinct species.
We have seen how certain foods affect the germ-cells and act as
blastogenetic factors; the preceding case and the following show how
_certain foods act as somatogenetic factors_ and modify the body-cells.
If the bullfinch be fed on hemp seed, its color is changed to black; if
the canary be fed on cayenne, its plumage becomes darker; if the common
green Amazonian parrot be fed on the fat of siluroid fishes, it assumes a
beautiful variegation of red and yellow.
The _character of the soil_ has a marked influence in inducing
somatogenetic variations. In France an experimenter collected seed from
the wild radish and sowed one lot in heavy soil in the country, while
another lot was sown by him in the dry, light soil near the Museum of
Natural History in Paris. The radish “roots” grown in these two places
presented marked differences in color and form. Those grown in Paris
were either of a rose or white color and elongated; while those from
the country were violet, dark-brown or nearly black in color, and more
rounded than the former.
In the summer of 1847 Professor Buckman gathered seed from wild parsnips,
and sowed them in the spring of 1848 under changed conditions of life.
Most of the plants grown from these seeds were like the wild parsnips,
but some of them developed the light-green color and hairless, smooth
appearance characteristic of the cultivated plant. The roots also were
found to be more fleshy than those of the wild variety.
Peas and squashes, when grown in different soils, often show remarkable
variations.
There is one species of shrimp that inhabits brackish water, and another
that lives in water which is much more salt. These crustaceans differ
from one another in the character of the spines they bear and in the form
of the tail-lobes. They have been regarded as distinct species, and yet
either of them can be transformed into the other in the course of a few
generations, by gradually altering the saline conditions of the water.
For a long while the siredon and amblystoma were regarded as being
distinct genera of amphibians. Siredon was looked upon as a permanent
gill-breather, while amblystoma passes through a metamorphosis and
becomes a permanent lung-breather. It is now known that the former can
change into the latter. If there is plenty of water the siredon remains
indefinitely a gill-breather and reproduces freely; but when the water
dries up it changes into the lung-breathing amblystoma. These two cases
illustrate very well the power of environment to modify the development
of organic forms.
As to “_use_” and “_disuse_”: It can readily be observed that exercise
increases the size of muscles; that by steady application the capacity
for thinking can be developed; that the oarsman’s constant use of his
hands leads to the hardening and thickening of the cuticle; that the arm
of the blacksmith and the legs of the mountaineer are much enlarged, etc.
When an organ is exercised properly, there is an increased blood supply
to it, and, consequently, stimulated nutrition and growth in various
parts, such as in the muscular, nervous or other tissues.
When an organ is disused there is diminished blood supply, and,
consequently, diminished growth and functional capacity. In man it is
known that certain activities, such as coal-heaving, shoemaking, etc.,
produce recognizable effects upon the muscular system, the skeleton, and
other parts of the body.
The peculiar habits of a tribe, such as tree-climbing among those natives
of the interior of New Guinea, who build their houses in the upper limbs
of lofty trees, modify the body in ways that are readily recognizable.
After considering many facts in connection with the brains of rabbits,
Darwin announced that this most complicated and important organ in an
animal is subject to the law of decrease in size from disuse. We have
very interesting illustrations of the effects of “use” and “disuse” in
causing somatogenetic variations, in the differences between domestic
ducks and the wild ones from which they have been undoubtedly derived.
The wild duck, which must constantly be on the alert for enemies, and
uses its wings so much more extensively and its legs comparatively less
than the domestic duck, is a much more intelligent fowl than the stupid,
well-protected domestic one. The wings of the wild duck are stronger and
its legs shorter than those of the barnyard duck. It has been shown that
in the wild duck the brain is nearly twice as heavy in proportion to the
body as it is in the comparatively imbecile domestic duck.
Many other useful illustrations of disuse, such as the cattle and goats
in India, that have dependent ears; also cats in China, and horses in
parts of Russia, whose ears are dependent, could be referred to. Use
and disuse are included among the factors of environment, because by
those terms we mean certain _groups of body-cells that are functionally
active or inactive_; for body-cells on any theory of modified pangenesis
constitute an exceedingly important environment of the germ-cells.
The surrounding conditions (environment) of an animal or plant having
the power to cause variations in the living creature by affecting its
germ-cells or its body-cells, the _environment_ may be spoken of as
_blastogenetic_ and _somatogenetic_.
Whether it is a fact or not that somatic variations can induce
corresponding variations in the germ-cells, and thus be transmitted by
heredity, it is certainly true that all heritages must come through the
germ-cells. For this reason, it is clearly seen that so far as evolution
is concerned the germ-cells are the factors of fundamental importance in
organisms. Therefore, we may repeat that environment is the sum-total of
the conditions of life that affect the germ-cells directly or indirectly.
ACQUIRED CHARACTERS.
All heritages, then, are derived directly through the germ cells.
Can there be any heritages indirectly from the somatic cells through
the germ-cells, as has hitherto been assumed? In other words, can
acquired characteristics be transmitted to the offspring? This question
has given origin to the battle royal that is still going on between
opposing schools of biology. The contending parties have appealed to
such biological evidence as is furnished by a study of use-inheritance,
reflex and instinctive actions in animals, etc., and to such experimental
evidence as the induction of traumatic epilepsy in guinea pigs, a change
in the shape of the ear by cutting the cervical sympathetic nerve,
protrusion of the eyeball through injury to the restiform body of the
brain, and such like, noting the effects on the offspring, and have drawn
very different conclusions.
As to the transmission or non-transmission of acquired characters, some
have maintained that only germinal variations are transmitted (because
they believe the germ cells are _insulated_ from the body cells, and
therefore from somatic influences). For instance, Ziegler, in his work
on _General Pathology_, says: “If a disease, such as nearsightedness,
is the product of a special inherited predisposition, _plus_ the effect
of harmful influences which have acted upon the body during life, only
that part can be transmitted which was received by inheritance, but not
that part which was derived from external influences.” In other words,
there is no transmission of acquired character. In this belief it will be
observed that he follows Weismann.
On the contrary, other investigators, like Darwin and Spencer, teach
that somatic variations—the plus element in Ziegler’s illustration of
nearsightedness—do influence the germ-cells (through some such agency as
Darwin’s theory of pangenesis suggests), and that, therefore, acquired
characters can be transmitted. The question is one of fundamental
importance, and yet no crucial experiment has been devised or fact
observed which can compel the correct answer. The evidence seems to favor
the view that acquired characters can be transmitted.
The theories as to the transmission or non-transmission of acquired
characters may be better understood by reference to schemes No. 1, 2 and
3. Scheme No. 1 represents the theory of =Pangenesis=, which teaches
that reproductive cells are not formed from pre-existing reproductive
cells, but by the body cells themselves. Darwin taught that all the
cells of the body, such as skeletal-cells, muscle-cells, nerve-cells,
and so on, are continually giving off infinitely small cell germs or
gemmules, which have the power of growing and forming cells exactly
like themselves. These gemmules have a great affinity for one another,
and, circulating in the blood in countless numbers, they finally come
together in the reproductive glands and form the reproductive cells.
On this theory the fact of the transmission of acquired characters can
readily be appreciated, and it can easily be understood how the parent
molds the child. Suppose, for instance, that the parent, by exercise, has
become a skillful athlete. In him certain muscles have become greatly
developed and strengthened. During all the time of the exercise of these
muscles, the modifying muscle cells have been continually giving off to
the blood modified gemmules, which collect in the reproductive cells and
make it possible for the offspring to develop into an athlete because the
modified gemmules develop into modified muscles like those of the athlete.
Scheme 1 shows the absence of any arrow like those shown in schemes 2
and 3, directly connecting germ-cell with germ-cell; this means that in
this theory there is no continuity of the germ-cells. But arrows are seen
extending from the various body-cells (skeletal, glandular, etc.) to the
germ-cell; this means that the germ-cells are formed by influences or
gemmules emanating from the various body cells.
Scheme 2 teaches that a germ-cell (when fertilized, of course) can
produce many cells, some of which differentiate, finally, into skeletal
cells, some into glandular, some into muscle and nerve cells, and some
into new germ-cells; so that an animal or plant, I, is formed. In like
manner a germ-cell of animal, I, can give rise to the germ and body cells
of animal, II, and so on indefinitely. This scheme shows that there is
a direct =continuity of the germ-cells=; and it also shows that the
germ-cells are entirely _insulated_, as it were, from the body-cells
(skeletal, glandular, etc.), inasmuch as no influences (arrows) extend
from the body-cells to the germ-cells. This means that the transmission
of acquired characters, bodily, mental, moral, etc., is impossible. It
means, in other words, that none of the advantages gained by a parent in
the course of his life can be handed on to his offspring by heredity.
There are many biologists and pathologists who teach this theory as the
correct one.
The majority of biologists accept the theory illustrated in Scheme 3.
This is the theory of =modified Pangenesis=, which teaches that there
is a direct continuity of the germ-cells and that these germ-cells are
not insulated from the body-cells, but that the latter, when modified as
the result of experience, can send off influences that correspondingly
modify the germ-cells; so that the latter, when developing into a new
individual, may cause the same body variations that exist in the parent.
In short, this scheme illustrates not only that there is a _germinal
inheritance_, but also an _inheritance of acquired characters_. In this
Scheme 3, the oblique arrows show that germ-cells produce other germ
cells; the perpendicular arrows show that the germ-cells are modified by
influences that proceed from the body cells.
_Germinal characteristics are transmitted with vastly greater amplitude
and swiftness than merely body (acquired) characteristics._ If, for
instance, a man were born with that physical constitution that makes
with ease a first-class pianist out of him, his sons may easily, through
heredity, be first-class pianists. But if a man be born without such a
congenital tendency and has by constant labor and practice so developed
the muscles of his forearm, his nerves, his brain, etc., that he becomes
a very good pianist (acquired characters); and, further, if his male
descendants for thousands of generations, in succession, have become very
good pianists by constant practice, we may expect that the sons of these
last generations may obtain a congenital tendency to become first-class
pianists quite easily. The constant improvement, by practice, of groups
of body-cells (muscle-cells, nerve-cells, etc.) for generations, has,
in each generation, tended to so correspondingly modify the germ-cells
that they have acquired the power to develop into men who may become very
good pianists with very little practice. This illustrates that there may
be a continuous summation of feeble germ-cell variations that have been
induced by prolonged influences emanating from somatic variations, so
that, in the course of many generations, robust acquired characters may
ultimately be translated into strong congenital characters (Scheme 3).
Scheme 1. =Illustrating the theory of Pangenesis.= Here the germ-cell (a)
develops into the body-cells, e, e, e, e, of animal I, as indicated by
the oblique arrows, but not into any germ-cells, as indicated by absence
of arrow between germ-cell (a) and germ-cells (b). The germ-cells (b) in
animal I are formed by the aggregation of infinite numbers of gemmules
from the various groups of body-cells, e, e, e, e, as indicated by the
perpendicular arrows. The germ-cell (a) transmits germinal heritages to
the body-cells e, e, e, e; these body-cells transmit the heritages to the
germ-cells (b) by means of the gemmules. If the body-cells are modified
in any way, correspondingly modified gemmules are sent to the germ-cells
(b), and these germ-cells are modified and thus transmit acquired
characters to animal II, and so on.
[Illustration:
I
—> Skeletal-cells (e)
(a) Germ-cell —> Glandular-cells (e)
—> Muscle-cells (e)
—> Nerve-cells (e)
| | | |
| | | | II
| | | |
| | | | —> Skeletal-cells (f)
v v v v —> Glandular-cells (f)
(b) Germ-cell —> Muscle-cells (f)
—> Nerve-cells (f)
| | | |
| | | | III
| | | | —> Skeletal-cells (g)
v v v v —> Glandular-cells (g)
(c) Germ-cell —> Muscle-cells (g)
—> Nerve-cells (g)
| | | |
| | | |
v v v v
(d) Germ-cell.
]
Scheme 2. =Illustrating the theory of Continuity of the Germ-Cells;
pure germinal inheritance; and the non-transmissibility of acquired
characters. The germ-cells are insulated from the body cells.= The
germ-cell (a) develops into the body-cells, e, e, e, e, and the
germ-cells (b), in animal I. The body-cells, e, e, e, e, do not
influence in any way the germ-cells (b), as indicated by the absence of
perpendicular arrows. The germ-cells (b) get all their heritages from the
antecedent germ-cell (a), as indicated by the oblique arrow from (a) to
(b). All heritages are purely through the germ-cells. The same with the
animals II and III. Germ-cells (a), (b), (c), (d), are connected together
by obliquely placed arrows, indicating the continuity of the germ-cells.
[Illustration:
I
—> Skeletal-cells (e)
(a) Germ-cell —> Glandular-cells (e)
\ —> Muscle-cells (e)
\ —> Nerve-cells (e)
\ | | | |
\ | | | | II
\ | | | |
\ v v v v —> Skeletal-cells (f)
(b) Germ-cell —> Glandular-cells (f)
\ —> Muscle-cells (f)
\ —> Nerve-cells (f)
\ | | | |
\ | | | | III
\ | | | |
\ v v v v —> Skeletal-cells (g)
(c) Germ-cell —> Glandular-cells (g)
\ —> Muscle-cells (g)
\ —> Nerve-cells (g)
\ | | | |
\ | | | |
\ v v v v
(d) Germ-cell.
]
Scheme 3. =Illustrating the theory of Continuity with Modified
Pangenesis.= A germ-cell (a) develops into the body-cells, e, e, e,
e, and the germ-cells (b) of animal I. The germ-cells (b) get their
heritages directly from the germ-cell (a), as indicated by the long,
obliquely-situated arrow (continuity of the germ-cells). The germ-cells
(b) are, moreover, modified by influences extending from the body-cells,
e, e, e, e, as indicated by the perpendicular arrows. A modified
germ-cell (b) can develop into a modified animal II, and the body-cells
of this animal can influence and modify the germ-cells (c); and so on,
indefinitely. The perpendicular arrows indicate that acquired characters
are transmitted, and that, too, through the germ-cells.
[Illustration:
I
—> Skeletal-cells (e)
(a) Germ-cell —> Glandular-cells (e)
\ —> Muscle-cells (e)
\ —> Nerve-cells (e)
\ | | | |
\ | | | | II
\ | | | |
\ | | | | —> Skeletal-cells (f)
\ v v v v —> Glandular-cells (f)
(b) Germ-cell —> Muscle-cells (f)
\ —> Nerve-cells (f)
\ | | | |
\ | | | | III
\ | | | |
\ | | | | —> Skeletal-cells (g)
\ v v v v —> Glandular-cells (g)
(c) Germ-cell —> Muscle-cells (g)
\ —> Nerve-cells (g)
\ | | | |
\ | | | |
\ v v v v
(d) Germ-cell.
]
Professor Morgan, of England, has advanced the ingenious theory, which
may reconcile the above-mentioned antagonistic views, that somatic
variations, in the direction of adaptation, pave the way for germinal
variations, so that, while somatic modifications _as such_ are not
inherited, they are yet the _favoring conditions_ under which germinal
variations are preserved by the great principle of natural selection.
If this is true, as we think it is, then we can safely state that each
man in his totality is the resultant of two great factors—_heredity_
and _environment_, the latter including not only food, water, climate,
occupation, etc., but also the character of the civilization, the state
of morals in society, the ideals and examples most frequently seen, etc.,
etc.
Heredity brings down to him the streams of tendency of former
generations, often of a healthy and beneficent character, but also often
surcharged with lust and passion, and reeking with disease.
Environment is the coöperating and, to us, vitally important factor,
inasmuch as it may supplement and thus reënforce the hereditary
tendencies, whether good or bad; or it may even tend to turn them into
new channels, correcting the evil or vitiating the good.
Man is not simply a creature of the present, but profoundly a product of
the past. Bodily structure, moral and intellectual tendencies, disease,
vices, and virtues are all in the marvelous stream of heritage that comes
to him from the past. “Diseases that no facts in the individual life can
account for point gaunt fingers of blame from one generation to another.
Not a murderer is hung, not a daughter starts on the downward way, but
a great company, like those who were present at the stoning of Stephen,
stand by inaugurating and consenting to the ruin.”[4]
Truly has it been said that the past is at work in the present, its
powers reaching down through the ages, to all the race, largely molding
every human life, touching and influencing every individual’s thought and
will, and, more than any other force, coloring history.
Studies in heredity illustrate most luridly that the continuity of the
human race is a terrible but remorseless reality.
If the ignorance and the perverted pleasures of one generation may
produce the vices and the crimes and the diseases of another, a question
of tremendous import arises: Is heredity as potent in the direction of
virtue and health as of vice and disease? At the first look one is almost
tempted to answer Nay! for the most striking examples of heredity seem
to be in the direction of evil. But this is perfectly natural. Decay is
always more rapid than growth. A cherry rots much more quickly than it
ripens. Vice and disease spread much more quickly and widely than virtue
and health. But all history and all social and medical science teach that
vice and disease carry within themselves the seeds of decay, and virtue
and health the seeds of endurance and growth.
Through the great Darwinian principle of natural selection, or survival
of the fittest, vice and disease will become less and less predominant,
and virtue and hygienic constitutions more and more disseminated.
As influencing a man’s life and character,[5] which is the stronger
factor, heredity or environment? Fatalism or choice? In our opinion, as
the result of long study and reading, where we have an average man of
“_mens sana in corpore sano_,” environment will be the stronger factor
whether for good or for evil—that is, in men in general, who have no
organic defect, such as insanity or idiocy, and allied affections, the
stronger force is environment; but in those having such defect, heredity
is the controlling power, and, we may add, the destroying power.
It must be recalled, though, that the average man with a “sound mind
in a sound body,” in his development to his present estate, has become
possessed of a vast aggregate of diverse heritages, of varying age,
strength and dignity. Some of them are so old and strong that they seem
to be cast in unyielding molds, while others are so weak and recent that
they fluctuate with every passing circumstance. The most dignified and
important of all his heritages is that of rational volition. It is the
play of this volition upon many of his other heritages that gives him the
power of selecting, to a limited extent, his environment.
Every man is born into the world with a certain physical constitution,
and, therefore, with a given temperament; with certain passions; with
the power of judgment; and with a certain strength of will. If the power
of his will be not equal to the strength of his passions, the latter
will surely predominate and will display him as the slave of heredity.
If he has such an organization of his nervous system that his volition
is superior to his passions, he will be none the less the servant of
heredity, though a being now possessed of the power of Free-Will.
Man is, to a far greater degree than is ordinarily realized, the servant
of heredity. It seems to us an incontrovertible fact that every living
creature, at any given moment, is swayed infinitely more by the _totality
of its heritages_ than by its environment. No one can possibly deny this
so far as plants and most animals are concerned. Nor, if one look below
the surface, can it be denied of the higher animals and of man. Happily,
the average man, with his present constitution, has his diverse heritages
so proportioned that we may repeat that his life and character (in
customs, morals, and religion) are vastly more influenced by environment
than by heredity.
The standards for estimating the life and character of men, namely,
human customs, morals, and religions, are such recent acquisitions,
_geologically_ speaking, that they have, as yet, very slightly if at all
influenced the germ-cells. They are acquired (somatic) characteristics,
and not congenital (germinal) qualities. They are preëminently the
creations of environment. If the infants of a Catholic family which is
descended from a long line of Catholic ancestors were to be placed and
retained in a purely Mohammedan environment, heredity would carry no
Christian customs, morals or religion into that environment, but, on
the contrary, the Mohammedan surroundings would instill new customs,
different ethical ideas, and a different religion. This illustrates
how very feebly indeed are germ-cells correspondingly impressed by
pure acquired characters. _It is almost certain that the translation
of somatic changes into germinal changes is appallingly slow._ As far,
then, as social customs, morals, and religion are concerned, the average
man is, in our opinion, infinitely more the creature of nurture than
of nature. But, as far as his temperament, his emotional nature, his
judgment, his strength of will, in short, his physical and therefore
his mental constitution, are concerned, he is _almost_ absolutely the
creature of heredity. The equilibrium of qualities or heritages in
the average man, resident in a given, stable community, is in harmony
with the average customs, ethical ideas, and religious beliefs of that
community. But in all stable communities there are men whose resultant of
heritages, some in one direction and some in another, places them out of
harmony with the average of their social environment, and they are looked
upon, some as idiots, some as geniuses, some as criminals, and others as
saints, and so on. So that again we may say that a man’s character in a
community is the resultant of an hereditary physical constitution, and
his environment. Some men may inherit such a physical constitution that
in spite of the best environment they are much debased below the average
man; others may possess such heritages that, notwithstanding adverse
circumstances, they reach a level of character much above the average
man. And there are all gradations between the two extremes.
SECTION III.
UNSTABLE ENVIRONMENT.
UNSTABLE ENVIRONMENT.
Where living creatures are in harmony with their surroundings,—where, in
other words, they are adapted to their environment,—and where, further,
this environment is apparently in a state of equilibrium; there we find
the fewest and least marked variations in the living creatures. To the
casual observer the face of nature maintains the same guise from year
to year. The earth seems solid and unyielding; the mountains appear to
be everlasting; the restless waters of rivers and brooks seemingly move
and throb in the same channel; the tides ebb and flow in apparently
unchanging ocean beds; the birds and flowers and woodlands look alike
from year to year; and all the varied phenomena of nature appear
completed and permanent, as if the present world were constructed in an
unyielding mold.
But nothing is fixed and rigid in nature. The earth itself travels
rapidly through space and brings in due season spring, summer, autumn
and winter; revolves upon its axis and alternates the starry night with
sunshine; and periodically changes its orbit so that at one time the
northern pole has a temperate climate where water lilies may grow, and
at another period presents an arctic climate with impassable barriers
of ice. Ice and frost and other forces are breaking up the rocks of
mountains, making larger and smaller fragments and even powder; the
rains descend and the mountain brooks are swollen to resistless torrents
which carry the fragments and mud to the rivers, and these latter take
the mud on to the ocean.
Thus, by degrees, the mountains, hills and all the earth are being
eroded and the great bulk of the detritus carried by the rivers to the
sea and deposited along the sea margins. Thus sedimentation goes along
with erosion, and gradually marginal sea bottoms of immense thickness
are formed, which will in time be consolidated into rocks and uplifted
as dry land. The ceaseless grinding of waves and tides erodes the coast
line and adds _débris_ to the marginal sea bottom. The finest sediment is
carried out by the tides so far as to reach the ocean currents, and thus
is strewn broadcast over portions of deep-sea bottom, and will also in
due time be consolidated into rock.
Myriads of animals that form calcareous shells live and die in the ocean.
The shells of the dead animals are falling like a perpetual shower on
certain ocean bottoms, year after year, so that immense accumulations
of calcareous substances occur there, which will also in time be
consolidated into limestone rocks, and uplifted as dry land.
Deltas are forming at present at the mouths of certain rivers, and
estuaries at others. Lands are now gradually emerging from the sea in
some places and at others sinking into the sea. The entire coast of
Scandinavia, both on the Baltic and Atlantic sides, is rising out of the
sea, and has been doing so for a long time. It is rising at the rate of
more than two feet in a hundred years. During an immense period of time
there has been a gradual elevation of all the southern part of the South
American continent. Sometimes a large elevation takes place rapidly. In
1822, and again in 1835, the southwest coast of South America, after
severe earthquakes, was elevated several feet along a distance of several
hundred miles. It is known that the coast of Greenland, for five hundred
miles, is subsiding. From a study of coral barriers and atolls it is
believed that an area of the mid-Pacific sea bottom covering over ten
million square miles is sinking and has been doing so for a long time.
The foregoing facts tend to illustrate the truth that nothing is
permanent in the environment of living creatures at present. All
surroundings are perpetually changing, though apparently ever so slowly.
The changes that are now going on were also taking place yesterday, last
week, last century, last æon, and so on throughout geologic time. Gradual
oscillations of the earth’s crust on a grand scale and affecting whole
continents, but usually so slowly as to escape popular observation,
have been taking place ceaselessly through inconceivable ages. These
oscillations have produced all the great inequalities of the earth’s
surface, such as ocean basins, continents and mountain chains. The
oscillations are probably due to the slow cooling and unequal shrinking
of the whole earth which has been progressive through all geologic time.
The state of the contest between the eroding and the uplifting agencies
of the world at any time determines the height of mountains and
continents, the depths of seas, the distribution of land and water, for
that period.
[Illustration: FIG. 11.—Archæan North America. The white part of the
drawing indicates the emerged land; the dark shading indicates the
submerged land covered by a shallow sea; the light shading indicates the
deep sea.
From Shaler’s First Book in Geology. By courtesy of the publishers, D. C.
Heath & Co.]
Knowing that the present physical agencies at work on the globe have been
acting through long ages,[6] it can readily be appreciated how small
effects have been accumulated and low elevations, for instance, have
become immense, high mountain ranges. The growing mountain ranges alter
the climate and the meteorological conditions. The rainfall on one side
differs from that on the other. The temperature varies with the altitude,
and so on.
Although continents have gradually and steadily grown from the earliest
times, there have been many local alterations of land and sea. Marginal
sea bottoms have become great mountain ranges. Islands have appeared and
sunk from view. Lakes have been gradually converted into solid land or
into peat bogs. Fresh water bodies have become brackish. Dry lands have
become marshes, and forests have been buried beneath the waves. Geologic
changes have caused great alterations in climate at given times and in
given areas.
These statements may be illustrated and emphasized by a brief reference
to the =development of the Continent of North America=. This Continent
has grown from comparatively a small beginning to its present great
proportions. In doing so it has passed through eras of stupendous
duration. These eras in the order of their occurrence are as follows:
(1) =Archæan era=; (2) =Palæozoic era= (subdivided into =Cambrian=,
=Silurian=, =Devonian= and =Carboniferous= periods); (3) =Mesozoic era=
(subdivided into =Triassic=, =Jurassic= and =Cretaceous= periods); (4)
=Cenozoic era= (subdivided into =Tertiary= and =Quaternary= periods); the
Tertiary is subdivided into =Eocene=, =Miocene= and =Pliocene= epochs;
the Quaternary is subdivided into =Glacial=, =Champlain= and =Terrace=
epochs; (5) =Psychozoic era=, or recent epoch.
The physical geography of the continent at the close of that early
geologic era known as the =Archæan= is shown on the map (Fig. 11). At
this time the vast portion of the continent, whose outlines nevertheless
existed, was submerged under a shallow sea, as indicated by the dark
shading on the figure. The white V-shaped mass, starting just above the
site of the great lakes and extending on the one hand in a northeasterly
direction to Labrador, and on the other in a northwesterly direction to
the Arctic Ocean, is the emerged land of this _Archæan_ time. Smaller
masses of Archæan land are also seen at the site of the Blue Ridge
Mountains in the east and at that of the Rocky Mountains in the west.
Around these lands as a nucleus the North American Continent has been
built. Therefore, at the close of the Archæan or beginning of the next,
or =Palæozoic era=, the whole interior portion of the continent was
covered by a shallow sea which beat against the Canadian Archæan land
on the north, the Blue Ridge Archæan land on the east, and the Rocky
Mountain Archæan land on the west. This shallow sea is known as the
_Palæozoic Sea_. Throughout the vast ages of the Palæozoic era, immense
sediments were being deposited along the marginal sea bottoms. The
deposition of these sediments was simultaneous with a further sinking
of the submerged continent, so that the shallowness of the Palæozoic
Sea was maintained; finally, the uplifting forces predominated, and the
submerged land along the margins of the Canadian Archæan appeared as dry
land, and thus increased the area of the infant continent. During all
this period there was a steady and slow growth of the land southward from
the Canadian Archæan, so that towards its close the visible continent had
increased nearly, though not exactly, to the proportions attained in a
still later (=Cretaceous=) period (Fig. 12).
[Illustration: FIG. 12.—Cretaceous North America. The white portion of
the figure indicates emerged land—the growing continent.
From Shaler’s First Book in Geology. By courtesy of the publishers, D. C.
Heath & Co.]
At the close of the Palæozoic era the slow, steady changes that had been
going on were replaced by more rapid and comparatively revolutionary
changes, which caused great alterations in the physical geography and
climate. Hitherto the continent had been comparatively low. Now the vast
sedimentary accumulations constituting the marginal sea bottom of the
eastern portion of the Palæozoic Sea, which had been accumulating through
all Palæozoic time, were uplifted into the great Appalachian chain of
mountains.
During the earlier ages (=Silurian= and =Devonian=) of this Palæozoic
era, the place of the Appalachian chain of mountains was marginal sea
bottom; but during the later ages (=Carboniferous=) it was, through
repeated oscillations, in an uncertain state, being sometimes swamp land,
sometimes covered with river sediment, and sometimes covered by the sea.
It was during this _Carboniferous age_ that the great coal measures were
formed; at this time also the climate was probably very uniform, warm
and moist, loaded with carbonic acid gas and deficient in oxygen. This
period was undoubtedly a paradise for the great coal-forming plants, but
was very unsuitable for the hot-blooded air-breathing animals, such as
mammals and birds, none of which existed at that period. Throughout all
geological time the excessive amount of moisture in the air has been
gradually removed by the growth of continents in size and height; also
the superabundant carbon dioxide in the atmosphere has been removed in
many ways, especially by the plants in the coal period appropriating
the carbon. Many ages later, at the close of the =Jurassic= period, the
Sierra Nevada range of mountains was uplifted. Up to this time the site
of these mountains was a marginal sea bottom receiving vast amounts
of sediment, and the Pacific coast-line was east of the site of the
Sierra range. Naturally vast changes in physical geography and climate
occurred in consequence. During these and the following =Cretaceous=
ages that the continent was growing, the great interior Palæozoic sea
and what may be called the Gulf of Mexico were more and more restricted,
as shown in the map of North America in the Cretaceous period of its
growth (Fig. 12). This great inland sea, separating the continent into
an eastern and western portion, is now called _Cretaceous Sea_ instead
of Palæozoic. This Cretaceous Sea covered the whole plains and plateau
region of the continent, and extended from the Gulf of Mexico to the
Arctic Ocean. At the end of the Cretaceous period of the continent
this sea was obliterated by the gradual upheaval of this region and
replaced by great lakes. At the same time the western marginal bottom
of the sea was uplifted into the Wahsatch range of mountains; also at
this time a line of islands in the Cretaceous Sea was uplifted into the
Colorado mountains. All these events were entailing tremendous changes in
physical geography and climate. Fig. 13 is a representation of the map of
North America in the early =Tertiary= period, the time succeeding the
Cretaceous period. In this period, the continent continuing to uplift,
the lakes that occupied the site of the Cretaceous Sea are obliterated;
the Coast Range mountains of California and Oregon are uplifted from
marginal sea bottom (Fig. 13, dark shading); the Atlantic and Gulf
borders are extended (dark shading), so that at the close of the Tertiary
period the North American continent had attained its present form, except
the southern portion of Florida and its keys. Since then the latter have
grown and are still growing.
[Illustration: FIG. 13.—Early Tertiary North America.
From Shaler’s First Book in Geology. By courtesy of the publishers, D. C.
Heath & Co.]
A later epoch still in the history of the globe is known as the
=Quaternary= period, the period that immediately preceded our present
epoch. The great features of this period, which is divided into
=Glacial=, =Champlain= and =Terrace= epochs, are the wide-spread
oscillations of the earth’s crust in high latitudes towards the north and
south poles, attended with great changes of climate from temperateness
to extreme cold.
The Glacial epoch was characterized by upward crust movements, the land
becoming over one thousand feet higher than at present. The land was
covered with ice, and an arctic severity of climate extended almost to
the Gulf of Mexico. The Champlain epoch was characterized by a downward
movement of the coast until it became five hundred feet or more below
the present level, so that many lower portions of the continent became
covered with sea. At this time there was a moderation of the temperature,
a melting of the vast sheets of ice, and consequently a flooding of
rivers and lakes, with many icebergs floating in them. The last or
Terrace epoch of the Quaternary period was characterized by a crust
movement up to the present condition of things.
What is true of the instability of the North American Continent is true
of _all_ the continents of the globe. They have all grown from small
beginnings to their present huge proportions, and are _now_ undergoing
slow but irresistible changes. When these facts are held in mind, one may
form a faint conception of the colossal changes that have taken place
throughout the sweep of bygone ages. _Environment means a complexity of
conditions almost infinite in their number and character, and almost
infinite in their variations._
SECTION IV.
TRANSMUTATION OF LIVING FORMS.
TRANSMUTATION OF LIVING FORMS.
It ought now to be understood that not only is the present environment
changing, but also that it has been changing from the earliest geologic
times. What, then, is to be said about the living creatures that have
existed in the changing environment during all these geologic ages?
Have they been rigid, unyielding forms? By no means! We know that they
can be modified by altering the conditions at present; and a study of
the fossils in the rock formations of the different ages of the world
shows conclusively that animals and plants have altered in the past with
the changing environment. The living creatures in the _Silurian ages_
differ from those in the succeeding _Devonian ages_, and these latter
differ from those in the still later _Carboniferous ages_; and so on,
to the present. Changing physical geography and climate are associated
with changing forms in animal and plant life. The growing amplitude and
complexity of a continent are associated with increasing complexity and
specialization of its living forms. Just as the North American Continent
of the Tertiary period differs from that of the Silurian ages, so also
do the animal and plant forms of the Tertiary period differ from those
of the Silurian ages. Just as there has been a continuity in the growth
of the Silurian continent to that of the Tertiary ages, and the present,
so, also, there has been a continuity of living creatures from Silurian
to Tertiary and present times. Changing conditions of life have compelled
modifications in living forms, and those creatures that were unable to
adapt themselves to the altering conditions of life have perished, while
those that did adapt themselves, through useful variations, lived and
progressed in organization.
A study of the fossils in the rock formations (see page 95) of different
ages reveals the fact that thousands of species have lived and flourished
in one age and then perished, never to appear in succeeding ages. A study
of the fossils also reveals that life-forms have passed on from age to
age, ever changing with the changing continent, some advancing to higher
and higher levels, while others remained lowly.
The facts enumerated above may be instructively illustrated by a hasty
reference to the history of organic life as unfolded by the rocks of
different ages.[7]
=Archæan Era.= No evidence of life has been discovered in the Archæan
rocks, but, inasmuch as with the dawning of the Palæozoic time, the
waters of the sea were peopled with plants and animals living in great
numbers and considerable variety, it is evident that the ancestors of
these creatures must have lived during the Archæan ages.
TABLE OF STRATIFIED ROCKS AND THE SUCCESSIVE APPEARANCE OF TYPICAL ANIMAL
LIFE-FORMS.
+----------+-----------------------+------------------------------------+
| | |=Man=, Mastodon, Saber-toothed |
| | Quaternary. | Tiger and other Vertebrates. |
| | | Invertebrates. |
| +---------+-------------+------------------------------------+
| | | |Equus and other Vertebrates. |
| | | Pliocene. | Pliohippus. Protohippus. |
| | | | Invertebrates. |
| | +-------------+------------------------------------+
|Cenozoic. |Tertiary.| Miocene. |Miohippus and other Vertebrates. |
| | | | Mesohippus. Invertebrates. |
| | +-------------+------------------------------------+
| | | |=Monkeys.= |
| | | |=Lemurs.= Primitive Carnivora and |
| | | Eocene. | Herbivora. Orohippus. |
| | | | Invertebrates. Eohippus. Fishes, |
| | | | Amphibians, Reptiles. Land Birds. |
| | | | Monotremes. Marsupials. |
| | | |=Prim. Monodelphs.= |
+----------+---------+-------------+------------------------------------+
| | |Marsupials. Monotremes. Reptiles. |
| | | Reptilian Birds. Amphibians. |
| | Cretaceous. | Teleosts and other Fishes. |
| | | Belemnites and other |
| | | Invertebrates. |
| +-----------------------+------------------------------------+
| | |Reptilian Birds, Reptilian Mammals. |
|Mesozoic. | Jurassic. | Rays, Chimæroids and other |
| | | Vertebrates. Invertebrates. |
| +-----------------------+------------------------------------+
| | |Primitive =Marsupials=, Primitive |
| | Triassic. | Monotremes, Reptiles, Amphibians, |
| | | Fishes. Ceratites and other |
| | | Invertebrates. |
+----------+--------------+--------+------------------------------------+
| | |Permian.|Primitive =Reptiles=, Amphibians, |
| | | | Fishes. Invertebrates. |
| |Carboniferous.+--------+------------------------------------+
| | | |Primitive =Amphibians=. |
| | | | Fishes, Invertebrates. |
| +--------------+--------+------------------------------------+
| | |Primitive =Crossopterygii=, |
| | Devonian. | Ganoidei, Dipnoi. Goniatites and |
| | | other Invertebrates. Sharks. |
|Palæozoic.+--------------+--------+------------------------------------+
| | | Upper. |Primitive =Sharks=. Ostracoderms. |
| | | | Invertebrates. |
| | Silurian. +--------+--------------------------------+---+
| | | Lower. |Blastids, Scorpions, Centipedes,| I |
| | | | Sea-urchins and other | n |
| | | | Invertebrates. | v |
| +--------------+--------+--------------------------------+ e |
| | |Marine =Worms=, Molluscs, | r |
| | | Trilobites, Brachiopods, | t |
| | Cambrian. | Crinoids, Star-fishes, | e |
| | | Corals, Graptolites, | b |
| | | Cystids, Sponges, | r |
| | | Foraminifera. | a |
+----------+-----------------------+--------------------------------+ t |
| Archæan. |=Protozoans=, though there is | e |
| | no evidence of life. | s |
+----------------------------------+--------------------------------+---+
=Cambrian Period.= The Cambrian rocks have furnished many different
species of marine animals. Seaweeds are the only plants found fossil
in the Cambrian rocks. Some plants and animals may possibly have dwelt
upon the land, but if so they have failed to leave any record of their
existence. The animals are all _Invertebrates_, but not of extremely low
forms; they have progressed since their appearance in an earlier period.
Siliceous Sponges are not uncommon. The Cœlenterates are represented
by Graptolites and Corals. Echinoderms are rare, and are principally
represented by Cystids, a very primitive type; true Crinoids and
Star-fishes appear before the close of the period. That marine worms
existed is indicated by borings and tracks in the sands, which have
since consolidated into rocks. Mollusca burrowed in the mud or crawled
over the ocean bed. Brachiopods existed, and Arthropods were represented
by primitive types. The most characteristic of Cambrian fossils are
_Trilobites_ and _Lampshells_.
The former are extinct, and are not represented in the modern ocean; the
latter, although greatly reduced in variety and numbers, are still found
in various parts of the sea. During all this period, no backboned animals
existed; then there were no fishes or amphibians, no reptiles or birds,
and no mammals; nothing but invertebrates. The Cambrian fauna shows
steady progress, being decidedly more advanced in the upper divisions
than in the lower ones.
=Lower Silurian (Ordovician) Period.= The life characteristics of this
period are very similar to those of the Cambrian. Brachiopods have
developed extensively, though they have not yet reached their height
of development. The Trilobites attained their greatest development in
this period; but after the Lower Silurian these creatures commenced to
decline in variety and numbers, and finally underwent extinction near the
close of the Palæozoic era. In America no plants have been discovered
above the grade of seaweeds, but a few of the higher Cryptogams are
doubtfully reported in Europe. The character of the flora in a later
(Devonian) period makes it highly probable that land plants were well
advanced in the Lower Silurian period. Professor Scott states that the
remains of land plants may be discovered at any time, though this must
remain a matter of chance, inasmuch as all known Ordovician rocks are
marine, and therefore not a favorable circumstance for the preservation
of land plants. Foraminifera and Radiolaria were abundant in the seas
of the Lower Silurian period. Sponges and Brachiopods are numerous and
varied. Among Cœlenterates the Graptolites are very numerous and varied;
the few and doubtful Cambrian Corals are succeeded by a considerable
number of Ordovician genera and species. They were characteristically
different from the reef-builders of modern seas. The Echinodermata have
greatly increased in importance, being more numerous and varied. The
_Cystids_ reach their maximum development in this period. The Crinoids
greatly increase in numbers and variety. The Star-fishes greatly expand;
and a new and higher order of Echinoderms, the _Sea-Urchins_, make their
first appearance in the later Ordovician period, but under very primitive
forms.
Among Arthropods the Trilobites increase greatly in numbers and variety,
and attain their maximum development in this period. The occurrence of
a Centipede in Ordovician rocks indicates the interesting fact that
terrestrial animal life had already begun.
One of the most striking differences between the Lower Silurian and
Cambrian periods is the great advance made by the Molluscs, in variety
and numbers, during the former period. Molluscs exhibit the most
significant change in the great expansion of the _Cephalopods_, a few of
which had appeared in the uppermost Cambrian rocks. In the Lower Silurian
period the Cephalopods became one of the predominant types in the marine
life. In modern times nearly all Cephalopods are naked (_Cuttlefish_ and
_Squid_), only a few having a shell (_Nautilus_ and _Argonaut_). The
naked forms are higher creatures than those with shells. In the Lower as
well as in the Upper Silurian periods no naked forms existed, but only
the lower forms with shells (Nautiloids). In modern times and throughout
later geological periods only Nautiloids with coiled shells were in
existence. In both of the Silurian periods the shells were all straight,
and the animals were called Orthoceratites. Such animals were extremely
abundant in those times, and often reached an enormous size. Specimens
have been found which were ten inches in diameter and over fifteen feet
long. They were the most formidable animals of those early ages, and
were the rulers and scavengers of the seas; so that the Lower and Upper
Silurian periods are known as the =Age of Molluscs=.
=Upper Silurian Period.= In this period great progress is made in the
history of life on the globe. Upper Silurian life is the continuation and
advance of the organic system that flourished in the Ordovician, certain
groups expanding, others diminishing; and some new groups now appear
for the first time. Sponges are still common. Among Cœlenterates the
Graptolites have greatly diminished; Hydroid Corals have become important
features of the seas and in the formation of the reefs. True Corals
increase largely and play a more important part than in the preceding
period. Honeycomb and Chain Corals are quite characteristic of this
period.
Among Echinoderms there is a diminution of the Cystids, and a marked
increase of the Crinoids. A new class of Echinoderms, the Blastids,
now make their first appearance. The Sea-urchins and Star-fishes
have increased in variety and abundance. Brachiopods still exist in
multitudes, but under changed forms. Among Molluscs the Orthoceratites
are still the rulers of the seas. Among Arthropods the Trilobites are
still numerous, though decidedly less so than in the preceding period.
The land animals are insects of low types, mainly allied to cockroaches.
Scorpions are also present as fossils in the Upper Silurian rocks. These
animals prove the existence of a contemporaneous land vegetation.
During all the many millions of years that constitute the Silurian
periods, hosts of species lived and died; hosts of variations were
induced in the living creatures by the ever-changing environment; so
that at the close of this time the Silurian rocks show that some of the
life-forms, lowly as they were, had yet climbed higher in the scale of
organization.
The later Silurian rocks reveal the remains of _an entirely new branch
of living forms, a higher branch of animals_ (=Vertebrates=) than
had ever before existed. These remains are those of =Ostracoderms=
and =primitive Sharks=. But at that early time they held a very
subordinate position among the hosts of living creatures; the Molluscan
Orthoceratites were still the rulers of the seas; it was still the Age of
Molluscs.
=Devonian Period.= The next set of ages succeeding the Silurian time
is known as the Devonian period. Many of the kinds of creatures living
in the Silurian ages are also found in these ages, but under changed
forms. The Devonian seas had a great abundance and variety of Corals
and Crinoids. The Chain Corals have perished, but the Cup and Honeycomb
Corals still live on with modified appearance. The Graptolites are almost
extinct. The Orthoceratites still live on, much reduced in numbers and
size. The Molluscan Cephalopods have been revolutionized. New forms have
grown out of the variations of the past, so that now in Devonian times
we have the introduction of the great Molluscan _Ammonite family_, under
the forms known as _Goniatites_, which are characteristic of this and the
succeeding Carboniferous ages. The Trilobites still continue under new
forms, but much reduced in size and number. Brachiopods are abundant and
diversified.
In this age, for the first time, land plants become conspicuous. The
Devonian forests consisted of the highest flowerless plants, such as
ferns, horsetails, and club mosses; and also the lowest flowering plants,
such as cycads, pines, cypresses, etc.—plants which have imperfect
and inconspicuous flowers. In all ages, as now, land vegetation has
been closely related with _insects_. Insects, though rare as fossils,
are found in connection with the forests in the Devonian period. They
are among the lower orders of the class, and are somewhat allied to
cockroaches and dragon flies.
The most characteristic feature of the Devonian age is the expansion
of that new and higher class of animals, =the backboned animals=; for
during the earliest Devonian or latest Silurian times the =Fishes= made
their appearance. At first many of them were comparatively small in size,
they were few in numbers, and of strange, unfishlike forms. Such were
the _Ostracoderms_, which, though generally called fishes, belong to a
type much below the true fishes, and more nearly allied to the Lampreys,
for they were devoid of jaws and paired fins. There was a great variety
and wealth of true fishes in the Devonian period. The _Elasmobranchii_
(Sharks) were well represented, _though very generalized ones_.
_Crossopterygii_, _Dipnoi_ and _Ganoidei_ were important elements of the
fish fauna of this period. At this period there was an entire absence of
those highly specialized fishes (_Teleosts_) which in modern times make
up the vast majority of fishes, both marine and fresh-water.
The true fishes soon developed to so great an extent in size and numbers
that they swarmed in the Devonian seas and quickly became the rulers of
the age; hence Devonian time is known as the =Age of Fishes=.
These early Devonian Fishes were of a more lowly organization than modern
ones, and were what is called generalized forms; that is, they combined
in themselves the characters of two distinct classes. They had distinct
_amphibian characters_. From these generalized Fishes were afterwards
formed, through many transitions, the _Amphibians_ and the _Fishes_ as
branches from a common trunk. This illustrates what is a very general
law, viz.: that the first-introduced examples of a class are not typical
forms of that class, but intermediate forms or connecting links with
other classes. Certain footprints recently discovered in the upper
Devonian rocks of Pennsylvania indicate that the Amphibia, the lowest of
air-breathing vertebrates, commenced their career in the latter part of
the Devonian period; but they were inconspicuous among the monarch fishes.
=Carboniferous Age.= As in the Devonian Age so in the Carboniferous
times, we find flowerless plants, such as ferns, horsetails, and club
mosses; but in this coal-forming age they culminate, and have become
gigantic in size, especially the two latter. At this time we again meet
with the next higher order of plants, as cycads, pines, cypresses, etc.
These plants of the coal period were remarkable, generalized types,
connecting classes now widely separated. During this period the insects
increase in variety and numbers along with the advancing vegetation.
It is interesting to find that as the highest flowering plants are not
yet in existence, so those highest orders of insects, the flower-loving
and honey-loving ones, such as bees, butterflies and moths, are not yet
in existence. Corals and Echinoderms, Molluscs and Crustaceans, etc.,
continue through the ages with ever shifting forms. Brachiopods have
greatly diminished. Foraminifera for the first time assume considerable
importance in the earth’s economy.
The Molluscan Goniatites continue through this age with changing forms
and advancing organization, and are very numerous. The Trilobites, which
are characteristic of Palæozoic times, continue under new forms through
this age, and then perish. In this age are introduced for the first time
typical Crustaceans of the long-tailed kind, such as shrimps.
Devonian fishes still prevail. The Elasmobranchii are numerous and
varied, and some of them are highly specialized. _Pleuracanthus_ is a
remarkable shark which has many features in common with the lung-fishes
(Dipnoi), such as the character of the pectoral fins, the shape of the
tail, the bones which form a roof for the skull, while the skin is naked.
The Dipnoi continue, though in diminished numbers.
The Crossopterygians are much less abundant. The Ganoidei increase in
numbers and varieties.
The fact of greatest interest concerning the Carboniferous period is the
_expansion of the true land-breathing, backboned animals, such as the_
=Amphibians=. _Their expansion marks a distinct step forward in the scale
of life._
The Carboniferous Amphibia all belong to the extinct order of
_Labyrinthodonts_ (_Stegocephala_), in which the skull is well covered
with a roof of sculptured bones. The Amphibia of the lower Carboniferous
rocks are of small or moderate size, not exceeding eight feet in length
and mostly much smaller. A great number of these Amphibians are known,
most of them like the Salamanders in shape, but some are snake-like
in form, being long and slender. An example of the Stegocephala is
_Archegosaurus_.
The upper Carboniferous rocks represent the later Carboniferous period
(=Permian Period=). The life of this period is transitional between that
of the Palæozoic and of the Mesozoic eras. Here we meet with the last
of many types which had persisted from Cambrian times, associated with
forms which are prophetic of the characteristic types of the Mesozoic
era. We also meet with types in the Permian that are peculiar to the
period. In this section of the Carboniferous period many of the genera
of the fishes are the same, while new ones are introduced. Among the
lung-fishes the genus _Ceratodus_ is introduced, a creature very closely
allied to the modern lung-fish of Australia. The Amphibia are still
represented by the Stegocephala, several of the older genera persisting,
while many new forms appear for the first time; several of the latter
surpass the earlier Carboniferous genera greatly in size. The transitions
from many of the Devonian fishes to the Carboniferous Labyrinthodonts
are so gradual that it is sometimes difficult to say whether we are
dealing with Fish or Amphibian. In other words, the Devonian fishes are
generalized fishes, that is, connecting links between Fish and Amphibian.
When the Amphibians finally separated from the fishes they were not the
highly specialized forms of more recent times; but they were generalized
Amphibians, having some reptilian characteristics. As time passed on
and the creatures continued to modify, some varied more and more in the
direction of true amphibians, and others more and more in the direction
of reptiles, until in the Permian stage early, generalized Reptiles, of
lizard-like form, appeared in large numbers. The most interesting of
these primitive Reptiles are the _Theromorpha_ (beast forms), which
present many remarkable approximations to the structure of the mammals.
As yet no snakes or turtles, no alligators or crocodiles had come into
existence. In spite of the fact that great advance in animal life was
made during Carboniferous times, there was little of the life in those
ancient woods that we associate with the forests of the present; they
were gloomy wastes of shade, without the presence of bright flowers, no
humming of the bees, no song of birds, and few sounds save the gurgling
of running streams, the sighing of the wind through the leaves, the
splash of waves upon the shore, and the bursting of the thunder clouds.
The interest and importance of the Carboniferous Amphibians as the first
land backboned animals, is so great as to cause the Carboniferous period
to be spoken of as the =Age of Amphibians=.
=Triassic Period.= In this period the ferns and horsetails continue
under new forms; but the next higher orders of plants, the Cycads and
Conifers, now predominate. The Goniatites are replaced by the Molluscan
_Ceratites_, the latter being characteristic of the Triassic period.
One of the most characteristic changes from the Palæozoic to the Mesozoic
era consists in the great reduction of the Brachiopods.
The =Vertebrata= of this period are of extraordinary interest and show
great progress. The fishes exhibit the least progress. The Dipnoan
_Ceratodus_ is very characteristic, continuing from the Permian. The
Crossopterygians have greatly declined. The Ganoidei continue to be
the dominant fish-type, and are most like the existing gar-pikes. The
Amphibia (Stegocephala) culminate in this period, multiplying and
diversifying greatly, and far surpass in size the Carboniferous and
Permian genera, and then become extinct.
It is in the =Reptilian= class that we find the most remarkable changes.
The abundance and diversity of the reptiles in this and the two
succeeding periods are incomparably greater than those in the Permian
age. The Triassic rocks have representatives of almost all the orders of
Mesozoic reptiles, though often these are comparatively small and rare
forms.
The reptiles with mammalian characters (Theromorpha), which first
appeared in the Permian period, culminate in the Triassic, especially in
southern Africa, and then become extinct. No birds, or reptiles which can
be regarded as the ancestors of birds, have been found in this period.
In this period one of the greatest advances in the progress of life is
indicated by the first appearance of _low mammals_,—_mammals having very
decided reptilian characters_, and belonging to the orders of generalized
=Monotremes= and =Marsupials= (_Dromatherium_; _Microlestes_).
=Jurassic Period.= The _Fishes_ have advanced greatly beyond those of
the Triassic rocks. The Sharks have advanced practically to their modern
condition, and a new order of Elasmobranchs, the broad and flat _Rays_,
are introduced.
The _Chimæroids_ occur in this period, and were more numerous than in
modern times. Dipnoans have become very scarce. The Crossopterygians are
greatly reduced. The Ganoidei are still the dominant type; some of these
latter approximate the Teleosts so closely that it seems arbitrary to
call them Ganoidei. In Europe the _Reptiles_ culminate in this period
and show extraordinary development in variety, huge size, number and
degree of organization. They were rulers in every department of nature.
They were the rulers in the air in place of birds; rulers on the land in
place of mammals; and rulers in the sea instead of sharks and whales.
Immense land reptiles (_Dinosauria_) as large as our largest mammals,
and in some cases larger than the elephant, moved sluggishly over the
land. Some walked on all fours; others were occasionally or usually
bipedal, and walked upright like birds, and had many structural features
in common with the latter; some were herbivorous, feeding on plants
and even reaching into the branches of trees for their food, others
were carnivorous, feeding on their fellow-creatures. Huge reptiles
(_Ichthyosauria_) swam about in the sea in great numbers. Immense
bat-like forms (_Pterosauria_) sailed through the air like birds, being
literally flying dragons.
These reptiles, which had branched off from the generalized Amphibians,
were themselves very generalized creatures. It is interesting to remember
that the Monotreme and Marsupial mammals found in this age were very low
reptilian mammals; they were not typical, specialized Monotremes and
Marsupials, like the modern creatures, but very generalized forms, being
probably connecting links with low generalized Insectivora, which were
the first of the true mammals.
These early Monotremes and Marsupials were quite small animals, varying
in size from a mole to a rabbit. They were insignificant creatures among
the mighty giant reptiles, but they carried in their warm blood the
promise of future mammalian supremacy.
Birds appear for the first time in this period, but very different
from modern birds. Not only did many of the reptiles of this time have
bird-like characters, but all the birds of this period were distinctly
_reptilian_ birds (_Archæopteryx_). Birds came off from primitive
reptiles as branches from a stem (see Diagram of Development). It was
only with the passing epochs that these early birds changed more and more
from their reptilian characters and assumed more and more the features
of modern birds. Many fossil connecting links between reptiles and birds
have been discovered, and afford most useful illustrations of those
changes in creatures that we call _Evolution_.
=Cretaceous Period.= In the Cretaceous period the aspect of plant life
has changed greatly. Now, for the first time, we meet with ordinary
hard-wood trees, such as beech, oaks, hickory, maples, poplar, etc., but
of very different genera and species from those existing to-day.
In this period, for the first time, we find the highest order of
Cephalopods, viz., the naked ones, allied to cuttlefishes and squids.
They are known as the _Belemnites_. Sometimes the fossil ink-bags of
these creatures are found so that they can be drawn in their own fossil
ink.
The Ammonites proper, which were introduced in the Triassic period
and culminated in Jurassic time, become extinct at the close of the
Cretaceous.
The =Vertebrates= form the most characteristic features of the Cretaceous
fauna. A revolution has occurred among the Fishes. Sharks of modern
type are numerous. Crossopterygians and Ganoidei are rare. There has
been an immense expansion of _Teleosts_ or Bony Fishes, which now become
the dominant fishes. Most of the Cretaceous Teleosts belong to modern
families and even genera.
The _Reptiles_, in this period, continue to be the dominant types of the
land, air, and sea, and it is difficult to decide whether the Cretaceous
or the Jurassic is to be regarded as the culminating period of Reptilian
history. The flying Reptiles (Pterosauria) of this period are remarkable
for their great size, far exceeding, in this respect, those of the
Jurassic time. The land Reptiles (Dinosauria) are in greater numbers than
in the preceding period. The sea Reptiles are less numerous than in the
Jurassic, but are of greatly increased size.
Cretaceous _Birds_ are much more numerous and advanced than the Jurassic
ones.
The _Mammals_ of the Cretaceous are much more abundant and varied than
those of Jurassic times, but they are nearly all of very small size, and
continue to play a very modest rôle. The lower Cretaceous mammals differ
but little from those of the Jurassic, except for the larger number of
genera. The mammals of the latest Cretaceous time are much more numerous
and diversified than those of the early Cretaceous. They also show
affinities with the mammals of the next succeeding or Tertiary period.
The birds and mammals, though they have varied with the passing time and
changing surroundings like all other living creatures, are very different
from those around us now. They have thrown off some of their reptilian
characters, yet they are still distinctly and pronouncedly reptilian.
The Triassic, Jurassic and Cretaceous periods together constitute the
Mesozoic Era, or =Age of Reptiles=; for never before and never in
succeeding ages were reptiles so huge, and varied, and masters in all the
realms of nature.
=Tertiary Period.= In reaching Tertiary time we enter upon the threshold
of our modern world. The reptiles have dwindled to a few low forms,
such as alligators and crocodiles, to the small lizards, to turtles and
tortoises, and to those low-grade reptiles, the snakes, which now for the
first time are the most numerous of the class. In these ages, as now, the
Teleost fishes vastly predominate, and the Ganoid and Crossopterygian
fishes are nearly extinct. In Tertiary times, as in the present, all the
reptilian birds had disappeared, and only typical birds remain. In other
words, the bird-class had now separated from the reptilian class, and the
connecting links became extinct.
In this age for the first time the highest flowering plants are abundant,
and now for the first time also the highest orders of insects are
abundant, such as bees, ants, butterflies, etc. On account of the greater
warmth and moisture in the Tertiary period, insect and plant life were
fuller then than now. That the climate was warmer in those times is shown
by the following facts: In America, during the early Tertiary period,
figs, evergreens and palms grew in Dakota, showing a temperature there at
that time equal to the temperature in Florida at present. In the middle
Tertiary period trees like the Redwood of California, and Magnolias,
were abundant in Greenland.
Although _Reptilian Mammals_ (_Multituberculata_) lived in the preceding
era, true or typical Mammals first came to view in the earliest Tertiary
times. They soon succeeded the vanished giant reptiles as the rulers
of the world; so that this and the succeeding (Quaternary) period are
known as the =Age of Mammals=. At this period, for the first time,
appear generalized _primitive flesh-eating mammals_ (_Creodonta_), and
_primitive grass-eating ones_ (_Condylarthra_ and _Amblypoda_); also
_primitive Primates_ (_primitive Lemuroids_, and, later, _primitive types
of Monkeys_, e. g., _Anaptomorphus_).
The evolution of mammals, compared with that of other animal groups, has
been so rapid that each stage of even the Eocene has its own mammalian
fauna, differing from those of the succeeding and preceding stages. All
through the Tertiary period, as through all the preceding ages, the
species that are advancing in life are undergoing greater and greater
specialization. Animals at first closely related finally become more
and more separated from one another. This is well illustrated by a
study of the hoofed animals. In the earliest Tertiary period all these
animals seem to unite into one branch but now they consist of many widely
separated sub-branches. As we trace the branch down to the earliest
Tertiary period, we find that even in early Eocene times it divides into
the even-toed and odd-toed ungulates. In the later Miocene times, each
of these again separates,—the former, even-toed ones, into the hog and
hippopotamus families with four toes, and the ruminant family with two
toes; the latter, odd-toed ones, into the elephant family with five toes,
the rhinoceros and tapir families with three toes, and the horse family
with one toe.
[Illustration: FIG. 14.—Illustrating genesis of horse’s feet. Fore-feet
(a) and hind-feet (b) of Orohippus; fore-feet (c) and hind-feet (d) of
Mesohippus; fore-feet (e) and hind-feet (f) of Miohippus; fore-feet (g)
and hind-feet (h) of Protohippus; fore-feet (k) and hind-feet (l) of
Pliohippus; fore-feet (m) and hind-feet (n) of Equus.]
It will be exceedingly instructive to trace briefly the progressive
specialization of the horse family through the Tertiary period. A
wonderful series representing this family has been found in the American
Tertiaries. First of all, the =Eohippus= is found in the earliest Eocene
rocks. This little animal was about the size of a fox and had four
perfect toes (hoofed) and a fifth, much smaller, imperfect one (splint)
on the fore-feet; the hind-feet had three perfect hoofed toes. Later on,
in the middle Eocene rocks, was found the =Orohippus= (Fig. 14), with
three toes behind (b), and four in front (a)—the fifth imperfect toe
(splint) being lost. This animal was also about the size of a fox. Still
later on were found, in the Miocene rocks, the =Mesohippus= (c, d) and
the =Miohippus= (e, f), with three toes behind (d, f) and three toes and
a splint in front (c, e). The splint in the Miohippus is much smaller
than in the Mesohippus, and also in the former the two side toes have
become smaller and farther removed from the ground. Both of these animals
were about the size of sheep. Further on, in the early Pliocene rocks,
appears the =Protohippus= (g, h), with three toes on all the feet, but
the middle toe considerably larger and longer than the side toes. This
animal was about the size of an ass. Then, finally, came the =Pliohippus=
(k, l) and =Equus= (m, n) in the latest Pliocene rocks. Here the middle
toe is greatly enlarged and the side toes are reduced to useless splints.
Thus by degrees, through slight modifications not only of the feet, but
also of the skull, teeth, brain, etc., and by adaptations from age to
age, was formed the modern horse. In like manner, by gradual changes and
adaptation to surroundings, all the early generalized mammals pass into
the higher specialized ones.
=Quaternary Period.= The mammals of this age differ from those of the
Tertiary period and from living species. Never before this period,
and never since, have mammals been so large. They culminate in this
period and then decline. The great mastodon, the great cave-bear, and
saber-toothed tiger, the Irish elk, and gigantic sloths and armadillos
lived in this age.
Most interesting of all, the remains of _man_ now first appear associated
with these extinct animals. Man must have been at first an apparently
insignificant creature among the mighty mammals that surrounded him, and
must for a time have contended more or less doubtfully with them for
mastery. But as he increased in numbers and intelligence he became more
and more the ruler of the brute creation; so that this age in which he
rules may fittingly be spoken of as the Psychozoic Era, or =Age of Man=.
[Illustration: FIG. 15.—A snake and two lizards; a, snake; c, Bipes
(lizard); b, Cheirotes (lizard).
From Shaler’s First Book in Geology. By courtesy of the publishers, D. C.
Heath & Co.]
Fig. 15 is introduced to show how easy may be the transitions from one
order of animals to another. Two long, slender Lizards are shown and
also a Snake. Bipes has four limbs, but they are very small and weak.
Cheirotes has lost, probably through disuse, the hind-limbs and the front
ones are small and weak, almost useless. The snake has no limbs at all.
The two lizards are quite snake-like in external forms. Just as changing
environment, use and disuse, etc., can effect transitions in external
forms by slight gradations, so also may the whole internal structures
undergo marked alterations by slight modifications through long ages.
The brief references we have made to the changing life-forms during the
geologic ages, should be very instructive even to a reader not familiar
with zoölogy. They teach the important lesson that life, in the main, has
ever advanced to higher and higher levels. At one time in the history of
the earth no animals were in existence higher than the Invertebrates;
these lived through the ages with ever-changing forms. Later, in the
course of geologic history, some of the primitive Invertebrates evolved
into the lowest Vertebrates, and Fishes finally appeared, at first
very primitive and generalized. For long ages there were no creatures
on the globe higher than these. Then as the æons slowly rolled on some
of the early fishes evolved finally into a higher group of animals,
the Amphibians, and these for long ages were the highest creatures in
existence. As time slowly passed, some of the primitive amphibians
evolved into primitive Reptiles, and these creatures for long ages were
the highest in existence and monarchs of the world. Some of the primitive
reptiles branched off in one direction leading to modern Birds, and some
advanced in another direction that led through primitive mammals to man
and other modern mammals. And now in modern times man is monarch among
the animals.
We may now begin to realize that truly with the changing and growing
continents during the geologic ages, many life-forms have varied and
advanced to higher levels, culminating in the final appearance of _man_
as well as other living creatures.
SECTION V.
NATURAL SELECTION.
NATURAL SELECTION.
In briefly outlining the transmutations of living forms that took place
during the Geologic Ages, we have said that changing conditions of
life—through an ever-shifting environment—have compelled modifications
in the form, structure, and habits of living creatures; and that those
creatures which were unable to _adapt_ themselves, through _useful
variations_, to the altering conditions of life have perished, while
those that _did_ adapt themselves lived and progressed in organization.
What, then, is the great agency through which some life forms have been
_eliminated_ during the ages, while others have been _selected_ to
continue through these ages? This agency is =Natural Selection=. The
phrase “natural selection” is simply a convenient, condensed statement of
observable and easily verifiable facts, viz.: that animals and plants are
so situated in this world that they can only secure their food and mates
by work, by effort, by struggles, whether consciously or unconsciously,
and whether directly or indirectly; and that in these struggles those
that are best equipped for their life duties are the ones that are
most naturally successful in living and procreating their kind. The
survival of those best adapted to their environment may be spoken of,
in the language of Spencer, as the =Survival of the Fittest=. Darwin’s
phrase—=Natural Selection=—has precisely the same significance and means
that those creatures which are best fitted to their surroundings are the
survivors. The working of Natural Selection may be made clearer by a
brief reference to the =Artificial Selection by Man= of various animals
and plants. Variations frequently take place in domesticated animals and
plants. Some of these variations appeal to man as being of practical
value, others as beautiful, and others again as curious or interesting.
He selects those individuals whose variations he wishes to preserve,
breeding only them together, and in this way accentuates those variations
he desires to perpetuate. In course of time the accumulation of these
differences becomes so marked as to make the animals differ greatly from
the original stock from whence they came. A well-known illustration of
this process is the pigeon. All our domestic pigeons, forming a large
number of well-marked races, such as the fantail, the tumbler, the
pouter, etc., have been produced from the ordinary wild rock pigeon
of Europe. The bird fancier, noticing individual differences in the
offspring of the wild rock pigeon, selected the peculiar individuals, and
bred only them together. By this simple process of artificial selection
and isolation of the chosen or selected individuals, all the races of
pigeons have been produced. Plate I shows the wild rock pigeon _Columba
livia_ and the domesticated pouter. The forms of these pigeons are very
different, yet the wild rock pigeon has been transmuted into the pouter
through the agency of Artificial Selection. The same is the case with
our pigs, dogs, cats, apples, grapes, and other domesticated animals and
plants. Fig. 16 shows the domesticated pig that has been derived from
the wild boar by Artificial Selection. By this process, such distinct
races as the Newfoundland, the Skye Terrier, and the Bulldog have been
produced—creatures that have all come from common ancestors, yet so
different looking, one from the other, that if they had been found in the
wild state, they would not only have been ranked as distinct species, but
as even distinct genera. The same method has given us different races
of horses, cows, sheep, flowers, grains, etc. The swiftest horses, for
instance, are selected to breed together; then the fleetest offspring
of these, time after time, until horses are produced whose speed far
surpasses that of the originally selected pair from whence they were
derived. Darwin has taught us that what man does on a small scale, in
a comparatively short time, Nature has been doing on a vast scale for
long ages and has thus given rise, from simple forms, to the infinite
variety and complexity of animal and plant life, as we behold it on the
globe to-day. The selection by man of useful variations in domesticated
creatures being appropriately called Man’s Selection, or Artificial
Selection; the vastly greater selection by nature of animals and plants
with useful variations and on an infinitely grander scale, through
inconceivably long ages, is most fittingly called =Natural Selection=.
The struggles—of animals, for instance—that necessarily lead to the
survival of the fittest, are intensified and made exceedingly acute and
severe by the fact that _all animals tend to increase in a geometrical
ratio, and by the further fact that the food and place for animals are
limited_. In other words, the population of the animals in a given area
tends greatly to outrun the means of subsistence. And since animals are
constantly varying in many directions and are as plastic in the hands of
Nature as clay under the chisel of the modeler, those that possess any
useful variations, whether congenital or acquired, that give them any
advantages in this great battle of life, will most likely come out of the
struggle as victors.
[Illustration: FIG. 16.—Wild Boar contrasted with a modern Domesticated
Pig. Reproduced from Romanes’ “Darwin, and After Darwin.” By courtesy of
The Open Court Publishing Company.]
=Multiplication of Animals.= Even in the slow-breeding elephant, the
offspring tend to increase threefold in each generation. Some animals
tend to increase twenty or thirty fold in each generation, while still
others tend to increase a thousand fold or even ten thousand fold. If all
the offspring of the elephant lived, in eight hundred years there would
be over nineteen million elephants alive. If the eight million eggs which
the roe of certain fishes, such as the cod or the eel, contains, were to
develop into adult forms, the ocean would quickly become a solid mass.
The aphis or plant louse is so very prolific that it has been estimated
that the tenth brood of one female alone would contain more ponderable
matter than all the population of China,—estimating this population at
five hundred millions. Yet, in spite of this tendency on the part of
animals and plants to increase in numbers at such a stupendous rate,
it is found that, in any given area, the conditions of which are not
changing, the number of the animals and plants remains fairly constant.
This is because of the fact that, _along with the stupendously large
birth rate, there is an equally stupendous death rate_. This high death
rate is to a large extent indiscriminate, for it involves those that are
physically fit to live, as well as those that are unfit to live. At the
edge of a coral-reef, free-swimming, active embryos are found in immense
numbers. After a while some of these settle at too great a depth in the
water or on the muddy bottom, and die; others get into a more suitable
position and live. Again, whole nests of bees are destroyed by the
badger; tongue loads of ants are engulfed at one gulp by the ant-bear;
hundreds of thousands of fry are destroyed by the Greenland whale at
one swallow. In all these cases, the destruction is indiscriminate,—the
good, bad, and indifferent are alike decimated, but in spite of this
wholesale and indiscriminate destruction, keeping down, as it does, the
stupendous birth rate of living creatures, _more animals and plants are
born than are required to keep up the normal number of individuals that
can be supported in a given area. Among these creatures there arises a
struggle for existence, a struggle for food and place, and those that
are the best fitted to live come out of the contest as conquerors._ In
this struggle those creatures that emerge as victors, on account of
having been best adapted to their conditions of life, may be spoken of
as having been selected by Nature; or they may be spoken of as chosen by
Natural Selection. In this great struggle, over which Natural Selection
presides as some _inexorable, ever-watchful, sharp-eyed task-master_,
the victory is to the cunning instead of the stupid; the race is to the
swift instead of the slow; and the battle is to the strong. The wolves
of keenest scent, the tigers of more supple spring and sharper sight,
secure their prey and thrive, while the weaker members fail to get their
food and starve. During migration the birds that are strongest on the
wing reach the land whither they are flying, while the weaker perish
on their course. Thus Natural Selection acts in two ways, _eliminating
the unfit_ and _selecting the fit_, and there are, besides, two special
modifications of Natural Selection which are called =Sexual Selection=
and =Insect Selection=.
The following analysis of Natural Selection may be useful to the reader,
viz.:
{ Physical and Climatic Causes.
{ Elimination { Enemies.
{ { Competition.
{
Natural Selection { { Natural Selection Proper.
{ {
{ { { By Preferential
{ { { Mating.
{ Selection { Sexual Selection. {
{ { By Battle.
{ Insect Selection.
=Elimination of the Unfit.= The elimination of the unfit takes place
through the agency of physical and climatic causes and also through
enemies, and competition of members of the same species. Elimination
through the action of surrounding physical and climatic conditions is
shown by the following facts: if certain tropical animals be transferred
to sub-Arctic or even temperate regions they are unable to adapt
themselves to the requirements of the new climatic conditions, and die
sooner or later; many animals are killed if the fresh-water lake in
which they live be invaded by the waters of the ocean; fishes which
live at great depths in the sea and are, therefore, subject to great
pressure, are killed when they are brought to the surface, on account
of the expansion of the gases in their tissues; if the water where
corals are living becomes too fresh, too muddy, or too cold, they will
die. The change of climate to a much colder temperature at the close
of the Jurassic Ages was probably the cause of the extinction of the
huge reptiles that took place at that time. In the winter of 1854-5,
four-fifths of the birds in Darwin’s grounds perished on account of the
severity of the cold.
As to elimination by enemies, it is well known to naturalists that
throughout nature battle within battle is continually recurring with
varying success. When weaker animals are preyed upon by stronger ones,
and self-defense is useless, the bulky and slow animals are eliminated,
while the swift and agile ones escape; the stupid are destroyed, while
the cunning often survive. As to elimination by competition, the
stronger animals kill the weaker ones, and then quarrel and fight with
one another over the prey, the strongest, etc., getting the food. While
weaker animals are being preyed upon by various enemies, and are thus
eliminated, these enemies are also competing with one another for the
prey. At the same time that the stupid and slow creatures are being
destroyed by their captors, thus leaving the more cunning and agile
animals in possession of their habitat, the stupider and less active
captors are gradually eliminated by competition, through failing to
capture their more agile and cunning prey.
The agency of Natural Selection in bringing about the innumerable
adaptations of animals and plants, and, therefore, causing transmutations
of living creatures, can most interestingly and instructively be
illustrated by a study of the _coloration of animals and plants_.
As a correct idea of the mode of operation of Natural Selection, and the
pronounced results attained thereby, is very desirable, it will well
repay the reader to study _in extenso_ the relations of _color-patterns_
to _environment_. The whole subject is nothing but repeated
illustrations of one principle, viz.: Natural Selection. This fact and
the interest of the subject will justify the numerous details.
=The Coloration of Animals and Environment.= The colors of animals often
harmonize most wonderfully with their surroundings. Thus green is a
common color of animals in the evergreen forests of the tropics; white is
the prevailing color in the arctic regions; and a yellowish hue in desert
places. In the evergreen forests of tropical America, whole groups of
birds are found whose fundamental color is green; there the parrots and
fruit-eating pigeons are commonly green; the bee-eaters, leaf-thrushes,
and many other birds, have so much green in their color as to add greatly
to their concealment in the dense green foliage. In the desert places,
the lion, the desert antelope and the camel harmonize with the color of
the rocks and sand among which they live. In the Arctic regions the polar
bear, the Greenland falcon, and the American polar hare are white. We
have further the dusky hue of creatures that haunt the night, such as
mice, moles, and bats; and the gorgeous tints of fishes that swim among
the coral reefs. These local color adaptations of animals are of great
use to them, either enabling them to escape the notice of their enemies
or to come upon their prey with the least risk of being detected. Certain
groups of animals have a local color-adaptation, and may be noticed under
the heading of _Protective Coloration_; others have acquired a wonderful
resemblance to surrounding inanimate objects, such as leaves, twigs,
bird-droppings, flowers, etc., and may be described under the heading of
Protective Imitation of particular objects, or _Protective Resemblance_;
closely allied to the latter are those resemblances to surrounding
objects which are not so much for the purpose of protecting the animals
from enemies as for attracting their prey, and these resemblances,
therefore, will be described under the title of _Alluring Coloration_.
Other animals have such color patterns as to be very conspicuous in their
surroundings; these animals are usually very poisonous or possess other
deleterious qualities that cause beasts of prey to avoid them; hence
these animals may be said to possess _Warning Coloration_. Many animals
that are very desirable food for carnivorous creatures have acquired,
in past ages, a remarkable resemblance to these dangerous animals with
warning coloration, and are treated of under the title of _Mimicry_.
There are still other groups of animals whose peculiar coloration enables
the member of a herd or flock which may have become separated from the
herd to readily recognize its companions at a distance as friends, and
thus distinguish them from enemies. The color patterns of these animals
may be classed under the heading of _Recognition Marks_.
=Protective Coloration, or Local Color Adaptation.= In forest-haunting
animals of large size, such as forest-cats, and forest-deer, rounded
spots are frequently noticed. Animals like the tiger, that spend a great
deal of their time among high grasses and reeds, are striped vertically.
The combined artistic effects of these spots and stripes, in connection
with the lights and shades of the forest and the reeds, are such as quite
effectually to conceal the animals from view: for the black stripes of
the tiger, for instance, correspond with the black shadows of the reeds
or grasses; and his yellow stripes with the yellow of the reeds. In like
manner the rounded spots of the forest-deer harmonize with the spotty
shadows of the leaves in the forest. An experienced tiger hunter has
stated that in following up a wounded tiger the natives saw the animal
at a distance of about twenty meters, under a tree among the reeds, and
pointed out the animal to him; but the color effects of the stripes of
the tiger so harmonized with the artistic effect of the light and shade
of the reeds as to effectually prevent his seeing the animal for a minute
or so. The zebra, which is such a conspicuous animal in our zoölogical
gardens, on its native soil and in a bright star-light night, may be
so close to one as to be heard breathing, and yet cannot be seen, so
completely are its color patterns in harmony with its native habitat.
Marine organisms that float on the surface of the water are beautifully
tinged with blue in harmony with the color of the ocean as it appears to
their enemies above, the birds; while, looked at from below, they are
white, thus harmonizing with the white clouds and the foam as seen by
enemies from below.
There are many animals that are very conspicuous when removed from their
native haunts, yet when in their proper environment are invisible or
detected with the greatest difficulty. Such a large animal as the giraffe
is effectually concealed by its form and color when standing among the
broken and dead trees that exist on the edges of the thickets where it
may be seeking its food. The odd shape of the head, with its horns that
resemble broken branches, and the blotchy spots on the skin, so harmonize
with its surroundings that even the keen eyes of the natives sometimes
mistake giraffes for trees and trees for giraffes.
There is a bat (_Kerivoula picta_) found in the island of Formosa that
has a very conspicuous black and orange color. The body of this bat is
of an orange color, and its wings are black and orange-yellow. When
resting it suspends itself, head downwards, from the branches of an
evergreen tree. During all the year some part of the foliage of this tree
is undergoing decay, so that many of the leaves assume tints of orange
and black. When the bat is suspended among such decaying leaves its
colors and those of the leaves so harmonize that the animal is perfectly
concealed, and thus eludes its enemies.
The sunbirds of Africa are very conspicuous when out of their natural
environment, being brilliant and gorgeously colored. These birds find
their main food supply among plants that have very conspicuous flowers;
the aloe-blossoms, especially, which they frequent, are brilliantly
colored. The colors of these birds so completely harmonize with the gay
colors of the blossoms that even the keen eye of the hawk is unable to
detect them. One species of these birds, the black sunbird, is never
absent from a forest tree known as the Kaffir boom. This tree has not a
single green leaf on it, but consists of a great mass of purplish-black
and scarlet blossoms. A dozen of the black sunbirds may be feeding in
this tree, and their notes may be heard among its branches all the day,
yet their color adaptation to their environment is so complete that they
are seen with the greatest difficulty or are entirely invisible.
Those birds whose colors have varied in such a way that they have not
harmonized with their surroundings,—that have not become adapted to
their environment,—are seen by the hawks and are exterminated; but those
whose colors were more favorably arranged and more in harmony with their
surroundings have been most often undetected by their enemies, the hawks,
and have lived and transmitted their useful color patterns by heredity
to their offspring. This process going on, age after age, has developed
such perfect adaptations of the sunbirds to their environment as the
naturalist observes at present.
These examples are illustrations of the fact that those creatures that
are most in harmony with their surroundings are the ones that live and
procreate their kind. They are cases of the survival of those animals
that are best adapted to their environment,—the survival of the fittest;
the selection by nature of favored creatures; in short, Natural Selection.
Among our native birds, the woodcock and snipe have such tints and
markings as strikingly to harmonize them with the dead marshy vegetation
which constitutes their native haunts. The ptarmigan in winter has a
light coloration in harmony with the environment of snow, while in
its summer plumage it is tinted and mottled in harmony with the color
effects of the lichen-covered stones among which it spends a great deal
of its time. Young unfledged plovers are spotted in such a way as very
accurately to resemble the beach pebbles among which they remain for
protection.
The white-headed fruit pigeon (_Ptilopus cinctus_) is a very conspicuous
bird when taken from its native haunts. It has a pure white neck and
head, black back, yellow belly, and well-marked, deeply-curved black band
across the breast, and black wings. It is a handsome as well as very
conspicuous bird. It frequents trees that are a species of Eucalyptus in
the island of Timor, and which have very open foliage and yellowish or
whitish bark. The pigeons may be sitting motionless on exposed branches
of the tree during the glaring heat of the day. The yellow and white bark
of the tree, the deep blue sky seen through the openings of the leaves,
with the intense tropical sunlight casting black shadows of one branch
upon another, make color effects that harmonize so completely with the
color patterns of the pigeons that they are entirely invisible.[8] Here
again the complete color adaptation of the pigeons to their environment
has been accomplished through the agency of Natural Selection,—Nature
selecting those pigeons most frequently that varied most in the direction
of useful color patterns, by concealing them from their enemies, the
hawks.
There are some birds that are not protectively colored, which therefore
do not possess a local color adaptation. The common raven, which inhabits
the Arctic regions, is black instead of being white. The raven is found
as far north as any known bird or mammal. It is a powerful and fearless
bird, and needs no protective coloring; and since it feeds on dead
animals it needs no concealing coloration to enable it to secure its food.
The bright and conspicuous coloration of many birds’ eggs have often
been looked upon as a difficulty on the theory of adaptive coloration.
But Wallace thinks that a careful consideration of the subject in all
its bearings shows that in a great number of cases these colorations
are instances of protective coloration. He further thinks that when we
cannot see the meaning of the particular colors, we may suppose that in
some ancestral forms they have been protective, and, being harmless,
have persisted under changed conditions which rendered the protection
needless. He states, in illustrating the protective coloration of
eggs, that “the beautiful blue or greenish eggs of the hedge-sparrow,
the song-thrush, the blackbird, and the lesser redpole, seem at first
sight especially calculated to attract attention; but it is doubtful
whether they are really so conspicuous when seen at a little distance
among their surroundings. For the nests of these birds are either in
evergreens, as holly or ivy, or surrounded by the delicate green tints
of the early spring vegetation, and may thus harmonize very well with
the colors around them. The great majority of the eggs of our smaller
birds are so spotted or streaked with brown or black on variously tinted
grounds, that when lying in the shadow of the nests and surrounded by the
many colors and tints of bark and moss, of purple buds and tender green
or yellow foliage, with all the complex glittering lights and mottled
shades produced among these by the spring sunshine and by the sparkling
raindrops, they must have a quite different aspect from that which they
possess when we observe them away from their natural surroundings.” We
have here, probably, according to Wallace, a similar case, of general
protective harmony, to that of the green caterpillars with beautiful
white or purple bands and spots, which, though gaudily conspicuous when
seen alone, become practically invisible among the complex lights and
shadows of the foliage they feed upon.
Eggs that are not protectively colored are usually white or of some
uniform pale color, and are concealed by the birds in covered nests or in
holes in trees or in the ground. Many birds lay white eggs in open nests,
but even here the devices for concealing them are very effective and
interesting. In some cases, such as the partridge, the goat-sucker, and
others, the birds have the habit of sitting close and almost continuously
on the eggs. These birds are protectively colored. Ducks, pheasants,
and other birds have the habit of covering their white eggs with dead
leaves or other material when they leave the nest. There are some large
and powerful birds that lay conspicuous white eggs in open nests. Such
are the cormorants, herons, storks, pelicans, and others. But they guard
their nests carefully, and are able to drive away any enemies.
It is thus seen that there are many devices by which birds’ eggs are
protected, and these have all been developed through the agency of
Natural Selection. For example, those exposed eggs of timid birds that
varied most in the direction of protectively colored ones were the
ones that were most likely to be overlooked by egg-eating creatures,
and those that were least protectively colored, and therefore the most
conspicuous, were the ones most likely to be destroyed. The protectively
colored eggs being thus, in the nature of things, the ones that have
suffered less destruction from enemies, have developed into birds that
have transmitted, by heredity, their characteristics to succeeding
generations of birds’ eggs. And thus in the course of time have many of
the colorations of eggs been developed from simple to elaborate patterns.
Many snakes, frogs, butterflies, caterpillars, and so on, are colored
green in harmony with the foliage of the trees among which they live. By
being colored green these animals are more or less effectually hidden
from their enemies, such as carnivorous birds. If they were not concealed
by protective coloration they would quickly be exterminated by hungry and
greedy enemies. The green frogs are greatly protected by their colors
from their enemies, the green snakes. If they were not so colored, they
would quickly be exterminated by these snakes. Even protectively colored
as they are, large numbers of them are caught by the snakes, which are
also protectively colored and keener witted. It may be stated that the
protectively colored frogs are hunting for their food, the protectively
colored insects; but, at the same time, they try to avoid their
protectively colored enemies, the snakes, though they are often caught;
the protectively colored snakes are hunting for their food, the frogs,
but, in their green surroundings, endeavor to avoid their enemies, the
reptile-eating birds, though often unsuccessful. And so on, from day to
day, the tragedies of the animal world are enacted.
It may be well to pause a moment here and ask why it is that animals are
not completely exterminated which are thus perpetually being persecuted
and preyed upon by stronger foes. Why, for instance, are any frogs left
in a green locality, when they are so eagerly sought for by their
enemies, the snakes? What are the factors that permit the average or
normal number of them to exist in the given locality? The most important
of them have already been referred to separately, but it will be useful
to recapitulate, briefly, a few of them now. One of the most important
of them is the tendency of the frogs to increase in geometrical ratio.
In the breeding season great numbers of young are brought into the
world, thus reinforcing the depleted ranks of the adults. Another factor
is the instinctive effort of each frog to avoid its enemies, and their
protective coloration greatly facilitates their concealment and escape.
Another factor is the circumstance that the snakes also have enemies.
They must be wary and careful in hunting prey lest they be unduly
exterminated by their foes, the snake-eating animals. Then another factor
is the alternating day and night, by which the warfare, offensive and
defensive, must be periodically checked. Then again, the hibernating
season, winter, checks or rather suspends the life-destroying crusades.
It may thus be recognized that many complex factors occur to explain the
circumstance that a given locality generally contains the normal number
of individuals that constitute the species of frogs.
The complex factors at work in these relations and inter-relations of
animals and plants are so nicely balanced that with a comparatively
stable environment the number of species of the different classes of
animals may remain more or less constant. But suppose one of these
factors is profoundly diminished, such, for instance, as a great
diminution in the number of the snake-eating birds. Then the snakes,
not being much persecuted by their enemies, will be in a most favorable
environment; they will increase greatly in numbers; they will be eagerly
on the look-out for their food, the frogs; the frogs, being thus
unusually persecuted and hard-pressed, will diminish greatly in numbers.
Now, this will be a golden opportunity for the insects; their environment
becomes much more favorable. The snakes do not bother the insects, but
destroy their enemies, the frogs. Therefore, the insects increase greatly
in numbers and profoundly affect the vegetation upon which they live
and thrive. The injury to the vegetation may thus seriously affect an
altogether different class of animals—the grass-eating or foliage-eating
animals, like the ruminants.
It may thus be understood how profoundly complex are the relations and
correlations of living creatures, and how a disturbance of some of the
links in these living chains may very extensively affect the other links.
The different creatures referred to above are probably the simplest
illustrations that can be given of protectively colored animals. For
here we have green animals adapted to a green environment—the green
foliage of trees or grass. This adaptation has been brought about by
Natural Selection. Suppose, for instance, that the habitat of the
_non-protectively_ colored _ancestors_ of the frogs was for any reason
unduly crowded by their enemies, the snakes. The frogs would be hard
pressed and much persecuted. Suppose that among the young of these
frogs there were some that varied in the direction of grass-green or
leaf-green colors, while others did not so vary, or possibly varied in
the direction of even conspicuous colors, such as black or white. It is
evident that the latter groups would be easily detected by the snakes and
destroyed, while the green group would frequently escape notice and would
thrive and procreate their kind. This process being repeated generation
after generation, there would come a time when the given habitat would
contain none but frogs with a protective coloration of green. All of
these protective colorations of snakes, butterflies, and caterpillars,
as well as of frogs, are adaptations. They are illustrations of the
survival of the fittest; the survival of those best adapted to their
environment—in short, Natural Selection.
[Illustration: PLATE II.—_Kallima paralekta._ A butterfly of Sumatra
illustrating the work of Natural Selection: C, butterfly with expanded
wings (dorsal surface) which are conspicuously colored through Sexual
Selection; B, same butterfly with wings closed (ventral surface) and
presenting a close resemblance to a dead leaf, A, through the agency of
Natural Selection. B, illustrates the Protective Resemblance of an animal
to an inanimate object.]
=Protective Imitation of Particular Objects.= Insects often exhibit a
very great amount of detailed resemblance to the leaves, flowers, and
twigs of plants among which they live. Those that live on grass are
striped longitudinally, while those that feed on ordinary leaves have
an oblique striation. There is a larva of a Georgia butterfly (_Sphinx
fuciformis_) which feeds on a plant having small blue flowers and linear,
grass-like leaves. This larva has a blue head and a green body striated
like the leaves. The resemblance of the insect to its environment is very
striking. There is another species that feeds on a plant with small red
flowers situated in the axils of the leaves, and this larva has a row of
seven red spots of unequal size, which corresponds quite closely with
the size and color of the flowers. There is a caterpillar in Borneo that
resembles a piece of moss with two exquisite pink-white seed-capsules.
Its general hue is greenish, with two little pink spots on its upper
surface, and it is covered with hair. Its movements are very slow, and
when eating it withdraws its head beneath a mobile fleshy hood that it
possesses, so that its motions in feeding are not noticeable. When living
in its native haunts it is all but impossible to detect it, so completely
does it resemble the surrounding moss. Other insects resemble green or
dead leaves in all their varieties of form and color, and to show what
a great protection such resemblance affords to insects in concealing
them from view the following observation of a naturalist in Nicaragua
may be related. In that country there are armies of foraging ants that
devour every insect they can catch. Among a multitude of these ants he
observed a locust that looked very much like a green leaf. The ants, many
of them, were continually running over the body and legs of the insect
without detecting its character. In many parts of the world there are
many butterflies (_Kallima_, for example) the under surfaces of whose
wings very closely resemble dead leaves. They frequent dry forests and
are rapid flyers. They are rather large, and the upper surfaces of their
wings are quite showy, having bluish and orange colors (Plate II). It is
their habit always to settle on some twig where there are decaying or
dead leaves. In doing so it folds its wings together over the back, thus
concealing the gay upper surfaces and presenting the protectively colored
under surfaces. The resemblance to a dead leaf is much more striking from
the fact that the short tails of the hind wings just touch the branch on
which the insect rests and look very much like the stalk of a leaf. From
this stalk a dark curved line extends to the elongated tip of the upper
wings, thus imitating the midrib of a leaf. On both sides of this midrib
are oblique lines that are partly markings and partly nervures, which
give the appearance of a leaf with its veining. The head and antennæ
fit in such a way between the closed upper wings as not to interfere
with that irregular outline which is characteristic of the withered and
dry leaves. Often the closed wings are covered with small black dots
gathered into circular groups that exactly resemble the minute fungi
found on decaying leaves, and it is sometimes difficult to believe that
the insects themselves are not attacked by a fungus. Wallace states that
this wonderful imitation is most complete, and that in Sumatra he has
often seen a butterfly enter a bush and then disappear as if by magic. He
states that once he was so fortunate as to see the exact spot on which
the insect settled, but even then lost sight of it for some time, and was
able to discover it close to his eyes only after persistent and careful
search.
The curious and interesting leaf-insects of Java are veined and colored
in such a way that, with the leaf-like expansions from various parts
of the body, not one person in a dozen can detect them when they are
resting upon their food-plants right under one’s eyes. Other insects
resemble pieces of stick (Plate III), with all the minute details of
branches and knots. An eminent naturalist has stated that after being a
practical entomologist for thirty years, he was deceived by one of these
stick insects and took out his pruning knife to cut from a plum-tree
what seemed to him to be a projecting spur. This spur proved to be the
caterpillar of a geometer-moth, about two inches in length. He placed
a portion of the plum-tree on a table, and showed it to several members
of his family, designating a space of several inches in which the
caterpillar was to be found, but none of them could detect the insect
until it was pointed out to them. These protective resemblances of living
creatures to inanimate objects are beautiful illustrations of adaptation
to environment through Natural Selection.
Beautiful illustrations of protective resemblance to particular objects
are furnished by leaf-hoppers (insects) in Central America. They resemble
the thorny and prickly growths of the plants on which they presumably
live. Some of them also resemble gall growths on the plants (Plate IV).
[Illustration: PLATE IV.—Central American Leaf Hoppers resembling the
prickly and thorny growths of plants on which they presumably live.
Certain of them also represent gall growths on the plants. Protective
Resemblance. [Figures collected by Dr. L. O. Howard, from various plates
published in the Biologia Centrali-Americana.]]
=Alluring Coloration.= Besides those insects which secure protection from
enemies by their resemblance to the inert objects among which they live,
there are others whose adaptive resemblance, and therefore concealment,
is for the purpose of securing their food,—for alluring their prey. A
most interesting case of alluring coloration is that furnished by a
wingless insect of India, the mantis. Its color and form are such as to
closely resemble such a fantastic flower as the pink orchis. The insect
rests motionless among the bright green foliage, being very conspicuous
on account of its pink color, and looking so much like a flower that it
allures and captures the butterflies which settle upon it.
There is a species of spider (_Thomisus citreus_) of a creamy-white color
whose abdomen completely resembles in color and contour the unopened buds
of the flowers among which it rests. It has been seen to capture flies
that were attracted to the flowers. There is another species of spider
that looks exactly like the excreta of birds, and through this alluring
resemblance captures certain butterflies. A naturalist has related how,
in pursuing a butterfly through a jungle in Java, he was stopped by a
dense growth of bushes. Here he observed a leaf with a bird’s dropping
upon it, and sitting on this dropping was a beautiful butterfly.
Surprised at such a usually dainty and pretty butterfly seeking such
inappropriate food, he carefully approached to study the actions of the
insect. The insect permitted him to get so close that he seized it by
the wings, and to his astonishment a part of the body remained behind as
if the bird’s dropping was very adhesive. He touched the dropping to see
if it really was sticky, and found that his eyes had been deceived and
that what he took for the excreta of a bird was a most artfully colored
spider, lying on its back with its feet crossed and depressed closely to
the body. The spider had been firmly holding the butterfly.
[Illustration: PLATE III.—Caterpillar, B, of a Geometer Moth
(_Prochœrodes transverrata_) on the stem of a plant (_Ailanthus_), A.
Illustrating Protective Resemblance.]
A very pretty illustration of alluring coloration is furnished by the
common spider (_Misumena vatia_), which is often found spread out upon
the yellow heart of an ox-eyed daisy and in like position upon Coreopsis
(Plate V). It so closely resembles the flower upon which it lurks that
the ordinary observer might well fail to notice its presence. The
coloration facilitates the taking of prey and protects the creature from
the assaults of enemies (Rev. H. C. McCook). It will be observed from the
illustration that the flower is mostly yellow with some red; the same
is true of the spider. This case is a very instructive illustration of
alluring coloration by which the insect has become a living bait for
entrapping butterflies and other insects. Nature has brought about this
complete color adaptation, from the variations of myriads of spiders.
For those ancestral spiders that varied most in the direction of color
adaptation to their environment were less often shunned by shy insects
which could serve as prey. The spiders with useful color variations
would thus most likely secure an abundance of food, and, thus living,
transmit to many of their offspring their useful variations; while those
with inharmonious, and therefore harmful, variations would not be so
able to deceive their food insects, and would thrive poorly or starve
altogether. This is another illustration of the survival of the fittest,
the selection by nature of those best adapted to or in harmony with the
environment; in short, it is Natural Selection.
Wallace, from whom many of these illustrations are taken, says that to
many persons it will seem impossible that such beautiful and detailed
adaptations and resemblances—and these are only samples of thousands
that occur in all parts of the world—can have been brought about by the
preservation of fortuitous useful variations. Yet this will not seem so
surprising, continues Wallace, if we keep in mind the facts of the rapid
multiplication of animals, the severe struggle for existence, and the
constant variability of these and all other organisms; and, further,
that we must remember that these delicate adjustments are the result of
a process, Natural Selection, which has been going on for millions of
years, and that we now see the small percentage of successes among the
myriads of failures. “From the very first appearance of insects, for
instance, and their various kinds of enemies, the need for protection
arose and was usually most easily met by modifications of color. Hence
we may be sure that the earliest leaf-eating insects acquired a green
color as one of the necessities of their existence; and, as the species
became modified and specialized, those feeding on particular species
of plants would rapidly acquire the peculiar tints and markings best
adapted to conceal them upon those plants. Then, every little variation
that, once in a hundred years perhaps, led to the preservation of some
insect which was thereby rather better concealed than its fellows, would
form the starting-point of a further development, leading ultimately to
that perfection of imitation in details which now astonishes us.” So it
is with the beautiful color adaptation of birds, mammals, lizards, and
other animals. There is a lizard (_Phrynocephalus mystaceus_) inhabiting
certain sandy districts in Asia, whose body is protectively colored and
some of whose mouth-parts have alluring coloration and form. The general
surface harmonizes with the sand in which it is found, while the skin
at each angle of its mouth is of red color and so folded as to closely
resemble a little red flower which grows in the sand. The lizard, being
thus in harmony with its surroundings, resembling the sand and the
flowers, is hidden from its enemies, the reptile-eating creatures. But at
the same time insects, being attracted by what they take to be flowers,
approach the lizards and are thus captured, being allured to their
destruction.
[Illustration: PLATE V.—A spider (_Misumena vatia_) lurking for prey on
the center of a flower (_Coreopsis_). Illustrating especially alluring
Coloration (for attracting prey), but also Protective Resemblance
(against enemies). Reproduced from “American Spiders.” By courtesy of
Rev. Henry C. McCook.]
=Warning Coloration.= Many animals possess color patterns that render
them very _conspicuous_ in their environment. It is a very interesting
fact that most of these creatures are the possessors of some deadly
weapons, as poison-fangs or stings, or that they are very disagreeable
and unpalatable food for other animals. Warning colors are most abundant
and best developed among insects. A family of butterflies (Heliconidæ),
in tropical South America, possesses very pronounced and conspicuous
color patterns, so that they are easily seen in their native haunts. Many
of them have deep blue-black with vivid red, white, and yellow spots and
bands, totally unlike those butterflies in the same locality that are
protectively colored and palatable. Their bodies have juices that exhale
a powerful odor. If one kill them by pinching the body, a liquid exudes
that stains the fingers yellow and leaves an odor on them that can be
removed only by repeated washing of the hands. There is a great deal
of evidence to show that this odor is very offensive to insect-loving
animals. Protectively-colored butterflies fly with great rapidity and are
very wary and seek concealment; while the butterflies with conspicuous
colors fly slowly, and do not conceal themselves, as if conscious that
they have no enemies.
Many caterpillars have gay and conspicuous colors and do not conceal
themselves. Bates noticed one in South America four inches long, striped
across the body with yellow and black bands, and with bright red head,
tail, and legs. It could be seen by any one who passed by, even at a
distance of many meters. All of these conspicuous and brightly-colored
caterpillars are unpalatable, and are refused as food by insect-eating
creatures.
Grasshoppers and locusts generally possess green protective tints and
are very palatable, but in tropical regions there are many species most
gaudily decorated with blue, red, and black colors. They are inedible and
are invariably rejected as food by lizards and birds.
A spider whose bite is exceedingly poisonous is found in Queensland. Its
bite will kill a dog, and produces serious illness in man, with agonizing
pain. It is black with a bright red patch on the middle of its body. This
warning coloration is so conspicuous that even the spider-hunting wasp
avoids it.
In all parts of the world frogs are usually protectively colored with
browns or greens; and little tree-frogs are either curiously mottled to
imitate dead leaves or bark, or they are green like the leaves they rest
upon. These protectively colored frogs are always eagerly sought after
by snakes and other enemies. But there are some frogs that are very
conspicuously colored and that hop about with impunity, being avoided by
the snakes and birds of prey. Such is a little frog in Nicaragua which
with its “scarlet vest and stockings of blue” is very conspicuous in its
native haunts.[9] Such, also, is a small toad found in South America,
which is colored a bright vermilion and an intense black, which crawls
about in the sunshine over the sands of arid places. Both of these
animals are altogether avoided by the frog-eating creatures, because they
have disagreeable properties that make them inedible.
In tropical America the very poisonous snake Elaps (Plate VI) is found
abundantly. Its style of coloration is very conspicuous and one that
does not occur in any other group of snakes, consisting alternately of
rings of red, black, and yellow, or red and black of varying width and
arranged in different patterns. Snake-eating birds and mammals have
learned, through hereditary experiences, to avoid these snakes with gay
livery because they are poisonous and therefore dangerous. In Plate VII
the conspicuously-colored black and yellow salamander is an animal with
warning coloration. It is inedible and avoided by carnivorous birds.
These warning colorations have been evolved through the Natural Selection
of fortuitous useful color variations in the ancestors during the
Geologic Ages.
[Illustration: PLATE VI.—Illustrating Warning Coloration (_Elaps_) and
especially Mimicry (_Erythrolamprus_). Elaps is a very poisonous reptile
and Erythrolamprus is harmless. Reproduced (and modified) from Romanes’s
“Darwin and after Darwin.” By courtesy of the Open Court Publishing
Company.]
=Mimicry.= Protective resemblance of a harmless animal to another
of a different species that is harmful is known as mimicry. Mimicry
is bound up with and altogether dependent upon warning coloration.
Some beetles are protected by having integuments, etc., of very great
hardness. Several genera of weevils are in this way saved from attack
by insect-loving birds. These weevils are often closely imitated in
appearance by softer and more eatable species of different genera from
the weevils. Wasps and bees are often mimicked by insects of other orders.
Insectivorous birds are very active in hunting out the edible beetles
(Longicornia), and everywhere in tropical regions these beetles so
closely resemble other insects which are avoided by the birds that the
longicorns are very frequently avoided and thus protected.
In tropical America many butterflies (Heliconidæ) are found that possess
warning coloration. They possess an offensive taste and odor which
almost entirely exempt them from the attacks of insect-eating animals.
The insectivorous birds have learned, by transmitted experiences
(heredity) to avoid the Heliconidæ. It is an interesting fact that in
the same locality with these distasteful butterflies are other species
that are very palatable to insectivorous creatures; but they so closely
resemble the non-edible species that the birds pass them by, not
recognizing their character.
There are some cases of mimicry among birds. There is a genus of large
honey-suckers known as friar birds found in the Malay Archipelago. They
are noisy and powerful birds which go in small flocks. They have sharp
beaks which are long and curved, and also powerful grasping claws. They
are perfectly able to defend themselves, often driving away such birds
of prey as hawks and crows when they approach them too closely. In the
same environment are weak and timid birds known as orioles, which trust
chiefly to their retiring habits and concealment for protection. The
orioles, although an entirely distinct species from the friar birds, very
closely resemble the latter. In each of the great islands of the Malayan
Archipelago there is a distinct species of friar birds, and always in the
same locality is a species of oriole that exactly mimics it. The separate
species often look so thoroughly alike that competent naturalists, prior
to a very close examination, have considered them as belonging to the
same species.[10]
The most remarkable cases of mimicry are those in which poisonous snakes
are mimicked by harmless ones. There is an egg-eating snake in South
Africa that possesses neither teeth nor fangs and is not poisonous. It
very closely resembles the poisonous Berg adder. When alarmed it still
more closely resembles the adder by the habit of flattening its head and
darting forward as if to strike an enemy, hissing at the same time.
[Illustration: PLATE VII.—An Amphibian (_Salamandra maculosa_)
illustrating Warning Coloration.]
In tropical America, in the localities where the poisonous genus Elaps
is found so abundantly, are several genera of harmless snakes of other
families, some species of which so closely resemble or mimic the
poisonous species that they are distinguished from them with difficulty.
The peculiar color patterns of the poisonous snakes serve as warning
colors to snake-eating mammals and birds. The mimicking snakes by flying
these danger-flags are protected.
In Plate VI Elaps is the venomous snake, and illustrates warning
coloration; Erythrolamprus is the edible, non-venomous reptile that has
acquired, through Natural Selection, a protective resemblance to Elaps,
and illustrates mimicry. At the first glance these two snakes look
very much alike; but a closer inspection will show that the detailed
color patterns differ in the two cases. Elaps, though a very poisonous
snake, has the reputation of not being venomous. This error has probably
originated from the fact that it has a gentle disposition and mild
temper, and also from the fact that no doubt it is frequently mistaken
for the mimicking non-venomous species.
Both warning coloration and mimicry are interesting illustrations of
adaptation to environment through Natural Selection; for the myriads
of ancestral forms were continually giving slight variations in color
patterns, some of which were useful to the creatures and others harmful.
Those that harmonized mostly with the environment gave their possessors
an advantage in the fierce struggle for life,—the struggle for food and
place and safety; and procreating their kind age after age, led to the
perfection of mimicry as we behold it to-day.
=Coloration as Recognition Marks.= In gregarious animals, whether
herbivora or carnivora, and whether mammals or birds, a ready recognition
of their own kind at a distance, in the dim twilight, or during rapid
motion, is of the greatest use, and probably often leads to the
preservation of life. Gregarious animals will not usually permit a
stranger in their midst. So long as these animals keep together they are
generally safe from enemies; but a single animal straggling off by itself
may become an easy prey to enemies. In such cases it is of the highest
importance to an animal that it should have every facility for quickly
discovering its companions at any distance within the field of vision.
Also to the young and inexperienced of each herd some means of easy
recognition is of vital importance. Recognition marks also enable the
sexes to identify their kind readily. The necessity for easy recognition
probably is at the basis of the bilateral symmetry in the coloration of
animals.[11] In the struggle for existence those gregarious creatures
that have the best color patterns for recognition marks are the most
likely to get the scattered members of a herd together with the greatest
rapidity, and thus to save them from their enemies. The surviving
members, transmitting their useful variations in recognition marks
to their offspring, are thus able in the course of ages to bring into
existence pronounced color patterns. Thus Natural Selection can account
for much of the coloration in animals known as recognition marks.
One or two illustrations of recognition marks in creatures will be
sufficient. A rabbit when alarmed and fleeing to its burrow displays a
conspicuous, upturned white tail. The rest of the body is protectively
colored. This conspicuous white surface of the upturned tail is a signal
flag of danger. The rabbit mostly feeds during moonlight nights, or
soon after sunset. The white upturned tails of alarmed rabbits serve as
signals and guides to the feeble and young, and also to those at a more
remote distance. Thus a number of rabbits, each following the one or two
in front, are all able in the quickest manner to reach a place of safety.
The spring-bok has a white patch on the face and one on the sides. It
also has a curiously well-marked white stripe above the tail. When
the animal is at rest this last-mentioned white stripe is very nearly
concealed by a fold of skin, but when it is in motion it comes into
full view, like the upturned tail of the rabbit, and serves as a guide
to friends. There are some animals inhabiting the Arctic regions
that are not white,—they are not protectively colored. Such is the
musk-sheep. This animal, though living in Arctic regions, is yet brown
and conspicuous. Its safety depends upon its association in small herds.
It is gregarious. Therefore it is of much more importance to this animal
that it should be able to quickly recognize its companions at a distance
than that it should be protectively colored and so concealed from its
enemies. So long as they keep together in herds they are abundantly able
to protect themselves. This is an exception to the rule of local color
adaptation that proves the rule.
=Sexual Selection.= Among most backboned animals it is the rule that both
sexes should be alike in color. This is especially true among the fishes,
reptiles, and mammals. But in birds the diversity of sexual coloring is
very frequent. It is among this class, therefore, that Sexual Selection
can best be studied. One of the most fundamental characteristics of
birds is the greater conspicuousness of coloration in the males. In the
tropical regions especially are found the most striking examples of
divergence in sexual color patterns. In humming birds, the pheasants,
the peacocks, chatterers, tanagers, and birds of paradise, the females
are exceptionally dull-colored and plain, while the male birds are
gorgeously colored and conspicuously attractive. The male birds of
paradise, for instance, are not only brilliantly colored, but also have
remarkable gorgets, plumes, and crests; whereas the female paradise birds
are without these decorations and as plain as our thrushes in their
ornamental plumage (Plate VIII).
The splendor of plumage which characterizes the male pheasants is
entirely wanting in the females. The intense crimsons and pure whites,
the gorgeous purples and blues of the male chatterers contrast strikingly
with the dull browns or olive greens of the females. The sober hues of
the females have been accentuated by Natural Selection.[12] When the
females were brooding on the eggs in their nests, those of them that had
varied in the direction of conspicuousness would most readily be detected
by their enemies, the hawks, and would be exterminated; but those that
had quiet and dull ornamentation would most frequently escape discovery,
and would pass successfully through the brooding season; thus living and
transmitting their color patterns to posterity,—Natural Selection ever
eliminating the conspicuous and preserving the sober-hued,—in the course
of time the dull ornamentation of the females would become more and more
pronounced.
[Illustration: PLATE VIII.—Male and Female Paradise Birds (_Paradisea
minor_). Illustrating the effects of Sexual Selection. The upper figure
(male bird) is much more beautiful than the lower (female bird).]
But another factor has been at work in accentuating the marked
differences in the ornamentation of the sexes. This factor is Sexual
Selection.[13] In the brooding season there is an intense rivalry
among the males for the possession of the females. Among them the art
of courting has become, indeed, one of the fine arts. The male birds,
like the males of almost all animals, have stronger passions than
the females, and with rarest exceptions are much more eager than the
females. In courtship they display their adornments and accomplishments
most zealously before the females; they strut around them in most eager
courtship and pompous vanity, displaying the utmost rivalry. The males
charm the females in various ways, such as dancing, or performing
fantastic antics either in the air or on the ground; and then again by
most melodious song. After man, the female birds appear to be the most
æsthetic of all animals; therefore, those male birds that are the most
pleasing songsters, or the most attractive in their dances and fantastic
performances, are the ones selected by the females for mating. In this
selection the female birds have paid the minutest attention to fleeting
fashions in strut and dance, in form and color,—the progeny of those
males that have been selected by the females for mating, transmitting
the inherited peculiarities of the parents, have tended more and more to
stamp as fixtures these fleeting fashions, and in this way the males have
become endowed with all sorts of decorations and accomplishments.[14]
Thus have been produced in them the many forms of topknots, wattles,
combs, plumes, and feathers elongated and springing gracefully from many
portions of the body; also the naked skin of the head and the beak,
frequently colored gorgeously. The feathers, through this means, are
often most beautifully tinted in charming patterns. As bearing upon this
theory of Sexual Selection, it can be observed that birds pay the closest
attention to the songs of each other. A bullfinch, for instance, had
been taught to pipe a German waltz, and in doing so was a most excellent
performer. He was placed in a room where there were kept some eighteen
canaries and linnets, and immediately commenced producing his melodies.
The birds all ranged themselves on the sides of their cages nearest
the performer, listening to his singing with the greatest interest.
Undoubtedly this singing is most often a matter of courtship; the female
finch selects that one out of a hundred males whose notes charm her the
most; the female canary always chooses the best singer. The soft cooing
of pigeons and of turtledoves is a matter of courtship. In the breeding
season there is the most intense rivalry between the males in singing; a
bird will sometimes sing until he drops down almost dead.
That female birds exercise choice in mating was believed by Audubon.
He describes how a woodpecker hen was followed by six gay suitors who
continued to perform strange antics until a marked preference was shown
for one of them. A study of the Australian bower-birds illustrates both
the courting antics of the males and the exercise of choice by the
females. These birds build bowers which are sometimes quite large. That
of one species is raised on a thick platform of sticks and is nearly four
feet in length and eighteen inches in height. These bowers are built
on the ground, and are for the sole purpose of courtship, since the
nests are formed in the trees. They are highly decorated with leaves,
berries, feathers, shells, and kindred objects. Both sexes assist in the
erection of the bower, although the male bird is the principal worker.
The bower-constructing instinct is so strong that it is practiced even
in confinement. A naturalist in describing the habits of some satin
bower-birds kept in an aviary says that at times the male will chase the
female all over the aviary, then go to the bower, pick up a gay feather
or a large leaf, utter a curious kind of note, set all his feathers
erect, run round the bower, and become so excited that his eyes appear
to start from his head. He continues opening first one wing and then the
other, uttering a low, whistling note, and, like the domestic cock, seems
to be picking up something from the ground, until at last the female goes
gently toward him and the wooing is completed.
Instances of love dances may be taken from all classes of the animal
kingdom. “Mr. Peckham has described a very interesting love-dance by a
certain species of spider (_Saitis pulex_). He placed a male in a box
with a female. As soon as the former saw the latter, about twelve inches
away, he became excited and at once moved towards her; when some four
inches from her, he stood still, and then began the most remarkable
performances that an amorous male could offer to an admiring female.
She eyed him eagerly, changing her position from time to time so that
he might always be in view. He, raising his whole body on one side by
straightening out the legs, and lowering it on the other by folding the
first two pairs of legs up and under, leaned so far over as to be in
danger of losing his balance, which he maintained only by sidling rapidly
towards the lowered side. The palpus, too, on this side, was turned back
to correspond to the direction of the legs nearest it. He moved in a
semicircle of about two inches, and then instantly reversed the position
of the legs, and circled in the opposite direction, gradually approaching
nearer and nearer the female. Now she dashes towards him, while he,
raising his first pair of legs, extends them upward and forward as if to
hold her off, but withal slowly retreats. Again and again he circles from
side to side, she gazing towards him in a softer mood, evidently admiring
the grace of his antics. This is repeated until are counted one hundred
and eleven circles made by the ardent little male. Now he approaches
nearer and nearer, and when almost within reach whirls madly around and
around her, she joining and whirling with him in a giddy maze. Again he
falls back and resumes his semicircular motions, with his body tilted
over; she, all excitement, lowers her head and raises her body, so that
it is almost vertical; both draw nearer; she moves slowly under him, he
crawling over her head, and the mating is accomplished.”[15]
In addition to that form of Sexual Selection where the female chooses a
mate from among a number of competing males, and which may be designated
_preferential mating_, there is another form of selection in which the
males fight with one another for the mastery and the possession of the
females. Among the higher mammals it is a very general fact that the
males fight together for the possession of the females. This leads,
especially in polygamous animals, to the better armed or stronger
males becoming the parents of the next generation, which inherits the
peculiarities of the parents. Thus the offensive weapons and the vigor
of the males are continually increased, resulting in the antlers of the
stag, the tusks of the boar, the fighting instinct and spurs of the
gamecock, and the horns and strength of the bull. Even mammals that are
not specially armed fight to the death for the possession of the females,
such as beavers, moles, squirrels, and hares. Almost all male birds are
especially pugnacious during the breeding season. Battles have been
observed in such different groups as ducks, finches, woodpeckers, humming
birds, and waders. Among fishes deadly battles occur between the males
of sticklebacks. Also the males of salmons engage in deadly contests;
among reptiles fighting occurs among the male tortoises, crocodiles, and
lizards. Spiders and many butterflies often fight for the females. Thus
Sexual Selection through the _law of battle_ occurs widely throughout
the animal kingdom. This form of Natural Selection greatly increases the
vigor and fighting power of male animals; for, in every case, the weaker
males are either driven away, killed or wounded, and the field is left to
the most vigorous for procreating their kind.
The male stickleback is a little fish that builds its nest among the
weeds, weaving the material together by a secretion from its kidneys.
It is a very passionate little animal, and is exceedingly pugnacious in
relation to its male rivals. The battles of the males are often very
desperate. The combatants fasten tight to each other for a time, tumbling
over and over again, until they appear to be completely exhausted. The
males of the rough-tailed stickleback, when fighting, swim round and
round one another, endeavoring to pierce each other with their raised
lateral spines. In fighting they are perfect little furies, and their
bite is very severe. Their lateral spines are used with such fatal effect
during a battle that a male has been observed to rip open his opponent,
so that the latter sank to the bottom in a dying condition. The females
are very peaceful. When they come out of their hiding-place and view the
nest that the male has made he is mad with delight.
The male salmon is as pugnacious as the little stickleback. Two males
have been known to virtually battle with each other all day long. In
breeding ponds the males can be seen constantly fighting and tearing one
another on the spawning beds, and so many are injured in consequence
that they may be seen swimming near the banks in a state of exhaustion,
many of them apparently dying.
Among birds the law of battle holds as well as the law of preferential
mating. During the breeding season they are exceedingly pugnacious. The
humming birds, the smallest of any, are among the most quarrelsome. Two
males rarely meet without a fierce fight on the wing.
Darwin gives the following illustration of the invincible courage and
fighting instinct of the gamecock. One of these birds had both of its
legs broken in a cockpit, and its owner made a wager that if his legs
could be supported with splints and bandages so that he could stand
upright he would keep on fighting. This was accomplished, and the bird
fought on with dauntless courage until he received a death stroke.
It is probable that even with the most pugnacious species of birds
the pairing does not depend alone on the courage and strength of the
male, for these males are usually decorated with various ornaments.
Furthermore, these decorations during the breeding season often become
more brilliant, and are eagerly displayed before the females. Darwin
states that twenty or more males of the _Tetrao cupido_ (species of
grouse) will assemble at a particular spot, keeping up a tremendous
chattering and strutting about. At the first response from a female the
males take to fighting furiously, and the weaker are vanquished. Both the
victors and the vanquished pay court to the female, so that the latter
must make a choice or the battle is renewed. Here we have the combined
action of selection through battle and by preferential mating.
Among mammals the males win the females much more through fighting than
through the display of charms. In the breeding season the most timid
male animals, which are not even supplied with any special weapons for
fighting, engage in the most desperate conflicts. Two male hares have
been seen to fight until one was killed. Those male mammals which are
provided with special weapons for fighting enter into the fiercest and
most deadly conflicts. The wild male elephant, during the period of love,
is one of the fiercest fighters in the world. Lions engage in terrible
battles, and a young lion dare not approach an old one.
Male seals fight most desperately during the breeding season, using
both their claws and teeth. The conquerors appropriate the females and
transmit their qualities to their offspring.
These are all cases of the survival of the fittest; of the survival of
the males best adapted to the exigencies of their surroundings—in short,
additional illustrations of Natural Selection.
=Insect Selection.= Flowers usually consist of several parts, such as
the stem, the calyx composed of green sepals, the corolla formed of
attractively colored petals, the stamens, the pistil, and finally of
certain nectar-forming organs situated at the base of the last-named. The
upper portions of the stamens are known as antheridia. The free extremity
of each pistil is called a stigma, the intermediate stalk is the style,
and the base is the ovary. The flowers constitute the sexual parts of the
plant. The stamens are the male elements and the pistils are the female
structures. In some species of plants the flowers possess the stamens
but not the pistils,—they are male flowers; in others the flowers have
pistils but not stamens,—they are female flowers. In still other plants
the flowers possess both the male and the female structures, and are
therefore bisexual or hermaphroditic flowers. The ovary of a pistil has a
number of cells in it called ovules (female germ cells); the antheridia
on the stamens have cells in them called pollen (male germ cells). When a
pollen cell is carried by any means to the stigma of a pistil, it sends
down through the latter a tubular prolongation by which the nucleus and
protoplasm of the pollen cell unite with the nucleus and protoplasm of
the ovule; so that we now have a fertilized egg,—the germ of a new plant.
This fertilized ovule by repeated cell multiplication can grow into an
adult plant.
There are two agencies by which the pollen is carried to the pistil;
first, by the wind, and, secondly, by insects (or, occasionally, by
humming birds). Flowers that are fertilized through the agency of insects
are the most beautiful in existence, displaying all the varied hues and
gorgeous patterns that are found in the organic world. On the other hand,
the flowers which are fertilized through the agency of the wind are
incomparably less beautiful than those of insect production, and they do
not secrete sweet juices or nectar. The earliest flowers in geologic time
consisted only of those essential portions, the stamens and pistils, and
had no colored whorl of petals within another colored whorl of sepals.
The poorly developed nectaries secreted only small quantities of honey.
The food-seeking insects visited these primitive flowers for the pollen
and nectar, even as they do now. The nectaries in the plants were so
situated that the insects could not get at the honey without rubbing off
some of the pollen and carrying it to other plants which it visited for
honey. In this way the nectar-seeking insects would often carry pollen
from the flower of one plant to the stigma of another plant’s flower,
and thus secure cross-fertilization. Undoubtedly often the stigma of a
plant’s flower was fertilized by pollen from the same flower; but it is
known that seeds produced by cross-fertilization are much more vigorous
and hardy than those produced by self-fertilization in the same flower;
therefore, those plants that varied most in the direction best adapted
for securing cross-fertilization would have decided advantages in the
struggle for existence. Their fertilized eggs (seeds) would be most
vigorous, and would most readily secure nutriment and withstand adverse
circumstances. The variations of the primitive flowers most calculated
to secure cross-fertilization would be those that made the flower more
conspicuous by the appearance of bright colorations and delightful odors,
such as would attract the attention and visits of nectar-seeking insects.
These variations being transmitted, by heredity, to the descendants and
accentuated as the ages passed would ultimately lead to all the wonderful
adaptations of flower and insect structure to one another that are found
in nature.
[Illustration: PLATE IX.—Two Primrose flowers (_Primula elatior_). A,
with a long style; B, with a short one. Vertical sections have been made
through the flowers.]
Natural Selection has acted in a double manner here, preserving those
flowers that had the most delightful odors or the most conspicuous and
enticing colorations and patterns; and at the same time selecting those
insects that varied most in the direction of keenness of scent, acuteness
of vision, and color perceptions. It will be instructive to briefly
describe the fertilization of the primrose and an orchis by bees. The
_primrose_ (Plate IX) has two sorts of flowers that are never found on
the same plant; one has stamens high up the corolla tube and a short
style with its stigma below the anthers; the other has the stamens far
down the tube and a long style with the stigma above the anthers. In
both cases the nectar is at the very bottom of the corolla tube. When a
bee visits a short-styled flower, it extends its proboscis to the bottom
of the tube and in withdrawing it brings away some pollen cells at its
base. If it should next visit another short-styled primrose, it would not
fertilize it because the pollen on the base of the proboscis could not
reach the stigma; it would only gather still more pollen. But when it
visits a long-styled primrose, it will necessarily deposit some pollen
cells on the stigma, inasmuch as that is at the commencement of the
corolla tube. If the bee should first visit a long-styled form of flower,
it will carry off pollen on the tip of its proboscis, and when it visits
a short-styled primrose will deposit the pollen on the stigma.
In the _orchis_ the stigma is placed below the anther. The stigma is
in the front part of the flower and at the base of the lip, the latter
being prolonged into a long tube full of nectar. The stigmatic surface
is composed of very viscid matter. A bee when seeking the nectar pushes
its head against the anther, and in so doing detaches the two sticky
glands to which the club-shaped masses of pollen cells are attached
(Plate X). It carries these away on the front part of its head. So long
as the masses of pollen cells remain erect on the bee’s head, they cannot
reach the stigma of any other orchis that it visits. As the sticky glands
on the head contract, the pollen masses incline forward and become
horizontal, so that they touch the next sticky stigma that is visited.
The greater stickiness of the stigma detaches the pollen masses from the
bee’s head, so that the flower is fertilized. It takes so long for the
pollen masses on the bee’s head to assume the horizontal position that
the insect has visited all the flowers on one orchis and then visits
another plant. By this time the pollen masses are in the proper position
(horizontal) to fertilize the flowers of another plant. In this way
cross-fertilization is secured and the vigor of the plant maintained.
It may now perhaps be appreciated how intimate are the relations between
the form and habits of insects and the structure and coloration of
flowers. Our standards of beauty have largely been created for us through
Insect and Sexual Selection. If insects had not been developed on the
earth, plants would not be ornamented by beautiful flowers, but would
show only such poor and inconspicuous ones as are found on grasses, on
oak, ash, and fir trees. Grant Allen has beautifully written that, “while
man has tilled only a few level plains, a few great river-valleys, a few
peninsular mountain slopes, leaving the vast mass of earth untouched by
his hand, the insect has spread itself over every land in a thousand
shapes, and has made the whole flowering creation subservient to his
daily wants. His buttercup, his dandelion, and his meadowsweet grow
thick in every English field. His thyme clothes the hillside; his heather
purples the bleak grey moorlands. High up among the Alpine heights his
gentian spreads its lakes of blue; amid the snows of the Himalayas his
rhododendrons gleam with crimson light. Even the wayside pond yields
him the white crowfoot and the arrowhead, while the broad expanses of
Brazilian streams are beautified by his gorgeous water lilies. The insect
has turned the whole surface of the earth into a boundless flower-garden,
which supplies him from year to year with pollen or honey, and itself in
turn gains perpetuation by the baits that it offers to his allurement.”
[Illustration: PLATE X.—Illustrating the fertilization of an orchis by an
insect. A, represents a section of the flower and shows a bee standing on
the flower’s lip with its head touching the sticky portion of the pollen
masses; C, shows the pollen masses stuck to the bee’s head and erect; B,
shows the pollen masses horizontal, the proper position to leave them
detached from the bee by the sticky stigma.]
Natural Selection is the great agency that accounts not only for the
color patterns and forms of living creatures, but also for the great
majority, if not all, of the useful characteristics of organic creatures,
including their internal organization.
One more illustration of the power of Natural Selection may be given,
outside of the subject of color patterns. It may be interesting to
readers who are not familiar with the elements of zoölogy to know that
whales are not fishes but mammals. They belong to the same class that
man does. The embryology of a whale reveals that it is descended from
ancestors that were _land_ mammals, and that these mammals had a scanty
covering of hair, teeth of different shape, broad tails like beavers,
short fore and hind legs, and well developed sense organs. The olfactory
organ was especially well developed. It is probable that these ancestors
of the whale lived in marshy districts and were omnivorous, eating both
plant and animal food. They sought their food in both shallow water and
in swamps. As the conditions of life became more and more unpropitious
on land, they were slowly modified through the ages under the action of
Natural Selection into creatures somewhat like dolphins. At first they
lived in fresh water, but finally they found their way into the sea and
became the rulers of the ocean, from which the giant sea reptiles of
earlier epochs had vanished. Hence are explained the adaptive changes
of structure: the fore-limbs were modified into flippers enclosed in a
fin-like sac, but retaining the bones corresponding to like structures
in other _mammals_, as in the arm of man, the wing of the bat, and the
fore-leg of the horse. Traces of the hind legs may be detected in a few
species; the tail, which acted as a powerful swimming organ, became
divided into two lobes; the head became fish-like in shape; the seven
bones of the neck, common to most mammals, grew together; the skin became
hairless; and the teeth, which appear in the young of the true whale, but
are never cut, gave place to hanging fringes of whalebone, in the meshes
of which the animal entangles the minute organisms it feeds upon.[16]
ISOLATION OF VARIETIES IN NATURE.
The following analysis of Isolation will be useful:
{ Preferential Mating.
{ Sexual. {
Isolation { { Cross-Sterility.
{ Geographical.
It has been stated on an earlier page that the commingling of diverse
hereditary units accomplished through the fertilization of an ovum by a
spermatozooid is the source of many variations in the offspring. In this
fertilized ovum the complexity of chemical substance, and, therefore,
the complexity of inheritance, gives instability to the embryo, and
thus produces variations in the offspring. In this embryo there is
a struggle among the hereditary units,—a struggle among the various
qualities inherited from both sides,—and a survival of the fittest, a
veritable intra-cellular Natural Selection. It is a well-established
law in biology that the union of germ cells of very closely related
individuals, that is, of consanguineous individuals (in and in breeding)
leads to less vigorous and variable offspring, and the parents are
less prolific; while the commingling of diverse heritages by the union
of germ cells from individuals belonging to strong but different
varieties leads to vigorous and quite variable offspring. The union of
such individuals is also most prolific. On the other hand the union of
individuals belonging to very diverse varieties becomes less and less
prolific until the cross-sterility of species is reached, although there
are many exceptions to this rule of cross-sterility. The individuals
of a species living in a state of nature are constantly varying. With
every generation trivial variations take place in all directions and
of all kinds. But these variations are all funded in the common stock,
for the varieties freely mingle among one another and cross-breeding
is constant not only between them, but with the parent stock. Of the
variations that are constantly taking place some are advantageous to
the creatures, some are disadvantageous, while many are neutral, being
neither useful nor harmful. Natural Selection is ever alert, selecting
the advantageous variations and eliminating the disadvantageous ones.
The neutral variations are not touched by Natural Selection; among these
intercrossing of varieties probably affords Nature an opportunity to
make almost endless combinations, some of which might be useful to the
animals, and others harmful, and in either case would come under the
influence of Natural Selection. The commingling of diverse heritages
due to the union of more or less pronounced varieties of the species in
nature not only leads to a funding of varietal characteristics, but also
increases the instability of the offspring, augmenting their plasticity,
so that more numerous and diverse variations take place. According to
Romanes the reproductive organs are among the most variable in the body.
Of the numerous variations taking place in the individuals of a species
under nature, some, therefore, affect the reproductive organs in such a
way that certain of these individuals are cross-fertile with one another,
but _cross-sterile with other varieties and with the parent stock_. This
interesting and very important kind of variation is known to occur in
some individuals of the human species. It is well known that a man and
woman have been cross-sterile with one another, being unable to have
children; yet when separating and mating with others they have both been
cross-fertile, families being reared by both of them.
Variations are commencing species; isolated variations diverge more and
more into distinct species. This fact, then, of the occurrence in nature
of variations in some of the individuals of a species by which they are
cross-fertile with one another, but cross-sterile with other varieties
and with the parental stock, shows that Nature has a most effectual means
by which varieties may be isolated from one another,—just as effective
means as man, the breeder of varieties of domestic animals, possesses
in isolating these domestic varieties by physical barriers, as fences,
etc. Cross-sterility, therefore, in nature, is a most effective sexual
barrier. The special form of it under consideration is what Romanes has
called Physiological Selection. The varieties that are isolated by this
sexual barrier have got to run the risks of in and in breeding, which
Darwin has shown occur in domesticated animals, but which Wallace thinks
are much less in a state of nature.
Another very important mode of Nature for isolating varieties is that
which arises out of the instinctive preferences of animals. There is a
tendency for like to breed with like where varieties are formed. The pale
and dark colored herds of fallow deer in the Forest of Dean have never
been known to interbreed. In the Falkland Islands all the cattle are
known to have descended from the same stock. Here there are differently
colored herds of cattle, and those cattle of the same color will
interbreed with each other, but not with individuals outside their own
color-caste, as Morgan expresses it. When two flocks of heath sheep and
merino sheep are mixed together, they do not interbreed. This isolation
of varieties by instinctive preferences for those individuals with
like color patterns may be spoken of as _preferential mating_ through
_recognition marks_. A very obvious mode of isolation in nature is by
geographical barriers (including migration). In treating of environment
we learned that during the geologic ages of the globe, the physical
geography and climate have repeatedly changed. A very cold temperature, a
mountain chain, a body of water, a stretch of desert land, may completely
prevent interbreeding, on either side of the barrier, between the
individuals of a species.
It should now be understood that Nature, like man, produces divergences
from the parental stock, and isolates them by various effective
agencies. Natural Selection ever carefully watches over these processes,
eliminating the unfit variations and selecting the useful ones.
Variation, Heredity, Environment, Isolation, and Natural Selection,
having been acting and reacting through the ages, have produced, from a
common parental stock, all the innumerable divergent and adaptive forms
of living creatures that can be traced through the geologic strata to
those on the surface of the earth to-day; have produced, therefore, _man_
also as the inflorescence of the topmost branch of the tree of life.
SECTION VI.
EVOLUTION OF MAN.
EVOLUTION OF MAN.
The detailed study of the development (ontogenetic and phylogenetic)
of man is so vastly intricate and extensive a subject that it will be
impossible in a work of this character to do more than refer to it in
brief outline. One of the best and simplest methods to approach the study
of such a subject is to acquire some idea of the _development of the
frog_.
The fertilized frog’s egg, which is the starting point in the life of
a new frog, is deposited in water and hatched by the warmth of spring.
After fertilization the egg or cell divides into two cells, these two
into four, the four into eight, the eight into sixteen, and so on till a
large number of small cells, associated together, is formed (Fig. 10).
These cell phases represent different stages in the life of the growing
frog. It is thus seen that the frog, in its earliest stages, consists of
nothing but many small cells. These cells, through the mysterious powers
of heredity, are going to differentiate as development proceeds into the
various organs (groups of various kinds of cells) that form the tadpole
and finally the frog. For further stages in the development of the egg
(oösperm) towards the tadpole, works upon Comparative Embryology should
be consulted.
At length the tadpole is hatched from the egg, and then soon swims about
in the water (Fig. 17).
The creature that comes from the egg looks nothing whatever like a frog.
It has no limbs whatever, and consists mainly of a bulky head and tail.
This is the tadpole stage in the development of the frog. It can exist
only in water, breathing air therefrom by means of gills. Like the fish,
it has a two-chambered heart. At this stage it has no lungs, and the
gills consist of an external (Fig. 17, a) and an internal pair. The mouth
is small, with only horny toothless jaws, with no tongue. The creature
is herbivorous, living on decaying vegetable matter. The vertebræ of the
spinal column are bi-concave, as in fishes. The tadpole is essentially a
fish, and would be so classed if it did not develop further. An evolving
fish does not go beyond this stage. But the developing frog does go
beyond this stage to a higher one. As its evolution proceeds through the
multiplication and differentiation of the cells that form its body, limbs
begin to bud out, first posteriorly (Fig. 17, b) and then anteriorly
(Fig. 17, c). The lungs now begin to develop, and the external gills
dwindle more and more until they soon disappear, the internal ones
persisting for a while longer. The tongue, at this stage, also makes its
appearance. The creature now can breathe both air and water. This is
the permanent condition of many adult amphibians belonging to a lower
order than the mature frog, such as the _siren_, _menobranchus_, etc.
The siren in developing also passes through the fish stage, but does not
get beyond the siren stage. But the evolving frog does go beyond this
stage, for with the growth of the legs the tail dwindles slowly by its
gradual absorption (Fig. 17, d). The internal gills now disappear through
absorption, and the lungs develop more thoroughly. Great changes take
place in the blood-vascular system, the fish-like, two-chambered heart
evolving into the three-chambered, amphibian heart. In spite of its
dwindling, the tail is still a very conspicuous organ. In this phase of
its development the frog can breathe only air, and must frequently come
to the surface of the water for that purpose, and soon leaves the water
altogether. Now this stage of the creature’s development corresponds to
the permanent adult condition of another order of amphibians, which is
higher than that to which the siren belongs but lower than the order of
the adult frog. This intermediate order has such creatures in it as the
_triton_. The triton in developing passes through the fish and siren
stages, but does not get higher than the triton stage. But the evolving
frog goes even higher than this triton-like condition. Its tail is more
and more absorbed until it finally disappears, and then the young but
perfect frog appears (Fig. 17, e). During this period the teeth develop
and the creature becomes carnivorous, feeding on insects. It is thus seen
that the developing frog passes by small gradations from one class (the
fish class) to an altogether different and higher class (the amphibian
class). When it has evolved to this higher class, it then passes from
the lower order (“siren” order) to a higher one (“triton” order), and
then to the highest order (“frog” order). The bi-concave vertebræ of the
fish-like tadpole have now developed into vertebræ with the cup-and-ball
joints of the higher amphibian. It is the same with all the complex
organs of the adult frog; they evolve from the much simpler structures of
the tadpole.
[Illustration: FIG. 17.—Tadpoles and Frog; a, tadpole with branching
external gills; b, gills absorbed and hind legs have appeared; c, fore
legs have appeared; d, tail shrunk and legs enlarged; e, perfect, young
frog,—tail entirely disappeared. The figures represent some stages in the
life history of the frog.]
This study of the frog’s evolution from the fertilized egg is profoundly
instructive. It reveals to us, through direct observation, that a
creature varies in its form and structure at succeeding intervals of
time. These variations diverge more and more, so that specific, generic,
and even ordinal and class distinctions are revealed as the development
proceeds. Owen, the distinguished comparative anatomist, in speaking of
the transmutation of one species into another in the course of geologic
history, says, though with a hostile purpose in view, that in the
metamorphoses of the amphibians we seem to have such process carried on
before our eyes to its extremest extent. Not merely is one specific
form changed to another of the same genus; not merely is one generic
modification of an order substituted for another, the transmutation is
not even limited by passing from one order (Urodela) to another (Anura);
it affects a transition from class to class. The fish becomes the frog
(amphibian); the aquatic animal changes to the terrestrial one; the
water-breather becomes the air-breather; an insect diet is substituted
for a vegetable one. And these changes, moreover, proceed gradually,
continuously, and without any interruption of active life. Such is the
language of Owen in reference to these remarkable transmutations of the
developing frog.
The development of the frog is a brief recapitulation, an epitome,
through heredity, of the main transmutations of its ancestral forms
in geologic time. It is not true that the embryonic phases in the
development of a higher form always resemble the adult stages of lower
forms. This may or may not be the case; but what always does occur is
that the embryonic phases of a higher form resemble the corresponding
phases of the lower forms. So far as the frog’s development is
concerned, it is very instructive to know that the order of succession
of its embryonic forms undoubtedly parallels the order of succession
of corresponding forms in past geologic ages. Fishes appeared in the
Upper Silurian rocks with amphibian characteristics. In the succeeding
Carboniferous Ages the fishes still continued under new forms; but also
the lowest forms of amphibians, the most fish-like forms, now appeared.
They were somewhat like the sirens, they were perennibranchs. In the next
succeeding rocks, the Permian and Triassic, higher, triton-like forms
appeared. They were caducibranchs. Finally, in the Tertiary rocks, the
highest forms of amphibians are found, such as the frogs.
In order to understand the relation of Ontogeny to Phylogeny, it must be
carefully borne in mind that the simple and lowly organized creatures on
the globe at the first appearance of life were performing the two great
functions that all living creatures perform, viz.: those of nutrition
and reproduction. These functions imply that organisms were reacting to
environment, and, therefore, undergoing modifications and adaptations;
and at the same time the organisms were giving origin to offspring—they
were reproducing their kind through heredity. As these simple organisms
lived through the ages and became more and more complex by modifications
and adaptations to an ever-changing environment, they still evolved
their kind in reproduction. Every new adaptation gained by the parent
was transmitted by heredity, in the course of time, to the offspring;
every form and structure modified in the parent was modified by heredity
in the offspring; and every structure lost by the parent was finally
lost in the offspring. Just in proportion as the parents, through the
ages, became modified, often becoming more complex by the addition of
adaptation to adaptation, retaining some structures of their ancestors
by heredity (through use) and losing others, eventually, through disuse;
so the offspring of these modifying parents became correspondingly
modified, and acquired by heredity the modified structures and habits
of the parents, while losing other structures in time that the parents
had lost. Just as complex _organisms_ of later ages have been evolved
from the simpler organisms of earlier ages by the addition of adaptation
to adaptation, in an orderly sequence (Phylogeny); so, therefore, the
complex _offspring_, while growing, unfold these inherited adaptations
in the order of their acquisition. This last process is called Ontogeny
or Embryology. Ontogeny is undoubtedly an illustration of the results
of Natural Selection’s activity; for, during the phylogeny of the frog
throughout the incalculable ages of the past its ancestors undoubtedly
assumed innumerable forms and structures which were adaptations to
the times and surroundings. But with the advancing time and changing
environment, some of the old forms and structures continued useful and
were retained, while others became useless and were eliminated by Natural
Selection. In addition to the old useful structures that were retained
changing environment often modified some of the retained structures and
added still other adaptations to these. And so on, throughout the ages,
in building up a frog, through geologic embryos, geologic “infants,”
geologic “children,” and finally geologic adult frogs, Natural Selection
has retained during ontogeny many useful structures in the order of
their first appearance, and eliminated innumerable others that became
useless. The ontogeny of the frog, which has been built up by its
phylogeny, reveals the useful structures that have been retained, and in
the order of their appearance; often showing structures that have been
lost in the parent, but are not yet quite lost in the embryo, while it
fails to show innumerable useless structures that have been lost in the
past. This is the reason why we say that the ontogeny of a frog is a
brief outline recapitulation of the main points in the phylogeny of the
frog, with even some main points occasionally omitted altogether. The
geologic ancestors of the frog were the scaffoldings by which it climbed
from simple creatures up to its present complex organization; just as
the embryological phases at present are the scaffoldings by which a
simple, unicellular, fertilized ovum climbs up through heredity to the
huge complexity of the multicellular adult frog. What is true of the
development of the frog, ontogenetically and phylogenetically, is also
true of all living creatures, and is therefore true of =man=.
Man, in his individual development, commences life as a small,
microscopic cell—the fertilized ovum—which is only one-fifth of a
millimeter in size. His first stage resembles an encysted protozoan
animal. As cell-multiplication proceeds he soon gets into the morula
stage, which resembles a colony of undifferentiated protozoans. He soon
evolves into a stage which may be compared to a colony of protozoans some
of the members of which have undergone differentiation. Then comes the
gastrula stage, which is distinctly suggestive of a low metazoan, and
in which the developing germ assumes fundamental anatomical qualities
such as characterize lowly animals like polyps. Then, by gradual
transmutations, the vertebrate characteristics appear; but it could not
be said at this stage of development, if one did not know, whether one
is observing a fish, an amphibian, a reptile, or a mammal. Finally, the
developing man passes through his fish and reptile phases and reaches the
mammal stage. But as yet it cannot be said to which order the animal
belongs. The evolution of the individual continuing, he finally assumes
those anatomical characteristics that stamp him as belonging to the order
of man.
The theory of evolution, then, teaches that this development of man in
the course of a few short months, like the development of the frog, is a
very condensed and abbreviated epitome of the evolution of mankind from
primitive protozoans during the incalculable ages of the past.
Drummond has prettily written that “the developing human embryo is
like a subtle phantasmagoria, a living theater in which a weird
transformation scene is being enacted and in which countless strange and
uncouth characters take part. Some of these characters are well known
to science, some are strangers. As the embryo unfolds, one by one these
animal-actors come upon the stage, file past in phantom-like procession,
throw off their drapery, and dissolve away into something else. Yet,
as they vanish, each leaves behind a vital portion of itself, some
original and characteristic memorial, something itself has made or won,
that perhaps it alone could make or win,—a bone, a muscle, a ganglion,
or a tooth,—to be the inheritance of the race. And it is only after
nearly all have played their part and dedicated their gift that a human
form, mysteriously compounded of all that has gone before, begins to be
discerned as the resultant.”
As has been stated in the introductory part of this book, if all the
animals that have ever lived on the globe should be represented by a tree
those existing on the earth to-day would be indicated by the topmost
twigs and leaves, while the extinct forms would be represented by the
trunk and main branches. Just as the leaves, twigs, branches, and trunk
of the tree have a common origin, viz., the seed that developed into the
tree, so all the different species of animals of the present and the past
are the trunk, branches, twigs, and leaves of the “tree of life,” and
have had a common origin from a primitive protozoan cell (see Diagram of
Development, Fig. 18). Therefore all creatures, living and past, have a
more or less blood relationship.
The Diagram of Development will indicate in a very general way the
possible track taken by a man as he evolved,—grew higher and higher as
the central, straight trunk of the expanding tree of life,—during the
geologic ages; and finally appeared as the inflorescence of the topmost
branch of this central trunk. It is seen from this scheme that the
tree of life commenced in a primitive cell. Without entering into any
discussion of the various theories of evolution and epigenesis, we may
say that the primitive protozoan contained potentially all the animal
forms (each being a cell or group of cells) that have existed on the
globe, just as the fertilized egg contains potentially all the tissues
and organs (groups of cells) of the adult man.
As the tree of animal life unfolded and expanded—like a germinating
seed—from the primitive protozoan, certain of the descendants evolved
along the straight and central branch, through the primitive colonial
protozoans, on through primitive vermes, and still on through primitive
fishes (elasmobranchii), amphibians, reptiles, and on through primitive
ornithodelphia (monotremes), and didelphia (marsupials) to a primitive
order of monodelphia, viz.: primitive primates. The evolution of man
continued through primitive anthropoidea to primitive anthropopithecus.
At this point we meet with the common ancestors of the _higher anthropoid
apes_ (chimpanzee and gorilla) and _man_.
[Illustration: FIG. 18.—Diagram of Development: Portion of the “Tree of
Life,” showing approximately the relative places of the great groups of
animals. The _Central Trunk_ and _Primary Branches_ represent _Primitive_
(geologic) forms; the _Terminal Twigs_ represent _Modern_ forms.]
At each stage of the evolution some of the descendants of the animals of
this stage diverged obliquely, modifying the characters they possessed at
this stage in a direction that varied more and more from those characters
that led on to man. So that all along the central trunk of the tree of
animal life collateral branches were given off. The collateral branches
given off at each upward stage of evolution represent animals higher in
the scale than those that departed from the central trunk lower down.
To illustrate what has occurred at each stage in the evolution of man,
pause for a moment to consider that phase of progress represented by the
primitive reptilia. If we study the anatomy of the specialized reptiles,
birds, and monotremes of the present, we will find that they all have
many characters in common. These characters are _reptilian_. Each class
has its own distinctive specialized peculiarities in addition to its
common reptilian characters. The study of the fossils of the rocks shows
that in the Jurassic and Cretaceous ages animals existed that were
undoubtedly reptiles, but had also very distinct bird characters; also
reptiles existed that had distinct monotreme characters. These reptiles
came from those of earlier times that were still more generalized. As the
ages passed, some of the generalized reptiles (primitive reptiles) lost
more and more the reptilian features and gradually assumed more and more
distinct bird characters, until finally the highly specialized modern
birds (“glorified reptiles”) were evolved as a branch from primitive
reptiles. The specialized reptiles of modern times likewise came from
the primitive reptiles. In like manner those primitive reptiles that had
mammalian (monotreme) characters, by getting into a suitable environment,
gradually lost more and more their reptilian characters and assumed
with increasing accentuation the characters of primitive monotremes—the
lowest of the mammalian class. But observe particularly that the earliest
introduced monotremes were not the specialized monotremes on the globe
to-day, but generalized, primitive monotremes. These gave origin to the
specialized modern monotremes, and also to the generalized primitive
marsupials. The evolution of man continued through the primitive
marsupials to primitive anthropoidea.
Here we meet with the common, generalized ancestors of man and the
monkeys. These creatures contained, potentially at least, _anthropoid_
as well as _pithecoid_ characters. From them were derived the primitive
New World monkeys (primitive Platyrrhines) and the primitive Old
World monkeys (primitive Catarrhines). Some of the descendants of the
primitive Old World monkeys, migrating into an environment which favored
particularly the pithecoid characters, eventually developed into the
tailed monkeys of the Old World (Cercopithecidæ). Others of their
descendants, migrating into a different environment, found conditions
that favored the anthropoid characters especially, and by greater
and greater use of these, with the diminished use of the pithecoid
ones, the characters of the anthropoid apes (primitive Simiidæ and
primitive Simiinæ) became clearer and clearer until, in time, primitive
anthropopithecus appeared,—a tailless anthropoid ape of the Old World.
More than likely this anthropoid ape bore a close resemblance, as Dr.
Theodore Gill long since taught, to the modern chimpanzee. If there were
any differences they could scarcely have been of even a generic value.
This primitive chimpanzee was undoubtedly a quadrupedal, quadrumanous
creature leading an arboreal life. His descendants specialized along
two distinct but closely related lines. Those that continued to live in
trees specialized along the oblique path that led finally to the gorilla
on the one hand and the chimpanzee on the other. Those descendants that
abandoned the trees and lived on the ground used the feet more and more
for purposes of locomotion and less for grasping; while they employed
with increasing frequency the hands for grasping exclusively. Associated
with these adaptations were many other correlated adaptations, such as
the upright posture, an enlarging brain, a change in the character of the
face and of the dentition, etc. As man evolved further and further along
the central trunk of the tree of life, he discarded, through disuse, many
of the characters that are peculiar to the anthropoid apes; and assumed
with increasing emphasis, through use, many of the characters that are
distinctive of man. He passed through the phases of pithecoid man and
pre-palæolithic (primitive) man, until eventually, in palæolithic man,
the visage of humanity is clear and unmistakable.
It is extremely interesting to attempt to form some rough picture of
primitive man. It may help us to do so if we recall what Darwin has said
about the Fuegians, who are among the lowest of savages. He has written
that they are men whose very signs and expressions are less intelligible
to us than those of the domesticated animals—men who do not possess the
instinct of those animals, nor yet appear to boast of human reason, or at
least of arts consequent on that reason.
The Fuegians are much nearer to the ape than to a Shakespeare or Sir
Isaac Newton. In the words of Clodd, primitive man was doubtless much
lower than the lowest Fuegians. “He was a powerful, cunning biped, with
keen sense organs (always sharper, in virtue of constant exercise, in
the savage than in the civilized man, who supplements them by science),
strong instincts, uncontrolled and fitful emotions, small faculty of
wonder, and nascent reasoning power; unable to forecast to-morrow or to
comprehend yesterday, living from hand to mouth on the wild products of
nature, clothed in skin or bark, or daubed with clay, and finding shelter
in trees and caves; ignorant of the simplest arts, save to chip a stone
missile, and perhaps to produce fire; strong in his need of life and
vague sense of right to it and to what he could get, but slowly impelled
by common perils and passions to form ties, loose and haphazard at the
outset, with his kind, the power of combination with them depending on
sounds, signs, and gestures.”
Through the theory of evolution it can readily be understood why the
anatomical characters of the anthropoid apes and of man are so very
closely alike. They have a common origin, and are blood relations—the
one group of animals having specialized from common ancestors in one
direction (obliquely), and the other group having specialized in another
(straight) direction. (Vid. Diagram of Development.)
Man, in his individual development from a fertilized ovum, comes from a
source infinitely lower than the ape. Why, therefore, should he feel such
reluctance to believe that he has passed, during geologic ages, through
the phase of generalized simian ancestors? Is there not much more of hope
in the knowledge that he has risen higher and higher through the æons of
the past than in the belief that he was created an innocent and noble
character and then fell to utter wretchedness through great temptation?
The motto of evolution is Excelsior. For it shows that the human race,
through all the incalculable ages of the past, has risen to higher and
higher levels,—to nobler and nobler phases of being. His progress in
the almost infinite past suggests the hope that he will mount higher
and higher towards perfection during the limitless future. Not only may
we hope that there will be boundless improvement of the human race, but
boundless evolution of each individual human being as well. Evolution’s
motto for each individual may also be Excelsior. And, therefore,
may we say with some assurance of hope that love, while kissing the
pathetic lips of death, need not entertain in vain the splendid hope of
immortality. For if there be no immortality of personal consciousness,
then the evolution of the cosmos, of man, of the highest mind in man,
have no intelligible meaning for us; they are unfathomable enigmas—idiot
stories without meaning.
Man, in specializing along certain lines since separating from the
ancestral simian stock, has displayed more and more that structure of
his skeleton and of the soft parts molded upon it that is best adapted
to the needs of the mind resident within him. His bones are not merely
the jointed framework of an animal, but a framework adapted to that erect
attitude which so befits his intellectual nature. His feet are not the
climbing and grasping feet of the ape, but organs for giving firmness
to the tread and dignity to the bearing of a creature capable of high
thought. The arms and hands are not for strength alone, for these members
are much stronger in many a brute; but they also give greater expression
and power to the thoughts that come from within. The hands possess
such molding of fingers, thumbs, and palms, such delicacy for tactile
impressions, and such capacity for nice adjustments, that they are not
alone used for feeding the mouth and fighting antagonists; but they also
contribute pre-eminently to the desires of a large mind, and are the
efficient servants of its promptings. As Dana well says, “The face, with
its expressive features, is formed so as to respond not solely to the
emotions of pleasure and pain, but to shades of sentiment and interacting
sympathies the most varied, high as heaven and low as earth,—ay, lower,
in debased human nature; the whole being, body, limbs, and head, with
eyes looking, not towards the earth, but beyond an infinite horizon, is a
majestic expression of the divine feature in man and of the infinitude of
his aspirations.”
But it is well to remember that man’s structure is riddled with evidences
that he passed from an ancestral, quadrupedal condition, through the
semi-erect to his present upright posture, slowly and laboriously. His
erect attitude, geologically speaking, is a very recent accomplishment,
and his anatomy, therefore, reveals many imperfect adaptations to his
newly acquired posture. These imperfect adaptations are the sources
of many grave diseases in mankind. It would require too technical a
knowledge of anatomy to explain these imperfect adaptations, and I will
therefore simply mention _rupture_ and _uterine displacements_ as due to
imperfect adaptations to the upright attitude.
The common origin of man and the ape accounts for many interesting
and otherwise inexplicable facts in anatomy. There is, for instance,
a muscle that is normally present in the orang-outang known as the
Opponens Hallucis. This muscle enables the orang to oppose his big toe
to the other toes, just as we can oppose our thumb to the other fingers
of our hand. This muscle is absent from the foot of man ordinarily. But
occasionally it is found in man, in the dissecting-room, as a rarity—as
an anomaly. The question naturally arises, why should this muscle be
present normally in the orang and absent normally in man, occurring in
the latter only as an abnormality? The theory of evolution gives the only
rational answer. The man-like, ape-like generalized ancestors of man and
the orang possessed this muscle, which was useful to them in grasping
the branches of the trees among which they lived. These ancestors used
the feet and hands alike for purposes of grasping (prehension) and
locomotion. But those descendants that evolved more and more man-ward
used the feet more for purposes of locomotion and less for grasping,
while they used the hands more for grasping and less for locomotion,
until, finally, man was created—a creature that uses his feet exclusively
for locomotion, and the hands entirely for grasping. Through disuse,
therefore, the _opponens hallucis_ gradually disappeared in man; so that
now it occurs only as a rare abnormality. The hereditary units that make
this muscle still lie dormant in most men are usually so weak, through
disuse, that they do not develop. Some unusual stimulus occasionally
causes the latent hereditary units to develop and makes it appear in man.
The same is the case with many other muscles and structures that are
normal in the modern anthropoid apes, and only occur as rarities in man.
The appearance of those muscles in man are instances of _atavism_, i. e.,
reversions to conditions that were normal in the ancestors of man and the
apes, as they are still normal in the latter.
USELESS SCAFFOLDING LEFT IN THE BODY.
Man, in his post-natal growth, as well as during his embryological
development, exhibits reminiscences of his animal ancestry. In the
structure and movement of the new-born babe, as well as in the adult
frame, we find continuous witnesses to the ancient animal strain.
On the theory that men in bygone ages were closely allied to simian
creatures in habit as well as structure; that they led an arboreal life;
and that, like the baby-monkeys to-day, the baby-men of other ages clung
to their mothers as they climbed among the trees, Dr. Louis Robinson
predicted that a =baby’s power for grasping= would likely be found to
equal that of a young monkey which had reached a corresponding period
of growth. He tested a large number of new-born infants in reference to
this power by extending his finger or a cane, to imitate the branch of
a tree, and observed how long they would hang there without any other
support (Plate XI). He made experiments on about sixty children under
a month old. About thirty of the children experimented upon were not
over an hour old. Dr. Robinson states that each of the infants, with two
exceptions, was able to hang to the finger or cane by its hands, like
an acrobat from a horizontal bar, and sustain the whole weight of its
body for at least ten seconds. Twelve of the infants, less than an hour
old, held on for half a minute before the grasp relaxed; while four of
this age held on for one minute. Over fifty of the infants when four
days old could continue the grip for half a minute. Three weeks after
birth the faculty for holding on reached its maximum, for at this age
several succeeded in hanging on for a minute and a half; two held on for
over two minutes; and one infant held on over two minutes and a half.
One infant that was less than an hour old hung by both hands to Dr.
Robinson’s finger for ten seconds, and then deliberately let go with his
right hand, as if to seek a better hold, and continued his grasp with the
left hand only, for five seconds longer. In none of these experiments
did the limbs of the infants hang down in the attitude of the erect
position, but the thighs were invariably in the baby-monkey attitude,
at right angles to the body. The doctor says that this attitude and
the disproportionately large development of the arms compared with the
legs give the photographs of the infants a striking resemblance to a
well-known picture of the celebrated chimpanzee, Sally, at the Zoölogical
Garden in London. In these experiments the infants very seldom gave any
sign of distress, and uttered no cry until the grasp began to give way.
The fact that the flexor muscles of the forearm of a new-born infant show
such remarkable strength while the other parts of the muscular system
are so conspicuously weak and flaccid,—that they are able to perform a
feat of muscular strength that will tax the powers of many a healthy
adult,—can be explained only on the theory of inherited instinct from
simian ancestors that lived in trees. This instinct is no longer useful
to an infant. It is a vestigial instinct, a useless scaffolding in its
life history.
[Illustration: PLATE XI.—Illustrating the grasping power of infants. Two
infants, ten and thirteen days old, respectively, supporting their weight
by the hands only (vestigial instinct.) Reproduced from a photograph
taken by Dr. Louis Robinson. By courtesy of the Open Court Publishing
Company.]
=Club-foot.= There is an ordinary case of malformation in the foot of a
child known as club-foot. The most common kind of this deformity is that
where the sole is turned inwards and upwards and the heel is raised.
Before birth all children pass through this condition as a perfectly
normal and natural one, and only gradually outgrow it (evolve beyond it).
But some children fail to evolve beyond this condition and have club-feet
throughout life, unless relieved by the surgeon. It is a very instructive
fact that this particular form of club-foot is the normal condition
of the adult gorilla and orang-outang. The foot of every child passes
through this gorilla phase, and if it does not develop beyond this phase
it retains the simian characters, and we call it an abnormality. In this
abnormality the anatomist finds that those bones that enter into the
formation of the ankle joint have the pronounced anatomical characters of
the adult orang-outang.
=Ribs.= Adult man possesses twelve pairs of ribs. The chimpanzee and
gorilla possess fourteen pairs. An older comparative anatomy predicted
that in an early embryonic condition man would be found to possess
thirteen or fourteen pairs. The prophecy has been verified.
=Hair.= The apes have hair over the entire body. At the sixth month
of the embryonic development the human fœtus is thickly covered with
a somewhat long, dark hair over all the body, except those parts that
are uncovered in the apes, viz.: the palms of the hands and the soles
of the feet. This covering of hair is called lanugo. Since it covers
all the body except the points noted, it extends, of course, all over
the ears, face and forehead. It is usually shed before birth. It is a
simian characteristic, and sometimes fails to disappear, but persists
and develops greatly. Therefore there are occasionally found such men
(“dog-faced men”) as the Russian Jeftichjeff. The Ainos of one of the
Japanese Islands also possess this extreme hairiness.
=Vermiform Appendix.= There are a number of vestigial structures in man
that are not only useless but even a menace to life. The most striking
of the vestigial structures that come under this category is a portion
of man’s large intestine which is called the Appendix Vermiformis. This
useless structure is a veritable death trap. In some animals, such as the
herbivorous ones, the appendix is very large, sometimes longer than the
body itself, and is of great use in digestion. But in man it has shrunken
to a small rudiment varying from two to six inches in length, which is
very liable to a grave form of disease that frequently causes death
unless timely treated by the surgeon. In the early embryo the appendix is
equal in caliber to the rest of the bowel, but at a certain date ceases
to grow _pari passu_ with it. At birth it has become a small rudiment of
the large intestine. In the new-born infant the appendix is often of the
same size as it is in the adult. This precocity of an organ is always an
indication that it was of great importance to the ancestors of the human
species.
=Tail.= Man, like the anthropoid apes, has no external tail; but, exactly
like them, he has a rudimentary one concealed beneath the skin. The
embryos of man and the ape at an early stage of growth possess a very
conspicuous tail, which is even longer than the limbs. In the embryo
of man even the muscles for wagging the tail are still found. In the
adult man these muscles are represented, normally, by bands of fibrous
tissue. In the dissecting-room one occasionally finds these muscles well
developed in the adult man. Man and the anthropoid apes have descended
from more primitive simian ancestors that possessed tails.
=Hearing.= Prominent among vestigial structures, though less easy for
beginners to understand, are those that point to piscine ancestors and
which, therefore, smack of the sea. Embryology points indubitably to the
fact that the ancient, geologic progenitors of man once lived a marine
life. In the history of the globe there was a time when all the animals
lived in the sea. Land animals appeared as later creations. Man, in
evolving from the primitive protozoan, passed through a marine-worm phase
and finally, through the ages, attained to the fish stage. The chief
characteristic of a fish is its apparatus for breathing the air dissolved
in the water. This apparatus consists of gills—strong bars with delicate,
highly vascular, fringe-like curtains hung on them, and through which the
blood is continually circulating. The circulating blood throws out its
impure gases and takes in from the water the pure air, thus breathing.
These bars or arches are five or seven in number in many fishes. Slits
extend from the surface of the fish between the bars to the throat, so
that the water which the fish takes into its mouth is forced out between
the bars, thus bathing the delicate curtains on them by which air is
breathed from the water. Sometimes the slits between the bars are open
and unprotected, as in the sharks; but in the modern fishes (teleosts)
they are protected by a lid (operculum). If these slits did not exist in
the neck all fishes would quickly perish. They are of so great use to
the fish that Natural Selection has taken exceptional care in perfecting
their mechanism.
It is one of the most interesting facts in evolution that these slits
in the fish’s neck are still represented in the neck of man. One of the
most prominent features in every mammalian embryo is the presence of four
clefts of the old gill-slits. So persistent are these characters that
children are occasionally born with persistent fissures leading to the
throat, so that milk, when swallowed, will come out on the neck through
an opening. Thus we have a persistent piscine characteristic as an
abnormality in the child.
When the fish-like ancestors of man left the water the elaborate
breathing apparatus was no longer needed for respiration. Nature, in
creating new adaptations for the land animal, did not discard the
elaborate gill apparatus that had been evolved through the ages;
but utilized this old apparatus for the new adaptations. Nature is
exceedingly economical and does not discard old organs when they can be
molded for new functions.
In the course of ages, through minute gradations, the first gill-slit and
portions of its adjacent bars were molded for purposes of hearing. In
man there are two passages leading to the drum or middle ear; one is the
external auditory canal (the opening which is seen in what is popularly
called the ear), and the other is a canal leading from the throat to the
middle ear. In the adult these two channels are partitioned off from
each other by the membrane of the drum. These canals are the counterpart
or homologues of the spiracle associated in the shark with the first
gill-slit. The external ear is developed by the coalescence of six
rounded tubercles appearing in the bars or branchial arches that surround
the first gill-slit. In the course of ages the remaining gill-bars
(branchial arches) were also modified for special uses.
In relation with the external ear of man are found rudimentary muscles
that are no longer useful and ordinarily are not under the control of
the will. These muscles are the exact counterparts of well developed
functional muscles found in great numbers of the lower animals. They are
present in man as vestigial structures, because he is descended from
animals in whom these muscles were well developed and functional.
The anatomy of man reveals so many additional vestigial structures
that we may look upon him as a museum of obsolete anatomies; he is
an old curiosity shop containing many discarded tools, many outgrown
and aborted organs. The lower animals as well as man contain so many
useless (vestigial) structures among their useful organs, and they are
so significant of a former state of things in which they were useful,
that anatomists are willing to stake the theory of evolution upon their
presence alone. Evolution explains a multitude of other facts about man
that are inexplicable on any other theory.
[Illustration: FIG. 19. Brain of Fish (Bluefish). A, dorsal view; B, side
view; of, olfactory lobe; cr, cerebrum; ol, optic lobes; cb, cerebellum;
m, medulla; th, thalami.]
In addition to pointing out the possible track along which man has
evolved from a primitive protozoan it would be interesting as well as
exceedingly instructive to trace the development of each structure and
organ in his body. But the subject is a vast one, and cannot be presented
here even in briefest outline. Yet it will be very valuable to trace the
unfolding of one organ, and that the highest, as a sample of what occurs
with every part of the body. I refer to the _development of the brain_.
THE DEVELOPMENT OF THE BRAIN IN PHYLOGENY AND ONTOGENY.
Fig. 19 represents the brain of an average bony fish. It consists of
six swellings in a line, one before the other. Beginning from the
end towards the spinal cord, they are designated as follows, viz.: a
single median lobe, the medulla (Metencephalon), m; then in front of
this is another single median lobe, the cerebellum (Epencephalon),
cb; then the optic lobes (Mesencephalon), right and left, ol; then
the thalami (Thalamencephalon), which are small and hidden from
view by the encroachment of the two adjacent segments; then the
cerebrum (Prosencephalon), cr; then, finally, the olfactory lobes
(Rhinencephalon), of. In this fish the largest of the segments are the
optic lobes, ol.
[Illustration: FIG. 20.—Brain of Reptile (Turtle). A, dorsal view; B,
side view; of, olfactory lobe; cr, cerebrum; th, thalami; ol, optic
lobes; cb, cerebellum; m, medulla.]
The reptile’s brain (Fig. 20) shows similar parts with the same serial
arrangement. The reptile is a higher creature, a more intelligent
animal, than the fish; and in consonance with this fact the cerebrum, cr,
is the larger and more dominant part of the brain instead of the optic
lobes, ol.
[Illustration: FIG. 21.—Brain of Marsupial (Opossum). A, side view; B,
dorsal view; of, olfactory lobes; cr, cerebrum; ol, optic lobes; cb,
cerebellum; m, medulla. Thalami concealed from view by the backwardly
extended cerebrum; also the optic lobes are partially covered by the
cerebrum.]
[Illustration: FIG. 22.—Brain of Lemur (Lemur nigrifrons). A, dorsal
view; B, side view; cr, cerebrum; cb, cerebellum; m, medulla.]
In the marsupial (Fig. 21), a more intelligent animal still, the
cerebrum, cr, has grown so large that it extends backwards and partially
covers the optic lobes. It is to be observed that in the marsupial the
cerebellum, cb (like the cerebrum, cr), has evolved to a higher phase. It
consists of a median lobe, cb, which is larger than the median cerebellum
of the lower creatures mentioned, and of two lateral lobes, one on either
side, which have been acquired in the course of evolution. The median
lobe, the homologue of the single, median cerebellum of lower animals,
is larger than the lateral ones. The cerebellum of the marsupial has its
surface increased by fissures, while that of the fish and reptile is
smooth. The fissured cerebellum is a higher evolution than the smooth
ones. In the groups of animals referred to so far the cerebrum is smooth
and the olfactory lobes are still in front, though much encroached upon
in the marsupial by the enlarging cerebrum. In those animals still
higher in the scale of life, such as the prosimiæ (Lemurs), the cerebrum
has reached yet larger proportions and complexity, and has grown still
farther backwards towards the medulla, so that it hides from view a
considerable portion of the cerebellum (Fig. 22); it has also grown
forward, thus concealing largely the olfactory lobes. The cerebrum is
no longer smooth, but has a number of simple fissures and convolutions
(the higher animals have numerous complex fissures and convolutions). The
lateral lobes of the cerebellum have increased relatively more than the
central lobe, and the whole organ has advanced in complexity of fissures.
In the higher simiæ (monkeys and apes) the cerebrum has grown so far
backwards as to almost completely cover the cerebellum and medulla,
and its convolutions have become much more numerous and complex. The
cerebellum has also grown greatly, and its lateral lobes are now larger
and more complex than the central lobe.
[Illustration: PLATE XII.—Brain of man: dorsal and side views. The
cerebrum has grown so far backwards and forwards as completely to hide
the other segments of the brain when looked at from the dorsal surface.
From Carus’s “The Soul of Man.” By courtesy of The Open Court Publishing
Company.]
Finally, in man (Plate XII), the whole brain has grown so enormously that
it is three times larger than the brain of the highest simian creature.
The cerebrum, especially, has increased enormously in size. It has grown
not only backwards (overlapping cerebellum), upwards, and downwards
on the sides, it has grown so far forwards as not only to cover the
olfactory lobes, but also to project far beyond them. The cerebellum has
also increased in size and complexity, especially the lateral lobes. The
ideal vertical section (Fig. 23) shows diagrammatically in one figure all
these stages in the evolution of the human brain through the geologic
ages.
[Illustration: FIG. 23.—Ideal, vertical and sagital section, representing
the ontogeny and phylogeny of the human brain. of, olfactory lobe; crf,
cerebrum of fish; ol, optic lobes of fish; cbf, cerebellum of fish; m,
medulla of fish; cbr, cerebellum of reptile; cbo, cerebellum of opossum;
cbl, cerebellum of lemur; cbm, cerebellum of man; cr, cerebrum. Cerebrum
convoluted in lemur; much more convoluted in man. Cerebellum convoluted
from opossum upwards; mm, medulla of man.
Modified from Le Conte.]
It is a very interesting and instructive fact that in the development of
the human brain from the fertilized ovum these same stages, which are
permanent conditions in the zoölogical (taxonomic) series, are passed
through by it as transient stages.
One of the earliest conditions of the human brain is that in which it
presents three swellings in a serial arrangement. They are known from
behind, forwards as hindbrain, midbrain, and forebrain. For our purposes
it is sufficiently accurate to say that the =fœtal brain=, in developing
from this early condition to a later and higher condition, differentiates
the hindbrain into the _medulla_ (Fig. 24, m) and the _cerebellum_
(cb); the midbrain becomes the _optic lobes_ (ol); and the forebrain
differentiates into the _thalami_ (th) and the _cerebrum_ (cr). A little
later the cerebrum buds forth the olfactory lobes (of), so that the human
brain will consist of six fundamental segments,—one behind the other.
This is the _fish stage_ in the growth of the human brain. (Compare Fig.
24 with Fig. 19.)
[Illustration: FIG. 24.—Diagrammatic representation of the brain of
a human fœtus of the third week. Representing the fish-phase in the
ontogeny of the human brain. Side view. cr, cerebrum; th, thalamus; ol,
optic lobes; cb, cerebellum; m, medulla. The olfactory lobes at this
stage are very small and are not shown.
FIG. 25.—Dorsal view of the brain of a human fœtus of about seven weeks.
Representing the reptilian phase in the ontogeny of the human brain. cr,
cerebrum; th, thalami; ol, optic lobes; cb, cerebellum; m, medulla.
FIG. 26.—Side view of the brain of a human fœtus of about three months.
Representing the marsupial phase in the ontogeny of the human brain.
cr, cerebrum; ol, optic lobes; cb, cerebellum; m, medulla. The thalami
are completely, and the optic lobes partially, covered by the greatly
enlarged cerebrum.]
As development proceeds the most conspicuous growth of the brain is
observed in connection with the cerebrum and cerebellum. The cerebrum
particularly grows relatively and actually larger and larger, but does
not yet cover any portion of the optic lobes. This is the _reptile
stage_, represented in Fig. 25. The cerebrum, continuing to grow, finally
covers the front portion of the optic lobes. This is the _marsupial
stage_, and is shown in Figs. 26 and 27. Growing further, it soon covers
a greater or less portion of the cerebellum. These are the prosimian
(Lemur) and simian stages. Finally it grows so far backward as to
completely cover the cerebellum, and so far forward as to project much
beyond the olfactory lobes. This is the human stage (Plate XII).
[Illustration: FIG. 27.—Dorsal view of the brain (and spinal cord) of a
human fœtus of about three months. Representing the marsupial phase of
development. cr, cerebrum; ol, optic lobes; cb, cerebellum; m, medulla;
bs, brachial enlargement of the spinal cord; ls, lumbar enlargement. The
thalami are entirely covered and hidden from view by the cerebrum.]
In the study of the phylogeny of the brain we found that the cerebrum
in fish, reptile, and lower marsupial is smooth. In the primitive
primates (Lemuroidea) it is convoluted; in the simiidæ it is still more
convoluted, while in man it reaches the climax of complexity in the
size, number, and sinuosity of its convolutions. The object of these
convolutions is to increase the surface of the cortex of the brain,
the cortex being the seat of psychic phenomena. Other things being
equal, the greater the amount of cortex the greater is the intelligence.
During its embryonic development the human cerebrum passes also through
the stage of smoothness to a convoluted condition; then through stages
of increasing complexity of convolutions. Simultaneously with this
advance of cerebral organization, there is an unfolding of increasing
intelligence.
The cerebellum presides over the co-ordination of the muscular movements
of the body. It also, like the cerebrum, passes through the fish,
reptile, marsupial, lemur, and simian phases. At first it consists only
of the median lobe; then the lateral lobes appear, at first small in
size, but getting larger and larger until they greatly surpass in bulk
the more primitive median portion. At first the cerebellum is smooth,
but as it develops, its fissures become greater and greater, thus
increasing its cortex, which presides over the muscular movements. With
the developing cerebellum are associated increasing powers of muscular
co-ordination; increasing delicacy and complexity of muscular movements.
Thus the ontogeny of the brain recapitulates its phylogeny.
THE BRAIN AND PSYCHIC PHENOMENA.
The bearing of the theory of evolution on ideas of creation, design, and
kindred subjects may briefly be referred to in connection with our views
about the relation of psychic phenomena to the brain.
The study of the human brain in its anatomical, physiological and
psychological aspects has brought great thinkers, in all ages, into
the presence of phenomena that still baffle some of the most subtle
philosophers. Here we meet with such realities as self-consciousness,
perception, intellection and volition. Are these material entities of
such character that we may say they are exclusively products of the
activity of the brain, as the secretion of bile is the product of the
activity of the liver, as Cabanis taught? To us it seems clear that
such is not the case. One cannot take the specific gravity of love or
hate, of fear or joy, as one can that of bile; one cannot find a single
physical characteristic in any psychic phenomenon. The most physical of
all mental processes, viz., perception, has its psychological as well
as its physiological phases. The instreaming, through the senses, of
impressions from the external world, may be traced by the physiologist
along the different nerves of the body to the cortex cells of the brain.
All the phenomena that occur at and between these cortex cells and the
peripheral endings of the nerves may be formulated in terms of molecular
physics. But not so with that consciousness of these impressions which
we call perception. In the light of the present knowledge that we
possess, it seems to us that the only induction which the physiologist is
warranted in making is that, associated with molecular movements in the
brain is the phenomenon of perception. This leaves the field clear for
each thinker to speculate about the subject in such manner as seems to
him most rational. And the history of philosophy shows that many thinkers
have formulated theories upon the subject that range in character from
the materialism of Büchner to the idealism of Berkeley.
The view which teaches that psychic phenomena are correlated with
the physiological phenomena of the brain; that these phenomena have
undergone parallel[17] evolution, and “are as inseparable as are the
two sides of a sheet of paper” (Dr. Carus), appeals to us as the most
comprehensible one and at the same time the one most in consonance with
the known phenomena. We accept the view, then, that there is a mind
immanent in the brain.[18] The mind is conscious of its personality;
conscious of the external world through the innumerable perceptions
which reach it through the nervous system; conscious of its power to
build its percepts into concepts, and to reason about them; conscious
of its power of choice and of causing motion; and conscious of itself,
therefore, as a cause in producing effects; and, finally, it is conscious
of its power to adapt means to an end,—in short, it knows that it has the
power to design.
These facts are at the bottom of much of the philosophy of the present
and the past. The untutored savage, knowing that his personality can
cause motion, and beholding moving objects in nature, instinctively made
the induction that all these objects had personalities behind them. He
saw a spirit in his own voice that came back to him as an echo from
the rocks; he saw a personality in his shadow; he saw personalities in
falling stones, in running brooks, in waving foliage; he beheld them in
the raging tempest, in the thunder and the lightning, as well as in the
blazing sun and the twinkling stars; he saw spirits in the dead that came
back to him in dreams. In short, he recognized a separate personality
in every isolated phenomenon in nature. The child talking to its doll,
petting it, rebuking it, or whipping it; Xerxes castigating the ocean
for wrecking his ships, are illustrations of the strong human tendency
to project (or eject)[19] personalities into the inanimate objects of
nature. This natural, but lowly, phase of culture and philosophy is known
as _Fetichism_.
As encephalic and psychic evolution advanced; as men, with wider
knowledge and broadening experience, ascertained the laws that govern
the isolated phenomena of nature, the separate beings in every distinct
object and occurrence vanished from thought; but they still beheld a
separate personality in every great department of nature. The Romans,
for instance, saw Neptune as God of the Ocean, Pluto as God of the lower
world, Jupiter as God of the Heavens, and so on. This phase of culture
and philosophy, and therefore of religion, is _Polytheism_.
In the two phases of culture now briefly outlined the personalities
were grossly anthropomorphic. They were like human beings, capricious,
revengeful, subject to flattery, good and evil, and were therefore to be
placated and cajoled by sacrifices and offerings.
Psychic evolution continuing, there appeared from time to time great
thinkers who saw one “Infinite Personality” behind the cosmos.[20]
This “personality” is still in every phenomenon, though no longer as a
separate soul, but only as the separate manifestation of the Soul of
the Universe. This is _Monotheism_, a phase of culture which marks the
culmination of philosophy and religion through psychic evolution.
Our knowledge of the universe can be only a shadowy symbol of the
reality. The poverty of language is so great and the power of thought so
limited that the most subtle philosopher can form only an empty symbol
of the cosmic soul. The most ethereal symbols of the greatest thinkers
are necessarily incomplete in detail and anthropomorphic, in order to be
intelligible. The history of philosophy and religion shows that with the
evolution of mind and the acquisition of knowledge, the anthropomorphic
ideas of the soul of the cosmos become less crudely coarse and vulgar,
until the most elevated and refined ideas of monotheism are reached. But
even these refined ideas about the soul of the universe are necessarily
anthropomorphic, though in a vastly less degree than in the lower phases
of culture. One’s conceptions of this all-pervading soul immanent in the
universe are therefore profoundly modified by one’s kind and degree of
culture. In the words of Professor Fiske, the great scholar and subtle
thinker who has delved in the deepest mines of philosophy and come forth
weary and heavy-laden with their boasted treasures, has framed a very
different conception of God from that entertained by the priest at the
confessional.
A study of the human brain, then, and the soul resident therein prepares
us to believe that the cosmos has a soul (God) immanent in it. We can
readily grasp the idea that the soul of the cosmos may be self-conscious,
wills, thinks, acts, and designs.
This cosmic soul has been and is active in creation. In a low phase of
culture every distinct object of nature is looked upon as a separate
creation—a manufacture. With the progress of science the conception of
separate creative acts becomes greatly modified. The creative acts are
judged to be fewer in number and nobler in character. Finally, that phase
of highest culture which recognizes the law of universal evolution,
formulates the view of one continuous creative act, in which every
object is still a creation but not a separate creation,—only a separate
manifestation of one eternal act of creative energy. The history of
creation, which means the same thing as the history of evolution, shows
innumerable adaptations which may surely be considered as the work of
a cosmos designer. Evolution has profoundly modified our conceptions
of design in nature as it has those of creation. Every separate work
of nature, presents a separate, distinct and man-like design to the
uncultured. But, with advancing science, all these separate and petty
designs are swallowed up into fewer and grander designs, until at last,
through evolution, we reach the magnificent and ennobling conception of
one infinite and all-embracing design, persisting through infinite time
and extending throughout infinite space, which embraces every apparently
separate design.
Thus, while evolution destroys low anthropomorphic notions of the mode
of working of the Designer and simplifies while it purifies and vastly
ennobles our conceptions of this Designer, it yet replaces as much
teleology as it destroys. But the highest conceptions that the subtlest
philosophers are able to form of a cosmic Designer are necessarily
anthropomorphic in some degree, for they can only think in man-like ways.
We have seen in earlier pages of this book how, throughout the
incalculable ages of geologic time, innumerable living forms have
come upon the stage at different epochs, the forms of one epoch being
transmutations from those of an earlier one, and so on, back to the
beginning of life. The theory of universal evolution teaches that in
the abysmal depths of still earlier æons there was a time when no life
existed on the globe, for the globe was then a whirling ball of intensely
hot vapor; still further back there was a time when this ball of vapor
had not yet been born from that giant nebula—the primitive sun. Through
all the sweep of infinite time we see the multitudinous objects of
nature coming into existence, one after another, from primeval vapor,
and in accordance with laws the character and scope of which we begin to
partially understand. It is after the recounting of such well-known facts
as these that Professor Fiske makes the statement that Paley’s simile of
the watch is no longer applicable to such a world as ours. It must be
replaced, he says, by the simile of the flower; for the universe is not a
machine, but an organism with an indwelling principle of life; the world
was not made offhand, it has grown from more primitive conditions.
In studying the Diagram of Development (Fig. 18) it will be observed that
man is the highest and greatest fruitage of the tree of animal life. He
is the highest animal in the taxonomic series, as he is in the phylogenic
series. He has been the goal, and is the completion of organic evolution.
As Dana says, “there is a prophecy of man which runs through the whole of
geologic history, which was uttered by the winds and waves at their work
over the sands, by the rocks in each movement of the earth’s crust, and
by every living thing in the long succession, until man appeared to make
the mysterious announcements intelligible.”
The vital path from primitive protozoan to man has been a straight
and narrow one, and innumerable groups of animals have branched off
laterally. In so doing they departed forever from the man-ward path, and
developed obliquely along the diverging roads and bypaths of lower life
organizations. They may diverge still farther from the original parting
point, but can never get back into the man-ward road. They have lost the
golden opportunity and can never regain it.
Man is not only the highest creature that has ever appeared on the globe,
but it seems a safe induction to say that he is also the highest animal
that evolution will ever develop here.[21] Evolution, through Natural
Selection and other agencies, having spent most of its force in creating
the innumerable species of animals and plants that have lived in the past
and that are now living on the globe to-day, and having had as its goal
the creation of that highest and noblest of all creatures—man—is now
concentrating its force in further evolving man. Anatomists have reasons
to believe that man is now evolving, in many portions of his body, as
rapidly as did the horse through Tertiary Ages. Evolution is pushing him
on to higher and higher planes, along the straight and perpendicular
man-ward track that he has traveled from his protozoan ancestors; while
his simian relatives are diverging obliquely more and more from the
man-ward track. Through Natural Selection and _rational selection_
evolution seems now to be spending its main force especially on one
particular part of man’s body, viz.: his brain and its immanent mind.
The brain of a living, highly civilized man is larger than the brains
of men of the tenth century; the brains of these latter are larger than
those of palæolithic men. Evolution, having raised the body of man to
nearly its highest possible level, is now perfecting more and more his
brain, and therefore his thinking power, or, better, his mind. Through
his intelligence he is eliminating more and more the noxious plants and
dangerous animals that surround him, and is preserving and improving
those that are useful to him, and thereby making the organic world more
and more subservient to his purposes. He is even getting larger and
larger control over the mechanical, physical, and chemical forces of
nature, and the possibilities of his improvement in these directions are
almost boundless. Evolution for man now means psychic evolution, social
evolution; in short, civilization.
From what has been said it can readily be perceived that man,
zoölogically and psychologically, is by far the most important creature
on the globe. He seems to be the goal towards which evolution has
been steadily advancing throughout the geologic ages. It is for these
reasons that we believe no higher animal than man will be evolved on
the earth. Man himself will continue to evolve higher and higher. Well
may we say, with Sir William Hamilton, that there is nothing great
in the world but _man_, and nothing great in man but _mind_. Is it
a shallow philosophy which teaches that it was through design that
this most important creature was evolved as the topmost flower on the
highest and straightest branch of the tree of life? We do not think so.
One of the most profoundly interesting facts to be observed in that
higher evolution—psychic evolution—which is now mostly molding man,
is the fact of rational selection supplementing and largely replacing
Natural Selection. With the creation of man, _choice_ or will comes in
as a factor of ever-increasing importance. The active will to _use_
certain capacities and _disuse_ others will play a part in the further
development of man of ever-increasing importance and widening influence.
Use and disuse have been factors of commanding importance in modifying
the bodies and minds of the animal forms that led up to man. Use and
disuse will be factors of commanding influence in profoundly modifying
the brain, and therefore the mental constitution of man as he advances
in social evolution. The use of the brain along chosen lines will, on
well-known physiological principles, increase its organization and
therefore its power for manifesting psychic phenomena. These two factors
will continue to act and react in the future as they have in the past,
increased psychical activity enlarging the brain, and the more highly
organized brain augmenting the psychic phenomena. What is true of the
mind in general is also true of its varied manifestations. The history of
psychic evolution gives reason to believe that not only will the capacity
for thought be augmented and the power of the will increased in future,
but also the strength of selfishness will still further be weakened by
disuse and the power of sympathy augmented by practice. As our half-human
ancestors were evolving man-ward, and Natural Selection was augmenting
their brains, thus increasing their capacity for thought and, therefore,
their capacities for more varied experiences through life, there was a
concomitant increase in the period of infancy. The activities of the
lower animals are mostly of a simple character. They are for the purpose
of securing food, escaping enemies, and reproducing their kind. These
activities are comparatively so simple and have been repeated so often,
generation after generation for ages, that they have become thoroughly
organized, by heredity, in the offspring before they are born. When the
offspring are born they seek their food, they endeavor to avoid enemies,
and in due time procreate their kind without any teaching. With them
heredity is almost everything, and experience exceedingly small. These
facts can well be exemplified in studying the young of such animals
as fishes, amphibians, and reptiles. In the higher birds and mammals
Natural Selection has so augmented the size of the brain that their
psychic capacities are greatly increased. This increased intelligence is
accompanied with an augmented variety and complication of experiences.
The acts performed by animals now become so complex, numerous, and varied
that they are repeated with much less frequency than are the acts of
animals lower in the scale. Consequently, heredity has not had sufficient
time to so mold them into the germ-cells that they unfold as perfect
reflex or instinctive acts at birth. The hereditary units that carry
these acquired experiences of the parents in the developing embryo lie
dormant for a while and unfold slowly under the teaching and protection
of the parents for a varying period known as infancy. As Natural
Selection still further evolved the brains of our advancing half-human
ancestors, thus increasing their intelligence and making their lives
more replete with complex and varied experiences, there was a concomitant
prolongation of the period of infancy—the period of helplessness and
dependency. During this evolution of infancy Natural Selection compelled
the parents, especially the mother, to possess feelings other than those
of utter selfishness. They had to give thought not only to themselves but
also to the helpless creatures they brought into the world. The offspring
increasing in numbers, all associated together in varying degrees of
helpless infancy and dependent upon the care and protection of common
parents, the relationships of mother and father, brother and sister, must
by degrees have become more and more intimate as evolution proceeded,
until finally that social unit appears—the family. In the family personal
selfishness can no longer be the exclusively dominant motive to action.
Rudimentary sympathies appear. The individuals must conduct themselves so
as not to jeopardize the interests of the family. Thus other interests
than those of a purely personal character must influence their actions.
And thus, finally, the adumbrations of right and wrong conduct appear,
and we now find in the newly-created human species the germs of morality
and conscience. As social evolution proceeded, the self-regarding
faculties were more and more curtailed, and the other-regarding
sentiments were extended with ever-enlarging amplitude. Sympathy and
helpfulness for others were broadened more and more, including first the
clan, then the tribe, then the nation, and, finally, groups of the latter
were welded into empires. And the writing on the wall seems to indicate
the future federation of all the nations.
Among primeval men, who obtained their food by hunting out such edible
objects as were already in existence, war was universal. The supply of
fruit, fish, and game being strictly limited, men were compelled to
fight under penalty of starvation. As intelligence advanced and men
learned to cultivate useful plants and to domesticate animals, and as
they learned further to exchange by barter the products of their labor,
a much greater population could live upon a given area. These tribes
would be more powerful than their neighbors who still lived by hunting,
fishing, and such like, and would flourish at their expense. Through
agriculture and commerce men slowly learned that one man’s interest was
not necessarily opposed to another’s; they also learned, though it may be
ever so feebly, that fighting and plundering one another hindered rather
than promoted their welfare. Thus man slowly evolved from a primitive,
predatory civilization, in which war was universal and chronic, to the
higher industrial civilization, in which war is much less frequent and
less universal. Out of this primitive industrial civilization, which
has grown more and more complex with the passing years, have come the
arts and sciences, which give such added interest and value to modern
life. This evolving industrial civilization, by furnishing a wider
basis for political union through community of interest instead of mere
blood-relationship, has greatly extended the field over which moral
obligations are recognized as binding.[22] Social evolution is tending
to eradicate more and more, through disuse, the brutish instincts of
man; weakening his fighting propensities, his cruelty, his selfishness,
his passions; and strengthening, by use, his sympathies, his kindness,
his mercy, his sense of justice and honor, and his charity. The goal of
social evolution seems to be _men of character_,—men with the widest
possible knowledge of the laws of nature, physical, intellectual, and
moral; and with the desire and will to rightly obey these laws. Such
men will be both loving and lovable characters. In view of this may we
not supplement Sir William Hamilton’s aphorism, and say that there is
nothing great in mind but character? Since evolution is producing such
characters, though it may be seemingly ever so slowly, is it again a
shallow philosophy which teaches that there is a designer unfolding these
characters? We do not think so. And if there is a designer who has been
making towards this goal throughout the infinite sweep of bygone ages,
do we not have at least some faint adumbration of knowledge as to the
character of this designer? It seems to us that we do. Well may we say,
with Matthew Arnold, that there is immanent in the cosmos an eternal
soul, not ourselves, that makes for righteousness. This double assertion,
that there is a soul in the universe outside of ourselves, and that this
soul makes for right conduct, is the basis of fundamental importance in
all religions. There are many religions in the world, and many creeds
of the one great religion of christendom. They differ in many of the
transcendental doctrines that they teach, and in many of the rules of
conduct that they prescribe for their adherents; but they all contain as
their most fundamental and vitally important basis the double assertion
that there is a soul of the universe, and that this soul makes for
right conduct. The assertion may be thickly overlaid with superstitions
and petty rites by the untrained and dull intelligence of low races,
as in the Eskimos; or it may attain a high degree of development and
perfection, as among the Jews. The refinement and beauty of the double
conception are more and more enhanced with social evolution. Just
in proportion as civilization advances, and men come to reason more
carefully and entertain wider views of life, just to that extent do they
come to value more highly the essential truths of religion, while they
attach less and less importance to many superficial details. It is of
vastly greater moment to us that there is a cosmic soul in the universe
that makes for righteousness than that this soul is threefold or onefold
in its transcendental nature. Also of vastly more moment to us is a
belief in this soul than any opinions we may entertain about eating meat
on Friday or listening to attractive music on Sunday. A thoughtful mind,
penetrated with the conviction of the truth of evolution, entertains
views on all subjects pertaining to man, very different from those held
by one not familiar with the great theory. His conceptions of the first
Adam are profoundly modified by a flood of facts. If this flood sweep
him on irresistibly, and equally profoundly modifies his conceptions of
the second Adam, can it not be seen that even this is a fact of small
significance compared with that other fact of overwhelming importance,
viz.: the fact of the existence in the universe of a cosmic soul that
makes for righteousness? Man is essentially a religious animal, and
there is a very substantial philosophical basis for his religion.[23]
His religion may be highly colored with emotion, or it may be coldly
philosophical. When Herbert Spencer speaks of the eternal Power in the
universe which makes for righteousness and is manifested in every event
of the universe as the Unknowable, does he not do what Holy Writ has
already done? “Canst thou find out the Almighty unto perfection?” When
Carlyle speaks of the Universe as in very truth the star-domed city of
God, and reminds us that through every crystal and through every grass
blade, but most through every living soul, the glory of a present God
still beams, he means much the same thing that Mr. Spencer does when
he speaks of a Power that is inscrutable in itself, yet is revealed
from moment to moment in every throb of the mighty rhythmic life of
the universe. The only difference is that Mr. Spencer speaks in the
colorless, precise, and formal language of science, while Carlyle’s
language is colored by emotion; is, in fact, poetical.[24]
EVOLUTION AND SOCIAL PROBLEMS.
The relation of evolution to many social problems of vital importance
is a fascinating as well as very extensive subject. We have only space
to say that in order to understand the normal actions, as well as the
abnormal ones, of the members of society, and in order, therefore, to
understand and inaugurate rational methods of conducting education,
minimizing pauperism, vice, disease, and crime, it must constantly be
borne in mind that two great streams of tendencies have come down from
the ages in the germ cells—what we may call the diseased and animal
tendencies on the one hand, and the distinctively human and healthy
tendencies on the other.
The most characteristic of the human tendencies are abstract thought and
reflection, and therefore the power of choice or will, and altruism.
Also it must be borne in mind that environment is a force of commanding
influence. This environment (which the individual may make for himself
to a limited extent) may be propitious or adverse to the best human
and normal tendencies. The relative preponderance of the animal or the
human, the healthy, or the diseased tendencies, taken in conjunction with
the character of the environment, stamp man’s actions as normal (and
therefore right or wrong) or as abnormal, and therefore irresponsible.
Not to discriminate between such normal and abnormal persons is not in
accordance with either common morality or common sense. Neither is it
in accord with common sense, or morality, or humanity, for society to
deal with its habitual criminals and paupers, and subjects of hereditary
disease, in the utterly irrational manner that it does. When society
takes away from the criminal his personal liberty and places him in an
environment that theoretically reforms him and protects itself, why does
it not take cognizance of the fact that its theories are often woful
failures in practice? The criminal is often not reformed and he gets
into the category of habitual offenders; but society permits him, during
his intervals of freedom, to procreate his kind and send his polluted
cargoes of vicious heritages to helpless offspring. Is this humanity to
these offspring? It is the grossest inhumanity! Does society protect
itself by its intermittent detentions of habitual criminals? It probably
breeds three habitual criminals while it is failing in its efforts to
reform one. It is mostly by Nature’s prematurely killing off incorrigible
criminals by their diseases and intemperance, that these social pests
are kept within due bounds, and not through reformations accomplished in
improperly conducted prisons. It seems to us that every consideration of
justice and humanity cries aloud for the destruction of the procreating
glands in _habitual criminals_.[25] Castration should go hand in hand
with detention behind prison bars. Why should the habitual drunkard, for
instance, be permitted to evolve his poisoned germ cells into helpless
beings, giving them diseased bodies and vitiated moral characters, thus
foredooming them to life-long physical ailments and moral turpitude?
Removal of the procreating glands should be the penalty for chronic
alcoholism. In objection to this suggestion, some may prate of personal
liberty. What a multitude of outrages and brutalities the broad mantle of
personal liberty is often made to cover! In allowing personal liberty to
an undeserving individual, which more often means unbridled license to
that individual, a whole generation of offspring are frequently enslaved
by poverty, vice, crime, and disease in its manifold manifestations.
During organic evolution Natural Selection has been incessantly on the
watch for weaknesses of any kind, ruthlessly exterminating the helpless,
the weak, the sick, and those that in any way are unfit. In social
evolution Natural Selection has often been of necessity no less ruthless.
But during social evolution characters that are unfolding more and more
loving and lovable traits have so largely subordinated Natural Selection
as to permit the helpless, the old, the sick, and the unfit, to live,
thus strengthening those highest attributes of the greatest minds, viz.:
intelligent sympathy, pity and love.
But it seems to us that the highest altruism, in dealing kindly with an
abnormal, possible parent, will not continue long to stupidly overlook
the weighty rights of unborn children. Human selection of the socially
unfit will be dominated more and more, as social evolution unfolds
its fruits, by those minds that are advancing to the highest goals of
evolution, viz.: large minds of high character—widely informed minds, of
strong will and broad sympathies. And under these circumstances we may
hope that unborn generations will not be given over to total oblivion.
Well may we repeat, before concluding this little book, that man is not
only a creature of the present, but profoundly a product of the abysmal
ages of a bygone eternity. He is not only a composite chip of many old
human blocks, but of innumerable geologic ancestral blocks. He has in his
constitution simian, reptilian, piscine, and innumerable other chips,
so to speak, and is indeed of the earth earthy; for studies in heredity
not only illustrate the continuity of the human race, but also clearly
indicate the continuity of this race with more lowly animals. Man has
in his structure the indelible impress of the handiwork of these lowly
relatives. Upon him, as upon them, and upon all living creatures, the
forces of heredity and variation, of use and disuse, of environment and
Natural Selection, have been and are perpetually playing, evolving him in
one direction and innumerable creatures in other directions.
The goal of evolution seems to be men with Great Minds of High Character.
_There is nothing great in the world but man, nothing great in man but
mind, and nothing great in mind but character._
SECTION VII.
CLASSIFICATION OF ANIMALS AND PLANTS.
A SYNOPSIS OF THE ANIMAL KINGDOM.
In order that the reader may appreciate to some extent the relative
positions of the different groups of animals, extinct and living, in the
scale of life, the following brief classification may be useful. This
synopsis is especially intended to help readers who are not familiar
with elementary zoölogy to understand the significance of the different
types of animals found in the strata of different geologic periods, and
more particularly to grasp the meaning of the Diagram of Development. The
animals are usually mentioned in the order of their position in the scale
of life, commencing with the lowest and simplest.
SYNOPSIS OF GROUPS.
A. PROTOZOA. Unicellular animals, dissociated, or associated in simple,
loose colonies of similar organisms. Many have an exoskeleton of lime,
flint, or other material. Reproduction by fission and by temporary or
permanent conjugation.
B. METAZOA. Multicellular animals, consisting of a large number of cells
associated together to form single, complex individuals. The cells of
an individual are usually differentiated into several kinds performing
special functions. Reproduction in the higher forms is sexual; in the
lower forms it is often by budding as well as sexual.
SYNOPSIS OF THE BRANCHES OF ANIMALS.
GROUP A. PROTOZOA.
Branch I.—=Protozoa.= Characteristics already defined.
Class 1.—_Monera._
Class 2.—_Rhizopoda_: Amœba, Arcella, Foraminifera, Difflugia, Quadrula.
Class 3.—_Gregarinida_: Gregarina.
Class 4.—_Infusoria_: Noctiluca, Paramecium, Stylonychia.
GROUP B. METAZOA.
Branch II.—=Porifera.= Sponges are animals with their cells arranged in
two well-defined layers, one of which is internal (endoderm) and the
other external (ectoderm). There is a middle stratum of cells (mesoglœa)
which does not attain to the definiteness of a mesoderm. Sponges do not
possess a body cavity (cœlome); they possess, essentially, a bilateral
symmetry. The body varies greatly in shape, and is traversed by canals
having large openings (oscula) and numerous small openings (pores) on
the surface. The ectoderm is continued through the pores into afferent
canals; the endoderm cells line most of the internal (efferent) cavities,
and are mostly flagellate; the mesoglœa contains a skeleton of flint,
lime, or spongin. Reproduction may be by budding or sexual (either
hermaphroditic or unisexual).
Branch III.—=Cœlenterata.= Animals possessing radial symmetry. There
is no body cavity (cœlome), but there is a primitive digestive cavity
(enteron). The body consists of two layers, an ectoderm and endoderm;
between these two layers there is a mesoglœa of jelly-like consistency;
in the simplest cases there are no cells in the mesoglœa, but secondarily
endodermal cells may migrate into it. Stinging cells are generally
present.
There are two divergent types of structure. The more primitive one is the
sessile tubular hydroid, which may be compared to a gastrula furnished at
one end with a crown of tentacles surrounding the opening of the enteron,
and fixed at the opposite end. The less primitive, derived form, is the
active jellyfish (medusoid) type. The hydroid type often constructs a
calcareous skeleton known as coral. One life history may present both
types (alternation of generations). Reproduction is sexual or by budding,
in the latter case often resulting in the formation of colonies.
Class 1.—_Hydrozoa_: Hydra, Jellyfish.
Class 2.—_Actinozoa_: Sea-Anemones, Coral Polyps.
Class 3.—_Ctenophora_: Comb-Bearers.
Branch IV.—=Echinodermata.= Animals, the larvæ of which possess bilateral
symmetry, while the adults have radial symmetry. Even the adults exhibit
to a varying extent a tendency to bilateral symmetry. Lime is always
deposited in the mesodermic substance (mesenchyme). From the primitive
digestive canals of the larvæ pouches grow out to form the usually
spacious body cavity and the characteristic water vascular system. The
latter and the nervous system exhibit generally a typical five-rayed
arrangement. During development there is a distinction between mesoblast
derived from gut pouches and mesenchyme produced from migrated amœboid
cells. Complicated metamorphosis.
Class 1.—_Cystoidea._
Class 2.—_Blastoidea._
Class 3.—_Crinoidea_: Stone-lily.
Class 4.—_Asteroidea_: Star-fishes.
Class 5.—_Echinoidea_: Sea-urchins.
Class 6.—_Holothuroidea_: Sea-cucumbers.
Branch V.—=Vermes.= The term “worms” includes a “heterogeneous mob,” a
collection of classes whose relationships are poorly understood. But
they are of great zoölogical interest, for, amid the diversity, there
can be discerned affinities with Cœlenterata, Echinodermata, Arthropoda,
Mollusca, and Vertebrata. They possess a well-defined mesoderm. They
possess bilateral symmetry and have, as a rule, a head, tail, dorsal
and ventral surfaces, and right and left sides. The lower worms are
unsegmented. In the higher ones the digestive tract extends from the
head to the end of the body; a dorsal vessel is usually present above
the digestive tract; the nervous system consists of a supra-œsophageal
ganglion (brain) and a simple or more commonly double, ventral,
ganglionated cord; there is a body cavity (cœlome) lined with mesoderm;
true jointed appendages are never present.
Class 1.—_Platyhelminthes_: Flat-worms.
Class 2.—_Nemathelminthes_: Round-worms.
Class 3.—_Rotatoria_: Rotifer.
Class 4.—_Bryozoa._
Class 5.—_Brachiopoda_: Lampshells.
Class 6.—_Nemertina._
Class 7.—_Enteropneusta_: Balanoglossus.
Class 8.—_Gephyrea_: Star-worms.
Class 9.—_Annulata_: Earth-worms, Leeches, Sea-worms.
Branch VI.—=Arthropoda.= Animals with bilateral symmetry. Bodies
segmented, but not uniformly so. Several or all of the segments bear
paired jointed appendages variously modified. Chitinous exoskeleton.
Digestive canal beneath the heart. Supra-œsophagel ganglion (“brain”)
connected by a nerve ring round the gullet with a double chain of ventral
ganglia. Cœlome small in the adult. Sexes almost always separate. Often
some metamorphosis.
Class 1.—_Crustacea_: Trilobites, Shrimps, Crabs.
Class 2.—_Arachnida_: Spider, Scorpion.
Class 3.—_Onychophora_: Peripatus.
Class 4.—_Myriapoda_: Centipede.
Class 5.—_Insecta_: Cockroach, Ants, Butterfly.
Branch VII.—=Mollusca.= Unsegmented animals, possessing, fundamentally,
a bilateral symmetry. A very characteristic structure is the “foot”—a
muscular protrusion of the ventral surface. Typically, a projecting fold
from the dorsal surface of the body forms a mantle, or pallium; the
mantle often secretes a single or double shell covering the viscera.
The mantle and shell may both be absent. The central nervous system
consists of paired ganglia with connecting commissures, viz.: cerebral,
pleural, pedal, and visceral ganglia. Heart possesses two auricles and
one ventricle. Respiration generally by gills. Frequently there are two
larval stages. Development is often direct.
Class 1.—_Lamellibranchiata_: Clam, Oyster.
Class 2.—_Scaphopoda._
Class 3.—_Gasteropoda_: Snail, Whelks, Slugs.
Class 4.—_Amphineura_: Chitons.
Class 5.—_Cephalopoda_: Squids and Cuttlefish.
Branch VIII.—=Vertebrata or Chordata.= Vertebrates are animals having a
distinct body cavity (cœlome) and a segmental arrangement of parts. A
hypoblastic skeletal notochord is always present in the embryo, but tends
to be replaced by an axial skeleton of mesoblastic origin (backbone).
Gill slits are always present in the embryo and may or may not persist in
adult life. Gill-lamellæ do not occur above Amphibians. Heart is ventral.
Central nervous system is dorsal. Eye begins to develop as an outgrowth
from the brain.
Class 1.—_Tunicata._
Class 2.—_Leptocardii._
Class 3.—_Marsipobranchii._
Class 4.—_Pisces._
Class 5.—_Amphibia._
Class 6.—_Reptilia._
Class 7.—_Aves._
Class 8.—_Mammalia._
Class 1.—_Tunicata._ The tunicates are remarkable animals, and seem
to stumble on the border line between Invertebrates and Vertebrates.
Their vertebrate characteristics—gill slits, notochord, dorsal nervous
system, and brain eye—are generally discernible only in the free-swimming
larval state. They generally degenerate as they progress towards the
adult condition, and diverge greatly from the vertebrate type. They are
mostly stationary. They are multicellular animals possessing bilateral
symmetry. The body is enveloped by a thickened cuticle containing
cellulose. The pharynx, perforated with the gill slits, is surrounded by
a peribranchial chamber (atrium) which communicates with the exterior
by an atrial opening. Heart is simple and tubular. The nervous system
is generally reduced to a single ganglion. Nephridia are absent.
Hermaphrodites. Usually a metamorphosis.
Class 2.—_Leptocardii._ Simple, worm-like vertebrate animals represented
by a single distinct type—amphioxus or lancelet. The central nervous
system consists of a spinal cord, and a very ill-defined, rudimentary
brain. No skeleton other than an unsegmented and persistent notochord
which projects beyond the anterior end of the nerve cord. No scales. Gill
slits are very numerous in the adult. Amphioxus is widely removed from
the fishes by the absence of skull, jaws, definite brain, sympathetic
nervous system, ear, eye, genital ducts, spleen, and definite heart, the
latter being simple and tubular. No pectoral or pelvic limbs (fins).
Blood colorless; gastrula ciliated and free-swimming. Metamorphosis.
Class 3.—_Marsipobranchii._ Worm-like vertebrates having round mouths
without distinctly developed jaws; no jaw-bones. Without scales and
without paired limbs (fins). Six or seven gill pouches. Skeleton consists
of persistent, unconstricted, cartilaginous notochord. No sympathetic
nervous system. Single nasal sac. No conus arteriosus, no spleen or
pancreas. Undivided segmental duct.
Class 4.—_Pisces._[26] Aquatic, cold-blooded vertebrates, with a movable
lower jaw. Cartilaginous or osseous skeleton, with paired pectoral and
pelvic fins, supported by fin rays (_radials_ diverging from several
_basal_ pieces); also unpaired fins. No sternum. Exoskeleton of bony
plates or scales. Skull has usually one occipital condyle. Breathing
by permanent gills attached to gristly or bony arches on the sides of
the gill clefts. In most fishes the digestive cavity gives origin to an
air bladder which may or may not remain permanently connected with the
digestive cavity. It mostly serves a hydrostatic purpose, but in some of
the more primitive fishes (Amia, Lepidosteus) it is occasionally of some
slight use in respiration. Heart consists of single auricle and single
ventricle, and contains only venous blood; there is a sinus venosus and
often a conus arteriosus. No inferior vena cava. No allantois. Most
fishes lay eggs which are fertilized in the water.
Sub-class 1.—_Elasmobranchii._
Order 1.—_Plagiostomi_: Sharks, Rays.
Order 2.—_Holocephali_: Chimæroids.
Sub-class 2.—_Teleostomi._
Order 1.—_Crossopterygii_: Polypterus, Calamoichthys.
Order 2.—_Ganoidei_: Sturgeon, Garpike, Amia, Polyodon.
Order 3.—_Dipnoi_: Lung-fishes, e. g., Ceratodus, Protopterus, and
Lepidosiren.
Order 4.—_Teleostei_: Perch, Cod, Salmon, Eel.
Class 5.—_Amphibia._ In the evolution of vertebrates the Amphibians
represent those forms which made the transition from aquatic to
terrestrial life, but have lingered near the water. Certain acquisitions
gained by the Dipnoi, such as a three-chambered heart and lungs, have
been accentuated and firmly established by the Amphibians.
Amphibia are cold-blooded vertebrates whose larval forms always have
gill arches bearing gills. In some forms the gills are retained
throughout life, though the adults always possess functional lungs.
Nasal sacs open posteriorly into the mouth. In existing forms there
is rarely any exoskeleton. There are two occipital condyles. Unpaired
fins are frequently present, though they possess no fin rays. When
limbs are present they possess distinct digits and conform to the same
type as those of the higher vertebrates. Heart has two auricles and
one ventricle. There is an inferior vena cava. The intestine ends in a
cloacal chamber, as do also the urinogenital ducts. Eggs almost always
laid in the water. Often a marked metamorphosis.
Order 1.—_Urodela._ Amphibia which retain the tail throughout life.
The order is subdivided into:
a. _Perennibranchiata_, which retain the gills throughout life:
_Siren_, _Proteus_.
b. _Caducibranchiata_; no persistent gills: _Triton_, _Salamandra_.
Order 2.—_Gymnophiona._ Body snake-like; no feet; young with gills:
_Cœcilia_.
Order 3.—_Stegocephala._ Extinct forms: _Archegosaurus_.
Order 4.—_Anura._ Tailless amphibia; body short, with four limbs;
larvæ tailed: _Frog_, _Toad_.
Class 6.—_Reptilia._ Cold-blooded, air-breathing vertebrates. Limbs
usually ending in claws; limbs sometimes absent; exoskeleton of
scales; ribs well developed; incomplete double circulation; heart is
four-chambered in the highest forms; oviparous; no metamorphosis; embryo
with an amnion and allantois.
The following are some of the orders that have become extinct, viz.:
a. _Theromorpha_: Mammal-like saurians.
b. _Ichthyosauria_: Swimming saurians.
c. _Pterosauria_: Flying saurians.
d. _Dinosauria_: Colossal land saurians capable of rising and resting
on the hind legs.
The following are the living orders, viz.: a, _Ophidia_; b, _Lacertilia_;
c, _Chelonia_; d, _Crocodilia_.
Class 7.—_Aves._ Feathered vertebrata; heart four-chambered;
warm-blooded; lungs with accessory air-sacs; bones dense and hollow;
jaws encased in horny beaks in modern forms; the fore-limbs form wings;
oviparous; eggs are very large and covered by calcareous shell.
Sub-class 1.—_Saururæ_: Archæopteryx.
Sub-class 2.—_Odontornithes_: Ichthyornis, Hesperornis.
Sub-class 3.—_Ratitæ_: Smooth sternum.
Sub-class 4.—_Carinatæ_: Keeled sternum.
Class 8.—_Mammalia._ Animals having the body covered with hair;
warm-blooded; young nourished with milk secreted from mammary glands;
lower jaw articulating directly with the skull, the quadrate becoming the
malleus (ear-bone); heart four-chambered and with the aorta reflected
over the left bronchus; red blood-corpuscles non-nucleated; complete
diaphragm; brain large, especially the cerebrum and cerebellum; uterine
gestation; viviparous.
Sub-class 1.—_Ornithodelphia_: Order Monotremes. Urinary and genital
canals opening into cloaca. Laying large eggs.
Sub-class 2.—_Didelphia_: Order Marsupials. Animals having pouch for
protection and growth of prematurely born embryos.
Sub-class 3.—_Monodelphia_: Placental Mammals.
Order 1.—_Edentata._
Order 2.—_Rodentia._
Order 3.—_Insectivora._
Order 4.—_Cheiroptera._
Order 5.—_Cetacea._
Order 6.—_Sirenia._
Order 7.—_Proboscidea._
Order 8.—_Hyracoidea._
Order 9.—_Ungulata._
Order 10.—_Carnivora._
Order 11.—_Primates._
_Primates_ are an order of Monodelphia or Placentalia, including lemurs,
monkeys, and man. They are nearly all adapted to an arboreal life. The
hand (manus) and the foot (pes) nearly always have five digits provided
with flat nails. The pectoral and pelvic limbs are prehensile, owing to
the fact that the thumb (pollex) and big toe (hallux) are more or less
completely opposable to the other digits. The orbital fossa is completely
surrounded by a bony rim. The femur does not have a third trochanter. The
internal condyle of the humerus does not have a foramen above it. The
clavicles are always well developed. The testes descend into a scrotum.
On the thoracic region there are nearly always two teats. The placenta
may be non-deciduate, or deciduate and metadiscoidal.
The order of Primates is subdivided into the following sub-orders, viz.:
Sub-order 1.—_Lemuroidea._
Sub-order 2.—_Anthropoidea._
_Lemuroidea._ The Lemurs are small, monkey-like quadrupeds. They are
mostly nocturnal, arboreal creatures of comparatively low organization.
The body is furry. The orbital and temporal fossæ freely communicate. The
lachrymal foramen is situated outside the orbital fossa. The dentition
of the Lemurs varies greatly; in some of them it is 2/2 1/1 3/3 3/3 for
both jaws. In nearly all of them the median incisors of the upper jaw are
separated by a median space. Both feet have flat nails on all the digits,
except the second of the hind-foot, which has a claw. The thumb (pollex)
and the big toe (hallux) are well developed. The cerebral hemispheres are
only slightly convoluted, and do not entirely overlap the cerebellum. The
transverse colon is almost always folded on itself. There may be a pair
of teats on the abdomen. The uterus is two-horned, and the placenta is
diffuse.
This sub-order comprises the Lemurs proper (_Tarsius_, _Lemur_, and other
genera) and the Aye-Ayes (_Chiromys_).
_Anthropoidea._ The Anthropoidea are the most highly organized Primates.
They are chiefly modified for an arboreal life. The body is hairy instead
of furry, but only slightly so in man. The incisors do not exceed 2/2;
the molars are 3/3, except in the marmosets, where they are 2/2. The
upper, median incisors are in close contact. The orbital and temporal
fossæ are separated by a broad vertical plate. The lachrymal foramen
is situated inside the orbital fossa. All of the digits are provided
with flat nails, except in the Hapalidæ, in which all except the big
toe (hallux) are provided with a claw. In some the thumb (pollex) is
rudimentary or absent. The clavicle is well developed. The cerebrum
is usually richly convoluted, and more or less completely covers the
cerebellum. The uterus has no horns. The placenta is deciduate and
metadiscoidal.
The Anthropoidea are subdivided into the two following groups:
Super-family 1.—_Platyrrhinæ_ (New-World Monkeys).
Super-family 2.—_Catarrhinæ_ (Old-World Monkeys).
The Platyrrhinæ or New-World Monkeys are subdivided into the following
families, viz.:
Family 1.—_Hapalidæ._
Family 2.—_Cebidæ._
The Catarrhinæ or Old-World Monkeys are subdivided into the following
families, viz.:
Family 1.—_Cercopithecidæ._
Family 2.—_Simiidæ._
Family 3.—_Hominidæ._
_Hapalidæ._ The Hapalidæ or Marmosets are no larger than squirrels, being
the smallest monkeys. They are found mostly in Brazil.
There is a broad septum between the nostrils. Their dentition is 2/2 1/1
3/3 2/2, and is distinctive, for the remaining Anthropoidea have 3/3
molars. The tail is long, hairy, and non-prehensile. The arms are not
longer than the legs. The thumb (pollex) is long, but is not opposable.
All the digits except the great toe (hallux), which is small, have
curved, pointed claws. There is no bony external auditory meatus. There
are no cheek pouches, or ischial callosities. The Hapalidæ often bear
three young ones at a birth, whereas the other Anthropoidea commonly bear
but one. There are two genera of Marmosets, viz.: _Midas_ and _Hapale_.
_Cebidæ._ The Cebidæ are most at home in Brazil. They have a broad
septum between the nostrils. Many of them have prehensile tails. The
dental formula is 2/2 1/1 3/3 3/3, and is characteristic. There is no
bony external auditory meatus. There are no cheek pouches, or ischial
callosities. All the digits are provided with flat nails. The thumb
(pollex) is not opposable.
This family includes the following genera, viz.: Tee Tees (_Callithrix_),
Howling Monkeys (_Mycetes_), Spider Monkeys (_Ateles_), Squirrel Monkeys
(_Chrysothrix_), and Capuchin Monkeys (_Cebus_).
_Cercopithecidæ._ This family includes the Old-World dog-like Apes. They
are quadrupeds, and the muzzle or snout is quite dog-like. There is a
narrow septum between the nostrils. The dental formula is 2/2 1/1 2/2
3/3. The sternum is narrow. The tail is not prehensile. The cæcum has no
appendix vermiformis. There is a bony external auditory meatus. There may
or may not be cheek pouches. Over the rough surface of the everted ischia
the skin forms callosities (ischial callosities) which are often brightly
colored. The thumb (pollex), when present, is opposable. This family
includes two genera, Macaques (_Macacus_) and Baboons (_Cynocephalus_).
_Simiidæ._ This family includes the Anthropoid Apes of the Old World.
They are less quadrupeds than the former, often walking in a semi-erect
position. The dental formula is 2/2 1/1 2/2 3/3. The sternum is broad.
The cæcum has an appendix vermiformis. The nasal septum is narrow. The
pectoral limbs are much longer than the pelvic ones. There is a bony
external auditory meatus. There are no cheek pouches. Only in the Gibbons
are there ischial callosities, in whom they are small. The thumb (pollex)
is opposable. No visible tail. This family includes the following genera,
viz.: Chimpanzees (_Anthropopithecus_), Gorillas (_Gorilla_), Orangs
(_Simia_), and the Gibbons (_Hylobates_).
_Hominidæ._ This family of Anthropoidea includes only the human species
(_Homo sapiens_). The dental formula is 2/2 1/1 2/2 3/3. The tail is
not visible. The Hominidæ differ from the Simiidæ, structurally, mainly
in the more perfect assumption of the erect attitude. There is a more
complete adaptation of the pelvic limbs to bearing the weight of the
body, correlated with compensating alteration in the curvature of the
spinal column. The big toe (hallux) is not opposable, and also it is
often longer, never shorter than the other toes, and is not abducted
from them. He has a far better heel than the Simiidæ. The thumb is far
more opposable in man. There is a greater length of the pelvic limbs
compared with the pectoral limbs. The canine teeth are much smaller and
do not project beyond the level of the others. The brain has a much
greater size and complexity. Man has a larger forehead, smaller cheek
bones, smaller supraorbital ridges, a less protrusive face, and a true,
well-marked chin.
The Simiidæ are subdivided into the two following groups, viz.:
Sub-family 1.—_Hylobatinæ._
Genus 1.—_Hylobates_ (Gibbons).
Sub-family 2.—_Simiinæ._
Genus 1.—_Simia_ (Orangs).
Genus 2.—_Gorilla_ (Gorillas).
Genus 3.—_Anthropopithecus_ (Chimpanzees).
SYNOPSIS OF THE PLANT KINGDOM.
GROUP A. PROTOPHYTA.
GROUP B. METAPHYTA.
The Metaphyta are subdivided into:
1. _Cryptogams_: Flowerless plants.
2. _Phanerogams_: Flowering plants.
The Cryptogams are subdivided into:
1. _Thallophyta_: Seaweeds, Fungi, Lichens.
2. _Bryophyta_: Mosses, Liverworts.
3. _Pteridophyta_: Ferns, Horsetails, Clubmosses.
The Phanerogams are subdivided into:
1. _Gymnospermæ_:
Order a.—_Cycadaceæ_: Cycads.
Order b.—_Coniferæ_: Pines, Spruces, Cypresses.
2. _Angiospermæ_:
Class 1.—_Monocotyledones_: Grasses, Palms.
Class 2.—_Dicotyledones_: Oaks, Poplars, Elms.
SECTION VIII.
WORKS OF REFERENCE.
WORKS OF REFERENCE.
The following books have been the constant companions of the author
during the preparation of his “First Book in Organic Evolution”:—
GRANT ALLEN, The Colours of Flowers.
A. C. ABBOT, Principles of Bacteriology.
FRANK BAKER, The Ascent of Man.
THOMAS BELT, Naturalist in Nicaragua.
H. W. BATES, Naturalist of the Amazons.
F. E. BEDDARD, Animal Coloration.
A. H. BRADFORD, Heredity and Christian Problems.
F. M. BALFOUR, A Treatise on Comparative Embryology.
D. G. BRINTON, Races and Peoples.
P. C. BURT, A History of Modern Philosophy.
PAUL CARUS, The Soul of Man.
PAUL CARUS, The Ethical Problem.
PAUL CARUS, The Idea of God.
PAUL CARUS, Homilies of Science.
PAUL CARUS, Fundamental Problems.
ARTHUR CLARKSON, A Text-Book of Histology.
EDWARD CLODD, The Story of Creation.
EDWARD CLODD, The Story of Primitive Man.
EDWARD CLODD, A Primer of Evolution.
CARPENTER-DALLINGER, The Microscope and its Revelations.
A. DE QUATREFAGES, The Natural History of Man.
E. D. COPE, The Primary Factors of Organic Evolution.
CHARLES DARWIN, The Origin of Species.
CHARLES DARWIN, The Descent of Man.
CHARLES DARWIN, Animals and Plants under Domestication.
J. D. DANA, New Text-Book of Geology.
BASHFORD DEAN, Fishes, Living and Fossil.
J. W. DRAPER, History of the Intellectual Development of Europe.
J. W. DRAPER, Conflict between Religion and Science.
H. H. DONALDSON, The Growth of the Brain.
R. L. DUGDALE, The Jukes.
HENRY DRUMMOND, The Ascent of Man.
HAVELOCK ELLIS, Man and Woman.
HAVELOCK ELLIS, The Criminal.
JOHN FISKE, The Unseen World.
JOHN FISKE, The Idea of God.
JOHN FISKE, The Destiny of Man.
JOHN FISKE, Excursions of an Evolutionist.
JOHN FISKE, Myths and Myth-Makers.
ENRICO FERRI, Criminal Sociology.
SIR W. H. FLOWER, Osteology of the Mammalia.
FUNK and WAGNALL, Standard Dictionary of the English Language.
THEODORE GILL, The Families of Fishes.
THEODORE GILL, Articles on Fishes in the Riverside Natural History.
JOHN C. GALTON, Ecker’s The Human Brain.
FRANCIS GALTON, Hereditary Genius.
FRANCIS GALTON, Natural Inheritance.
FRANCIS GALTON, English Men of Science, their Nature and Nurture.
C. GEGENBAUR, Elements of Comparative Anatomy.
J. M. GUYAU, Education and Heredity.
GEDDES and THOMSON, The Evolution of Sex.
HARPER’S Latin Dictionary.
T. H. HUXLEY, Anatomy of Vertebrated Animals.
T. H. HUXLEY, Man’s Place in Nature.
T. H. HUXLEY, Origin of Species.
T. H. HUXLEY and MARTIN, Practical Biology.
T. H. HUXLEY, Science and Culture, and other Essays.
HERTWIG-MARK, Text-Book of Embryology.
DAVID J. HILL, Genetic Philosophy.
HERTWIG-CAMPBELL, The Cell.
ROBERT HARTMAN, The Anthropoid Apes.
GEORGE HASLAM, Ecker’s Anatomy of the Frog.
REV. W. HOUGHTON, Sketches of British Insects.
E. KLEIN, Micro-organisms and Disease.
G. T. LADD, Outlines of Physiological Psychology.
CESARE LOMBROSO, The Man of Genius.
SIR JOHN LUBBOCK, The Beauties of Nature.
SIR JOHN LUBBOCK, Ants, Bees, and Wasps.
ARNOLD LANG, Text-Book of Comparative Anatomy.
JOSEPH LEIDY, Fresh-water Rhizopoda of North America.
LIDDELL and SCOTT, Greek-English Lexicon.
SIR CHARLES LYELL, Antiquity of Man.
SIR CHARLES LYELL, Principles of Geology.
JOSEPH LE CONTE, Evolution and its Relation to Religious Thought.
JOSEPH LE CONTE, Elements of Geology.
C. S. MINOT, Human Embryology.
ST. GEORGE MIVART, The Genesis of Species.
ST. GEORGE MIVART, Lessons in Elementary Anatomy.
ST. GEORGE MIVART, The Common Frog.
ST. GEORGE MIVART, The Cat.
A. M. MARSHALL, Vertebrate Embryology.
HENRY C. MCCOOK, American Spiders.
F. MAX MÜLLER, Anthropological Religion.
C. LLOYD MORGAN, Animal Life and Intelligence.
C. LLOYD MORGAN, Animal Biology.
O. T. MASON, Woman’s Share in Primitive Culture.
DANIEL OLIVER, Lessons in Elementary Botany.
RICHARD OWEN, Anatomy of Vertebrates.
A. S. PACKARD, Zoölogy.
PARKER and HASWELL, Text-Book of Zoölogy.
OSCAR PESCHEL, The Races of Man.
E. P. POULTON, The Colours of Animals.
J. W. POWELL, Truth and Error, or, The Science of Intellection.
TH. RIBOT, Heredity.
ERNEST RENAN, The Life of Jesus.
G. J. ROMANES, Darwin and After Darwin.
S. H. REYNOLDS, The Vertebrate Skeleton.
OSCAR SCHMIDT, The Mammalia.
OSCAR SCHMIDT, Descent and Darwinism.
SCHAFER and THANE, Quain’s Elements of Anatomy.
KARL SEMPER, Animal Life.
HERBERT SPENCER, Principles of Biology.
W. B. SCOTT, An Introduction to Geology.
N. S. SHALER, First Book in Geology.
J. B. SUTTON, Evolution and Disease.
R. S. TARR, Elementary Geology.
J. A. THOMSON, Outlines of Zoölogy.
E. B. TYLOR, Anthropology.
JAMES TYSON, The Cell Doctrine.
LESTER F. WARD, Dynamic Sociology.
LESTER F. WARD, Outlines of Sociology.
ALFRED WEBER, History of Philosophy.
A. D. WHITE, A History of the Warfare of Science with Theology.
A. WEISMANN, Essays upon Heredity.
A. WEISMANN, The Germ-Plasm.
A. R. WALLACE, The Malay Archipelago.
A. R. WALLACE, Darwinism.
E. B. WILSON, The Cell in Development and Inheritance.
R. WIEDERSHEIM, Comparative Anatomy of Vertebrates.
R. WIEDERSHEIM, The Structure of Man.
C. F. WINSLOW, Force and Nature.
WILLIAM WHEWELL, History of the Inductive Sciences.
B. G. WILDER, Anatomical Technology.
B. G. WILDER, Article “Brain,” Reference Handbook of the Medical
Sciences.
ERNST ZIEGLER, General Pathology.
SECTION IX.
GLOSSARY.
GLOSSARY.
=A-chro´ma-tin= [Gr. _a_-priv.; _chroma_, color.] The nuclear hyaloplasm.
=A-chro-ma-top´si-a= [Gr. _a_-priv.; _chroma_, color; _opsis_, sight.]
Color-blindness.
=Ac-ti-no-zo´a= [Gr. _aktis_, ray; _zoon_, animal.] A division of
Cœlenterates embracing the sea-anemones and coral-polyps.
=Al-lan´to-is= [Gr. _allas_, sausage; _eidos_, form.] A membranous,
sack-like appendage developed from the hinder part of the embryonic
alimentary tract and which serves the purpose of effecting oxygenation
and other changes in the blood in reptiles, birds, and mammals.
=Am-blyp´o-da= [Gr. _amblys_, blunt; _pous_, foot.] An extinct order of
ungulates having elephantine feet and whose navicular bone was supported
by the cuboid.
=Am-blys´to-ma= [Gr. _amblys_, blunt; _stoma_, mouth.] A genus of
amphibians remarkable for the transformations they undergo. When
undeveloped they represent the formerly recognized genus _Siredon_. Some
species are called _axolotls_.
=Am´i-a= [Gr. _amia_, a kind of tunny.]
=Am-i-to´sis= [Gr. _a_-priv.; _mitos_, thread.] Direct cell-division;
cell-division without the formation of nuclear figures.
=Am´mon-ites= [Egyptian _Amon_.] Fossil cephalopod shells.
=Am´nion= [Gr. _amnion_, fœtal membrane.] A membranous sack containing
fluid which envelopes the embryo in the classes of reptiles, birds and
mammals.
=A-mœ´ba pro´te-us= [Gr. _amoibe_, change; Proteus.] A unicellular
animal; a Protozoan.
=Am-phib´i-a= [Gr. _amphi_, double; _bios_, life.] A class of vertebrates
whose young are fish-like and have gills: the skull has two condyles and
a parasphenoid.
=Am-phi-mix´is= [Gr. _amphi_, double; _mixis_, mingling.]
=Am-phi-ox´us= [Gr. _amphi_, double; _oxys_, sharp.] A small worm-like
vertebrate whose body tapers at both ends. The skeleton is notochordal;
skull, brain, auditory, and renal organs are absent.
=An-ab´o-lism= [Gr. _ana_, up; _ballo_, throw.] Constructive metabolism;
the series of chemical changes by which a cell builds up simple and
stable food into the highly complex and unstable living material.
=An-ap-to-mor´phus= [Gr. _an_-priv.; _hapto_, fasten; _morphe_, shape.]
=An-gi-o-sper´mæ= [Gr. _angeion_, vessel; _sperma_, seed.] Plants whose
seeds are contained in a closed seed-vessel.
=An-nu-la´ta= [Lat. _annulatus_, ringed.] A division of Vermes, including
marine worms, leeches, and earthworms.
=An-the-rid´i-a= [NL., < _anthera_, anther; Gr. dim. _idion_.] The male
sexual organ in cryptogams answering to the anthers in phanerogams.
=An-thro-po-pi-the´cus= [Gr. _anthropos_, man; _pithekos_, ape.]
=An´thro-poid= [Gr. _anthropos_, man; _eidos_, form.] Manlike: said
especially of the gibbons, orangs, gorillas, and chimpanzees.
=An-ti-tox´ine= [Gr. _anti_, opposed to; _toxikon_, poison.]
=A-nu´ra= [Gr. _an_, not; _oura_, tail.] An order of amphibians without a
tail in the adult, including the toads and frogs.
=A´phis= [Gr. _apheideis_, lavish.] In Entomology a genus typical of
Aphididæ. An aphid; a plant-louse.
=Ap-pen´dix ver-mi-for´mis= [Lat. _appendo_, to hang from; _vermis_,
worm; _forma_, form.] A vestigial structure attached to commencement of
the large intestine.
=A-rach´ni-da= [Gr. _arachne_, spider.] A class of Arthropods embracing
the spiders, mites, scorpions, etc.
=Ar-cel´la= [Lat. dim. _arca_, a box.] Belonging to a group of protozoans
having a chitinous shell.
=Ar-chæ´an= [Gr. _archaios_, ancient.] Pertaining to the oldest strata of
rocks in geological history.
=Ar-chæ-op´ter-yx= [Gr. _archaios_, ancient; _pteryx_, bird.] A fossil
bird with reptilian characteristics.
=Ar-che-go-sau´rus= [Gr. _archegos_, beginning; _sauros_, lizard.] A
carboniferous amphibian (labyrinthodont.)
=Ar´go-naut= [Gr. _argo_, swift; _nautes_, sailor.]
=Ar-ma-dil´los= [Sp. dim. of _armado_, armed.] Edentate mammals having a
carapace formed by ossification of the greater part of the skin and the
union of the bony scutes.
=Ar-throp´o-da= [Gr. _arthron_, joint; _pous_, foot.] A branch of animals
(invertebrates) with jointed legs, as insects, spiders, and crabs.
=As´ter= [Gr. _aster_, star.]
=As-ter-oi´de-a= [Gr. _aster_, star; _eidos_, form.] Echinoderms having
radiating arms with ambulacral grooves below, embracing the true
star-fishes.
=At´a-vism= [Lat. _atavus_, grandfather.] Reversion; recurrence to an
ancestral type.
=At´e-les= [Gr. _ateles_, imperfect.]
=Au´ri-cles= [Lat. _auricula_, little ear.] A chamber of the heart which
receives blood from the veins and transmits it to the ventricle.
=A´ves= [Lat. pl. of _avis_, bird.] Birds, a class of vertebrata.
=Ba-cil´lus= [Lat. _bacillum_, a little stick.] A genus of bacteria
consisting of rod-like cells. They multiply by transverse division and by
the formation of endogenous spores. Unicellular plants.
=Bac-te´ri-a= [Gr. _bakterion_, stick.] Microscopic unicellular plants. A
genus of Schizomycetes (fission-fungi).
=Bal-a-no-glos´sus= [Gr. _balanos_, acorn; _glossa_, tongue.] Supposed by
some biologists to belong to the Chordata.
=Beams= [AS. _beam_, tree.] The main stem of a deer’s antler.
=Bel-em´nites= [Gr. _belemnon_, dart.] A belemnitoid cuttlefish.
=Bi´o-phores= [Gr. _bios_, life; _phero_, bear.] Biological units of
hereditary mass.
=Bi´pes= [Lat. _bis_, twice; _pes_, foot.]
=Blas´tid= [Gr. _blastos_, sprout.]
=Blas-to-ge-net´ic= [Gr. _blastos_, a germ; _genesis_, generation.]
Originating in the germ cells.
=Blas´tu-la= [Gr. _blastos_, sprout.] A stage in the growth of
the embryo; a hollow sphere of one layer of cells enclosing a
segmentation-cavity.
=Brach-i-op´o-da= [Lat. _brachium_, arm; Gr. _pous_, foot.] Molluscoid
animals with bivalve shells, one of which is dorsal and the other
ventral; also with brachial appendages coming from the sides of the
mouth. Lamp shells.
=Brach´i-o-pod= [Vid. Brachiopoda.] Lamp shell.
=Bry-oph´y-ta= [Gr. _bryon_, moss; _phyton_, plant.] A division of the
vegetable kingdom consisting of liverworts and mosses.
=Bry-o-zo´a= [Gr. _bryon_, moss; _zoon_, animal.] Moss animals.
=Ca-du-ci-bran-chi-a´ta= [Lat. _caducus_, falling; _branchia_, gills.]
Urodeles that lose their gills before maturity.
=Ca-du-ci-bran´chi-ates= [Vid. Caducibranchiata.]
=Cal´li-thrix= [Gr. _kalos_, beautiful; _thrix_, hair.]
=Cal-a-mo-ich´thys= [Gr. _kalamos_, reed; _ichthys_, fish.]
=Ca´lyx= [Gr. _kalyx_, cover.] The outermost series of leaves (sepals) of
a flower; usually green.
=Cam´bri-an= [_Cambria_, _Wales_.] The name given by Sedgwick to those
Palæozoic rocks that underly the Silurian, in Cambria (or Wales).
=Car-bon-if´er-ous= [Lat. _carbo_, coal; _fero_, bear.]
=Car-i-na´tæ= [Lat. _carinatus_, keel-shaped.] Birds having a keeled
(carinate) breast-bone.
=Car-niv´o-ra= [Lat. _caro_, flesh; _voro_, devour.] Flesh-eating mammals.
=Cas-tra´tion= [Lat. _castratus_.] Removal of the glands that bear the
Germ-Cells.
=Cat-ar-rhi´næ= [Gr. _kata_, down; _rhis_, nose.] Old World monkeys. The
septum of the nose is narrow; the tail is short and not prehensile.
=Cat´ar-rhines= [Vid. Catarrhinæ.] Old World monkeys.
=Ceb´i-dæ= [Gr. _kebos_, long-tailed monkey.] A family of New World
monkeys.
=Ce´bus= [Gr. _kebos_, long-tailed monkey.]
=Cen-o-zo´ic= [Gr. _kainos_, new; _zoe_, life.] Relating to the
Quaternary and Tertiary eras.
=Cen´ti-pede= [Lat. _centum_, hundred; _pes_, foot.] A many jointed
myriapod having a pair of legs to each joint.
=Cen´tro-some= [Gr. _kentron_, center; _soma_, body.] A body just outside
of the nucleus of a cell and that governs the mitotic phases of a cell.
=Ceph-a-lop´o-da= [Gr. _kephale_, head; _pous_, foot.] Molluscs with a
subcentral head, a beaked mouth, and tentacles taking the place of feet,
including cuttlefishes, etc.
=Cer´a-tites= [Gr. _keras_, horn; _ites_, like.] A fossil cephalopod with
the habitation chamber short and sutural saddles mostly simple.
=Cer´a-to-dus= [Gr. _keras_, horn; _odous_, tooth.] So-called from the
horn-like ridges of the teeth. A lung-fish.
=Cer-co-pi-the´ci-dæ= [Gr. _kerkopithekos_, a long-tailed ape; _eidos_
form.] A family of catarrhine anthropoidea.
=Cer-e-bel´lum= [Lat. dim. of _cerebrum_, brain.] A subdivision of the
encephalon.
=Cer´e-brum= [Lat. brain.] A subdivision of the encephalon.
=Cer´e-bral= [Vid. Cerebrum.] Pertaining to the cerebrum.
=Ce-ta´ce-a= [Lat. _cetus_, whale.] An order of fish-like mammals
including the whales and porpoises.
=Chei-rop´te-ra= [Gr. _cheir_, hand; _pteron_, wing.] Including the
Bats,—an order of mammals.
=Chei-ro´tes= [Gr. _cheirotos_, having a hand.] A native lizard of Mexico.
=Che-lo´ni-a= [Gr. _chelone_, tortoise.] An order of reptiles, including
the turtles and tortoises.
=Chi-mæ´roids= [Gr. _chimaira_, a fabled monster; _eidos_, form.] An
order of elasmobranchii (holocephali) with opercular membrane and smooth
skin.
=Chi´ro-mys= [Gr. _cheir_, hand; _mus_, mouse.]
=Chim-pan´zee= [W. Afr.] Anthropopithecus. A West African arboreal,
anthropoid ape; five feet high; distinct eyelashes, eyebrows, and
whiskers; very large ears. It approximates to man in its dentition and
the length of its arms. Has darker hair than gorilla.
=Chi´tin-ous= [Gr. _chiton_, tunic.] Pertaining to chitin, the horny
substance in the skin of insects.
=Chro´ma-tin= [Gr. _croma_, color.] Nuclear threads.
=Chor-da´ta= [Lat. _chorda_, chord.] A subkingdom of animals with a
notochord persistent or evanescent.
=Chro´mo-somes= [Gr. _croma_, color: _soma_, body.] Nuclear threads.
=Chry´so-thrix= [Gr. _chrysos_, gold; _thrix_, hair.]
=Clo-a´ca= [Lat. _cloaca_, a common sewer.] The common cavity into which
the digestive, urinary, and genital canals empty in most vertebrates
below placentals, and in all mammalian embryos.
=Coc´ci= [Gr. _kokkos_, berry.] Pl. of _coccus_. Isolated spherical cells
(bacteria).
=Co-coons´= [F. _cocon_, dim. of _coque_, shell; < Lat. _concha_, shell.]
The protective envelopes spun by certain larval insects, as silkworms, in
which they are inclosed in the chrysalis state.
=Co-do-si´ga um-bel-la´ta= [Gr. _kodon_, a bell; _sige_, silence; Lat.
_umbella_, dim. of _umbra_, shade.]
=Cœ-cil´i-a= [Lat. _cæcus_, blind.] Footless amphibians of snake-like
form; rudimentary eyes; no neck.
=Cœ-len-te-ra´ta= [Gr. _koilos_, hollow; _enteron_, intestine.]
=Cœ-len´ter-ate= [Vid. Cœlenterata.]
=Cϫlome= [Gr. _koilos_, hollow.] The body-cavity of a metazoan between
the viscera and the body-wall.
=Combs= [AS. _camb_, crest or ridge.] The fleshy crests on the heads of
roosters, etc.
=Con-dy-lar´thra= [Gr. _kondylos_, knuckle; _arthron_, joint.] An Eocene
group of ungulates in which the astragalus is not interlocked laterally
with the tibia and its head rounded.
=Co-nif´e-ræ= [Lat. _conus_, cone; _fero_, bear.] The pine family of
trees.
=Co´nus ar-te-ri-o´sus= [_Latin phrase_.] The arterial, cone-shaped
portion of the left ventricle of the heart.
=Co-rol´la= [Lat., dim. of _corona_, crown.] The inner set of leaves
of flowers and usually bright-colored. The individual parts are called
petals.
=Crests= [Lat. _crista_, tuft.] Projecting natural growths on the tops
of animals’ heads and usually ornamental, as the cock’s comb, or the
lengthened feathers of a bird.
=Cre-o-don´ta= [Gr. _kreas_, flesh; _odous_, tooth.] A group of fossil
animals containing forms ancestrally related to existing Carnivora.
=Cre-ta´ceous= [Lat. _creta_, chalk.] Pertaining to the latter part of
the Reptilian age.
=Cri-noi´de-a= [Gr. _krinon_, lily; _eidos_, form.] Stone-lilies; stalked
star-fishes. A division of Echinoderms.
=Cri´noids= [Vid. Crinoidea.]
=Croc-o-dil´i-a= [Lat. _crocodilus_, lizard.] An order of reptiles
including crocodiles, alligators, and gavials. They are the highest order
of reptiles. In them the heart and brain approximate very closely to that
of birds.
=Cros-sop-te-ryg´i-a= [Gr. _krossoi_, tassels; _pterygion_ dim. of
_pteryx_, wing.] A group of fishes with paired, lobate fins, and with an
endodermal skeletal, axis fringed with dermal rays.
=Crus-ta´ce-a= [Lat. _crusta_, crust.] A division of arthropods
containing crabs, lobsters, shrimps, crawfish, barnacles, etc.
=Cryp´to-gams= [Gr. _kryptos_, hidden; _gamos_, marriage.] The lower
of the two great subdivisions of the plant kingdom. They have no true
flowers containing stamens, pistils, and seeds; they propagate by means
of spores.
=Cten-oph´o-ra= [Gr. _kteis_, comb; _phero_, bear.] A subdivision of
cœlenterates with paddle-like locomotive plates arranged in eight
meridional rows on the outer surface of the body.
=Cyc-a-da´ce-æ= [Gr. _kykos_, African coco-palm.] The cycad family of
plants (gymnospermous), of fern-like or palm-like aspect.
=Cys-toi´de-a= [Gr. _kystis_, bladder; _eidos_, form.]
=Cy-no-ceph´a-lus= [Gr. _kyon_, dog; _kephale_, head.]
=Cy´to-plasm= [Gr. _kyo_, be pregnant; _plasma_, < _plasso_, form.]
Protoplasm; especially that portion of a cell apart from the nucleus.
=Dal´ton-ism= [Dalton, chemist, who had color-blindness.]
Color-blindness, especially red-blindness.
=De-cid´u-ate= [Lat. _deciduus_, falling off.] Shed at periodic times.
=Des´mids= [Gr. _desmos_, band.] Unicellular plants of minute size;
bright-green in color; mainly solitary, fresh-water algæ.
=Dev-o´ni-an= [Devonshire, England.] The name given by Murchison to
Palæozoic rocks in Devonshire, England.
=Di´a-toms= [Gr. _dia_, through; _tome_, cutting.] Microscopic
unicellular algæ inhabiting salt or fresh water. Each individual
(frustule) consists of two flint valves which are more or less
symmetrical. They are either isolated or attached together in a series.
=Di-cot-y-le´don-es= [Gr. _dikotylos_, with two hollows.] The most
important and largest class of flowering plants. Characterized by
having seeds with two cotyledons, exogenous stems, and leaves that are
netted-veined; the parts of the flower mostly in fours or fives.
=Di-del´phi-a= [Gr. _di_-, two; _delphys_, womb.] A sub-class of mammals,
as the Marsupials, having a double womb and no placenta.
=Dif-flu´gi-a pyri-form´is= [Lat. _diffluere_, to flow apart; _pyrum_,
pear; _forma_, form.]
=Di-no-sau´ri-a= [Gr. _deinos_, terrible; _sauros_, lizard.] Mesozoic
land reptiles.
=Dip´no-i= [Gr. _di_-, two; _pneo_, breathe.] Fishes with regular gills,
a double or single lung, and nostrils inside as well as outside the
mouth.
=Dro-ma-the´ri-um= [Gr. _dromos_, running; _therion_, small wild beast.]
=Dys-chro-ma-top´si-a= [Gr. _dys_, bad; _chroma_, color; _opsis_, sight.]
Partial color-blindness; difficulty in distinguishing colors.
=E-chi-no-der´ma-ta= [Gr. _echinos_, hedgehog; _derma_, skin.]
=E-chi´no-derms= [Vid. Echinodermata.]
=Ech-i-noi´de-a= [Gr. _echinos_, hedgehog; _eidos_, form.] Echinoderms
including sea urchins.
=Ec´to-derm= [Gr. _ektos_, outside; _derma_, skin.]
=Ec´to-plasm= [Gr. _ektos_, outside; _plasso_, form.]
=E-den-ta´ta= [Lat. _e_, out of; _dens_, tooth.] An order of placentals
with a small, one-lobed cerebrum; without median, cutting teeth:
including armadillos, ant-eaters, and sloths.
=El-as-mo-bran´chi-i= [Gr. _elasmos_, metal plate; _branchia_, gills.]
Fish-like vertebrates which have no membrane bones in the skull or the
shoulder-girdle; five pairs of strap-like gills attached by their distal
ends; claspers to the ventral fins of males; complicated brain with optic
nerves forming a decussation.
=Em´bry-o= [Gr. _en_, in; _bruein_, swell.] The term applied to an animal
in the earlier stages of development.
=Em-bry-ol´o-gy= [Gr. _embryon_, embryo; _logos_, < _lego_, speak.] The
study of embryos.
=En´do-derm= [Gr. _endon_, within; _derma_, skin.]
=En´do-plasm= [Gr. _endon_, within; _plasso_, form.]
=En-ter-op-neus´ta= [Gr. _enteron_, intestine; _pneustos_, breathing.]
Acorn-tongue worms. Smooth-bodied, footless worms, having a large
exserted soft proboscis; breathing by a series of respiratory sacs
opening into the digestive canal, and communicating externally
by spiracles; nervous system situated above a seeming notochord.
Balanoglossus. Included by some biologists among the chordata.
=E-o-hip´pus= [Gr. _eos_. dawn; _hippos_, horse.]
=E´o-cene= [Gr. _eos_, dawn; _kainos_, recent.]
=Ep-en-ceph´a-lon= [Gr. _epi_, upon; _enkephalos_, brain.] A fundamental
subdivision of the brain (encephalon).
=Ep´i-blast= [Gr. _epi_, upon; _blastos_, bud.]
=E´quus= [Lat. horse.]
=E-ryth-ro-lam´prus= [Gr. _erythros_, red; _lampros_, shining.]
=Eu-ca-lyp´tus= [Gr. _eu_, good; _kalypto_, cover.] A large genus of
evergreen trees of the myrtle family.
=Ev-o-lu´tion= [Lat. _e_, out; _volvo_, roll.]
=Ex-o-skel´e-ton= [Gr. _exo_, outside; _skeleton_, dried body.] External
skeleton; bony or horny hardening of the integument.
=Fla-gel´lum= [Lat., dim. of _flagrum_, scourge.] A slender protoplasmic
extension of a cell, for purposes of locomotion.
=Fo-ram-i-nif´e-ra= [Lat. _foramen_, opening; _fero_, bear.] A division
of protozoans secreting a shell perforated by many minute apertures.
=Fos´sil= [Lat. _fodio_, dig.] Any organic body so situated in the earth,
and so buried in solid rock or in earthy deposits, as to be capable of
indefinite preservation.
=Gan´gli-on= [Gr. _ganglion_, tumor.] A swelling that consists of an
aggregation of nerve-cells. It receives and discharges nervous impulses
and serves to stimulate psychical and organic activities.
=Ga-noi´de-i= [Gr. _ganos_, brightness; _eidos_, appearance.]
=Gas-ter-op´o-da= [Gr. _gaster_, stomach; _pous_, foot.] Including all
snails and slugs.
=Gas´tru-la= [Dim. of Lat. _gaster_, stomach.]
=Gem´mæ= [Lat. buds.]
=Geph-y-re´a= [Gr. _gephyra_, bridge.] A division of worms with an
œsophageal nervous ring and ventral chord; no distinct segments or legs;
a terminal or dorsal anus.
=Go´ni-a-tites= [Gr. _gonia_, corner; _lithos_, stone.] A genus of fossil
Ammonites.
=Gor´gets= [Fr. _gorgette_, dim. of _gorge_, throat.] Throat-patches
distinguished by color or texture, especially in humming birds.
=Grap´to-lites= [Gr. _graptos_, written; _lithos_, stone.] Fossil
hydroids.
=Greg-a-ri´na= [Lat. _gregarius_, < _grex_, flock.] A genus typical of
Gregarinidæ. _Gregarina gigantea_ is sixteen millimeters in length and is
one of the largest unicellular animals known.
=Greg-a-rin´i-dæ= [Vid. Gregarina.] More or less elongated amœba-like
Protozoa, having a well-defined cell-wall, and a “subcuticular” system
of muscular fibrillæ; nucleus, but no contractile vacuole; reproduction
by encystment and subdivision of the central cell mass or protoplasm, by
which shelly psorosperms are formed and from which escape the moner-like
young, which undergo a metamorphosis.
=Gro´mi-a o-vi-form´is= [Lat. _gromia_; _ovum_, egg; _forma_, form.] A
characteristic imperforate foraminifer.
=Gym-no-phi´o-na= [Gr. _gymnos_, naked; _ophis_, serpent]
=Gym-no-sper´mæ= [Gr. _gymnos_, naked; _sperma_, seed.] Plants whose
seeds are not contained in a closed seed-vessel, as Cycads and Conifers.
=Hap´a-le= [Gr. _hapalos_, gentle.]
=Ha-pal´i-dæ= [Gr. _hapalos_, gentle] A family of New World monkeys
including the Marmosets.
=Hel-i-co-nid´æ= [N., < _heliconius_, of Helicon; idæ.] A family of
butterflies.
=Hes-per-or´nis= [Gr. _hesperos_, western; _ornis_, bird.] Cretaceous
carinate birds with rudimentary wings, short tail, and pointed teeth
implanted in grooves.
=Hip-po-pot´a-mus= [Gr. _hippos_, horse; _potamos_, river.]
=Hol-o-ceph´a-li= [Gr. _holos_, whole; _kepale_, head.] A subdivision of
Elasmobranchii in which the suspensorium of the lower jaw is continuous
with the cranium, as chimæroids, etc.
=Hol-o-thu-roi´de-a= [Gr. _holos_, whole; _thouros_, rushing.] Worm-like
echinoderms, with skin-like integuments, and circum-oral tentacles;
including sea-cucumbers, sea-slugs, etc.
=Ho-min´i-dæ= [Lat. _homo_, man; idæ.] A family of primates restricted to
mankind.
=Hy´a-lo-plasm= [Gr. _hyalos_, glass; _plasma_, < _plasso_, form.]
=Hy´dra= [Gr. _hydra_, Lernæan serpent, < _hudor_, water.] A fresh-water
polyp, having the form of a cylindrical tube, surrounded at the mouth
with a circle of thread-like tentacles, by which it captures its prey.
=Hy´droid= [Gr. _hudor_, water; _eidos_, form.] Resembling the _hydra_;
pertaining to the Hydroidea.
=Hy-dro-zo´a= [Hydro-; _zoon_, animal.] Cœlenterates including Hydroids
and jelly-fishes.
=Hy-lob-a-ti´næ= [Gr. _hylobates_, one who walks the wood.] An Asiatic
subfamily of apes; the long-armed apes or gibbons.
=Hy-lob´a-tes= [Gr. _hylobates_.] A gibbon,—an Asiatic ape.
=Hy-ra-coi´de-a= [Gr. _hyrax_, shrew-mouse; _eidos_, appearance.]
=Ich-thy-or´nis= [Gr. _ichthys_, fish; _ornis_, bird.] Cretaceous
toothed birds of tern-like form, with socketed acute teeth, and
bi-concave vertebræ
=Ich-thy-o-sau´ri-a= [Gr. _ichthys_, fish; _sauros_, lizard.]
=Id´i-o-blast= [Gr. _idios_, individual; _blastema_, sprout.]
=In-fu-so´ri-a= [Lat. _in_, into; _fundo_, pour.] So called because
including many animalcules that occur in infusions of decaying substances.
=In-sec´ta= [Lat. _in_, into; _seco_, cut.]
=In-sec-tiv´o-ra= [Lat. _insectum_, insect; _voro_, devour.]
=In-ver-te-bra´ta= [Lat. _in_, not; _vertebratus_, jointed.] Including
all animals that do not possess a notochord or backbone: opposed to
Vertebrata.
=In-ver´te-brates= [Vid. Invertebrata.]
=Ju-ras´sic= [Jura mountains.]
=Kaf´ir-boom= [Erythrina caffra.] A prickly-stemmed tree of South Africa.
=Kal´li-ma para-lek´ta= [Gr. _kallimos_, beautiful; _para_, along side
of; _lektos_, picked out.]
=Keri-vou´la pic´ta.=
=Lab-y-rin´tho-donts= [Gr. _labyrinthos_, labyrinth; _odous_, tooth.]
Extinct amphibians.
=Lac-er-til´i-a= [Lat. _lacertus_, lizard.]
=La-ge´na= [Gr. _lagynos_, flask.]
=La-mel-li-bran-chi-a´ta= [Lat. _lamella_, a plate; _branchia_, gills.]
Bivalve molluscs.
=La-nu´go= [Lat. _lana_, wool.]
=Lar´væ= [Lat. pl. of _larva_, mask.] The early forms of animals when
they are unlike the parent. In insects the first stages after leaving the
eggs, preceding the pupa, as maggots or caterpillars.
=Lem-u-roi´de-a= [Lemur; Gr. _eidos_, appearance.] A sub order of
Primates. Prosimiæ.
=Lep-i-do-si´ren= [Gr. _lepis_, scale; _siren_, a genus of amphibians.]
One of the lung-fishes.
=Lep-to-car´di-i= [Gr. _leptos_, fine, small; _kardia_, heart.]
=Liv´er-worts.=
=Lon-gi-cor´ni-a= [Lat. _longus_, long; _cornu_, horn.] A division of
beetles having very long filiform antennæ.
=Ma-caques´= [F., < Afr. _macaquo_.] Cercopithecine monkeys of the genus
_macacus_. Their form is stout; large ischial tuberosities: muzzle
considerably produced.
=Ma-ca´cus.=
=Mam´mal= [Lat. _mamma_, breast; suffix -_al_; in analogy with
Animal. Dr. Th. Gill.] Vertebrate animal whose female has mammæ, or
milk-secreting organs.
=Mam-ma´li-a= [Vid. mammal.]
=Man´tis= [Gr. _mantis_, prophet.] The mantises are insects noted for the
manner in which they carry the large spinous fore legs when waiting for
prey. They have the attitude, then, as if praying.
=Mar´mo-set.= A small South-American monkey.
=Mar-si-po-bran´chi-i= [Gr. _marsipos_, bag; _branchia_, gills.]
=Mar-su´pi-al= [Lat. _marsupium_, pouch.] Animals having a marsupium or
pouch for retaining the young.
=Mas´to-don= [Gr. _mastos_, breast; _odous_, tooth.] An extinct elephant.
=Me-dul´la= [Lat. _medius_, middle.] A subdivision of the brain—that
portion especially that is continuous with the spinal chord.
=Men-o-bran´chus= [Gr. _meno_, remain; _branchia_, gills.] A large
American aquatic amphibian, of salamander-like form, with persistent
gills, as the mud-puppy.
=Mens sana in corpore sano.= A Latin phrase meaning a sound mind in a
sound body.
=Mes-en-ceph´a-lon= [Gr. _mesos_, middle; _enkephalos_, brain.] A
fundamental segment of the brain.
=Mes´en-chyme= [Gr. _mesos_, middle; _enchyma_, infusion.]
=Mes´o-blast= [Gr. _mesos_, middle; _blastos_, germ.]
=Mes-o-glϫa= [Gr. _mesos_, middle; _gloia_, glue.]
=Mes-o-hip´pus= [Gr. _mesos_, middle; _hippos_, horse.]
=Mes-o-zo´ic= [Gr. _mesos_, middle; _zoe_, life.]
=Met-a-dis-coi´dal= [Gr. _meta_, after; _diskos_, disk; _eidos_,
appearance.] Resembling a discoidal form.
=Met-a-mor´pho-sis= [Gr. _meta_, over; _morphe_, form.] The series of
pronounced external changes through which an animal passes after leaving
the egg-envelopes and before reaching sexual maturity.
=Met-a-phy´ta= [Gr. _meta_, above, higher; _phyton_, plant.]
=Met´a-plasm= [Gr. _metaplasmos_, transformation.]
=Met-a-zo´a= [Gr. _meta_, after, higher; _zoon_, animal.]
=Met-en-ceph´a-lon= [Gr. _meta_, after; _enkephalos_, brain.] A
fundamental segment of the brain.
=Mi-cro-ceph-a´li-a= [Gr. _mikrokephalos_, small-headed.] Imperfect
development of the cranium.
=Mi-cren-ceph-a´li-a= [Gr. _mikros_, small; _enkephalos_, brain.]
Small-brained.
=Mi´cro-cosm= [Gr. _mikros_, small; _kosmos_, world.]
=Micro-gro´mi-a so-ci-al´is= [Gr. _mikros_, small; _gromia_; Lat.
_socialis_ < _socius_, companion.]
=Mi-cro-les´tes.=
=Mi´das.= A wealthy king of Phrygia.
=Mi-o-hip´pus= [Miocene; Gr. _hippos_, horse.]
=Mi´o-cene= [Gr. _meion_, less; _kainos_, recent.]
=Mi-to´sis= [Gr. _mitos_, thread.]
=Mol-lus´ca= [Lat. _mollis_, soft.]
=Mon-o-cot-y-le´don-es= [Gr. _monos_, single; _kotyledon_, cup-shaped
cavity.] A group of flowering plants in which the first leaves of
the embryo are alternate, for which reason they are said to have one
seed-leaf or cotyledon.
=Mon-o-del´phi-a= [Gr. _monos_, single; _delphys_, womb.] A sub-class of
mammals having a single vagina and uterus; embryo attached by a placenta;
brain has a corpus callosum. Includes all animals above Monotremes and
Marsupials.
=Mon´o-tremes= [Gr. _monos_, single; _trema_, hole.] An order of
ornithodelphians.
=Mor´u-la= [Lat. dim. of _morum_, mulberry.]
=Mul-ti-tu-ber-cu-la´ta= [Lat. _multus_, many; _tuberculum_, tubercle.]
=My-ce´tes= [Gr. _myketes_, bellower.]
=Myr-i-ap´o-da= [Gr. _myrios_, numberless; _pous_, foot.] Insects with
numerous pairs of legs, as centipedes.
=Nau´ti-loids= [Gr. _nautilos_, sailor; _eidos_, like.] A group of
cephalopods.
=Nau´ti-lus= [Gr. _nautilos_, sailor.] A cephalopod.
=Nem-a-thel-min´thes= [Gr. _nema_, thread; _helmins_, worm.]
=Nem-er-ti´na= [Gr. _nemertes_, unerring.] Worms with skin ciliated,
proboscis retractile, and nervous, muscular, and vascular systems
characteristically developed.
=Ne-o-lith´ic= [Gr. _neos_, new; _lithos_, stone.]
=Noc-ti-lu´ca mi-li-a´ris= [Lat. _nox_, night; _luceo_, shine;
_miliarius_, < _milium_, millet.]
=No´to-chord= [Gr. _notos_, the back; _chorda_, a chord.] A cartilaginous
rod found in the young chordate embryo in a situation that is later
on occupied by the centers of the bodies of the vertebræ. It separates
a dorsal nervous system from a ventral alimentary (digestive) canal.
The notochord is persistent in its entirety in Leptocardians and
Marsipobranchs and also in some pisces, as the sturgeon.
=O-don-tor´ni-thes= [Gr. _odous_, a tooth; _ornis_, bird.] Including all
those extinct birds having teeth.
=Œ-soph´a-gus= [Gr. _oiso_, will bear; _phagein_, eat.] The gullet; the
membranous tube through which food passes from the pharynx to the stomach.
=On-tog´e-ny= [Gr. _on_, being; _genesis_, origin.] The history of the
evolution of the individual; the development of the individual.
=On-to-ge-net´ic= [Gr. _on_, being; _genesis_, origin.] Pertaining to
ontogeny.
=On-y-choph´o-ra= [Gr. _onyx_, claw; _pherein_, bear.] Arthropods
including only a single genus, the curious caterpillar-like Peripatus.
=Oösperm= [Gr. _oon_, egg; _sperma_, semen.] A fertilized ovum. The first
stage in the existence of a human being is called oösperm.
=O-per´cu-lum= [Lat. lid.] The gill-cover.
=O-phid´i-a= [Gr. _ophis_, serpent.] Serpents; snakes.
=Op-po´nens Hal-lu´cis= [Lat. _ob_, _pono_, to place over against;
_hallux_, great toe.] The name of a muscle in the foot.
=Or-do-vi´cian= [_ordovices_, ancient Celtic tribe in Wales.]
=Or-nith-o-del´phi-a= [Gr. _ornis_, bird; _delphys_, womb.] A sub-class
of oviparous mammals.
=Or-o-hip´pus= [Gr. _oros_, mountain; _hippos_, horse.]
=Or-tho-cer´a-tites= [Gr. _orthos_, straight; _keras_, horn.]
=Os´te-o-blasts= [Gr. _osteon_, bone; _blastano_, sprout.]
=Os´te-o-clasts= [Gr. _osteon_, bone; _klao_, destroy.]
=Os´tra-co-derms= [Gr. _ostrakon_, shell; _derma_, skin.]
=Ovum= [Lat. _egg_.] Female germ-cell; female, encysted, sexual cell.
=O-vip´a-rous= [Lat. _ovum_, egg; _pairo_, produce.] Producing eggs that
mature and are hatched outside the body.
=Pal´li-um= [Gr. _mantle_.]
=Pa-læ-o-lith´ic= [Gr. _palaios_, ancient; _lithos_, stone.]
=Pa-læ-o-zo´ic= [Gr. _palaios_, ancient; _zoe_, life.]
=Pan-do-ri´na mor´um= [Gr. Pandora; _moron_, mulberry.]
=Pan-gen´e-sis= [Gr. _pas_, all; _genesis_, origin.]
=Par-a-me´ci-um= [Gr. _paramekes_, of longish shape.]
=Par-then-o-gen´e-sis= [Gr. _parthenos_, virgin; _genesis_, origin.]
Production of a new individual from a virgin female without intervention
of a male; reproduction by means of unfertilized eggs.
=Per-en-ni-bran-chi-a´ta= [Lat. _perennis_, perpetual; _branchia_, gills.]
=Per-en-ni-bran´chi-ates= [Vid. Perennibranchiata.]
=Ped´al= [Lat. _pes_, foot.]
=Per´mi-an= [Perm, Russia.]
=Phan´er-o-gams= [Gr. _phaneros_, visible; _gamos_, marriage.] Flowering
plants.
=Phos-phor-es´cence.=
=Phryn-o-ceph´a-lus mys-ta´ce-us.=
=Phy-log´e-ny= [Gr. _phylon_, tribe; _genesis_, origin.] The history of
the evolution of a species or group; distinguished from ontogeny.
=Phy-lo-ge-net´ic= [Vid. phylogeny.] Pertaining to phylogeny.
=Pith´e-coid= [Gr. _pithekos_, ape; _eidos_, like.]
=Pith-e-can-thro´pus= [Gr. _pithekos_, ape; _anthropos_, man.]
=Pla-gi-os´to-mi= [Gr. _plagios_, oblique; _stoma_, mouth.] A division of
Elasmobranchii, including sharks and rays.
=Pla-cen´tal= [Lat. _placenta_, cake.] So called on account of its
shape. Pertaining to the _placenta_, the organ of attachment of higher
vertebrate (monodelph) embryos to the wall of the uterus of the female.
=Plas´tids= [Gr. _plastos_, formed.]
=Plat-y-hel-min´thes= [Gr. _platys_, flat; _helminos_, worm.]
=Plat-y-rhi´næ= [Gr. _platys_, broad, flat; _rhis_, nose.] Monkeys of the
New World having long tails and a wide septum to the nose.
=Pleur-a-can´thus= [Gr. _pleuron_, rib; _akantha_, thorn.]
=Pleu´ral= [Gr. _pleura_, rib, side.]
=Pli-o-hip´pus= [Pliocene; Gr. _hippos_, horse.]
=Pli´o-cene= [Gr. _pleion_, more; _kainos_, recent.]
=Plumes= [Lat. _pluma_, small soft feather.] Feathers, especially when
ornamental or large; or tufts of large and ornamental feathers.
=Pneu-mo-coc´ci= [Gr. _pneumon_, lung; _kokkos_, berry.] Bacteria
(spheroidal) found in those suffering from pneumonia.
=Pol-y-dac´tyl-ism= [Gr. _polys_, many; _daktylos_, finger, toe.] The
possession of an abnormally large number of fingers or toes.
=Pol-y-mor´phism= [Gr. _polys_, many; _morphe_, form.] Exhibition by a
group of animals, as a species, of different types of form or structure.
=Po-lyp´te-rus= [Gr. _polypteros_, many-winged.]
=Po-ly´o-don= [Gr. _polys_, many; _odous_, tooth.]
=Pol´yp= [Gr. _polys_, many; _pous_, foot.]
=Pol´y-the-ism= [Gr. _polys_, many; _theos_, god.]
=Po-rif´e-ra= [Lat. _porus_, pore; _fero_, bear.]
=Pre-Pa-læ-o-lith´ic= [Lat. _præ_, before; Palæolithic.] The period of
time preceding the Ancient Stone Age.
=Pri-ma´tes= [Lat. _primus_, first.] An order of mammals.
=Pro-bos-cid´e-a= [Gr. _pro_, before; _bosko_, feed.]
=Pro-nu´cle-us= [Lat. _pro_, before; _nucleus_, kernel.]
=Pros-en-ceph´a-lon= [Gr. _pro_, before; _enkephalos_, brain.] A
fundamental segment of the brain.
=Pro-to-hip´pus= [Gr. _protos_, first; _hippos_, horse.]
=Pro-toph´y-ta= [Gr. _protos_, first; _phyton_, plant.]
=Pro´to-plasm= [Gr. _protos_, first; _plasma_, < _plasso_, form.]
=Pro-top´te-rus= [Gr. _protos_, first; _pteron_, wing.]
=Pro-to-zo´a= [Gr. _protos_, first; _zoon_, animal.]
=Pseu-do-he-red´i-ty= [Gr. _pseudes_, false; Lat. _heredita_, heirship.]
=Pseu-do-po´di-a= [Gr. _pseudes_, false; _pous_, foot.]
=Psy-cho-zo´ic= [Gr. _psyche_, soul; _zoe_, life.]
=Pter-i-doph´y-ta= [Gr. _pteris_, fern; _phyton_, plant.]
=Pter-o-sau´ri-a= [Gr. _pteron_, wing; _sauros_, lizard.]
=Pti-lo´pus cinc´tus.=
=Pu´pa=, pl. =pupæ= [Lat. doll, girl, f. of _pupus_, boy.] The third
stage of those insects that undergo a complete metamorphosis. Pupæ are
often surrounded by protective envelopes called cocoons.
=Quad-ru´la sym-met´ri-ca.=
=Qua-ter´na-ry= [Lat. _quaternarius_, consisting of four.]
=Ra-ti´tæ= [Lat. _ratis_, raft.] A group of birds whose sternum is
without a keel; aborted wings. Including ostriches, emus, moas, rheas,
etc.
=Rhi-noc´e-ros= [Gr. _rhis_, nose; _keras_, horn.]
=Rhi-zop´o-da= [Gr. _rhiza_, root; _pous_, foot.]
=Ro-den´ti-a= [Lat. _rodo_, gnaw.]
=Ro-ta´li-a Frey´er-i= [Lat. _rota_, wheel; Freyer.]
=Ro-ta-to´ri-a= [Lat. _rota_, wheel.]
=Ro´ti-fer= [Lat. _rota_, wheel; _fero_, bear.]
=Ru´mi-nant= [Lat. _ruminans_, ruminate.]
=Sai´tis pu´lex.=
=Saur-u´ræ= [Gr. _sauros_, lizard; _oura_, tail.] Jurassic birds having
lizard-like tails with distichous feathers, as Archæopterygidæ.
=Sca-phop´o-da= [Gr. _skaphos_, bowl, skiff; _pous_, foot.] A division of
molluscs.
=Sep´al= [Lat. _separ_, separate.] One of the individual leaves of a
calyx.
=Si-lu´ri-an= [Silures, ancient Celts in Wales.]
=Sim´i-a= [Lat. _simia_, ape.] A genus typical of Simiidæ and now
restricted to the orang.
=Si-mi´i-dæ= [Lat. _simia_, ape.] A family of Old World Anthropoidea.
=Sim-i-i´næ= [Lat. _simia_, ape.] A subfamily of Simiidæ with robust form
and molars tuberculated as in man and no ischial tuberosities, including
Chimpanzees, Gorillas, and Orangs.
=Si´nus veno´sus= [Lat.] Venous cavity. (1) In higher vertebrates the
main part of the auricular cavity. (2) In the lower vertebrates, a
dilitation at the termination of venous channels, forming a separate
chamber.
=Si-re´ni-a= [Lat. _siren_, siren.]
=Snags= [Norw. _snag_, a projecting point.] A branch on the antler of a
deer.
=So-mat´ic= [Gr. _soma_, body.] Pertaining to the body.
=So-ma-to-ge-net´ic= [Gr. _soma_, body; _genesis_, generation, origin.]
Originating in the body or soma through external influences.
=Sper-ma-to-zo´id= [Gr. _sperma_, seed, semen; _zoon_, animal.] Male
germ-cell; male, flagellate, (“ciliated”) sexual cell. At one time
supposed to be minute parasites in the semen, hence often called
_spermatozooa_.
=Sphinx fu-ci-form´is.=
=Spon´gi-o-plasm= [Gr. _spongion_, little sponge; _plasso_, form.]
=Steg-o-ceph´ala= [Gr. _stego_, cover; _kepale_, head.] Another name for
Labyrinthodonts.
=Sty-lo-nych´i-a.=
=Su-pra-œ-soph-ag´e-al= [Lat. _supra_, above; œsophagus.]
=Tar´si-us= [Gr. _tarsos_, any flat surface.]
=Tax-o-nom´ic= [Gr. _taxis_, orderly arrangement; _nemein_, distribute.]
Pertaining to systematic classification.
=Tel-e-os´to-mi= [Gr. _teleos_, perfect; _stoma_, mouth.] A division of
fishes with well-developed dentary and maxillary and membrane bones;
includes all fishes except Elasmobranchii and lower forms.
=Tel´e-osts= [Gr. _teleos_, perfect; _osteon_, bone.] A subdivision
of Teleostomi that includes most fishes; decussation of optic nerves;
non-contractile arterial bulb.
=Ter´ti-a-ry= [Lat. _tertius_, third.]
=Tet´ra-o cu´pi-do= [Lat. _tetrao_, pheasant; _Cupido_, the God of Love.]
=Thal-am-en-ceph´a-lon= [Gr. _thalamos_, chamber; _enkephalos_, brain.] A
fundamental segment of the brain.
=Thal´a-mi= [Gr. _thalamos_, chamber.] The lateral boundaries of the
thalamencephalon.
=Thal´loph´y-ta= [Gr. _thallos_, young branch; _phyton_, plant.]
=The-ro-mor´pha= [Gr. _ther_, beast; _morphe_, form.]
=Tho-mi´sus cit´re-us.=
=Ti-mor´.=
=Top´knots.= Crests or tufts of feathers growing on the heads of birds.
=Toxalbu´min= [Gr. _toxikon_, poison; _albumin_, < Lat. _albus_, white.]
=Tri-as´sic= [Gr. _trias_, three.]
=Tri´lo-bites= [Gr. _treis_, three; _lobos_, lobe.]
=Tu-ni-ca´ta= [Lat. _tunica_, tunic.] A class of Chordata called
Sca-squirts or Ascidians.
=Tynes= [AS. _tind_, prong.] The spike or prong of an antler.
=Un-gu-la´ta= [Lat. _unguis_, nail.] The order of hoofed mammals.
=U-ro-de´la= [Gr. _oura_, tail; _delos_, manifest.] The tailed Amphibians.
=U´te-rus= [Lat. _uterus_, womb.] The organ of a female animal in which
the young are protected and developed before birth.
=Vac´u-ole= [Lat. _vacuus_, empty.] The little cavities in cells
containing watery solutions.
=Ves´i-cle= [Lat. _vesicula_, little bladder.] Synonymous with vacuoles.
=Ve´na ca´va= [Lat.] _Hollow vein._ Either of the two great veins that
empty into the right auricle of the heart.
=Ven´tri-cles= [Lat. _ventriculus_, little belly.] One of the cavities of
the heart or brain.
=Ven´tral= [Lat. _venter_, belly.] Applied to the front (under) side of
the body.
=Ver´mes= [Lat. _vermis_, worm.]
=Ver-te-bra´ta= [Lat. _vertebratus_, jointed.]
=Ver´te-brate= [Lat. _vertebratus_, jointed.]
=Vi-vip´a-rous= [Lat. _vivus_, alive; _pario_, bear.] Applied to animals
which bring forth their young alive.
=Vis´ce-ra= [Lat. _viscera_, organs.] The internal organs of the body.
=Vol´vox glo-ba´tor= [Lat. _volvo_, roll; _globatus_, made into a ball.]
=Wat´tles= [AS. _watel_, hurdle.] Fleshy, naked processes depending from
the neck or head of a bird.
FOOTNOTES.
[1] One cubic millimeter of human blood alone, not to mention other
tissues of the body, contains over five million cells.
[2] Except in the maturation of _ova_ and _spermatozoids_.
[3] Bradford.
[4] Bradford.
[5] Socially, morally, and religiously.
[6] Lyell.
[7] Readers not familiar with Elementary Zoölogy will do well to consult
the Classification of Animals in Section VII.; and also the Diagram of
Development.
[8] Wallace.
[9] Belt.
[10] Wallace.
[11] Wallace.
[12] Wallace.
[13] Darwin.
[14] Darwin.
[15] Lloyd Morgan.
[16] Clodd.
[17] “Feelings and motions run parallel to each other, and where we do
not meet with actual feelings we suppose the presence of the elements of
feeling. But this parallelism would be most wonderful indeed if it were
a true parallelism consisting of two different and distinct lines. The
simplest conception of the case is the monistic view, which considers
the parallelism as an identity. Both motion and feeling are abstract
conceptions. A motion exists of itself no more than a feeling. The
reality from which the ideas motion and feeling have been abstracted is
one inseparable whole, which if viewed as an objective process appears
as motion, and if viewed from the subjective side appears as feeling.
Feelings can only be felt, not seen; but if we _could_ see them, we might
observe the elements of feeling wherever motion takes place.
“Fechner seems to have hit the mark, when he compared feeling and
motion to the inside and the outside curves of a circle; they are
entirely different and yet the same. The inside curve is concave,
the outside curve is convex. If we construct rules relating first to
the concave inside and then to the convex outside, we shall notice a
parallelism in the formulas; yet this parallelism will appear only in
the abstractions which have been made of one and the same thing from a
different aspect. It results from making two different abstractions. The
abstract conceptions form two parallel systems, but the real thing can be
represented as parallel only in the sense that it is parallel to itself;
it is the parallelism of identity. There is but one line and this one
line is concave if viewed from the inside, if viewed from the outside
convex.” Dr. Carus in “The Soul of Man,” p. 20.
[18] Central Soul (Dr. Carus).
[19] Clifford.
[20] It is more scientific to say a _Cosmic Soul immanent_ in the Cosmos.
“God, as I conceive him to be, is not less than a person, but more than a
person.” Dr. Paul Carus.
[21] Fiske.
[22] Fiske.
[23] “Religion is the conception by man of his relation to the infinite
universe and its source; and morality is the ever present guide of life
proceeding only from this relation.” Tolstoi.
[24] Fiske.
[25] Society also utterly ignores the rights of unborn children in
permitting the constant marriages of men and women having constitutions
tainted with hereditary diseases, as insanity, syphilis, tuberculosis,
etc.
[26] In Dipnoi, which are fishes with Amphibian characters, the paired
fins have each a central segmented axis which bears on each side a series
of radial pieces. The air bladder is a true lung, and is frequently used
as such. The heart shows indications of becoming three chambered (two
auricles and one ventricle). The left auricle contains arterial blood
from the lungs. There is an inferior vena cava. The nasal sacs open
posteriorly into the mouth.
INDEX.
Achromatin, 6.
Acquired Characters, 65, 71, 72, 76.
Actinozoa, 232.
Age, of Amphibians, 105.
Age, of Fishes, 101.
Age, of Mammals, 111.
Age, of Man, 114.
Age, of Molluscs, 98, 100.
Age, of Reptiles, 110.
Air-bladder, 236.
Allantois, 238.
Altruism, 223, 225.
Amblypoda, 111.
Amblystoma, 62, 63.
America, Central, 141.
America, South, 83, 145, 146.
America, North, development of, 85.
America, Archæan, 85.
America, Cretaceous, 87.
America, Tertiary, 88, 89.
America, tropical, 146, 147, 149.
Amia, 236, 237.
Amitosis, 28.
Ammonites, 100, 108.
Amnion, 238.
Amœba proteus, 10, 35, 230.
Amphibia, 96, 102, 103, 104, 105, 235, 238.
Amphibia, of snake-like form, 103.
Amphibia, generalized, 107.
Amphimixis, 46.
Amphineura, 234.
Amphioxus, 235.
Anaptomorphus, 111.
Ancon sheep, 49.
Angiospermæ, 245.
Animals, backboned, 96, 101, 103, 152.
Animals, birth rate of, 123.
Animals, coloration of, 126, 127.
Animals, death rate of, 123.
Animals, grass-eating, 137.
Animals, gregarious, 150.
Animals, multicellular, 4, 229.
Animals, multiplication of, 122.
Animals, snake-eating, 136.
Animals, segmented, 233, 234.
Animals, unicellular, 4, 229.
Animals, unsegmented, 233.
Annulata, 233.
Ant-bear, 123.
Antelope, desert, 127.
Antitoxines, 15.
Anthropoid Apes, 243.
Anthropoid Characters, 185.
Anthropomorphism, 211.
Anthropopithecus, 243, 244.
Anthropoidea, 240, 241.
Antlers, of deer, 14, 157.
Ants, 110, 123, 233.
Anura, 238.
Apes, anthropoid, 243.
Arachnida, 233.
Arcella, 16, 231.
Archæan land, Canadian, 86.
Archæan land, Blue Ridge, 86.
Archæan land, Rocky Mountain, 86.
Archæopteryx, 108, 238.
Archegosaurus, 103, 238.
Arctic regions, 151.
Argonaut, 98.
Armadillos, 114.
Arthropoda, 233.
Arthropods, 96, 98, 99.
Artificial Selection, 120, 121, 122.
Asteroidea, 232.
Atavism, 51, 52, 191.
Ateles, 242.
Attraction-sphere, 27.
Aves, 234, 238.
Aye-Ayes, 241.
Baboons, 243.
Baby, grasping power of, 192.
Bach, family of, 40.
Bacillus diphtheriæ, 16.
Bacillus, tetanus, 15.
Bacteria, 14.
Bacteria, nitrifying, 16.
Badger, 123.
Balanoglossus, 233.
Barriers, geographical, 166, 169.
Barriers, sexual, 166, 169.
Bat, 127, 130.
Bear, polar, 127.
Beavers, 157.
Bees, 59, 60, 102, 105, 110, 123, 163, 164.
Bee-eaters, 127.
Beetles, 147.
Belemnites, 108.
Berg adder, 149.
Biophors, 6.
Bipes, 115.
Blastids, 99.
Blastoidea, 233.
Blastula, 32.
Bird fancier, 120.
Birds, 96, 105, 107, 109, 144, 146, 147, 148, 152, 159.
Birds, courtship of, 153, 154.
Birds, eggs of, 132, 133, 134, 135.
Birds, excreta of, 142.
Birds, humming, 152, 157, 159.
Birds, paradise, 152.
Birds, reptilian, 108.
Birds, singing of, 154, 155.
Birds, snake-eating, 147, 149.
Boar, wild, 121, 157.
Body-cells, 45, 64.
Borneo, 138.
Bower birds, 155.
Brachiopoda, 232.
Brachiopods, 96, 97, 100, 102, 105.
Brain, 232, 233, 234, 235, 239.
Brain, development of, 199, 214, 215.
Brain, fœtal, 203, 204.
Brain, ideal section of, 203.
Brain, of fish, 199.
Brain, of lemur, 201.
Brain, of man, 203, 206, 211.
Brain, of marsupial, 200.
Brain, mind immanent in, 208.
Brain, of monkeys, 202.
Brain, psychic phenomena of, 206.
Brain, of reptile, 199.
Bryophyta, 244.
Bryozoa, 232.
Bull, 157.
Bullfinch, 154.
Butterflies, 59, 102, 110, 135, 139, 140, 141, 142, 143, 145, 147,
148, 158, 233.
Bulldog, 121.
Caducibranchiata, 178, 237.
Calamoichthys, 236.
Callithrix, 242.
Camel, 127.
Canaries, 154.
Carinatæ, 238.
Carnivora, 239.
Carus, Dr. Paul, 208.
Castration, 224.
Catarrhinæ, 241.
Caterpillar, 135, 138, 139, 140, 141, 145.
Cats, forest, 128.
Cattle, 169.
Cave bear, 114.
Cebidæ, 241, 242.
Cebus, 242.
Cells, xiii. 4.
Cells, body or somatic, xiv. 45, 64.
Cells, chemistry of, 4, 5.
Cells, daughter, 8.
Cells, encysted, 5.
Cells, flagellate, 29.
Cells, germ, xiv. 45, 54, 57, 65, 67, 161.
Cells, mother, 8.
Cells, nutrition of, 7.
Cells, reproduction of, 7, 25.
Cells, stinging, 231.
Cells, structure of, 5, 6.
Centipede, 98, 233.
Centrosome, 6, 27.
Cephalopoda, 234.
Cephalopods, 98, 100.
Ceratites, 105.
Ceratodus, 104, 105, 237.
Cercopithecidæ, 241, 242.
Cerebellum, 199, 206, 239.
Cerebrum, 199, 205, 239.
Cetacea, 239.
Character, 220, 226.
Characters, acquired, 65, 68.
Characters, anthropoid, 185.
Characters, congenital, 68.
Characters, non-transmission of acquired, 66, 70.
Characters, pithecoid, 185.
Characters, transmission of acquired, 66, 76.
Chatterers, 152.
Cheiroptera, 239.
Cheirotes, 115.
Chelonia, 238.
Children, rights of unborn, 224, 225.
Chimæroids, 106, 236.
Chimpanzee, 243, 244.
Chiromys, 241.
Chitons, 234.
Choice, 216, 223.
Chordata, 234.
Chromosomes, 6, 31.
Chrysothrix, 242.
Civilization, 215.
Classification, xi. xii.
Club-foot, 193.
Clubmosses, 100, 102, 245.
Cockroaches, 100, 234.
Codosiga umbellata, 23.
Cœcilia, 238.
Cœlenterata, 32, 96, 97, 99, 230, 231, 232.
Coloration, alluring, 128, 141.
Coloration, protective, 127, 128, 135.
Coloration, as recognition marks, 150.
Coloration, warning, 128, 144.
Columba livia, 120.
Comb-bearers, 231.
Condylarthra, 111.
Coniferæ, 105, 215.
Corals, 96, 97, 100, 102.
Corals, chain, 99, 100.
Corals, honeycomb, 99, 100.
Coral, hydroid, 99, 100.
Coreopsis, 142.
Cormorants, 134.
Cosmic Designer, 220.
Cosmos, Soul of, 210, 211.
Cows, 121.
Crabs, 233.
Creation, 211, 212.
Creodonta, 111.
Criminals, 223, 224.
Crinoidea, 96, 97, 99, 100, 232.
Crocodilia, 157, 238.
Crossopterygii, 101, 103, 105, 106, 109, 110, 236.
Cross-sterility, 167, 168, 169.
Crustacea, 102, 103, 233.
Cryptogams, 97, 244.
Ctenophora, 231.
Cuttlefish, 98, 234.
Cycadaceæ, 100, 102, 105, 245.
Cynocephalus, 243.
Cypresses, 100, 102, 245.
Cystids, 96, 97, 99.
Cystoidea, 232.
Cytoplasm, 4.
Daisy, ox-eyed, 142.
Deer, fallow, 169.
Deer, forest, 128, 129.
Design, 212.
Designer, 212.
Desmids, 12.
Diatoms, 12, 18.
Dicotyledones, 245.
Didelphia, 239.
Difflugia, 17, 230.
Dinosauria, 107, 109, 238.
Dipnoi, 101, 103, 106, 236, 237.
Disuse, 60, 63, 64, 216.
Dogs, 146.
Dragon flies, 100.
Dragons, flying, 107.
Dromatherium, 106.
Ducks, 134, 157.
Echinodermata, 96, 97, 99, 102, 231, 232.
Echinoidea, 232.
Ectoderm, 32, 230, 231.
Ectoplasm, 11.
Edentata, 239.
Elaps, 146, 149.
Elasmobranchii, 101, 103, 236.
Elephant, 112, 160.
Elimination, 125.
Elimination, climatic, 125.
Elimination, by enemies, 126.
Elimination, physical, 125.
Elimination, through competition, 126.
Elms, 216.
Embryo, coral, 123.
Embryo, instability of, 167.
Embryology, 33.
Endoderm, 32, 230, 231.
Endoplasm, 11.
Enteron, 231.
Enteropneusta, 233.
Environment, 54, 55, 64, 72, 73, 74, 75, 76, 77, 90, 127, 223.
Environment, complexity of, 90.
Environment and coloration, 126, 127.
Environment, unstable, 81.
Eohippus, 113.
Epencephalon, 199.
Epiblast, 32.
Epoch, Champlain, 85, 89.
Epoch, Eocene, 85.
Epoch, Glacial, 85, 89.
Epoch, Miocene, 85.
Epoch, Pliocene, 85.
Epoch, Terrace, 85, 89.
Equatorial-plate, 27.
Equus, 113.
Era, Archæan, 85, 94.
Era, Cenozoic, 85.
Era, Mesozoic, 85, 110.
Era, Palæozoic, 85, 86.
Era, Psychozoic, 85, 114.
Erythrolamprus, 149.
Eucalyptus, 132.
Evolution, 108.
Evolution, factors of, xiii.
Evolution, definition of, xiii.
Evolution, psychic, 215.
Evolution, social, 215, 225.
Evolution, goal of, 226.
Falcon, 127.
Fantail, 120.
Ferns, 100, 102, 244.
Fertilization, 29, 42.
Fertilization, cross, 162.
Fertilization, by humming birds, 161.
Fertilization, by insects, 161.
Fertilization, by the wind, 161.
Fertilization, of flowers, 161.
Fertilization, of frog’s eggs, 173.
Fertilization, of ovum, 29.
Fetichism, 209.
Finches, 157.
Fishes, 96, 101, 103, 104, 106, 109, 127, 152.
Fishes, Age of, 101.
Fishes, generalized, 102.
Fishes, with Amphibian characters, 101.
Flagellum, 19, 29.
Flies, 142.
Flower, simile of the, 213.
Flowers, 105, 144.
Flowers, conspicuous, 162.
Flowers, female, 161.
Flowers, fertilization of, 151.
Flowers, male, 160, 161.
Flowers, parts of, 160.
Flowers, primitive, 161.
Food, 58, 61.
Foraminifera, 12, 97, 102, 230.
Forest of Dean, 169.
Fossils, 94.
Friar Birds, 148.
Frog, development of, 173, 177.
Frogs, 135, 136, 137, 138, 146, 238.
Fuegians, 187.
Fungi, 244.
Game-cock, 157, 159.
Ganglia, 232, 233.
Ganoidei, 101, 103, 105, 106, 107, 109, 110, 237.
Garpikes, 105, 237.
Gasteropoda, 234.
Gastrula, 32.
Gastrulation, 32.
Gemmæ, 6.
Gemmules, 6.
Generations, alternations of, 231.
Geometer Moth, caterpillar of, 140.
Gephyrea, 2, 3.
Germ-cells, 45, 54, 57, 161.
Germ-cells, continuity of, 67, 70, 71.
Germ-cells, insulated, 65, 68, 70.
Gibbons, 243, 244.
Giraffe, 129, 130.
Globigerina, 13, 23.
Goat-sucker, 134.
Goniatites, 100, 102, 105.
Gorillas, 243, 244.
Graptolites, 96, 97, 99.
Grasses, 245.
Gregarina, 230.
Gregarinida, 230.
Gromia oviformis, 20.
Grouse, 159.
Gymnophiona, 238.
Gymnospermæ, 244.
Habitat, 54, 60.
Hair, 194.
Hapale, 242.
Hapalidæ, 241, 242.
Hares, 157, 160.
Hare, Polar, 127.
Hawk, 132.
Hearing, 195.
Heliconidæ, 145, 147, 148.
Hereditary Mass, 41, 43, 44, 46, 51.
Hereditary Mass, reduction of, 46.
Hereditary Threads, 31, 41.
Hereditary Units, ancestral, 43, 45.
Hereditary Units, maternal, 42.
Hereditary Units, paternal, 42.
Heredity, xiii. 39, 53, 54, 72, 73, 74, 75, 76.
Heredity, examples of, 40.
Heritages, atavistic, 49.
Heritages, augmentation of, 47.
Heritages, blending of, 47.
Heritages, latent, 49.
Heritages, mutually exclusive, 47.
Heritages, prepotency of, 47.
Heritages, struggle of, 48.
Heritages, totality of, 75.
Herons, 134.
Hesperornis, 238.
Hippopotamus, 111.
Hog, 111.
Holocephali, 236.
Holothuroidea, 232.
Hominidæ, 242, 243.
Homo delinquens, 52.
Homo sapiens, 52.
Honey-suckers, 148.
Horse, 112, 121, 122.
Horse, feet of, 113.
Horse, swiftness of, 122.
Horsetails, 100, 102, 244.
Hyaloplasm, 5.
Hydra, 231.
Hydroids, 231.
Hydrozoa, 231.
Hylobatinæ, 244.
Hylobates, 243, 244.
Hypoblast, 32.
Hyracoidea, 239.
Ichthyornis, 238.
Ichthyosauria, 107, 238.
Idioblasts, 6.
India, 141.
Infancy, 217, 218.
Infant, grasping power of, 192.
Infection, congenital bacterial, 53.
Infection, prenatal, 54.
Infusoria, 42, 230.
Insecta, 233.
Insectivora, 107, 239.
Insects, 100, 102, 110, 135, 137, 141, 143, 144, 147, 161, 162, 163,
164, 165.
Insect selection, 160, 164.
Invertebrates, 96, 234.
Irish elk, 114.
Isolation, geographical, 166.
Isolation, sexual, 166.
Java, 140, 142.
Jukes, the, 41.
Kaffir Boom, 130.
Kallima, 139, 140.
Kerivoula picta, 130.
Labyrinthodonts, 103, 104.
Lacertilia, 238.
Lagena, 13, 23.
Lamellibranchiata, 234.
Lampreys, 101.
Lampshells, 96, 232.
Lancelet, 235.
Larva, of Georgia butterfly, 138.
Law of battle, 158, 159.
Leaf-hoppers, 141.
Leaf insects, 140.
Leaf thrushes, 127.
Leeches, 233.
Lemuroidea, 111, 240.
Lepidosiren, 237.
Lepidosteus, 236.
Leptocardii, 234, 235.
Lichens, 244.
Life-forms, transmutations of, 93.
Life-forms, typical animal, 95.
Limestone, 13.
Lions, 127, 160.
Lislet-Geoffrey, 48.
Liverworts, 244.
Lizards, 144, 146, 158.
Locusts, palatable, 146.
Locusts, unpalatable, 146.
Longicornia, 147.
Lung-fishes, 103, 104, 237.
Macacus, 243.
Macaques, 243.
Magnolias, 111.
Malay Archipelago, 148.
Mammalia, 23, 240.
Mammals, 96, 107, 109, 111, 113, 144, 152, 160.
Mammals, Age of, 111.
Mammals, land, 165.
Mammals, placental, 239.
Mammals, reptilian, 106, 107, 111.
Mammals, snake-eating, 147, 149.
Man, 146, 216.
Man, age of, 114.
Man, ancestors of, 185, 186.
Man, brutish instincts of, 219.
Man, evolution of, 180, 188.
Man, imperfect adaptations of, 190.
Man, primitive, 187.
Man, quaternary, 114.
Mantis, 141.
Marmosets, 242.
Marsipobranchii, 234, 235.
Marsupials, 106, 107, 239.
Mastodon, 114.
Maturation, of ovum, 46.
Medulla, 199.
Mesencephalon, 199.
Mesenchyme, 231, 232.
Mesoblast, 32.
Mesoglœa, 230.
Mesoshippus, 113.
Metaphyta, 244.
Metaplasm, 4, 5.
Metazoa, 229, 230.
Metencephalon, 199.
Mice, 127.
Microgromia socialis, 22.
Microlestes, 106.
Midas, 242.
Mimicry, 128, 147.
Mind, 216.
Miohippus, 113.
Misumena vatia, 142.
Mitosis, 7, 25.
Moles, 127, 157.
Mollusca, 96, 98, 99, 100, 232, 233.
Monera, 230.
Monism, 208.
Monkeys, Capuchin, 242.
Monkeys, howling, 242.
Monkeys, New World, 241.
Monkeys, Old World, 241.
Monkeys, primitive, 111.
Monkeys, spider, 242.
Monkeys, squirrel, 242.
Monocotyledones, 245.
Monodelphia, 233.
Monotheism, 210.
Monotremes, 106, 107, 239.
Morula, 31.
Mosses, 244.
Moths, 59, 61, 102.
Mountains, Appalachian, 87.
Mountains, Coast Range, 89.
Mountains, Colorado, 88.
Mountains, Wahsatch, 88.
Multituberculata, 111.
Musk sheep, 151.
Mycetes, 242.
Myriapoda, 233.
Natural Selection, 119, 120, 124, 131, 132, 134, 137, 138, 141, 143,
147, 149, 152, 153, 158, 160, 162, 165, 225.
Nautiloids, 98.
Nautilus, 98.
Nemathelminthes, 232.
Nemertina, 233.
Newfoundland, 121.
Nicaragua, 146.
Noctiluca, 18, 230.
North America, development of, 85.
Notochord, 234, 235.
Nucleus, 6, 41, 44, 51.
Nucleus, as formative center, 8.
Nucleus, hermaphroditic, 43.
Nucleus, reduction of, 46.
Oaks, 245.
Odontornithes, 238.
Olfactory lobes, 199.
Optic lobes, 199.
Ontogeny, 178, 179, 180.
Onychophora, 233.
Oösperm, 31, 173.
Oösperm, segmentation of, 31.
Operculum, 196.
Ophidia, 238.
Opponens Hallucis, 190, 191.
Orangs, 243, 244.
Orchis, 141, 163.
Ornithodelphia, 239.
Orohippus, 113.
Orthoceratites, 98, 99, 100.
Osteoblasts, 13.
Osteoclasts, 13.
Ostracoderms, 100, 101.
Ova, 56.
Ovum, fertilized, 180.
Ovum, human, 28, 31.
Ovum, maturation of, 29, 43, 46.
Oyster, 234.
Palms, 245.
Pandorina morum, 24, 31.
Pangenesis, 66, 69.
Pangenesis, modified, 68, 71.
Pangennæ, 6.
Paramecium, 230.
Parrots, 127.
Parthenogenesis, 42, 59.
Partridge, 134.
Paupers, 223.
Peacocks, 152.
Pelicans, 134.
Perception, 207.
Perennibranchiata, 177, 238.
Period, Cambrian, 85, 96.
Period, Carboniferous, 85, 87, 102.
Period, Cretaceous, 85, 88, 108, 110.
Period, Devonian, 85, 87, 100.
Period, Jurassic, 85, 88, 106, 110.
Period, Ordovician, 96.
Period, Permian, 104.
Period, Quaternary, 85, 89, 113.
Period, Silurian, 85, 87, 96, 98.
Period, Tertiary, 85, 112.
Period, Triassic, 85, 105, 110.
Peripatus, 233.
Phanerogams, 244.
Pheasants, 134, 152.
Phosphorescence, 20.
Phrynocephalus mystaceus, 141.
Phylogeny, 178, 179, 180.
Pig, domesticated, 121.
Pigeons, Wild Rock, 120.
Pigeons, fantail, 120.
Pigeons, fruit-eating, 127.
Pigeons, pouter, 120.
Pigeons, tumbler, 120.
Pigeons, white-headed fruit, 131.
Pines, 100, 102, 245.
Pisces, 234, 236.
Plagiostomi, 236.
Plants, land, 96, 97, 99, 100.
Plants, flowering, 100, 110, 244.
Plants, flowerless, 100, 244.
Plants, generalized, 102.
Plants, unicellular, 4.
Plants, multicellular, 4.
Plastids, 5.
Platyhelminthes, 232.
Platyrrhinæ, 241.
Pleuracanthus, 103.
Pliohippus, 113.
Plovers, 131.
Polar bodies, 29.
Polyodon, 237.
Polyps, 32, 231.
Polypterus, 236.
Polytheism, 210.
Poplars, 245.
Porifera, 25, 230.
Pouter, 120.
Preferential mating, 157, 159, 169.
Primates, 239.
Primitive man, 187.
Primrose, 163.
Proboscidea, 239.
Pronucleus, female, 29, 31.
Pronucleus, male, 29, 31.
Prosencephalon, 199.
Protective Imitation of Particular Objects, 138.
Protective Resemblance, 128.
Proteus, 237.
Protohippus, 113.
Protophyta, 244.
Protoplasm, 4, 5, 33, 44.
Protopterus, 237.
Protozoa, 229, 230.
Protozoa, flagellate, 24, 25.
Protozoa, colonial, 22, 25.
Pseudo-heredity, 53.
Pseudopodia, 12.
Psychic phenomena, 207.
Ptarmigan, 131.
Pteridophyta, 244.
Pterosauria, 107, 109, 238.
Ptilopus cinctus, 131.
Quadrula, 17, 230.
Recognition Marks, 150.
Reducing process, 46.
Redwood, 111.
Regeneration of lost parts, 50.
Reptiles, 96, 104, 106, 107, 109, 110, 152, 157, 235, 238.
Reptiles, Age of, 110.
Reptiles, generalized, 104, 107.
Reptiles, land, 107.
Reptiles, sea, 107.
Reptiles, extinction of, 125.
Reptiles, of bat-like form, 107.
Reptiles, of lizard-like form, 104.
Rabbit, 151.
Radiolaria, 97.
Ratitæ, 238.
Raven, 132.
Rays, 106, 236.
Recognition Marks, 128, 150, 169.
Religion, 221, 222.
Rhinencephalon, 199.
Rhinoceros, 112.
Rhizopoda, 230.
Ribs, 194.
Rocks, table of stratified, 95.
Rodentia, 239.
Rotalia, 13, 23.
Rotatoria, 232.
Rotifer, 232.
Ruminants, 111, 137.
Rupture, 190.
Saitis pulex, 156.
Salamanders, 103, 147.
Salamandra, 237.
Salmons, 157, 158, 237.
Saururæ, 238.
Scaphopoda, 234.
Scorpions, 99, 233.
Sea, Cretaceous, 68.
Sea, Palæozoic, 86.
Sea-anemones, 231.
Sea-cucumbers, 232.
Seals, 160.
Seaweeds, 96, 97, 244.
Sea-urchins, 97, 99, 232.
Selfishness, 216.
Selection, artificial, 120, 121.
Selection, insect, 160, 164.
Selection, natural, 119, 120, 122, 124, 131, 132, 134, 137, 138, 141,
143, 147, 149, 152, 153, 158, 160, 162, 165, 225.
Selection, physiological, 169.
Selection, rational, 214.
Selection, sexual, 152, 153, 154, 157, 158, 164.
Sharks, 106, 107, 109, 235.
Sharks, primitive, 100.
Sheep, 121.
Sheep, heath, 169.
Sheep, merino, 169.
Shrimps, 103, 233.
Simia, 243, 244.
Simiidæ, 242, 243, 244.
Simiinæ, 244.
Sinus venosus, 236.
Siredon, 62, 63.
Siren, 237.
Sirenia, 239.
Skye-terrier, 121.
Sloths, 114.
Snail, 234.
Snakes, 135, 136, 137, 138, 147, 148, 149.
Snipe, 131.
Social evolution, goal of, 220.
Soil, 69.
Somatic-cells, 45.
Spermatozoid, 29, 43, 56.
Sphinx fuciformis, 138.
Spider, 141, 142, 143, 146, 158, 233.
Spider, love-dance of, 156.
Spindle, 27.
Sponges, 25, 96, 97, 99, 230.
Spongioplasm, 5.
Sports, 48, 49, 53.
Spring-bok, 151.
Spruces, 245.
Squids, 98, 234.
Squirrels, 157.
Stag, 157.
Star-fishes, 96, 97, 99, 232.
Stegocephala, 103, 104, 106, 238.
Sticklebacks, 157, 158.
Stone-lily, 232.
Storks, 134.
Struggle for Existence, 124.
Sturgeon, 237.
Stylonychia, 10, 230.
Sumatra, 140.
Sunbirds, 130, 131.
Survival of the Fittest, 120, 122, 138, 143.
Symmetry, bilateral, 231, 232, 233.
Symmetry, radial, 231.
Sympathy, 216.
Tadpoles, 58, 59, 174, 175.
Tail, 195.
Tanagers, 152.
Tapir, 112.
Tarsius, 241.
Tee Tees, 242.
Teleostomi, 236.
Teleosts, 101, 106, 109, 110, 237.
Temperature, 54, 61.
Tetrao cupido, 159.
Thalamencephalon, 199.
Thalami, 199.
Thallophyta, 244.
Theromorpha, 104, 105, 106, 238.
Thomisus citreus, 141.
Threads, chromatin, 6.
Threads, hereditary, 31, 41.
Threads, nuclear, 6.
Tiger, protective coloration of, 128, 129.
Tiger, saber-toothed, 114.
Timor, island of, 132.
Toad, 238.
Tortoises, 157.
Toxalbumin, 16.
Toxines, 15.
Tree of Life, 182, 183, 184.
Trilobites, 96, 97, 98, 99, 100, 103, 233.
Triton, 175, 237.
Tumbler, 120.
Tunicata, 234.
Turtledoves, 154.
Ungulata, 239.
Ungulates, even-toed, 111.
Ungulates, odd-toed, 111.
Units, hereditary, 41, 42, 43, 45.
Units, invisible, 7.
Units, morphological, 4.
Units, physiological, 6, 8.
Units, structural, 4.
Units, visible, 7.
Urodela, 237.
Use, 60, 63, 64, 216.
Uterus, displacements of, 190.
Vacuole, 5.
Variations, 39, 46, 54, 120, 143, 167, 168.
Variations, blastogenetic, 54, 55, 56.
Variations, examples of, 39.
Variations, harmful, 168.
Variations, neutral, 168.
Variations, somatogenetic, 54, 55, 60.
Variations, through amphimixis, 46, 166.
Variations, useful, 168.
Varieties, commencing species, 168.
Varieties, isolation of, 166.
Velvet, 14.
Vena cava, 236, 237.
Ventricles, 233, 236, 237.
Vermes, 232.
Vermiform appendix, 194.
Vertebrata, 100, 105, 108, 234.
Vestigial structures, 198.
Volvox globator, 24, 32.
Waders, 157.
Wasp, 146, 147.
Weevils, 147.
Whales, 107, 124, 165.
White blood-corpuscles, 15.
Will, 207, 223.
Woodcock, 131.
Woodpecker, 155, 157.
Worms, 232.
Worms, earth, 233.
Worms, flat, 232.
Worms, round, 232.
Worms, sea or marine, 96, 233.
Worms, star, 233.
Worms, unsegmented, 232.
Zebra, 129.
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