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THE

SCIENCE- HISTORY
OF THE UNIVERSE

FRANCIS ROLT - WHEELER

Managing Editor

IN TEN VOLUMES

THE CURRENT LITERATURE PUBLISHING COMPANY

NEW YORK

1909

( )

INTRODUCTIONS BY

Professor E. E. Barnard, A.M., Sc.D.,
Yerkes Astronomical Observatory.

Professor Charles Baskerville, Ph.D., F.C.S.
Professor of Chemistry, College of the City of New York.

Director William T. Hornaday, Sc.D.,
President of New York Zoological Society.

Professor Frederick Starr, S.B., S.M., Ph.D.,
Professor of Anthropology, Chicago University.

Professor Cassius J. Keyser, B.S., A.M., Ph.D.,
Adrain Professor of Mathematics, Columbia University

Edward J. Wheeler, A.M., Litt.D.,
Editor of 'Current Literature.'

Professor Hugo Munsterberg, A.B., M.D., Ph.D., LL.D.,
Professor of Psychology, Harvard University.

EDITORIAL BOARD

Vol. I — Waldemar Kaempffert,
'Scientific American/

Vol. II — Harold E. Slade, C.E.

Vol. Ill — George Matthew, A.M.

Vol. Ill — Professor William J. Moore, M.E.,

Assistant Professor of Mechanical Engineering, Brooklyn

Polytechnic Institute.

Vol. IV — William Allen Hamor,

Research Chemist, Chemistry Department, College of the

City of New York.

Vol. V — Caroline E. Stackpole, A.M.,
Tutor in Biology, Teachers' College, Columbia University.

Vol. VI— Wm. D. Matthew, A.B., Ph.B., A.M., Ph.D.,

Assistant Curator, Vertebrate Paleontology, American

Museum of Natural History.

Vol. VI — Marion E. Latham, A.M.,
Tutor in Botany, Barnard College, Columbia University.

Vol. VII— Francis Rolt-Wheeler, S.T.D.

Vol. VII— Theodore H. Allen, A.M., M.D.

Vol. VIII — L. Leland Locke, A.B., A.M.,
Brooklyn Training School for Teachers.

Vol. VIII— Franz Bellinger, A.M., Ph.D.

Vol. IX— S. J. Woolf.

Vol. IX— Francis Rolt-Wheeler, S.T.D.

Vol. X — Professor Charles Gray Shaw, Ph.D.,
Professor ol Ethics and Philosophy, New York University.

Leonard Abbott,
Associate Editor 'Current Literature/

Digitized by the Internet Archive

in 2012 with funding from

The Institute of Museum and Library Services through an Indiana State Library LSTA Grant

http://archive.org/details/sciencehistoryofOOrolt

THE

SCIENCE - HISTORY
OF THE UNIVERSE

VOLUME V

BIOLOGY

By CAROLINE E. STACKPOLE

Copyright, 1909, by
CURRENT LITERATURE PUBLISHING COMPANY

CONTENTS

CHAPTER PAGE

I The Science of Life i

II The Nature of Life 8

III The Physiological Idea of Life 22

IV The Origin of Life 38

V Cell Life 55

VI Cell Division yy

VII Organic Functions 89

VIII Life Processes 106

IX Origin of Species 124

X Morphology and Embryology 138

XI Evidences of Organic Evolution 161

XII Natural Selection 180

XIII Sexual Selection 213

XIV Factors Other Than Selection 224

XV Heredity 237

XVI Adaptation 265

BIOLOGY

CHAPTER I
biology: the science of life

Life, that strange, mysterious, unknown something
which flies through the viewless air, flashes through the
ocean's depths, blushes in the petals of a rose and mani-
fests itself in a thousand marvelous forms — can science
grasp, define or explain it? Death, that wondrous change
which sooner or later stills the activities of all forms of
life and returns them to the realm of the lifeless — what is
its nature? Why is it necessary? Can science understand
or control it? These inquiries and others like them
which have troubled the human mind in all ages are the
fundamental problems of the science of life.

With the dawn of human consciousness there must have
come the realization that this is an earth with two worlds
— the living and the lifeless. The progress of the ages
has not lessened the contrast; and to-day, men of science,
recognising the great chasm between life and death, be-
tween the living and the lifeless on the earth, are com-
pelled to group the natural sciences into the Biological
Sciences dealing with living things or organisms; and
the Abiological Sciences, or Physical Sciences, dealing
with lifeless matter. The biological sciences are known
collectively as biology, which is therefore often defined as
the science of life, of living things, or of living matter.
"But living matter," say Sedgwick and Wilson in their
'General Biology/ "is only ordinary matter which has en-

2 BIOLOGY

tered into a peculiar state or condition. And hence biology
is more precisely defined as the science which treats of
matter in the living state."

If the term biology be used in its widest sense of Life-
lore to include all the results of the scientific study of
living creatures, it may be said to have had its foundations
in antiquity. But if the term is restricted to the use as
defined above — that is, to the study of the vital phenomena
common to both plants and animals — it is quite modern.

Biology is not a new name for the older science known
as Natural History, nor is it, as is often thought, a com-
bination of botany and zoology, it is rather a unified
science of life. Taken in this sense, the science has been
in existence but little more than a hundred years. The
history of its development is the history of the splitting up
of the Natural History of earlier times into the separate
sciences known to-day, physics, chemistry, botany, zoology,
etc. ; a recognition of the essential similarity of the vital
functions of all living things, plants or animals; and the
development of a separate science for the study of these
phenomena. Huxley, in his essay "On the Study of
Biology," writes of its history in these words :

"At the revival of learning, knowledge was divided into
two kinds — the knowledge of nature and the knowledge
of man ; for it was the current idea then — and a great deal
of that ancient conception still remains — that there was a
sort of essential antithesis, not to say antagonism, between
nature and man; and that the two had not very much to
do with one another, except that the one was oftentimes
exceedingly troublesome to the other. Tho it is one of
the salient merits of our great philosophers of the seven-
teenth century, that they recognised but one scientific
method, applicable alike to man and to nature, we find this
notion of the existence of a broad distinction between
nature and man in the writings both of Francis Bacon
and of Thomas Hobbes. Hobbes says: 'The register of
knowledge of fact is called history. Whereof there be two

THE SCIENCE OF LIFE 3

sorts, one called natural history; which is the history of
such facts or effects of nature as have no dependence on
man's will; such as are the histories of metals, plants,
animals, regions and the like. The other is civil history;
which is the history of the voluntary actions of men in
commonwealths/ "

Thus all history of fact was divided into these two
great groups of natural and of civil history. As time went
on, and the various branches of human knowledge became
more distinctly developed and separated from one an-
other, it was found that some were much more susceptible
of precise mathematical treatment than others. The publi-
cation of the "Principia" of Newton showed that precise
mathematical methods were applicable to those branches
of science such as astronomy, and what is now called
physics, which occupy a very large portion of the domain
of what the older writers understood by natural history.

Time went on, and yet other branches of science de-
veloped themselves. Chemistry took a definite shape; and
since all these sciences, such as astronomy, natural philos-
ophy and chemistry, were susceptible either of mathemati-
cal treatment or of experimental treatment, or of both, a
broad distinction was drawn between the experimental
branches of what had previously been called natural his-
tory and the observational branches — those in which ex-
periment was (or seemed) of doubtful use, and where, at
that time, mathematical methods were inapplicable.

Under these circumstances the old name of "Natural
History" stuck by the residuum of those phenomena which
were not, at that time, susceptible of mathematical or
experimental treatment; that is to say, those phenomena
of nature which come now under the general heads of
physical geography, geology, mineralogy, the history of
plants, and the history of animals. It was in this sense that
the term was understood by the great writers of the middle
of the last century, Buffon and Linnaeus, by Buffon in his
great work, the 'Histoire Naturelle Generate/ and by

4 BIOLOGY

Linnaeus in his splendid achievement, the "Systema
Naturae." The subjects they deal 'with are spoken of as
"Natural History," and they called themselves and were
called "Naturalists." It is clear that such was not the
original meaning of these terms; but that they had by this
time, acquired a signification widely different from that
which they possessed primitively.

Despite the marvelous progress made by science at
the latter end of the eighteenth and the beginning
of the nineteenth century, thinking men began to discern
that under this title of "Natural History" there were in-
cluded very heterogeneous constituents. For example, it
was not hard to see that geology and mineralogy were,
in many respects, widely different from botany and
zoology; that a man might obtain an extensive knowledge
of the structure and functions of plants and animals with-
out having need to enter upon the study of geology or
mineralogy, and vice versa; and, further as knowledge
advanced, it became clearer that there was a great analogy,
a very close alliance, between those two sciences, of bot-
any and zoology, which deal with living beings, while
they are much more widely separated from all other
studies. Therefore, it is not wonderful that, at the begin-
ning of the nineteenth century, in two different countries,
and apparently without any intercommunication, two
famous men clearly conceived the notion of uniting the
sciences which deal with living matter into one whole,
and of dealing with them as one discipline.

In fact, there were three men to whom this idea oc-
curred contemporaneously, altho but two who carried it
into effect, and only one who worked it out completely.
These persons were the eminent physiologist Bichat; the
great naturalist Lamarck, in France, and a distinguished
German, Treviranus. Bichat assumed the existence of a
special group of "physiological" sciences. Lamarck, in a
work published in 1801, for the first time made use of the
name "Biologie," from the two Greek words which signify

THE SCIENCE OF LIFE 5

a discourse upon life and living things. About the same
time it occurred to Treviranus, that all those sciences
which deal with living matter were essentially and funda-
mentally one, and ought to be treated as a whole; and, in
the year 1802, he published the first volume of what he
also called "Biologic" Treviranus's great merit lies in
this, that he carried out his idea, and wrote the very re-
markable work above mentioned. It consists of six vol-
umes, and occupied its author for twenty years — from
1802 to 1822. That is the origin of the term "Biology,"
which denotes the whole of the sciences which deal with
living things, whether they be animals or whether they
be plants.

After discussing the origin of the science of biology,
the next questions that naturally present themselves are
with reference to the extent and nature of its scope. In
its strict technical sense, Biology denotes all the phe-
nomena which are exhibited by living things, as dis-
tinguished from those which are not living; but while
that secondary definition suffices in the domain of the lower
animals and plants, it is found to involve considerable
difficulties in an investigation of the higher forms of
living things. For whatever views may be entertained
about the nature of man, one thing is perfectly certain,
that he is to be considered a living creature. Hence, a
strict interpretation of such a definition must include
man and all his ways and works under the head of biology ;
in which case, psychology, politics, and political economy
would be absorbed into the province of Biology.

It has been found convenient to set human psychology
and sociology apart from biology, but the progress of these
sciences in the past century has clearly shown that they
are intrinsically inseparable from biology or that they at
least find many of their fundamental principles in the gen-
eral science of life.

Even without the psychological and sociological phases
of human life, the field covered by biology as thus under-

6 BIOLOGY

stood is so wide as to necessitate a subdivision of the sub-
ject into a number of branches, to which are usually as-
signed the rank of distinct sciences. As already pointed
out, the usual division of biology into botany and zoology
has the great advantage of practical convenience, since, as
a matter of fact, most biologists devote their attention
mainly either to plants alone, or to animals alone. From
a scientific point of view, however, a better subdivision is
into Morphology and Physiology. The former is based
upon the facts of form, structure and arrangement, and is
essentially statical ; the latter upon those of action or func-
tion, and is essentially dynamical. But morphology and
physiology are so intimately related that it is impossible to
separate either subject absolutely from the other, for which
reason authors speak of plant morphology and animal mor-
phology, plant physiology and animal physiology.

There are further subdivisions. Thus on the plant or
animal side of biology there are the following subsciences :
Anatomy — the science of structure, the term being usually
applied to the coarser and more obvious composition of
plants or animals; Histology — microscopical anatomy, the
ultimate analysis of structure by the aid of the micro-
scope, separated from anatomy only as a matter of con-
venience; Taxonomy — the classification of living things,
based chiefly on the phenomena of structure; Distribution
— considering the position of living things in space and
time, their distribution over the present face of the earth
and their distribution and succession at former periods,
as displayed in fossil remains; Embryology — the science
of development from the germ, including many problems
pertaining both to morphology and physiology; and Phys-
iology (including pathology) — the special science of the
functions of the individual in health and in disease. The
very highly specialized biological sciences, ornithology
(birds), entomology (insects), herpetology (reptiles),
conchology (shells), lichenology (lichens), bryology
(mosses), mycology (fungi), etc., apply to the groups of

THE SCIENCE OF LIFE 7

animals and plants indicated by the names of these
sciences. They are chiefly concerned with classification
and hence deal largely with details of structure.

While the scope of biology may be thus skeletonized, it
must be pointed out with emphasis that the common con-
ception of biology as simply a combination of botany and
zoology is one which tho convenient and indeed neces-
sary for practical purposes, and for extended study and re-
search, does not concern the present treatment. Dealing
with organic structures and functions in connection with
their causes, conditions, concomitants and consequences,
Biology cannot divide itself into Animal Biology and Veg-
etable Biology; since the same fundamental classes of
phenomena are common to both. It is with these general
vital phenomena common to both plants and animals that
this work is concerned, hence in considering the general
problems of the science of biology the familiar division
into botany and zoology is recognised only occasionally as
a matter of convenience. Undoubtedly confusion will be
avoided if it is kept in mind that 'General Biology' is the
subject under view. This term does not designate a par-
ticular member of the group of biological sciences, "but is
only a convenient phrase, which has recently come into
use for the general introductory study of biology. It in-
cludes a description of the general properties of living
matter as revealed in the structures and actions of living
things, and may serve as the basis for subsequent study of
more special branches of the science. It deals with the
broad characteristic phenomena and laws of life as they
are illustrated by the thoro comparative study of a series
of plants and animals taken as representative types; but
inasmuch as all the varied phenomena which come under
observation are in the last analysis due to the properties
of matter in the living state, the biologist ever remembers
that this matter and these properties are the goal of study."

CHAPTER II

THE NATURE OF LIFE

More puzzling than the riddle propounded by the fabled
Sphynx is the problem suggested by the title of this chap-
ter. "What is life?" is a question which has been asked
by the scholars of all ages and man to-day is no nearer
a final answer than were the philosophers in the earliest
centuries of the historic era. Modern science has vastly
extended knowledge of the phenomena which are called
vital but has failed to tell what life is. Thus according to
Herbert Spencer's so-called proximate definition, which of
the many definitions of life has attracted most attention,
life is the continuous adjustment of internal relations to
external relations. This definition Spencer has explained
as follows:

"All vital actions, considered not separately but in their
ensemble, have for their final purpose the balancing of cer-
tain outer processes by certain inner processes. There are
unceasing external forces tending to bring the matter of
which organic bodies consist, into that state of stable
equilibrium displayed by inorganic bodies; there are inter-
nal forces by which this tendency is constantly antago-
nized, and the perpetual changes which constitute Life
may be regarded as incidental to the maintenance of the
antagonism. To preserve the erect posture, for instance,
we see that certain weights have to be neutralized by cer-
tain strains: each limb or other organ, gravitating to the
Earth and pulling down the parts to which it is attached,

THE NATURE OF LIFE 9

has to be preserved in position by the tension of sundry
muscles; or in other words, the group of forces which
would if allowed bring the body to the ground, has to be
counterbalanced by another group of forces. Again, to
keep up the temperature at a particular point, the external
process of radiation and absorption of heat by the sur-
rounding medium, must be met by a corresponding internal
process of chemical combination, whereby more heat may
be evolved ; to which add, that if from atmospheric changes
the loss becomes greater or less, the production must be-
come greater or less. And similarly throughout the or-
ganic actions in general.

"When we contemplate the lower kinds of life, we see
that the correspondences thus maintained are direct and
simple; as in a plant, the vitality of which mainly consists
in osmotic and chemical actions responding to the co-
existence of light, heat, water and carbonic acid around it.
But in animals, and especially in the higher orders of them,
the correspondences become extremely complex. Materials
for growth and repair not being, like those which plants
require, everywhere present, but being widely dispersed
and under special forms, have to be found, to be secured,
and to be reduced to a fit state for assimilation. Hence the
need for locomotion ; hence the need for the senses ; hence
the need for prehensile and destructive appliances; hence
the need for an elaborate digestive apparatus.

"Observe, however, that these successive complications
are essentially nothing but aids to the maintenance of the
organic balance in its integrity, in opposition to those
physical, chemical and other agencies which tend to over-
turn it. And observe, moreover, that while these succes-
sive complications subserve this fundamental adaptation of
inner to outer actions, they are themselves nothing else but
further adaptations of inner to outer actions. For what
are those movements by which a predatory creature pur-
sues its prey, or by which its prey seeks to escape, but
certain changes in the organism fitted to meet certain

io BIOLOGY

changes in its environment? What is that compound
operation which constitutes the perception of a piece of
food, but a particular correlation of nervous modifications,
answering to a particular correlation of physical proper-
ties ? What is that process by which food when swallowed
is reduced to a fit form for assimilation, but a set of me-
chanical and chemical actions which distinguish the food?
Whence it becomes manifest, that while Life in its simplest
form is the correspondence of certain inner physico-chem-
ical actions with certain outer physico-chemical actions,
each advance to a higher form of life consists in a better
preservation of this primary correspondence by the estab-
lishment of other correspondences.

"Divesting this conception of all superfluities and reduc-
ing it to its most abstract shape, we see that Life is de-
finable as the continuous adjustment of internal relations
to external relations."

It is clear that this definition in the last analysis is but
a general statement of the fundamental vital relations
existing between living matter and lifeless phenomena. It
does not really define life. Other authors have done no
better, in fact their definitions have been less inclusive.
But aside from attempts at forming abstract definitions of
life there are some significant considerations regarding
living matter which have been important in the develop-
ment of knowledge of the differences between the living
and the lifeless and of the working of the mechanism of
life.

The living and the lifeless present a fundamental con-
trast. "If the development of the conception of life be fol-
lowed back," says Verworn, "when mankind had no pre-
sentiments of all the occupations that accompany a highly
developed culture, .when he was unacquainted with fire,
when he did not know how to make even the most primi-
tive tools, the conclusion is reached that the conception
sprang from the combination of a number of simple phe-
nomena, which early man discovered by self-observation,

THE NATURE OF LIFE u

especially those phenomena that are associated with evi-
dent movements, such as locomotion, breathing, nutrition,
the heartbeat and others. In fact, it is not difficult to
analyze into their primary constituents the complex occu-
pations of our present life, and to recognise that its
diversity is produced by various combinations of a few-
elementary phenomena, such as nutrition, respiration,
growth, reproduction, movement and the production of
heat."

It must be remembered, however, that such a concep-
tion of life is limited to the vital phenomena of human
beings, while the field of life is far greater. Animals and
plants likewise exhibit vital phenomena, and it may be
asked whether these latter are the same as or different
from the phenomena that prevail among men. It is evident
that all living organisms must be included in the sphere
of physiological investigation, the flower and the worm
equally with man. Hence the first duty of physiology is to
mark out the field of the living, to determine what is living
and what is not living — an undertaking that is more diffi-
cult than it appears.

The conception of life has not always been the same.
It has experienced fundamental changes in the course of
the development of the human species. Formed first with
respect to mankind, it was early extended to other objects.
With primitive races, the conception was much wider than
?t present, and they termed living what is no longer re-
garded as such. With them stars, fire, wind and waves
were beings endowed with life and mind, and they were
personified in the image of man. The remains of these
ideas are still found in the mythology of the classic and
modern races. In the course of time the distinction be-
tween living and lifeless has been made constantly
sharper, but even to-day a child regards a steam engine
as a living animal. The child is guided more or less con-
sciously by the same criterion as the primitive races, who,
from the fact of motion, considered as living the dancing

12 BIOLOGY

flame of a fire or a moving wave. In fact, of all vital
phenomena, motion is that which gives most strongly the
impression of living.

It may be said that only primitive races and children are
misled by the criterion of motion, and that the civilized and
adult man, who is versed in a knowledge of life, is capable
of deciding easily in any given case between the living
and the lifeless. But this is not always true. For example,
are dried grains living or lifeless ? Is a lentil that has lain
unchanged in a chest for years living? Scientific men
themselves are not agreed upon this point. The lentil,
when dry, does not show phenomena of life, but, if placed
in moist earth, it can at any moment be induced to do so.
It then sprouts and grows into a plant.

The decision between the living and the lifeless becomes,
however, much more difficult with objects that are not
commonly seen in daily life — e.g., certain microscopic
things. Long observation and very detailed investigation
are frequently required in order to determine whether
certain bodies that are found in a liquid by microscopic
examination are living or not. If a drop of the dregs be
taken from a bottle of weissbeer and examined with the
microscope, it will be found that the liquid contains in-
numerable small pale globules, often clinging together in
groups of two or three, completely at rest so long as they
are observed, and showing no trace of movement or other
change. Very similar small globules may be observed with
a microscope in a drop of milk. The two kinds of globules
can be distinguished from one another by strong magnify-
ing powers only.

No trace of vital phenomena can be found in either by
the most patient and continued microscopic examination,
yet the two objects are as widely different as a living
organism and a lifeless substance ; for the globules from
the beer are the so-called yeast-cells, the active agent in
the fermentation of the beer, and are fully developed,
unicellular, living organisms, while the globules from the

THE NATURE OF LIFE 13

milk are lifeless droplets of fat, which, by their abundant
presence and their reflection of light from all sides, give
to the milk its white color. The manifestation of motion,
which is often ascribed to an internal source because no
external source is directly visible, thus frequently misleads
to the assumption of life.

Hence, under certain circumstances it is not at all
easy to distinguish the living from the lifeless, and it is
accordingly clear that the first duty of physiology must be
to inquire after the criteria of such a distinction — i.e.,
mentally to circumscribe the subject-matter, life, in rela-
tion to non-living nature.

The distinction between living and lifeless matter is
made still more complicated by the fact that the living
substance of the human body, or of any animal or plant, is
only the transformed lifeless matter of the food which has
been taken into the body and has there assumed, for a time,
the living state. Lifeless matter in the shape of food is
continually streaming into all living things on the one hand
and passing out again as waste on the other. In its
journey through the organism some of this matter enters
into the living state and lingers for a time as part of the
bodily substance. But sooner or later it dies, and is then
for the most part cast out of the body (tho a part may
be retained within it, either as an accumulation of waste
material, or to serve some useful purpose). Matter may
thus pass from the lifeless into the living state and back
again to the lifeless, over and over in never-ending cycles.
A living plant or animal is like a whirlpool into which,
and out of which, matter is constantly streaming, while the
whirlpool maintains its characteristic form and indi-
viduality.

''To put the matter in the most general shape," says
Huxley, "the body of the organism is a sort of focus to
which certain material particles converge, in which they
move for a time, and from which they are afterward
expelled in new combinations. The parallel between a

H BIOLOGY

whirlpool in a stream and a living being, which has often
been drawn, is just as it is striking. The whirlpool is
permanent, but the particles of water which constitute it
are incessantly changing. Those which enter it on the one
side are whirled around and temporarily constitute a part
of its individuality; and as they leave it on the other side,
their places are made good by newcomers.

"Those who have seen the .wonderful whirlpool, three
miles below the Falls of Niagara, will not have forgotten
the heaped-up wave which tumbles and tosses, a very em-
bodiment of restless energy, where the swift stream hurry-
ing from the Falls is compelled to make a sudden turn
toward Lake Ontario. However changeful in the contour
of its crest, this wave has been visible, approximately in
the same place and with the same general form, for cen-
turies past. Seen from a mile off, it would appear to be a
stationary hillock of water. Viewed closely it is a typical
expression of the conflicting impulses generated by a swift
rush of material particles.

"Now, with all our appliances, we cannot get with
a good many miles, so to speak, of the living organism.
If we could, we should see that it was nothing but the
constant form of a similar turmoil of material molecules,
which are constantly flowing into the organism on the
one side and streaming out on the other."

What are the distinctive properties of living matter
as contrasted with lifeless matter? What are the element-
ary vital phenomena? The composition of living sub-
stance has long been supposed to hold the key to the mys-
teries of life manifestations. The ancients naively believed
that they were able to explain the substance of living
bodies by the intermixture of certain materials. Thus,
Hippocrates believed that the normal human body consists
of blood, phlegm and bile, which are mixed together in
certain proportions. In the middle ages, when people
endeavored to solve the riddle of nature by the great power
of alchemy, they thought that they were upon the track

THE NATURE OF LIFE 15

of the secret of living substance. How strong this de-
lusion was is shown by the many attempts of the middle
ages to produce living substance artificially.

The ardent expectation with which the medieval
alchemist in the somber dusk of his laboratory, surrounded
by skilled workers and strange apparatus, hoped every
moment to see the homunculus arise complete from the
retorts or crucibles is a very characteristic feature of the
developmental stage of science during these centuries. But,
however proud moderns may be of the advancement of
science, they have no right to look with scorn upon
those attempts of the middle ages, when it is realized
that from that time even to the most recent period
the attempts have been continued to produce artificially
not man himself, but the simplest forms of living substance.
Yet all these attempts resemble the endeavor of a man
to put together a complicated clock-work without knowing
its essential parts.

"However simple the problem of the artificial produc-
tion of living substance appeared to the middle ages,"
says Verworn, "the progress of sober thought and critical
investigation has shown constantly how far we are yet
from a knowledge of the intimate composition of such
substance. How is it possible to produce chemically a
substance the chemical composition of which is not at
all known? Modern research has been directed, therefore,
more and more toward an examination of the composition
of living substance. It has penetrated deeply, and con-
tinues to penetrate, into the morphological, physical and
chemical relations, and the intimate structure of living
matter."

Altho this accumulated knowledge concerning the com-
position of living matter does not distinguish between the
living and the lifeless, it has given many interesting facts
concerning the properties of living matter. In its physical
properties living matter in animal and plant tissues behaves
like a liquid. The idea that vital phenomena can be asso-

16 BIOLOGY

dated with a solid substratum only is not only unjustified,
but even untenable. Not only is it unsupported on any
acceptable ground, but it even contradicts facts that may
easily be observed. It is quite impossible to understand
how protoplasm in the more or less stiff condition of a
framework or network can be capable of streaming and
flowing as can be observed so easily in certain plant-cells
and in Amoeba. It is impossible for a solid network to
flow in such a manner that the individual particles of its
mass mix continually with one another, as may be seen so
clearly in Amoeba. If at first sight the theory of the solid
consistency may not be incompatible with the behavior of
cells that possess a constant form, it is absolutely so with
the phenomena exhibited by naked protoplasmic masses.
Hence various investigators, especially Berthold and
Butschli, have recently defended strongly the idea of the
liquid nature of the cell-contents, and no investigator who
is familiar with the phenomena need hesitate to accept
this view.

Living matter has a greater density than water. That
some animals and plants float is due to the accumulation
in their tissues of certain lifeless matters such as fat and
gasses, which diminish their specific gravity.

In chemical structure the differences between living and
lifeless matter, altho not distinctive, are of importance.
Only twelve elements are found constantly in living mat-
ter: carbon, nitrogen, sulphur, hydrogen, oxygen, phos-
phorus, chlorine, potassium, sodium, magnesium, calcium
and iron. A few others, silicon, fluorine, bromine, iodine,
aluminium and manganese are found occasionally. But all
these elements are also found in the lifeless matter com-
posing the air, water and the surface of the earth.

Since the chemical analysis of living substance has
shown that no constituents but these organic elements are
to be found in the organism, the important fact follows
that an elementary vital substance exists no more than a
specific vital force. The conception of a "vital ether,"

THE NATURE OF LIFE 17

a "spiritus animalis," a "vital matter," etc., with which the
earlier physiology so freely dealt, have, therefore, in
harmony with the advanced development which analytical
chemistry has undergone at the present time, completely
disappeared from the present theory of life; living sub-
stance is composed of no different chemical materials from
those occurring within lifeless bodies.

Nevertheless, one fact deserves mention, viz., that the
few general organic elements are not scattered irregularly
here and there through the natural system of elements, but
they occupy a definite position, being remarkable as ele-
ments having very low atomic weights. "Hence," writes
Verworn, "the conclusion may with great probability be
drawn that in the evolution of the elements the organic
elements arose by condensation very early, and therefore
existed in the very early stages of the development of our
planetary system, at a time when other elements, such as
the heavy metals, had not yet been formed."

Following the discovery that living matter contains
no distinctive chemical elements, physiological chemists
turned their attention to the search for specific chemical
compounds. Here the investigation is most difficult. It
is not possible to apply the methods of chemistry to
living substance without killing it. Every chemical reagent
that comes in contact with it disturbs it and changes it,
and what is left for investigation is no longer living sub-
stance, but a corpse — a substance that has wholly different
properties. Hence ideas upon the chemistry of the living
object can be obtained only by deductions from chemical
discoveries in the dead object, deductions the correctness
of which can be proved experimentally in the living object
only in rare cases.

This alone is responsible for the excessively slow ad-
vance of the knowledge of the chemistry of the vital
process. It is evident that the greatest foresight is neces-
sary in applying results obtained upon the dead object to
conditions in the living, and it must constantly be borne in

18 BIOLOGY

mind that the chemical relations of the latter are to be
distinguished sharply from those of the former.

Altho there is no fundamental difference between the
elements composing living and those composing lifeless
substance, in other words, altho no special vital element
exists in the organic world, some of the elements in living
substance form unique compounds which characterize it
only, and are never found in lifeless substance. Thus,
there exist in the former, besides chemical compounds that
occur also in the latter, specific organic complexes of
atoms. Many of these organic compounds, especially those
that are of special importance to living substance, possess
so complicated a constitution that thus far chemistry has
not succeeded in obtaining an insight into the spatial rela-
tions of the atoms in their molecules, altho the percentage
composition of the molecules is known to a greater extent.

There are especially three chief groups of chemical
bodies and their transformation-products, by the presence
of which living substance is distinguished from lifeless sub-
stance; these are proteids, fats and carbohydrates. Of
these only the proteids and their derivatives have been
demonstrated with certainty as common to all cells ; hence
they must be set apart among the organic constituents of
living matter as the essential or general substances, in con-
trast to all special substances.

It is not, however, the mere presence of proteids which
is characteristic of living matter. White of egg (albumen)
contains an abundance of a typical proteid and yet is abso-
lutely lifeless. Living matter does not simply contain pro-
teids, but has the power to manufacture them out of other
substances; and this is a property of living matter exclu-
sively. While the other organic compounds — carbohy-
drates, fats and some simpler substances — have not been
found in all living matter, it is a significant fact that they
are derived from proteids and are necessary to the con-
struction of proteids.

But even the presence of the so-called organic com-

THE NATURE OF LIFE 19

pounds — proteids, carbohydrates and fats — is an uncer-
tain distinction between the living and the lifeless, for
chemistry is rapidly breaking down the supposed barrier
between the organic and the inorganic. Each year records
new synthetic combinations of compounds supposed to be
produced by living matter. Who knows when even the
proteid molecule may yield its secret to some synthetic
chemist?

Thus the conclusion is reached, strange at first sight, that
the matter constituting the living world is identical with
that which forms the inorganic world. "And not less
true," says Huxley, "is it that, remarkable as are the
powers, or, in other words, as are the forces which are
exerted by living beings, yet all these forces are either
identical with those which exist in the inorganic world, or
they are convertible into them. I mean in just the same
sense as the researches of physical philosophers have
shown that heat is convertible into electricity, that elec-
tricity is convertible into magnetism, magnetism into
mechanical force or chemical force, and any one of them
into the other, each being measurable in terms of the
other — even so, I say that great law is applicable to the
living world."

The composition of living matter as known in modern
chemistry then does not satisfactorily distinguish between
living and lifeless matter, and the question, what is the
characteristic difference? again forces itself to the center
of attention. The generally accepted answer is that this
difference is to be found in certain powers or properties
of living matter. These are the power of waste, repair
and growth and the power of reproduction. "Living mat-
ter," to quote from Sedgwick and Wilson, "is continually
wasting away by a kind of internal combustion, but con-
tinually repairs the waste by the process of growth.
Moreover, this growth is of a characteristic kind, differing
absolutely from the so-called growth of lifeless things.
Crystals and other lifeless bodies grow, if at all, by accre-

20 BIOLOGY

tion, or the addition of new particles to the outside.
Living matter grows from within by intussusception, or
taking in new particles, and fitting them into the interstice*
between those already present, throughout the whole
mass. And lastly, living matter not only thus repairs its
own waste, but also gives rise by reproduction to new
masses of living matter which become detached from the
parent mass and enter forthwith upon an independent
existence.

"We may perceive how extraordinary these properties
are by supposing a locomotive engine to possess like
powers : to carry on a process of self-repair in order to
compensate for wear, to grow and increase in size, detach-
ing from itself at intervals pieces of brass or iron endowed
with the power of growing up step by step into other loco-
motives capable of running themselves, and of reproducing
new locomotives in their turn. Precisely these things are
done by every living thing, and nothing in any degree
comparable with them takes place in the lifeless world."

In connection with the foregoing it should be noted that
some modern authors, notably Verworn, hold that even
metabolism (the power of waste, repair and growth)
does not constitute a fundamental contrast between living
organisms and inorganic bodies. For example, there are
rare cases known to chemists in which simple chemical
compounds under certain conditions undergo a regular
succession of destructions and constructions, always with
the gain or loss of substances which correspond in prin-
ciple to the continued streaming of matter through the
constructive and destructive changes in the metabolism of
living substances. Metabolism, then, cannot be said to be
absolutely distinctive, as a general principle, of living
matter, but practically the metabolism of proteid which is
found in nature only in organic bodies, is sufficiently dis-
tinctive of living matter. The discovery of apparently
analogous processes in inorganic substances simply sug-
gests that the chemical changes concerned in the powers

THE NATURE OF LIFE 21

or activities of living matter are subject to the same fun-
damental laws as govern change in lifeless matter.

Certain critical physiologists have pointed out that repro-
duction is not absolutely distinctive. It is true that in
higher organisms in which reproduction involves develop-
ment of eggs, seeds or germs, reproduction is absolutely
incomparable with any process in lifeless matter, but many
microscopic organisms reproduce by simple division with-
out development, and such simple reproduction is not far
removed from similar changes which may occur in lifeless
matter. But here again these are really only suggestions
of similarity between living and lifeless processes. To
most present-day biologists the known facts of reproduc-
tion, like those of metabolism, are not in any scientific
sense paralleled by processes occurring in inorganic matter.

Finally, even the method of growth by intussusception
of particles has been said to offer no criterion of distinc-
tion, for liquids (and living matter is liquid) grow by in-
tussusception. However, this strikes many biologists as a
mere quibble with words, for growth by intussusception in
organisms involves other changes — e.g., foods not proteids
may be the material for growth of plant proteid, and plant
proteid may in turn serve as food for growth and give
rise to animal proteid.

Such critical comparisons suggesting that metabolism,
growth and reproduction are not entirely absent from life-
less matter are interesting, but in the present state of
scientific knowledge the processes involved in waste, repair,
growth and reproduction are to be considered strikingly
characteristic of living matter. These are probably compli-
cations of simple chemico-physical processes, some of
which suggest similarity between living and lifeless mat-
ter, but the very complexity of the metabolic and repro-
ductive processes in living forms is distinctive. A parallel
case is that of proteid of which, as has been stated, the
most distinctive feature is the complexity of its molecule.

CHAPTER III

PHYSIOLOGICAL IDEA OF LIFE

Accepting the complicated processes of metabolism and
reproduction as distinguishing characteristics of life, the
force back of these distinctive powers or properties of
living matter becomes a fruitful topic for investigation.
Thompson in the 'Science of Life' discusses this question.
"Over and over again in the history of Biology the doctrine
of a special vital force has arisen, held sway for a time,
and then disappeared. It arises as a reaction from the
false simplicity of premature solutions, or as a despairing
retreat in the face of baffling problems, or as the result of
misunderstanding the real aim of science.

"The doctrine is an old one, for even if we ignore the
speculations of the ancients, it must date at least from
Paracelsus and Van Helmont. As it has naturally taken
very different forms in different generations, the word
'vitalism,' so often used, has little definite meaning. There
is a sense in which no modern physiologist is a vitalist,
since none rejects physico-chemical interpretations as the
early French vitalists did; there is a sense in which all
modern physiologists are vitalists, since none pretends to
know the secret of that particular synthesis which even the
simplest of organisms illustrates.

"The phrase 'vital force' may be used as a general ex-
pression for the energies resident in living matter, and
may serve to suggest that we do not at present understand
them, or how they are related in the unity of the organism.

PHYSIOLOGICAL IDEA OF LIFE 23

But the phrase was originally used to denote a 'hyper-
mechanical force/ a mystical power, resident in living
creatures, and quite different from thermic, electric, and
other forms of energy. This was the meaning attached
to the phrase by the disciples of Haller, by Louis Dumas
(1765-1813), by Reil (1759-1813), and the other early
vitalists. It can only be said that an appeal to such a force
violates the scientific method, and abandons the scientific
problem. Again and again, in regard to particular points,
subsequent progress has shown that the loss of faith in
science was premature.

"According to the hypothesis of vitalism the phenomena
of life are inexplicable apart from a special vital force
exclusively resident in organisms, and different from the
chemico-physical energies of the inanimate world. Thus
the great pathologist and anatomist Henle (d. 1885) be-
lieved in a non-material agent associated with the organ-
ism, 'presiding over the metabolism of the body, capable
of reproducing the typical form, and of endless partition
without diminution of intensity.' It is altogether an error
to suppose that a refusal to believe in such a special 'vital
force' implies materialism. The questions are quite sep-
arate; the former has to do with scientific method, the
latter is a philosophical theory. Thus Huxley was certainly
no believer in 'a vital force,' yet he was clearly an idealist ;
and the same might be said of many.

"Every physiologist will, I believe, admit that he cannot
at present give a physico-chemical interpretation of con-
tractility or of irritability, of digestion or of absorption, of
respiration or of circulation. What he can give is a partial
analysis of these functions in simpler terms. This must
remain the case until we discover the secret of the syn-
thesis which the simplest unicellular organism expresses.
The 'neo-vitalists,' such as Bunge and Rindfleisch, empha-
size the fact that there is no present possibility of giving
a complete chemico-physical restatement of any observed
function; that there are always residual phenomena; and

24 BIOLOGY

that the known physico-chemical causes do not seem
adequate to the result. In other words, the categories of
mechanism, of chemistry and physics, cannot be forced
upon vitality without doing violence to the very idea of the
organism — a complex adaptive synthesis of matter and
energy whose secret remains unread. When the neo-
vitalists go further, and insist on an idealistic as opposed
to a materialistic conception, they may be quite correct,
but they are raising another question, which is philosophi-
cal rather than biological."

Huxley, in his famous address 'On the Physical Basis
of Life,' has well stated the case against the existence of
a vital force. "What justification is there, then," he says,
"for the assumption of the existence in the living matter
of a something which has no representative, or correlative,
in the not living matter which gave rise to it ? What better
philosophical status has 'vitality* than 'aquosity'? And
why should 'vitality' hope for a better fate than the other
'itys' which have disappeared since Martinus Scriblerus
accounted for the operation of the meat-jack by its inherent
'meat-roasting quality,' and scorned the 'materialism' of
those who explained the turning of the spit by a certain
mechanism worked by the draft of the chimney?

"If scientific language is to possess a definite and con-
stant signification whenever it is employed, it seems to
me that we are logically bound to apply to the protoplasm,
or physical basis of life, the same conceptions as those
which are held to be legitimate elsewhere. If the phe-
nomena exhibited by water are its properties, so are those
presented by protoplasm, living or dead, its properties. If
the properties of water may be properly said to result from
the nature and disposition of its component molecules, I
can find no intelligible ground for refusing to say that the
properties of protoplasm result from the nature and dis-
position of its molecules."

This idea of the physical basis of life, so clearly stated
by Huxley, has been further developed by Dr. Michael

PHYSIOLOGICAL IDEA OF LIFE 25

Foster, whose line of thought is as follows : "The more
the molecular problems of physiology are studied, the
stronger becomes the conviction that the consideration of
what we call structure and composition must, in harmony
with the modern teachings of physics, be approached under
the dominant conception of modes of motion. The phys-
icists have been led to consider the qualities of things as
expressions of internal movements; even more imperative
does it seem to us that the biologist should regard the
qualities of living matter (including structure and com-
position) as in like manner the expressions of internal
movements. He may speak of living matter as a complex
substance, but he must strive to realize that what he means
by that is a complex whirl, an intricate dance, of which
what he calls chemical composition, histological structure
and gross configuration are, so to speak, the figures ; to him
the renewal of protoplasm is but the continuance of the
dance, its functions and actions the transferences of the
figures. It seems to us necessary, for a satisfactory study
of the problems, to keep clearly before the mind the con-
ception that the phenomena in question are the result, not
of properties of kinds of matter, but of kinds of motion."

Before passing from the consideration of vital force and
the physical basis of life, it will be of interest to compare
the views of the biologists Huxley and Foster with that
expressed in a lecture by the great physicist, Tyndall.

"The origin, growth and energies of living things," he
reminded his hearers, "are subjects which have always en-
gaged the attention of thinking men. To account for them
it was usual to assume a special agent, free to a great extent
from the limitations observed among the powers of inor-
ganic nature. This agent was called vital force ; and, under
its influence, plants and animals were supposed to collect
their materials and to assume determinate forms. Within
the last few years, however, our ideas of vital processes
have undergone profound modifications ; and the interest,
and even disquietude, which the change has excited are

26 BIOLOGY

amply evidenced by the discussions and protests which are
now common, regarding the phenomena of vitality. In
tracing these phenomena through all their moidfications,
the most advanced philosophers of the present day declare
that they ultimately arrive at a single source of power,
from which all vital energy is derived ; and the disquieting
circumstance is that this source is not the direct fiat of a
supernatural agent, but a reservoir of what, if we do not
accept the creed of Zoroaster, must be regarded as inor-
ganic force. In short, it is considered as proved that all
the energy which we derive from plants and animals is
drawn from the sun.

"A few years ago, when the sun was affirmed to be the
source of life, nine out of ten of those who are alarmed by
the form which this assertion has latterly assumed would
have assented, in a general way, to its correctness. Their
assent, however, was more poetic than scientific, and they
were by no means prepared to see a rigid mechanical
signification attached to their words. This, however, is the
peculiarity of modern conclusions: that there is no cre-
ative energy whatever in the vegetable or animal organism,
but that all the power which we obtain from the muscles
of man and animals, as much as that which we develop by
the combustion of wood or coal, has been produced at the
sun's expense.

"To most minds, however, the energy of light and heat
presents itself as a thing totally distinct from ordinary
mechanical energy. Either of them can nevertheless be
derived from the other. Wood can be raised by friction
to the temperature of ignition ; while by properly striking
a piece of iron a skilful blacksmith can cause it to glow.
Thus, by the rude agency of his hammer, he generates light
and heat. This action, if carried far enough, would pro-
duce the light and heat of the sun. In fact, the sun's light
and heat have actually been referred to the fall of meteoric
matter upon his surface ; and whether the sun is thus sup-
ported or not, it is perfectly certain that he might be thus

PHYSIOLOGICAL IDEA OF LIFE 27

supported. If, then, solar light and heat can be produced
by the impact of dead matter, and if from the light and
heat thus produced we can derive the energies which we
have been accustomed to call vital, it indubitably follows
that vital energy may have a proximately mechanical
origin.

"In what sense, then, is the sun to be regarded as the
origin of the energy derivable from plants and animals?
Let us try and give an intelligible answer to this question.
Water may be raised from the sea-level to a high elevation,
and then permitted to descend. In descending it may be
made to assume various forms — to fall in cascades, to spurt
in fountains, to boil in eddies, or to flow tranquilly along
a uniform bed. It may, moreover, be caused to set complex
machinery in motion, to turn millstones, throw shuttles,
work saws and hammers, and drive piles. But every form
of power here indicated would be derived from the original
power expended in raising the water to the height from
which it fell. There is no energy generated by the
machinery: the work performed by the water in descend-
ing is merely the parceling out and distribution of the
work expended in raising it.

"In precisely this sense is all the energy of plants and
animals the parceling out and distribution of a power
originally exerted by the sun. In the case of the water,
the source of the power consists in the forcible separation
of a quantity of the liquid from a low level of the earth's
surface, and its elevation to a higher position, the power
thus expended being returned by the water in its descent.
In the case of vital phenomena, the source of power con-
sists in the forcible separation of the atoms of compound
substances by the sun. We name the force which draws
the water earthward 'gravity,' and that which draws atoms
together 'chemical affinity' ; but these different names must
not mislead us regarding the qualitative identity of the two
forces. They are both attractions ; and, to the intellect, the
falling of carbon atoms against oxygen atoms is not more

28 BIOLOGY

difficult of conception than the falling of water to the
earth.

"The building up of the vegetable, then, is effected by the
sun, through the reduction of chemical compounds. The
phenomena of animal life are more or less complicated
reversals of these processes of reduction. We eat the
vegetable, and we breathe the oxygen of the air; and in
our bodies the oxygen, which had been lifted from the
carbon and hydrogen by the action of the sun, again falls
toward them, producing animal heat and developing animal
forms. Through the most complicated phenomena of
vitality this law runs : the vegetable is produced while a
weight rises, the animal is produced while a weight falls.

"But the question is not exhausted here. The water
employed in our first illustration generates all the motion
displayed in its descent, but the form of the motion depends
on the character of the machinery interposed in the path
of the water. ' In a similar way, the primary action of
the sun's rays is qualified by the atoms and molecules
among which their energy is distributed. Molecular forces
determine the form which the solar energy will assume.
In the separation of the carbon and oxygen this energy
may be so conditioned as to result in one case in the
formation of a cabbage, and in another case in the forma-
tion of an oak. So also, as regards the reunion of the
carbon and the oxygen, the molecular machinery through
which the combining energy acts may, in one case, weave
the texture of a frog, while in another it may weave the
texture of a man.

"The matter of the animal body is that of inorganic
nature. There is no substance in the animal tissues which
is not primarily derived from the rocks, the water and the
air. Are the forces of organic matter, then, different in
kind from those of inorganic matter? The philosophy of
the present day negatives the question. It is the com-
pounding, in the organic world, of forces belonging equally
to the inorganic, that constitutes the mystery and the

PHYSIOLOGICAL IDEA OF LIFE 29

miracle of vitality. Every portion of every animal body
may be reduced to purely inorganic matter. A perfect
reversal of this process of reduction would carry us from
the inorganic to the organic ; and such a reversal is at least
conceivable. The tendency, indeed, of modern science is
to break down the wall of partition between organic and
inorganic, and to reduce both to the operation of forces
which are the same in kind, but which are differently
compounded.

"Consider the question of personal identity, in relation
to that of molecular form. Thirty-four years ago, Mayer
of Heilbronn, with that power of genius which breathes
large meanings into scanty facts, pointed out that the
blood was 'the oil of the lamp of life,' the combustion of
which sustains muscular action. The muscles are the
machinery by which the dynamic power of the blood is
brought into play. Thus the blood is consumed. But the
whole body, tho more slowly than the blood, wastes also,
so that after a certain number of years it is entirely re-
newed. How is the sense of personal identity maintained
across this flight of molecules ? To man, as we know him,
matter is necessary to consciousness ; but the matter of any
period may be all changed, while consciousness exhibits no
solution of continuity. Like changing sentinels, the
oxygen, hydrogen and carbon that depart seem to whisper
their secret to their comrades that arrive, and thus, while
the Non-ego shifts, the Ego remains the same. Constancy
of form in the grouping of the molecules, and not constancy
of the molecules themselves, is the correlative of this con-
stancy of perception. Life is a wave which in no two
consecutive moments of its existence is composed of the
same particles.

"Supposing, then, the molecules of the human body,
instead of replacing others, and thus renewing a preexist-
ing form, to be gathered first hand from nature and put
together in the same relative positions as those which
they occupy in the body. Supposing them to have the

30 BIOLOGY

selfsame forces and distribution of forces, the selfsame
motions and distribution of motions — would this organized
concourse of molecules stand before us as a sentient think-
ing being? There seems no valid reason to believe that it
would not. Or, supposing a planet carved from the sun,
set spinning round an axis, and revolving round the sun
at a distance from him equal to that of our earth, would
one of the consequences of its refrigeration be the develop-
ment of organic forms? I lean to the affirmative. Struc-
tural forces are certainly in the mass, whether or not those
forces reach to the extent of forming a plant or an animal.
In an amorphous drop of water lie latent all the marvels
of crystalline force ; and who will set limits to the possible
play of molecules in a cooling planet? If these statements
startle, it is because matter has been defined and maligned
by philosophers and theologians, who were equally unaware
that it is, at bottom, essentially mystical and transcen-
dental."

Summarizing the foregoing discussion concerning the
nature and general conditions of life and living matter,
the fact stands out clearly and distinctly that life from its
beginning has been dependent upon the external condi-
tions of the earth's surface. In a mathematical sense,
life is a function of the earth's development. Living sub-
stance could not exist while the earth was a molten sphere
without a solid, cool crust; it was obliged to appear with
the same inevitable necessity as a chemical combination,
when the necessary conditions were given, and it was
obliged to change its form and its composition in the same
measure as the external conditions of life changed in the
course of the earth's development. It is only a portion of
the earth's matter.

The combination of this matter into living substance
was as much the necessary product of the earth's develop-
ment as was the origin of water. It was an inevitable
result of the progressive cooling of the masses that formed
the earth's crust. Likewise, the chemical, physical and

PHYSIOLOGICAL IDEA OF LIFE 31

morphological characteristics of existing living substance
are the necessary result of the influence of the external
conditions of life upon the internal relations of past living
substance. Internal and external vital conditions are in-
separably correlated and the expression of this correlation
is life.

The artificial production of life would thus seem a theo-
retical possibility. It has been several times suggested in
the discussion of the chemical aspects of life that living
matter may sooner or later be produced in the chemists'
laboratories. However improbable this suggestion may
seem, there are many facts which point to its possibility.
Heraclitus compared life with fire. Such a comparison
is a pertinent one. Consideration of vital conditions makes
this more evident. "It has been shown that life," to quote
Verworn, "like fire, is a phenomenon of nature which ap-
pears as soon as the complex of its conditions is fulfilled.
"If these conditions are all realized, life must appear with
the same necessity as fire appears when its conditions are
realized; likewise life must cease as soon as the complex
of its conditions has undergone disturbance and with the
same necessity with which fire is extinguished when the
conditions for its maintenance cease. If, therefore, all
vital conditions had been investigated in their minutest
details, and it were possible artificially to establish them
exactly, life would be produced synthetically, just as fire
is produced, and the ideal that existed in the imagination
of the medieval alchemists in their attempted production
of the homunculus would be achieved."

But, notwithstanding the fact that this theoretical pos-
sibility cannot be denied, every attempt at the present time
to produce life artificially and to imitate in the laboratory
the obscure act of spontaneous generation must appear
preposterous. So long as knowledge of the composition
of living substance is so imperfect as it is now, the attempt
artificially to compound living substance will be like
the undertaking of an engineer to put together a machine,

32 BIOLOGY

the most important parts of which are wanting. For the
present the task of physiology can consist only in the in-
vestigation of life. When physiology shall actually have
accomplished this, it may think of testing the completeness
and correctness of its achievement by the artificial crea-
tion of life.

The nature of life has become better understood by the
study of death, which to the biologist is simply the cessa-
tion of the activities of life. In the first place it is some-
times extremely difficult to distinguish between life and
apparent death. Several illustrations will make this clear.
In India, where mystery and magic have always prevailed,
the belief seems to have existed for a long time that many
men, especially the so-called fakirs whose existences are
full of privation and self-inflicted torture and who are
supposed to possess special holiness, have the remarkable
power of voluntarily putting a complete stop to their lives
for a time and later resuming them undisturbed and un-
changed. A great number of such cases, in which the
fakirs have been buried in this condition of suspended ani-
mation and after some time have been taken from their
graves, have been reported by travelers from India.

It is not to be denied that these tales, especially those of
the Indian fakirs, are calculated to awaken distrust, and a
sound skepticism is the basis of all good criticism. If,
however, from all the known stories their more or less
sensational accompaniments be removed, the simple state-
ment remains that certain men can voluntarily put them-
selves into a state in which no vital phenomena are demon-
strable by a more or less superficial examination and can
awaken later to normal life. Now sufficient cases are
known where physicians by the usual methods of their
practice are able to discover absolutely no traces of vital
phenomena, where pulse, respiration, movement and ir-
ritability are not to be observed ; and yet where the person,
supposedly dead, has after a time returned to life.

These phenomena are usually termed 'apparent death'

PHYSIOLOGICAL IDEA OF LIFE 33

and are connected with those of normal sleep by a series
of transition phenomena. Such transition phenomena are
the continual sleep in which persons, such as the 'sleeping
soldier' and the 'sleeping miner' (authenticated medical
cases), continue in a state of depressed vital activity and
are absolutely incapable of being awakened, and especially
the phenomena of the winter sleep of warm-blooded ani-
mals.

However doubtful may be the reported powers of repre-
sentatives of the vertebrate (or backboned) animals to
suspend for a time all vital phenomena, there is no longer
any question that many of the lower animals have this
power highly developed. As long ago as 1719 Leeuwen-
hock, the famous improver of the microscope, dis-
covered that small animals, now known as rotifers, may
be dried completely to dust and again restored to active
life by being placed in water. One of the most remarkable
cases of this kind described by Verworn is that of the
tardigrade, or bear-animalcule, which, so long as it is in
water, performs all its vital phenomena like other animals.
"But if it be isolated and allowed to dry slowly upon a
slide, it is seen that the more the water evaporates the.
slower become its movements, until finally they cease en-
tirely when the drop is dried up. Then the body gradually
shrinks, the skin become wrinkled and folded, the form
becomes gradually indistinguishable, and some time after
the animal has become dried it can scarcely be distinguish-
ed from a grain of sand. In this dried condition it can
remain for many years without undergoing the slightest
change. If it be moistened again with water, the return
of life to the desiccated body after its sleep can be followed
with the microscope. The awakening of the tardigrade or
the anabiosis, as Preyer has termed the process, takes
place somewhat as follows: The body swells up and be-
comes extended, the folds and wrinkles slowly disappear,
the extremities project and the animal soon assumes its
normal shape." At first it remains quiet; then, after a

34

BIOLOGY

time, varying, according to the duration of the drying,
from a quarter of an hour to several hours, movements,
at first slow and feeble, begin and gradually become
stronger and more frequent until after some time the
animal, unaided, creeps away to resume life at the point
where it was interrupted.

Fig. i — A Tardigrade.
a., Creeping in the living state. (Hertwig.) b., Dried, in the
ttate of apparent death. (Verworn.)

Likewise the seeds of many plants retain their power of
germination for long periods of time. Here it might be
well to add that the well-known story that wheat seeds
taken from the graves of Egyptian mummies will germi-
nate, tho thousands of years old, has been disproved by
Mariette, the famous Egyptologist. However, from many

PHYSIOLOGICAL IDEA OF LIFE 35

observations it seems certain that many plant seeds, when
completely dried, can retain their power to germinate for
more than a hundred or perhaps two hundred years.
These rare facts are of great importance in forming a con-
ception of life and demand exhaustive investigation. The
question to be considered is whether it is allowable to re-
gard organisms in this peculiar condition as really lifeless.

It has been pointed out in the earlier part of this chapter
that it is metabolism in which the living organism differs
from lifeless matter. But this is difficult to settle in some
of the concrete cases mentioned above. Do dust-dry ani-
mals and seeds possess no metabolism or is this metabolism
so depressed or so slight that investigation cannot deter-
mine whether the life-process is at a standstill or whether
a Vita minima' exists? Delicate experiments within the
last twenty years show no evidence of the use of oxygen
or the production of carbonic acid or other products of
metabolism in dried organisms sealed for months in air-
tight tubes.

From the results of these experiments it can no longer
be doubted that in desiccated organisms there is a complete
standstill of life. Can organisms in this peculiar condition
be termed dead? In reality they are lifeless but not dead,
for anabiosis is possible after the application of water,
while nothing can bring dead organisms back to life. The
distinction between the dried and the dead organism lies
in the fact that in the former all the internal vital condi-
tions are still fulfilled and only the external conditions in
part have appeared, while in the latter the internal vital
conditions have experienced irreparable disturbances, altho
the external conditions can still be fulfilled.

Preyer illustrates this distinction very happily. He com-
pares the dried organism to a clock that has been wound
but has stopped, so that it needs only a push to set it going,
and the dead organism to a clock that is broken and cannot
be made to go by a push. Hence a sharp distinction must
be made between dried and dead organisms. But dried or-

36 BIOLOGY

ganisms cannot be called living, for they exhibit no vital
phenomena, and, as has been seen, vital phenomena are the
criterion of life. It is best, therefore, to apply to them
the expression 'apparently dead.'

Still more difficult than cases of apparent death is the
determination of an exact limit between life and active
death. In daily life it is easy to distinguish the dead or-
ganism from the living, for from the human body and from
the higher animals a general conception of death has been
formed and it is usual to consider it as occurring at the
moment when the heart, hitherto never quiet, stands still
and the individual ceases to breathe. But this is merely
following the superficial habits of daily life and taking
into consideration only the gross differences that make
their appearance at that time, without noticing the con-
tinuance of certain phenomena after this all-important
moment.

The criterion of life is formed only by the vital phe-
nomena— i.e., by the various phases in which the vital
process, or the metabolism, becomes evident to the senses.
But if this criterion be applied to the human being at the
moment usually termed the moment of death, it is found
that in reality he is not dead.

It is true that the spontaneous gross muscular move-
ments cease, the man becomes relaxed and quiet. But the
muscles frequently remain for several hours sensitive to
external influences, responding to the latter with twitch-
ings and movements of the limbs, in other words, showing
vital phenomena. A moment even comes when the mus-
cles gradually contract once more spontaneously, this is
the death-stiffening (rigor mortis). Not until this has
passed is the life of the muscles extinguished. Neverthe-
less, even then the body is not entirely dead. Certain parts
only, certain organs or cell-complexes, such as the cells of
the nervous system and of the muscles, no longer show
vital phenomena ; but other cells and cell-complexes con-
tinue to live unchanged long after rigor mortis has passed.

PHYSIOLOGICAL IDEA OF LIFE 37

What moment then shall be designated as the moment
of death ? If the existence of vital phenomena be employed
as the criterion, then the moment when spontaneous mus-
cular movement, especially the activity of the heart,
ceases, cannot consistently be regarded as the moment of
death, for other cell-complexes continue to live for a long
time thereafter. It is evident, therefore, that there is no
definite point of time at which life ceases and death begins ;
but there is a gradual passage from normal life to complete
death which frequently begins to be noticeable during the
course of a disease. Death is developed out of life,

It is true that the above example is that of a highly com-
plicated organism. But even in the lowest and simplest
microscopic organisms death comes on gradually, and, as
in the higher animals, is the end-result of a long series of
processes which begin with an irreparable injury to the
normal body and lead, step by step, to complete cessation
of life activities. To this series of stages in the develop-
ment of death Schultze and Virchow (1870), famous in
pathology, have given the term 'necrobiosis/ the gradual
transition between life and death.

It is seen, therefore, that it is impossible to draw a
sharp line between life and death, that life and death are
only the two end-results of a long series of changes which
run their course successively in the organism. "But if,
after having established this fact," says Verworn, "the
transition stages be left out of consideration for the mo-
ment and only the two end-results be considered, on the
one side, the uninjured living organism and, on the other,
the same organism killed and preserved in alcohol by the
modern technical methods, a sharp distinction between
these two can be recognised in the fact that in the former
the life-process goes on undisturbed, as is evident from the
appearance of all vital phenomena, while in the latter it is
forever at a complete standstill, as is shown by the absence
of even the slightest phenomena of life."

CHAPTER IV

THE ORIGIN OF LIFE

The discussion of the origin of life is introduced by J.
Arthur Thomson, of Aberdeen University, in 'The Science
of Life' with the following words: "If it were the object
of this book to give a statement of the established facts of
biology, our discussion of the origin of life might be con-
densed into a single sentence : We do not know anything
in regard to the origin of life. The only certainty is a
negative one — there is no established case in which living
organisms have arisen apart from parent organisms of the
same kind."

There are two distinct questions connected with the ori-
gin of life : First, how did it first originate in the early eras
of the world's history? and, second, does life to-day origi-
nate spontaneously in inorganic matter? It seems best to
consider these separately. Professor Max Verworn, of the
University of Jena, gives a good summary of the various
theories concerning the origin of life, and it is from his
'General Physiology' that some of the following illustra-
tions have been taken.

The origin of life upon the earth is a first and leading
problem. The idea that the earth was once in a highly
heated condition is accepted in modern science. And this
fact that it once was in a condition in which the tempera-
ture was enormously high and not a drop of water existed
upon it, in short, a condition in which the vital conditions
that are now regarded as indispensable to the existence of

THE ORIGIN OF LIFE 39

organisms were wanting, will always be an important fac-
tor with which all speculations upon the origin of life upon
the earth must deal. Obviously in that highly heated con-
dition life in its present form, at least, could not have ex-
isted. Then one of two things must have happened after
the earth cooled down — either inorganic matter must have
become living matter or living matter must have come
from other planets than this.

But if life came hither from other worlds, the interesting
question as to the beginning of life remains. Helmholtz
has said, "Organic life either has begun to exist at some
one time or has existed for eternity." Evidently the two
notions are mutually exclusive. Which affords the most
reasonable basis of explanation? The idea that life has
existed in the universe from eternity and has simply been
transferred from one world to another is known as the
theory of 'cosmozoa.' It was suggested by H. E. Richter
(1865, '70 and '71), who assumed that among particles
moving about in space, like meteorites, there are the germs
of microscopic organisms capable of establishing life on
the earth. Helmholtz and Sir William Thomson have dis-
cussed this question of the transference of living matter
from other heavenly bodies to this earth and both term this
view not unscientific. Helmholtz (1884) held that meteors
which swarm everywhere in space might be the bearers of
such germs in their cool interior cavities. He thought it a
correct scientific procedure to question whether life may
not be even as old as matter and its germs passed from
world to world and developed wherever favorable condi-
tions exist.

In the present condition of knowledge it is scarcely pos-
sible to obtain a direct contradiction of this doctrine and
conclusive proof of its impossibility. This will be true so
long as experience does not suffice to enable man to recog-
nise as wholly impossible the transfer of protoplasmic
germs of life from one world to another. But, altho direct
contradiction of the doctrine is at present impossible, the

40 BIOLOGY

thought that living substance has existed from eternity
and has never originated from inorganic substance appears
in the highest degree improbable.

Setting aside the 'cosmozoa' theory as improbable,
and before considering the alternative view of the
spontaneous generation of life from lifeless matter
on the earth, mention should be made of Preyer's view
that living matter is the primary thing and that lifeless
matter has been derived from the living. According to
this view, life must have existed when the earth was in-
candescent. Preyer fits his theory to this fact by giving
to his conception of life a scope wider than that usually
allowed, including not only present living matter but also
incandescent liquid masses as they once existed. Life then
had no origin; it existed even in the beginning of the
material universe. In fact, the view seems to identify life
with motion. Evidently the language used constitutes the
chief difference between this and the doctrine that living
matter as now recognised was spontaneously generated
from matter customarily termed lifeless. Whether from
primeval conditions incandescent matter, which from our
usual standpoint would certainly be considered lifeless, was
really living and separated out that which we call lifeless
or whether it was lifeless with the power to evolve into
living matter are questions of greater metaphysical flavor
than of direct interest in the biological science of to-day.
In either case the original incandescent matter must
have possessed the potentiality of evolving and differentia-
ting into what is now recognised as living and lifeless
matter. It matters little whether in philosophical moods
it is sought to establish the primary vital force, for after
all, as has been shown, vital force is not unique among
the forces of the universe.

One of the most suggestive works discussing the origin
of life from lifeless matter on the earth is by the famous
German physiologist Pfliiger (1875). He discussed the
problem from the standpoint of physiological chemistry

THE ORIGIN OF LIFE 41

and follows it out far into detail. The essential point of
Pfliiger's investigation is constituted by the chemical char-
acteristics of proteid as that substance with which life in
its essentials is inseparably united. There exists a funda-
mental difference between dead proteid, as it occurs — e.g.,
in egg-albumen, and living proteid, as it constitutes living
substance; this difference is the self-decomposition of the
latter. All living substance is continually being decom-
posed, in some degree spontaneously and more through
outside influences, while dead proteid under favorable con-
ditions remains intact for an unlimited time.

Further, Pfliiger assumes on scientific grounds that
the presence of cyanogen in living matter is responsible for
the characteristic properties of living proteid, especially its
great powers of decomposition. From this he concludes
that the beginning of organic life was in cyanogen.
Hence the problem of the origin of living substance cul-
minates in the question: How does cyanogen arise?
Here, organic chemistry presents the highly significant
fact, that cyanogen and its compounds, such as potassium
cyanide, ammonium cyanide, hydrocyanic acid, cyanic
acid, etc., arise only in an incandescent heat — e.g., when
the necessary nitrogenous compounds are brought in con-
tact with burning coal, or when the mass is heated to a
white heat. "Accordingly, nothing is clearer than the
possibility of the formation of cyanogen-compounds when
the earth was wholly or partially in a fiery or heated
state." Moreover, chemistry shows how the other essen-
tial constituents of proteid, such as the hydrocarbons, the
alcohol radicals, etc., can likewise arise synthetically in
heat.

"It is seen," says Pfliiger, "how strongly and remarkably
all facts of chemistry point to fire as the force that has
produced by synthesis the constituents of proteid. In other
words, life is derived from fire, and its fundamental
conditions were laid down at a time when the earth was
still an incandescent ball. If now we consider the im-

42 BIOLOGY

measurably long time during which the cooling of the
earth's surface dragged itself slowly along, cyanogen and
the compounds that contain cyanogen and hydrocarbon
substances had time and opportunity to indulge exten-
sively their great tendency toward transformation and
polymerization and to pass over with the aid of oxygen,
and later of water and salts, into that self-destructive
proteid, living matter."

Pfliiger thereupon summarizes his ideas in the follow-
ing sentences: "Accordingly, I would say that the first
proteid to arise was living matter, endowed in all its
radicals with the property of vigorously attracting similar
constituents, adding them chemically to its molecule, and
thus growing ad infinitum. According to this idea, living
proteid does not need to have a constant molecular weight ;
it is a huge molecule undergoing constant, never-ending
formation and constant decomposition, and probably be-
haves toward the usual chemical molecules as the sun
behaves toward small meteors.

"In the plant, living proteid simply continues to do what
it has always done since its origin — i.e., regenerate or
grow; wherefore I believe that all proteid existing in the
world to-day was derived directly from the first proteid."

This idea of Pfliiger's in essentials is generally accepted,
for most present-day biologists prefer to think of life as
having originated directly from substances usually re-
garded as lifeless and of all existing living proteid as
having descended in direct continuity from the first pro-
teid. Moreover, some biologists follow Helmholtz and
others in thinking that the first proteid may possibly have
originated in some other part of the universe, but astron-
omy and geology offer good reason for believing that
living matter might have originated on the earth when
in its evolution to its present state conditions became
right for its development.

However, notwithstanding all the speculations concern-
ing the subject, it must be recognised that the problem is

THE ORIGIN OF LIFE 45

one of metaphysics rather than of natural science. The
ordinary methods of scientific investigation are not appli-
cable to the problem and one can only theorize as to the
basis of life as it is known. But there cannot be any
certainty that life in its beginning, under possibly vastly
different conditions from those obtaining to-day, possessed
the distinctive properties discovered in it by modern
science.

That master of modern philosophical biology, Thomas
H. Huxley, discussed the origin of life in his Presidential
Address before the British Association for the Advance-
ment of Science, forty years ago, and his words, while
expressing the ideas outlined above, stand high among
the statements of the philosophical problems of biology.
"Looking back through the prodigious vista of the past,"
he writes, "I find no record of commencement of life, and
therefore I am devoid of any means of forming a definite
conclusion as to the condition of its appearance. Belief,
in the scientific sense of the word, is a serious matter and
needs strong foundations. To say, therefore, in the ad-
mitted absence of evidence, that I have any belief as to
the mode in which the existing forms of life have originat-
ed, would be using words in a wrong sense.

"But expectation is permissible where belief is not; and
if it were given to me to look beyond the abyss of geolog-
ically recorded time to the still more remote period when
the earth was passing through physical and chemical con-
ditions which it can no more see again than a man can
recall his infancy, I should expect to be a witness of the
evolution of living substance from non-living matter. I
should expect to see it appear under forms of great sim-
plicity, endowed, like existing fungi, with the power of
determining the formation of new living matter from such
matters as ammonium carbonates, oxalates and tartrates,
alkaline and earthy phosphates, and water, without the
aid of light. That is the expectation to which analogical
reasoning leads me; but I beg you once more to recollect

44 BIOLOGY

that I have no right to call my opinion anything but an
act of philosophical faith."

The second question to be considered is that of spon-
taneous generation. The view that life originally began
in non-living matter — i.e., was spontaneously generated,
is commonly accepted by twentieth-century biology. But
it should be noted that "belief in the spontaneous genera-
tion of simple living matter in the early ages of the world's
history is quite different from the belief that even to-day
new living matter originates spontaneously without the in-
fluence of preexisting living matter."

This idea that living things, including even animals as
complicated as flies and frogs, originate directly from life-
less matter, long after the first origin of life, has been
widely accepted and is believed even to-day by many un-
scientific people. It is to this supposed origin of living
matter within the period of human history that the term
'spontaneous generation' ('archegony,' 'abiogenesis/
'generatio spontanea' or 'aequivoca') is most commonly
applied and few authors of articles on the subject have
included discussion of the first origin of life. Obviously
the fundamental problems would be the same, no matter
whether the spontaneous appearance of life in lifeless mat-
ter occurred in the beginning of all life or occurs to-day.
But the first is entirely beyond the power of scientific
investigation, while if life now originates spontaneously a
critical application of the methods of modern science ought
to prove it and to throw light on the method of origin.
Investigators have therefore been stimulated to test the
truth of the theory and to look for the key which will
unlock the mystery of the first origin of life.

A vast amount of critical work has been done with the
result that the biologists of the Victorian era proved that
life does not originate spontaneously in any of the cases
claimed to have been observed. In other words, life does
not now spontaneously originate in lifeless matter so far
as is known. This does not mean that it cannot or does

THE ORIGIN OF LIFE 45

not originate in some unknown form. This is a possibility
which biologists recognise, and so they stand in an open-
minded attitude ready to witness the origin of life from
lifeless matter and really somewhat disappointed in that
this opportunity has not yet come.

The story of the theory of spontaneous generation is one
of the most fantastic in all biology. Thomson says: "If
the longevity of a belief were an index to its' truth, the
theory of spontaneous generation should rank high among*
the veracities, for it flourished throughout twenty centuries
and more. We cannot trace the history of the theory in
all its details, but the story may be recommended to the
psychological historian as a labyrinth of error, with
glimpses of truth at every turn."

The belief in spontaneous generation is recorded in
literature back as far as Anaximander (611-547 B.C.). He
believed that eels and other aquatic forms are produced
directly from lifeless matter. His pupil Anaximenes (588-
524 B.C.) "introduced the idea of primordial terrestrial
slime, a mixture of earth and water, from which, under
the influence of the sun's heat, plants, animals and human
beings are directly produced — in the abiogenetic fashion,"
says Osborn in 'From the Greeks to Darwin.' Diogenes
and Xenophanes, the first to recognise the true nature of
fossils, also believed in spontaneous generation. Then
came the "father of natural history," Aristotle (384-322
b.c), who fostered this idea so strongly that it has per-
sisted for more than twenty centuries. He taught that not
only small animals, but even frogs, snakes and eels are
produced spontaneously from mud.

Long after Aristotle, men found no difficulty in believing
in cases of spontaneous generation which would now be
rejected as monstrous by the most fanatical supporter of
the doctrine. Shell-fish of all kinds were considered to
be without parental origin. Eels were supposed to spring
spontaneously from the fat ooze of the Nile. Caterpillars
were the spontaneous products of the leaves on which they

46 BIOLOGY

fed; while winged insects, serpents, rats and mice were
all thought capable of being generated without sexual
intervention.

The development of embryology and the knowledge of
the life-histories of plants and animals gradually set aside
many supposed cases of spontaneous generation. A little
observation showed that individuals of these species de-
veloped from eggs produced by parents of the same species.
But it is interesting to note that certain philosophers,
notably among them being Augustine (353-430), still held
to spontaneous generation as occasionally happening in
animals reproducing by the sexual method. According to
Augustine, from the beginning there had existed two kinds
of germs of living things : first, visible ones, placed by
the Creator in animals and plants; and second, invisible
ones, latent and becoming active only under certain con-
ditions of combination and temperature. It is these which
produce plants and animals in great numbers without any
cooperation of existing organisms. This was a naturalis-
tic way of explaining the sudden appearance of countless
numbers of frogs, insects and other animals which to-day
offers no difficulty, now that the remarkable fertility of
animals is known.

Even a man like Cesalpino (1519-1603), who did some
excellent botanical work, and had, long before Harvey,
some clear ideas as to the circulation of the blood, "be-
lieved that frogs might be generated from the mud with
the help of sunshine/' says Thompson, "and even suggested
a similar origin of the aboriginal Americans. The botan-
ists were no better than the zoologists. One of their
favorite notions was that the green dust which grows in
damp weather on trees and stones, which is now known to
consist of unicellular Algae, such as Tleurococcus/ was
a standing evidence of the genetic connection between
the dead and the living, between the mineral and the vege-
table; even Bacon of Verulam believed in the spontaneous
origin of some higher plants, like thistles, from earth; and

THE ORIGIN OF LIFE 47

the Italian botanist Matthioli regarded the duckweed,,
whose leaf-like shoots are so common on the surface of
pools, as a condensation of the still water, and a starting-
point for higher forms of plant life; while even Harvey
continued to believe in spontaneous generation."

A scientific experiment to test spontaneous generation
was first undertaken by Francesco Redi, a distinguished
Italian physician and scholar. The origin of maggots from
putrefying flesh had long been accepted as a clear case of
spontaneous generation. Tyndall, in an article on spon-
taneous generation, writes of this as follows: "Lacking
the checks imposed by fuller investigation, the conclusion
that flesh possesses and exerts this generative power is a
natural one. I well remember when a child of ten or
twelve seeing a joint of imperfectly salted beef cut into,
and coils of maggots laid bare within the mass. Without
a moment's hesitation I jumped to the conclusion that
these maggots had been spontaneously generated in the
meat. I had no knowledge which could qualify or oppose
this conclusion, and for the time it was irresistible. The
childhood of the individual typifies that of the race, and
the belief here enunciated was that of the world for nearly
two thousand years."

To the examination of this very point the celebrated
Francesco Redi addressed himself in 1668. He had seen
the maggots of putrefying flesh, and reflected on their pos-
sible origin. But he was not content with mere reflection,
nor with the theoretic guesswork which his predecessors
had founded upon their imperfect observations. Watching
meat during its passage from freshness to decay, prior to
the appearance of maggots he invariably observed flies
buzzing round the meat and frequently alighting on it.
The maggots, he thought, might be the half-developed
progeny of these flies.

"The inductive guess precedes experiment, by which,
however, it must be finally tested. Redi knew this, and
acted accordingly. Placing fresh meat in a jar and cover-

48 BIOLOGY

ing the mouth with paper, he found that, tho the meat put-
refied in the ordinary way, it never bred maggots, while
the same meat placed in open jars soon swarmed with these
organisms. For the paper cover he then substituted fine
gauze, through which the odor of the meat could rise.
Over it the flies buzzed, and on it they laid their eggs, but
the meshes being too small to permit the eggs to fall
through, no maggots were generated in the meat. They
were, on the contrary, hatched upon the gauze. By a series
of such experiments Redi destroyed the belief in the spon-
taneous generation of maggots in meat, and with it doubt-
less many related beliefs. The combat was continued by
Vallisneri, Schwammerdam and Reaumur, who succeeded
in banishing the notion of spontaneous generation from the
scientific minds of their day. Indeed, as regards such com-
plex organisms as those which formed the subject of their
researches, the notion was banished forever, so far as ac-
cepted science was concerned." However, to this day many
untutored persons firmly believe that dead horse-hairs
placed in water transform themselves into horse-hair eels
and that meat generates maggots and other forms of life.
In the latter half of the seventeenth century the great
improvement of the microscope as an instrument of inves-
tigation paved the way to a new phase of the discussion
of spontaneous generation. This came about because of
the fact that the instrument brought into view a world
of life formed of individuals so minute — so close as it
seemed to the ultimate particles of matter — as to suggest
an easy passage from atoms to organisms. Animal and
vegetable infusions exposed to the air were found clouded
and crowded with creatures far beyond the reach of
unaided vision, but perfectly visible to an eye strengthened
by the microscope. With reference to their origin these
organisms were called 'Infusoria/ Stagnant pools were
found full of them, and the obvious difficulty of assigning
a germinal origin to existences so minute furnished the

THE ORIGIN OF LIFE 49

precise condition necessary to give new play to the notion
of heterogenesis or spontaneous generation.

Many scientific men of that day took up the question of
the origin of the microscopic organisms. A Scotch priest,
Turbervill Needham (1750), showed that animalcules (In-
fusorians and the like) appeared even in decoctions which
had been boiled and corked up. As we should now say, this
result was due to imperfect sterilization and imperfect
corking of the tubes ; but it was used by Buffon, who was
much interested in Needham's work, to bolster up a pet
theory of his, that life resided in indestructible organic
molecules, and that these were liberated after death or in
decomposition as the aforesaid Infusorians or animalcules.

This result of Needham's was contradicted in 1777 by
the Abbe Spallanzani who charged his flasks with organic
infusions, sealed their necks with the blowpipe, subjected
them in this condition to the heat of boiling water, and
subsequently exposed them to temperatures favorable to
the development of life. The infusions continued un-
changed for months, and when the flasks were subsequently
opened no trace of life was found. Spallanzani's flasks
must have contained but little air and it was objected by
the chemists, who had now discovered oxygen, that life
could not be expected where this gas was more or less
absent, and that the boiling process might irretrievably
injure the 'organic molecules.'

Schultze and Schwann (1836, 1837) were thus led to
make fresh experiments ; they carefully boiled the infusions
and supplied air which had been passed through red-hot
tubes or acids — , no animacules appeared; they then sup-
plied air which had not been so purified, and in the same
infusions the animalcules appeared. Schwann's final con-
clusion was "that putrefaction is due to decompositions of
organic matter attendant on the multiplication therein of
minute organisms. These organisms are derived not from
the air but from something contained in the air, which is
destroyed by a sufficiently high temperature."

50 BIOLOGY

The next step in advance came in 1854, when Schroeder
and Dusch did what is now so often done as a class
experiment : they boiled infusions, and while the steam was
coming off plugged the neck of the flask with cotton-wool.
This allows the passage of oxygen, but keeps back germs ;
and in most cases the sterilization is quite effective. In
1859 a book was published which seemed to overturn some
of the best established facts of previous investigators. Its
title was 'Heterogenic,' and its author was F. A. Pouchet,
Director of the Museum of Natural History at Rouen,
a strong believer in the theory of spontaneous generation.
"Never," says Tyndall, "did a subject require the exercise
of the cold critical faculty more than this one. To a man
of Pouchet's temperament the subject was full of danger —
danger not lessened by the theoretic bias with which he
approached it."

Pasteur's work in chemistry and in special research in
fermentation had prepared him for this investigation. He
knew more than Pouchet as to the insidious ways of
microbes; he showed the weak point of his antagonist's
experiments, and gained the prize offered in i860 by the
Academy, for "well-contrived experiments to throw new
light upon the question of spontaneous generation." Pas-
teur threw light on the subject by his study of the organ-
ized particles — many of them living or dead bacteria —
which float in the air. He opened twenty sealed flasks
containing organic infusions in the pure air of the Mer
de Glace, and only one thereafter showed signs of life ; but
eight out of twenty opened on the plains, and all of the
twenty opened in town, developed germs. These and other
experiments, carried out with a severity perfectly obvious
to the instructed scientific reader, and accompanied by a
logic equally severe, restored the conviction that, even in
these lower reaches of the scale of being, life does not
appear without the operation of antecedent life. Pasteur's
brusque conclusion was that "spontaneous generation is a
chimera."

THE ORIGIN OF LIFE 51

These experiments by Pasteur laid the foundation for a
long series of studies of micro-organisms by himself, Tyn-
dall and others. Tyndall describes the famous experiment
in which he proves that "not in the air, nor in the in-
fusions, nor in anything continuous diffused through the
air, but in discrete (organic) particles, suspended in the
air and nourished by the infusions, we are to seek the
cause of life" as follows: "Supposing an infusion intrinsic-
ally barren, but readily susceptible of putrefaction when
exposed to common air, to be brought into contact with
unilluminable air (air freed from dust particles), what
would be the result? It would never putrefy. Let a con-
densed beam be sent through a large flask or bolthead con-
taining common air. The track of the beam is seen within
the flask — the dust revealing the light, and the light reveal-
ing the dust. Cork the flask, stuff* its neck with cotton-
wool, or simply turn its mouth downward and leave it un-
disturbed for a day or two. Examined afterward with the
luminous beam, no track is visible ; the light passes through
the flask as through a vacuum. The floating matter has
abolished itself, being now attached to the interior surface
of the flask. Were it the object effectually to detain the
dirt, that surface might be coated with some sticky sub-
stance. Here, then, without 'torturing' the air in any way,
is a means of ridding it, or rather of enabling it to rid
itself, of floating matter.

"We have now to devise a means," he continues, "of
testing the action of such spontaneously purified air upon
putrescible infusions. Wooden chambers, or cases, accord-
ingly are constructed, having glass fronts, side-windows
and back-doors. Through the bottoms of the chambers
test-tubes pass air-tight; their open ends, for about one-
fifth of the length of the tubes, being within the chambers.
Provision is made for a free connection through sinuous
channels between the inner and the outer air. Through
such channels, tho open, no dust will reach the chamber.
The top of each chamber is perforated by a circular hole

52 BIOLOGY

two inches in diameter, closed air-tight by a sheet of india-
rubber. This is pierced in the middle by a pin, and through
the pinhole is pushed the shank of a long pipette, ending
above in a small funnel. The shank also passes through
a stuffing-box of cotton-wool moistened with glycerine;
so that, tightly clasped by the rubber and wool, the pipette
is not likely in its motions up and down to carry any dust
into the chamber.

'The chamber is carefully closed and permitted to remain
quiet for two or three days. Examined at the beginning
by a beam sent through its windows, the air is found laden
with floating matter, which in three days has wholly disap-
peared. To prevent its ever rising again, the internal sur-
face of the chamber was at the outset coated with glycerine.
The fresh but putrescible liquid is introduced into the six
tubes in succession by means of the pipette. Permitted to
remain without further precaution, every one of the tubes
would putrefy and fill itself with life. The liquid has been
in contact with the dust-laden air outside by which it has
been infected, and the infection must be destroyed. This is
done by plunging the six tubes into a bath of heated oil
and boiling the infusion. The time requisite to destroy
the infection depends wholly upon its nature. Two min-
utes' boiling suffices to destroy some contagia, whereas two
hundred minutes' boiling fails to destroy others. After the
infusion has been sterilized, the oil-bath is withdrawn, and
the liquid, whose putrescibility has been in no way affected
by the boiling, is abandoned to the air of the chamber.

"With such chambers I tested, in the autumn and winter
of 1875-6, infusions of the most various kinds, embracing
natural animal liquids, the flesh and viscera of domestic
animals, game, fish and vegetables. More than fifty
chambers, each with its series of infusions, were tested,
many of them repeatedly. There was no shade of uncer-
tainty in any of the results. In every instance we had,
within the chamber, perfect limpidity and sweetness, which
in some cases lasted for more than a year — without the

THE ORIGIN OF LIFE 53

chamber, with the same infusion, putridity and its char-
acteristic smells. In no instance was the least countenance
lent to the notion that an infusion deprived by heat of its
inherent life, and placed in contact with air cleansed of
its visibly suspended matter, has any power to generate life
anew.

"The argument is now to be clenched by an experiment
which will remove every residue of doubt as to the ability
of the infusions here employed to sustain life. We open
the back doors of our sealed chambers, and permit the
common air with its floating particles to have access to
our tubes. For three months they have remained pellucid
and sweet — flesh, fish and vegetable extracts purer than
ever cook manufactured. Three days' exposure to the
dusty air suffices to render them muddy, fetid and swarm-
ing with infusorial life. The liquids are thus proved, one
and all, ready for putrefaction when the contaminating
agent is applied."

Many such experiments as these established beyond a
doubt the fact that no known case of spontaneous genera-
tion occurs under the present conditions of life. 'Omne
vivum e vivo' would correctly express the accepted view of
the twentieth-century biologists, provided it be translated
'all life from life' under known existing conditions, but
probably life from the lifeless in its first origin on this
earth or elsewhere.

That all living matter existing to-day has descended
directly from preexisting living matter is the doctrine of
'Biogenesis,' the rival of the dethroned doctrine of 'Abio-
genesis.' Observe that the doctrine of biogenesis refers
simply to what is now happening and has been happening
in all times of which we have strictly scientific records.
The theory of biogenesis thus understood as the prevailing
natural process will still stand even if, as seems probable,
some lucky physiological chemist succeeds in synthesizing
under artificial conditions new living matter, entirely inde-
pendent of preexisting living matter. He will have done

54 BIOLOGY

nothing more than repeat under unusual and artificially
controlled conditions the processes which probably occurred
when in the evolution of matter in the post-incandescent
ages of the earth living proteid, progenitor of all future
organisms, first came into existence. So far as the future
succession of organisms on this earth is concerned, it can-
not even be imagined that living matter synthesized in
scientific laboratories will play any part. The law of bio-
genesis, now established as firmly as that of gravitation,
may be expected to stand as the very rock of ages in
the science of biology.

Such is in outline the story of one of the greatest
fallacies with which modern science has had to deal. But,
strange to say, the establishment of the truth of biogenesis,
which directly is of little importance to man, has laid the
foundation for practical researches of a most momentous
kind. To Pasteur and the other great generals in the
last battles against the theory of spontaneous generation
is due the honor of the establishment of the new science
of bacteriology which in the last two decades has come to
play such a mighty part in the development of modern life.

CHAPTER V

CELL LIFE

In the two preceding chapters living substance has
been spoken of as existing in separate organic individuals,
plants and animals. It is not known to exist in a mass
not organized as an individual plant or animal. Many
early philosophers did conceive of living matter as exist-
ing without individualization. Thus Oken (1805), in his
Ur-Schleim theory, when he says that every organic thing
came from primitive slime which originated in the sea
from organic matter in the course of planetary evolution,
simply repeated an idea passed down by the Greek philos-
opher Anaximenes and others.

Haeckel's theory of the Monera as the simplest of living
things allies him to this belief. He says : "In the Monera,
the simplest conceivable organisms, the whole body con-
sists merely of plasm, corresponding to the 'primitive
slime' of the earlier natural philosophers." And again, in
'The Natural History of Creation/ he describes the
Monera as "simple, soft, albuminous lumps . . . without
component parts, whose whole albuminous body is as
homogeneous in itself as an inorganic crystal."

Huxley also for a time supported this view. In 1869 he
described a peculiar sticky mud from the bottom of the
Atlantic. The stickiness was apparently due to the pres-
ence of innumerable lumps of a transparent gelatinous
substance without discoverable nuclei or membranous,
envelopes. Huxley interpreted this matter to be masses
55

56

BIOLOGY

of protoplasm. He thought it a new form of the simple
animate things (Monera) which had been described by
Haeckel, and therefore named it Bathybius Haeckelii.
Haeckel himself examined the mud and agreed with
Huxley's interpretation. Later studies, however, con-

Fig. 2 — Unicellular Animals and Plants.
A., animal, 'Paramecium caudatum' ; c. vac, contractile vacuole ;
gul., gullet ; mth., mouth ; f . vac, food vacuole ; B. and C,
plants, 'Micrasterias' and 'Cosmarium.'

vinced Huxley that the slime was in reality some sort of
inorganic precipitate, and at the British Association meet-
ing in 1879 ne made a public renunciation of Bathybius.
Leaving this interesting historical conception of living
matter in extensive undifferentiated masses, the idea of

CELL LIFE 57

the individualization of living substance prevails in mod-
ern biological science. An organic individual is a unitary-
mass of living substance. Microscopic study of plants
and animals shows them to be made up of these unitary
masses — the cells. An illustration will make this point
clear. Dissection shows that an organ of an animal's
body is composed of several building materials, or tissues,
such as muscular tissue, nervous tissue, bony tissue, etc.
The microscopic study of these tissues reveals the fact
that they are composed of small masses of protoplasm — ■
the cells. Hence a plant or animal with several tissues
is a multicellular organism. There are many simple plants
and animals whose body consists of a single cell and
these are called unicellular animals. Every such simple
organism is an individual. The cell then is the lowest
stage of individuality.

It is true, as will be explained in detail later, that the
microscope reveals different structures in cells. Especially
characteristic are the main body of the cell, the 'cytoplasm,"
and the 'nucleus' imbedded in it. This suggests the possi-
bility that the cell is composed of still lower individuals.
However, many studies have shown that neither nucleus
nor cytoplasm can exist independently, and hence they can-
not be regarded as unit masses or individuals. The cell is
the lowest stage of individuality known to modern
biology.

Looking at the organic world synthetically, the cell
stands prominent in a scheme of the five stages of indi-
viduality found there.

Individuals of the first order are cells. They represent
elementary organisms that are not composed of lower
units capable of life. An example is any unicellular
animal or plant.

Individuals of the second order are tissues. The tissues
are associations of individuals of the first order, each one
of which is like the others. Examples are the muscular

58 BIOLOGY

and nervous tissues of an animal, the conducting and sup-
porting tissues of a plant.

Individuals of the third order are organs. The organs
are associations of various kinds of individuals of the
second order. Examples are the stomach and heart of
an animal, the leaf and root of a plant.

Individuals of the fourth order are complex organisms.
These are associations of various individuals of the third
order. Examples are common animals and plants, whose
bodies consist of organs united.

Individuals of the fifth order are communities. The
communities are associations of individuals of the fourth
order.

It should be noted that an individual of a higher order
consists of an assemblage of those of the next lower order.
Thus communities consist of persons, persons of organs,

Fig. 3 — Connective Tissues — Animal.
, cells ; e., elastic fibers ; w., white fibers all embedded in a deli-
cate ground substance. (Parker and Parker.)

organs of tissues, and tissues of cells. In the end all
living individual plants and animals are composed of cells
and the cell is the seat of those events the expression of
which is life. The cell is the life unit, the elementary
organism, or as Virchow has said, the vital elementary-
unit.

The realization that it is in the cell that the answers

CELL LIFE

59

to the great problems of biology are to be found is quite
modern. Nevertheless this fact has already profoundly
modified many phases of the science of life. Professor
Wilson of Columbia University, justly regarded as one
of the foremost biologists who have worked at the prob-
lems of cytology, or the biology of cells, has well outlined
the influence of the cell theory on modern biology. He
says : "It was the cell-theory that first brought the struc-
ture of plants and animals under one point of view, by
revealing their common plan of organization. It was
through the cell-theory that Kolliker, Remak, Nageli and
HofTmeister opened the way to an understanding of the
nature of embryological development, and the law of

Fig. 4 — Bony and Cartilaginous Tissue.

genetic continuity lying at the basis of inheritance. It
was the cell-theory again which, in the hands of Goodsir,
Virchow and Max Schultze, inaugurated a new era in the
history of physiology and pathology, by showing that all
the various functions of the body, in health and in disease,
are but the outward expression of cell-activities. And at a
still later day it was through the cell-theory that Hertwig,
Fol, Van Beneden and Strasburger solved the long-stand-
ing riddle of the fertilization of the Qgg and the mechanism
of hereditary transmission. No other biological generali-
zation, save only the theory of organic evolution, has
brought so many apparently diverse phenomena under a
common point of view or has accomplished more for the
unification of knowledge. The cell-theory must, therefore,

60 BIOLOGY

be placed beside the evolution-theory as one of the foun-
dation stones of modern biology."

The history of the development of the idea that cells
are the elementary units of living matter is essential to an
understanding of present-day problems, and therefore a
rapid survey of the important historical points may be
made. These have been well traced by Oscar Hertwig,
Professor at Berlin, in his famous 'Die Zelle und die
Gewebe.' "The conception or idea connected with the
word 'cell,' used scientifically," he says, "has been con-
siderably altered during the last fifty years. The history
of the various changes in this conception, or the history
of the cell-theory, is of great interest, and nothing could
be more suitable than to give a short account of this his-
tory in order to introduce the beginner to the series of
conceptions connected with the word 'cells'; this, indeed,
may prove useful in other directions. For while, on the
one hand, we see how the conception of the cell which
is at present accepted, has developed gradually out of
older and less complete conceptions, we realize, on the
other hand, that we cannot regard it as final or perfect;
but on the contrary, we have every ground to hope that
better and more delicate methods of investigation, due
partly to improved optical instruments, may greatly add
to our present knowledge, and may perhaps enrich it
with a quite new series of conceptions.

"The theory that organisms are composed of cells was
first suggested by the study of plant-structure. At the
end of the seventeenth century the Italkn, Marcellus
Malpighi, and the Englishman, Grew, gained the first in-
sight into the more delicate structure of plants ; by means
of low magnifying powers they discovered, in the first
place, small room-like spaces, provided with firm walls,
and filled with fluid, the cells; and in the second, various
kinds of long tubes, which, in most parts, are embedded
in the ground tissue, and which, from their appearance, are
now called spiral ducts or vessels. Much greater impor-

CELL LIFE 6r

tance, however, was attached to these facts after the in-
vestigations which were carried on in a more philosophical
spirit by Bahn toward the end of the eighteenth century
were published.

"Caspar Friedrich Wolff, Oken, and others, raised the
question of the development of plants, and endeavored to
show that the ducts and vessels originated in cells. Above
all, Treviranus rendered important service by proving in
his treatise, entitled 'Vom inwendigen Bau der Gewachse/
published in 1808, that vessels develop from cells.

"The study of the lowest plants has also proved of the
greatest importance in establishing the cell-theory. Small
algae were observed, which during their whole lifetime
remain either single cells, or consist of simple rows of
cells, easily to be separated from one another. Finally,
the study of the metabolism of plants led investigators to
believe that, in the economy of the plant, it is the cell
which absorbs the nutrient substances, elaborates them,
and gives them up in an altered form. Thus, at the begin-
ning of the last century, the cell was recognised by many
investigators as the morphological and physiological ele-
mentary unit of the plant."

These views, however, only obtained general acceptance
after the year 1838, when M. Schleiden, who is so fre-
quently cited as the founder of the cell-theory, published
in Miiller's 'Archives' his famous paper, 'Beitrage zur
Phytogenesis.' In this paper Schleiden endeavored to
explain the mystery of cell-formation. He thought he had
found the key to the difficulty in the discovery of the
English botanist, R. Brown, who, in the year 1833, while
making investigations upon orchids, discovered nuclei.
Schleiden made further discoveries in this direction; he
showed that nuclei are present in many plants, and as they
are invariably found in young cells, the idea occurred to
him that the nucleus must have a near connection with
the mysterious beginning of the cell, and in consequence
must be of great importance in its life-history.

62 BIOLOGY

The way in which Schleiden made use of this idea,
which was based upon erroneous observations, to build up
a theory of phytogenesis, must now be regarded as a mis-
take; on the other hand, it must not be forgotten that his
perception of the general importance of the nucleus was
correct up to a certain point, and that this one idea has in
itself exerted an influence far beyond the narrow limits
of the science of botany, for it is owing to this that the
cell-theory was first applied to animal tissues. For it is
just in animal cells that the nuclei stand out most dis-
tinctly from among all the other cell-contents," thus
showing most evidently the similarity between the his-
tological elements of plants and animals. Thus this little
treatise of Schleiden's in 1838 marks an important his-
torical turning-point, and since this time the most impor-
tant work in the building up of the cell-theory has been
done upon animal tissues.

Attempts to represent the animal body as consisting of
a large number of extremely minute elements had been
made before Schleiden's time, as is shown by the hy-
potheses of Oken, Heusinger, Raspail, and many other
writers. However, it was impossible to develop these
theories further, since they were based upon so many
incorrect observations and false deductions that the good
in them was outweighed by their errors.

Schwann, however, was the first to attempt to frame a
really comprehensive cell-theory which should refer to all
kinds of animal tissues. During the year 1838 Schwann,
in the course of a conversation with Schleiden, was in-
formed of the new theory of cell-formation, and of the
importance which was attached to the nucleus in plant-
cells. It immediately struck him, as he himself relates,
that there are a great many points of resemblance between
animal and vegetable cells. He therefore, with most
praiseworthy energy, set on foot a comprehensive series of
experiments, the results of which he published in 1839.

Thus Schwann originated a theory which, altho imper-

CELL LIFE 63

feet in many respects, yet is applicable both to plants and
animals, and which, further, is easily understood, and in
the main correct. According to this theory, every part of
the animal body is either built up of elements, correspond-

$.m l.m,.m

Fig- 5 — Transverse Section of Frog's Stomach.

Showing the muscular, connective and epithelial tissues of which

it is composed. 1. m., longitudinal muscles ; b. v., blood

yessel ; c. m., circular muscles ; s. m., connective tissue ; ep.,,

epithelical tissue; g. gl., gastric gland. (Parker and Parker.)

ing to the plant-cells, massed together, or is derived from
such elements which have undergone certain meta-
morphoses. This theory has formed a satisfactory foun-

64 BIOLOGY

dation upon which many further investigations have been
based.

However, as has been mentioned already, the conception
which Schleiden and Schwann formed of the plant and
animal element was incorrect in many respects. They
both defined the cell as a small vesicle, with a firm mem-
brane enclosing fluid contents, that is to say as a small
chamber, or 'cellula/ in the true sense of the word. They
considered the membrane to be the most important and
essential part of the vesicle, for they thought that in con-
sequence of its chemico-physical properties it regulated
the metabolism of the cell.

The series of conceptions which now associate with
the word 'cell' are, thanks to the great progress made
during the last fifty years, essentially different from the
above. Schleiden and Schwann's cell-theory has under-
gone a radical reform, having been superseded by the
Protoplasmic theory, which is especially associated with
the name of Max Schultze.

The History of the Protoplasmic theory is also of
supreme interest. Even Schleiden observed in the plant-
cell, in addition to the cell sap, a delicate transparent
substance containing small granules; this substance he
called plant slime. In the year 1846 Mohl called it
Protoplasm, a name which has since become so significant,
and which before had been used by Purkinje for the sub-
stance of which the youngest animal embryos are formed.
Further, he presented a new picture of the living appear-
ance of plant protoplasm ; he discovered that it completely
filled up the interior of young plant cells, and that in
larger and older cells, it absorbed fluid, which collected
into droplets or vacuoles. Finally, Mohl established the
fact that protoplasm, as has been already stated by
Schleiden about the plant slime, shows strikingly peculiar
movements; these were first discovered in the year 1772
by Bonaventura Corti, and later in 1807 by C. L. Tre-

CELL LIFE 65

viranus, and were described as "the circulatory move-
ments of the cell-sap."

By degrees further discoveries were made, which added
to the importance attached to these protoplasmic contents
of the cell. In the lowest algae, as was observed by Cohn
and others, the protoplasm draws itself away from the cell
membrane at the time of reproduction, and forms a naked
oval body, the swarm-spore, which lies freely in the cell
cavity ; this swarm-spore soon breaks down the membrane
at one spot, after which it creeps out through the opening,
and swims about in the water by means of its cilia, like
an independent organism ; but it has no cell membrane.

Similar facts were discovered through the study of the
animal cell, which could not be reconciled with the old
conception of the cell. A few years after the enunciation
of Schwann's theory, various investigators, Kolliker, Bi-
schoff and others, observed many animal cells in which
no distinct membrane could be discovered, and in conse-
quence a lengthy dispute arose as to whether these bodies
were really without membranes, and hence not cells, or
whether they were true cells. Further, movements similar
to those seen in plant protoplasm were discovered in the
granular ground substance of certain animal cells, such as
the lymph corpuscles. In consequence Remak applied the
term protoplasm, which Mohl had already made use of for
plant cells, to the ground substance of animal cells.

Important insight into the nature of protoplasm was
afforded by the study of the lowest organism, Rhizopoda
(Amoebae), Myxomycetes, etc. Dujardin had called the
slimy, granular, contractile substance of which they are
composed 'Sarcode.' Subsequently, Max Schultze and de
Bary proved, after most careful investigation, that the
protoplasm of plants and animals and the sarcode of the
lowest organisms are identical.

In consequence of these discoveries, investigators, such
as Nageli, Alexander Braun, Leydig, Kolliker, Cohn, de
Bary, etc., considered the cell membrane to be of but minor

66 BIOLOGY

importance in comparison to its contents; however, the
credit is due to Max Schultze, above all others, of having
made use of these later discoveries in subjecting the cell
theory of Schleiden and Schwann to a searching critical
examination, and of founding a protoplasmic theory. He
attacked the former articles of belief, which it was neces-
sary to renounce, in four excellent tho short papers, the
first of which was published in the year i860.

He based his theory that the cell-membrane is not an
essential part of the elementary organisms of plants and
animals on the following three facts : First, that a certain
substance, the protoplasm of plants and animals, and the
sarcode of the simplest forms, which may be recognised
by its peculiar phenomena of movement, is found in all
organisms ; secondly, that altho as a rule the protoplasm of
plants is surrounded by a special firm membrane, yet under
certain conditions it is able to become divested of this
membrane, and to swim about in water as in the case of
naked swarm-spores ; and finally, that animal cells and the
lowest unicellular organisms very frequently possess no
cell-membrane, but appear as naked protoplasm and naked
sarcode. It is true that he retains the term 'cell/ which
was introduced into anatomical language by Schleiden
and Schwann; but he defines it as a small mass of pro-
toplasm endowed with the attributes of life.

Hence it is evident that the term 'cell' is incorrect.
That it, nevertheless, has been retained, may be partly
ascribed to a kind of loyalty to the vigorous combatants,
who, as Briicke expresses it, conquered the whole field of
histology under the banner of the cell-theory, and partly
to the circumstance, that the discoveries which brought
about the new reform were only made by degrees, and
were only generally accepted at a time when, in conse-
quence of its having been used for several decades of
years, the word cell had taken firm root in the literature
of the subject.

Since the time of Briicke and Max Schultze knowledge

CELL LIFE

67

of the true nature of the cell has increased considerably.
Great insight has been gained into the structure and the
vital properties of the protoplasm, and in especial, knowl-
edge of the nucleus, and of the part it plays in cell-multi-
plication, and in sexual reproduction, has recently made
great advances. The earlier definition, "the cell is a little
mass of protoplasm," must now be replaced by the follow-

B8S8S8SSSS55pnB

6 — Cross-section of a Leaf Showing Tissues and the
Cells of Which They Are Composed.
epidermal tissue showing epidermal cells ; p., palisade paren-
chyma ; sp., spongy parenchyma cells ; b., vein composed of
conducting and supporting tissue; a., air spaces; s., stoma.
(Bergen and Davis.)

ing: "The cell is a little mass of protoplasm, which con-
tains in its interior a specially formed portion, the
nucleus."

It is evident from the preceding history of the cell-
theory that the term 'cell' is a biological misnomer; for
cells only rarely assume the form implied by the word of
hollow chambers surrounded by solid walls. The term is
merely a historical survival of a word casually employed
by the botanists of the seventeenth century to designate
the cells of certain plant-tissues which, when viewed in

68

BIOLOGY

section, give somewhat the appearance of a honeycomb.
The cells of these tissues are, in fact, separated by con-
spicuous solid walls which were mistaken by Schleiden,
followed by Schwann, for their essential part. The living-
substance contained within the walls was at first over-
looked or was regarded as a waste-product, a view based
upon the fact that in many important plant-tissues such
as cork or wood it may wholly disappear, leaving only the
lifeless walls. Researches showed, however, that most

Fig. 7 — Section Through a Part of a Sunflower Stem Show-
ing Tissues and the Cells of Which They Are Composed.
a., conducting tissue ; b., supporting tissue ; c, parenchyma.
(Vines.)

living cells are not hollow but solid bodies, and that in
many cases — for example, the colorless corpuscles of blood
and lymph — they are naked masses of protoplasm not
surrounded by definite walls. Thus it was proved that
neither the vesicular form nor the presence of surrounding
walls is an essential character, and that the cell-contents —
i.e., the protoplasm — must be the seat of vital activity.

Within the cell contents lies a body, usually of definite
rounded form, known as the nucleus, and this in turn

CELL LIFE 69

often contains one or more smaller bodies or nucleoli.
By some of the earlier workers the nucleus was supposed
to be, like the cell-wall, of secondary importance, and
many forms of cells were described as being devoid of a
nucleus ('cytodes' of Haeckel). Nearly all later researches
have indicated, however, that the characteristic nuclear
material, whether forming a single body or scattered in
smaller masses, is always present, and that it plays an
essential part in the life of the cell. Besides the presence
of protoplasm and nucleus, no other structural features of
the cell are yet known to be of universal occurrence.

"We may," says Wilson, "therefore still accept as valid
the definition given more than thirty years ago by Leydig
and Max Schultze, that a cell is a mass of protoplasm con-
taining a nucleus, to which we may add Schultze's state-
ment that both nucleus and protoplasm arise through the
division of the corresponding elements of a preexisting
cell."

The form of cells is highly variable. In isolated cells,
especially those floating freely in a fluid and not subjected
to unequal pressure, the spherical form is common, but
even such free cells may be modified in form by internal
movements and differentiations of the cell-substance. For
example, some egg-cells are spherical while others are
ovoidal; muscle cells are elongated; nerve cells much
branched; the white cells of the blood are irregular in
shape because of their movements. But no matter how
diverse the form of the cells, their structure is essentially
the same.

As already suggested, a cell-wall or membrane is usually,
tho not always present. Sometimes the cell-substance has
no more of a limiting membrane than has a drop of oil
floating in water, that is, there is simply an undifferenti-
ated film separating it from its surroundings. The cell-mass
or cell-substance consists of protoplasm, the active living
substance, in which may be embedded granules of lifeless
substances. If the term protoplasm is accepted as syn-

70

BIOLOGY

Fig. 8 — Examples of Cell-shapes.
epidermal cell of 'Callitriche' ; b., stellate cell of flowering-
rush ; c, bast cell of larch ; d., stellate hair of 'Deutzia' ; e.,
stellate cell of yellow water-lily ; £., part of a branching-
lactiferous cell of 'Euphorbia' ; g., h., i., p., one-celled plants ;
j., a human cartilage cell; k., outer cell-wall of a pollen grain
of 'Thunbergia' ; m., diagram of a one-celled animal ; n.,
nerve-cell ; o., germ-cell of a stonewort, unequally magnified.
(Sedgwick and Wilson.)

CELL LIFE 71

onymous with living matter, then there is protoplasm both
in the main body of the cell and also in the specially dif-
ferentiated mass, most commonly central in position,
known as the nucleus. It is convenient to call the proto-
plasm outside the nucleus 'cytoplasm' and that within
the nucleus the 'karyoplasm' or 'nucleoplasm.'

In the cytoplasm there are various lifeless substances
(metaplasm). Some of these, like fat and starch, are
reserve food absorbed but not yet used by the cell, others,
like pigment and the cell-wall, are the lifeless products of
life activity. The amount of metaplasm is frequently
vastly greater than the amount of protoplasm in a cell. For
example, a hen's egg just before leaving the ovary is a
cell about one inch in diameter (the yolk of the egg). A
small white disk on the upper surface consists of con-
centrated protoplasm, but the greater part of this enor-
mous egg-cell is made up of stored yolk (metaplasm) to
be used as food by the chick in its development during
incubation.

The nucleus is usually surrounded by a definite mem-
brane, the nuclear membrane. Within this membrane and
embedded in the general protoplasmic basis, there are
granules or masses of a substance which has a strong
affinity for certain chemical dyes, hence called 'chromatin,'
When this chromatin is massed into rod-shaped bodies, as
happens in the process of cell-division, the term 'chro-
mosomes' is applied to these masses of chromatin. Then,
too, other bodies, nucleoli, are often present. Their nature
is not clearly understood, probably because they are ex-
tremely variable.

Careful study of the nucleus during all its phases gives
reason to believe that its structural basis is similar to that
of the cell-body; and that during the course of cell-
division, when the nuclear membrane usually disappears,
cytoplasm and karyoplasm come into direct continuity.
For these and other reasons the terms 'nucleus' and 'cell-
body' should probably be regarded as only topographical

72 BIOLOGY

expressions denoting two differentiated areas in a common
structural basis. The terms 'karyoplasm' and 'cytoplasm'
possess, however, a specific significance owing to the fact
that there is on the whole a definite chemical contrast be-
tween the nuclear substance and that of the cell-body, the
former being characterized by the abundance of a sub-
stance rich in phosphorus known as 'nuclein,' while the
latter contains no true nuclein and is especially rich in
albuminous substances such as nucleoalbumins, albumins,
globulins, and the like, which contain little or no phos-
phorus.

"Both morphologically and physiologically," says Wilson,
"the differentiation of the active cell-substance into nucleus
and cell-body must be regarded as a fundamental char-
acter of the cell because of its universal, or all but univer-
sal, occurrence, and because there is reason to believe
that it is in some manner an expression of the dual aspect
of the fundamental process of metabolism, construc-
tive and destructive, that lies at the basis of cell life."

In addition to the cytoplasm or cell-body and the nucleus
recent biologists believe that an extremely minute body
lying just outside the nuclear membrane, and known as
the 'centrosome,' is an essential element of the cell. The
centrosome has been seen in a large number of cells, is
known to play an important part in cell-division and in the
fertilization of egg-cells and has been regarded by some
cytologists as the 'dynamic center' of the cell. It is still
under investigation, and the interested reader should refer
to such technical books as Wilson's 'The Cell in Develop-
ment and Inheritance' for the latest studies of its structure.
Some animal and plant-cells appear to differ so much from
one another as to their form and contents, that, at first
sight, they seem to have nothing in common, and hence it
seems impossible to compare them. For instance, if a
cell at the growing-point of a plant be taken and com-
pared with one filled with starch granules from the tuber
of a potato, or if the contents of an embryo cell from a

CELL LIFE 73

germinal disk be compared with those of a fat cell, or o£
one from the egg of an Amphibian filled with yolk
granules, the inexperienced observer sees nothing but con-
trasts. Nevertheless, all these exceedingly different cells
are seen on closer examination to be similar in one respect
— i.e., in the possession of a very important, peculiar mix-
ture of substances, which is sometimes present in large
quantities, and sometimes only in traces, but which is never
wholly absent in any elementary organism. In this mix-
ture of substances the wonderful vital phenomena may very
frequently be observed (contractility, irritability, etc.) ;
and, moreover, since in young cells, in lower organisms,
and in the cells of growing-points and germinal areas, it
is in the cell-substance alone (the nucleus of course being
excepted) that these properties have been observed, this
substance has been recognised as the chief supporter ot
the vital functions. It is the protoplasm or 'forming
matter.'

In order to know what protoplasm is, it is advisable to
examine it in those cells in which it is present in large
quantities, and in which it is as free as possible from ad-
mixture with other bodies; and among such the most
suitable are those organisms from the study of which
the founders of the protoplasmic theory formed their con-
ception of the nature of this substance. Such organisms
are young plant-cells, Amoebae, and the lymph corpuscles
of vertebrates.

The protoplasm of unicellular organisms, and of plant
and animal cells appears as a viscid substance, which is
almost always colorless, which will not mix with water,
and which, in consequence of a certain resemblance to
slimy substances, was called by Schleiden the 'slime of the
cell.' Its refractive power is greater than that of water,
so that the most delicate threads of protoplasm, altho
colorless, may be distinguished in this medium. Minute
granules, the 'microsomes,' which look only like dots, are
always present in greater or less numbers in all protoplasm,

74 BIOLOGY

and may be seen with a low power of the microscope to
be embedded in a homogeneous ground substance.

As to the very minute structure of protoplasm, "most
of the earlier observers," says Wilson, "regarded the
meshwork as a fibrillar structure, either forming a con-
tinuous network or reticulum somewhat like the fibrous
network of a sponge or consisting of disconnected threads,
whether simple or branching ("filar theory" of Flem-
ming), and the same view is widely held at the present
time. The meshwork has received various names in ac-
cordance with this conception, among which may be men-
tioned 'reticulum/ 'threadwork,' 'spongioplasm,' 'mitome,'
'filar substance,' all of which are still in use. Under this
view the 'granules' described by Schultz, Virchow and
still earlier observers have been variously regarded as
nodes of the network, optical sections of the threads, or
as actual granules ("microsomes") suspended in the net-
work as described above."

Widely opposed to these views is the 'alveolar theory'
of Biitschli, which has won an increasing number of ad-
herents. Biitschli regards protoplasm as having a foam-
like alveolar structure ("Wabenstruktur"), nearly similar
to that of an emulsion and he has shown in a series of
beautiful experiments that artificial emulsions variously
prepared, may show the microscope a marvelously close
resemblance to living protoplasm, and further that drops
of oil-emulsion suspended in water may even exhibit
amoeboid changes of form.

The two (three) general views hereinbefore outlined
may justly be designated respectively as the fibrillar
(reticular or filar) and alveolar theories of protoplas-
mic structure, and each of them has been believed by
some of its adherents to be universally applicable to all
forms of protoplasm. Beside them may be placed, as a
third general view, the granular theory especially asso-
ciated with the name of Altmann, by whom it has been
most fully developed, tho a number of earlier writers have

CELL LIFE 75

held similar views. According to Altmann's view, which
apart from its theoretical development approaches in some
respects that of Biitschli, protoplasm is compounded of
innumerable minute granules which alone form its essen-
tial active basis ; and while fibrillar or alveolar structures
may occur, these are of only secondary importance.

Which of these views is correct ? The present tendency
of cytologists is toward the conclusion that none of them
is of universal application and that all exist under certain
conditions. In support of this may be cited the studies
of Professor Wilson, who has been led to the conclusion
that "no universal formula for protoplasmic structure can
be given. In that classical object, the echinoderm-egg, for
example, it is easy to satisfy oneself, both in the living
cell and in sections, that the protoplasm has a beautiful
alveolar structure, exactly as described by Biitschli in the
same object. This structure is here, however, entirely of
secondary origin; for its genesis can be traced step by
step during the growth of the ovarian eggs through the
deposit of minute drops in a homogeneous basis, which
ultimately gives rise to the interalveolar walls. In these
same eggs the astral systems formed during their subse-
quent division are, I believe, no less certainly fibrillar ; and
thus we see the protoplasm of the same cell passing suc-
cessively through homogeneous, alveolar, and fibrillar
phases, at different periods of growth and in different con-
ditions of physiological activity.

"There is good reason to regard this as typical of pro-
toplasm in general. Biitschli's conclusions, based on re-
searches so thoro, prolonged and ingenious, are entitled
to great weight; yet it is impossible to resist the evidence
that fibrillar and granular as well as alveolar structures
are of wide occurrence ; and while each may be character-
istic of certain kinds of cells, or of certain physiological
conditions, none is common to all forms of protoplasm. If
this position be well grounded, we must admit that the
attempt to find in visible protoplasmic structure any ade-

y6 BIOLOGY

quate insight into its fundamental modes of physiological
activity has thus far proved fruitless. We must rather
seek the source of these activities in the ultramicroscopical
organization, accepting the probability that apparently
homogeneous protoplasm is a complex mixture of sub-
stances which may assume various forms of visible struc-
ture according to its modes of activity.

"Much discussion has been given to the question as to
which of the visible elements of the protoplasm should be
regarded as the 'living' substance proper. Later dis-
cussions have shown the futility of this discussion, which
is indeed largely a verbal one, turning as it does on the
sense of the word iiving.' In practice we continually
use the word 'living' to denote various degrees of vital
activity. Protoplasm deprived of nuclear matter has lost,
wholly or in part, one of the most characteristic vital
properties, namely, the power of synthetic metabolism ;
yet we still speak of it as 'living,' since it still retains for
a longer or shorter period such properties as irritability
and the power of coordinated movement; and, in like man-
ner, various special elements of protoplasm may be termed
'living' in a still more restricted sense.

"In its fullest meaning, however, the word 'living' im-
plies the existance of a group of cooperating activities
more complex than those manifested by any one substance
or structural element. I am, therefore, entirely in accord
with the view urged by Sachs, Kolliker, Verworn, and
other recent writers, that life can only be properly re-
garded as a property of the cell-system as a whole ; and the
separate elements of the system would, with Sachs, better
be designated as 'active' or 'passive,' rather than as 'living'
or 'lifeless.' Thus regarded, the distinction between
'protoplasmic' and 'metaplasmic' substances, while a real
and necessary one, becomes after all one of degree."

CHAPTER VI

CELL DIVISION

Among the vital phenomena exhibited by cells and vis-
ible through the microscope, none is so strikingly distinc-
tive of living matter as is the process of cell-division.
Closely connected with it are some of the greatest problems
of biology. By the continued division of an original germ-
cell or egg-cell all the tissue cells of a multicellular animal
arise and the germ-cell itself arises in the parent body from
other cells by cell-division. Thus the problem is one of
the central facts of development and inheritance.

The rapid advance of biological research is continually
adding weight to the conclusions reached years ago that
every cell originates by division of some preexisting cell
(Omnis cellula e cellula). This is now regarded as one
of the fundamental laws of biology and obviously is a
corollary of the biogenetic law spoken of which states
that all living matter (known to exist only in cells) origi-
nates from preexisting living matter.

"How do cells originate?" was the problem which
troubled the biologists of the early part of the nineteenth
century. Schleiden and Schwann tried to answer the
question, but their answer was entirely wrong. They held
that cells, which they were fond of comparing to crystals,
formed themselves like crystals in a mother-liquor.
Schwann even went further, teaching that young cells de-
veloped, not only within the mother-cell (as propounded
by Schleiden), but also outside of it, in an* organic sub-
77

78 BIOLOGY

stance, which is frequently present in animal tissues as
intercellular substance, and which he called also 'Cyto-
blastem.' Thus Schwann taught that cells were formed
spontaneously both inside and outside of the mother-cell,
which would be a genuine case of spontaneous generation
from formless germ substance."

These were indeed grave fundamental errors, from
which, however, the botanists were the first to extricate
themselves. In the year 1846 a general law was formulated
in consequence of the observations of Mohl, Unger, and
above all, Nageli. This law states that new plant cells
only spring from those already present, and further that
this occurs in such a manner, that the mother-cell becomes
broken up by dividing into two or more daughter-cells.
This was first observed by Mohl.

It was much more difficult to disprove the theory, that
the cells, of animal tissues arise from cytoblasts, and this
was especially the case in the domain of pathological anat-
omy, for it was thought that the formation of tumors and
pus could be traced back to cytoblasts. At last, after many
mistakes, more light was thrown upon the subject of the
genesis of cells in the animal kingdom also, until finally
the cytoblastic theory was absolutely disproved by Vir-
chow, who originated the formula, "Omnis cellula e
cellula." No spontaneous generation of cells occurs either
in plants or animals. The many millions of cells of which,
for instance, the body of a vertebrate animal is com-
posed, have been produced by the repeated division of one
cell, the ovum, in which the life of every animal com-
mences.

The older histologists were unable to discover what part
the nucleus played in cell-division. For many decades two
opposing theories were held, of which now one and now
the other obtained temporarily the greater number of
supporters. According to the one theory, which was held
by most botanists, the nucleus at each division was sup-
posed to break up and become diffused throughout the

CELL DIVISION 79

protoplasm, in order to be formed anew in each daughter-
cell. According to the other, the nucleus was supposed
to take an active part in the process of cell-division, and,
at the commencement of it, to become elongated and con-
stricted at a point, corresponding with the plane of division
which is seen later, and to divide into halves, which sep-
arate from one another and move apart.

Later discoveries (1873-1880) revealed the extremely
interesting formations and metamorphoses, which are seen
in the nucleus during cell-division. These investigations
have all pointed to the same conclusion, that the nucleus
is a permanent and most important organ of the cell, and
that it evidently plays a distinct role in the cell life during
division. Just as the cell is never spontaneously gen-
erated, but is produced directly by the division of another
cell, so the nucleus is never freshly created, but is derived
from the constituent particles of another nucleus. The
formula 'omnis cellula e cellula' might be extended by
adding 'omnis nuclei e nucleo.'

Since about 1876 it has been recognised that there are
two widely different types of cell-division. In one type
there appears to be a simple constriction of the nucleus
and cell-body. This is known as 'direct,' 'akinetic' or
'amitotic' division. The second type is vastly more com-
plicated, as will be described. To this are now applied the
terms 'direct division,' 'karyokinesis' or 'mitosis.' The
terms mitosis and amitosis (referring to the presence or
absence of chromosomes in the dividing cells) are pre-
ferred by most biologists.

As to the occurrence of these two types, modern re-
search has demonstrated the fact that amitosis or direct
division, regarded by Remak and his immediate followers
as of universal occurrence, is in reality a rare and excep-
tional process ; and there is reason to believe, furthermore,
that it is especially characteristic of highly specialized cells
incapable of long-continued multiplication or such as are
in the early stages of degeneration, for instance, in glandu-

8o BIOLOGY

lar epithelia and in the cells of transitory embryonic en-
velopes, where it is of frequent occurrence. Whether this
view be well founded or not, it is certain that in all the
higher and in many of the lower forms of life, indirect
division or mitosis is the typical mode of cell-division. It
is by mitotic division that the germ-cells arise and are pre-
pared for their union during the process of maturation,
and by the same process the oosperm segments and gives
rise to the tissue-cells. It occurs not only in the highest
forms of plants and animals, but also in such simple forms
as the rhizopods, flagellates and diatoms. It may, there-
fore, be justly regarded as the most general expression of
the 'eternal law of continuous development' on which
iVirchow insisted.

The phenomena which occur during the process of
mitosis are very varied and very complicated ; nevertheless
they conform to certain laws which are wonderfully con-
stant in both plants and animals. The main feature of the
process consists in this, that the various substances which
are present in the resting nucleus, undergo a definite
change of position, and the nuclear membrane being dis-
solved, enter into closer union with the cytoplasmic sub-
stance.

During this process the whole mass of chromatin in
the nucleus becomes transformed into fine thread-like
segments, the chromosomes, the number of which remains
constant for each species of plant or animal. These
chromosomes are arranged in a characteristic manner on a
spindle-like structure of achromatic material extending
between the two centrosomes. Each chromosome then
divides longitudinally into two daughter chromosomes
which for a time lie parallel with each other and are
closely connected. Next, these daughter chromosomes sep-
arate into two groups, dividing themselves equally between
the two groups to form the foundation of the daughter
nuclei. The cell itself meanwhile becomes divided in such

CELL DIVISION 81

a way that each of the two cells formed by the division
possesses one of the daughter nuclei.

The manner in which these changes are brought about
is so interesting that it seems wise to give a more
detailed outline of the process. Professor Wilson, in
"The Cell in Development and Inheritance" gives a
description in essentials as follows:

"In the present state of knowledge it is somewhat diffi-
cult to give a connected general account of mitosis, owing
to the uncertainty that hangs over the nature and functions
of the centrosome. For the purpose of the following pre-
liminary outline, we shall take as a type mitosis in which
a distinct and persistent centrosome is present, as has been
mostly clearly determined in the maturation and cleavage
of various animal eggs, and in the division of the testis-
cells.

"In such cases the process involves three parallel series
of change, which affect the nucleus, the centrosome and
the cytoplasm of the cell-body respectively. For descrip-
tive purposes it may conveniently be divided into a series
of successive stages or phases, which, however, graduate
into one another and are separated by no well-defined
limits. These are: (i) The 'Prophases,' or preparatory
changes; (2) the 'Metaphase,' which involves the most es-
sential step in the division of the nucleus; (3) the 'Ana-
phases,' in which the nuclear material is distributed; (4)
the 'Telophases,' in which the entire cell divides and the
daughter-cells are formed.

"1. Prophases. — As the cell prepares for division, the
most conspicuous fact is a transformation of the nuclear
substance, involving both physical and chemical changes.
The chromatin-substance rapidly increases in staining-
power, loses its net-like arrangement and finally gives rise
to a definite number of separate intensely staining bodies,
usually rod-shaped, known as chromosomes. As a rule
this process takes place as follows: The chromatin re-
solves itself little by little into a more or less convoluted

Fig- 9 — Diagrams Illustrating Mitosis.

A., the resting cell; B., early prophase; G., metaphase ; H.,

anaphase; I., telophase; J., division complete. (Wilson.)

CELL DIVISION 83

thread, known as the skein or spireme, and its substance
stains far more intensely than that of the reticulum. The
spireme-thread is at first fine and closely convoluted, form-
ing the 'close spireme.' Later the thread thickens and
shortens and the convolution becomes more open.

"In some cases there is but a single continuous thread,
in others the thread is from its first appearance divided
into a number of separate pieces or segments, forming a
segmented spireme. In either case it ultimately breaks
transversely to form the chromosomes, which in most cases
have the form of rods, straight or curved, tho they are
sometimes spherical or ovoidal and in certain cases may
be joined together in the form of rings. The staining-
power of the chromatin is now at a maximum. As a rule
the nuclear membrane meanwhile fades away and finally
disappears, tho there are some cases in which it persists
more or less completely through all the phases of division.
The chromosomes now lie naked in the cell and the ground-
substance of the nucleus becomes continuous with the
surrounding cytoplasm.

"The remarkable fact has now been established with
high probability that every species of plant or animal has a
fixed and characteristic number of chromosomes, which
regularly occurs in the division of all of its cells and in
all forms arising by sexual reproduction the number is
even. Thus in some of the sharks the number is thirty-
six ; in the mouse, the salamander, the trout, the lily, twen-
ty-four; in the ox, guinea-pig and in man the number is
said to be sixteen and the same number is characteristic of
the onion. In the grasshopper it is twelve. Under certain
conditions the number of chromosomes may be less than
the normal in a given species, but these variations are only
apparent exceptions.

"The nucleoli differ in their behavior in different cases.
True nucleoli or plasmosomes sooner or later disappear,
and the greater number of observers agree that they do
not take part in the chromosome-formation.

84 BIOLOGY

"Meanwhile more or less nearly parallel with these
changes in the chromatin a complicated structure known
as the amphiaster makes its appearance in the position
formerly occupied by the nucleus. This structure consists
of a fibrous spindle-shaped body, the spindle, at either pole
of which is a star or aster formed of rays or astral fibers
radiating into the surrounding cytoplasm, the whole
strongly suggesting the arrangement of iron filings in the
field of a horseshoe magnet. The center of each aster is
occupied by a minute body, known as the centrosome
(Boveri, '88), which may be surrounded by a spherical
mass known as the centrosphere (Strasburger, '93). As
the amphiaster forms the chromosomes group themselves
in a plane passing through the equator of the spindle, and
thus form what is known as the equatorial plate.

"The entire structure, resulting from the foregoing
changes, is known as the karyokinetic or mitotic figure.
It may be described as consisting of two distinct parts,
namely, the chromatic figure, formed by the deeply stain-
ing chromosomes ; and the achromatic figure, consisting of
the spindle and asters which in general stain but slightly.

"2. Metaphase. — The prophases of mitosis are, on the
whole, preparatory in character. The metaphase, which
follows, forms the initial phase of actual division. Each
chromosome splits lengthwise into two exactly similar
halves, which afterward diverge to opposite poles of the
splindle, and here each group of daughter-chromosomes
finally gives rise to a daughter-nucleus. In some cases
the splitting of the chromosomes cannot be seen until they
have grouped themselves in the equatorial plane of the
spindle, and it is only in this case that the term 'metaphase'
can be applied to the mitotic figure as a whole.

"In a large number of cases, however, the splitting may
take place at an earlier period in the spireme-stage or even
in a few cases in the reticulum of the mother-nucleus.
Such variations do not, however, affect the essential fact
that the chromatic network is converted into a thread

CELL DIVISION 85

which, whether continuous or discontinuous, splits
throughout its entire length into two exactly equivalent
halves. The splitting of the chromosomes, discovered by
Flemming in 1880, is the most significant and fundamental
operation of cell-division, for by it, as Roux first pointed
out ('83), the entire substance of the chromatic network is
precisely halved and the daughter-nuclei receive precisely
equivalent portions of chromatin from the mother-nucleus.
It is very important to observe that the nuclear division
always shows this exact quality, whether division of the
cell-body be equal or unequal.

"3. Anaphases. — After splitting of the chromosomes, the
daughter-chromosomes, arranged in two corresponding
groups, diverge to opposite poles of the spindle, where
they become closely crowded in a mass near the center of
the aster. As they diverge the two groups of daughter-
chromosomes are connected by a bundle of achromatic
fibers, stretching across the interval between them and
known as the interzonal fibers or connecting fibers. In the
division of plant cells and often in that of animal cells
these fibers show during this period a series of deeply
staining thickenings in the equatorial plane forming the
cell-plate or mid-body.

"4. Telophases. — In the final phases of mitosis the entire
cell is divided in two in a plane passing through the equa-
tor of the spindle, each of the daughter-cells receiving a
group of chromosomes, half of the spindle and one of the
asters with its centrosome. Meanwhile a daughter-nucleus
is reconstructed in each cell from the group of chromo-
somes it contains. When first formed the daughter-nuclei
are of equal size. If, however, division of the cell-body
has been unequal, the nuclei become, in the end, corres-
pondingly unequal, a fact which, as Conklin and others
have pointed out, proves that the size of the nucleus is
controlled by that of the cytoplasmic mass in which it lies.

"The fate of the achromatic structures varies consider-
ably and has been accurately determined in only a few

86 BIOLOGY

cases. As a rule the spindle fibers disappear more or less
completely, but a portion of their substance sometimes per-
sists in a modified form. In dividing plant cells the cell
plate finally extends across the entire cell and splits into
two layers, between which appears the membrane by which
the daughter-cells are cut apart. A nearly similar process
occurs in a few animal cells, but as a rule the cell-plate is
here greatly reduced and forms no membrane, the cell
dividing by constriction through the equatorial plane."

Such is a general description of mitosis. The variations
from the type, the origin and fate of the various struc-
tures taking part in the division, their relation to each
other and the mechanism by means of which the chromo-
somes divide and separate to form the new nuclei are in-
teresting problems which are to-day being subjected to
keen investigation in the laboratories of the cytologists.
But most interesting of all perhaps is the problem of the
chromosomes in relation to inheritance. This problem will
be more fully discussed in the chapter on Heredity.

Some of the most important studies on the physiological
relations of nucleus and cytoplasm have been made with
one-celled animals. Brandt in 1877 and Nussbaum in
1884 cut certain protozoons into pieces and observed that
pieces containing nuclear matter quickly regenerate and
produce perfect animals, while the enucleated fragments
soon die. One of the most remarkable animals with this
power to regenerate is the trumpet animalcule Stentor.
Gruber in 1885 found that when this animalcule was frag-
mented, pieces possessing a large fragment of the nucleus
completely regenerated within twenty-four hours. If the
nuclear fragment were smaller, the regeneration proceeded
more slowly. If no nuclear substance were present, no re-
generation took place, tho the wound closed and the frag-
ment lived for a considerable time.

The only exception — but it is a very significant one — was
the case of individuals in which the process of normal fis-
sion had begun. In these a non-nucleated fragment in

CELL DIVISION 87

which the formation of a new peristome had already been
initiated healed the wound and completed the formation of
the peristone. Lillie (1896) has recently found that Sten-
tor may by shaking be broken into fragments of all sizes
and that nucleated fragments as small as one-twenty-
seventh the volume of the entire animal are still capable
of complete regeneration, non-nucleated fragments perish.

Many other such experiments on one-celled animals
show that life for a considerable period, perfectly normal
movements, susceptibility to stimulus and the power of
taking food may continue in enucleated parts of unicellular
animals. They lack, however, the power of digestion and
secretion and hence cannot continue to live as do the
nucleated parts. These facts demonstrate that the nucleus
plays an important part in metabolism. Experiments on
plants have supported this conclusion. It will be noted
that if a unicellular organism be divided into two parts, the
part with the nucleus is a complete cell (a mass of proto-
plasm with a nucleus), while the other part possesses no
longer the individuality of a cell and perishes.

It is well known that all animals and plants have a defi-
nite limit of growth. From the cytological point of view
the limit of body-size appears to be correlated with the to-
tal number of cells formed rather than with their individ-
ual size. This relation has been carefully studied by Conk-
line C96) in the case of the gasteropod Crepidula, an ani-
mal which varies greatly in size in the mature condition,
the dwarfs having in some cases not more than one-twenty-
fifth the volume of the giants. The eggs are, however, of
the same size in all and their number is proportional to the
size of the adult. The same is true of the tissue-cells.
Measurements of cells from the epidermis, the kidney, the
liver, the alimentary epithelium and other tissues show that
they are on the whole as large in the dwarfs as in the
giants. The body-size therefore depends on the total num-
ber of cells rather than on their size, individually consid-
ered, and the same appears to be the case in plants.

88 BIOLOGY

It is in the cells of both plant and animal organisms
that the vital functions are carried on. All the vital proc-
esses of a complex animal appear to be nothing but the
highly developed result of the individual vital processes of

Fig. io — Regeneration in Unicellular Animal. (Stentor.)

A., animal divided into three pieces, each containing a fragment

of the nucleus ; B., the fragment shortly afterward ; C, after

twenty-four hours, each regenerated into a perfect animal.

(Wilson.;

its innumerable variously functioning cells. The study of
the processes of digestion, of the changes in muscle and
nerve cells leads finally to the examination of the functions
of gland, muscle, ganglion and brain.

CHAPTER VII

ORGANIC FUNCTIONS

The facts dealing with the physiology of organisms, the
activities associated with that which we call life are often
designated Organic Functions. The terms animal physi-
ology, plant physiology and human physiology are in com-
mon use and often suggest to the lay reader that the func-
tions or workings of the organs of plants, animals or man
are quite distinct, so much so as to require discussion in
different treatises. This is true only as a matter of detail,
for in the past fifty years it has been made evident that in
general principles all living things are fundamentally simi-
lar. One of the most important summaries of this similar-
ity is Huxley's famous essay, 'The Border Territory Be-
tween the Animal and Vegetable Kingdoms/ written in
1876, extracts from which follow.

In the second edition of the 'Regne Animal,' published
in 1828, Cuvier devotes a special section to the 'Division
of Organised Beings into Animals and Vegetables,' in
which the question is treated with that comprehensiveness
of knowledge and clear critical judgment which character-
ize his writings and justify biologists in regarding them
as representative expressions of the most extensive, if not
the profoundest, knowledge of his time. He affirms that
living beings have been subdivided from the earliest times
into animated beings, which possess sense and motion, and
inanimated beings, which are devoid of these functions and
simply vegetable.

90 BIOLOGY

Altho the roots of plants direct themselves toward
moisture and their leaves toward air and light, altho the
parts of some plants exhibit oscillating movements without
any perceptible cause and the leaves of others retract when
touched, yet none of these movements justify the ascription
to plants of perception of will. From the mobility of ani-
mals Cuvier, with his characteristic partiality for teleo-
logical reasoning, reduces the necessity of the exist-
ence in them of an alimentary cavity, or reservoir of
food, whence their nutrition may be drawn by vessels,
which are a sort of internal roots; and, in the presence
of this alientary cavity he naturally sees the pnmary and
the most important distinction between animals and plants,
logical reasoning, reduces the necessity of the existence in
them of an alimentary cavity, or reservoir of food, whence
their nutrition may be drawn by the vessels, which are a
sort of internal roots; and in the presence of this alimen-
tary cavity he naturally sees the primary and the most im-
portant distinction between animals and plants.

Following out his teleological argument, Cuvier remarks
that the organization of this cavity and its appurtenances
must needs vary according to the nature of the aliment and
the operations which it has to undergo before it can be con-
verted into substances fitted for absorption, while the at-
mosphere and the earth supply plants with juices ready
prepared and which can be absorbed immediately. As the
animal body required to be independent of heat and of the
atmosphere, there were no means by which the motion of
its fluids could be produced by internal causes. Hence
arose the second great distinctive character of animals, or
the circulatory system, which is less important than the
digestive, since it was unnecessary, and therefore is absent,
in the more simple animals.

Animals further needed muscles for locomotion and
nerves for sensibility. Hence, says Cuvier, it was neces-
sary that the chemical composition of the animal body
should be more complicated than that of the plant ; and it is

ORGANIC FUNCTIONS 91

so, inasmuch as an additional substance — nitrogen — enters
into it as an essential element ; while in plants nitrogen is
only accidentally joined with the three other fundamental
constituents of organic beings — carbon, hydrogen and oxy-
gen. Indeed, he afterward affirms that nitrogen is peculiar
to animals, and herein he places the third distinction be-
tween the animal and the plant. The soil and the at-
mosphere supply plants with water composed of hydrogen
and oxygen and carbonic acid containing carbon and oxy-
gen. They retain the hydrogen and the carbon, exhale the
superfluous oxygen and absorb little or no nitrogen. The
essential character of vegetable life is the exhalation of
oxygen, which is effected through the agency of light.
Animals, on the contrary, derive their nourishment either
directly or indirectly from plants. They get rid of the
superfluous hydrogen and carbon and accumulate nitrogen.
The relations of plants and animals to the atmosphere are
therefore inverse. The plant withdraws water and car-
bonic acid from the atmosphere, the animal contributes
both to it. Respiration — that is, the absorption of oxygen
and the exhalation of carbonic acid — is the specially animal
function of animals and constitutes their fourth distinctive
character.

Thus wrote Cuvier in 1828. But in the fourth and fifth
decades of this century the greatest and most rapid revolu-
tion which biological science has ever undergone was ef-
fected by the application of the modern microscor e to the
investigation of organic structure, by the introduction of
exact and easily manageable methods of conducting the
chemical analysis of organic compounds and finally by the
employment of instruments of precision for the measure-
ment of the physical forces which are at work in the living
economy.

That the semi-fluid contents (which we now term proto-
plasm) of the cells of certain plants, such as the Charae, are
in constant and regular motion was made out by Bona-
ventura Corti a century ago; but the fact, important as it

92 BIOLOGY

was, fell into oblivion and had to be rediscovered by Tre-
viranus in 1807. Robert Brown noted the more complex
motions of the protoplasm in the cells of Tradescantia in
1831, and now such movements of the living substance of
plants are well known to be some of the most widely
prevalent phenomena of vegetable life.

Agardh and other of the botanists of Cuvier's generation
who occupied themselves with the lower plants had ob-
served that, under particular circumstances, the contents
of the cells of certain water-weeds were set free and moved
about with considerable velocity and with all the appear-
ances of spontaneity as locomotive bodies, which, from
their similarity to animals of simple organization, were
called 'zoospores.' Even as late as 1845, however, a
botanist of Schleiden's eminence dealt very skeptically
with these statements, and his skepticism was the more
justified since Ehrenberg in his elaborate and comprehen-
sive work on the infusoria, had declared the greater num-
ber of what are now recognised as locomotive plants to be
animals.

"At the present day," writes Huxley, "innumerable
plants and free plant cells are known to pass the whole or
part of their lives in an actively locomotive condition, in
nowise distinguishable from that of one of the simpler
animals, and while in this condition their movements are,
to all appearances, as spontaneous — as much the product of
volition — as those of such animals.

"Hence the teleological argument for Cuvier's first diag-
nostic character — the presence in animals of an alimentary
cavity, or internal pocket, in which they can carry about
their nutriment — has broken down, so far, at least, as his
mode of stating it goes. And, with the advance of micro-
scopic anatomy, the universality of the fact itself among
animals has ceased to be predicable. Many animals of
even complex structure which live parasitically within
others are wholly devoid of an alimentary cavity. Their
food is provided for them, not only ready cooked but ready

ORGANIC FUNCTIONS 93

digested, and the alimentary canal, become superfluous,
has disappeared, and, again, the males of most Rotifers
have no digestive apparatus. Finally amid the lowest
forms of animal life the speck of gelatinous protoplasm,
which constitutes the whole body, has no permanent diges-
tive cavity or mouth, but takes in its food anywhere and
digests, so to speak, all over its body.

"But altho Cuvier's leading diagnosis of the animal from
the plant will not stand a strict test, it remains one of the
most constant of the distinctive characters of animals.
And if we substitute for the possession of an alimentary
cavity the power of taking solid nutriment into the body
and there digesting it, the definition so changed will cover
all animals, except certain parasites, and the few and ex-
ceptional cases of non-parasitic animals which do not feed
at all. On the other hand, the definition thus amended will
exclude all ordinary vegetable organisms. Cuvier himself
practically gives up his second distinctive mark when he
admits that it is wanting in the simpler animals.

"The third distinction is based on a completely erroneous
conception of the chemical differences and resemblances
between the constituents of animal and vegetable organ-
isms, for which Cuvier is not responsible, as it was current
among contemporary chemists. It is now established that
nitrogen is as essential a constituent of vegetable as of
animal living matter and that the latter is, chemically
speaking, just as complicated as the former. Starchy sub-
stances, cellulose and sugar, once supposed to be exclu-
sively confined to plants, are now known to be regular and
normal products of animals. Amylaceous and saccharine
substances are largely manufactured, even by the highest
animals. Cellulose is widespread as a constituent of the
skeletons of the lower animals and it is probable that amy-
loid substances are universally present in the animal or-
ganism, tho not in the precise form of starch.

"Moreover, altho it remains true that there is an inverse
relation between the green plant in sunshine and the ani-

94 BIOLOGY

mal, in so far as under these circumstances the green plant
decomposes carbonic acid and exhales oxygen while the
animal absorbs oxygen and exhales carbonic acid, yet the
exact researches of the modern chemical investigators of
the physiological processes of plants have clearly demon-
strated the fallacy of attempting to draw any general dis-
tinction between animals and vegetables on this ground.
In fact, the difference vanishes with the sunshine, even in
the case of the green plant, which in the dark absorbs oxy-
gen and gives out carbonic acid like any animal. On the
other hand, those plants, such as the fungi, which contain
no chlorophyll and are not green, are always, so far as
respiration is concerned, in the exact position of animals.
They absorb oxygen and give out carbonic acid. Thus, by
the progress of knowledge, Cuvier's fourth distinction be-
tween the animal and the plant has been as completely in-
validated as the third and second, and even the first can be
retained only in a modified form and subject to exceptions."
But has the advance of biology simply tended to break
down old distinctions without establishing new ones?
With a qualification, to be considered presently, the answer
to this question is undoubtedly in the affirmative. The
famous researches of Schwann and Schleiden in 1837 and
the following years founded the modern science of his-
tology or that branch of anatomy which deals with the
ultimate visible structure of organisms as revealed by the
microscope, and from that day to this the rapid improve-
ment of methods of investigation and the energy of a host
of accurate observers have given greater and greater
breadth and firmness to Schwann's great generalization
that a fundamental unity of structure obtains in animals
and plants, and that, however diverse may be the fabrics
or tissues of which their bodies are composed, all these
varied structures result from the metamorphosis of mor-
phological units (termed cells in a more general sense than
that in which the word 'cells' was at first employed),
which are not only similar in animals and in plants respec-

ORGANIC FUNCTIONS 95

tively, but present a close resemblance when those of ani-
mals and those of plants are compared together.

"The contractility which is the fundamental condition of
locomotion," continues Huxley, "has not only been discov-
ered to exist far more widely among plants than was for-
merly imagined, but in the plants the act of contraction has
been found to be accompanied, as Dr. Burdon Sanderson's
interesting investigations have shown, by a disturbance of
the electrical state of the contractile substance comparable
to that which was found by Du Bois Reymond to be a con-
comitant of the activity of ordinary muscle in animals.
Again, I know of no test by which the reaction of the
leaves of the Sundew and of other plants to stimuli, so
fully and carefully studied by Mr. Darwin, can be distin-
guished from those acts of contraction following upon
stimuli, which are called 'reflex' in animals.

"On each lobe of the bilobed leaf of Venus flytrap are
three delicate filaments which stand out at right angles
from the surface of the leaf. Touch one of them with the
end of a fine human hair and the lobes of the leaf instantly
close together in virtue of an act of contraction of part
of their substance, just as the body of a snail contracts into
its shell when one of its 'horns' is irritated.

"The reflex action of the snail is the result of the pres-
ence of a nervous system in the animal. A molecular
change takes place in the nerve of the tentacle, is propa-
gated to the muscles by which the body is retracted, and
causing them to contract, the act of retraction is brought
about. Of course the similarity of the acts does not
necessarily involve the conclusion that the mechanism by
which they are effected is the same, but it suggests a sus-
picion of their identity which needs careful testing."

The results of inquiries into the structure of the nervous
system of animals converge toward the conclusion that the
nerve fibers, which have been regarded as ultimate elements
of nervous tissue, are not such, but are simply the visible
aggregations of vastly more attenuated filaments, the di-

96 BIOLOGY

ameter of which dwindles down to the limits of our present
microscopic vision, greatly as these have been extended by
modern improvements of the microscope, and that a nerve
is, in its essence, nothing but a linear tract of specially
modified protoplasm between two points of an organism —
one of which is able to affect the other by means of the
communication so established. Hence it is conceivable that
even the simplest living being may possess a nervous sys-
tem. And the question whether plants are provided with
a nervous system or not thus acquires a new aspect and
presents the histologist and physiologist with a problem of
extreme difficulty, which must be attacked from a new
point of view and by the aid of methods which have yet
to be invented.

"Thus it must be admitted," he says again, "that plants
may be contractile and locomotive; that, while locomotive,
their movements may have as much appearance of spon-
taneity as those of the lowest animals, and that many ex-
hibit actions comparable to those which are brought about
by the agency of a nervous system in animals. And it must
be allowed to be possible that further research may reveal
the existence of something comparable to a nervous system
in plants. So that I know not where we can hope to find
any absolute distinction between animals and plants, unless
we return to their mode of nutrition and inquire whether
certain differences of a more occult character than those
imagined to exist by Cuvier, and which certainly hold good
for the vast majority of animals and plants, are of univer-
sal application.

"A bean may be supplied with water in which salts of
ammonia and certain other mineral salts are dissolved in
due proportion, with atmospheric air containing its ordi-
nary minute dose of carbonic acid and with nothing else
but sunlight and heat. Under these circumstances, unnatu-
ral as they are, with proper management, the bean will
thrust forth its radicle and its plumule; the former will
grow down into roots, the latter grow up into the stem and

ORGANIC FUNCTIONS 97

leaves of a vigorous bean-plant, and this plant will, in due
time, flower and produce its crop of beans just as if it were
grown in the garden or in the field.

"The weight of the nitrogenous protein compounds, of
the oily, starchy, saccharine and woody substances con-
tained in the full-grown plant and its seeds will be vastly
greater than the weight of the same substances contained
in the bean from which it sprang. But nothing has been
supplied to the bean save water, carbonic acid, ammonia,
potash, lime, iron and the like in combination with phos-
phoric, sulphuric and other acids. Neither protein, nor fat,
nor starch, nor sugar, nor any substance in the slightest
degree resembling them has formed part of the food of
the bean. But the weights of the carbon, hydrogen, oxy-
gen, nitrogen, phosphorus, sulphur and other elementary
bodies contained in the bean-plant and in the seeds which
it produces are exactly equivalent to the weights of the
same elements which have disappeared from the materials
supplied to the bean during its growth. Whence it follows
that the bean has taken in only the raw materials of its
fabric and has manufactured them into bean-stuffs.

"The bean has been able to perform this great chemical
feat by the help of its green coloring matter, or chloro-
phyll, for it is only the green parts of the plant which,
under the influence of sunlight, have the marvelous power
of decomposing carbonic acid, setting free the oxygen and
laying hold of the carbon which it contains. In fact, the
bean obtains two of the absolutely indispensable elements
of its substance from two distinct sources. The watery
solution, in which its roots are plunged, contains nitrogen
but no carbon; the air, to which the leaves are exposed,
contains carbon, but its nitrogen is in the state of a free
gas, in which condition the bean can make no use of it,
and the chlorophyll is the apparatus by which the carbon is
extracted from the atmospheric carbonic acid, the leaves
being the chief laboratories in which this operation is
effected.

9^ BIOLQGY

"The great majority of conspicuous plants are, as every-
body knows, green, and this arises from the abundance of
their chlorophyll. The few which contain no chlorophyll
and are colorless are unable to extract the carbon which
they require from atmospheric carbonic acid and lead a
parasitic existence upon other plants, but it by no means
follows, often as the statement has been repeated, that the
manufacturing power of plants depends on their chloro-
phyll and its interaction with the rays of the sun. On the
contrary, it is easily demonstrated, as Pasteur first proved,
that the lowest fungi, devoid of chlorophyll or of any sub-
stitute for it as they are, nevertheless possess the charac-
teristic manufacturing power of plants in a very high de-
gree. Only it is necessary that they should be supplied
with a different kind of raw material; as they cannot ex-
tract carbon from carbonic acid, they must be furnished
with something else that contains carbon. Tartaric acid
is such a substance, and if a single spore of the commonest
and most troublesome of molds — Tenicillium' — be sown in
a saucerful of water in which tartrate of ammonia, with a
small percentage of phosphates and sulphates is contained,
and kept warm, whether in the dark or exposed to light,
it will in a short time give rise to a thick crust of mold,
which contains many million times the weight of the origi-
nal spore in protein compounds and cellulose. Thus we
have a very wide basis of fact for the generalization that
plants are essentially characterized by their manufacturing
capacity — by their power of working up mere mineral mat-
ters into complex organic compounds.

"Contrariwise, there is a no less wide foundation for the
generalization that animals, as Cuvier put it, depend di-
rectly or indirectly upon plants for the material of their
bodies ; that is, either they are herbivorous or they eat oth-
er animals which are herbivorous. But for what constitu-
ents of their bodies are animals thus dependent upon
plants? Certainly not for their horny matter; nor for
chondrin, the proximate chemical element of cartilage;

ORGANIC FUNCTIONS 99

nor for gelatin ; nor for syntonin, the constituent of mus-
cle; nor for their nervous or biliary substances; nor for
their amyloid matters ; nor, necessarily, for their fats.

"It can be experimentally demonstrated that animals can
make these for themselves. But that which they cannot
make, but must in all known cases obtain directly or indi-
rectly from plants, is the peculiar nitrogenous matter, pro-
tein. Thus the plant is the idea! proletariat of the living
world — the worker who produces — the animal, the ideal
aristocrat, who mostly occupies himself in consuming,
after the manner of that noble representative of the line of
Zahdarm, whose epitaph is written in 'Sartor Resartus.'

"Here is our last hope of rinding a sharp line of demar-
cation between plants and animals, for, as I have already
hinted, there is a border territory between the two king-
doms, a sort of no man's land, the inhabitants of which
certainly cannot be discriminated and brought to their
proper allegiance in any other way.

"Some months ago Professor Tyndall asked me to ex-
amine a drop of infusion of hay, placed under an excellent
and powerful microscope, and to tell him what I thought
some organisms visible in it were. I looked and observed,
in the first place multitudes of 'Bacteria* moving about
with their ordinary intermittent spasmodic wriggles. As
to the vegetable nature of these, there is now no doubt.
Not only does the close resemblance of the 'Bacteria' to
unquestionable plants, such as the 'Oscillartoria' and the
lower forms of 'Fungi,' justify this conclusion, but the
manufacturing test settles the question at once. It is only
needful to add a minute drop of fluid containing 'Bacteria'
to water in which tartrate, phosphate and sulphate of am-
monia are dissolved, and in a very short space of time the
clear fluid becomes milky by reason of their prodigious
multiplication which, of course, implies the manufacture
of living bacterium-stuff out of these merely saline mat-
ters.

"But other active organisms, very much larger than the

ioo BIOLOGY

bacteria, attaining, in fact, the comparatively gigantic
dimensions of one-three-thousandth of an inch or more,
incessantly crossed the field of view. Each of these had a
body shaped like a pear, the small end being slightly in-
curved and produced into a long curved filament, or cilium,
of extreme tenuity. Behind this, from the concave side of
the incurvation, proceeded another long cilium, so delicate
as to be discernible only by the use of the highest powers
and careful management of the light. In the center of the
pear-shaped body a clear, round space could occasionally
be discerned, but not always, and careful watching showed
that this clear vacuity appeared gradually and then shut
up and disappeared suddenly at regular intervals. Such a
structure is of common occurrence among the lowest
plants and animals and is known as a contractile vacuole.

"The little creature thus described sometimes propelled
itself with great activity, with a curious rolling motion,
by the lashing of the front cilium, while the second cilium
trailed behind; sometimes it anchored itself by the hinder
cilium and was spun around by the working of the other,
its motions resembling those of an anchor buoy in a heavy
sea. Sometimes, when two were in full career toward one
another, each would appear dexterously to get out of the
other's way; sometimes a crowd would assemble and jostle
one another with as much semblance of individual effort
as a spectator on the Grands Mulets might observe with a
telescope among the specks representing men in the valley
of Chamounix.

"The spectacle, tho always surprising, was not new to
me. So my reply to the question put to me was that these
organisms were what biologists call 'Monads/ and tho
they might be animals, it was also possible that they might,
like the 'Bacteria,' be plants. My friend received my ver-
dict with an expression which showed a sad want of re-
spect for authority. He would as soon believe that a sheep
was a plant. Naturally piqued by this want of faith, I
have thought a good deal over the matter, and as I still rest

ORGANIC FUNCTIONS 101

in the lame conclusion I originally expressed must even
now confess that I cannot certainly say whether this
creature is an animal or a plant."

Thus in the question of making proteid there are
all gradations from plants able to make proteid from inor-
ganic matter to plants which are as much animal as
vegetable in structure, but are animal in the dependence
on other organisms for their food. The singular circum-
stance observed by Meyer that the torula of yeast, tho an
indubitable plant, still flourishes most vigorously when
supplied with the complex nitrogenous substance pepsin,
the probability that the potato blight is nourished directly
by the protoplasm of the potato-plant, and the wonderful
facts which have recently been brought to light respecting
insectivorous plants all favor this view and tend to the
conclusion that the difference between animal and plant
is one of degree rather than of kind and that the problem
whether, in a given case, an organism is an animal or a
plant may be essentially insoluble.

This conception that animals and plants differ not in
kind has been of great importance in the development of
biology as a unified science of life. But, altho the differ-
ences in the organic functions are of degree rather than
of kind, it is true that the differences of degree are clear
enough, except in certain unicellular organisms which are
on the border line, to enable us to distinguish between
animals and plants and to make it convenient to divide
physiology, the science of function, into plant and animal
physiology. These differences will be clearer by adding
to Huxley's general comparison of plants and animals a
concrete comparison of an animal and a plant. For this
purpose one of Huxley's most famous students, T. Jeffery
Parker, chose the unicellular animal 'Amoeba' and the
unicellular plant 'Haematococcus,' also known as 'Sphaer-
ella.' Both of these live in water. In their nutrition there
are some differences, for Amoeba can take in solid food
(other small animals and plants), formed of protoplasm as

102 BIOLOGY

complex as its own. These it breaks up by means of diges-
tive juices into soluble proteids and then recombines them
to form its own protoplasm. Haematococcus has not this
ability to take in solid food ; it never feeds in the ordinary
sense of the word. Nevertheless it must take in food in
some way or other or the decomposition of its protoplasm
would soon bring it to an end. The water in which it
lives is never pure, but always contains certain mineral

(c7it

Fig. II HAEMATOCOCCUS.

c. w., cell wall; chr., chromatophores ; pyr., pyrenoids; fl., fia-
gella. (Parker.)

salts in solution, especially nitrates, ammonia salts and
often sodium chloride or common table salt. These salts,
being crystalloids, can and do diffuse into the water of the
organism so that we may consider its protoplasm to be
constantly permeated by a very weak saline solution, the
most important elements contained in which are oxygen,
hydrogen, nitrogen, potassium, sodium, calcium, sulphur

ORGANIC FUNCTIONS 103

and phosphorus. It must be remarked, however, that the
diffusion of these salts does not take place in the same uni-
form manner as it would through parchment or other dead
membrane. The living protoplasm has the power of deter-
mining the extent to which each constituent of the solution
shall be absorbed.

"If water containing a large quantity of Haematococcus
is exposed to sunlight minute bubbles are found to appear
in it, and these bubbles, if collected and properly tested,
are found to consist largely of oxygen. Accurate chemical
analysis has shown that this oxygen is produced by the
decomposition of the carbon dioxide contained in solution
in rain-water, and indeed in all water exposed to the air,
the gas, which is always present in small quantities in the
atmosphere, being very soluble in water.

"As the carbon dioxide is decomposed in this way, its
oxygen being given off, it is evident that its carbon must
be retained. As a matter of fact, it is retained by the or-
ganism, but not in the form of carbon. In all probability
a double decomposition takes place between the carbon
dioxide absorbed and the water of organization, the result
being the liberation of oxygen in the form of gas and the
simultaneous production of some extremely simple form
of carbohydrate — i.e., some compound of carbon, hydrogen
and oxygen, with a comparatively small number of atoms
to the molecule.

"The next step seems to be that the carbohydrate thus
formed unites with the ammonia salts or the nitrates ab-
sorbed from the surrounding water, the result being the
formation of some comparatively simple nitrogenous com-
pound. Then further combinations take place, substances
of greater and greater complexity are produced, sulphur
from the absorbed sulphates enters into combination and
proteids are formed. From these finally fresh living pro-
toplasm arises.

"From the foregoing account, which only aims at giving
the very briefest outline of a subject as yet imperfectly

104 BIOLOGY

understood, it will be seen that, as in Amoeba, the final
result of the nutritive process is the manufacture of proto-
plasm, and that this result is attained by the formation of
various substances of increasing complexity. But it must
be noted that the steps in the process of constructive met-
abolism are widely different in the two cases. In Amoeba
we start with living protoplasm — that of the prey which is
killed and broken up into diffusible proteids, these being
afterward recombined to form new molecules of the living
protoplasm of Amoeba. So that the food of Amoeba is, to
begin with, as complex as itself, and is broken down by
digestion into simpler compounds, these being afterward
recombined into more complex ones. In Haematococcus,
on the other hand, we start with extremely simple com-
pounds, such as carbon dioxide, water, nitrates, sulphates,
etc. Nothing which can be properly called digestion — i.e.,
a breaking up and dissolving of the food, takes place, but
its various constituents are combined into substances of
gradually increasing complexity, protoplasm, as before,
being the final result.

"To express the matter in another way: Amoeba can
only make protoplasm out of proteids already formed by
some other organism ; Haematococcus can form it out of
simple liquid and gaseous inorganic materials.

"Speaking generally, it may be said that these two meth-
ods of nutrition are respectively characteristic of the two
great groups of living things. Animals require solid food
containing ready-made proteids and cannot build up their
protoplasm out of simpler compounds. Green plants — i.e.,
all the ordinary trees, shrubs, weeds, etc. — take only liquid
and gaseous food and build up their protoplasm out of car-
bon dioxide, water and mineral salts. The first of these
methods of nutrition is conveniently distinguished as holo-
zoic, or wholly-animal, the second as holophytic, or wholly-
vegetal.

"It is important to note that only those plants or parts
of plants in which chlorophyll is present are capable of

ORGANIC FUNCTIONS 105

holophytic nutrition. Whatever may be the precise way
in which the process is effected, it is certain that the de-
composition of carbon dioxide which characterizes this
form of nutrition is a function of chlorophyll, or to speak
more accurately, of chromatophores, since there is reason
for thinking that it is the protoplasm of these bodies, and
not the actual green pigment, which is the active agent in
the process.

"Moreover, it must not be forgotten that the decomposi-
tion of carbon dioxide is carried on only during daylight,
so that organisms in which holophytic nutrition obtains
are dependent upon the sun for their very existence.
While Amoeba derives its energy from the breaking down
of the proteids in its food, the food of Haematococcus is
too simple to serve as a source of energy, and it is only by
the help of sunlight that the work of constructive metabo-
lism can be carried on. This may be expressed by saying
that Haematococcus, in common with other organisms
containing chlorophyll, is supplied with kinetic energy (in
the form of light or radiant energy) directly by the sun.

"As in Amoeba, destructive metabolism is constantly
going on, side by side with constructive. The protoplasm
becomes oxidized, water, carbon dioxide and nitrogenous
waste matters being formed and finally got rid of. Obvi-
ously then absorption of oxygen must take place, or in
other words, respiration must be one of the functions of
the protoplasm of Haematococcus as of that of Amoeba.
In many green — i.e., chlorophyll containing — plants this
has been proved to be the case ; respiration — i.e., the tak-
ing in of oxygen and giving out of carbon dioxide — is con-
stantly going on, but during daylight is obscured by the
converse process, the taking in of carbon dioxide for
nutritive purposes and the giving out of the oxygen liber-
ated by its decomposition. In darkness, when this latter
process is in abeyance, the occurrence of respiration is
more readily ascertained."

CHAPTER VIII

LIFE PROCESSES

Nutrition thus, as has been pointed out, makes ic pos-
sible to classify most organisms as animals or plants. Yet
there are many unicellular forms in which both kinds of
nutrition go on at the same time; that is, the forms may
possess a mouth for the ingestion of solid food and green
coloring matter, chlorophyll, for the manufacture of
starchy food from gaseous matter.

Many of the lowest forms of life have long been puzzles
and the beginner in biological study is surprised to find
them described in text-books of both botany and zoology.
The fact is that they are on the border line, are neither
plants nor animals but simply organisms. Since they can-
not be classified, it is necessary that they be listed both
under botany and zoology, in order to make sure that they
will not be omitted entirely. Because of these uncertain
forms of life, Haeckel proposed once to include all one-
celled animals and plants in a third kingdom to be called
Protista (meaning the first of all life).

Parker's definition of animals and plants, based on the
foregoing considerations, is convenient for distinguishing
between animals and plants in all cases except the doubtful
unicellar forms. He says:

"Animals are organisms of fixed and definite form, in
which the cell-body is not covered with a cellulose wall.
They ingest solid proteinaceous food, their nutritive proc-
esses result in oxidation, they have a definite organ of ex-
cretion and are capable of automatic movement
106

LIFE PROCESSES 107

"Plants are organisms of constantly varying form in
which the cell-body is surrounded by a cellulose wall ; they
cannot ingest solid food, but are nourished by a watery
solution of nutrient materials. If chlorophyll is present,
the carbon dioxide of the air serves as a source of carbon,
nitrogen is obtained from simple salts and the nutritive
processes result in deoxidation ; if chlorophyll is absent,
carbon is obtained from sugar or some similar compound,
nitrogen either from simple salts or from proteids, and the
process of nutrition is one of oxidation. There is no spe-

Fig. 12 EUGLENA VIRIDIS.

Contains chlorophyll, therefore it can manufacture food as a
plant does ; it also has a simple mouth, therefore it can ingest
solid food as an animal does ; its nutrition is both holophytic
and holozoic; magnified. (Kent.) nu., nucleus; c. vac, con-
tractile vacuole.

cial excretory organ, and, except in the case of certain re-
productive bodies, there is usually no locomotion."

The important point to recognise is that these boundaries
are artificial and that there are no scientific frontiers in
Nature. As in the liquefaction of gases, there is a 'critical
point' at which the substance under experiment is neither
gaseous nor liquid; as in a mountainous country, it is im-
possible to say where mountain ends and valley begins ;
as in the development of an animal, it is futile to argue
about the exact period when, for instance, the egg becomes
a tadpole or the tadpole a frog, so in the case under dis-
cussion. The distinction between the higher plants and
animals is perfectly sharp and obvious, but when the two
groups are traced downward they are found gradually to

io8 BIOLOGY

merge, as it were, into an assemblage of organisms which
partake of the characters of both kingdoms and cannot
without a certain violence be either included in or excluded
from either. When any given 'protist' has to be classified
the case must be decided on its individual merits; the
organism must be compared in detail with all those which
resemble it closely in structure, physiology and life history,
and then a balance must be struck and the doubtful form
placed in the kingdom with which it has, on the whole,
most points in common.

It will no doubt occur to the reader that, on the theory
of evolution, the fact of the animal and vegetable kingdoms
being related to one another like two trees united at the
roots may be accounted for by the hypothesis that tR*e
earliest organisms were protists and that from them ani-
mals and plants were evolved along divergent lines of de-
scent. And in this connection the fact that some bacteria
— the simplest organisms known and devoid of chloro-
phyll— may flourish in solutions wholly devoid of organic
matter is very significant.

The lower plants and animals referred to above are so
far from everyday observation and hence so unfamiliar
that to most people the comparison made will mean little
in terms of ordinary green flowering plants and common
vertebrate animals. In order to emphasize the fun-
damental similarity of organic function in higher and
lower animals and plants, let us compare any higher plant
— e.g., a bean plant with a higher animal, e.g., frog or even
man. In each the life is the sum total of a series of defi-
nite processes — nutrition or food supply, circulation, met-
abolism, excretion, oxygenation (part of respiration),
movement, irritability (nervous activity) and reproduction.
In turn these will be compared for the animal and the
plant, following in part the comparisons of certain animals
and plants by Sedgwick and Wilson and others. These
comparisons will, however, be translated into terms ap-
plicable to any species of higher plants or animals.

LIFE PROCESSES 109

In the nutrition of the animal the most essential and
characteristic part of the food supply is derived from
vegetable or animal matter in the form of various organic
compounds, of which the most important are proteids
(protoplasm, albumen, etc.), carbohydrates (starch, cellu-
lose) and fats. These materials are used by the animal in
the manufacture of new protoplasm to take the place of
that which has been used up. It is, however, impossible
for the animal to build these materials directly into the
substance of its own body. They must first undergo cer-
tain preparatory chemical changes known collectively as
digestion, and only after the completion of this process
can all the food be absorbed into the circulation.

For this purpose the food is taken not into the body
proper, but into a kind of tubular chemical laboratory;
called the alimentary canal, through which it slowly passes,
being subjected meanwhile to the action of certain chemi-
cal substances or reagents, known as digestive ferments.
These substances, which are dissolved in a watery liquid
to form the digestive fluid, are secreted by the walls of the
alimentary tube. Through their action the solid portions
are liquefied and the food is rendered capable of absorption
into the body proper.

The food supply of the higher plant, like that of the
animal, is the source of the required matter and energy,
but unlike that of the animal, it is not chiefly an income of
foods, but only of the raw materials of food. Matter en-
ters the plant in the liquid or gaseous form by diffusion,
both from the soil through the roots (liquids) and from
the atmosphere through the leaves (gases). We have here
the direct absorption into the body proper of food-stuffs
precisely as the animal takes in water and oxygen. Energy
enters the plant, to a small extent, as the potential energy
of food-stuffs, but comes in principally as the kinetic
energy of sunlight absorbed in the leaves.

Of the substances the solids (salts, etc.) must be dis-
solved in water before they can be taken in. Water and

no BIOLOGY

dissolved salts continually pass by diffusion from the soil
into the roots, where together they constitute the sap. The
sap travels throughout the whole plant, the main tho not
the only cause of movement being the constant transpira-
tion (evaporation) of watery vapor from the leaves, espe-
cially through the stomata. The gaseous matters (carbon
dioxide, oxygen, nitrogen) enter the plant mainly by diffu-
sion from the atmosphere, are dissolved by the sap in the
leaves and elsewhere and thus may pass to every portion
of the plant.

The green plant owes its power of absorbing the energy
of sunlight to the chlorophyll-bodies or chromatophores,
tor plants which, like fungi, etc., are devoid of chlorophyll,
are unable thus to acquire energy. Entering the chloro-
phyll-bodies, the kinetic energy of sunlight is applied to
the decomposition of carbon dioxide and water. After
passing through manifold but imperfectly known processes,
the elements of these substances finally reappear as starch,
often in the form of granules embedded in the chlorophyll-
bodies and free oxygen, most of which is returned to the
atmosphere. Thus the leaf of a green plant in the light is
continually absorbing carbon dioxide and giving forth free
oxygen.

Carbon dioxide and water contain no potential energy,
since the affinities of their constituent elements are com-
pletely satisfied. Starch, however, contains potential en-
ergy, since the molecule is relatively unstable — i.e., capable
of decomposition into simpler, stabler molecules in which
stronger affinities are satisfied. And this is due to the
fact that in the manufacture of starch in the chlorophyll-
bodies the kinetic energy of sunlight was expended in lift-
ing the atoms into position of vantage, thus endowing them
with energy of position. In this way some of the radiant
and kinetic energy of the sun comes to be stored up as
potential energy in the starch. In short, the green plant
is able by cooperation with sunlight to use simple raw
materials (carbon dioxide, water, oxygen, etc.) poor in

LIFE PROCESSES in

energy or devoid of it, and out of them to manufacture
food — i.e. j complex compounds rich in available potential
energy. This power is possessed by green plants alone;
all other organisms being dependent for energy upon the
potential energy of ready-made food. This must, in the
first instance, be provided for them by green plants, and
hence without chlorophyll-bearing plants, animals (and
colorless plants as well) apparently could not long exist

The plant absorbs also a small amount of kinetic energy,
independently of the sunlight, in the form of heat. This,
however, is probably not a source of vital energy, but only
contributes to the maintenance of the body temperature.

Food (starch) thus produced in the green leaves of
higher plants and the inorganic foods (water, nitrites or
nitrates and various mineral substances in solution in
water) furnish the materials and energy required for the
life and growth of the plant.

The circulatory system distributes these foods. In ani-
mals foods prepared for absorption in the stomach and
intestine (by digestion) are absorbed by the circulating
liquids (blood and lymph) and transported to all cells of
the animal body. In the plant the inorganic mat-
ter in water from the soil are absorbed by the
roots and carried up definite tubes in the woody-
part of the stem. The causes of this ascent are
not clear, but root-pressure due to osmosis, capillary
action and evaporation from the leaves are factors. Just
as the solid food of animals must be digested in prepara-
tion for absorption, so starch manufactured in the leaves
must be digested (dissolved) before it can be transported.
This is done by diastase, an enzyme of plant cells. The
change is from starch to a sugar capable of diffusion.
Dissolved in water, the sugar is transported down delicate
tubes, chiefly in the growing bark region of the stem. It
is clear that there are upward and downward currents of
water containing food (comparable to blood of an animal),
but no system of complete circulation as in the blood ves-

112 BIOLOGY

sels of a higher animal. However, the result in distributed
food is the same in the plant and in the animal.

In the cells the foods undergo metabolic changes. In an
animal the foods in the circulating liquids, blood and
lymph, are selected and absorbed by the cells. Only pro-
teid foods form new protoplasm and even of proteids only
a limited amount, seventy-five to one hundred grams a
day for a man, is built into new protoplasm. The excess
undergoes oxidation and forms nitrogen excretions. The
foods containing only the elements carbon, hydrogen and
oxygen (fats and carbohydrates) are directly oxidized to
excretions and, lacking nitrogen, cannot serve for making
new animal protoplasm. Fat and carbohydrate foods,
then, never become living matter. They may be stored,
especially as fat, until needed for oxidation to supply
energy. The building up of the protoplasm from proteids
is anabolism, constructive metabolism. The destruction of
protoplasm, excess proteids or the fat and carbohydrate
foods is katabolism, destructive metabolism. Katabolism
is probably due to enzyme action, but the final result is
chiefly carbon dioxide and water, which could be deiived
by the ordinary chemical evolution of protoplasm, proteid,
sugar, starch or fats.

In the plant, starch, as has been seen, is first formed in
the chlorophyll-bodies. But the formation of starch, all-
important as it is, is after all only the manufacture of food
as a preliminary to the real processes of nutrition. These
processes must take place everywhere in ordinary proto-
plasm, for it is here that oxidation occurs and the need for
a renewal of matter and energy consequently arises.
Sooner or later the starch grains are changed into a kind
of sugar (glucose), which, unlike starch, dissolves in the
sap and may thus be easily transported to all parts of the
plant. Wherever there is need for new protoplasm,
whether to repair previous waste or to supply materials for
growth, after absorption into the cells the elements of the
starch (or glucose) are, by the living protoplasm, in some

LIFE PROCESSES 113

unknown way combined with nitrogen and sulphur (prob-
ably also with salts, water, etc.) to form proteid matter.
The particles of this newly formed compound are incor-
porated into the protoplasm.

If a larger quantity of starch is formed in the chloro-
phyll-bodies than is immediately needed by the protoplasm
for purposes of repair or growth, it may be reconverted
into starch after journeying as glucose through the plant
and be laid down as "reserve starch" in the cells of root
or stem or elsewhere. Apparently when this reserve sup-
ply is finally needed at any point in the plant, it is again
changed to glucose and transported thither. It is probable
that new leaves and new tissues generally are always
formed in part from this reserve starch.

In the plant as in the animal metabolism must consist
of anabolic and katabolic processes. The construction in
the cells of new proteid from the absorbed carbohydrate
and the materials from the soil is true anabolism. It is
also clear that katabolism or oxidation for the liberation
of energy occurs as in animals, but this process is slower.
Probably foods containing carbon, hydrogen and oxygen
are the sources of energy in the higher plants as in ani-
mals.

In both plants and animals simple waste substances re-
sult from the katabolic processes in the cells. In the ani-
mal carbon dioxide, water and nitrogen compounds are the
chief excretions. They are absorbed by the circulating
liquids and carried to the eliminating organs, lungs and
kidneys chiefly, for elimination. In the higher plants the
excretions are carbon dioxide, which escapes through the
epidermis of root, stem and leaf and through the stomata ;
water which is lost by evaporation, especially from the leaf
surface through the stomata; excretions which are lost
by osmosis through the roots and the accumulated but use-
less mineral substances which are eliminated by leaf fall.

In both animals and plants oxygen is essential to the
katabolic part of metabolism. Hence oxygen must be sup-

ii4 BIOLOGY

plied to the cells. Oxygenation is the term used to denote
the oxygen-supplying part of respiration; the other part
of respiration, elimination of carbon dioxide, has been
treated under excretions. In the animal oxygen is ab-
sorbed by the blood, in excess by the hemoglobin of the
red cells of the blood and later is absorbed from the blood
and lymph by all the living cells. In the plant also oxygen
is absorbed through the epidermis and stomata from the
air. This process is, however, obscured during the day
because of the oxygen freed in the manufacture of starch
which goes on at that time. Probably this freed oxygen
is used for the purpose of oxygenation, but more is freed
in the photosynthetic process than is needed for oxygena-
tion and hence the excess oxygen is eliminated while
starch manufacture is in process.

In comparing a higher animal and a green plant con-
fusion must be avoided regarding the part played by oxy-
gen and carbon dioxide in true respiration with the part
played by the same substances in starch formation (photo-
synthesis). In non-green plants like the Indian pipe and
mushrooms the breathing of oxygen and the excretion of
carbon dioxide are as in the animal. This is true also of
green plants in darkness and even in the light of all parts
of green plants except the chlorophyll-bodies. These con-
stitute a sort of extra mechanism, enabling green plants to
make their own carbohydrate food. Imagine a higher ani-
mal with an attachment for turning the carbon dioxide and
water excreted back to starch usable as food and the com-
parison of the green plant and the animal would be com-
plete.

The power of movement or locomotion is curiously
thought of as peculiar to animals, but biologists know
dozens of examples of movement in plants. Some of the
lower plants possess the power of locomotion and even in
plants as high as mosses and ferns there is a locomotion of
the male germ-cells. Among the flowering plants there is
no actual locomotion, but there are numerous forms of

LIFE PROCESSES

"5

movement. Most striking perhaps are the so-called "sleep-
movements" of plants by means of which the leaves of
some plants — e.g., the oxalis, bean, clover, locust and others
— can assume decidedly different positions at night from
those which they occupy by day; the movements of the
sensitive plant (Mimosa) when "shocked" by touch or in

2~D^> pojiflo*

Fig- 13 — Rkdbud, 'Cercis Canadensis/ Showing Day abtd Night
Positions of the Leaves.

other ways, and the movements of the leaves of the Venus
lytrap (Dionea), which close with a quick jerk when the
sensitive hairs with which they are bordered are stimu-
lated.

It is in nervous functions that the most striking differ-

n6

BIOLOGY

ence between the animal and the plant is to be found.
Plants have no true nervous system, nevertheless irritabil-
ity or response to stimulus is well marked in many plants.
It would carry. us far beyond the limits of this volume to
trace satisfactorily the powers of plants to respond to
stimuli of gravity, light, heat, water, electricity, chemicals,
contact, injury and so on. Suffice it to say that the total
effect of such responses is for the plant equal to that of the
nervous system for the animal.

Reproduction is a most important function. The
life of every organic species runs in regularly

Fig. 14 — Sensitive Plant, Before and After 'Alarm.'
(Duchartre.)

recurring cycles, for every individual life has its
limit. In youth the constructive processes preponderate
over the destructive and the organism grows. The normal
adult attains a state of apparent physiological balance in
which the processes of waste and repair are approximately
equal. Sooner or later, however, this balance is disturbed.
Even tho the organism escapes every injury or special dis^
ease, the constructive process falls behind the destructive,

LIFE PROCESSES 117

old age ensues and the individual dies from sheer inability
to live. Why the vital machine should thus wear out is a
mystery, but that it has a definite cause and meaning is
indicated by the familiar fact that the span of natural life
varies with the species ; man lives longer than the dog, the
elephant longer than man.

It is a wonderful fact that living things have the power
to detach from themselves portions or fragments of their
own bodies endowed with fresh powers of growth and de-
velopment and capable of running through the same cycle
as the parent. There is therefore an unbroken material
(protoplasmic) continuity from one generation to another
that forms the physical basis of inheritance and upon
which the integrity of the species depends. As far as
known, living things never arise save through this process.
In other words, every mass of existing protoplasm is the
last link in an unbroken chain that extends backward in
the past to the first origin of life.

The detached portions of the parent that are to give
rise to offspring are sometimes masses of cells, as in the
separation of branches or buds among plants, but more
commonly they are single cells, known as germ-cells, like
the eggs of animals and the spores of ferns and mosses.
Only the germ-cells (which may conveniently be distin-
guished from those forming the rest of the body or the
somatic cells) escape death, and that only under certain
conditions.

All forms of reproduction fall under one or the other
of two heads, viz., agamogenesis (asexual reproduction)
or gamogenesis (sexual reproduction). In the former
case the detached portion (which may be either a single
cell or a group of cells) has the power to develop into a
new individual without the influence of other living mat-
ter. In the latter, the detached portion, in this case always
a single cell (ovum, oosphere, etc.), is acted upon by a sec-
ond portion of living matter, likewise a single cell, which
in most cases has been detached from the body of another

n8 BIOLOGY

individual. The germ is called the female germ-cell, the
cell acting upon it the male germ-cell, and in the sexual
process the two fuse together (fertilization, impregna-
tion) to form a single new cell endowed with the power
of developing into a new individual. In some organisms
(e.g., the yeast-plant and bacteria) only agamogenesis has
been observed; in others (e.g., vertebrates) only gamo-
genesis; in others still both processes take place as in
many higher plants.

The earthworm, for example, is not known to multiply
by a natural process of agamogenesis. It possesses in a
high degree, however, the closely related power of regen-
eration, for if a worm be cut transversely into two pieces
the anterior piece will usually make good or regenerate the
missing portion, while the posterior piece may regenerate
the anterior region. Thus the worm can to a certain lim-
ited extent be artificially propagated, like a plant, by cut-
tings, a process closely related to true agamogenesis. Its
usual and normal mode of reproduction is by gamogenesis ;
that is, by the formation of male germ-cells (spermato-
zoa) and female germ-cells (ova). In higher animals the
two kinds of germ-cells are produced by different individu-
als of opposite sex. The earthworm, on the contrary, is
hermaphrodite or bisexual; every individual is both male
and female, producing both eggs and spermatozoa.

As in the animal so in the plant, whether the individual
dies or not, ample provision against the death of the race
is made in the act of reproduction. Altho reproduction
appears to be useless to the individual and even entails
upon it serious annual losses of matter and energy, yet
to this function every part of the plant directly or indi-
rectly contributes. The reproductive germs are carefully
prepared, are provided with a stock of food sufficient for
the earliest stages of development, and are endowed with
the peculiar powers and limitations of each species which
influence their life history at every step and are by them
transmitted in turn to their descendants. They are living

LIFE PROCESSES ri9

portions of the parent detached for reproductive purposes
and they contain a share of protoplasm directly descended
from the original protoplasm from which the parent came.
In short, reproduction is the supreme function of the plant.

As in the animal, reproduction in the higher plants is
by the process of gamogenesis. Male germ-cells and
female germ-cells are formed in separate organs. In many
of the higher plants these organs are both found in the
same individual, but often they are produced by different
individuals of opposite sex. Agamogenesis, or asexual re-
production, also takes place in many higher plants by
means of runners, buds, bulbs, tubers, etc., but in most of
these cases provision is made for sexual reproduction also.

In relation to the environment animals and plants are
masses of living matter occupying definite positions in
space and time and existing amid certain definite and
characteristic physical surroundings which constitute their
"environment." As ordinarily understood the term en-
vironment applies only to the immediate surroundings of
the animal and plant. Strictly speaking, however, the
environment includes everything that may in any manner
act upon the organisms— that is, the whole universe out-
side them. For they are directly and profoundly affected
by rays of light and heat that travel to them from the sun ;
they are extremely sensitive to the alternations of day and
night and the seasons of the year; they are acted on by
gravity; and to all these, as well as to more immediate
influence, they make definite responses.

The body of the animal is a complicated piece of
mechanism constructed to perform certain definite actions.
But every one of these actions is in one way or another
dependent upon the environment and directly or indirectly
relates to it. At every moment of its existence the organ-
ism is acted on by its environment; at every moment it
reacts upon the environment, maintaining with it a con-
stantly shifting state of equilibrium which finally gives
way only when the life of the animal draws to a close.

120 BIOLOGY

The action of the environment upon the animal has
been sufficiently stated. It remains to point out the
changes worked by the animal on the environment. These
changes are of two kinds, mechanical (or physical) and
chemical. The general effect of the metabolism of the
animal is the destruction by oxidation of organic matter;
that is, matter originally taken from the environment in
the form of complex proteids, fats, and carbohydrates is
returned to it in the form of simpler and more highly
oxidized substances, of which the most important are
carbon dioxide and water (both inorganic substances).
This action furthermore is accompanied by a dissipation
of energy — that is, a conversion of potential into kinetic
energy.

On the whole, therefore, the action of the animal upon
the environment is that of an oxidizing agent, a reducer of
complex compounds to simpler ones, and a dissipator of
energy.

The actions of the environment upon the plant have
been sufficiently dwelt upon. It still remains, how-
ever, to consider the actions of the plant upon the environ-
ment. These are partly physical, but mainly chemical. By
pushing its stems and leaves into the air and slowly thrust-
ing its roots through the soil, the atmosphere and the
earth are alike displaced. But it is by its chemical activity
that it most profoundly affects its environment. Absorb-
ing from the latter water, salts, carbon dioxide, and other
simple substances, as well as sunlight, it produces with
them a remarkable metamorphosis. It manufactures from
them as raw materials organic matter in the shape of
starch, fats, and even proteids. These it gives back to the
environment in some measure during life, and surrenders
wholly after sudden death. But the most striking fact is
that the plant is on the whole constructive and capable of
producing and accumulating compounds rich in energy
and in this respect it is unlike the animal.

Thus, while animals are destroyers of energized com-

LIFE PROCESSES 121

pounds, green plants are producers of them. Animals,
therefore, in the long run, are absolutely dependent on
plants; and animals and colorless plants alike upon green
plants. But it must never be forgotten that most plants
are enabled to manufacture organic from inorganic matter
by virtue of the chlorophyll which they contain. Without
this they are powerless in this respect.

It is evident that to the superficial observer the plant
and animal seem to have little or nothing in common,
except that both are what we call alive. But whoever has
studied the preceding pages must have perceived beneath
manifold differences of detail a fundamental likeness be-
tween the plant and animal, not only in the substantial
identity of the living matter in the two but also in the
construction of their bodies and in the processes by which
they come into existence. "Each arises from a single cell,"
to quote Sedgwick and Wilson, "which is the result of the
union of two differently constituted cells, male and female.
In both the primary cell multiplies and forms a mass of
cells, at first nearly similar but afterward differentiated in
various directions to enable them to perform different
functions — i.e., to effect a physiological division of labor.
In both, the tissues thus provided are associated more or
less closely into distinct organs and systems, among which
the various operations of the body are distributed. And
in both the ultimate goal of individual existence is the
production of germ-cells which form the starting-point of
new and similar cycles.

"This fundamental likeness extends also to most of the
actions (physiology) of the two organisms. Both possess
the power of adapting themselves to the environments in
which they live. Both take in various forms of matter
and energy from the environment, build them up into
their own living substance, and finally break down this
substance more or less completely into simpler compounds
by processes of internal combustion, setting free by this
action the energy which maintains their vital activity.

122 BIOLOGY

And, sooner or later, both give back to the environment
the matter and energy which they have taken from it. In
other words, both effect an exchange of matter and of
energy with the environment."

Nevertheless the plant and the animal differ. They
differ widely in form, and the plant is fixed and relatively
rigid, while the animal is flexible and mobile. The body
of the plant is relatively solid ; that of the animal contains
numerous cavities. The plant absorbs matter directly
through the external surface; the animal partly through
the external and partly through an internal (alimentary)
surface. The plant is able to absorb simple chemical com-
pounds from the air and earth, and kinetic energy from
sunlight; the animal absorbs, for the most part, complex
chemical compounds and makes no nutritive use of the
sun's kinetic energy. By the aid of this energy the plant
manufactures starch from simple compounds, carbon diox-
ide and water ; the animal lacks this power. The plant can
build up proteids from the nitrogenous and other com-
pounds of its food. And by manufacturing proteids within
its living substance, the plant is relieved of the necessity of
carrying on a process of digestion in order to render them
diffusible for entrance into the body.

Still, great as these differences appear to be at first
sight, all of them, with a single exception, fade away upon
closer examination. This exception is the power of
making foods. Plants and animals differ in form because
their mode of life differs; but a wider study of biology
reveals the existence of innumerable animals (corals,
sponges, hydroids, etc.) which have a close superficial
resemblance to plants, and of many plants which resemble
animals, not only in form, but also in possessing the
power of active locomotion. The stomach of the animal,
as shown by its development, is really a part of the general
outer surface which is folded into the body; and the ani-
mal, like the plant, therefore, really absorbs its income
over its whole surface — oxygen through the general outer

LIFE PROCESSES 123

surface, other food-matters through the infolded aliment-
ary surface.

In like manner it is easy to show that not one of the
differences between the plant and animal is fundamentally
important save the power of making foods. The animal
must have complex ready-made food, including proteid
matter. So must the plant ; but the plant is able to manu-
facture this complex food out of very simple compounds.
In terms of energy, the animal requires ready-made food
rich in potential energy; the plant, aided by the sun's
energy, can manufacture food from matters devoid of
energy. Hence it appears, broadly speaking, that the plant
by the aid of solar energy is constructive, and stores up
energy; the animal is destructive, and dissipates energy.
And this difference becomes of immense importance in
view of the fact that it is true in this respect of all green
plants, as of all animals.

Even this difference, great as it is, is partly bridged
over by colorless plants like yeast, molds, bacteria, etc.,
which have no chlorophyll, are therefore unable to use
the energy of light, and hence must have energized food.
But these organisms do not, like animals, require proteid
food, being able to extract all needful energy from the
simpler fats, carbohydrates, and even from certain salts.
When it is considered that the distinctive peculiarities of
animals can thus be reduced to the sole characteristic of
dependence on proteid food, it cannot be doubted that the
difference between plants and animals is of immeasurably
less importance than their fundamental likeness, the more
so when it is kept in mind that each of the principles
of organic function will be found to apply to all animals
including man himself and to all plants, however complex
they may be.

CHAPTER IX

ORIGIN OF SPECIES OF PLANTS AND ANIMALS

There are in the museums of the world at the present
time representatives of several hundred thousand — prob-
ably more than a million — kinds or species of plants and
animals, and thousands of new species are being discov-
ered and named each year. A single group of insects has
classified under it more species than there are stars to be
seen in the heavens with the unaided eye on a clear night.
Aristotle knew about five hundred kinds of animals, but a
single new botanical or zoological work may now
describe more than that number of species new to the
records of Science. Linnaeus in 1758 published the tenth
edition of his 'Systema Naturae' and named about four
thousand animals, and every year since 1864 the 'Zoolog-
ical Record' has listed three or four times this number
of species previously undescribed, yet now, as in Lin-
naeus's time, it is certain that not half of the number of
species of animal organisms is, yet known. The six hun-
dred thousand, more or less, on the registers of Science
to-day are certainly far less than half of the millions
which actually exist.

In botany the same conditions are to be found. There
are fewer known species of plants than animals by half,
and they are more easily preserved and handled, while the
work of collection and investigation proceeds on a scale
even more extensive, yet it would be a bold statement to
say that to-day half the species of plants that exist are
known.

124

ORIGIN OF SPECIES 125

All this refers to the forms now living, without refer-
ence to the host which composes their long ancestry,
extending backward toward the dawn of creation. The
species have come down through the geological ages,
changing in form and function to meet the varying needs
of changing environment. This enumeration takes no ac-
count of the still vaster myriads of forms almost endlessly
varied, which have perished utterly in the pressure of
environment, leaving no trace in the line o fdescent.

It is evident that variety in life is a factor in the history
of the globe, that it may be expressed in terms of number
of species, but that the actual range of variation is far
greater than the number of species, and that if causes
are to be judged by range of effects, in the origin of spe-
cies must be found the operation of world-wide forces, the
cooperation of great influences, far-reaching in time and
space, as broad as the surface of the globe and as endur-
ing as its life.

The cause of this amazing variety in life, and the man-
ner of accounting for origin of species are questions
necessarily asked when attention is called to the existence
of such vast numbers of species of plants and animals. In
earlier chapters the theories of the origin of life have been
described and proof that present living matter has de-
scended from preexisting living matter has been outlined.
It is, in fact, accepted in modern science that there has
been a continuity of descent from the first living matter
to that of the present time. But the form or species in
which life first originated is another subject, and almost
as great. Such a subject must deal with the questions
as to whether life first appeared in each species of animal
or plant separately, or whether it began in simple proto-
plasm from which have been evolved the almost number-
less species known to-day.

It is quite clear that there are only two hypotheses in
the field whereby it is possible so much as to suggest an
explanation of the origin of species. Either all the species

126 BIOLOGY

of plants and animals must have been supernaturally
created, or else they must have been naturally evolved.
There is no third hypothesis possible; for no one can
rationally suggest that species have been eternal.

It should be noticed that whichever of the two rival
theories is entertained, the concern is not with any ques-
tion touching the origin of life, but only with the origin
of particular forms of life — that is to say, with the origin
of species. The theory of descent starts from life as a
'datum' already granted. How life itself came to be, the
theory of descent, as such, is not concerned to show.
Therefore, in the present discussion, the existence of life
is taken as a fact which does not fall within its range of
debate.

The history of biology in the nineteenth century will be
famous because of the discussion of these two hypotheses
which attempt to account for the existence of the innumer-
able species of living things which inhabit the earth :
the theory of creation and the theory of evolution.
According to the theory of creation, all the individuals
of every species existing at the present day — the tens of
thousands of dogs, oak trees, amoebae, and what-not — are
derived by a natural process of descent from a single
individual, or from a pair of individuals — in each case
precisely resembling, in all essential respects, their exist-
ing descendants — which came into existence by a process
outside the ordinary course of nature, and known as
Creation.

According to the rival theory — that of Descent or
Organic Evolution — every species existing at the present
day is derived by a natural process of descent from some
other species which lived in a former period of the world's
history. If from generation to generation the individuals of
any existing species could be traced back, on this hypoth-
esis, their characters would be found gradually to change,
until finally a period was reached at which the differences
were so considerable as to necessitate the placing of the

ORIGIN OF SPECIES 127

ancestral forms in a different species from their descen-
dants at the present day. And in the same way if the
species of any one genus could be traced back they would
gradually approach one another in structure until they
finally converged in a single species, differing from those
now existing but standing to all in a true parental relation.

In regard to the present standing of these two theories
it should be stated that the theory of descent is now
generally accepted by men of science and the theory of
special creation rejected. In fact no great naturalist since
Agassiz has attacked the general theory, tho some have
debated many of its minor details. As David Starr Jordan
has said: "There is to-day no doubt in our minds of the
truth, the actuality, of descent. It is not the theory of
descent: it is the fact, the law, of descent, of which we
talk and write. Organisms are blood-related; they are
transformed, descended from one another."

At this point it will clarify some later considerations
if it is emphasized that there is a great distinction to be
drawn between the fact of evolution and the manner of
it, or between the evidence of evolution as having taken
place somehow, and the evidence of the causes which have
been concerned in the process. This most important dis-
tinction is frequently disregarded by popular writers on
evolution, and, therefore, in order to mark it as strongly
as possible, it will be necessary to effect a complete separa-
tion between the evidence of evolution as a fact, and the
evidence as to its method. In other words, not until the
evidence of organic evolution as a process, which somehow
or another has taken place, has been fully considered, is
it advisable to consider how it has taken place, or the
causes which Darwin and others have suggested as having
probably been concerned in this process.

First there is to be considered, therefore, the evidences
pointing to the fact of organic descent (evolution) ot
species of animals and plants and later there will be out-
lined the trend of the enormous amount of investigation

128 BIOLOGY

which has been and now more actively than ever is being
done toward the solution of the problems concerned with
the causes or the factors of evolution. In passing, it must
be noted that while Darwin wrote both concerning the
evidences of evolution and the manner or causes of evolu-
tion, it is not correct, as many authors assume, to regard
the 'Darwinian Theory' or 'Darwinism' as synonymous
with the theory of descent or evolution. Rather should
the terms 'Darwinism' and Darwinian Theory' be applied
to the theory of natural selection, Darwin's great explana-
tion of the cause of the origin of species by evolution or
descent.

The late Professor Cope, of Philadelphia, defines evolu-
tion in the broadest sense, including both organic and
inorganic evolution, as follows : "The doctrine of evolution
may be defined as the teaching which holds that creation
has been and is accomplished by the agency of the energies
which are intrinsic in the evolving matter, and without the
interference of agencies which are external to it. It holds
this to be true of the combinations and forms of inorganic
nature, and of those of organic nature as well. Whether
the intrinsic energies which accomplish evolution be forms
of radiant or other energy only, acting inversely as the
square of the distance, and without consciousness, or
whether they be energies whose direction is affected by
the presence of consciousness, the energy is a property of
the physical basis of tridimensional matter, and is not
outside of it."

But a distinction must be made between organic and
inorganic evolution. Professors Jordan and Kellogg have
stated this most clearly in 'Evolution and Animal Life' :
"Biological evolution and cosmic evolution are not the
same. From the biological side a certain objection must
be made to this philosophical theory of universal or cosmic
evolution. In organic and inorganic evolution there is
much in common, so far as conditions and results are
concerned; but these likenesses belong to the realm of

ORIGIN OF SPECIES 129

analogy, not of homology. They are not true identities
because not arising from like causes. The evolution of
the face of the earth forces parallel changes in organic
life, but the causes of change in the two cases are in no
respect the same. The forces or processes by which
mountains are built or continents established have no
homology with the forces or processes which transformed
the progeny of reptiles into mammals or birds.

"Tendencies in organic development are not mystic pur-
poses, but actual functions of actual organs. Tendencies
in inorganic nature are due to the interrelations of mass
and force, whatever may be the final meanings attached to
these terms or to the terms matter and energy. It is not
clear that science has been really advanced through the
conception of the essential unity of organic evolution and
cosmic evolution. The relatively little the two groups of
processes have in common has been overemphasized as
compared with their fundamental differences.

"The laws which govern living matter are in a large
extent peculiar to the process of living. Processes which
are functions of organs cannot exist where there are no
organs. The traits of protoplasm are shown only in the
presence of protoplasm. For this reason we may well
separate the evolution of astronomy, the evolution of
dynamic geology and of physical geography, as well as the
purely hypothetical evolution of chemistry, from the ob-
served phenomena of the evolution of life.

"To regard cosmic evolution and organic evolution as
identical or as phases of one process is to obscure facts by
verbiage. There are essential elements in each not shared
by the other — or which are at least not identical when
measured in terms of human experience. It is not clear
that any force whatever or any sequence of events in the
evolution of life is homologous with any force or sequence
in the evolution of stars and planets. The unity of forces
may be a philosophical necessity. A philosophical necessity
or corner in logic is unknown to science. We can recog-

130 BIOLOGY

nise no logical necessity until we are in possession of all
the facts. No ultimate fact is yet known to science.

"For reasons indicated above the term 'evolution' is
not wholly acceptable as the name of a branch of science.
The term 'bionomics' is a better designation of the chan-
ging of organisms influenced through unchanging laws. It
is a name broader and more definite than the term organic
evolution, it is more euphonious than any phrase meaning
life adaptation, it involves and suggests no theory as to the
origin of the phenomena it describes."

The theory of descent of plants and animals is defined
by the same authors as the "belief that organs and species
as we know them are derived from other and often simpler
forms by processes of divergence and adaptation. Accord-
ing to this theory all forms of life now existing, or that
have existed on the earth, have risen from other forms
of life which have previously lived in turn. All characters
and attributes of species and groups have developed with
changing conditions of life. The homologies among
animals are the results of common descent. The differ-
ences are due to various influences, one of the leading
forces among these being competition in the struggle for
existence between individuals and between species, where-
by those best adapted to their surroundings live and pro-
duce their kind."

This theory is now the central axis of all biological
investigation in all its branches, from ethics to histology,
from anthropology to bacteriology. In the light of this
theory every peculiarity of structure, every character or
quality of individual or species, has a meaning and a cause.
It is the work of the investigator to find this meaning as
well as to record the fact. "One of the noblest lessons left
to the world by Darwin," says Frank Cramer, "is this,
which to him amounted to a profound, almost religious
conviction, that every fact in nature, no matter how in-
significant, every stripe of color, every tint of flowers,
the length of an orchid's nectary, unusual height in a

ORIGIN OF SPECIES 131

plant, all the infinite variety of apparently insignificant
things, is full of significance. For him it was an historical
record, the revelation of a cause, the lurking place of a
principle." It is therefore a fundamental principle of the
science of bionomics that every structure and every func-
tion of to-day finds its meaning in some condition or in
some event of the past.

Darwin's own view of the doctrine of descent is clearly
set forth in the following passages from the 'Origin of
Species' : "Authors of the highest eminence seem to be
fully satisfied with the view that each species has been
independently created. To my mind it accords better with
what we know of the laws impressed on matter by the
Creator, that the production and extinction of the past
and present inhabitants of the world should have been due
to secondary causes, like those determining the birth' and
death of the individual.

"When I view all beings not as special creations, but
as the lineal descendants of some few beings which lived
long before the first bed of the Cambrian system was
deposited, they seem to me to become ennobled. Judging
from the past, we may safely infer that not one living
species will transmit its unaltered likeness to a distant
futurity. And of the species now living very few will
transmit progeny of any kind to a far distant futurity ;
for the manner in which all organic beings are grouped,
shows that the greater number of species in each genus,
and all the species in many genera, have left no descend-
ants, but have become utterly extinct. We can so far take
a prophetic glance into futurity as to foretell that it will
be the common and widely spread species, belonging to
the larger and dominant groups within each class, which
will ultimately prevail and procreate new and dominant
species. As all the living forms of life are the lineal
descendants of those which lived long before the Cambrian
epoch, we may feel certain that the ordinary succession by

132 BIOLOGY

generation has never once been broken, and that no
cataclysm has desolated the whole world.

"It is interesting to contemplate a tangled bank, clothed
with many plants of many kinds, with birds singing on the
bushes, with various insects flitting about, and with worms
crawling through the damp earth, and to reflect that these
elaborately constructed forms, so different from each other,
and dependent upon each other in so complex a manner,
have all been produced by laws acting around us. There
is grandeur in this view of life, with its several powers,
having been originally breathed by the Creator into a few
forms or into one; and that, while this planet has gone}
cycling on according to the fixed law of gravity, from so
simple a beginning endless forms most beautiful and most
wonderful have been and are being evolved."

What organic evolution does not mean is a topic which
deserves some attention before discussing the evidences for
evolution. President Jordan has written in 'Foot-Notes
to Evolution' a strong statement concerning this, wherein
he says : "Evolution is not a theory that 'man is a de-
veloped monkey." The question of the immediate origin
of man is not the central or overshadowing question
of evolution. This question offers no special diffi-
culties in theory, altho the materials for exact knowledge
are in many directions incomplete. Homologies more per-
fect than those connecting man with the great group of
monkeys could not exist. These imply the blood relation-
ship of the human race with the great host of apes and
monkeys. As to this there can be no shadow of a doubt,
and, as similar homologies connect man with all members
of the group of mammals, similar blood relationship must
exist; and homologies less close but equally unmistakable
connect all backboned animals one with another, and the
lowest backboned types are closely joined to wormlike
forms not usually classed as vertebrates.

"It is perfectly true that in the higher or anthropoid
apes the relations with man are extremely intimate; but

ORIGIN OF SPECIES 133

man is not simply 'a developed ape.' Apes and men have
diverged from the same primitive stock — apelike, manlike,
but not exactly the one nor the other. No apes nor
monkeys now extant could apparently have been ancestors
of primitive man. None can ever 'develop' into man. As
man changes and diverges, race from race, so do they.
The influence of effort, the influence of surroundings, the
influence of the sifting process of natural selection, each
acts upon them as it acts upon man.

"The process of evolution is not progress, but better
adaptation to conditions of life. As man becomes fitted
for social and civic life, so does the ape become fitted for
life in the tree-tops. The movement of monkeys is toward
simianity, not humanity. The movement of cat life is
toward felinity, that of the dog races toward caninity.
Each step in evolution upward or downward, whatever it
may be, carries each species or type farther from the
primitive stock. These steps are never retraced. For an
ape to become a man he must go back to the simple char-
acters of the simple common type from which both have
sprung. These characters are shown in the ape baby and
in the human embryo in its corresponding stages, for an-
cestral traits lost in the adult are evident in the young.
This persistence comes through the operation of the great
force of cell memory which we call heredity.

"The evidence of biology points to the descent of all
mammals, of all vertebrates, of all animals, of all organic
beings, from a common stock. Of all the races of animals
the anthropoid apes are nearest man. Their divergence
from the same stock must be comparatively recent. Man
is the nomadic, the apes are the arboreal, branch of the
same great family.

"Evolution does not teach that all or any living forms
are tending toward humanity. It does not teach, as in
Bishop Wilberforce's burlesque, 'that every favorable
variety of the turnip is tending to become man.' It is not
true that evolutionists expect to find, as Dr. Seelye has

134 BIOLOGY

affirmed, 'the growth of the highest alga into a zoophyte, a
phenomenon for which sharp eyes have sought, and which
is not only natural but inevitable on the Darwinian hy-
pothesis, and whose discovery would make the fame of any
observer/

"It is no wonder that a clear thinker should have re-
jected 'the Darwinian hypothesis' when stated in such
terms as this. The line of junction in evolution is always
at the bottom. It is the lowest mammals which approach
the lowest reptiles; it is the lower types of plants which
approach the lower types of animals ; it would be the lowest
Alga, to use Dr. Seelye's illustration, which would be
transmutable into the lowest zoophyte ; it is the unspecial-
ized, undifferentiated type from which branches diverge in
different ways. Humanity is not the 'goal of evolution,'
not even that of human evolution. There will be no second
creation of man, except from man's own loins. There will
not be a second Anglo-Saxon race unless it has the old
Anglo-Saxon blood in its veins.

"Adaptation by divergence — for the most part of slow
stages — is the movement of evolution. While occasional
leaps or sudden changes occur in the process, they are by
no means the rule. In most cases of 'saltatory evolution'
the suddenness is in appearance only. It comes from our
inability to trace the intermediate stages. When an
epoch-making character is acquired, as the wings of a
bird or the brain of man, the process of readjustment of
other characters goes on with greatly increased rapidity.
But this rapidity of evolution is along the same lines as the
slower processes. Radical changes from generation to
generation never occur.

"We do not expect to find birds arising from a 'flying-
fish in the air, whose scales are disparting into feathers.'
A flying-fish is no more of the nature of a bird than any
other fish is. A cow will never give birth to a horse, nor a
horse to a cow. The slow operation of existing causes is
the central fact of organic evolution, as it is of the evolu-

ORIGIN OF SPECIES 135

tion of mountains and valleys. Seasons change as the
relations which produce them change. But midsummer
never gives way to midwinter in an instant. Nor does the
child in an instant become a man, tho in some periods of
growth epoch-marking causes may make development more
rapid. Life is conservative. The law of heredity is the
expression of its conservatism. Life changes slowly, but
it must constantly change, and all change is, by necessity,
divergence.

"There is in Nature no single 'law of progress/ nor is
progress in any group a necessity regardless of conditions.
That which we call progress rests simply on the survival
of the better adapted, their survival being accompanied by
their reproduction. Those that live repeat themselves.
The 'innate tendency toward progression' of the early
evolutionists is a philosophic myth. Progress and degen-
eration are alike the resultants of the various forces at
work from generation to generation on and within a race
or species. The same forces which bring progress to a
group under one set of conditions will bring degradation
under another. In their essence the factors of evolution
are no more laws of progress than the attraction of gravi-
tation is. Cosmic order comes from gravitation. Organic
order comes from the factors of evolution. Evolution is
simply orderly change.

"Nor is evolution identical with the notion of spontane-
ous generation. There is no necessary connection between
the one theory and the other. If there is now spontaneous
generation of protoplasm, it cannot take the form of any
creature we know. An organism fresh from the mint of
creation would be too small for us to see with any micro-
scope. It would be too simple for us to trace by any
instrumentality now in our possession. It would contain
but a few molecules, and a molecule in a drop of water is
as small as an orange beside the sun. Such a race of
creatures, spontaneously generated, without concessions
to environment, would grow hoary with the centuries

136 BIOLOGY

before it came to our notice. Its descendants would have
belonged for ages to the unnumbered hosts of microbes
before we should be aware of its creation.

"Evolution is not a creed or a body of doctrine to be
believed on authority. There is no saving grace in being
an evolutionist. There are many who take this name and
have no interest in rinding out what it means or in making
any application of its principles to the affairs of life. For
one who cares not to master its ideas there is no power in
the word. Evolution is not a panacea or a medicine to be
applied to social or personal ills. It is simply an expression
of the teaching of enlightened common sense as to the
order of changes in life. If its principles are mastered, a
knowledge of evolution is an aid in the conduct of life,
as knowledge of gravitation is essential in the building of
machinery.

"There is nothing 'occult' in the science of evolution.
It is not the product of philosophic meditation or of
speculative philosophy. It is based on hard facts, and
with hard facts it must deal. It seems to me that it is
not true that 'Evolution is a new religion, the religion
of the future.' There are many definitions of religion,
but evolution does not fit any of them. It is no more a
religion than gravitation is.

"One may imagine that some enthusiastic follower of
Newton may, for the first time, have seen the majestic
order of the solar system, may have felt how futile was
the old notion of guiding angels, one for each planet, to
hold it up in space. He may have received his first clear
vision of the simple relations of the planets, each forever
falling toward the sun and toward one another, each one
by the same force forever preserved from collision. Such
a man might have exclaimed, 'Great is gravitation; it is
the new religion, the religion of the future !' In such
manner, men trained in dead traditions, once brought to
a clear insight of the noble simplicity and adequacy of the
theory of evolution, may have exclaimed, 'Great is evolu-

ORIGIN OF SPECIES 137

tion ; it is the new religion, the religion of the future !'
But evolution is religion in the same sense that every
truth of the physical universe must be religion. That
which is true is the truest thing in the world, and the
recognition of the infinite soundness at the heart of the
universe is an inseparable part of any worthy religion."

The evidences which have convinced men of science
that the origin of the various species of plants and ani-
mals through descent is a fact are many and are drawn
from various sources; however, no more than an outline
of those facts which help best to an understanding of the
doctrine can be given here. The same facts were once
used in debate concerning the probabilities of the truth
or untruth of the doctrine of descent, but to-day the biolo-
gist feels it unnecessary to stand as an advocate arguing
for belief in evolution. As the days have long passed when
the shape of the earth, or the behavior of the members
of the solar system, was a fit subject for debate, so the
days are now closed when the truth or falsity of the law
of organic descent is a debatable thesis. That the earth
is subspherical, that the planets revolve about the sun, and
that species of organisms descend from other species,
are now to be considered matters uncontrovertible.

Darwin wrote for a generation which had not accepted
evolution, and which poured contempt on those who upheld
the derivation of species from species by any natural law
of descent. He did his work so well that "descent with
modification" is now universally accepted as the order of
nature in the organic world; and the rising generation of
naturalists can hardly realize the novelty of this idea, or
that their fathers considered it a scientific heresy to be
condemned rather than seriously discussed.

CHAPTER X

EVIDENCES OF ORGANIC DESCENT J MORPHOLOGY AND EM-
BRYOLOGY

The facts of biology which admit of adequate explana-
tion only in connection with the theory of descent are
grouped by Romanes and other writers on organic evolu-
tion under the heads of morphology, embryology, classifi-
cation, paleontology, distribution and domestication. In
all these lines the facts are drawn together by a strong
thread of unity. There are numberless similarities and
correlations and surprising uniformities. The great
variety of life as exhibited in the countless species of
plants and animals has been referred to, and yet, great as
this variety is, there are, after all, only a few types of
structure among all animals and plants, some three or four
or eight or ten general modes of development, and all the
rest are modifications from these few types.

It is, moreover, true that all living forms are but series
of modifications and extensions of one single plan or struc-
ture. All have the same ultimate substance — the mys-
terious semi-fluid network of protoplasm, which is, so far
as is known, the physical basis of all life; and the equally
mysterious nuclear substance or chromatin which in some
fashion presides over all the movements of the protoplasm
and is the physical basis of the phenomena of heredity.
The same laws of heredity, variability and of response to
outside stimulus hold in all parts of the organic world.
All organisms have the same need of reproduction. All are
138

EVIDENCES OF ORGANIC DESCENT 139

forced to make concession after concession to their sur-
roundings, and in these concessions all progress in life
consists. And at last each organism or each alliance of
organisms must come to the greatest concession of all,
which is called death. The unity in life, then, is not less a
fact than is life's great diversity. Whatever emphasis is
laid upon the diversity of life, the essential unity of all
organisms must not be forgotten.

An examination of the facts in each of the lines of
evidence makes it clear that the only reasonable explana-
tion for the existence of a fundamental unity in organic
life is the theory of descent — i.e., that similarities are due
to blood relationship and that differences come from adapt-
ive modifications. The facts adduced from morphology,
being the result of researches into the structure of adult
animals and plants, lead to a preview of certain principles
of adaptation, necessary for their interpretation.

First, it must be noted that some structures are not non-
adaptive, that is, do not change to fit changed habits or
conditions of life. Such structures or organs are most
often found internally. For illustration : a change in the
locomotive habit of a bird from that of flying to that of an
ostrich is associated with an adaptive modification of loco-
motor structures, legs and wings, but not in any striking
way is there change in the internal organs. Internal
organs may persist unchanged and hence they offer good
guides to classification. On the other hand, external struc-
tures are likely to undergo adaptation when habits or con-
ditions of life change. Hence, as Jordan has said, "the
inside of an animal tells the real history of its ancestry;
the outside tells us only where its ancestors have been."

In the second place, it must be noted that adaptations to
similar conditions may result in superficial resemblances.
For example, there is a superficial resemblance between the
wing of an insect and the wing of a bird — both adaptations
to an aerial environment; between the heart of an insect
and the heart of a vertebrate animal — both adaptations for

140

BIOLOGY

pumping blood ; between the fin of a fish and the paddle of
a whale — both adaptive swimming organs, yet the resem-
blance in these cases does not go deeper than the surface —
it is one of function only. All such cases of resemblance
in function but not in detailed plan of structure are called
'analogies,' and mean nothing more than similarity of
environment. Turning to more fundamental resemblances,
such as the wing of a bat and the wing of a bird, careful
study shows detailed internal as well as external similar-
ities of structure. Such cases are 'homologies/

Bat. Bird. Archseopteryx. Pterodactyl.

Fig. 15 — Homologies in Wings. (LeConte.)

On the one hand, then, are found structures which are
perfectly analogous and yet in no way homologous : totally
different structures are modified to perform the same
functions. On the other hand are found structures which
are perfectly homologous and yet in no way analogous :
the structural elements remain, but are profoundly modi-
fied to perform totally different functions. Homology thus
means identity of structure which is the result of identity

EVIDENCES OF ORGANIC DESCENT 141

of parentage. It is the stamp of heredity. It means blood
relationship. These principles of homology are essential
to a correct interpretation of the facts of morphology.

The most striking fact of similar structure among plants
and among animals is the existence of a common general
plan in any group. Since backboned animals are best
known to most readers, they may be taken as an illustra-
tion. "All vertebrate animals, and none other," says Le
Conte, "have an internal jointed skeleton worked by
muscles on the outside. The relation of skeleton and
muscle in arthropods is exactly the reverse.

"In all vertebrates, and in none other, the axis of this
skeleton is a jointed backbone (vertebral column) inclosing
and protecting the nervous centers (cerebro-spinal axis).
These, therefore, may well be called backboned animals.

"All vertebrates, and none other, have a number of their
anterior vertebral joints enlarged and consolidated into a
box to form the skull, in order to inclose and protect a
similar enlargement of the nervous center, viz., the brain ;
and also usually, but not always, a number of posterior
joints, enlarged and consolidated to form the pelvis, to
serve as a firm support to the hind-limbs.

"All vertebrates, and none other, have two cavities, in-
closed and protected by the skeleton, viz., the neural cavity
above, and the visceral or body cavity below, the vertebral
column.

"All vertebrates, with few exceptions, and no other
animals, have two and only two pair of limbs. The excep-
tions are of two kinds, viz.: (a) some lowest fishes, amphi-
oxus and lampreys, which probably represent the verte-
brate condition before limbs were acquired; and (b)
degenerate forms like snakes and some lizards, which have
lost their limbs by disuse.

"So much concerns the general plan of skeletal struc-
tures and is strongly suggestive of — in fact it is inex-
plicable without — common origin. But much more re-
mains which is not only suggestive, but demonstrative of

142

BIOLOGY

such origin. By extensive comparison in the taxonomic
and ontogenic series, the whole vertebrate structure in all
its details in different animals may be shown to be modifi-
cations one of another. Sometimes a piece is enlarged,
sometimes diminished, or even becomes obsolete; some-
times several pieces are consolidated into one ; but, in spite
of all these obscurations, corresponding parts usually may
be made out."

These remarkable similarities in the common general

Man. Dog. Hog, Sheep.

Fig. 1 6 — Homologies in Forehinds.

Horse.
(LeConte.)

plan alone are convincing evidences of descent, but atten-
tion may be called to a like similarity extending to the
details of structure. For example: the wings of a bat (a
mammal), a bird and a fossil flying reptile all show the
same bones adaptively modified; a series of either fore
or hind limbs of a mammal with one toe (horse), two toes
(sheep), four toes (hog) and five toes (dog) exhibit a
remarkable series of homologies pointing to a five-toed
ancestor, and any other series of organs of vertebrates

EVIDENCES OF ORGANIC DESCENT 143

would give the same evidence of fundamental resemblances
(homologies). For such a series of facts the reader must
be referred to special books like Wiedersheim's 'Compara-
tive Anatomy of the Vertebrates/ Romanes's 'Darwin and
After Darwin/ and Le Contes 'Evolution/

The existence of great similarities in vertebrate struc-
ture is not always fully recognised. To the superficial
observer the bodies of animals of different classes seem to
differ fundamentally in plan, to be entirely different

Man. Gorilla. Dog. Sheep. Horse.

Fig. 17 — Homologies in Hind Limbs.. Romanes.)

machines, made each for its own purposes, at once, out of
hand. Extensive comparison, on the contrary, shows them
to be the same, altho the essential identity is obscured by
adaptive modifications. The simplest, in fact the only
scientific, explanation of the phenomena of vertebrate
structure is the idea of a primal vertebrate, modified more
and more through successive generations by the necessities
of different modes of Hfe.

See, then, the difference between man's mode of work-

144 BIOLOGY

ing and Nature's. A man having made a steam-engine,
and desiring to use it for a different purpose from that
for which it was first designed and used, will nearly always
be compelled to add new parts not contemplated in the
original machine. Nature rarely makes new parts — never,
if she can avoid it — but, on the contrary, adapts an old
part to the new function. It is as if Nature were not
free to use any and every device to accomplish her end,
but were conditioned by her own plans of structure; as,
indeed, she must be according to the derivation theory.
Thus, in the fin of a fish, the fore-paw of a reptile or a
mammal, the wing of a bird, and the arm and hand of a
man, is found the same part, variously modified for many
purposes.

Another striking class of the facts of morphology which
admit of scientific explanation only along the line of
homology are the thousands of cases of rudimentary or
vestigial structures to be found. Throughout both the ani-
mal and vegetable kingdoms dwarfed and useless repre-
sentatives of organs are constantly met with, which in
other and allied kinds of animals and plants are of large
size and functional utility. Thus, for instance, the unborn
whale has rudimentary teeth, which are never destined to
cut the gums; and throughout its life this animal retains,
in a similarly rudimentary condition, a number of organs
which never could have been of use to any kind of creature
save a terrestrial quadruped.

Other well-known examples among vertebrates are:
Vestiges of hind limbs in certain snakes, reduced wings in
the Apteryx and ostriches, rudiments of eyes in cave
fishes, hind limbs beneath the skin of whales, the vermi-
form appendix in man, as well as useless muscles to move
the ears and the skin, and also a very much reduced hairy
covering over the surface of the body. Wiedersheim has
recorded more than one hundred and eighty such struc-
tural reminiscences in man.

Now, rudimentary organs of this kind are of such

Fig. 18 — Homologies of Foot and Hand Bones.
I., man; 2., gorilla; 3., orang-utan; 4., dog; 5., sea lion ; 6., dol-
phin; 7, bat; 8, mole; 9, ornithorhynchus. (Haeckel.)

146

BIOLOGY

frequent occurrence, that almost every species of organism
presents one or more of them — usually, indeed, a consider-
able number. How, then, are they to be accounted for?
Of course the theory of descent with adaptive modification
has a simple answer to supply — namely, that when, from
changed conditions of life, an organ which was previously
useful becomes useless, it will be suffered to dwindle away

Fig. 19 — Vestigial Structures in Apteryx.
External wing is drawn to scale in the upper part of the cut.

in successive generations, under the influence of certain
natural causes.

On the other hand, the theory of special creation can
only maintain that these rudiments are formed for the
sake of adhering to an ideal type.

"Now, here again the former theory appears to be
triumphant over the latter," says Romanes, "for, without
waiting to dispute the wisdom of making dwarfed and use-
less structures merely for the whimsical motive assigned,

EVIDENCES OF ORGANIC DESCENT 147

surely if such a method were adoptecl in so many cases,
we should expect that in consistency it would be adopted in
all cases. This reasonable expectation, however, is far
from being realized. In numberless cases, such as that of
the fore-limbs of serpents, no vestige of a rudiment is
present. But the vacillating policy in the matter of rudi-
ments does not end here; for it is shown in a still more
aggravated form where within the limits of the same nat-
ural group of organisms a rudiment is sometimes present
and sometimes absent. For instance, altho in nearly all the
numerous species of snakes there are no vestiges of limbs,
in the Python we find very tiny rudiments of the hind-
limbs. Now, is it a worthy conception of Deity that, while
neglecting to maintain his unity of ideal in the case of
nearly all the numerous species of snakes, he should have
added a tiny rudiment in the case of the Python — and even
in that case should have maintained his ideal very in-
efficiently, inasmuch as only two limbs, instead of four, are
represented ?"

Convincing as are the evidences of descent recorded
in the structure of plants and animals, these evidences
have been in the past thirty years somewhat over-
shadowed by the far more surprising evidences of descent
discovered in the development of plant and animal em-
bryos. A dozen volumes would be necessary to present
the mass of embryological evidence, but a few salient facts
will illustrate the kind of evidence to be deduced from
embryology.

Most remarkable of all the principles which have been
(discovered by embryologists is the 'Recapitulation Doc-
trine/ which, briefly stated, is that individual development
(ontogeny) recapitulates ancestral history (phylogeny).
Illustrations quoted from the works of Romanes and
Le Conte will make this principle clear. "It is an observ-
able fact," says Romanes, "that there is often a close cor-
respondence between developmental changes as revealed
by any chronological series of fossils which may happen

148

BIOLOGY

to have been preserved, and developmental changes which
may be observed during the life-history of now existing
individuals belonging to the same group of animals. For

Wvr

Fig. 20 — Development of Stags' Antlers.
Horns of fossil deer show in species the same increase of com-
plexity that present species shows in lifetime.

instance, the successive development of prongs in the
horns of deer-like animals, which is so clearly shown in
the geological history of this tribe, is closely reproduced

EVIDENCES OF ORGANIC DESCENT 149

in the life-history of existing deer. Or, in other words, the
antlers of an existing deer furnish in their development a
kind of 'resume,' or recapitulation, of the successive phases
whereby the primitive horn was gradually superseded by
horns presenting a greater and greater number of prongs
in successive species of extinct deer.

"Now, it must be obvious that such a recapitulation in
the life-history of an existing animal of developmental
changes successively distinctive of sundry allied, tho now
extinct species, speaks strongly in favor of evolution. For
as it is of the essence of this theory that new forms arise
from older forms by way of hereditary descent, we should
antecedently expect, if the theory is true, that the phases
of development presented by the individual organism would
follow, in their main outlines, those phases of development
through which their long line of ancestors had passed.
The only alternative view is that as species of deer, for
instance, were separately created, additional prongs were
successively added to their antlers; and yet that, in order
to be so added to successive species, every individual deer
belonging to later species was required to repeat in his
own lifetime the process of successive additions which had
previously taken place in a remote series of extinct species.
Now I do not deny that this view is a possible view ; but I
do deny that it is a probable one. According to the evolu-
tionary interpretation of such facts, we can see a very
good reason why the life-history of the individual is
thus a condensed 'resume' of the life-history of its ances-
tral species. But according to the opposite view no reason
can be assigned why such should be the case."

"It is well known," likewise comments Le Conte, "that
the embryo or larva of a frog or toad, when first hatched,
is a legless, tail-swimming, water-breathing, gill-breath-
ing animal. It is essentially a fish, and would be so classed
if it remained in this condition. The fish retains per-
manently this form, but the frog passes on. Next, it forms
first one pair and then another pair of legs; and mean-

150 BIOLOGY

while it begins to breathe also by lungs. At this stage it
breathes equally by lungs and by gills — i.e., both air and
water. Now, the lower forms of amphibians, such as
siredon, menobranchus, siren, etc., retain permanently this
form, and are therefore called 'perennibranchs,' but the
frog still passes on. Then the gills gradually dry up, as
the lungs develop, and they now breathe wholly by lungs,
but still retain the tail. Now this is the permanent, ma-
ture condition of many amphibians, such as the triton, the
salamander, etc., which are therefore called 'caducibranchs/
but the frog still passes on. Finally, it loses the tail, or
rather its tail is absorbed and its material used in further
development, and it becomes a perfect frog, the highest
order (anoura) of this class.

'Thus, then, in ontogeny the fish goes no further than
the fish stages. The perennibranch passes through the fish
stage to the perennibranch amphibian. The caducibranch
takes first the fish- form, then the perennibranch-form, and
finally the caducibranch-form, but goes no further. Last,
the anoura takes first the fish-form, then that of the peren-
nibranch, then that of the caducibranch, and finally be-
comes anoura. Now, this is undoubtedly the order of suc-
cession of forms in geological times — i.e., in the phylogenic
series. Fishes first appeared in the Devonian and Upper
Silurian in very reptilian or rather amphibian forms.
Then in the Carboniferous, fishes still continuing, there
appeared the lowest — i.e., most fish-like forms of amphib-
ians. These were undoubtedly perennibranchs. In the
Permian and Triassic higher forms appeared, which were
certainly caducibranch. Finally, only in the Tertiary, so
far as we yet know, do the highest form (anoura) appear.
The general similarity of the three series is complete.

"It is a curious and most significant fact that the suc-
cessive stages of the development of the individual in the
higher forms of any group (ontogenic series) resemble
the stages of increasing complexity of differentiated struc-
ture in ascending the animal scale in that group (taxo-

0

PL. .t:

152 BIOLOGY

nomic series), and especially the forms and structure of
animals of that group in successive geological epochs
(phylogenic series). In other words, the individual
higher animal in embryonic development passes through
temporary stages, which are similar in many respects to
permanent or mature conditions in some of the lower forms
in the same group.

"Surely this fact is wholly inexplicable except by the
theory of derivation or evolution. The embryo of a
higher animal of any group passes now through stages
represented by lower forms, because in its evolution
(phylogeny) its ancestors did actually have these forms.
From this point of view the ontogenic series (individual
history) is a brief recapitulation, as it were, from mem-
ory, of the main points of the philogenic series, or family
history. We say brief recapitulation of the main points,
because many minor points are dropped out. Even some
main points of the earliest stages of the family history
may be dropped out of this sort of inherited memory.

"This resemblance between the three series must not,
however, be exaggerated. Not only are many steps of
phylogeny, especially in its early stages, dropped out in
the ontogeny, but, of course, many adaptive modifications
for the peculiar conditions of embryonic life are added.
But it is remarkable how even these — for example, the
umbilical cord and placenta of the mammalian embryo —
are often only modifications of egg-organs of lower ani-
mals, and not wholly new additions. It is the similarity
in spite of adaptive modifications that shows the family
history."

But even these recapitulations are not so convincing as
are those of many internal structures which are not now of
any possible use. In the fishes, the lowest class of verte-
brates, gills are the organs of breathing. Water taken
into the mouth is ejected from the throat through the
gill-slits, which are lined with delicate vascular mem-
branes. Blood circulating through these membranes ab-

EVIDENCES OF ORGANIC DESCENT 153

sorbs oxygen from the water and gives off carbon dioxide
gas. Thus in the fishes the gills play the part performed
by lungs in higher forms, and are essential organs
throughout life. Passing up the scale of animal life, am-
phibian embryos develop gill-slits and they are present and
functionally active for a few days in the early life of cer-
tain tadpoles. In all amphibians the slits close soon and the
fully developed frogs and salamanders do not use them for
breathing. Certain amphibians have gills throughout life,
but they are not the gills corresponding to those of fishes.

Now, in interpreting these facts, it should be noted
that the embryos of the higher classes, reptiles, birds and
mammals, never have access to water and yet in every
species whose development is known gill-slits are present
in the embryos. For example, in a chick of three to five
days' incubation there are four slits on the side of the
neck. Likewise there are several gill-slits in human
embryos of three to five weeks' development. In all
reptiles, birds and mammals the gill-slits, however, are
temporary; they serve no function and close long before
hatching or birth. The only interpretation which appeals
to the biologist as reasonable is that gill-slits in the
higher vertebrates are reminiscences of ancestral history
and, originally fish organs, they appear regularly in the
fish-like stage of every embryo of higher forms which
in their development pass through stages comparing in a
general way to the adults of lower forms.

There are dozens and dozens of similar cases known
to occur in the embryology of vertebrates. The notochord,
which is the dorsal stiffening axis in the lowest verte-
brate (amphioxus), appears in the embryos of all higher
forms. In them it is purely temporary and disappears as
the backbone is developed around it. The lungs of
amphibia and higher forms develop in the embryo iden-
tically with the air-bladder of fishes.

In the embryonic development of man and other mam-
mals three pairs of kidneys are formed, only one remain-

Fig. 22 — Embryonic Stages. Fish, Salamander, Tortoise, Chick.

156 BIOLOGY

ing at birth. The first kidneys (pronephros) develop in
the stage when gills and other structures correspond to a
fish-embryo stage, and in some of the lowest fishes this
pair becomes the permanent kidneys. The second kidneys
(mesonephros) correspond to an amphibian-reptilian
stage, and this pair persists throughout life in the
amphibia, in the embryos of which the first kidneys are
temporarily present. The third kidneys (metanephros)
succeed the first and second in mammalian development
and remain throughout life. In the higher forms the first
and second kidneys are absolutely useless. The only rea-
sonable explanation of this fact is that the appearance
of the first kidneys in amphibian embryos and of the first
and second in mammalian embryos is due to this repetition
or recapitulation of ancestral history.

If space permitted it would be easy to present abun-
dance of additional evidence to the same effect from the
development of the skeleton, the skull, the brain, the sense-
organs, and, in short, of every constituent part of the
vertebrate organization. Even without any anatomical
dissection, the similarity of all vertebrate embryos at
comparable stages of development admits of being strik-
ingly shown, if the embryos are merely placed one beside
the other. Here, for instance, are the embryos of a fish,
a salamander, a tortoise, a bird, and four different mam-
mals. In each case three comparable stages of develop-
ment are represented. Now if the series is read horizon-
tally, it can be seen that there is very little difference
between the eight animals at the earliest of the three
stages represented — all having fish-like tails, gill-slits, and
so on. In the next stage further differentiation has taken
place, but it will be observed that the limbs are still so
rudimentary that even in the case of man they are con-
siderably shorter than the tail. But in the third stage
the distinctive characters are well marked.

So far examples have been drawn entirely from the
vertebrate animals ; it should be pointed out, however, that

EVIDENCES OF ORGANIC DESCENT 157

there is a repetition of just the same kind of evidence in
all the other groups of animals, and as well in the plant
kingdom. When all this mass of evidence is taken to-
gether, it is not to be wondered at that the science of
comparative embryology should be considered as the prin-
cipal witness to the theory of descent.

But why should ontogeny repeat the steps of phylogeny ?
Professor Le Conte replies that "the general answer is
doubtless to be found in the law of heredity — that wonder-
ful law, so characteristic of living things. We have com-
pared it to a brief recapitulation from memory — the minor
points, especially if they be also early, dropping out. But
can we not explain it further? It is probable that we
find a more special explanation in 'the law of acceleration/
first brought forward by Prof. Cope. By the law of
heredity each generation repeats the form and structure
of the previous, and in the order in which they succes-
sively appeared. But there is a tendency for each suc-
cessively appearing character to appear a little earlier in
each successive generation ; and by this means time is left
over for the introduction of still higher new characters.
Thus, characters which were once adult are pushed back
to the young, and then still back to the embryo, and thus
place and time are made for each generation to push on
still higher. The law of acceleration is a sort of young-
Americanism in the animal kingdom. If our boys acquire
knowledge and character similar to that of adults of a
few generations back, they will have time while still young
and plastic to press forward to still higher planes."

These similarities or homologies of embryology appeal
to the thinker, as has been said, as explainable only on
the theory of descent. Agassiz, however, held an opposing
view. His statements on this point are classical in bio-
logical literature. He says : "If we now pass to the
highest type of the Animal Kingdom, the Vertebrates,
there is no lack of evidence to show the identity in their
mode of development, as well as the striking resemblance

158 BIOLOGY

of the young in their earliest stages of growth. The
young Fish, the young Reptile, the young Bird, the
young Mammal, resemble one another to an astonishing
degree, while they have not one feature in their mode of
growth which recalls either the Articulate, the Mollusk,
or the Radiate. It is, therefore, not true, tho so often
stated, that in their development the higher animals pass
successively through the condition of all the lower ones;
while it is emphatically true that in each of the four great
branches of the Animal Kingdom there is a common mode
of development. It is equally true tha.t in certain fea-
tures the higher classes of each branch in their younger
condition recall the characteristic features of the lower
ones, tho each class has its own structural character, and
early diverges from the common starting-point.

"Indeed, modern Embryology leads at once to the con-
sideration of the most occult problem, as to the origin of
animals, suggested by these comparisons. What do these
resemblances mean, from some of which we shrink as
unnatural and even revolting? If we put a material inter-
pretation upon them, and believe that even Man himself has
been gradually developed out of a Fish, they are repugnant
to our better nature. But looked at in their intellectual
significance, they truly reveal the unity of the organic con-
ception of which Man himself is a part, and mark not only
the incipient steps in its manifestation, but also, with equal
distinctness, every phase in its gradual realization. They
mean that when the first Fish was called into existence,
the Vertebrate type existed as a whole in the creative
thought, and the first expression of it embraced poten-
tially all the organic elements of that type, up to Man
himself. To me the fact that the embryonic form of the
highest Vertebrate recalls in its earlier stage the first rep-
resentatives of its type in geological times and its lowest
representatives at the present day, speaks only of an ideal
relation, existing not in the things themselves, but in the
mind that made them.

EVIDENCES OF ORGANIC DESCENT 159

"It is true that the naturalist is sometimes startled at
these transient resemblances of the young among the
higher animals in one type to the adult condition of the
lower animals in the same type ; but it is also true that he
finds each one of the primary divisions of the Animal
Kingdom bound to its own norm of development, which
is absolutely distinct from that of all the others ; it is also
true, that, while he perceives correspondences between
the early phases of the higher animals and the mature
state of the lower ones, he never sees any one of them
diverge in the slightest dgree from its own structural char-
acter— never sees the lower rise by a shade beyond the
level which is permanent for the group to which it be-
longs— never sees the higher ones stop short of their
final aim, either in the mode or the extent of their trans-
formation.

"I cannot repeat too emphatically, that there is not a
single fact in Embryology to justify the assumption that
the laws of development, now known to be so precise and
definite for every animal, have ever been less so, or have
ever been allowed to run into each other. The philoso-
pher's stone is no more to be found in the organic than
the inorganic world; and we shall seek as vainly to
transform the lower animal types into the higher ones by
any of our theories, as did the alchemists of old to change
the baser metals into gold."

Thus did Agassiz reject the theory of descent in the
face of the most overwhelming evidence. His view that
similarity of development is simply an expression of type
in creative thought appeals to scientists to-day as absurd.
Agassiz was the last prominent naturalist who could be-
lieve that such things as gill-slits were put into embryos
of higher forms in order to adhere to an ideal plan "in
the mind that made them."

The paragraphs quoted above from Agassiz suggest
that it may not be known what hidden reasons there may
have been for the creation of animals with such remark-

160 BIOLOGY

able similarities in development or adult structure. But
as Romanes has pointed out, a man "may quite legitimately
say, Assuming that the theory of special creation is true,
it is not for us to anticipate the form or method of the
process. But where the question is as to whether or not
the theory is true, it becomes a mere begging of this
question to take refuge in the argument from ignorance,
or to represent in effect that there is no question to be
discussed. And if, when the form or method is investi-
gated, it be found everywhere charged with evidence in
favor of the theory of descent, the case becomes the same
as that of a supposed revelation, which has been discred-
ited by finding that all available evidence points to a nat-
ural growth.

"In short, the argument from ignorance is in any case
available only as a negative foil against destructive criti-
cism. In no case has it any positive value or value of a
constructive kind. Therefore, if a theory on any subject
is destitute of positive evidence, while some alternative
theory is in possession of such evidence, the argument
from ignorance can be of no logical use to the former,
even tho it may be of such use to the latter. For it is only
the possession of positive evidence which can furnish a
logical justification of the argument from ignorance. In
the absence of such evidence even the negative value of
the argument disappears and it then implies nothing more
than the gratuitous assumption of a theory."

CHAPTER XI

EVIDENCES OF ORGANIC EVOLUTION; CLASSIFICATION, PA-
LEONTOLOGY, DISTRIBUTION, DOMESTICATION

If a child in the kindergarten be given an assortment
of cards of various colors and shapes and a number of
boxes into which to put them, it becomes evident that the
natural tendency is to group together the cards according
to their striking resemblances, for most children probably
of color. This is simply an elementary exercise in classifi-
cation and in fundamentals is parallel with the accepted
grouping of plants and animals on the basis of resem-
blances. Many authors have discussed the bearing of
classification on the theory of descent, and among the best
is the popular statement of the case by Romanes.

"It is a matter of observable fact," he remarks, "that
different forms of plants and animals present among them-
selves more or less pronounced resemblances. From the
earliest times, therefore, it has been the aim of philosophi-
cal naturalists to classify plants and animals in accord-
ance with these resemblances. Of course the earliest at-
tempts at such classification were extremely crude. The
oldest of these attempts with which we are acquainted —
namely, that which is presented in the books of Genesis
and Leviticus — arranges the whole vegetable kingdom in
three simple divisions of Grass, Herbs and Trees, while
the animal kingdom is arranged with almost equal sim-
plicity with reference first to habitats in water, earth or
air and next as to modes of progression. These, of course,
161

i62 BIOLOGY

were what may be termed common-sense classifications,
having reference merely to external appearances and hab-
its of life.

"But when Aristotle laboriously investigated the com-
parative anatomy of animals, he could not fail to perceive
that their entire structures had to be taken into account in
order to classify them scientifically and also that for this
purpose the internal parts were of quite as much impor-
tance as the external. Indeed, he perceived that they were
of greatly more importance in this respect, inasmuch as
they presented so many more points for comparison, and
in the result he furnished an astonishingly comprehensive
as well as an astonishingly accurate classification of the
larger groups of the animal kingdom. On the other hand,
classification of the vegetable kingdom continued pretty
much as it had been left by the book of Genesis — all
plants being divided into three groups, Herbs, Shrubs and
Trees. Nor was this primitive state of matters improved
upon till the sixteenth century, when Gesner, and still
more Cesalpino, laid the foundations of systematic botany.

"But the more that naturalists prosecuted their studies
on the anatomy of plants and animals, the more enor-
mously complex did they find the problem of classification
become. Therefore they began by forming what are called
artificial systems in contradistinction to natural systems.
An artificial system of classification is a system based on
the more or less arbitrary selection of some one part or
set of parts, while a natural classification is one that is
based upon a complete knowledge of all the structures of
all the organisms which are classified.

"Thus the object of classification has been that of ar-
ranging organisms in accordance with their natural affini-
ties, by comparing organism with organism, for the purpose
of ascertaining which of the constituent organs are of the
most invariable occurrence and therefore of the most typi-
cal signification. A porpoise, for instance, has a large
number of teeth, and in this feature resembles most fish,

EVIDENCES OF ORGANIC EVOLUTION 163

while it differs from all mammals. But it also gives suck
to its young. Now, looking to these two features alone,
should we say that a porpoise ought to be classed as a
fish or as a mammal? Assuredly as a mammal, because
the number of teeth is a very variable feature both in fish
and mammals, whereas the giving of suck is an invariable
feature among mammals and occurs nowhere else in the
animal kingdom.

"This, of course, is chosen as a very simple illustration*
Were all cases as obvious, there would be but little dis-
tinction between natural and artificial systems of classifi-
cation. But it is because the lines of natural affinity are,
as it were, so interwoven throughout the organic world,
and because there is, in consequence, so much difficulty in
following them that artificial systems have to be made in
the first instance as feelers toward eventual discovery of
the natural system. In other words, while forming their
artificial systems of classification, it has always been the
aim of naturalists — whether consciously or unconsciously
—to admit as the bases of their systems those characters
which, in the then state of their knowledge, seemed most
calculated to play an important part in the eventual con-
struction of the natural system.

"If we were dealing with the history of classification, it
would here be interesting to note how the course of it has
been marked by gradual change in the principles which
naturalists adopted as guides to the selection of characters
on which to found their attempts at a natural classification.
Some of these changes, indeed, I shall have to mention
later on, but at present what has to be specially noted is
that through all these changes of theory or principle and
through all the ever-advancing construction of their taxo-
nomic science naturalists themselves were unable to give
any intelligible reason for the faith that was in them or
the faith that over and above the artificial classifications
which were made for the mere purpose of cataloguing the
living library of organic nature, there was deeply hidden

164 BIOLOGY

in nature itself a truly natural classification, for the even-
tual discovery of which artificial systems might prove to
be of more or less assistance.

"Linnasus, for example, expressly says, 'You ask me for
the characters of the natural orders ; I confess that I can-
not give them.' Yet he maintains that, altho he cannot
define the characters, he knows, by a sort of naturalist's
instinct, what in a general way will subsequently be found
to be the organs of most importance in the eventual group-
ing of plants under a natural system. 'I will not give my
reasons for the distribution of the natural orders which I
have published,' he said; 'y°u> or some other person, after
twenty or after fifty years, will discover them and see
that I was right.' Thus we perceive that in forming their
provisional or artificial classifications, naturalists have
been guided by an instinctive belief in some general prin-
ciple of natural affinity, the character of which they have
not been able to define, and that the structures which they
selected as the bases of their classifications when these
were consciously artificial were selected because it seemed
that they were the structures most likely to prove of use in
subsequent attempts at working out the natural system.

"This general principle of natural affinity, of which all
naturalists have seen more or less well-marked evidence
in organic nature, and after which they have all been
feeling, has sometimes been regarded as natural, but more
often as supernatural. Those who regarded it as super-
natural took it to consist in a divine ideal of creation ac-
cording to types, so that the structural affinities of organ-
isms were to them expressions of an archetypal plan, which
might be revealed in its entirety when all organisms on
the face of the earth should have been examined. Those,
on the other hand, who regarded the general principle of
affinity as depending on some natural causes, for the most
part concluded that these must have been utilitarian
causes; or, in other words, that the fundamental affini-
ties of structure must have depended upon fundamental

EVIDENCES OF ORGANIC EVOLUTION 165

requirements of function. According to this view, the
natural classification would eventually be found to stand
upon a basis of physiology.

"Therefore all the systems of classification up to the
earlier part of the present century went upon the apparent
axiom that characters which are of most importance to the
organisms presenting them must be characters most in-
dicative of natural affinities. But the truth of the matter
was eventually found to be otherwise. For it was eventu-
ally found that there is absolutely no correlation between
these two things; that, therefore, it is a mere chance
whether or not organs which are of importance to or-
ganisms are likewise of importance as guides to classifica-
tion, and, in point of fact, that the general tendency in
this matter is toward an inverse instead of a direct pro-
portion. More often than not the greater the value of a
structure for the purpose of indicating natural affinities,
the less is its value to the creatures presenting it.

"Enough has now been said to show three things. First.1
that long* before the theory of descent was entertained by.
naturalists, naturalists perceived the fact of natural affini-
ties and did their best to construct a natural system of
classification for the purpose of expressing such affinities.'
Second, that naturalists had a kind of instinctive belief in
some one principle running through the whole organic
world, which thus served to bind together organisms in
groups subordinate to groups — that is, into species, genera,
orders, families, classes, sub-kingdoms and kingdoms.
Third, that they were not able to give any very intelligible
reason for this faith that was in them ; sometimes suppos-
ing the principle in question to be that of a supernatural
plan of organization, sometimes regarding it as dependent
on conditions of physiology and sometimes not attempting
to account for it at all.

"Of course it is obvious that the theory of descent fur-
nishes the explanation which is required. For it is now
evident to evolutionists that, altho these older naturalists

166 BIOLOGY

did not know what they were doing when they were trac-
ing these lines of natural affinity, and thus helping to con-
struct a natural classification — I say it is now evident to
evolutionists that these naturalists were simply tracing the
lines of generic relationship. The great principle pervad-
ing organic nature, which was seen so mysteriously to bind
the whole creation together as in a nexus of organic affin-
ity, is now easily understood as nothing more or less than
the principle of Heredity."

Darwin first called attention to this line of evidence for
evolution in the following words : "Naturalists try to ar-
range the species, genera and families in each class on
what is called the Natural System. But what is meant by
this system? Some authors look at it merely as a scheme
for arranging together those living objects which are
most alike and for separating those which are most unlike
or as an artificial method of enunciating, as briefly as pos-
sible, general propositions — that is, by one sentence to
give the characters common, for instance, to all mammals,
by another those common to all carnivora, by another those
common to the dog-genus, and then, by adding a single
sentence, a full description is given of each kind of dog.
The ingenuity and utility of this system are indisputable.
But many naturalists think that something more is meant
by the Natural System ; they believe that it reveals the
plan of the Creator, but unless it be specified whether order
in time or space, or both, or what else is meant by the
plan of the Creator, it seems to me that nothing is thus
added to our knowledge. Expressions such as that famous
one by Linnaeus, which we often meet with in a more or
less concealed form, namely, that the characters do not
make the genus, but that the genus gives the characters,
seem to imply that some deeper bond is included in our
classifications than mere resemblance. I believe that this
is the case and that community of descent — the one known
cause of close similarity in organic beings — is the bond,

EVIDENCES OF ORGANIC EVOLUTION 167

which tho observed by various degrees of modification, is
partially revealed to us by our classifications."

Before the days of Darwin naturalists had classified
plants and animals on a tree-like plan and had rejected the
old ladder series of early systematists. The tree system is
the one which all naturalists regard as the true one. "Ac-
cording to this system," Romanes points out, "a short
trunk may be taken to represent the lowest organisms
which cannot properly be termed either plants or animals.
This short trunk soon separates into two large trunks, one
of which represents the vegetable and the other the animal
kingdom. Each of these trunks then gives off large
branches signifying classes, and these give off smaller but
more numerous branches, signifying families, which
ramify again into orders, genera and finally into the leaves,
which may be taken to represent species. Now, in such a
representative tree of life, the height of any branch from
the ground may be taken to indicate the grade of organiza-
tion which the leaves, or species, present; so that, if we
picture to ourselves such a tree, we may understand that
while there is a general advance of organization from
below upward, there are many deviations in this respect.
Sometimes leaves growing on the same branch are grow-
ing at a different level — especially, of course, if the branch
be a large one, corresponding to a class or sub-kingdom.
And sometimes leaves growing on different branches are
growing at the same level ; that is to say, altho they repre-
sent species belonging to widely divergent families, orders
or even classes, it cannot be said that the one species is
more highly organized than the other.

"Now, this tree-like arrangement of species in nature
is an arrangement for which Darwin is not responsible.
For, as we have seen, the detecting of it has been due to
the progressive work of naturalists for centuries past, and
even when it was detected, at about the commencement of
the present century, naturalists were confessedly unable
to explain the reason of it or what was the underlying

168 BIOLOGY

principle that they were engaged in tracing when they
proceeded ever more and more accurately to define these
ramifications of natural affinity. But now we can clearly
perceive that this underlying principle was none other than
Heredity as expressed in family likeness — likeness, there-
fore, growing progressively more unlike with remoteness
of ancestral relationship.

"First of all, and from the most general point of view,
it is obvious that the tree-like system of classification,
which Darwin found already and empirically worked out
by the labors of his predecessors, is as suggestive as any-
thing could well be of the fact of genetic relationship. For
this is the form that every tabulation of family pedigree
must assume, and therefore the mere fact that a scientific
tabulation of natural affinities was eventually found to
take the form of a tree is in itself highly suggestive of the
inference that such a tabulation represents a family tree.
If all species were separately created, there can be no as-
signable reason why the ideas of earlier naturalists touch-
ing the form which a natural classification would eventu-
ally assume should not have represented the truth — why,
for example, it should not have assumed the form of a
ladder (as was anticipated in the seventeenth century), or
of a map (as was anticipated in the eighteenth), or, again,
of a number of wholly unrelated lines, circles, etc. (as cer-
tain speculative writers of the nineteenth century have
imagined). But, on the other hand, if all species were
separately and independently created, it becomes virtually
incredible that we should everywhere observe this pro-
gressive arborescence of characters common to larger
groups into more and more numerous and more and more
delicate ramifications of characters distinctive only of
smaller and smaller groups. A man would be deemed in-
sane if he were to attribute the origin of every branch
and every twig of a real tree to a separate act of special
creation, and altho we have not been able to witness the
growth of what we may term in a new sense the Tree of

EVIDENCES OF ORGANIC EVOLUTION 169

Life, the structural relations which are now apparent be-
tween its innumerable ramifications bear quite as strong a
testimony to the fact of their having been due to an or-
ganic growth as is the testimony furnished by the branches
of an actual tree."

Summarizing, it is established that "all the general prin-
ciples and particular, facts appertaining to the natural
classification of plants and animals are precisely what they
ought to be according to the theory of genetic descent,
while no one of them is such as might be — and, indeed,
used to be — expected upon the theory of special creation.

"First of all we must take note that the classification of
plants and animals in groups subordinate to groups is not
merely arbitrary or undertaken only for a matter of con-
venience and nomenclature — such, for instance, as the
classification of stars in constellations. On the contrary,
the classification of a naturalist differs from that of an
astronomer, in. that the objects which he has to classify
present structural resemblances and structural differences
in numberless degrees, and it is the object of his classifica-
tion to present a tabular statement of these facts. Now,
long before the theory of evolution was entertained, nat-
uralists became fully aware that these facts of structural
resemblances running through groups subordinate to
groups were really facts of nature and not merely poetic
imaginations of the mind. No one could dissect a number
of fishes without perceiving that they were all constructed
on one anatomical pattern which differed considerably
from the equally uniform pattern on which all mammals
were constructed, even altho some mammals bore an ex-
traordinary resemblance to fish in external form and habits
of life. And similarly with all the smaller divisions of the
animal and vegetable kingdoms.

"Everywhere investigation revealed the bonds of close
structural resemblances between species of the same genus,
resemblance less close between genera of the same fam-
ily, resemblance still less close between families of the

170 BIOLOGY

same order, resemblance yet more remote between orders
of the same class and resemblance only in fundamental
features between classes of the same sub-kingdom, beyond
which limit all anatomical resemblance was found to dis-
appear— the different sub-kingdoms being formed on
wholly different patterns. Furthermore, in tracing all
these grades of structural relationship, naturalists were
slowly led to recognise that the form which a natural
classification must eventually assume would be that of a
tree, wherein the constituent branches would display a
progressive advance of organization from below upward.

"Now we have seen that altho this tree-like arrangement
of natural groups was as suggestive as anything could
well be of all the forms of life being bound together by the
ties of genetic relationship, such was not the inference
which was drawn from it. Dominated by the theory of
special creation, naturalists either regarded the resem-
blance of type subordinate to type as expressive of divine
ideals manifested in such creation or else contented them-
selves with investigating the facts without venturing to
speculate upon their philosophical import. But even those
naturalists who abstained from committing themselves to
any theory of archetypal plans did not doubt that facts so
innumerable and so universal must have been due to some
one coordinating principle — that, even tho they were not
able to suggest what it was, there must have been some
hidden bond of connection running through the whole of
organic nature. Now, as we have seen, it is manifest to
evolutionists that this hidden bond can be nothing else
than heredity, and, therefore, that these earlier naturalists,
altho they did not know what they were doing, were really
tracing the lines of genetic descent as revealed by degrees
of structural resemblance — that the arborescent grouping
of organic forms which their labors led them to begin, and
in large measure to execute, was in fact a family tree of
life.

"Here, then, is the substance of the argument from

EVIDENCES OF ORGANIC EVOLUTION 171

classification. The mere fact that all organic nature thus
incontestably lends itself to a natural arrangement of
group subordinate to group, when due regard is paid to
degrees of anatomical resemblance — this mere fact of itself
tells so weightily in favor of descent with progressive
modification in different lines, that even if it stood alone
it would be entitled to rank as one of our strongest pieces
of evidence. But, as we have seen, it does not stand alone.
When we look beyond this large and general fact of all the
innumerable forms of life being thus united in a tree-like
system by an unquestionable relationship of some kind, to
those smaller details in the science of classification which
have been found most useful as guides for this kind of
research, then we find that all these details, or empirically
discovered rules, are exactly what we should have ex-
pected them to be, supposing the real meaning of classifica-
tion to have been that of tracing lines of pedigree."

Equally illumining is the massed evidence from Paleon-
tology. The record of the rocks as shown by fossils has
always been one of the most important lines of evidence
for the theory of descent. In Darwin's time the critics
never grew tired of demanding proof from paleontology.
A great deal of such proof has been brought forth, but
paleontologists caution against expecting a complete record
of the animal and plant life of the past. The record is
very imperfect, "but," to quote from Metcalfs 'Organic
Evolution' "so far as it goes it is an actual record. Only
very unusual circumstances will secure the preservation of
any animal or plant as a fossil. An organism, or portion
of an organism, to be so preserved usually must be hard ; it
must be buried beneath soil of the proper kind and when
buried must be impregnated with mineral salts or in some
other way preserved from disintegration.

"When once converted into a fossil it must escape de-
struction at the hands of those agencies that are constantly
destroying the rocks ; heat, pressure, the disintegration that
comes from exposure to the atmosphere, abrasion by ice

172 BIOLOGY

and especially erosion by water. The character of whole
continents has been repeatedly changed by these agencies.
No wonder then, since fossilization is rare and the destruc-
tion of fossils when once formed so easy, that our record
of past faunas and floras is so scant. It is a cause for con-
gratulation that we have so much of a record as we do
possess. Thousands of species of fossil plants and animals
are known, and as yet but a small portion of the earth has
been searched." Attention will be given to but a few illus-
trations of the kind of record found in the fossil-bearing
rocks, and those records naturally will be chosen that are
fairly complete.

Turning to a few illustrations of the origin of par-
ticular species or organs, the same principle of gradual
increase in complexity is found in coming from the older
to the younger geological formations. The record of the
evolution of branching antlers in the deer, as before men-
tioned, is fairly complete. The first deer in the early Mio-
cene had no antlers at all. In the middle Miocene are
found deer with two-pronged antlers of small size. In the
tipper Miocene and lower Pliocene are found three-
pronged antlers somewhat larger. In the later Pliocene
four-pronged and five-pronged antlers and still larger are
met, while in the Pleistocene clays are seen arborescent
antlers like those of the modern deer. (Fig. 21.)

Out of the mass of evidence, one further illustration
must needs be sufficient. The record of the origin of the
horse, worked out by American paleontologists from Amer-
ican fossils, is probably the best example of paleontological
evidence of evolution. The horse is especially peculiar in
the character of its feet and teeth, and attention will be
directed to these points as shown in the accompanying il-
lustrations. In the lower Eocene rocks an animal, Phena-
codus, about the size of a fox, is found having five well-
developed toes on each foot, and with short and but mod-
erately corrugated teeth. This is one of the simplest
known relatives of the hoofed mammals, and from forms

RECENT.
Equua.

PLIOCENE.
Tliohippus.

EOCENE.
Orohippus.

Fig. 24 — Evolution of the Horse.
Foot Bones and Teeth.

174

BIOLOGY

something like Phenacodus must have been developed the
elephant, rhinoceros, hog, sheep, camel, and all the other
hoofed mammals, including the horse and its long line of
ancestors. Observe the steps in the transformation of the
five-toed limb of a form like Phenacodus into the one-toed
limb of the horse.

These are, of course, but illustrations of the kind of
testimony which the study of the rocks contributes to-
ward the proof of the theory of descent. There is, how-
ever, an enormous body of uniform evidence to prove two
general facts of the highest importance in regard to the
theory. The first of these general facts is that an increase

Fig. 25 — Virginia Opossum, an American Marsupial.

in the diversity of types both of plants and animals has
been constant and progressive from the earliest to the
latest times, as it is rational to anticipate that it
must have been on the theory of descent in ever-ramifying
lines of pedigree. And the second general fact is that
through all these branching lines of ever-multiplying types,
from the first appearance of each of them to their latest
known conditions, there is overwhelming evidence of one,
great law of organic nature — the law of gradual advance
from the general to the special, from the low to the high,
from the simple to the complex.

EVIDENCES OF ORGANIC EVOLUTION 175

The argument for the theory of descent deduced from a
comparative study of the phenomena of paleontology — the
distribution of species in time — can be supplemented by a
like argument derived from a comparative study of the
phenomena of geographical distribution, a distribution of

Fig. 26 — Kangaroo, an Australian Marsupial.

the species of to-day in space. In considering the distribu-
tion of living things on the earth, the first thing to be
noted is that there is a decided difference in the animals
and plants of different regions. At first sight, differences
of climate and other physical conditions would seem to ac-

176 BIOLOGY

count for this, but there are many phenomena of distribu-
tion which cannot thus be explained. Countries exceed-
ingly similar in climate and physical conditions may have
quite a different fauna and flora, while those that are
unlike may be characterized by similar species of plants
and animals.

If regions in Australia, South Africa and western South
America, between latitudes twenty-five and thirty-five de-
grees, are compared, it will be found that they are ex-
tremely similar in climate and physical conditions; yet it
would not be possible to point out three faunas and floras
more utterly dissimilar. Or, on the other hand, if the
productions of South America south of latitude thirty-five
be compared with those north of twenty-five degrees it
will be noted that altho climatic conditions are decidedly
different, these productions are incomparably more closely
related than they are to the productions of Australia or
Africa under almost the same climatic conditions.

The most interesting evidences of all, however, are de-
rived from a study of distribution in combination with
geological records. A good sample of this sort of evidence
is to be found in the distribution of marsupials (kangaroos,
bandicoots, etc.) over the earth. This singular and lowly
organized type of mammals constitutes almost the sole
representative of the class in Australia and New Guinea,
while it is entirely unknown in Asia, Africa or Europe.
It reappears in America, where several species of opos-
sums are found. This anomaly of distribution at first was
a puzzle to evolutionists, for it seemed unreasonable to
postulate an earlier direct connection of these countries,
which are too distant from each other to allow for migra-
tion in any other way. When, however, the geological
history of the marsupial is taken into consideration the
difficulty vanishes, for fossil records give abundant evi-
dence that at one time before the more complex types of
mammals came into existence the marsupials were spread
over the whole eastern and western hemispheres and that

EVIDENCES OF ORGANIC EVOLUTION 177

as the higher mammals developed they exterminated the
more primitive marsupials, except that in Australia and
New Guinea the earlier forms persisted and in America
the opossums remained.

That this wide distribution of marsupials was possible
in early geologic times is further supported by the fact that
other geological evidence shows that Australia and New
Guinea were once connected, or nearly connected, with the
Malay Peninsula, making migration from the mainland
possible. Moreover, the evidence shows that at that early
time a very mild climate prevailed far up into the Arctic
regions, hence it is not difficult to believe that migration
from Europe and Asia was not unusual. There are many
other kinds of evidence to be derived from the study of
distribution, some of the illustrations being even more
striking than those quoted, but these will be sufficient to
show the relation of this kind of evidence to the doctrine
of evolution.

The last line of evidence to be considered is that of
'domestication.' Every one is familiar with the great
modifications which have been brought about in domestic
animals, such as horses, cattle, dogs, pigeons, canary
birds, etc.; in food plants, as cereals, cabbages, lettuce,
radishes, berries, fruits, etc. ; and in ornamental plants, as
roses, carnations, dahlias, pansies and a host of other
forms. Moreover, the ease with which varieties of a given
form can be produced is attested to by the work of ex-
perimental breeders.

Moreover, many of these varieties differ markedly from
the forms from which they were derived. "Even during
the brief history of man," says Le Conte, "have been
formed races of different domesticated animals and use-
ful and ornamental plants, differing so greatly from each
other that if found in the wild state they would unhesitat-
ingly be called different species, or even in some cases
different genera."

It is on this last point that objection is often taken to

178 BIOLOGY

this line of proof. Are even the extreme artificial va-
rieties of any form distinct species or must they be con-
sidered but varieties of the original form? This question
shows the opportunity for opposing views hinging on the
definition to be given to the term species.

It might well be asked, What are the differences between
the artificially-made extreme varieties (often called races),
equivalent, so far as difference of form is concerned, to
species, and real natural species? On this question much
technical discussion could be given. It will be necessary,
however, to allude here only to the most broadly recog-
nised difference, namely, that artificially-made varieties in-
tercross freely in breeding, producing offspring which are
indefinitely fertile, while natural species do not intercross.

A great deal of study has been given this phenomenon.
Darwin sums up his attitude toward it as follows : "It can
no longer be maintained that varieties when crossed are
invariably quite fertile. From the great difficulty of ascer-
taining the infertility of varieties in a state of nature, for
a supposed variety, if proved to be infertile in any degree,
would almost universally be ranked as a species; from
man attending only to external characters in his domestic
varieties, and from such varieties not having been exposed
for very long periods to uniform conditions of life; from
these several considerations we may conclude that fertility
does not constitute a fundamental distinction between vari-
eties and species when crossed. The general sterility of
crossed species may safely be looked at, not as a special
acquirement or endowment, but as incidental on changes
of an unknown nature in their sexual elements."

It is true that horticulturists and breeders are intent
only on making varieties along the lines of use or beauty
from man's standpoint — that is, in size, structure, color,
habits, etc., so-called morphological varieties — and not on
making physiological species. There is, however, little
doubt that mutually infertile races could be bred if the
selection of individuals for breeding should be chosen with

EVIDENCES OF ORGANIC EVOLUTION 179

this idea in mind. Breeders have not cared to breed with
this object in view. On the contrary, cross-sterile varieties
would be a positive disadvantage to them in limiting the
range of their experiments.

The important point so far as evidence of the truth of
organic descent is concerned is to be found in the known
changes in type which have been seen to occur in domesti-
cated animals and plants and in the diversity of forms
which are known to have been derived from a few simpler
types. As Professor Bailey has said, "If the prejudices of
scientists respecting the so-called artificial production of
species could be overcome, he could just as well draw his
proofs of evolution from what has already been done with
cultivated plants and domesticated animals as from similar
results which might arise in the future from independent
efforts."

The trend of the evidence which has been used to prove
the truth of the theory of descent having been outlined, the
various causes or factors which have brought about or-
ganic evolution demand attention. These bear within
themselves many problems of no little subtilty and are
borne out by certain correlations of facts which are of
absorbing interest.

CHAPTER XII

FACTORS OF EVOLUTION — SELECTION

Altho concerning the truth of descent there is now no
idoubt in the minds of biologists, there are many and vari-
ous views as to the causes or factors which have brought
about the origin of species of plants and animals. Most
prominent of the theories concerning the factors of evolu-
tion is that of Natural Selection. This theory was con-
ceived independently by Darwin and Wallace, and strange
to say, the idea came to both from the perusal of the same
book, Malthus's 'Essay on Population/

On reading this book in 1838 Darwin first conceived the
idea of natural selection. But he writes, "I was so anxious
to avoid prejudice that I determined not for some time to
write even the briefest sketch of it. In June, 1842, I first
allowed myself the satisfaction of writing a very brief
abstract of my theory in pencil, in thirty-five pages, and
this was enlarged during the summer of 1844 into one of
230 pages."

And Wallace writes: "In February, 1858, I was suffer-
ing from a rather severe attack of intermittent fever at
Ternate, in the Moluccas, and one day while lying on my
bed during the cold fit something led me to think of the
'positive checks' described by Malthus in his 'Essay on
Population/ a work I had read several years before and
which had made a deep and permanent impression on my
mind. These checks . . . must, it occurred to me, act
on animals as well as man . . . and while pondering
180

Fig. zj — Variations Under Domestication. — Dogs. (Romanes.)

i82 BIOLOGY

vaguely on this fact, there suddenly flashed upon me the
idea of the survival of the fittest. In the two hours that
elapsed before my ague fit was over I had thought out
almost the whole of the theory, and the same evening I
sketched the draft of my paper and in the two succeeding
evenings wrote it out in full and sent it by the next post
to Mr. Darwin."

It thus appears, to use Professor Locy's words, "that
the announcement of the Darwin-Wallace theory of natu-
ral selection was made in 1858 and in the following year
was published the book, the famous 'Origin of Species/
upon which Darwin had been working when he received
Mr. Wallace's essay." The theory has come to bear Dar-
win's name and is frequently referred to as 'Darwinism/

From time to time there appear articles and pamphlets
bearing many titles announcing the decline of Darwinism,
and in many periodicals this is often taken to mean that
scientific men are giving up the theory of descent or evo-
lution. Not at all. The truth is simply that some scientific
men do not accept Darwin's natural selection explanation
of the causes which brought about the descent of species*
But Darwin's whole theory of natural selection might be
discarded without injuring the general theory of descent,
for the facts outlined in preceding pages have no necessary
relation to theories as to causes — natural selection or other
theories.

The confusion on this point is doubtless emphasized in
the popular mind because Darwin not only set forth his
natural selection theory in his book, the full title of which
is 'The Origin of Species by Means of Natural Selection;
or, The Preservation of Favored Races in the Struggle for
Life,' but he also argued for the truth of evolution so well
that it came to be generally accepted. However, the gen-
eral idea of descent was clearly mapped out long before
Darwin's time and he simply put the evidence into more
convincing form. Hence evolution (the fact) is not Dar-

TURMT-

Fig. 28 — Variations Under Domestication. — Pigeons.
(Romanes.)

184 BIOLOGY

win's theory, but natural selection (a factor) deserves to
bear his name.

In order to grasp the full significance of natural selec-
tion, it is first necessary to appreciate the astounding facts
relating to the struggle for existence. On this point Dar-
win's classical statement deserves to be given. "The elder
De Candolle and Lyell," he said, "have largely and philo-
sophically shown that all organic beings are exposed to
severe competition. Nothing is easier than to admit in
words the truth of the universal struggle for life, or more
difficult than constantly to bear this conclusion in mind.
Yet unless it be thoroly ingrained in the mind, the whole
economy of nature, with every fact on distribution, rarity,
abundance, extinction and variation, will be dimiy seen or
quite misunderstood. We behold the face of nature bright
with gladness, we often see superabundance of food; we
do not see or we forget that the birds which are idly sing-
ing round us mostly live on insects or seeds, and are thus
constantly destroying life; or we forget how largely these
songsters, or their eggs, or their nestlings are destroyed
by birds and beasts of prey; we do not always bear in
mind that altho food may be now superabundant, it is not
so at all seasons of each recurring year.

"I should premise that I use the term 'struggle for
existence' in a large and metaphorical sense, including de-
pendence of one being on another and including not only
the life of the individual, but success in leaving progeny.
Two canine animals, in a time of dearth, may be truly said
to struggle with each other which shall get food and live.
But a plant on the edge of a desert is said to struggle for
life against the drought, tho more properly it should be
said to be dependent on the moisture. A plant which an-
anually produces a thousand seeds, of which only one of
an average comes to maturity, may be more truly said to
struggle with the plants of the same and other kinds which
already clothe the ground. The mistletoe is dependent on
the apple and a few other trees, but can only in a far-

FACTORS OF EVOLUTION— SELECTION 185

fetched sense be said to struggle with these trees, for, if
too many of these parasites grow on the same tree, it lan-
guishes and dies. But several seedling mistletoes, growing
close together on the same branch, may more truly be said
to struggle with each other. As the mistletoe is dissemi-
nated by birds, its existence depends on them ; and it may
metaphorically be said to struggle with other fruit-bearing
plants in tempting the birds to devour and thus disseminate
its seeds. In these several senses, which pass into each
other, I use for convenience* sake the general term of
Struggle for Existence.

"A struggle for existence inevitably follows from the
high rate at which all organic beings tend to increase.
Every being which during its natural lifetime produces
several eggs or seeds must suffer destruction during some
period of its life and during some season or occasional
year, otherwise, on the principle of geometrical increase,
its numbers would quickly become so inordinately great
that no country could support the product. Hence, as
more individuals are produced than can possibly survive,
there must in every case be a struggle for existence, either
one individual with another of the same species, or with
the individuals of distinct species, or with the physical
conditions of life. Altho some species may be now in-
creasing, more or less rapidly, in numbers, all cannot do
so, for the world would not hold them.

"There is no exception to the rule that every organic
being naturally increases at so high a rate that, if not
destroyed, the earth would soon be covered by the progeny
of a single pair. Even slow-breeding man has doubled in
twenty-five years, and at this rate in less than a thousand
years there would literally not be standing-room for his
progeny. Linnaeus has calculated that if an annual plant
produced only two seeds — and there is no plant so unpro-
ductive as this — and their seedlings next year produced
two, and so on, then in twenty years there would be a
million plants. The elephant is reckoned the slowest

186 BIOLOGY,

breeder of all known animals, and I have taken some pains
to estimate its probable minimum rate of natural increase ;
it will be safest to assume that it begins breeding when
thirty years old and goes on breeding till ninety years old,
bringing forth six young in the interval and surviving till
one hundred years old ; if this be so, after a period of from
740 to 750 years there would be nearly nineteen million
elephants alive, descended from the first pair.

"But we have better evidence on this subject than mere
theoretical calculations, namely, the numerous recorded
cases of the astonishingly rapid increase of various ani-
mals in a state of nature, when circumstances have been
favorable to them during two or three following seasons.
Still more striking is the evidence from our domestic ani-
mals of many kinds which have run wild in several parts
of the world. If the statements of the rate of increase of
slow-breeding cattle and horses in South America, and
latterly in Australia, had not been well authenticated, they
would have been incredible. So it is with plants; cases
could be given of introduced plants which have become
common throughout whole islands in a period of less than
ten years.

"There are plants which now range in India from Cape
Comorin to the Himalaya which have been imported from
America since its discovery. In such cases, and endless
others could be given, no one supposes that the fertility of
the animals or plants has been suddenly and temporarily
increased in any sensible degree. The obvious explanation
is that the conditions of life have been highly favorable,
and that there has consequently been less destruction of
the old and young, and that nearly all the young have been
enabled to breed. Their geometrical ratio of increase,
the result of which never fails to be surprising, simply ex-
plains their extraordinarily rapid increase and wide diffu-
sion in their new homes.

"In a state of nature almost every full-grown plant an-
nually produces seed, and among animals there are very,

FACTORS OF EVOLUTION— SELECTION 187

few which do not annually pair. Hence we may confi-
dently assert that all plants and animals are tending to
increase at a geometrical ratio — that all would rapidly
stock every station in which they could anyhow exist —
and that this geometrical tendency to increase must be
checked by destruction at some period of life. Our famili-
arity with the larger domestic animals tends, I think, to
mislead us; we see no great destruction falling on them,
but we do not keep in mind that thousands are annually
salughtered for food, and that in a state of nature an equal
number would have somehow to be disposed of.

"The only difference between organisms which annually
produce eggs or seeds by the thousand and those which
produce extremely few is that the slow-breeders would
require a few more years to people, under favorable con-
ditions, a whole district, let it be ever so large. The con-
dor lays a couple of eggs and the ostrich a score, and yet
in the same country the condor may be the more numerous
of the two; the Fulmar petrel lays but one egg, yet it is
believed to be the most numerous bird in the world. One
fly deposits hundreds of eggs and another, like the hippo-
bosca, a single one; but this difference does not determine
how many individuals of the two species can be supported
in a district. A large number of eggs is of some impor-
tance to those species which depend on a fluctuating
amount of food, for it allows them rapidly to increase in
number.

"But the real importance of a large number of eggs or
seeds is to make up for much destruction at some period
of life; and this period in the great majority of cases is
an early one. If an animal can in any way protect its
own eggs or young, a small number may be produced, and
yet the average stock be fully kept up; but if many eggs
or young are destroyed, many must be produced or the
species will become extinct. It would suffice to keep up
the full number of a tree which lived on an average for a
thousand years if a single seed were produced once in a

188 BIOLOGY

thousand years, supposing that this seed were never de-
stroyed and could be insured to germinate in a fitting place.
So that, in all cases, the average number of any animal or
plant depends only indirectly on the number of its eggs or
seeds.

"In looking at Nature, it is most necessary to keep the
foregoing considerations always in mind — never to forget
that every single organic being may be said to be striving
to the utmost to increase in numbers ; that each lives by a
struggle at some period of its life; that heavy destruction
inevitably falls either on the young or old during each
generation or at recurrent intervals. Lighten any check,
mitigate the destruction ever so little, and the number of
the species will almost instantaneously increase to any
amount."

Many marvelous facts concerning the rapid increase of
plants and animals have been collected since Darwin's
time. Jordan and Kellogg give many instances and among
them the following: "It is said that the conger eel lays
15,000,000 eggs yearly. If each hatched and the conger
grew to maturity, in a few years there would be no room
for any other kind of fish in the sea. The codfish has been
known to produce 9,100,000 eggs each year. If each egg
were to develop, in ten years the sea would be solidly full
of codfish. The female quinnat salmon of the Columbia
ascends the river at the age of about four years and lays
4,000 eggs, after which she dies. Half these eggs develop
into males. If each female egg came to maturity, we
should have at the end of fifty years 8,000,000,000,000,000,-
000,000,000,000,000,000,000,000,000 female salmon and as
many males as the offspring of a single pair. It takes
about one hundred of these salmon to weigh a ton. Could
all these fishes develop, in a very short time there would
be no room for them in all the rivers of the North nor in
all the waters of the sea."

The records of the spread of the English sparrow in
America and of rabbits in Australia are splendid examples

FACTORS OF EVOLUTION— SELECTION 189

of the possible rate of multiplication. Professor Sidney
Dickinson gives the following notes on the rabbit of Aus-
tralia: "The fecundity of the rabbit is amazing, and his
invasion of remote districts swift and mysterious. Careful
estimates show that under favorable conditions a pair of
Australian rabbits will produce six litters a year, averag-
ing five individuals each. As the offspring themselves
begin breeding at the age of six months, it is shown that,
at this rate, the original pair might be responsible in five
years for a progeny of over twenty millions. That the
original score that were brought to the country have
propagated after some such ratio, no one can doubt who
has seen the enormous hordes that now devastate the land
in certain districts. In all but the remoter sections the
rabbits are now fairly under control; one rabbiter with a
pack of dogs supervises stations where one hundred were
employed ten years ago, and with ordinary vigilance the
squatters have little to fear. Millions of the animals
have been killed by fencing in the water holes and dams
during a dry season, whereby they died of thirst and lay in
enormous piles against the obstructions they had frantic-
ally and vainly striven to climb, and poisoned grain and
fruit have killed myriads more."

These examples must suffice. Any other animal or plant
would illustrate the same principle, for each increases at
a rate which would make it cover the earth in a compara-
tively short time. That this is not the case is due to this
check known as the Struggle for Existence. This was
well known before Darwin's time, but he was the first to
see its great importance in the development of plant and
animal species.

The nature of the checks to increase is often complex.
One has but to watch a bit of natural land to see them
working. Climatic conditions play an important part in
limiting the increase, and a wet season will make some
crops exceedingly light and many insects very rare. Over-
crowding limits the supply of food and other needful

igo BIOLOGY

things, and hence some plants are 'choked' and many-
animals starve. Serving as prey to other animals causes
enormous destruction of both animals and plants, for thou-
sands of insects and other animal enemies must have food.
Thus Darwin in an observational experiment noted that
out of 357 weed seedlings under observation 295 were de-
stroyed by insects alone. Various bacterial and other fun-
gous diseases destroy countless thousands of plants and
animals in a single day, and it is well known that various
diseases due to animal and vegetable parasites are great
checks to increase in most species of vertebrate animals.

In some cases the struggle is with the elements, in others
special enemies constitute the most important check. The
history of the cottony-cushion scale in America, described
by Miall, offers a good example of a special check of this
sort. "About the year 1880 the orange groves of South
California seemed to be infected with a kind of leprosy.
White patches appeared on the trunks and branches, which
at length ran together and covered the bark, the leaves
turned yellow, and no fruit could be ripened. The plague
spread with rapidity, and all the time-honored remedies
were found to be ineffectual. It was soon made known
that the symptoms described were due to the attack of a
scale-insect, known in America as the fluted scale, or
cottony-cushion scale.

"This formidable plague gradually increased its range,
in spite of the vigorous use of poisonous washes. It
was not till 1888 that an effectual remedy was found. The
late C. V. Riley, Entomologist to the United States Depart-
ment of Agriculture, had anxiously considered the ways
of checking the fluted scale. He found out that it came
from Australia, where it infested the bushes called wattles
(Acacias) ; that it had been introduced into California
about 1868, probably on Acacias ; that in its native country-
it was not a serious plague, altho no remedies were em-
ployed. He concluded that it must be kept down in Aus-
tralia by natural enemies of some kind which did not exist

FACTORS OF EVOLUTION— SELECTION 191

in California and that the real policy was to discover and
import these remedies, whether parasitic or predatory.

"In 1888 Riley sent a trained entomologist, Albert
Koebele, to visit Australia, examine the gardens and re-
port. He found that the fluted scale, tho widespread, was
kept in check by several insect foes. The most promising
of these for Californian purposes was considered to be an
Australian lady-bird known to naturalists as 'Vedalia car-
dinalis/ This beetle, both as larva and adult, greedily
devours the scale-insect and its eggs, preys upon no other
species and is very prolific. Koebele was diligent in pro-
curing an abundant supply of Vedalia. The lady-birds
were*soon distributed and found plenty of occupation. In
a year and a half they had practically rid California of the
pest."

Nor is this case of the cottony-cushion scale alone. Any
text-book of economic entomology will cite hundreds of
cases of similar kinds. At the present time the United
States entomologist, Dr. L. O. Howard, is searching for a
special enemy supposed to keep in check the gipsy moth,
now so destructive in Massachusetts.

Such are some of the influences known to affect plants
and animals in the struggle for existence. It is clearly to
be seen that the whole question of the relation of the indi-
vidual to its environment— that is, the problems of plant
and animal ecology — are involved in the struggle for ex-
istence and in the checks to the tendency to overwhelming
increase. Science has only begun to understand these
problems of ecology. However, the principle of the strug-
gle for existence is not affected because its causes are not
known. This much is certain : organisms tend to increase
rapidly ; an untiring struggle for existence exists ; the vast
majority of individuals perish as a result of this struggle
with the environment — the result being as Darwin believed
that those organisms best fitted to their environment sur-
vive— i.e., the struggle for existence leads naturally to the
survival of the fittest. This is natural selection. Nature — -

192 BIOLOGY

meaning the sum total of the environmental factors which
affect an organism — selects those individuals best fitted to
the environment. How this works in detail is best ex-
plained after some consideration of the variation of organ-
isms.

The foundation of the Darwinian theory is the variabil-
ity of species, and it is quite useless to attempt even to
understand that theory, much less to appreciate the com-
pleteness of the proof of it, unless a clear conception of the
nature and extent of this variability is obtained. Varia-
tion in the state of nature has been discussed by Alfred
Russell Wallace in 'Darwinism/ Mr. Wallace shows in
some detail that individual variability is a general charac-
ter of all common and widespread species of animals or
plants; and, further, that this variability extends, so far
as is known, to every part and organ, whether external or
internal, as well as to every mental faculty, and that each
part or organ varies to a considerable extent independently
of other parts. Again, he shows by abundant evidence that
the variation that occurs is very large in amount — usually
reaching 10 or 20 and sometimes even 25 per cent, of the
average size of the varying part.

But a few examples can be given to illustrate this fea-
ture of life. The variability of plants is notorious, being
proved not only by the endless variations which occur
whenever a species is largely grown by horticulturists, but
also by the great difficulty that is felt by botanists in deter-
mining the limits of species in many large genera. As an
example may be taken the roses. In Mr. Baker's 'Re-
vision of the British Roses' he includes under the single
species Rosa canina — the common dog-rose — no less than
twenty-eight named varieties distinguished by more or less
constant characters and often confined to special localities,
and to these are referred about seventy of the species of
British and continental botanists.

Concerning individual variation, the distinguished bota-
nist, Alp. de Candolle, made a special study of the oaks of

FACTORS OF EVOLUTION— SELECTION 193

the whole world and has stated some remarkable facts as
to their variability. He declares that on the same branch
of oak he has noted the following variations : In the length
of the petiole, as one to three; in the form of the leaf,
being either elliptical or obovoid; in the margin being
entire, or notched, or even pinnatifid; in the extremity
being acute or blunt; in the base being sharp, blunt or
cordate; in the surface being pubescent or smooth; the
perianth varies in depth and lobing; the stamens vary in
number, independently; the anthers are mucronate or
blunt; the fruit stalks vary greatly in length, often as one
to three ; the number of fruits varies ; the form of the base
of the cup varies ; the scales of the cup vary in form ; the
proportions of the acorns vary; the times of the acorns
ripening and falling vary. Besides this, many species ex-
hibit well-marked varieties which have been described and
named.

Among birds copious evidence of variation is found.
The most systematic observations on the individual varia-
tion of birds have been made by J. A. Allen in his remark-
able memoir, 'On the Mammals and "Winter Birds of East
Florida.' He says: "The facts of the case show that a
variation of from 15 to 20 per cent, in general size, and an
equal degree of variation in the relative size of different
parts, may be ordinarily expected among specimens of the
same species and sex, taken at the same locality, while in
some cases the variation is even greater than this." He
then goes on to show that each part varies to a consider-
able extent independently of the other parts, so that when
the size varies, the proportions of all the parts vary, often
to a much greater amount. The wing and tail, for ex-
ample, besides varying in length, vary in the proportionate
length of each feather, and this causes their outline to vary
considerably in shape. The bill also varies in length,
width, depth and curvature.

Even tho one has not been impressed with the great
variety of individuals in the state of nature, variation in

194 BIOLOGY

domesticated plants and animals and the efficacy of artificial
selection in producing varieties of the different species of
plants and animals cannot have escaped notice. The fol-
lowing paragraphs are taken from Mr. Wallace's account
of variation in domesticated plants and animals:

"Every one knows that in each litter of kittens or of
puppies no two are alike. Even in the case in which sev-
eral are exactly alike in colors, other differences are
always perceptible to those who observe them closely.
They will differ in size, in the proportions of their bodies
and limbs, in the length or texture of their hairy covering
and notably in their disposition. They each possess, too,
an individual countenance, almost as varied when closely
studied as that of a human being. The same thing occurs
in the vegetable kingdom. All plants raised from seed
differ more or less from each other. In every bed of
flowers or of vegetables we shall find, if we look closely,
that there are countless small differences in the size, in the
mode of growth, in the shape or color of the leaves, in the
form, color or markings of the flowers, or in the size,
form, color or flavor of the fruit. These differences are
usually small, but are yet easily seen, and in their extremes
are very considerable; and they have this important qual-
ity, that they have a tendency to be reproduced, and thus
by careful breeding any particular variation or group of
variations can be increased to an enormous extent — appar-
ently to any extent not incompatible with the life, growth
and reproduction of the plant or animal.

"The way this is done is by artificial selection, and it is
very important to understand this process and its results.
Suppose we have a plant with a small edible seed and we
want to increase the size of that seed. We grow as large
a quantity of it as possible, and when the crop is ripe we
carefully choose a few of the very largest seeds or we may
by means of a sieve sort out a quantity of the largest seeds.
Next year we sow only these large seeds, taking care to
give them suitable soil and manure, and the result is found

FACTORS OF EVOLUTION— SELECTION 195

to be that the average size of the seeds is larger than in the
first crop and that the largest seeds are now somewhat
larger and more numerous. Again sowing these, we ob-
tain a further slight increase of size, and in a very few
years we obtain a greatly improved race, which will always
produce larger seeds than the unimproved race, even if
cultivated without any special care. In this way all our
fine sorts of vegetables, fruits and flowers have been
obtained, all our choice breeds of cattle or of poultry, our
wonderful race-horses and our endless varieties of dogs.
It is a very common but mistaken idea that this improve-
ment is due to crossing and feeding in the case of animals,
and to improved cultivation in the case of plants. Crossing
is occasionally used in order to obtain a combination of
qualities found in two distinct breeds, and also because it is
found to increase the constitutional vigor ; but every breed
possessing any exceptional quality is the result of the
selection of variations occurring year after year and ac~
cumulated in the manner just described. Purity of breed,
with repeated selection of the best varieties of that breed,
is the foundation of all improvement in our domestic ani-
mals and cultivated plants.

"The experience of breeders and cultivators proves that
variation is the rule instead of the exception, and that it
occurs, more or less, in almost every direction. This is
shown by the fact that different species of plants and ani-
mals have required different kinds of modifications to adapt
them to our use, and we have never failed to meet with
variation in that particular direction, so as to enable us
to accumulate it and so to produce ultimately a large
amount of change in the required direction. Our gardens
furnish us with numberless examples of this property of
plants. In the cabbage and lettuce we have found variation
in the size and mode of growth of the leaf, enabling us to
produce by selection the almost innumerable varieties,
some with solid heads of foliage quite unlike any plant in
a state of nature, others with curiously wrinkled leaves

196 BIOLOGY

like the savoy, others of a deep purple color used for
pickling. From the very same species as the cabbage have
arisen the broccoli and cauliflower, in which the leaves
have undergone little alteration, while the branching heads
of flowers grow into a compact mass forming one of our
most delicate vegetables.

"The most remarkable varieties are afforded by the apple,
and some account of these will be given as illustrating the
effects of slight variations accumulated by selection. All
our apples are known to have descended from the com-
mon crab of our hedges, and from this at least a thou-
sand distinct varieties have been produced. These differ
greatly in the size and form of the fruit, in its color, and
in the texture of the skin. They further differ in the
time of ripening, in their flavor, and in their keeping
properties ; but apple-trees also differ in many other ways.

"Coming now to our domesticated animals, we find still
more extraordinary cases; and it appears as if any special
quality or modification in an animal can be obtained if
we only breed it in sufficient quantity, watch carefully^
for the required variations, and carry on selection witK
patience and skill for a sufficiently long period. Thus*
in sheep we have enormously increased the wool, and
have obtained the power of rapidly forming flesh and fat;
in cows we have increased the production of milk; in
horses we have obtained strength, endurance, or speed,
and have greatly modified size, form, and color; in poul-
try we have secured various colors of plumage, increase
of size, and almost perpetual egg-laying; and in dogs and
pigeons marvelous changes have been effected."

The facts of individual variation from the viewpoint
of a prominent American botanist will supplement the
statements of Darwin and Wallace. Professor L. H.
Bailey based his lectures on 'Plant Breeding' on the uni-
versal difference in nature. He says: "No two living
things are exact counterparts, for no two are born into
exactly the same conditions and experiences. Every liv-

FACTORS OF EVOLUTION— SELECTION 197

ing object has individuality; that is, there is something
about it which enables the acute observer to distinguish
it from all other objects, even of the same class or spe-
cies. Every plant in a row of lettuce is different from*
every other plant, and the gardener, when transplanting
them, selects out, almost unconsciously, some plants which
please him and others which do not. If one were to make
the effort, he would find that it is possible to distinguish
differences between every two spears of grass in a meadow
or every two heads of wheat in a grain-field.

"All this is equivalent to saying that plants are infi-
nitely variable. The ultimate causes of all this variation
are beyond the purpose of the present discussion, but it
must be evident to the reflective mind that these differ-
ences are the means of adapting the innumerable indi-
viduals to every little difference or advantage in the envi-
ronment in which they live.

"If no two plants are anywhere alike, then it is not
strange if now and then some departure, more marked
than common, is named and becomes a garden variety.
We have been taught to feel that plants are essentially;
stable and inelastic, and that any departure from the
type is an exception, and calls for immediate explana-
tion. The fact is, however, that plants are essentially
unstable and plastic, and that variation between the indi-
viduals must everywhere be expected. This erroneous
notion of the stability of organisms comes of our habit
of studying what we call species. We set for ourselves!
a type of plant or animal and group about it all those
individuals which are more like this type than they are
like any other, and this group we name a species. Nowa-
days, the species is regarded as nothing more than con-
venient and arbitrary expression for classifying our
knowledge of the forms of life, but the older naturalists
conceived that the species is the real entity or unit in
nature, and we have not yet wholly outgrown the habit
of mind which was born of that fallacy.

198 BIOLOGY

"Nature knows nothing about species; she is concerned
with the individual, the ultimate unit. This individual
she molds and fits into the chinks of environment, and
each individual tends to become the more unlike its birth-
mates the more the environments of the various indi-
viduals are unlike. I would impress upon you, therefore,
the importance of the individual plant, rather than the
importance of the species; for thereby we put ourselves
as nearly as possible in a sympathetic attitude with Na-
ture, and, resting upon the ultimate object of her con-
cern, we are able to understand what may be conceived
to be her motive in working out the problems of life."

It should be noted that Darwin did not give much at-
tention to the causes of variation. He simply gathered!
together the data to show that organisms are highly
variable. Given the facts of the high variability of indi-
viduals of all plants and animals, and the intense struggle
for existence, how will this struggle act in regard to
variation? Can the principle of selection, which is seen
to be so potent in the hands of man in artificial selection,
apply to organisms in a state of nature? These are essen-
tially the questions which Darwin asked, and his own
answer, now become a classic in science, is still the most
satisfactory.

"I think we shall see," he says, "that it (the principle
of selection) can act most efficiently. Let the endless*
number of slight variations and individual differences oc-
curring in our domestic productions, and in a lesser degree
in those under nature, be borne in mind; as well as the
strength of the hereditary tendency. Under domestica-
tion, it may be truly said that the whole organization be-
comes in some degree plastic. But the variability, which
we almost universally meet with in our domestic produc-
tions, is not directly produced, as Hooker and Asa Gray
have well remarked by man; he can neither originate
varieties nor prevent their occurrence ; he can only pre-
serve and accumulate such as do occur. Unintentionally

FACTORS OF EVOLUTION— SELECTION 199

he exposes organic beings to new and changing condi-
tions of life, and variability ensues; but similar changes
of conditions might and do occur under nature. Let it
also be borne in mind how infinitely complex and close-
fitting are the mutual relations of all organic beings
to each other and to their physical conditions of life; and
consequently what infinitely varied diversities of struc-
ture might be of use to each being under changing con-
ditions of life.

"Can it, then, be thought improbable, seeing that varia-
tions useful to man have undoubtedly occurred, that other
variations useful in some way to each being in the great
and complex battle of life should occur in the course of
many successive generations? If such do occur, can we
doubt (remembering that many more individuals are born
than can possibly survive) that individuals having any
advantage, however slight, over others, would have the
best chance of surviving and of procreating their kind?
On the other hand, we may feel sure that any variation
in the least degree injurious would be rigidly destroyed.
This preservation of favorable individual differences and
variations, and the destruction of those which are inju-
rious, I have called Natural Selection, or the Survival
of the Fittest. Variations neither useful nor injurious;
would not be affected by natural selection, and would be
left either a fluctuating element, as perhaps we see in cer-
tain polymorphic species, or would ultimately become
fixed, owing to the nature of the organism and the nature
of the conditions.

"We have good reason to believe that changes in the
conditions of life give a tendency to increased variability;
and this would manifestly be favorable to natural selec-
tion, by affording a better chance of the occurrence of
profitable variations. Unless such occur, natural selec-
tion can do nothing. Under the term of 'variations' it
must never be forgotten that mere individual differences
are included. As man can produce a great result with

200 BIOLOGY

his domestic animals and plants by adding up in any given
direction individual differences, so could natural selection,
but far more easily, from having incomparably longer
time for action.

"Nor do I believe that any great physical change, as of
climate, or any unusual degree of isolation to check im-
migration, is necessary in order that new and unoccupied
places should be left, for natural selection to fill up by
improving some of the varying inhabitants. For as all the
inhabitants of each country are struggling together with
nicely balanced forces, extremely slight modifications in
the structure or habits of one species would often give
it an advantage over others; and still further modifica-
tions of the same kind would often still further increase
the advantage, as long as the species continued under the
same conditions of life and profited by similar means of
subsistence and defense.

"As man can produce, and certainly has produced, a
great result by his methodical and unconscious means
of selection, what may not natural selection effect? Man
can act only on external and visible characters. Nature,
if I may be allowed to personify the natural preservation
or survival of the fittest, cares nothing for appearances,
except in so far as they are useful to any being. She can
act on every internal organ, on every shade of consti-.
tutional difference, on the whole machinery of life. Man
selects only for his own good : Nature only for that of the
being which she tends. Every selected character is fully
exercised by her, as is implied by the fact of their selec-
tion. Man keeps the natives of many climates in the
same country; he seldom exercises each selected charac-
ter in some peculiar and fitting manner; he feeds a long
and a short beaked pigeon on the same food; he does
not exercise a long-backed or long-legged quadruped in
any peculiar manner; he exposes sheep with long and
short wool to the same climate. He does not allow the
most vigorous males to struggle for the females. He does

FACTORS OF EVOLUTION— SELECTION 201

not rigidly destroy all inferior animals, but protects dur-
ing each varying season, as far as lies in his power, all
his productions. He often begins his selection by some
half-monstrous form; or at least by some modification,
prominent enough to catch the eye or to be plainly useful
to him. Under nature, the slightest differences of struc-
ture or constitution may well turn the nicely balanced scale
in the struggle for life, and so be preserved. How fleeting
are the wishes and efforts of man ! how short his time !
and consequently how poor will be his results, compared
with those accumulated by Nature during whole geological
periods ! Can we wonder, then, that Nature's productions
should be far 'truer' in character than man's produc-
tions; that they should be infinitely better adapted to the
most complex conditions of life, and should plainly bear
the stamp of far higher workmanship?

"It may metaphorically be said that natural selection
is daily and hourly scrutinizing, throughout the world,
the slightest variations; rejecting those that are bad,
preserving and adding up all that are good; silently and
insensibly working, whenever and wherever opportunity*
offers, at the improvement of each organic being in rela-
tion to its organic and inorganic conditions of life. We
see nothing of these slow changes in progress until the
hand of time has marked the lapse of ages, and then so
imperfect is our view into long-past geological ages that
we see only that the forms of life are now different
from what they formerly were.

"In order that any great amount of modification should
be effected in a species, a variety when once formed must
again, perhaps after a long interval of time, vary or pre-
sent individual differences of the same favorable nature
as before; and these must be again preserved, and so
onward step by step. Seeing that individual differences of
the same kind perpetually recur, this can hardly be con-
sidered as an unwarrantable assumption. But whether it
is true, we can judge only by seeing how far the hypothe-

202 BIOLOGY

sis accords with and explains the general phenomena of
nature. On the other hand, the ordinary belief that the
amount of possible variation is a strictly limited quan-
tity is likewise a simple assumption.

"Altho natural selection can act only through and for
the good of each being, yet characters and structures,
which we are apt to consider as of very trifling impor-
tance, may thus be acted on. When we see leaf-eating
insects green, and bark-feeders mottled-gray, tne alpine
ptarmigan white in winter, the red grouse the color of
heather, we must believe that these tints are of service
to these birds and insects in preserving them from danger.
Grouse, if not destroyed at some period of their lives,,
would increase in countless numbers; they are known
to suffer largely from birds of prey ; and hawks are guided
by eyesight to their prey — so much so that on parts of the
Continent persons are warned not to keep white pigeons,
as being the most liable to destruction. Hence natural
selection might be effective in giving the proper color
to each kind of grouse, and in keeping that color, when
once acquired, true and constant. Nor ought we to think
that the occasional destruction of an animal of any par-
ticular color would produce little effect; we should re-
member how essential it is in a flock of white sheep to de-
stroy a lamb with the faintest trace of black.

"In looking at many small points of difference between
species, which, as far as our ignorance permits us to judge,
seem quite unimportant, we must not forget that climate,
food, etc., have no doubt produced some direct effect.
It is also necessary to bear in mind that owing to the
law of correlation, when one part varies, and the varia-
tions are accumulated through natural selection, other
modifications, often of the most unexpected nature, will
ensue.

"As we see that those variations which, under domes-
tication, appear at any particular period of life, tend to
reappear in the offspring at the same period — for instance,

FACTORS OF EVOLUTION— SELECTION 203

in the shape, size and flavor of the seeds of the many-
varieties of our culinary and agricultural plants; in the
caterpillar and cocoon stages of the varieties of the silk-
worm; in the eggs of poultry, and in the color of the
down of their chickens; in the horns of our sheep and
cattle when nearly adult — so in a state of nature natural
selection will be enabled to act on and modify organic
beings at any age, by the accumulation of variations profit-
able at that age, and by their inheritance at a correspond-
ing age.

"If it profit a plant to have its seeds more and more
widely disseminated by the wind, I can see no greater
difficulty in this being effected through natural selection
than in the cotton planter increasing and improving by
selection the down in the pods on his cotton-trees. Natu-
ral selection may modify and adapt the larva of an
insect to a score of contingencies wholly different from
those which concern the mature insect; and these modi-
fications may effect, through correlation, the structure of
the adult. So, conversely, modifications in the adult may
affect the structure of the larva; but in all cases natural
selection will ensure that they shall not be injurious;
for if they were so, the species would become extinct.

"Natural selection will modify the structure of the
young in relation to the parent, and of the parent in rela-
tion to the young. In social animals it will adapt the
structure of each individual for the benefit of the whole
community, if the community profits by the selected
change. What natural selection cannot do is to modify
the structure of one species, without giving it any ad-
vantage, for the good of another species; and tho state-
ments to this effect may be found in works of natural his-
tory, I cannot find one case which will bear investiga-
tion. A structure used only once in an animal's life, if
of high importance to it, might be modified to any extent
by natural selection; for instance, the great jaws pos-
sessed by certain insects, used exclusively for opening the

204 BIOLOGY

cocoon; or the hard tip to the beak of unhatched birds,
used for breaking the egg.

"It may be well here to remark that with all beings
there must be much fortuitous destruction, which can
have little or no influence on the course of natural selec-
tion. For instance, a vast number of eggs or seeds are
annually devoured, and these could be modified through
natural selection only if they varied in some manner which
protected them from their enemies. Yet many of these
eggs or seeds would, perhaps, if not destroyed, have
yielded individuals better adapted to their conditions of
life than any of those which happened to survive. So
again, a vast number of mature animals and plants, wheth-
er or not they be the best adapted to their conditions, must
be annually destroyed by accidental causes, which would
not be in the least degree mitigated by certain changes of
structure or constitution which would in other ways be
beneficial to the species.

"But let the destruction of the adults be ever so heavy,
if the number which can exist in any district be not
wholly kept down by such causes — or again, let the de-
struction of eggs or seeds be so great that only a hun-
dredth or a thousandth part are developed — yet of those
which do survive the best adapted individuals, supposing
that there is any variability in a favorable direction, will
tend to propagate their kind in larger numbers than the
less well adapted. If the numbers be wholly kept down
by the causes just indicated, as will often have been the
case, natural selection will be powerless in certain bene-
ficial directions; but this is no valid objection to its effi-
ciency at other times and in other ways, for we are far
from having any reason to suppose that many species
ever undergo modification and improvement at the same
time in the same area."

In concluding this sketch of Darwin's Natural Selection
theory it should be noted that Darwin believed natural
selection to be the most important, but not the sole, factor

FACTORS OF EVOLUTION— SELECTION 205

in producing new forms of organisms. His later follow-
ers, especially of the Weismann school, have held natural
selection to be the all-sufficient factor of evolution. It
will be necessary to return to this in discussing modern
criticisms of Darwinism. Summarizing the essential points
in the natural selection theory, Jordan and Kellogg say
that: "Of all the various factors of organic evolution,
the one which has been most relied on as the great de-
termining agent is that called Natural Selection, the sur-
vival of the individuals best fitted for the conditions of
life, with the inheritance of those species-forming adap-
tations in which fitness lies. The primal initiative is not
in natural selection, but in variation — germinal and indi-
vidual. This may be slight variation (fluctuation) or
large deviation (saltation), but in any case, all difference
in species or race must first be individual. The impulse
to change, once arisen, is continued through heredity.
From natural selection arises the choice among different
lines of descent, the adaptive tending to exclude the non-
adaptive, while traits which are neither helpful nor hurt-
ful, but simply indifferent, may be borne along by the cur-
rent of adaptive characters. Finally, separation or iso-
lation tends to preserve a special line of heredity from
being merged in the mass which constitutes the parent
stock or species. Without individual variation no change
could take place; all organisms would be identical in
structure."

Altho the Darwinian theory has been subject to no
popularly recognised attack during the last quarter of a
century, nevertheless there has been accumulating a mass
of criticism of it. Only a sketch of some of the leading
criticisms can be presented. These will be taken in large
measure from Kellogg's 'Darwinism To-day.'

''Among the critics of the selection theories," he says,
"we must note two groups, differing in the character of
their criticism more in degree than in kind, perhaps, but
still importantly differing. One group denies in toto any

2o6 BIOLOGY

effectiveness or capacity for species-forming on the part
of natural selection, while the other group, a larger one,
sees in natural selection an effective factor in directing
or controlling the general course of descent, holding it
to adaptive lines, but denies it outright any such 'Allmacht'
of species control as the more eager selectionists, the so-
called neo-Darwinians or Weismannians, credit it with.
This larger group of critics sees in natural selection an
evolutionary factor capable of initiating nothing, depend-
ent wholly for any effectiveness on some primary factor
or factors controlling the origin and direction of varia-
tion, but wholly capable of extinguishing all unadapted,
unfit lines of development, and in this way of exercising
decisive final control over the general course of descent —
i.e., organic evolution.

"The general impression left on one after a consider-
able course of anti-Darwinian reading is that there is
a very real and effective amount of destructive criticism
for Darwinians to meet; and at the same time a curious
paucity of satisfactory or at all convincing substitutionary
theory offered by the anti-Darwinians to replace that
which they are attempting to dethrone. The situation il-
lustrates admirably the varying worth of a few facts.
A few stubborn facts of the wrong complexion are fatal
things for a theory ; they are immensely effective offensive
weapons. But these same few facts make a pitiable show-
ing when they are called on to support a theory of their
own.

"It was exactly the greatest part of Darwin's great-
ness, it seems to me, that he launched his theory only
after making the most remarkable collection of facts yet
gathered together in biological science by any one man.
Testing his theory by applying to it successively fact after
fact, group after group, and category after category of
facts, he convinced himself of the theory's consonance
with all this vast array of observed biological actuality.

"Compare the grounding of any of the now offered re-

FACTORS OF EVOLUTION— SELECTION 207

placing theories with the preparation and founding of
Darwinism. In 1864 von Kolliker, a great biologist, con-
vinced of the incapacity of natural selection to do the
work assigned it by its founders and friends, suggested
a theory of the origin of species by considerable leaps;
in 1899 Korschinsky, on the basis of some few personal
observations and the compiling of some others, definitely
formulated a theory of species-forming by sudden con-
siderable variations, namely, mutations; in 1901 and 1903
appeared the two volumes of De Vries's 'Die Mutations-
theorie/ in which are revealed the results of long years
of careful personal observation, in truly Darwinian man-
ner, directed toward the testing and better grounding of
this mutations-theory of species-origin. The results are:
out of many plant species studies a few show at certain
times in the course of numerous generations a behavior
in accordance with the demands of a theory of species-
forming by sudden definitive modification ; that is, species-
forming by mutations.

"The mutations-theory thus launcned is offered as a
substitute for the natural selection theory obviously weak-
ening under the fire of modern scientific criticism. But
however effective De Vries's facts are in proving the
possibility of the occurrence of other variations than
those fortuitous ones occurring in continuous series from
mean to opposite extremes which Darwin recognised as
the basis of species-forming, and however effective they
are in proving the actual production of three or six or
ten species by mutation, and however effective in both
these capacities they are as weapons of attack on the domi-
nance of the Darwinian theory of species-making, how
really inadequate are they to serve as the basis of a great
all-answering theory explaining in a causo-mechanical
way the facts of descent, or even the primary facts of
general species-forming.

"The natural selection theory, as an all-sufficient ex-
planation of adaptation and species-forming, has always

208 BIOLOGY

had a weakness at its base; it depends absolutely, of
course, on the preexistence of variations, but it itself has
no influence whatever on the origin or control of these
variations to give birth to other individuals. Now one
of the chief problems in biology is exactly that of the
origin, the causes, and the primary control of these con-
genital variations.

"Three principal explanations, no one of them experi-
mentally proved or even fairly tested as yet, have been
given of this actually occurring congenital variation, viz.,
(i) that there exists in the germ-plasm an inherent tend-
ency or capacity to vary so that there is inevitable va-
riation in all individuals produced from germ-plasm, this
variation being wholly fortuitous and fluctuating accord-
ing to some (the belief of Darwin and his followers),
or, according to others, this variation following certain
fixed or determinate lines (determinate variation, ortho-
genetic variation, etc.) ; (2) that amphimixis — i.e., bi-
parental parentage — is the principal cause of variation, it
seeming logical to presume that individuals produced from
germ-cells derived from the fusion of germ-plasm com-
ing from two individuals more or less unlike would differ
slightly from either of the parental individuals; and (3)
that congenital variation is due to the influence of the
ever-varying environment of the germ-cell producing indi-
viduals.

"The objections to any one of these theories may be
very pertinent, as when one says regarding the first that
calling a thing 'inherent* is not clearing up in any degree
a phenomenon for which we are demanding a causo-
mechanical explanation ; or of the second, that it has been
proved that individuals produced parthenogenetically —
that is, from an unmated mother — vary, and in some cases
vary even more than do other individuals of the same
species produced by amphimixis; or of the third, that
as far as our study of the actual processes and mechanism
of the production of germ-cells and of embryos has gone,

FACTORS OF EVOLUTION— SELECTION 209

we have found no apparent means whereby this influence
of the ambient medium can be successfully impressed on
the germ-plasm. But however pertinent the objections
to the why of variation may be, they do not in any way
invalidate the fact that variations do continuously and
inevitably occur in all individuals, and that while many;
of these variations are recognisably such as have been
impressed on the individual during its personal develop-
ment as immediate results of varying temperature, amount
or kind of food, degree of humidity, etc., to which it may
be exposed in its young life, others seem wholly inex-
plicable on a basis of varying individual environment, and
are certainly due to some antenatal influence acting on
the germ-plasm from which the embryo is derived.

"Now, the natural selection theory, in its Darwinian
and neo- Darwinian form, presupposes fortuitously occur-
ring congenital variations of practically infinite variety
in all parts of all organisms. Actual observation shows
that all parts of all organisms do vary, and that they
vary congenitally ; that is, independently of any imme-
diate influence during development exercised from with-
out by environmental conditions, as well as in response)
to these environmental influences, and finally, that in many
cases this variation is fortuitous — that is, that it occurs
according to the laws of chance.

"The industrious statistical study of variations, including
the tabulation of the variation condition in long series
of individuals of the same species or race, and the mathe-
matical formulation of this variation condition, have
shown that in many specific cases, studied in numerousf
kinds of animal and plant forms, the character of the
variation in any particular character may be truly rep-
resented (with close approximation) by the mathemati-
cal expression and curve which would exactly define the
condition in which the variation would exist if it actually
followed the law of error. It is these continuous series
of slight variations, these variously called fluctuating, in-

210 BIOLOGY

dividual, or Darwinian variations, occurring in all organ-
isms at all times, and often following in their occurrence
the laws of chance, on which Darwin's theory of species-
forming by natural selection is based.

''But this same industrious statistical and quantitative
study of variation which has proved that some varia-
tions do occur regularly, fluctuating around a mean or
mode, has shown, as well, that in many cases the varia-
tions distinctly tend to heap up on one side or the other
of the mean; that is, that they tend to occur along cer-
tain lines or toward certain directions rather than uni-
formly out in all directions. Also it is true — and this has,
of course, been long known — that by no means all varia-
tions are so slight nor in such perfectly gradatory or
continuous series as is true of the gradatory Darwinian
variations. 'Sports' have been known to breeders of
plants and animals ever since plant and animal breeding
began. Bateson has filled a large book with records of
'discontinuous variations' in animals; variations, that is,
of large size and not occurring as members of continuous
gradatory series. So that biologists are acquainted with
many cases of variation that seem to be of a kind, or to
exhibit a tendency to institute special directions of de-
velopment, and thus not to be of the simple, non-initiating,
inert character of the fortuitous, slight, fluctuating varia-
tions, among which natural selection is presumed to choose
those that are to become the beginnings of new lines of
modification and descent. Many biologists believe firmly
that variations occur in many special cases, if not in
most cases, only along certain special lines. Paleontolo-
gists believe, practically as a united body, that variation
has followed fixed lines through the ages; that there has
been no such unrestricted and utterly free play of varia-
tional vagary as the Darwinian natural selection theory
presupposes.

"Now it is at least obvious that natural selection is
absolutely limited in its work to the material furnishedi

FACTORS OF EVOLUTION— SELECTION 211

by variation, so that if variation occurs in any cases along
certain determinate lines selection can do no more than
make use of these lines. Indeed, if variation can occur
persistently along determinate lines, natural selection's
function in controlling evolution in such cases is limited
to the police power of restricting or inhibiting further
development along any one or more of these lines which
are of a disadvantageous character; that is, a character
which handicaps or destroys the efficiency of its mem-
bers in the struggle for life. The question in many men's
mouths to-day is, Why may not variation be the actual
determinant factor in species-forming, in descent? It
actually is, respond many biologists and paleontologists.
Even Darwin believed such determinate variation to oc-
cur, as is indicated by repeated statements in the 'Origin
of Species.' "

This problem of the existence or non-existence of de-
terminate variations is one of the most important matters
in connection with the whole great problem of descent;
that is, of evolution. It is the basic problem of evolution,
for it is the problem of beginnings. Selection, isolation,
and the like factors are conditions of species-forming;
variation is a prerequisite. True variation must have its
causes, and these causes are to be determined before an
actual causo-mechanical explanation of evolution can ever
be found. But the determination of the relation of varia-
tion to species-forming is certainly the first step now
necessary in our search for the basic factors, the real
first cause of species change.

Space will not permit analysis of the general lines of
objections raised in the foregoing. These objections have
led many biologists to the totally ante-Darwinian position
that the struggle for existence and the corresponding
selection of the fit are not factors of evolution. But per-
haps the majority of biologists who recognise the objec-
tions cited are inclined to belief in natural selection as
the great 'conserving factor of evolution' while allowing

212 BIOLOGY

that it does not create new forms. To quote from T. H.
Morgan, ". . . the theory of natural selection has nothing
to do with the origin of species, but with the survival1
of already formed species. Not selection of the fittest
individuals, but the survival of the sufficiently fit species."

In summarizing the present-day standing of the Dar-
winian theory, Kellogg says: "I think I speak fairly in
saying that the believers and defenders of the natural
selection theory to-day admit in large measure the validity
of those criticisms which are directed at the incapacity
of Darwinism, in its long familiar form, to account for
the development of variations and modifications up to
the advantageous or disadvantageous stage. They admit,
also, the actual existence, and in abundant measure, of
species differences which are of indifferent character —
that is, of no special utility — and make the consequent!
admission that such species differences cannot for the
most part be explained by natural selection. And they
also concede, or at least most of them, including Weis-
mann, do, the force of the criticism that the assumption
of the occurrence of the right variations at the right
time is a necessity for the development by selection of
many, if not most, specializations of qualitative and of
coadaptive character, which assumption in turn demands
an explanation of causes anterior to selection.

"And finally, most selectionists concede that selection
cannot make new species by relying on the extremes of
series of fluctuating or Darwinian variations, because of
the inevitable extinguishing or swamping of these ex-
treme variations by interbreeding with the far more abun-
dant average or modal individuals of the species."

Making such concessions, it is necessary to recognise
that there are factors of evolution other than natural
selection, and these require separate treatment.

CHAPTER XIII

SELECTION — SEXUAL SELECTION

In building up the theory of Natural Selection Darwin
found that while this theory was sufficient to explain the
useful in organic structures it did not sufficiently explain
"that class of phenomena which go to constitute the
Beautiful." Darwin, therefore, suggested an auxiliary
theory to give a scientific explanation to these widespread
phenomena. To quote Romanes: "Just as by his theory
of natural selection he sought to explain the major fact
of utility, so did he endeavor to explain the minor fact
of beauty by a theory of what he termed Sexual Selection. "
Kellogg's exposition of this theory has been partly fol-
lowed in the following account.

Every zoologist is familiar with the striking differences
between the male and female individual of a single spe-
cies. The reader will recall the feathers of many male
birds which are in striking contrast to the sober plumage
of their mates. These differences in size, color, general
appearances, and various specific structural details in
head, trunk, wings, feet, plumage, etc., are over and be-
yond those primary radical differences existing in all
species in which the two sexes are differentiated. Some
of these differences may, however, have obvious relation
to the primary differences, in that they may be connected
immediately with the act of pairing or with the work of
rearing the young. The presence in male insects of com-
plexly developed holding organs, and in female mammals
213

214

BIOLOGY

of milk glands, exemplifies differences of this category.
A great many sexual differences, however, have no such
obvious direct relation to the function of producing and
rearing the young.

Fig. 29 — Secondary Sexual Characters in Copepods.
A., male of Calocalanus plumosus ; B., female of Calocalanus
pavo; C, male of same species. (Morgan and Giesbrecht.)

Such are the metallic purple and bronze colors of the
male grackles compared with the dull brown of the fe-
males; the long tails and brilliant coloration of the male
pheasants, the great spreading, patterned tail of the pea-
cock, the larger size or the winglessness of many female

SEXUAL SELECTION 215

insects, etc. All these differences between male and fe-
male of the same species of animal, beyond or in addition
to the differences between the actual primary reproductive
organs, are known as secondary sexual differences, or the
characters themselves, which may be characteristics of
physiology and habit, as well as the more familiar ones
of structure, are called, secondary sexual characters. The
layman may not readily appreciate the abundance and the
great variety of these characters, but it is a fact that
almost all species of animals, excepting those in the lower
invertebrate branches, show them, and if one will try to
recall the aspect of the two sexes in one after another
of the species of animals with which one is familiar, mam-
mals, birds, insects, etc., one will begin to realize how
widespread and significant are these secondary sexual
characters.

Many of these secondary sexual characters have uses
which are of a kind directly helpful in the struggle for
existence, as the strong antlers of the stags, useful in
defense against attacking enemies; the brood sacs of the
kangaroos and opossum, useful in caring for their help-
less young; the milk glands and teats of all female mam-
mals, and the protective colors and patterns of many in-
sects and birds. But others of these secondary sexual
characters are either of a kind apparently useless in the
struggle for life, or even of a kind actually harmful.

Of apparent harmfulness are the conspicuous staring
colors of many male birds, the long dangling plumes, the
weighty crests and heavy, dragging tails of others; all
these parts also usually being dangerously, conspicuously
colored. The lively loud song of many male birds, and the
dancing and leaping of numerous male spiders and some
male birds must also involve some danger to the perform-
ers by attracting the attention of their enemies. In fact,
most of those secondary sexual characters that are classi-
fied under the general head of 'exciting organs' are ap-
parently of a sort that should be actually disadvanta-

216 BIOLOGY

geous in the struggle for existence. They are of a char-
acter tending to make their possessors conspicuous, and
thus readily perceived by their carnivorous enemies. How
is to be explained the existence of so many and such
highly developed structural and physiological characters
of this kind, a condition that seems to stand in direct oppo-
sition-to the theory of natural selection? Darwin's an-
swer to this question is contained in his theory of sexual
selection.

This theory, in few words, is that there is practically
a competition or struggle for mating, and that those males
are successful in this struggle which are the strongest
and best equipped for battle among themselves, or which
are most acceptable, by reason of ornament or other at-
tractiveness, to the females. In the former case, mating
with a certain female depends upon overcoming in fight
the other suitors, the female being the passive reward of
the victor; in the second case the female is presumed to
exercise a choice, this choice depending upon the attract-
iveness of the male. The actual fighting among males,
and the winning of the females by the victor, are ob-
served facts in the life of numerous animal species. But
a special sexual selection theory is hardly necessary to
explain the development of the fighting equipment — ant-
lers, spurs, claws, etc. This fighting array of the male
is simply a special phase of the already recognised intra-
specific struggle; it is not a fight for room or food, but
for the chance to mate. But this chance often depends'
on the issue of a life-and-death struggle. Natural selec-
tion would thus account for the development of the weap-
ons for this struggle.

For the development, however, of such secondary sex-
ual characters as ornament and song, and special odors,
and 'love-dancing,' the natural selection theory can in no
way account; the theory of sexual selection was the logi-
cal and necessary auxiliary theory, and when first pro-
posed by Darwin met with quick and wide acceptance.

Characteristic 'Courting' Attitudes of Spiders.

SEXUAL SELECTION 217

Wallace, in particular, took up the theory and applied
it to explain many cases of remarkable plumage and pat-
tern development among birds. Later, as he analyzed)
more carefully his cases, and those proposed by others,
he became doubtful, and finally wholly skeptical of the
theory.

A few extracts from the 'Origin of Species' will pre-
sent the theory in Darwin's own words. "This form of
selection," he explains, "depends, not on a struggle for
existence in relation to other organic beings, or to ex-
ternal conditions, but on a struggle between the individu-
als of one sex, generally the males, for the possession
of the other sex. The result is not death to the unsuc-
cessful competitor, but few or no offspring. Sexual se-
lection is, therefore, less rigorous than natural selection.
Generally, the most vigorous males, those which are best
fitted for their places in nature, will leave most progeny.
But in many cases victory depends not so much on gen-
eral vigor as on having special weapons, confined to the
male sex. A hornless stag or spurless cock would have
a poor chance of leaving numerous offspring. Sexual
selection, by always allowing the victor to breed, might
surely give indomitable courage, length to the spur, and
strength to strike in the spurred leg, in nearly the same
manner as does the brutal cockfighter by the careful selec-
tion of his best cocks.

"Among birds the contest is often of a peaceful char-
acter. All those who have attended to the subject believe
that there is the severest rivalry between the males of
many species to attract, by singing, the females. The
rock-thrush of Guiana, birds of paradise, and some oth-
ers, congregate; and successive males display with the
most elaborate care, and show off in the best manner, their
gorgeous plumage; they likewise perform strange antics
before the females, which, standing by as spectators, at
last choose the most attractive partner. If man can in
a short time give beauty and an elegant carriage to his

218 BIOLOGY

bantams, according to his standard of beauty, I can see
no good reason to doubt that female birds, by selecting,;
during thousands of generations, the most melodious or
beautiful males, according to their standard of beauty,
might produce a marked effect."

Many difficulties in the way of the application of this
theory have been advanced in recent years as a result of
experimental work and more widespread observation.
Morgan lists twenty such objections. Space will allow
mention of only a few of the most important criticisms!
of the theory. These are outlined by Kellogg essentially
as follows.

The theory can be applied only to species in which
the males are markedly more numerous than the females,
or in which the males are polygamous. In other cases'
there will be a female for each male, whether he be
ornamented or not ; and the unornamented males can leave
as many progeny as the ornamented ones, which would
prevent any cumulation of ornamental variations by se-
lection. As a matter of fact, in a majority of animali
species, at least among the vertebrates, males and females
exist in approximately equal numbers.

Observation shows that in most species the female is
wholly passive in the matter of pairing, accepting the first
male that offers.

"Ornamental colors," moreover, as Kellogg points out,
"are as often a characteristic of males of kinds of ani-
mals in which there is no real pairing as among those
which pair,. How explain by sexual selection the remark-
able colors in the breeding season of many fishes, in which
the female never, perhaps, even sees the male which fer-
tilizes her dropped eggs?

"Choice on a basis of ornament and attractiveness im-
plies a high degree of esthetic development on the part
of the females of animals for whose development in this
line we have no (other) proof. Indeed, this choice de-
mands esthetic recognition among animals to which we

SEXUAL SELECTION 219

distinctly deny such a development, as the butterflies and
other insects in which secondary sexual characters of
color, etc., are abundant and conspicuous. Similarly with
practically all invertebrate animals. Further, in those
groups of higher animals where esthetic choice may be
presumed possible we have repeated evidence that prefer-
ences vary with individuals. Besides, even if we may at-
tribute fairly a certain amount of esthetic feeling to such

B

Fig. 30 — Secondary Sexual Characters.
Callionymus eyra, male and female. (Darwin.)

animals as mammals and birds, is this feeling to be so
keen as to lead the female to make choice among only
slightly differing patterns of songs? Yet this assump-
tion is necessary if the development of ornament and
other attracting and exciting organs is to be explained
by the selection and gradual cumulation through genera-
tions of slight fortuitously appearing fluctuating varia-
tions in the males.

''Even if the females do choose among the males on
a basis of attractiveness, how are the characters of the

220 BIOLOGY

more attractive males to become especially fostered and
accumulated by selection? Do such males produce more
offspring or more vigorous ones than the other males,
which, tho rejected by the first females, find their mates
among the females not already mated? Are we to at-
tribute to the more ornamental males a particular vigor?
If so, may not that very vigor be the cause of the extra-
production of color or plumage or wattles, etc.?

"Darwin admits, in order to explain the beginnings
of color and ornament development, a certain degree of
difference between the male and female in regard to
their reaction to environment influences. If so, may not
these admitted differences be really sufficient to account
for even a pretty high degree of difference in development
of secondary sexual characters?

"The special display of colors, tufts, plumes, spreading
tails, and other secondary sexual characters by the males
at mating time is an observed fact ; the 'dances' of cranes
and storks, the serenades of the song-birds, the evolutions
of the male spiders, are all familiar phenomena in the
mating season of these animals. And they probably do
exercise an exciting effect on the females, and are prob-
ably actually displayed for this purpose. But does this
in any way prove, or even give basis for, a reasonable
presumption for belief in a discriminating and definitive
choice among the males on the part of the female? And
it is this actual choosing which is the necessary basis for
the theory of sexual selection.

"How explain the well-known cases of a similar extra-
development of plumage in the nuptial season by both
males and females, as in certain herons and other birds?
And what of those cases in which it is the female that is
the brighter-colored individual of the pair? To explain
the latter case Darwin assumes that in these cases the
males have done the selecting, but even this rather too
easy removal of the situation postulated as a fundamental
generalization of the theory does not explain the first of

SEXUAL SELECTION 221

the questions in this paragraph. Do both sexes among}
the herons do selecting?"

To the objection that choice on the part of the female
assumes her possession of an esthetic ideal and a power
of selection in accordance with that ideal which is con-
trary to our knowledge of animal psychology, Lloyd Mor-
gan answers that the choice is not one of deliberation
but rather of impulse; it is simply a definite response to
an adequate stimulus. "She accepts that mate which by
his song or otherwise excites in sufficient degree the
pairing impulse; if others fail to excite this impulse they
are not accepted. It is a choice from impulse, not the
result of deliberation; but it is a choice which is deter-
mined by the emotional meaning of the conscious situa-
tion. And it is the reiterated revival of the associated
emotional elements which generates an impulse sufficiently
strong to overcome her instinctive coyness and reluctance.
It is a perceptual choice arising from impulse rather
than an ideational choice due to motive and volition."

The final line of criticism is that experimental evi-
dence is strongly opposed to the theory of sexual selec-
tion. Mayer, director of the Tortugas laboratory of the
Carnegie Institute, has proved by many careful experi-
ments that the striking differences between the wings of
male and female promethea moths, 'Callosamia promethea/
are absolutely without meaning in relation to sexual se-
lection. The animals mate normally when painted, or
after the wings have been cut off and others glued on in
their place. Mayer tried to test the selective action of
the female. The male promethea has blackish wings,
while the females are reddish-brown. In accordance
with the theory of sexual selection, the peculiar coloration
of the male should be due to the selection of dark-colored
males, so that under this influence the males would be-
come, in successive generations, darker until the present
coloration has been attained. Mayer's own account of

222 BIOLOGY

his experiments and conclusions to test the preferences
and selective action of the females is as follows :

"In order to test this hypothesis I cut off the wings of
a number of females, leaving only short stumps, from
which all the scales were carefully brushed. Male wings
were then neatly glued to the stumps, and thus the female
presented the appearance of a male. Under these cir-
cumstances the males mated with the female quite as
readily as they would have done under normal condi-
tions.

"I then tried the experiment of gluing female wings
upon the male. Here, again, the mating seemed to occur
with normal frequency, and I was unable to detect that
the females displayed any unusual aversion toward their
effeminate-looking consorts.

"It is also interesting to note that normal males pay
no attention to males with female wings.

"In another series of experiments the wings were cut
entirely off of males and females and the scales brushed
off their bodies, and yet these shabby males were readily
accepted by normal females; nor could I see that normal
males displayed any aversion to mating with wingless
females."

Mayer's next experiments were directed to the end of
determining if the males found the females by sight or
by smell. By enclosing females in numerous jars vari-
ously arranged, and covered or uncovered, it was readily
determinable- that males never pay any attention to fe-
males enclosed in transparent jars so closed as to pre-
vent the escape of any odors from the female, while to
females enclosed in boxes, or wrapped in cotton so as to
be invisible, but yet capable of giving odor off into the
air, males came promptly and hovered about. To locate
the organs of scent in the female, Mayer cut off abdo-
mens from various females and then placed abdomens
and abdomenless females at some little distance apart.
Males came to the abdomens and not to the thorax plus

SEXUAL SELECTION 223

wings, legs, and head parts. It was readily proved by
experiments with males whose antennae were covered
with shellac, photographic paste, etc., that the sense of
smell is seated in the antennae. Males with antennae
covered with photographic paste did not find females,
while the same males with this paste dissolved off did.

All this evidence showed quite clearly that it was odor
rather than color which served to attract the males to the
females. In lizards, too, in which sexual dimorphism is
conspicuous, females showed no preference for particular
patterns exhibited by the males in breeding coat. Many
such experiments, with like results, seem to make the re-
jection of Darwin's theory of sexual selection necessary.

But if it is rejected other explanations of the origin
of the secondary sexual characters are needed. Such
theories have been advanced. Kellogg says of them that
the theories proposed to account for secondary sexual:
characters "mostly rest on one or both of two principal
assumptions; first, that the secondary sexual characters
are produced as the result of the immediate stimulus (nat-
urally different) of the sexually differing primary repro-
ductive organs, this stimulus being usually considered to
result from an internal secretion of the genital organs
acting on certain tissues of the organism; and second,
that the males, in most species, possess an excess of
energy, which manifests itself in extra-growths, extra-
development of pigment, plumage, etc., and that displays
by the males of special movements, sound-making, etc.,,
are direct effects or manifestations of sexual excita-
tion."

It thus appears that the sexual selection theory, as a
special application, of natural selection, is far from being
in good standing with present-day biologists. The truth
is that most of the work recently done has been destruc-
tive, and there is, as yet, no satisfactory replacing theory.

CHAPTER XIV

FACTORS OF EVOLUTION OTHER THAN SELECTION

The most important question raised in biological sci-
ence by Darwin's work is whether natural selection has
been the sole, or but the main, cause of the descent of
species, or organic evolution. Darwin's own answer to
this question was quite distinct. ''He stoutly resisted/'
says Romanes, "the doctrine that natural selection was
to be regarded as the only cause of organic evolution."

In many parts of his works Darwin showed that he
believed in the possibility of the inheritance of the effects
of the use and disuse of organs, the Lamarckian factor.
This view, and also the admission of still other factors,
is clearly set forth in the first paragraph of the conclusion
to the 'Origin of Species.' It has been said that a more
strongly worded passage cannot be found in Darwin's
writings, and that the last sentences present the only note
of bitterness in all the thousands of pages Darwin wrote.

"I have now recapitulated," he says, "the facts and
considerations which have thoroly convinced me that spe-
cies have been modified during a long course of descent.
This has been effected chiefly through the natural selec-
tion of numerous successive, slight, favorable variations,
aided in an important manner by the inherited effects of
the use and disuse of parts, and in an unimportant manner,
that is, in relation to adaptive structures, whether past
or present, by the direct action of external conditions,
and by variations which seem to us, in our ignorance, to
224

FACTORS OTHER THAN SELECTION 225

arise spontaneously. It appears that I formerly under-
rated the frequency and value of these latter forms of
variation, as leading to permanent modifications of struc-
ture independently of natural selection.

"But as my conclusions have lately been much misrep-
resented, and it has been stated that I attribute the modi-
fication of species exclusively to natural selection, I may
be permitted to remark that in the first edition of this
work, and subsequently, I placed in a most conspicuous-
position — namely, at the close of the Introduction — the
following words : 'I am convinced that natural selection
has been the main, but not the exclusive, means of modi-
fication/ This has been of no avail. Great is the power
of steady misrepresentation; but the history of science
shows that, fortunately, this power does not long endure."

While Darwin thus admitted the possibility of other
factors of evolution, Alfred Russell Wallace, the co-
originator of the natural selection theory, has believed
natural selection to be the all-sufficient factor. Romanes
has thus contrasted the views of Darwin and Wallace :

According to Darwin, Natural Selection has been the
main means of modification, not excepting the case of
Man. (a) Therefore it is a question of evidence whether
the Lamarckian factors have cooperated, (b) Neither all
species, nor, a fortiori, all specific characters, have been
due to natural selection, (c) Thus the principle of Utility
is not of universal application, even where species are
concerned, (d) Thus, also, the suggestion as to Sexual
Selection, or any other supplementary cause of modifica-
tion, may be entertained; and, as in the case of the La-
marckian factors, it is a question of evidence whether,
or how far, they have cooperated, (e) No detriment
arises to the theory of natural selection as a theory of
the origin of species by entertaining the possibility, or
the probability, of supplementary factors, (f) Cross-
sterility in species cannot possibly be due to natural selec-
tion.

226 BIOLOGY

According to Wallace, Natural Selection has been the
sole means of modification, excepting in the case of Man.
(a) Therefore it is antecedently impossible that the La-
marckian factors can have cooperated, (b) Not only all
species, but all specific characters, must necessarily have
been due to natural selection, (c) Thus the principle of
Utility must necessarily be of universal application, where
species are concerned, (d) Thus, also, the suggestion as
to Sexual Selection, or of any other supplementary cause
of modification, must be ruled out; and, as in the case of
the Lamarckian factors, their cooperation deemed impos-
sible, (e) The possibility — and, a fortiori, the probabil-
ity— of any supplementary factors cannot be entertained
without serious detriment to the theory of natural selec-
tion, as a theory of the origin of species, (f) Cross-ster-
ility in species is probably due to natural selection.

This comparison makes it evident that the Darwinism
of Darwin is natural selection plus other factors, while
the Darwinism of Wallace is natural selection alone as
the cause of evolution. In late years this view of Wal-
lace's has been highly developed by Weismann and his
followers, who have argued for the all-sufficiency of natu-
ral selection, and have especially opposed other factors
which Darwin admitted might have aided natural selec-
tion. This view of Wallace and Weismann should be
called 'Neo-Darwinism' or 'Ultra-Darwinism/ In dis-
cussing the criticisms of natural selection it has been
shown that there are serious difficulties in the way of
universal application of neo-Darwinism. For this reason
even Weismann has been forced to modify his views.

Most prominent of the theories of the factors of evolu-
tion which have rivaled natural selection is that put forth,
before Darwin's work, by Lamarck (i 744-1 829). La-
marck's theory did not attract much attention during
his lifetime, but since Darwin's time Lamarckism has
become well known. The Lamarckian theory is com-
monly referred to as the theory of use and disuse and

FACTORS OTHER THAN SELECTION 227

the direct action of the environment in modifying organs.
Moreover, it holds that characteristics acquired during
the lifetime of an individual are transmissible by heredity.
The Lamarckian view, as given by Osborn, is formu-
lated in the four well-known propositions following:

(1) Life, by its internal forces, tends continually to
increase the volume of every body that possesses it, as
well as to increase the size of all the parts of the body up
to a limit which it brings about.

(2) The production of a new organ or part results
from a new need or want, which continues to be felt, and
from the new movement which this need initiates and
causes to continue. (This is the psychical factor in his
theory, which Cope later has termed Archesthetism.)

(3) The development of organs, and their force or
power of action, are always in direct relation to the em-
ployment of these organs. (At another point he expands
this into two sub-laws: "In every animal which has not
passed the term of its development, the more frequent
and sustained employment of each organ strengthens lit-
tle by little this organ, develops it, increases it in size,
and gives it a power proportioned to the length of its
employment; whereas the constant lack of use of the
same organ insensibly weakens it, deteriorates it, pro-
gressively diminishes its powers, and ends by causing}
it to disappear." This is now known as the Law of Use
and Disuse, or Kinetogenesis.)

(4) All that has been acquired or altered in the or-
ganization of individuals during their life is preserved
by generation and transmitted to new individuals which
proceed from those which have undergone these changes.

The greatest weakness in the Lamarckian theory is the
assumption of the inheritance of acquired characters;
this Lamarck took for granted, and did not try to demon-
strate. As Kellogg has well said :

"That an animal in its lifetime, and especially during
its immature life, can effect very considerable changes

228 BIOLOGY

in some of its body-parts by special use or disuse of
these parts, or that certain parts may be modified through
the influence of external stimuli, is familiar knowledge.
The heart and lungs can be enlarged by special use; in
short, almost any of the organs of the body which are
actively used can be modified either by unusual or extra
use, or by unusual lack of use. Now this use is, in Nature,
almost always of the character of a better aiding in suc-
cessful living; that is, it is adaptive use. If such better-
ment of organs and their functions acquired by individu-
als could be inherited by their young, it is obvious that
general adaptations of this sort could be rapidly developed
in the course of generations, and new species, new, that
is, because of the adaptive changes thus effected, be
formed. This is the essential thought in Lamarck's the-
ory of the method of adaptation and species-forming.

"The essential principle of Lamarckism is an ortho-
genetic evolutionary progress toward better and finer
adaptation and adjustment resulting from the inherited
effects of actual use, disuse, and functional stimulation
of parts. It is a great thought and a clear one, and only
needs the proof of the actuality of the inheritance of
individually acquired characters to make it one of the
principal causal explanations of adaptation and species
change.

"However, it is exactly this proof that is wanting. At
any rate, proof of the character and extent necessary to
convince all or even a majority of biologists is wanting.
The examples or cases brought forward by Lamarckians
of the alleged inheritance of mutilations, of the results
of disease, and of use and disuse, are not convincing. It
is one of Weismann's positive contributions to biology
to have analyzed case after case of alleged inheritance
of acquired characters and shown its falseness, or at
least uncertainty. Many of these cases he has been able
to explain as a result of selection; others remain inex-
plicable; a few only are insisted on by the Lamarckian,*

FACTORS OTHER THAN SELECTION 229

champions as indisputable examples of such inheritance..
But this very paucity of so-called proved cases, where
there should be thousands of obvious examples if the
principle were really sound, is argument against Lamarck-
ism.

"Our knowledge, too, of the mechanism of heredity
makes strongly against the theory of the inheritance of
acquired characters. Another of Weismann's positive
contributions to biology is his generally sound distinction
between the germ-plasm and the soma-plasm and parts
of the many-celled body. At maturity the animal body
is composed of a small mass of germ-plasm (germ-cells),
situated in the ovaries or testes, and a great mass of
somatic tissues and organs, all the rest of the body, in
fact. Now, what is the condition that exists in the body
after a somatic part is modified by use or disuse or by
other functional stimulus, as when a muscle is enlarged
by exercise, the sole of the foot calloused by going bare-
foot, an ear more finely attuned by training? We have a
definite physical change in a definite organ, but is the
germ-plasm in any way changed or affected by this super-
ficial or specific somatic modification, or, if changed, is
it changed so that it will produce in its future develop-
ment a similar change in the same organ of the future
new individual? What possible mechanism have we in
the body to produce or insure such an effect on the germ-
plasm? The answer is obvious and flat; we certainly
know of no such mechanism; in fact, what we do know
of the relation of the germ-cells to the rest of the body
makes any satisfactory conception of such a mechanism
as yet impossible.

"But even were the inheritance of acquired characters
now an established fact, or if it should come to be one,
it must be kept in mind that Lamarckism could be sub-
stituted only partly for Darwinism. There are many
adaptations and much species-forming that Lamarckism

230 BIOLOGY

might explain, but also there are hosts of adaptations that
Lamarckism cannot explain."

A number of American biologists have added to the
principles of Lamarck that of natural selection. Without
denying to natural selection a more or less important part
in the process of organic evolution, members of this school
believe that much greater importance ought to be assigned
to the inherited effects of use and disuse than was as-
signed to these agencies by Darwin. It is obvious that
neo-Lamarckism has to face the problem of the heredity
of acquired characters — this is the fundamental and as
yet unproved proposition of the theory.

The Darwinian theory is based upon variations which
occur in all directions, unfavorable as well as favorable,
and hence are known as indeterminate variations. Definite
lines of development are produced from these chance va-
riations by the elimination in the struggle for existence
of all other lines; that is, natural selection permits only
certain kinds of variation to persist and to accumulate.
According to this theory the persistence of the useful is
explained, but there are certain phenomena which cannot
so easily be explained. Among these may be mentioned
development along definite lines which are not advan-
tageous and over-development of parts to a harmful
degree. Moreover, there is difficulty in explaining the
beginnings of advantageous modifications from fluctuating
individual variations. It is to explain these phenomena
that the theory of 'Orthogenesis' has been developed.

According to the theory of orthogenesis variations are
predetermined and hence development is fixed along defi-
nite lines. There are various views as to the origin of
these predetermined variations. The Lamarckians would
base them on the perpetuation and accumulation of the
effects of use and disuse, etc.; Roux would explain them
on the battle of the parts theory and Weismann on the
germinal selection theory, referred to later in this chapter.

Many phases of the theory of orthogenesis have been

FACTORS OTHER THAN SELECTION 231

advanced by Nageli, Eimer, Cope and others. Some of
these go so far as to say that orthogenesis takes the place
of natural selection. Nageli belongs to this school, and he
"believes that animals and plants would have developed
about as they have even had no struggle for existence
taken place and the climate and geologic conditions and
changes been quite different from what they actually have
been," says Kellogg.

Others hold that orthogenesis is an adjunct of nat-
ural selection. Prominent among the latter is Professor
Whitman, of Chicago, who sees no fundamental contradic-
tions between the theories and who believes that ortho-
genesis and natural selection are factors of evolution
working together at times; in other words, determinate
orthogenetic variations are preserved by natural selection
— a conclusion which appeals to many biologists as most
reasonable.

Associated with the name of de Vries, the Amsterdam
botanist, is the Mutation Theory, or Heterogenesis. But
this general conception of species-forming on a basis of
the occurrence of occasional, sudden, fixed and often con-
siderable changes or variations in the offspring of a plant
or animal is a conception not of course new with de Vries,
but one variously expressed by numerous biologists from
Darwin's time on, especially by von Kolliker, Galton, Dall,
Bateson, Emery, Scott and Korschinsky. It is, however,
chiefly due to the patient, persistent, well-planned and ex-
tensive experiments and observations of de Vries that this
theory of species-forming by heterogenesis, or as called
by de Vries, by mutations, has recently received so much
renewed attention.

"The meaning of heterogenesis," says Kellogg, "in con-
nection with species-forming and descent is essentially
this: Whereas by the Darwinian theory species are trans-
formed slowly and by slight changes in at first one or two
or a few and only later in more parts, and all new species
are derived from the old ones (which usually disappear as

232 BIOLOGY

the new ones appear) by the gradual selection of the ad-
vantageous ones among the regular slight, fluctuating,
individual variations (known commonly as Darwinian
variations and which mostly occur according to the law of
error), by the theory of heterogenesis new species appear
suddenly, not by a selective choosing among the slight,
fluctuating Darwinian variations, but independently of
selection and largely independently of the so-called Dar-
winian variations by the appearance in fixed definite form
of several to many slight to considerable variations, which
give the new species definite characteristics differentiating
it often in many particulars from the old species, which
differentiating characteristics are fully and faithfully
transmitted to the succeeding generations of individuals
derived from this suddenly born new species."

Extensive observations and experimentation to test the
mutation theory are now in progress, and it is too early
to form a final opinion as to its bearing on the theory of
natural selection. It has been warmly welcomed, but even
its friends admit that it needs the support of more experi-
ments and more facts. T. H. Morgan sums up the advan-
tages of the theory as follows: "Since the mutations ap-
pear fully formed from the beginning, there is no difficulty
in accounting for the incipient stages in the development
of an organ, and since the organ may persist, even when
it has no value to the race, it may become further devel-
oped by later mutations and may come to have finally an
important relation to the life of the individual.

"The new mutations may appear in large numbers, and
of the different kinds, those will persist that can get a foot-
hold. On account of the large number of times that the
same mutations appear, the danger of becoming swamped
through crossing with the original form will be lessened
in proportion to the number of new individuals that arise.

"If the time of reaching maturity in the new form is
different from that in the parent forms, then the new
species will be kept from crossing with the parent form,

FACTORS OTHER THAN SELECTION 233

and since this new character will be present from the
beginning, the new form will have much better chances of
surviving than if a difference in time of reaching maturity-
had to be gradually acquired.

"The new species that appear may be in some cases
already adapted to live in a different environment from
that occupied by the parent form, and if so, it will be
isolated from the beginning, which will be an advantage in
avoiding the bad effects of intercrossing.

"It is well known that the differences between related
species consist largely in differences of unimportant or-
gans, and this is in harmony with the mutation theory, but
one of the real difficulties of the selection theory.

"Useless or even slightly injurious characters may ap-
pear as mutations, and if they do not seriously affect the
perpetuation of the race, they may persist."

Still another causal factor of the descent of species is
to be found in the isolation theories differently expressed
by various authors.

Altho to many biologists isolation alone is sufficient to
account for the origin of species, most evolutionists con-
sider it to be a very widespread and effective auxiliary
theory to natural selection. Selection needs help from
just such a factor. Just what is meant by this theory in
its different phases Kellogg describes as follows:

"If, in a species, a number of individuals show a certain
congenital variation, this variation will probably be lost
by cross-breeding with individuals not having it, unless
the individuals having it are in the majority or unless they
become in some way isolated from the others and segre-
gated so that they will breed among themselves. By such
isolation and such in-and-in breeding the newly appearing
congenital variations might soon become established, and
if advantageous be so considerably developed as soon to
distinguish as a variety or incipient species the members of
the isolated colony. With time a distinct new species

234 BIOLOGY

might result. Are there means to produce such isolation
of groups of individuals belonging to a common species ?

"The answer to this is certainly an affirmative one.
There seem to be, indeed, several means of producing
isolation, and the isolation may be variously named accord-
ingly. Undoubtedly the most important of these kinds of
isolation, at least in the light of our present knowledge, is
that known as geographical or topographical isolation.
Isolation produced in other ways may be called biologic
or physiologic or sexual isolation. In the case of geo-
graphic or topographic isolation the isolated group or
groups of individuals are actually in another region or
locality from the rest of the species, this being the result
of migration, voluntary or involuntary.

"In biologic isolation the individuals of the species all
inhabit the same territory, but become separated into
groups by structural or physiological characters which
prevent miscellaneous inter-breeding. The real founder
and most insistent upholder of the theory of species-
forming by isolation (geographic and topographic isola-
tion) was Moritz Wagner (1813-1887), a traveler and
naturalist, whose wanderings and observations brought to
him the conviction that while natural selection might
modify species and even produce continuous evolution it
could never differentiate species, that is, produce new
species."

In support of isolation theories, it is argued by biologists
that isolation is very important as one factor in forming
species. It is, however, obvious that isolation in itself
cannot be the basic and all-sufficient cause for the produc-
tion of specific differentiation, any more than any selective
factor can. The prerequisite in both cases is the occur-
rence of variation. What are the variations and how are
they produced? These are the fundamental questions in
species-forming. Isolation is a tremendously favoring
condition, but not a primary cause of species-forming. It

FACTORS OTHER THAN SELECTION 235

tends to help along, to hurry up species disintegration, not
to initiate it.

The Germinal Selection Theory advanced by Weis-
mann attempts to explain the origin of variations. Ac-
cording to Weismann's neo-Darwinism, only congenital
variations, those present at birth, are transmissible by
heredity. In brief, the theory holds that the germ-plasm
may be influenced by conditions under which an organism
lives and may 'acquire' variations in a determinate or
favorable direction. Knowing this factor, "we remove, it
seems to me," writes Weismann, "the patent contradiction
of the assumption that the general fitness of organisms or
the adaptations necessary to their existence are produced
by accidental variations — a contradiction which formed a
serious stumbling-block to the theory of selection. Tho
still assuming that primary variations are 'accidental,' I
yet hope to have demonstrated that an interior mechanism
exists which compels them to go on increasing in a definite
direction the moment selection intervenes. Definitely di-
rected variation exists, but not predestined variation run-
ning on independently of the life conditions of the organ-
ism as Nageli, to mention the position that the most ex-
treme advocate of this doctrine has assumed; on the con-
trary, the variation is such as is elicited and controlled by
those conditions themselves, tho indirectly."

There are numerous minor theories proposed to explain
difficulties in the more general theories. For these the
reader is referred to special books like Kellogg's 'Darwin-
ism To-day,' Jordan and Kellogg's 'Evolution and Animal
Life' and Morgan's 'Evolution and Adaptation.'

Most biologists at present seem inclined to look for truth
in a combination of the several theories. Thus Whitman
says: "Natural selection, orthogenesis and mutation ap-
pear to present fundamental contradictions, but I believe
that each stands for truth, and reconciliation is not distant.
The so-called mutations of 'Oenothera' are indubitable
facts, but two leading questions remain to be answered.

236 BIOLOGY

First, are these mutations now appearing, as is agreed, in-
dependently of variation, nevertheless a production of va-
riations that took place at an earlier period in the history
of these plants? Secondly, if species can spring into exist-
ence at a single leap, without the assistance of cumulative
variations, may they not also originate with such assist-
ance? That variation does issue a new species, and that
natural selection is a factor, tho not the only factor, in
determining results, is, in my opinion, as certain as that
grass grows altho we cannot see it grow. Furthermore, I
believe I have found indubitable evidence of species-form-
ing variation advancing in a definite direction (ortho-
genesis) and likewise of variations in various directions
(amphigenesis). If I am not mistaken in this, the recon-
ciliation for natural selection and orthogenesis is at hand."

Others, like H. F. Osborn, think that there are still
some unknown factors of evolution. In a lecture entitled
'The Unknown Factors of Evolution' Osborn says : "The
general conclusion we reach from a survey of the whole
field is, that for Buffon's and Lamarck's factors we have
no theory of heredity, while the original Darwin factor,
or neo-Darwinism, offers an inadequate explanation of
evolution. If acquired variations are transmitted, there
must be, therefore, some unknown principle in heredity ;
if they are not transmitted, there must be some unknown
factor in evolution."

The present plight seems to be that species-forming
and evolution are not susceptible of explanation without
the help of some Lamarckian factor; and, on the other
hand, the actuality of any such factor in the light of our
present knowledge of heredity cannot be assumed. The
discovery of the 'unknown factors of evolution' is there-
fore one of the most important quests of present-day
biologic research.

CHAPTER XV

HEREDITY

No topic in all biology has received so much attention in
recent times, both from investigators and from the intelli-
gent public at large, as Heredity. The reason for this
interest is to be found in the importance of heredity for
the individual human life, its practical importance in
breeding plants and animals and its bearing on the evo-
lutionary theory of biology. Its importance in these lines
is clearly related by J. Arthur Thomson, of Aberdeen, in
his recent book, 'Heredity' : "There are no scientific prob-
lems of greater human interest than those of Heredity,"
he declares, "that is to say, the genetic relation between
successive generations. Since the issues of the individual
life are in great part determined by what the living crea-
ture is or has to start with, in virtue of its hereditary re-
lation to parents and ancestors, we cannot disregard the
facts of heredity in our interpretation of the past, our
conduct in the present or our forecasting of the future.
Great importance undoubtedly attaches to Environment in
the widest sense — food, climate, housing, scenery and the
animate 'milieu'; and to Function in the widest sense, —
exercise, education, occupation or the lack of these; but
all these potent influences act upon an organism whose
fundamental nature is determined, tho not rigidly fixed,
by its Heredity, that is, we repeat, by its genetic relation
to its forebears. As Herbert Spencer said, 'Inherited con-
stitution must ever be the chief factor in determining
237

238 BIOLOGY

character.' And what is important in regard to Man's
heredity is even more demonstrably important in regard
to his domesticated animals and cultivated plants. What
has been achieved in the past in regard to horses and
cattle, pigeons and poultry, cereals and chrysanthemums,
"by experimental cleverness and infinite patience may be
surpassed in the future if breeders and cultivators can
attain to a better understanding of the more or less obscure
laws of inheritance on which all their results depend.

"The study of heredity is also of fundamental impor-
tance in the domain of pure science, in the biologist's at-
tempt to interpret the process of evolution by which the
complexities of our present-day fauna and flora have
gradually arisen from simpler antecedents. For heredity
is obviously one of the conditions of evolution, of continu-
ance as well as of progress. There would have been
heredity even if there had been a monotonous world of
Protists without any evolution at all, but there could not
have been any evolution in the animate world without
heredity as one of its conditions. The study of heredity is
inextricably bound up with the problems of development,
reproduction, fertilization, variation and so on; in short,
it is one of the central themes of Biology."

Some outline of the reproduction of organisms is a nec-
essary prelude to a discussion of the theories of heredity.
It has been stated that as a rule individual plants and ani-
mate start as a single cell. In the one-celled organisms
the simple division of the parent cell into daughter cells
constitutes reproduction. Each of the daughter cells thus
formed is a young organism with the power to grow to
mature size, divide and complete a life-cycle by reproduc-
ing. One unicellular organism to-day may merge its in-
dividuality into two offspring in a few hours and then into
four in the next few hours and so on.

Many-celled plants and animals begin their individual
existence as one-celled ova or ovules which by oft-re-
peated cell-division produce the thousands of cells found

Fig. 31 — Spermatozoa of Various Mammals.
A., badger (living) ; B., same after staining ; C.k bat ; D., same,
fiagellum and middle-piece ; E., same, head only ; F., pig,
head only ; G., opossum ; H., double sperm alozo from bat ;
I., rat. (h. c., head-cap; k., end-knob; m., middle piece; n.,
nucleus.) (Wilson.)

240 BIOLOGY

in the body of the larger plants and animals. In these,
certain cells are set apart as reproductive cells for the de-
velopment of new individuals.

As is well known, most higher plants and animals have
differentiated into male and female sexes. Each produces
a peculiar kind of reproductive or germ cell. In animals
the organs of the male known as spermaries produce
minute cells (sperm-cells or spermatozoa), provided with
a vibratile appendage capable of causing swimming in
fluids. The organs of the female known as ovaries pro-
duce ova or eggs. These eggs are simple cells, usually in-
capable of division without fertilization. By swimming a
sperm-cell comes into contact with an egg-cell, penetrates
and is transformed into a nucleus which moves to meet and
fuse with the female nucleus of the egg-cell. This en-
trance and fusion of sperm-nucleus with egg-nucleus is
fertilization. Immediately after the fusion the fertilized
egg or oosperm shows signs of preparation for division by
mitosis and soon the two-cell stage is formed. In like
manner by mitosis cleavage again takes place in each of
these two cells and there follow stages of four, eight, six-
teen, thirty-two, etc., cells until the egg has been divided
into a mass of cells. Cell-division continues, differentia-
tion into tissues takes place and a folding off of organs
goes on until the individual is completely formed.

In plants the process is in essentials the same. In the
lower plants, even including the mosses and the ferns, the
male germ-cells are motile and swim to meet the female
germ-cells. They enter and produce changes similar to
those described for animals. In the higher flowering
plants motile male-cells are not found. Instead there are
pollen grains adapted to being carried by winds, insects,
etc., from the anther of one flower to the pistil of another.
From the pollen grain a delicate tube grows down into the
ovary and into contact with the egg-cell or ovule of the
plant. Down this tube moves a small cell from the inside
of the pollen grain. Its nucleus fuses with the egg-

Fig. 32 — Spermatozoids of Plants.
A., Fucus analga ; B., Pellia, a liverwort; C, Sphagnum, a moss;
D., Marsilia ; E., Angiopteris, a fern ; F., Phegopteris, a fern.
(Wilson.)

242 BIOLOGY

nucleus, producing fertilization and leading soon to cell-
division.

In brief outline, the above is the story of the usual ori-
gin of higher plants and animals in sexual reproduction.
The essential point is that new individuals arise from two
cells, one derived from each parent.

Exceptional cases do occur. Some multicellular animals
like Hydra and certain worms may give rise to buds or
divide into two or more new animals. This is similar to

Fig. 33 — Fertilization in the Plant.
sp. ph., sporophylls or stamens ; mg. sp., megaspore ; mi. spg.,
microsporangia ; per., petals ; per., sepals ; fl. 2., receptacle ;
sp. ph., carpel ; stg., stigma ; St., style ; mg. spg., megaspo-
rangia; mg. sp., megaspore; p. t., pollen tube. (Parker.)

the power of many plants to reproduce from buds, shoots
or cuttings. This process is known as asexual reproduc-
tion, in which also is classed the simple division of one-
celled plants and animals. In most cases organisms with
the power of asexual reproduction also multiply by sexual
reproduction, but many plants seem to be able to multiply
indefinitely by runners, tubers and so on.

Another exception to the general rule that higher indi-

HEREDITY 243

viduals develop from the fusion of two germ-cells is found
among certain species of plant lice (Aphides), water fleas
(small Crustacea) and others which under certain condi-
tions develop from unfertilized eggs. This is partheno-
genesis. With the possible exception of certain scale in-
sects, parthenogenesis among animals is always temporary
and parthenogenetic generations are from time to time,
usually in the fall, succeeded by a generation reproducing
sexually. Among plants many species are believed to be
permanently parthenogenetic.

When such cases are considered, it must be admitted
that the vital processes may continue indefinitely simply
by repeated division of the cells themselves, without the
intervention of the act of fertilization ; still, on the other
hand, it is necessary to conclude, on account of the wide
distribution throughout the whole organic kingdom of the
phenomenon of fertilization, that this institution is of
essential importance among the vital processes and that
it is fundamentally connected with the life of the cell.

For an understanding of the problems of heredity the
method of development, of sperms, 'spermatogenesis,' and
of ova, 'oogenesis,' is necessary as well as the exact steps
of the process by which an oosperm or unicellular embryo
is formed by the union of the two sexual elements. In
plants and animals both ovary and spermary are at first
composed of cells of the ordinary kind, the primitive sex-
cells, and it is only by the further development of these
that the sex of the gonad is determined.

In the spermary the sex-cells undergo repeated fission,
forming what are known as the sperm-mother-cells, in
which the number of chromosomes is constant in any given
species. The sperm-mother-cell divides and the process
of division is immediately repeated, the result being that
each sperm-mother-cell gives rise to a group of four cells
having half the normal number of chromosomes, the four
cells so produced being the immature sperms. Thus the
sperm or male gamete is a true cell, and is specially modi-

244 BIOLOGY

fied in most cases for active movements. This mitotic
division by which the number of chromosomes in the
sperm-mother-cells is reduced by one-half is known as a
reducing division.

As already stated, the ova also arise from primitive
sex-cells. These divide and give rise to the egg-mother-
cells. The egg-mother-cells do not immediately undergo
division, but remain passive and increase, often enor-
mously, in size, by the absorption of nutriment from sur-
rounding parts; in this way each egg-mother-cell becomes
an ovum. In addition to increase in the bulk of the proto-
plasm itself, a formation of plastic products usually goes
on to an immense extent and the ovum may attain a com-
paratively enormous size, as, for instance, in birds, in
which the 'yolk' is simply an immense egg-cell.

Such an ovum is incapable of being fertilized or of de-
veloping into an embryo; before it is ripe for conjugation
with a sperm or able to undergo the first stages of segmen-
tation it has to go through a process known as the matura-
tion of the egg. Maturation consists essentially in a twice-
repeated process of cell-division by mitosis, and by its
means two small cells called polar cells are thrown off.
The ovum has now lost a portion of its protoplasm, to-
gether with three-fourths of its chromatin, half having
passed into the first polar cell and half of what remained
into the second : the remaining one-fourth of the chromatin
takes on a rounded form and is distinguished as the fe-
male pronucleus. The formation of both polar cells takes
place by a reducing division, so that while the immature
ovum contains the number of chromosomes found in the
ordinary cells of the species, the mature ovum, like the
sperm, contains only one-half the normal number.

Shortly after, or in some cases before maturation, the
ovum is fertilized by the conjugation with it of a single
sperm. Sperms are produced in vastly greater numbers
than ova, and it often happens that a single egg is seen
quite surrounded with sperms, all apparently about to con-

HEREDITY

245

jugate with it. It has, however, been found to be a gen-
eral rule that only one of these actually conjugates; the
others, like the drones in a beehive, perish without fulfil-
ling the one function they are fitted to perform.

qProrv

Fig- 34 — Maturation and Impregnation of Animal Ovum.

Memb., cell membrane ; cent., female centrosome ; pol., polar
cell ; microp., micropyle ; spermatozoids are seen near micro-
pole and female pronucleus ; cent., male centrosome ; pron.,
male pronucleus; seg. nucl., segmentation nucleus. (Parker
and Parker.)

246 BIOLOGY

The sperm and egg nuclei approach one another and final-
ly unite to form what is called the segmentation nucleus, the
single nucleus of what is not now the ovum, but the oosperm
— the impregnated egg or unicellular embryo. The fertiliz-
ing process is thus seen to consist of the union of two nu-
clear bodies, one contributed by the male gamete or sperm,
the other by the female gamete or ovum. It follows from
this that the essential nuclear matter or chromatin of the
oosperm is derived in equal proportions from each of the
two parents. Moreover, as both male and female pronu-
clei contain only half the number of chromosomes found in
the ordinary cells of the species, the union of the pro-
nuclei results in the restoration of the normal number to
the oosperm.

Fertilization being thus effected, the process of segmen-
tation, or division of the oosperm, takes place as described.
The significance of these observed phenomena of matu-
ration, fertilization and cell-division in modern theories
of inheritance will be apparent.

The main facts of organic reproduction which are fun-
damental to a consideration of the modern problems of
heredity having been outlined, a brief survey of some of
the most prominent theories of heredity which have been
advanced during the last two centuries will be given, after
which attention will be directed to the present-day prob-
lems of heredity, including 'Mendelism,' or the experi-
mental study of heredity, and those cytological problems
which have as their aim the identification of the inheri-
tance material in the germ-cells.

It is not strange that of the many attempts at theories
of heredity the early ones were essentially mystical and
fell back on the supernatural to explain what could not
be seen. Throughout the seventeenth and eighteenth cen-
turies there prevailed a theory of preformation. The be-
lievers in this theory, men like Bonnet and Haller, main-
tained the preformations of the organism and all its parts
within the egg. They regarded the apparent new forma-

HEREDITY

247

tion of organs during development as an illusion, and
held that development was merely an unfolding of this
preformed miniature. Moreover, they believed that the
germ contained not only a preformation of the organism
into which it was to grow, but of successive generations
as well. To quote from Thomson : "Preformed miniature
lay within preformed miniature in ever-increasing minute-

Fig- 35 — Segmentation of an Ovum.
Showing two, four, eight-cell and later stages. (Sedgwick and
Wilson.)

ness, as if in a conjurer's box. Thus it was computed that
Mother Eve must have included over 200,000 millions
of homunculi, or sometimes it was Adam who was made
to bear this burden. For according to one party, the
ovists — e.g., Malpighi — it was the ovum that contained the
miniature which had to be unfolded; while according to
others — the animalculists — it was the sperm which con-
tained the preformed model." But how the germ came to
have this preformed model they could not tell.

248 BIOLOGY

Caspar Friedrich Wolff was the first to raise a strong
protest against the speculations of the preformationists
and to advance a new theory. Appealing to facts, he
showed that in the early stages of the chick's development
there was no visible hint of a preformed miniature, but
that various organs made their appearance successively
and gradually and were to be seen being formed. He held
that there is a new formation, or 'epigenesis.' But how
the germ that seems to start anew every time can develop
as it does the upholders of the theory of epigenesis could
not tell. For their ultimate explanations of heredity both
schools fell back on the assumption of hyperphysical agen-
cies as the earlier theorists had done before them.

Passing from these mystical interpretations of the phe-
nomena of heredity, there are a whole series of theories
which are in varying degrees scientific and may be fairly
described by the general designation pangenetic. Thom-
son in 'The Science of Life' and in 'Heredity' gives good
accounts of the various theories of heredity. From these
works the material in this section has been taken. These
theories all have this in common, that they seek to ex-
plain the uniqueness of the germ-cell by regarding it as a
center of contributions from different parts of the organ-
ism— a collection of samples from the various organs.
Spencer, Darwin, Jager, Galton, Brooks and others at one
time or another contributed toward these theories.

In 1864 Spencer suggested the existence of 'physiologi-
cal units' derived from and capable of development into
cells, and supposed that they accumulated in the germ-
cells, which thus became in a conceivable sense miniature
organisms. The best-known theory of this class is the
'provisional hypothesis of pangenesis' enunciated by Dar-
win in 1868. The main suggestions of this theory are as
follows :

Every cell of the body, not too highly differentiated,
throws off characteristic gemmules;

HEREDITY 249

These multiply by fission, retaining their characteris-
tics;

They become specially concentrated in the reproductive
elements in both sexes;

In development the gemmules unite with others like
themselves, and grow into cells like those from which they
were originally given off, or they remain latent during
development through several generations.

By means of this theory Darwin attempted to explain
not only the simpler facts of heredity, but also "those very
curious but abundant cases in which a character is trans-
mitted in a latent form and at last reappears after many
generations, such cases being known as 'atavism,' or 're-
version' ; and again, those cases of latent transmission in
which characteristics special to the male are transmitted
to the male offspring through the female parent without
being manifest in her; and yet again, the appearance at a
particular period of life of characters inherited and re-
maining latent in the young organism," as Lankester ex-
presses it.

The great defect of this theory is obviously its entirely
hypothetical character — no one has ever observed any
gemmules. Moreover, it is not in harmony with the re-
sults of experiments — e.g., on transfusion of blood — or with
what is known of the physiology of cells or with the facts
of experimental inheritance.

The next theory to be noted is the theory of Genetic or
Germinal Continuity. This theory was first suggested by
Owen in 1849. Since then Hackel, Jager, Brooks, Galton,
Nussbaum, Weismann, and a score of others have con-
tributed toward it.

In its earlier conception this germinal continuity con-
sisted in a continuity of germ-cells. A summary of this
idea follows.

At an early stage in the embryo, the future reproductive
cells of the organism are often distinguishable from those
which are forming the body.

250 BIOLOGY

The latter develop in manifold variety and lose almost
all likeness to the mother germ.

The former — the reproductive rudiments — are not im-
plicated in the differentiation of the 'body/ remain vir-
tually unchanged, and continue the protoplasmic tradition
unaltered.

As the sex-cells of the offspring are thus continuous
with the parental sex-cells which give rise to it, they will
in turn develop into similar organisms.

In this view the reproductive cells form a continuous
chain and the reproduction of like by like is natural and
necessary. But a serious difficulty besets this doctrine, for
a direct chain of cellular continuity can only be said to
exist in a few cases. Thus this theory of the continuity
of the germ-cells has been replaced by the newer theory
of the continuity of the germ-plasm.

This is Weismann's theory. Weismann has worked it
out in the minutest details. The problems which he dis-
cusses are too intricate and technical for any but a special
student. For present purposes a very brief summary as
expressed by Thomson will be sufficient.

"A living creature usually takes its origin from a fer-
tilized egg-cell, from a union of an ovum and a spermato-
zoon. These germ-cells are descended by a continuous
cell-division from the fertilized ova which gave rise to the
two parents; they have retained the organization of the
fertilized ova, and this organization has its vehicle in the
chromatin of the nucleus — the germ-plasm. This germ-
plasm consists of several chromosomes or idants, each of
which is made up of several pieces or ids, each of which
(here hypothesis begins) is supposed to contain all the
potentialities — generic, specific, and individual — of a new
organism. Each id is a microcosm with an architecture
which has been elaborated for ages ; it is supposed to con-
sist of numerous determinants, one for each part of the
organism that is capable of varying independently or of
being independently expressed during development.

HEREDITY 251

Lastly, each determinant is pictured as consisting of a
number of ultimate vital particles of biophores, which are
eventually liberated in the cytoplasm of the various em-
bryonic cells. All these units of various grades are ca-
pable of growth and of multiplication by division."

In its more general aspects this view of Weismann's
represents what might be called the dominant modern
view. That is, there is general belief that the germ-cell
inherits from the parental germ-cells an organization of
great complexity, including an intricate architecture of
minute particles which are the material bearers of particu-
lar inheritance qualities. Not all biologists, however, agree
with Weismann in his limitation of the inheritance ma-
terial to the chromosomes. It is here that the inheritance
problems of to-day have their beginning.

Much attention has in recent years been given to the
experimental study of variation and heredity. These ex-
periments are of interest in connection with Mendel's law,
a law so important in the science of biology that Professor
Bateson has written of it, "The experiments which led
to this advance in knowledge are worthy to rank with
those that laid the foundation of the atomic laws of chem-
istry." The discoverer of this law was Gregor Johann
Mendel (1822-1884), an Augustinian monk. He was a
man of varied interests, and in his gardens performed
many hybridization experiments on plants. In 1866 he
published a paper giving the results of his experiments,
entitled 'Experiments in Plant Hybridization.' This paper
did not attract much attention at the time, probably be-
cause of the enthusiasm and the controversy evoked by the
natural selection theory, and lay practically unknown in
the Proceedings of the Natural History Society of Briinn
for over thirty years. A revival of interest in the ex-
perimental study of variation and heredity at about the
beginning of the present century led to the rediscovery
of the Mendelian principles of heredity by several bota-
nists working separately, and about that time Bateson

252 BIOLOGY

"brought into prominence Mendel's work and by a long
series of experiments confirmed and extended it.

To gain an idea of the scope of these principles one
cannot do better than turn to Mendel's own account of his
experiments. Punnett's 'Mendelism' and Thomson's 'He-
redity' give such an account, and from these sources the
following statements have largely been taken.

In the selection of a plant for experiment Mendel recog-
nised that two conditions must be fulfilled. In the first
place, the plant must possess differentiating characters,
and secondly, the hybrids must be protected from the in-
fluence of foreign pollen during the flowering period. In
the edible pea Mendel found an almost ideal plant to
work with. The separate flowers are self-fertilizing,
while complications from insect-interference are practi-
cally non-existent. As is well known, there are numer-
ous varieties of the eating-pea exhibiting characters to
which they breed true. In some varieties the seed color is
yellow, while in others it is green. In some varieties the
seeds are round and smooth when ripe; in others they are
wrinkled. Some peas have purple, others have pure
white flowers. Some peas again, when grown under or-
dinary conditions, attain to a height of 6 to 7 feet, while
others are dwarfs which do not exceed 1^2 to 2 feet.

Mendel selected a certain number of such differentiat-
ing characters and investigated their inheritance sepa-
rately for each character. Thus in one series of experi-
ments he concentrated his attention on the heights of the
plants. Crosses were made between tall and dwarf va-
rieties, which previous experience had shown to come true
to type with regard to these characters. It mattered not
which was the pollen-producing and which the seed-bear-
ing plant. In every case the result was the same. Tall
plants resulted from the cross. For this reason Mendel
applied the terms 'Dominant' (D) and 'Recessive' (R)
to the tall and dwarf habits respectively.

In the next generation the cross-bred plants (products

HEREDITY

255

of D and R or R and D, but all apparently like D) were
allowed to fertilize themselves, with the result that their
offspring exhibited the two original forms, on the average
three dominants to one recessive. Out of 1,064 plants,
787 were tall, 277 were dwarfs.

When these recessive dwarfs were allowed to fertilize
themselves they gave rise to recessive dwarfs only for any
number of generations. The recessive character bred
true.

When the dominants, on the other hand, were allowed

e©

ffcttttl«a/_. _J £gg. Cell

eeocDieecDCD
e®©0

Fig- 37 — Segregation of Germ-cells.
D., dominant parent ; R., recess of parent. The fertilized egg-
cell, showing both qualities, "tallness" (1) and "dwarf ness'*
(2), develops into an "impure" dominant. Suppose this plant
to produce 4 egg-cells and 4 male-cells. The mature egg-
cells consist of 2 sets — 2 with potential quality of "tall-
ness," 2 with potential quality of "dwarfness." The mature
male-cells also consist of 2 sets — 2 with the potential quality
of "tallness," 2 with the potential quality of "dwarfness."
What are the chances of fertilization? The result must be
as indicated. In other words, D. — 2 (D.) — R.

254 BIOLOGY

to fertilize themselves, they produced one-third of 'pure7
dominants (producing dominants only when self-fertil-
ized) and two-thirds of cross-bred dominants, which on
self-fertilization again gave rise to a mixture of dominants
and recessives in the proportion of 3: 1.

If in an experiment with mice a gray house-mouse is
crossed with a white mouse, the offspring are all gray.
Grayness is dominant ; albinism is recessive. The gray
hybrids are inbred; their offspring are gray and white in
the proportion 3:1. If these whites are inbred they
show themselves 'pure/ for they produce whites only for
subsequent generations. But when the grays are inbred
they show themselves of two kinds, for one-third of them
produce only grays, which go on producing grays; while
the other two-thirds, apparently the same, produce both
grays and whites. And so it goes on.

In his exceedingly clear exposition of Mendelism
(1905) R. C. Punnett states the result thus: " Wherever
there occurs a pair of differentiating characters, of which
one is dominant to the other, three possibilities exist:
there are recessives which always breed true to the re-
cessive character; there are dominants which breed true
to the dominant character, and are therefore pure; and
thirdly, there are dominants which may be called impure,
and which on self-fertilization (or inbreeding, where the
sexes are separate) give both dominant and recessive
forms in the fixed proportion of three of the former to
one of the latter."

To explain such phenomena Mendel suggested that the
hybrid produces in equal numbers two kinds of germ-cells
(two kinds of egg-cells or two kinds of pollen-grains) —
that there is is in the developing reproductive organ a
segregation of germ-cells into two equal camps, one camp
■with the potential quality of tallness, the other camp with
the potential quality of dwarfness. Thus, if there are six
ovules, three contain in their egg-cell the primary con-
stituent corresponding to tallness, and three contain the

HEREDITY

255

primary constituent corresponding to dwarfness. Each
of these is pollinated by a pollen-grain, which, by hypothe-
sis, contains the potential quality of tallness or of dwarf-
ness; and if the two kinds of pollen-grains are present in
equal numbers, each ovule has an equal chance of being
fertilized by a pollen-grain with a potential quality of
tallness or by a pollen-grain with a potential quality of
dwarfness. Therefore the result must be a set of off-

D x. R

[D]

D [D] [D] R

D DHJHK DMpp D

Fig. 36 — Mendelian Inheritance in Peas.
D., tall plant of pure strain; R., dwarf plant of pure strain; (D.),
tall plant in which the dwarf character is latent; (D.), plants
when self-fertilized produce plants in the following propor-
tion: 1 D., 2 (D.), 1 R. (Punnett.)

spring partly dominant and partly recessive in the pro-
portions of 3 : 1.

Mendel discovered an important set of facts, and he also
suggested a theoretical interpretation — the theory of
gametic segregation. As Bateson says, "The essential part
of the discovery is the evidence that the germ-cells or

256 BIOLOGY

gametes produced by cross-bred organisms may in respect
of given characters be of the pure parental types, and
consequently incapable of transmitting the opposite char-
acter; that when such pure similar gametes of opposite
sexes are united in fertilization, the individuals so formed
and their posterity are free from all taint of the cross;
that there may be, in short, perfect or almost perfect dis-
continuity between these germs in respect of one of each
pair of opposite characters."

This law of the segregation of gametes accords well
with the experimental and observed phenomena of hered-
ity. But this brings up the question, Is there any known
process by which such a segregation could be brought
about during the history of the germ-cells? "Is it," says
Thomson, "enough simply to say that the germ-cells are
little living unities with an organization, an equilibrium of
their own, and that they tend as they multiply to become
more stable — namely, by separating out incompatibilities
(dominant and recessive potential unit characters) and
becoming the vehicle of either the one or the other? Are
there differential divisions during the development of the
germ-cells which lead to there being two camps of gam-
etes which we may briefly describe as pure potential domi-
nants and pure potential recessives ? Is this not a possible
expression of a struggle between the hereditary items and
in line with Weismann's theory of germinal selection?"

"A more precise suggestion," says T. H. Morgan, "to
which it seems too soon to attach great significance, is the
fascinating hypothesis that the segregation occurs during
the maturation division. If we assume that the chromo-
somes are the vehicles of the hereditary qualities, which
seems highly probable; if we assume, further, that a par-
ticular potential unit character is contained in each germ-
cell in one chromosome and not in others, which seems
a difficult assumption; then it is possible that Sutton may
be correct in his suggestion that the segregation of

HEREDITY 257

gametes into two sets occurs in the course of the matura-
tion division."

A great deal of work confirming Mendel's experiences
has been done both with plants and animals in laborato-
ries in many countries, with the result that altho there are
some difficulties and not a few discrepancies, "the truth
of the law," as Bateson says, "is now established for a
large number of cases of most dissimilar character."

On the other hand, there has been much experimenta-
tion in which the results do not harmonize with the Men-
delian results. Thomson says : "There seems at present
no reason to believe that the Mendelian formula has more
than a limited application, tho it is of course possible
that apparent exceptions may eventually turn out to be
less formidable than they seem. There seems no reason
why there should not be several formulae of inheritance,
each applicable to particular sets of cases — e.g., to cases
where blending does occur and to cases where it never
occurs. As the method of experiment is obviously the
surest line of progress, the more it is prosecuted the sooner
will the mists surrounding heredity disappear, but prog-
ress cannot be secured by ignoring difficult cases or by
straining the formula in the eager desire to universalize
it."

Extensive theoretical and practical applications of Men-
del's law to problems of biology have been made. For the
technical discussion of Mendel's law in connection with
persistence in evolution and in relation to definite varia-
tions, reference must be made to some of the detailed
studies on Mendelism. The following illustrations from
Thomson and from Punnett will show its value to prac-
tical breeders.

Some kinds of wheat are very susceptible to the fun-
goid disease known as 'rust' ; others are immune. The
quality of immunity to rust is recessive to the quality of
predisposition to rust. When an immune and a non-im-
mune strain are crossed together the resulting hybrids are

258 BIOLOGY

all susceptible to 'rust.' On self-fertilization such hy-
brids produce seed from which appear dominant 'rusts'
and recessive immune plants in the expected ratio of 3 : 1.
From this simple experiment the phrase 'resistance to dis-
ease' has acquired a more precise significance, and the
wide field of research here opened up in this connection
promises results of the utmost practical as well as theoreti-
cal importance.

"The new science of heredity has much to teach the
practical man," says Punnett. "Let us suppose that he
has two varieties, each possessing a desirable character,
and that he wishes to combine these characters in a third
form. He must not be disappointed if he makes his cross
and finds that none of the hybrids approach the ideal which
he has set before himself; for if he raises a further gener-
ation he will obtain the thing which he desires. He may,
for example, possess tall green-seeded and dwarf yellow-
seeded peas, and may wish to raise a strain of green
dwarfs. He makes his cross — and nothing but tall yel-
lows result. At first sight he would appear to be further
than ever from his end, for the hybrids differ more from
the plant at which he is aiming than did either of the
original parents.

"Nevertheless, if he sow the seeds of these hybrids he
may look forward with confidence to the appearance of
the dwarf green. And owing to the recessive nature of
both greenness and dwarfness, he can be certain that for
further generations the dwarf greens thus produced will
come true to type. The green dwarfs are all fixed as soon
as they appear, and will throw neither tails nor yellows.
The less the hybrid resembles the form at which the
breeder aims, the more likely is that form to breed true
when it appears in the next generation.

In the years since 1900 there has been deep interest in
the microscopic study of germ-cells in the search for the
mechanism of heredity. Much observation and experi-
mentation has been done and there has been a rapid ad-

HEREDITY 259

vance in knowledge, but so intricate are the questions in-
volved that investigation is most difficult and only a start
at the problems has been made. In an address before the
American Association for the Advancement of Science in
December, 1907, E. G. Conklin well summarizes the argu-
ments in support of the two general views under which
opinions concerning the material bearers of inheritance
may be said to be grouped, namely, the view that the
chromosomes of the germ-cell are the bearers of heredity
and the view that inheritance may take place through the
cytoplasm of the germ-cells. A few of the less technical
paragraphs of this paper are as follows:

"In practically all theories of heredity it is assumed that
there is a specific 'inheritance material,' distinct from the
general protoplasm, whose function is the 'transmission'
of hereditary properties from generation to generation,
and whose characteristics, as compared with the general
protoplasm, are greater stability, independence and con-
tinuity. This is the Idioplasm of Nageli, the Germ-plasm
of Weismann. It is further assumed that this germ-
plasm is itself composed of ultramicroscopical units, which
are capable of undergoing transformation during the
course of development into the structures of the adult.
However necessary such units may be for a complete
philosophical explanation of development, it must be con-
fessed that at present they constitute a purely hypotheti-
cal system which may or may not correspond to reality.
We know that the germ-cells are exceedingly complex,
that they contain many visible units such as chromosomes,
chromomeres and microsomes, and that with every great
improvement in the microscope and in microscopical tech-
nique other structures are made visible which were in-
visible before, and whether the hypothetical units just
named are present or not seems to be a matter of no great
importance, seeing that, so far as the analysis of the mi-
croscope is able to go, there are differentiated units which

26o BIOLOGY

are combined into a system — in short, there is organiza-
tion.

"On the other hand, the evidence in favor of an inherit-
ance material, which is distinct from the general proto-
plasm of the germ and whose function is the reproduc-
tion of hereditary characters, is not convincing. All the
living substance of the egg cell is converted into the ma-
'ture organism. That there is a species plasm or an indi-
vidual plasm which is continuous from generation to gen-
eration, and from which all the qualities of the mature
organism are differentiated, is almost a certainty, but
there is no satisfactory evidence that this substance is dis-
tinct from the general protoplasm of the young germ-
cells.

"Differentiation, and hence heredity, consists in the
main in the appearance of unlike substances in proto-
plasm and their localization in definite regions or cells.

"Unfortunately, we do not know many of the steps
by which different substances appear within protoplasm.
But in all cases which have been carefully studied one
significant fact appears, viz., the importance of the inter-
action of the nucleus and cytoplasm. In many cases vari-
ous substances have been seen to come out of the nucleus
and to mingle with the cytoplasm, while the nucleus in
turn absorbs substances from the cytoplasm. It is known
that constructive metabolism, differentiation and regenera-
tion never occur in the absence of a nucleus.

"Turning now to the differentiations of the fertilized
egg cell, we find that different substances appear in the
egg cell and become localized in different regions of the
egg or embryo. It is known that there is an active inter-
change of nuclear and cytoplasmic substances. In the long-
growth period of the egg the nucleus grows enormously,
evidently at the expense of substances received from the
cell body. On the other hand, it is well established that
substances issue from the nucleus into the cell body and
mingle with the cytoplasm during this stage.

HEREDITY 261

"Finally, we may conclude that the nucleus plays a less
important role in the localization of different substances
than in the formation of those substances. Nevertheless,
in differentiation, as well as in metabolism, there is every
reason to believe that the entire cell is a physiological unit.
Neither the nucleus nor the cytoplasm can exist long in-
dependently of the other; differentiations are dependent
upon the interaction of these two parts of the cell ; the
entire germ-cell, and not merely the nucleus or cytoplasm,
is transformed into the embryo or larva; and it therefore
seems necessary to conclude that both nucleus and cyto-
plasm are involved in the mechanism of heredity.

"It may be considered as definitely settled that the early
development of animals is of purely maternal type, and
that it is only after the broad outlines of development and
the general type of differentiation have been established
that the influence of the spermatozoon begins to make
itself felt; and it is equally certain that this type of dif-
ferentiation is predetermined in the cytoplasm of the ma-
ture egg cell rather than in the egg nucleus.

"On the other hand, there is no doubt that the differ-
entiations of the egg cytoplasm have arisen, in the main,
during the ovarian history of the egg, and as a result of
the interaction of nucleus and cytoplasm; but the fact
remains that at the time of fertilization the hereditary
potencies of the two germ-cells are not equal, all the early
development, including the polarity, symmetry, type of
cleavage, and the relative positions and proportions of
future organs, being predetermined in the cytoplasm of
the egg-cell, while only the differentiations of later de-
velopment are influenced by the sperm. In short, the egg
cytoplasm fixes the type of development and the sperm
and egg nuclei supply only the details.

"This conclusion is not a refutation of the nuclear in-
heritance theory, but it is a profound modification of it.
At once it destroys the argument that since there is
equality of inheritance from both parents there must be

262 BIOLOGY

equivalence of inheritance material in egg and sperm. So
far as those characteristics are concerned which appear
late in development, it is highly probable that there is
equality of inheritance from both parents, but in the early
and main features of development, hereditary traits, as
well as material substance, are derived chiefly from the
mother.

"In the light of the conclusion that only the later and
more detailed differentiations are influenced by the sperm,,
it follows that experimental work which aims to modify
the fundamental features of an organism must be directed
to the ovarian egg rather than to the sperm or to the de-
veloping embryo."

In conclusion, the following paragraphs from E. B.
Wilson's 'The Cell in Development and Inheritance' will
indicate the present state of the cytological study of in-
heritance problems and the outlook for the future. "We
have now arrived," he says, "at the farthest outposts of
cell-research, and here we find ourselves confronted with
the same unsolved problems before which the investigators
of evolution have made a halt. For we must now inquire
what is the guiding principle of embryological develop-
ment that correlates its complex phenomena and directs
them to a definite end. However we conceive the special
mechanism of development, we cannot escape the con-
clusion that the power behind it is involved in the struc-
ture of the germ-plasm inherited from foregoing genera-
tions.

"What is the nature of this structure and how has it
been acquired? To the first of these questions we have
as yet no certain answer. The second question is merely
the general problem of evolution stated from the stand-
point of the cell-theory. The first question raises once
more the old puzzle of preformation or epigenesis. The
pangen-hypothesis of de Vries and Weismann recognises
the fact that development is epigenetic in its external
features ; but, like Darwin's hypothesis of pangenesis, it is

HEREDITY 263

at bottom a theory of preformation, and Weismann ex-
presses the conviction that it is an impossibility.

"The truth is that an explanation of development is at
present beyond our reach. The controversy between pre-
formation and epigenesis has now arrived at a stage
where it has little meaning apart from the general prob-
lems of physical causality. What we know is that a spe-
cific kind of living substance, derived from the parent,
tends to run through a specific cycle of changes during
which it transforms itself into a body like that of which it
formed a part; and we are able to study with greater or
less precision the mechanism by which that transforma-
tion is effected and the conditions under which it takes
place. But despite all our theories, we no more know
how the organization of the germ-cell involves the prop-
erties of the adult body than we know how the properties
of hydrogen and oxygen involve those of water. So long
as the chemist and physicist are unable to solve so simple
a problem of physical causality as this, the embryologist
may well be content to reserve his judgment on a problem
a hundredfold more complex.

"The second question, regarding the historical origin
of the idioplasm, brings us to the side of the evolution-
ists. The idioplasm of every species has been derived, as
we must believe, by the modification of a preexisting idio-
plasm through variation and the survival of the fittest.
Whether these variations first arise in the idioplasm of the
germ-cells, as Weismann maintains, or whether they may
arise in the body-cells and then be reflected back upon the
idioplasm, is a question to which the study of the cell has
thus far given no certain answer. Whatever position we
take on this question, the same difficulty is encountered,
namely, the origin of that coordinated fitness, that power
of active adjustment between internal and external rela-
tions, which, as so many eminent biological thinkers have
insisted, overshadows every manifestation of life. The

264 BIOLOGY

nature and origin of this power is the fundamental prob-
lem of biology.

"It may be true, as Schwann himself urged, that the
adaptive power of living beings differs in degree only,
not in kind, from that of unorganized bodies. It is true
that we may trace in organic nature long and finely grad-
uated series leading upward from the lower to the higher
forms, and we must believe that the wonderful adaptive
manifestations of the more complex forms have been de-
rived from simpler conditions through the progressive
operation of natural causes. But when all these admis-
sions are made, and when the conserving action of nat-
ural selection is in the fullest degree recognised, we can-
not close our eyes to two facts: first, that we are utterly
ignorant of the manner in which the idioplasm of the
germ-cell can so respond to the influence of the environ-
ment as to call forth an adaptive variation; and second,
that the study of the cell has on the whole seemed to
widen rather than to narrow the enormous gap that sep-
arates even the lowest forms of life from the inorganic
world.

"I am well aware that to many such a conclusion may
appear reactionary or even to involve a renunciation of
what has been regarded as the ultimate aim of biology.
In reply to such a criticism, I can only express my con-
viction that the magnitude of the problem of development,
whether ontogenetic or phylogenetic, has been under-
estimated; and that the progress of science is retarded
rather than advanced by a premature attack upon its ulti-
mate problems. Yet the splendid achievements of cell-
research in the past twenty years stand as the promise of
its possibilities for the future, and we need set no limit to
its advance. To Schleiden and Schwann the present
standpoint of the cell-theory might well have seemed unat-
tainable. We cannot foretell its future triumphs, nor can
we doubt that the way has already been opened to better
understanding of inheritance and development."

CHAPTER XVI

ADAPTATION

Altho but one element of organic evolution, the origin
of species, has been emphasized in the preceding pages, it
has been noticed perhaps in the various discussions brought
up that evolution is concerned not only with the great
variety of life kinds, but also with the "adaptedness or
adaptiveness of life kinds" to various sorts of life-condi-
tions. As Kellogg phrases it, "The task of an evolution
explanation is a double one; it must explain not only
diversity or variety in life, but adaptive diversity or
variety."

The most striking fact in nature is this adaptation of
organisms to their environment. On every side plants and
animals seem to be well fitted to their particular places in
nature. Every organism seems to have been constructed
after an ideal plan, and it is not surprising that so many
observers of nature have believed that plants and animals
were specially designed and created to fit the places in
nature which they fill. Verworn says:

"The fact of purposefulness in living nature, which was
so marvelous to men of science in early times even down
to the middle of the present century, forced them con-
stantly to embrace teleology — i.e., the hypothesis of a fore-
ordained plan of creation, such as dogmatic theology,
preserving faithfully the ancient venerated ideas, accepts
to-day. This purposefulness in nature is the simple ex-
265

266 BIOLOGY

pression — or, better, the result — of the adaptation of or-
ganisms to their vital conditions in the widest sense."

Thus all animals have their essential organs adapted to
habitat, food and various conditions of environment.
Fishes have limbs in the form of fins, which function
very perfectly as rowing-organs; terrestrial vertebrates
have in place of fins legs for walking and creeping upon
dry land ; birds have wings constructed most fittingly with
which their light bodies, supported by bones containing
air, soar through the air so perfectly that imitation of them
is difficult.

Likewise plants are so perfectly adapted to their sur-
roundings in the general plan and arrangement of root,
stem, leaf, flower, etc., that only the special student is
likely to recognise the adaptation. In fact, these general
adaptations of organs and functions of plants and animals
are so universal that they have ceased to excite wonder
and are taken as necessary phenomena of life. They are
necessary phenomena of life, for general adaptations are
as natural as breathing, eating and so on.

In addition to the general adaptations to widespread
conditions of environment — e.g., to the general conditions
under which all land animals and plants or all aquatic ani-
mals and plants must live — there are myriads of special
adaptations. For example, all fishes living in fresh water
have in common general adaptations to an aquatic life, but
fishes living in caverns have in addition to the general
adaptations certain special adaptive modifications in ac-
cordance with their special environment, especially in the
eyes, which are profoundly modified in accordance with a
life spent habitually in darkness. Likewise all plants
living on land have a general adaptation to terrestrial life,
but in addition many have special adaptations. All plants
which have green leaves use them for starch formation
under the action of sunlight, but special adaptations fit
certain species to different degrees of light intensity, and as

ADAPTATION 267

a result one plant may be fitted to grow in open fields while
another will grow but in shaded places.

Special adaptations have attracted much attention from
students because by contrast with general adaptations they
prove valuable in evolutionary studies. For the sake of
convenience the special adaptations of plants and animals
will be considered separately, and also color adaptations
will be treated in a separate section. However, this is
purely an arbitrary division, for all studies of the special
adaptations of plants and animals lead to the same con-
clusion— namely, that these adaptations have originated
through the processes of evolution.

One of the best collections of facts concerning special
adaptations is to be found in the extended chapter on this
subject in Jordan and Kellog's 'Evolution and Animal
Life,' from which some of the most striking examples have
been selected for use here.

The various types of special adaptations may be roughly
divided into five classes as follows: Food-securing, self-
defense, defense of young, rivalry and adjustment to sur-
roundings.

"For the purpose of capture of their prey, most carnivor-
ous animals are provided with strong claws, sharp teeth,
hooked beaks and other structures familiar to us in the
lion, tiger, dog, cat, owl and eagle. Insect-eating mammals
have contrivances especially adapted for the catching of
insects. The ant-eater, for example, has a long sticky
tongue which it thrusts forth from its cylindrical snout
deep into the recesses of the ant-hill, bringing it out with
its surface covered with ants. Animals which feed on
nuts are fitted with strong teeth or beaks for cracking
them. Strong teeth are found in those fishes which feed
on crabs or sea urchins. Those mammals like the horse
and cow, that feed on plants, have usually broad chisel-
like incisor teeth for cutting off the foliage, and teeth of
very similar form are developed in different groups of
plant-eating fishes. Molar teeth are found when it is nee-

268

BIOLOGY

essary that the food should be crushed or chewed, and the
sharp canine teeth go with a flesh diet. The long neck of
the giraffe enables it to browse on the foliage of trees in
grassless regions.

"Insects like the leaf-beetles and the grasshoppers, that
feed on the foliage of plants, have a pair of jaws, broad

Fig. 38 — Adaptation for Food-getting.

Head of a mosquito (female), showing the piercing, needle-like

mouth parts composing the "bill." (Joraan and Kellogg.)

but sharply edged, for cutting off bits of leaves and stems.
Those which take only liquid food, as the butterflies and
sucking bugs, have their mouth parts modified to form a
slender, hollow sucking beak or proboscis, which can be
thrust into a flower nectary or into the green tissues of
plants or the flesh of animals to suck up nectar or plant
•sap or blood, according to the special food habits of the

ADAPTATION 269

insect. The honey-bee has a very complicated equipment
of mouth parts fitted for taking either solid food like pollen
or liquid food like the nectar of flowers. The mosquito
has a 'bill' composed of six sharp, slender needles for
piercing and lacerating the flesh and a long tubular under
lip through which the blood can flow into the mouth. Some
predaceous insects, as the praying horse, have their fore
legs developed into formidable grasping organs for seizing
and holding their prey.

"For self-protection the higher animals depend largely
on the same organs and instincts as for the securing of
food. Carnivorous beasts use tooth and claw in their own
defense, as well as in securing their prey, but these, as
well as other animals, may protect themselves in other
fashions. Many of the higher animals are provided with
horns, structures useless in procuring food but effective
as weapons of defense. Others defend themselves by blows
with their strong hoofs. Among the reptiles and fishes
and even among the mammals the defensive coat of mail
is found in great variety. The crab an3 lobster, with claws
and carapace, are well defended against their enemies, and
the hermit crab, with its well-knowl habitude of thrust-
ing its unprotected body within a cast-off shell of a sea
snail, finds in this instinct a perfect defense. Insects also,
especially beetles, are protected by their coats of mail.
Scales and spines of many sorts serve to defend the bodies
of reptiles and fishes, while feathers protect the bodies of
birds and hair those of most mammals."

The ways in which animals make themselves disagree-
able or dangerous to their captors are almost as varied as
the animals themselves. Besides the teeth, claws and
horns of ordinary attack and defense, there are found
among the mammals many special structures or contriv-
ances which serve for defense through making their pos-
sessors unpleasant.

The turtles are all protected by bony shields, and some
of them, the box turtles, may close their shields almost

270 BIOLOGY

hermetically. The snakes broaden their heads, swell their
necks or show their forked tongues to frighten their ene-
mies. Some of them are further armed with fangs con-
nected with a venom gland, so that to most animals their
bite is deadly.

Even the fishes have many modes of self-defense
through giving pain or injury to animals who would swal-
low them. The catfish, or horned pout, when attacked
sets immovably the sharp spine of the pectoral fin, inflict-
ing a jagged wound. Pelicans which have swallowed a
catfish have been known to die of the wounds inflicted by
the fish's spine. In the group of scorpion fishes and toad
fishes are certain genera in which these spines are pro-
vided with poison glands. Many fishes are defended by a
coat of mail or a coat of sharp spines. The globe fishes
and porcupine fishes are for the most part defended by
spines, but their instinct to swallow air gives them an addi-
tional safeguard. When one of these fishes is disturbed
it rises to the surface, gulps air until its capacious stom-
ach is filled and then floats, belly upward, on the water.
It is thus protected from other fishes, tho easily taken by
man.

The torpedo, electric eel, electric catfish and star-gazer
surprise and stagger their captors by means of electric
shocks. The shock is felt severely if the fish be stabbed
with a knife or metallic spear. The electric eel of the
rivers of Paraguay and southern Brazil is said to give
severe shocks to herds of wild horses driven through the
streams, and similar accounts are given of the electric cat-
fisk of the Nile. In tropical seas the tangs, or surgeon
fishes, are provided with a knifelike spine on the side of
the tail, the sharp edge directed forward and slipping into
a sheath. This is a formidable weapon when the fish is
alive.

Other fishes defend themselves by spears (swordfish,
spearfish, sailfish), or by saws (sawfish, sawshark), or
by paddles (paddlefish). Others still make use of sucking

ADAPTATION 271

disks of one sort or another (as in the snailfish, the cling-
fish and the goby) to cling to the under side of rocks, or
as in the Remora, to the bodies of swift-moving sharks.
Blind fishes in the caves are adapted to their condition.
In similar circumstances salamanders, crayfishes and in-
sects are also blind. Some fishes, as the lancelet, lie buried
in the sand all their lives. Others, as the sand darter and
the hinalea, bury themselves in the sand at intervals to
escape from their enemies. Some fishes called the flying
fishes sail through the air with a grasshopper-like motion
that closely imitates true flight.

Among the insects the possession of stings is not un-
common. The wasps and bees are familiar examples of
stinging insects, but many other kinds less familiar are
similarly protected. All insects have their bodies covered
with a coat of armor, composed of a horny substance
called chitin. In some cases this chitinous coat is very
thick and serves to protect them effectually. This is espe-
cially true of the beetles. Some insects are inedible and
are conspicuously colored so as to be readily recognised
by insectivorous birds.

The protection of the young is the source of many adap-
tive structures as well as of the instincts by which such
structures are utilized. In general those animals are
highest in development, with the best means of holding
their own in the struggle for life, that take best care of
their young. Those instincts which lead to home building
are all adaptations for preserving the young. Among the
lower or more coarsely organized birds, such as the
chicken, the duck and the auk, as with the reptiles, the
young animal is hatched with well-developed muscular
system and sense organs and is capable of running about
and, to some extent, of feeding itself. Birds of this type
are known as praecocial, while the name altricial is applied
to the more highly organized forms, such as the thrushes,
doves and song birds generally. With these the young are
hatched in a wholly helpless condition, with ineffective

272 BIOLOGY

muscles, deficient senses and dependent wholly upon the
parent. The altricial condition demands the building of a
nest, the establishment of a home and the continued care
of one or both of the parents. In the Marsupials — the
kangaroo, opossum, etc. — the young are born in a very
immature state and are at once seized by the mother and
thrust into a pouch or fold of skin along the abdomen,
where they are kept until they are able to take care of
themselves. This is a singular adaptation, but less special-
ized and less perfect than the condition found in ordinary
mammals.

The movements of migratory fishes are mainly con-
trolled by the impulse of reproduction. Many fresh-water
fishes, as trout and suckers, forsake the large streams in
the spring, ascending the small brooks where their young
can be reared in greater safety. Still others, known as
anadromous fishes, feed and mature in the sea, but ascend
the rivers as the impulse of reproduction grows strong.
Among such fishes are the salmon, shad, alewife, sturgeon
and striped bass in American waters. Catadromous fishes,
as the true eel, reverse this order, feeding in the rivers
and brackish estuaries, apparently finding their usual
spawning ground in the sea.

In questions of attack and defense the need of fighting
animals of their own kind, as well as animals of other
races, must be considered. To struggles of species with
those of their own kind the term rivalry may be applied.
Actual warfare is confined mainly to males in the breeding
season, especially in polygamous species. Among those in
which the male mates with many females, he must struggle
with other males for their possession. The most notable
adaptation is seen in the superior size of teeth, horns,
mane or spurs. In the family of deer, buffalo and domestic
sheep and cattle the male is larger and more powerfully
armed than the female.

A large part of the life of the animal is a struggle with
the environment itself. In this struggle only those that are

ADAPTATION 273

adapted live and leave descendants fitted like themselves.
The fur of mammals fits them to their surroundings. As
the fur differs so may the habits change. Some animals
are active in winter; others, as the bear, and in northern
Japan the red-faced monkey, hibernate, sleeping in caves
or hollow trees or in burrows until conditions are favor-
able for their activity. Most snakes and lizards hibernate
in cold weather. Some animals in hibernation may be
frozen alive without apparent injury. As animals resist
heat and cold by adaptations of structure and habits, so
may they resist dryness. Certain fishes hold reservoirs
of water above their gills by means of which they can
breathe during short excursions from the water.

Another series of adaptations is concerned with the
places chosen by animals for their homes. The fishes that
live in the water have special organs for breathing under
water. The hooked claws of the bat hold on to rocks, the
bricks of chimneys or to the surface of hollow trees, where
the bat sleeps through the day. The tree frogs or tree
toads have the tips of the toes swollen, forming little pads
by which they cling to the bark of trees.

Among other adaptations relating to special surround-
ings or conditions of life are the great cheek pouches of the
pocket gophers, which carry off the soil dug up by the
large shovel-like feet when the gopher excavates its
burrow. Insects that live in water either come up to the
surface to breathe or take down air underneath their
wings, or in some other way, or have gills for breathing
the air which is mixed with the water. Many fishes, chiefly
of the deep seas, develop organs for producing light. These
are known as luminous organs, phosphorescent organs or
photophores.

While aming the higher or vertebrate animals, especially
the fishes and reptiles, most remarkable cases of adapta-
tion occur, yet the structural changes are for the most part
external, usually not affecting fundamentally the develop-
ment of the internal organs other than the skeleton. The

274 BIOLOGY

organization of these higher animals is much less plastic
than that of the invertebrates. In general the higher the
type the more persistent and unchangeable are those struc-
tures not immediately exposed to the influence of the
struggle for existence. It is thus the outside of an animal
that tells where its ancestors have lived. The inside, suf-
fering little change whatever the surroundings, tells the
real nature of the animal.

A special kind of adaptation is shown by animals which
are parasitic. These animals attach themselves to the
body of their prey or burrow into it, are carried about by
it and live upon it. Some parasites are adapted to an ex-
ternal parasitic life, such as bird lice, fleas, ticks, etc.;
others are adapted to an internal parasitic life, as is the
case in the tapeworm and trichina.

In nearly all cases the structure of the parasite is very
simple, much simpler than that of other animals which
live free, active lives. This simplicity, however, is not
primitive, but results from the degeneration of structures
rendered useless by the habit of life. Thus a fixed and
permanent parasite possesses no locomotor organs, no spe-
cial sense organs, no highly developed nervous system, no
alimentary system and but a very simple circulatory and
respiratory system. Lankester has well expressed the
effects of the parasitic habit of life: "Let the parasitic
life once be secured and away go legs, jaws, eyes and
ears; the active, highly gifted crab, insect or annelid may
become a mere sac, absorbing nourishment and laying
eggs."

This simplicity of structure in parasitic animals does
not, however, indicate that they belong to animals low in
the scale of animal life. It is rather the result of a mode
of life. This is shown by the fact that many parasites in
their young stages are free, active animals, very much
more complex in structure than they are in adult life.
Lankester's comparison of the life-history of the parasites
Sacculina and Lernaeocera with that of an active shrimp

Fig". 39 — Larv.3: and Adult Shrimp, Peneus; Showing Advan-
cing Complexity. (Lankester.)

2?6 BIOLOGY

will illustrate this point. Diagrams are given, showing the
advancing complexity of structure in the shrimp Peneus.

Compare these with the young stages of a number of
shrimp-like animals, viz., Sacculina, Lernseocera, Lepas,
Cyclops, Limnetis, some of which lead a parasitic life.
The eggs of all develop equally into the recapitulative
phase known as the Nauplius, but while the Nauplius of
the free-living shrimp grows more and more elaborate,
observe what happens to the parasites; they degenerate
into comparatively simple bodies, and this is true of their
internal structure as well as of their external appearance.
The most utterly reduced of these parasites is the curious
Sacculina, which infests hermit crabs and is a mere sac
filled with eggs, and absorbing nourishment from the
juices of its host by root-like processes.

Lernaeocera again, which in the adult condition is found
attached to the gills of fishes, has lost the well-developed
legs of its Nauplius childhood and become an elongated
worm-like creature fitted only to suck in nourishment and
carry eggs.

In this same group the life-history of the barnacle illus-
trates a similar degeneration not due to parasitism. This
again Lankester describes. Among these pictured Nauplii,
all belonging to the great group Crustacea, which includes
crabs and shrimps, is one which gives rise to an animal
decidedly degenerate but not precisely parasitic in its
habits. The tgg of the Barnacle gives rise to an actively
swimming Nauplius, the history of which is very aston-
ishing. After swimming about for a time the Barnacle's
Nauplius fixes its head against a piece of wood and takes
to a perfectly fixed, immobile state of life. Its organs of
touch and of sight atrophy, its legs lose their locomotor
function and are simply used for bringing floating particles
to the orifice of the stomach, so that an eminent naturalist
has compared one of these animals to a man standing on
his head and kicking his food into his mouth.

.Were it not for the recapitulative phases in the develop-

ADAPTATION

277

ment of the Barnacle, we may doubt whether naturalists
would ever have guessed that it was a degenerate Crusta-
cean. It was, in fact, for a long time regarded as quite
remote from them and placed among the snails and oysters.

»m PENEUS*1
rLERNAEOCBU ' 1 ' VI *

Fig. 40 — Nauplii of Various Crustacea.

Shrimps, water-fleas, barnacles, etc. (Lankester.)

Its true nature was only admitted when the young form
was discovered.

Very many other organisms among both plants and ani-
mals showing varying degrees of degenerative adaptation
might be cited. It should be noted in this connection that

278 BIOLOGY

degeneration in biology means an evolutionary method of
adaptation by means of which plants and animals are ad-
justed to special environmental conditions; it does not
mean weakness, decline, defects and decay in structural
and physiological conditions similar to those occurring in
human life. There is only a far-fetched analogous re-
semblance between human degeneration in the usual sense
and degeneration in biology which may be called adaptive
because as a result of such degeneration organisms are
better fitted for life under special conditions. In fact,
many naturalists believe that natural selection has often
preserved those individuals which because of certain de-
generations are better fitted to their life-conditions. Hence
adaptive degeneration in biology is a form of evolution,
and it is a highly significant fact that some species of ani-
mals and plants have been fitted to their special environ-
ment by adaptive degeneration.

It should be noted in passing that in animals and plants
there is non-adaptive and destructive degeneration that
is parallel to degeneration in human life. The effects of
disease in weakening and ultimately destroying animals
and plants is an example. In all such cases there is no
advantage gained which is exactly the case in the physio-
logical, mental and moral degeneration commonly referred
to in human life. Obviously adaptive degeneration has
occurred in human life, for the human body has dozens of
structures like the appendix which have been adapted by
a degenerative process.

Some of the most important special plant adaptations
are along these lines: nutritive adaptations, adaptations
for protection against animals, adaptations for pollination,
adaptations for the dispersal of fruits and seeds, and color
adaptations for attracting animals. Of the nutritive adap-
tations the parasitic habit of life in plants which draw
their food supply wholly or partially from another plant
or animal, called the host, should be mentioned. The
idodder shows an adaptation of this kind. It lives on the

ADAPTATION 279

stems of other plants, and instead of developing roots and
green leaves with which to carry on the processes of food
manufacture, it develops no green leaves but instead a
special absorbing organ, the 'haustoria,' which penetrates
the tissues of the host plant from which it obtains its
nourishment. There are many plants adapted to this para-
sitic habit of life; others are semi-parasitic. This is the
case with the mistletoe, the false foxgloves and with some
orchids.

A curious case of special nutritive adaptation is to be
found in carnivorous plants. These plants seem to require
animal food and have organs variously modified to obtain
it. In the common sundew insects are caught by a sticky
secretion which proceeds from hairs on the leaves. When
an insect touches one of these sticky hairs it is caught and
the hairs at once begin to close over it until it is held
fast on the leaf. Here it soon dies and then remains for
many days, while the leaf pours out a juice by which some
parts of the insect are digested. This digested material
is then absorbed, while the undigested parts drop off after
the hairs let go their hold. Other interesting adaptations
for the capture by plants of insects are to be found in the
Venus fly trap, the common pitcher plant and others.

Other modifications have been developed as a means of
protection from vegetable-feeding creatures. These are
chiefly along the lines of the formation of uneatable tissue,
as in the horsetails and rushes, the arming of exposed parts
with cutting edges, stinging hairs, prickles and thorns,
as in grasses, nettles, cactuses, etc., and the accumulation
of disagreeable or poisonous substances in exposed parts,
as in the tansy, ragweed, boneset, jimson weed and poison-
ous hemlock. One of the acacias (Acacia sphaerocephala)
has an interesting adaptation to attract ant dwellers as a
protection from insects and other creatures. At the bases
of the leaves there are developed large hollow stipules and
at the ends of the leaflets are nectaries. The ants bore
holes in the stipules, live in them, find food in the nectaries

280 BIOLOGY

and offer valuable protection to the plant in warding off
its enemies. A large number of plants offer inducements
of many sorts to attract ant visitors.

The special adaptations for the dispersal of seeds offer
an equally interesting field for study. It is obviously of
advantage to the plant that its seeds be disseminated as
widely as possible. Sometimes the seeds themselves are

Fig. 41 — Two Leaves of a Sundew.
In A. the glandulae hairs are fully extended ; in B. they are bent
inward in the position they assume when an insect has been
caught. (Kerner.)

modified for dispersal, sometimes the fruit in which they
are enclosed and often it is a larger part of the plant.
This is the case with the common tumbleweed, a pro-
fusely branching plant bearing many seeds which in the
fall is torn from its anchorage by the wind and rolled
about, scattering its seeds for great distances. Some fruits
which are distributed by the wind are provided with wings,
as in the maple, elm, ash, etc., while others bear plumes

Wound Parasite Growing on Bark of Tree.

ADAPTATION

281

and feathery tufts to enable them to float in the air, as in
the dandelions, thistles and others.

Not infrequently the adaptation for seed dispersal is in
the mechanical discharge provided for in the structure of
the seed-case. In such plants as the witch hazel, violet,
wild balsam and others the dry fruits burst with explosive

Fig. 42 — Seeds Adapted for Dispersal by Animals.
A., Cockle-bur; B., Burdock; C, Spanish Needles. (Kerner.)

force, throwing the seeds some distance away from the
parent plant.

When the adaptations are related to dispersal by means
of animals they take the form of grappling appendages, as
in the beggar ticks, stick tights, burdocks, cockleburs, etc.,
of hard seeds capable of passing through the digestive
tract unharmed or of attractive and brightly colored fruits
whose seeds are undesirable or indigestible. Good exam-
ples of conspicuously colored fruits whose seeds are scat-

282 BIOLOGY

tered in this way are cherries, raspberries, blackberries,
etc.

It will be noted that the color adaptations of plants re-
ferred to so far are supposed to relate plants to animals.
But aside from these, there are many general and special
adaptations in coloring substances, green, yellow and red,
which have a physiological value in plant life. These,
however, are special problems of botany and cannot be
referred to here.

The whole question of color adaptations in plants has
in recent years come up for rediscussion. This discussion
cannot be given here, but a good idea of the points at issue
can be gathered from the perusal of an essay entitled
'The Significance of Color' by Professor D. T. MacDougal,
of the Carnegie Institute.

In discussing the color adaptations of animals, it is con-
venient to group them in the following classes: Protec-
tive and aggressive resemblances; warning coloration;
mimicry and colors displayed in courtship.

The color pattern of animals is often such as to effectu-
all conceal them in their surroundings. Thus tree-dwell-
ing animals are often green in color, as is the case with
the tree-frog ; desert dwellers are often a mottled gray,
while arctic dwellers are a snowy white. Far more strik-
ing, however, than these cases of general color adaptation
are those cases of special adaptation in which the animal
resembles in color and shape some particular part of its
usual environment. Professors Jordan and Kellogg, in
'Animal Life,' give some good example of special color
adaptation. Among them are the following:

The larvae of the geometrid moths, called inch-worms
or span-worms, are twig-like in appearance and have the
habit, when disturbed, of standing out stiffly from the
twig or branch upon which they rest, so as to resemble in
position as well as in color and markings a short or a
broken twig. One of the most striking resemblances of
this sort is shown by a large geometrid larva found near

Fig. 43 — Protective Resemblance.
Larvae of geometrid moths concealed by their resemblance to
twigs. (Poulton.)

284

BIOLOGY

Ithaca, New York. The body of this caterpillar has a few
small, irregular spots or humps, resembling very exactly
the scars left by fallen buds or twigs. These caterpillars
have a special muscular development to enable them to
hold themselves rigidly for long times in this trying atti-

Fig. 44 — Protective Resemblance.
A 'leaf insect. A 'walking-stick' insect.

tude. They also lack the middle prop-legs of the body
common to other lepidopterous larvae, the presence of
which would tend to destroy the illusion so successfully
carried out by them. The common walking-stick, with its
wingless, greatly elongate, dull-colored body, is an excel-
lent example of special protective resemblance. It is quite

ADAPTATION 285

indistinguishable, when at rest, from the twigs to which it
is clinging. Another member of the family of insects to
which the walking-stick belongs is the famous green-leaf
insect. It is found in South America and is of a bright
green color, with broad leaf-like wings and bo3y, with
markings which imitate the leaf veins and small irregular
yellowish spots which mimic decaying, or stained, or
fungus-covered spots in the leaf.

There are many butterflies that resemble dead leaves.
But most remarkable of all is a large butterfly (Kallima)
of the East Indian region. The upper sides of the wings
are dark, with purplish and orange markings, not at all
resembling a dead leaf. But the butterflies when at rest
hold their wings together over the back, so that only the
under sides of the wings are exposed. The under sides
of Kallima's wings are exactly the color of a dead and
dried leaf, and the wings are so held that all combine to
mimic with extraordinary fidelity a dead leaf still attached
to the twig by a short pedicle or leaf-stalk imitated by a
short tail on the hind wings and showing mid-rib, oblique
veins, and, most remarkable of all, two apparent holes,
like those made in leaves by insects, but in the butterfly
imitated by two small circular spots free from scales and
hence clear and transparent. With the head and feelers
concealed beneath the wings, it makes the resemblance
wonderfully exact. In all cases of this kind the animals
are said to be protectively colored.

Special color resemblance sometimes does more than
conceal an animal from its enemies; it often assists it to
catch its prey. Such animals are said to be aggressively
colored or to have aggressive resemblance. The colors of
snakes, lizards and frogs are doubtless both protective and
aggressive, while those of the polar bear, the arctic fox,
the weasel, the wolf, the lion and the tiger are purely
aggressive. Poulton, in The Colors of Animals,' cites
some examples of a still more remarkable use of color
resemblance. He says:

286 BIOLOGY

"Special Aggressive Resemblance sometimes does more
than hide an animal from its prey; it may even attract frhe
latter by simulating the appearance of some object which
is of special interest or value to it. Such appearances have
been called Alluring Coloration by Wallace, and they are
some of the most interesting of all forms of Aggressive
Resemblance.

"An Asiatic lizard, Phrynocephalus mystaceus, is a good
example. Its general surface resembles the sand on which
it is found, while the fold of skin at each angle of the
mouth is of a red color and is produced into a flower-like
shape exactly resembling a little red flower which grows
in the sand. Insects, attracted by what they believe to be
flowers, approach the mouth of the lizard, and are of
course captured.

"The Angler, or Fishing Frog, possesses a lure in shape
of long, slender filaments, the foremost and longest of
which has a flattened and divided extremity. The fish
stirs up the mud so as to conceal itself and waves these
filaments about. Small fish are attracted by the lure, mis-
taking it for worms writhing about in the muddy waters;
they approach and are instantly engulfed in the enormous
mouth of the Angler.

"An Indian Mantis (Hymenopus bicornis) feeds upon
other insects which it attracts by its flower-like shape and
pink color. The apparent petals are the flattened legs of
the insect."

While many animals are very inconspicuously colored,
or are manifestly colored so as to resemble their surround-
ings, generally or specifically, many other animals are very
brightly and conspicuously colored and patterned. They
possess warning coloration. "A very common example of
an animal with warning colors," says Poulton, "is afforded
by the larva of the Currant Moth or Magpie Moth, which
is excessively abundant in gardens. The caterpillar is ex-
tremely conspicuous, being of a cream color, with orange
and black markings. Altho it belongs to the group of well-

ADAPTATION 287

concealed 'stick-caterpillars/ it makes no attempt to hold
itself in any of the attitudes characteristic of its group.
All observers agree that birds, lizards, frogs and spiders
either refuse this species altogether or exhibit signs of the
most intense disgust after tasting it."

The caterpillar of the Buff-tip Moth and the Cinnabar
Moth are also extremely abundant and are good examples
of the association of Warning Colors with a nauseous
taste. Both of them are gregarious, living in large com-
panies, so that their conspicuous appearance is greatly in-

Fig. 45 — Warning Coloration.
A salamander, showing gaudy coloring.

tensified. The colors of the first-named larva are black,
yellow and orange. It feeds on oak, elm, lime, birch, hazel,
etc., and the large bare branches which attest its appetite
are very familiar sights in autumn. The second caterpillar
is colored by alternate black and yellow rings; it feeds
upon ragwort in the summer. There is plenty of experi-
mental evidence for the unpleasant taste of both cater-
pillars.

The conspicuously black-and-yellow banded larva of the
common Monarch butterfly is a good example of the pos-
session of warning colors by distasteful caterpillars.

These warning colors are possessed not only by the ill-
tasting caterpillars but by many animals which have spe-

288 BIOLOGY

cial means of defense. The wasps and bees, provided
with stings — dangerous animals to trouble — are almost all
conspicuously marked with yellow and black. The lady-
bird beetles, composing a whole family of small beetles
which are all ill-tasting, are brightly and conspicuously
colored and spotted. The Gila Monster, the only poison-
ous lizard, differs from most other lizards in being strik-
ingly patterned with black and brown. Some of the
venomous snakes are conspicuously colored, as the coral
snakes or coralillos of the tropics.

All these animals with warning colors are described as
possessing some quality, a disagreeable taste or odor,
stings, hairs, etc., causing them to be obnoxious to other
animals that might seize them for food. Poulton says:
"The object of warning colors is to assist the education of
enemies, enabling them to easily learn and remember the
animals which are to be avoided."

Another special kind of color adaptation to be included
under Warning Coloration is known under the head of
recognition markings. Instead of attracting the attention
of enemies, these markings are of use in attracting the
attention of individuals of the same species. To this
category belong the white upturned tail of the rabbit,
the black tip of the weasel's tail and many of the bright
feathers in wings and tail displayed by birds in flight.

Certain animals which are without special means of
defense and are not at all formidable or dangerous are
yet so marked or shaped and so behave as to present a
threatening or 'Terrifying Appearance/ The large green
caterpillars of the Sphinx moths — the tomato-worm is a
familiar one of these larvae — have a formidable-looking,
sharp horn on the back of the next to last body ring.
When disturbed they lift the hinder part of the body,
bearing the horn, and move it about threateningly. As
a matter of fact, the horn is not at all a weapon of de-
fense, but is quite harmless. The larvae of the Puss
moth has been often referred to as a striking ex-

ADAPTATION

ample of terrifying appearances. When one of these
larvae is disturbed "it retracts its head into the first body
ring inflating the margin, which is of bright red color.
There are two intensely black spots on this margin in
the appropriate position for eyes, and the whole appear-
ance is that of a large flat face extending to the outer
edge of the red margin. The effect is an intensely exag-
gerated caricature of a vertebrate face, which is prob-
ably alarming to the vertebrate enemies of the caterpillar.
. . . The effect is greatly strengthened by two pink
whips which are swiftly protruded from the prongs of the
fork in which the body terminates . . . The end of the
body is at the same time curved forward over the back, so
that the pink filaments are brandished above the head."

Fig. 46 — Defensive Mimicry.
Durva of puss moth, showing

terrifying attitude when

disturbed.

Some of the instances of protective resemblance, warn-
ing coloration and "terrifying attitudes" that have been
given are sufficiently remarkable, but the phenomena of
mimicry are even more surprising. The term mimicry
has been reserved for those cases in which an otherwise
defenseless animal, one without poison, fang or sting, and
without an ill-tasting substance in its body, mimics some
other specially defended or inedible animal sufficiently to
be taken for it and so escape attack. These instances are
especially to be observed among insects. The most famil-
iar example perhaps is that of the Viceroy butterfly,
which mimics the Monarch.

The bees and wasps are protected by their stings. They
are usually conspicuous, being banded with yellow and

290 BIOLOGY

black. They are mimicked by numerous other insects,
especially moths and flies, two defenseless kinds of in-
sects. This mimicking of bees and wasps by flies is very
common, and can be observed readily at any flowering
shrub. The flower-flies (Syrphidse), which, with the bees,
visit flowers, can be distinguished from the bees only by
sharp observing. When these bees and flies can be caught
and examined in hand it will be found that the flies have
but two wings while the bees have four.

In addition to the colors and patterns which assist an
animal to evade or warn off its enemies or to secure its
prey there are also colors and appendages which must
have some very different meaning. These appearances
are seen in mature animals, and frequently undergo pe-
riodical development at times which correspond to the
breeding season; and when the two sexes differ, the
males are almost invariably the more brilliant. Instances
in which the colors of the males exceed those of the
females in brilliancy or pattern are many among fishes,
lizards, birds, spiders, insects, etc. It is most common
among insects and birds. Many of these sexual differ-
ences were described in the chapter on Sexual Selection.

However these colors may have arisen, every observer
must admit that they are in some way connected with
sex. Darwin accounted for them by his celebrated theory
of 'Sexual Selection/ He supposed that the esthetic
sense is widely distributed among the higher animals
(vertebrates and some of the most specialized inverte-
brates), and that the colors, which certainly appeal to
this sense in man, are not without effect in causing grati-
fication to the animals themselves. This explanation of
the origin and meaning of sexual coloring is not accepted
by Mr. Wallace, whose chief objection is the lack of evi-
dence that the female has any esthetic preferences at all
in the selection of her mate.

Concerning the whole question of the adaptations of
plants and animals there is much question to-day. It is

ADAPTATION 291

thought by many that the strength of the natural selec-
tion explanation rests on the logical nature of its premises
and conclusions rather than on scientific observation and
experiment. By others it is thought to be the best ex-
planation so far advanced. Professor Kellogg comments
on the present status of the theory in its relation to adap-
tations as follows : "There is no gainsaying to the selec-
tion explanation its claim to stand among all proposed ex-
planations of adaptation as that one least shaken by the
critical attack of its adversaries. However mightily the
scientific imagination must exert itself to deliver certain
difficult cases into the hands of selection, and however
sophisticated and lawyer-like the argument from the selec-
tion side may be for any single refractory example, the
fact remains that the selectionist seems to be able to stretch
his explanation to fit all adaptations, with less danger of
finding it brought up against positive adverse facts than
is possible to the champion of any other so far proposed
explanation."

So comprehensive is the doctrine of evolution that it
has been described as "one of the greatest acquisitions of
human knowledge." Professor Locy writes of it : "There
has been no point of intellectual vantage reached which is
more inspiring. It is so comprehensive that it enters into
all realms of thought." Weismann expresses the opinion
that "the theory of descent is the most progressive step
that has been taken in the development of human knowl-
edge," and further he says that this opinion "is justified
even by this fact alone: that the evolution idea is not
merely a new light on the special regions of biological
sciences, zoology and botany, but is of quite general im-
portance. The conception of an evolution of life upon
the earth reaches far beyond the bounds of any single
science and influences our whole realm of thought. It
means nothing less than the elimination of the miraculous
from our knowledge of nature, and the placing of the
phenomena of life on the same plane as the other natural

292 BIOLOGY

processes; that is, as having been brought about by the
same forces and being subject to the same laws."

Already the field of evolution is being still further ex-
tended by new problems in human evolution. The evi-
dences in reference to the evolution of the human body
are so conclusive that it is generally accepted that the
natural continuity of life includes the human species, and
students are turning their attention to the problem of the
evolution of mentality. In Professor Locy's words : "The
progressive intelligence of animals is shown to depend
upon the structure of the brain and the nervous system,
and there exists such a finely graded series in this respect
that there is strong evidence of the derivation of human
faculties from brute faculties."

The conception of evolution is no new idea — it is the
human idea of history grown larger, large enough to cover
the whole world. The extension of the idea was gradual
as men felt the need of extending it; and at the same
moment we find men believing in the external permanence
of one set of phenomena, in the creation of others, in the
evolution of others. One authority says human institu-
tions have been evolved; man was created; the heavens
are eternal. According to another, matter and motion
are eternal; life was created; the rest has been evolved,
except, perhaps, the evolution theory which was created
by Darwin.

Of the wise men of Greece and what they thought of
the nature and origin of things little will be said. Most
of them were philosophers, not naturalists, and we are
apt to read our own ideas into their words. They
thought, indeed, about the physical and organic universe,
and some of them believed it to be, as we do, the result
of a process ; but here in most cases ends the resemblance
between their thought and that of modern students.

Thus when Anaximander spoke of a fish-like stage in
the past history of man, this was no prophecy of the mod-
ern idea that a fish-like form was one of the far-off

ADAPTATION 293

ancestors of backboned animals; it was only a fancy in-
vented to get over a difficulty connected with the infancy
of the first human being.

Or, when several of these sages reduced the world to
one element, the ether, it is doing the progress of knowl-
edge an injustice to say that men are simply returning to
this after more than two thousand years. For that con-
ception of the ether which is characteristic of modern
physical science has been, or is being, slowly attained by
precise and patient analysis, whereas the ancient concep-
tion was reached by metaphysical speculation. If a return
is being made to the Greeks it is on a higher turn of the
spiral, so far at least as the ether is concerned.

When Empedocles sought to explain the world as the
result of two principles — love and hate — working on the
four elements one may, if so inclined, call these principles
"attractive and repulsive forces"; he may recognise in
them the altruistic and individualistic factors in organic
evolution and what-not; but Empedocles was a poetic
philosopher, no far-sighted prophet of evolution.

As in other departments of knowledge, so in biology
the work of Aristotle is fundamental. It is wonderful to
think of his knowledge of forms and ways of life, or the
insight with which he foresaw such useful distinctions as
that betwen analogous and homologous organs, or his
recognition of the fact of correlation, of the advantages
of division of labor within organisms, of the gradual dif-
ferentiation observed in development. He planted seeds
which grew after long sleep into comparative anatomy
and classification. Yet with what sublime humility he
says: "I found no basis prepared, no models to copy.
Mine is the first step, and therfeore a small one, though
worked out with much thought and hard labor."

Aristotle was not an evolutionist, for altho he recog-
nised the changefulness of life, the world was to him an
eternal fact, not a stage in a process.

"In nature the passage for inanimate things to

294 BIOLOGY

animals is so gradual that it is impossible to draw a

hard-and-fast line between them. After inanimate

things come plants, which differ from one another in

the degree of life which they possess. Compared

with inert bodies, plants seem endowed with life;

compared with animals, they seem inanimate. From

plants to animals the passage is by no means sudden

or abrupt; one finds living things in the sea about

which there is doubt whether they be animals or

plants."

Among the Romans Lucretius gave noble expression to

the philosophy of Epicurus. He was a cosmic, but hardly

an organic evolutionist, for according to his poetic fancy

organisms arose from the earth's fertile bosom and not

by the gradual transformation of simpler predecessors.

"In the first place, the first breed of lions and the
savage races their courage has protected, foxes their
craft, and stags their proneness to flight. But light-
sleeping dogs with faithful heart in breast, and every
kind which is born of the seed of beasts of burden,
and at the same time the woolly flocks and the horned
herds, are all consigned to the protection of man.
For they have ever fled with eagerness from wild
beasts, and have ensued peace, and plenty of food
obtained without their own labor, as we give it in
requital of their useful services. But those to whom
nature has granted none of these qualities, so that
they could neither live by their own means nor per-
form for us any useful service, in return for which
we should suffer their kind to feed and be safe under
our protection, those, you are to know, would lie ex-
posed as a prey and booty of others, hampered all
in their own death-bringing shackles, until nature
brought that kind to utter destruction."
From Lucretius to Buffon the intervening centuries
were uneventful as regards zoology. Hugo Spitzer, one
of the historians of evolution, finds analogies between

ADAPTATION 295

certain medieval scholastics and the Darwinians of the
nineteenth century, but these are subtle comparisons. Yet
long before Darwin's day there were evolutionists, and
the first of these who can be called great was Buffon.

One must guard against supposing that the works of
Buffon, or Lamarck, or Darwin were inexplicable crea-
tions of genius, or that they came like cataclysms, without
warning, to shatter the conventional traditions of their
time. For all great workers have their forerunners, who
prepare their paths. Therefore in thinking out the his-
tory of evolutionist theories before that of Buffon account
must be taken of many forces which began to be influential
from the twelfth century onward. "Evolution in social
affairs has not only suggested our ideas of evolution in
the other sciences, but has deeply colored them in accord-
ance with the particular phase of social evolution cur-
rent at the time." The evolution of theories of evolution
is bound up with the whole progress of the world.

Among the evolutionists before Darwin only three need
be noted — Buffon, Erasmus Darwin and Lamarck. Buffon
(1707-1788) was born to wealth and was wedded to For-
tune. As Director of the Jardin du Roi he had op-
portunity to acquire a wide knowledge of animals. He
commanded the assistance of able collaborateurs, and his
own industry was untiring. He was about forty years
old when he began his great Natural History, and he
worked till he was fourscore. He lived a full life, the
success of which we can almost read in the strong con-
fidence of his style.

Erasmus Darwin (1731-1802), grandfather to the author
of the Origin of Species, was a large-hearted, thoughtful
physician, whose life was as full of pleasant eccentricities
as his stammering speech of wit and his books of wisdom.
Buffon underrated the transforming influence of action,
and laid emphasis upon the direct influence of surround-
ings; Erasmus Darwin emphasized function, and re-

296 BIOLOGY

garded the influence of the environment as for the most
part indirect

On Lamarck (1744-1829) success did not shine as it
did on the Comte de Buffon or on Dr. Erasmus Dar-
win. His life was often so hard that it is wonder he
did not say more about the struggle for existence.

Of Lamarck's Philosophic Zoologique Haeckel says:
"This admirable work is the first connected and thoroly
logical exposition of the theory of descent." And again
he says : "To Lamarck will remain the immortal glory of
having for the first time established the theory of descent
as an independent scientific generalization of the first
order, as the foundation of the whole of Biology."

The condition of evolution is variability, or the tend-
ency which animals have to change. The primary factors
of evolution are those which produce variations, which
cause organic inequilibrium.

There are evidently three direct ways in which these
organic changes may be produced: (1) From the nature
of the organism itself — i.e., from constitutional or germi-
nal peculiarities which are ultimately traceable to in-
fluences from without; (2) from changes in its func-
tions or activity — in other words, from use and disuse;
or (3) from the direct influence of the external condi-
tions of life — food, temperature, moisture, etc.

It is with such problems as these that modern research
into the causes of the descent of species is concerned.
But of these to-day scientists are forced to confess almost
complete ignorance. As for the future, the keynote of
work is to examine life at closer range and from new
points of view, to observe life phenomena with a keener
and more critical eye, to evolve new methods of work, to
experiment more extensively, more intensively and more
critically, to classify, to organize and to deduce. And
with patient, careful and long-continued effort who will
say that even these mysteries may not yield up their se-
crets for the benefit of mankind?

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