BIOLOGY
LIBRARY

THE MAIN CURRENTS OF
ZOOLOGY

BY
WILLIAM A. LOCY, PH.D., Sc.D.

AUTHOR OF " BIOLOGY AND ITS MAKERS "
PROFESSOR OF ZOOLOGY IN NORTHWESTERN UNIVERSITY

NEW YORK

HENRY HOLT AND COMPANY
1918

Copyright 1918,

BY
HENRY HOLT AND COMPANY

PREFACE

THE conviction has been gradually forced upon the
writer that persons who wish to get an insight into
zoology as a science have difficulties in finding the
necessary helps. The conventional treatise on
zoology deals chiefly with facts about animals and
certain phenomena of their lives, but omits a con-
current account of the results of zoological advances.
In educational institutions, also, the method of
using animal types as the sole background of knowl-
edge, together with drill on the facts observed in the
laboratory, has resulted in a one-sided and inad-
equate conception of zoology.

Zoological progress represents a stream of
thought — not merely accretions of knowledge about
animals. In order to comprehend zoology in the
light of its progress it is necessary to trace its main
currents; merely to accumulate a certain set of facts
about animals will cause one ever to remain outside
of the subject. It is well to remember also that the
interpretations resulting from zoological observa-
tions have had great influence hi liberating thought
and on /general intellectual advancement.

iii

381031

iv PREFACE

It is the purpose of this volume to attempt to
picture zoology as a unified science. There are ex-
cellent books that supply a knowledge of the animal
kingdom — this one aims to add some knowledge of the
science itself. It is, therefore, intended to be a book
of collateral reading for courses in practical zoology,
and, while written with this primarily in mind, it
is, at the same time, adapted to the needs of the
general reader who wishes to become familiar with
the progress of zoology.

In the preparation of the material I have been
indebted for helpful suggestions to my colleagues,
Professor Sidney I. Kornhauser and Dr. Olof Larsell.
I am also indebted to the Macmillan Company for
permission to use verbatim a considerable portion
of my article "Zoology" published by that firm in
A Cyclopaedia of Education, 1913.

WILLIAM A. LOCY.

CONTENTS

CHAPTER PAGE

I. ZOOLOGY AS A SUBJECT OF GENERAL EDUCATION — OUTLINE

OP THE PROGRAM i

II. THE OUTSTANDING BIOLOGICAL ADVANCES OF THE NINE-
TEENTH CENTURY 10

The Discovery of Protoplasm and its Bearing on Bio-
logical Progress n

The Formulation of the Cell-Theory 16

Establishment of the Doctrine of Organic Evolution ... 22

in. THE OUTSTANDING BIOLOGICAL ADVANCES — CONTINUED .... 24
The Rise of Bacteriology and the Demonstration of the

Germ-Theory of Disease 25

The Experimental Study of Heredity 34

IV. ZOOLOGY EMERGES 43

V. LlNNJEUS AND HlS INFLUENCE 52

VI. CUVIER AND STRUCTURAL ZOOLOGY 62

VII. THE RISE OF EMBRYOLOGY 70

VHI. GENERAL PHYSIOLOGY AS A DIVISION OF ZOOLOGY 77

EX. THE ANIMAL KINGDOM 84

X. ZOOLOGY OF FOSSIL REMAINS 95

XI. MAIN PATHWAYS AND RECENT TENDENCIES OF ZOOLOGY . . . 106

XII. A CHAPTER ON INSECTS 125

Xm. THEORIES OF ORGANIC EVOLUTION 143

XIV. SOME MISCELLANEOUS TOPICS 165

Painless Surgery 165

Jenner and Vaccination 170

XV. THE TEN FOREMOST MEN OF ZOOLOGICAL HISTORY— NA-
TIONAL CONTRIBUTIONS TO ZOOLOGICAL PROGRESS —
THE RANK OF DIFFERENT NATIONS IN BIOLOGICAL

PROGRESS 174

XVI. SOME USEFUL BOOKS— A SELECTED READING-LIST WITH
BRIEF COMMENTS ON THE RELATIVE MERITS OF BOOKS
AND PERIODICAL ARTICLES ON ZOOLOGICAL SUBJECTS . 188

INDEX 209

v

ILLUSTRATIONS

FIG. PAGE

1. FELIX DUJARDIN 16

2. MAX SCHULTZE 16

3. THEODOR SCHWANN 16

4. THEODOR BOVERI 16

5. CHARLES DARWIN 22

6. Louis PASTEUR 28

7. SIR JOSEPH LISTER 36

8. ROBERT KOCH .'...,. ,.« 36

9. SIR FRANCIS GALTON 36

10. GREGOR MENDEL 36

11. ARISTOTLE 54

12. CAROLUS LINNAEUS 54

13. RUDOLPH LEUCKART 54

14. GEORGES CUVIER 54

15. ALBRECHT VON KOELLIKER 72

16. KARL ERNST VON BAER 72

17. FRANCIS M. BALFOUR 72

18. CLAUDE BERNARD 72

19. JOHANNES MULLER 80

20. E. D. COPE 96

21. JOSEPH LEIDY 96

22. CHARLES SEDGWICK MINOT 96

23. CHARLES Ons WHITMAN 96

24. Louis AGASSIZ 118

25. J. HENRI FABRE 136

26. WALTER REED 136

27. W. T. G. MORTON 136

28. EDWARD JENNER 136

29. J. B. LAMARCK 146

30. WILLIAM HARVEY 156

31. THOMAS H. HUXLEY 156

32. AUGUST WEISMANN 156

33. HUGO DE VRIES 156

vii

THE
MAIN CURRENTS OF ZOOLOGY

CHAPTER I

ZOOLOGY AS A SUBJECT OF GENERAL EDUCA-
TION. OUTLINE OF THE PROGRAM

THERE are no problems of greater human interest
than those of biology, and when we recognize that
zoology is the central subject of biology it imme-
diately emerges for consideration as a subject of
general education. The richness of zoology as a
science and its many-sided appeal is just beginning to
dawn on those who arrange courses of study. Owing,
however, to the way in which it is commonly pursued
attention is so exclusively confined to observations
of animals and the means of identifying them that
the student is not made aware of its other aspects
and, as a consequence, a narrow conception of its
scope has prevailed.

Although, in treatises on the subject, it has been
well expounded from the standpoint of the structure,
the development and the life histories of animals, the

2 THE MAIN CURRENTS OF ZOOLOGY

plain story of how zoology arose and of how it became
closely related to human affairs has not been told.

There has been too little attempt to picture
zoology as a unified science. Even among those who
have studied zoology, knowledge is little dissem-
inated regarding its scope, the results, both material
and intellectual, of its progress and the kind of work
that is being carried on at the present time. Scarcely
known are the names of its foremost men, their
relative rank and the reasons for their eminence.

These matters are not only important, they are
essential to an understanding of what zoology is and
what it stands for.

To say that zoology is the science that acquaints
us with animals and the phenomena of animal life —
which is a fair definition — gives no clue to the part
it has played in intellectual development and in the
interpretation of the organic world. Its advances
brought a new class of ideas into man's intellectual
horizon, which resulted in dispelling error, in spread-
ing enlightenment and produced some changes of
opinion of epoch-making importance.

There resulted from zoological discovery the
sweeping conclusion that the human body belongs
to the animal series and, consequently, that observa-

A SUBJECT OF GENERAL EDUCATION 3

tions regarding animals and their relation to nature
apply also to the human body and to the question of
man's place in nature.

This truth was a long time gaining credence since
it was hi conflict with ideas that had prevailed for
centuries and its final acceptance brought a revolu-
tion of opinion.

The recognition of this oneness of nature, especially
as applied to the animal world, is one of the most
dramatic results of scientific advancement. It is
continually illustrated in a great variety of rela-
tions:— the similarity of stages of embryonic develop-
ment of all animals, the gradual building of body and
of mind, the ultimate bearing of these questions on
human origin and destiny. It led to the analysis of
the phenomena of life, reduced to their simplest
expression hi the lower organisms, hi order to throw
light on the vital activities of higher animals. It also
led to including man in the scheme of organic evolu-
tion and opened many other new questions.

Naturally, a subject of such wide scope and of
such varied aspects presents particular difficulties of
treatment and it is further complicated by the
traditional method of the study of animal forms to
the exclusion of other major topics. The question of

4 THE MAIN CURRENTS OF ZOOLOGY

what must be included in the exposition of zoology
and what may be omitted becomes a perplexing one.

Accordingly, at the outset, it is of primary im-
portance to get an idea of what is embraced within
the zoological territory and to determine the method
of analysis so as to give, if possible, a unified view of
this many-sided science. Undoubtedly, the be-
wildering number of details makes it difficult to deal
with them clearly and coherently. The attempt to
unite them into an orderly whole runs the risk of
becoming merely discursive. The matter, however, is
greatly simplified by the circumstance that in the
progress of zoology, notwithstanding the continual
multiplication of details, there has been continuity of
development of zoological thought. If we can follow
the path, the large number of details serves to enrich
the subject with numerous illustrations without con-
fusing it.

The first step of our program should be to deter-
mine the main currents of zoological progress and,
thereafter, to become acquainted with the circum-
stances under which they were started and their
ultimate outcome.

The direct study of animal types will not suffice.
Laboratory exercises and observation of animals in

A SUBJECT OF GENERAL EDUCATION 5

the field are necessary, but experience has repeatedly
shown that this in itself is not sufficient. Such
studies should be supplemented by the story of the
rise of zoology and a systematic account of its dis-
coveries of first magnitude.

As indicated above, these aspects of zoology are so
commonly neglected that students emerge from the
study of the subject, possessing only a certain set of
facts about animals — with detached fragments of
zoological knowledge — and no conception of zoology
as a department of human learning. The fact is that
the outlook on zoology has been too narrow, and we
should become more aware of the results of zoological
study and not limit our vision merely to facts about
animals — in a word, more cognizant of the ideas and
theories of zoology.

Considerations of this nature serve to indicate that
a knowledge of the main currents of zoology should
be acquired in connection with the facts of observa-
tion learned in the laboratory and in the field. To
orient ourselves toward the subject we should at
least know the great movements, the foremost men,
in a broad way the influence of their researches, and
the present tendencies of the science.

It is the purpose of the following chapters to supply

6 THE MAIN CURRENTS OF ZOOLOGY

such an account — untechnical and not in too great
detail. There are excellent text-books, in which the
animal kingdom is systematically considered, but
there is need of a source of collateral reading to
supplement these text-books and to run parallel with
laboratory work and field observations.

Position of Zoology in Biology. — To fix the
place of zoology we need only to remember that one
of the most striking developments of the past half-
century has been the great extension of knowledge of
organic nature and the new interpretations that have
resulted. Since zoology is the central subject of
this biological advance, it has come about that this
science embodies our interpretations of organic
nature. There comes within its province considera-
tion of all the phenomena of animal life and of what
has grown out of their study: — Evolution, genetics,
heredity, biogenesis, Mendelism, transmission of
disease through animal agencies, structure, devel-
opment, habits, animal intelligence and behavior.
These and kindred matters find in zoology their
illustrations and their systematic treatment.

Inasmuch as most animals possess a nervous sys-
tem, which is lacking in plants, zoology gives a fuller
representation of vital phenomena than its sister

A SUBJECT OF GENERAL EDUCATION 7

science botany, and it has been more intimately con-
cerned than any other subject in expanding our ideas
of the human body in its relation to nature.

Owing to the character of the questions involved
and to its broad scope, the foremost claim of zoology
to attention is as a subject of general education.
Education to-day without some knowledge of the
phenomena of nature is inadequate. Some training
in the scientific method of observation, such as is
supplied by zoology, is an indispensable part of the
mental equipment of the liberally educated.

The results of zoological investigation have prac-
tical bearing in sanitary science, hi the conservation
of useful animals, for the agriculturist, the breeder
and the economic zoologist. While supplying train-
ing and important knowledge of the animal life
referred to, the subject affords opportunity for
diversion hi the study of birds, marine forms and
insects.

Besides its position in general education zoology is
basal to the study of medicine. Not only have
zoological discoveries enriched medicine, but, further-
more, they have supplied the foundations upon
which experimental medicine has been built. Zoology
is one of the important pre-clinical subjects, and all

8 THE MAIN CURRENTS OF ZOOLOGY

students preparing for the profession of medicine
should engage in the study of zoology, not merely as
supplying training in the kind of observation that is
needed for diagnosis, but as affording a broader
outlook on the structure, the development and the
physiology of the human body. It affords to-day the
best introduction to general physiology.

In addition to its inseparable connections with
botany, zoology is closely related to two other
sciences — physics and chemistry. Zoology and
botany are essentially the sciences of organic nature,
while physics is the science of inorganic nature. In
the study of nature the biological and physical
sciences are fundamental and reciprocal to one an-
other.

Chemistry is somewhat more closely allied to
biological phenomena since these phenomena are
physico-chemical in their nature and the great
development of physiological chemistry has brought
it into very close relation with biology. A certain
knowledge of chemistry is necessary to the under-
standing of any physiological problem. Chemistry,
physics and biology form the tripod of sciences
essential to the student of medicine.

Zoology has been made by the confluence of many

A SUBJECT OF GENERAL EDUCATION 9

scientific currents and it cannot be properly treated
in isolation. Especially that which is broadly
biological is a part of zoology as well as of botany.
In attempting to find the main currents of zoology
let us begin with the chief biological advances of the
nineteenth century.

CHAPTER II

THE OUTSTANDING BIOLOGICAL ADVANCES
OF THE NINETEENTH CENTURY

THE events of the nineteenth century have a
relatively near-by interest. Accordingly, it will be
first in order to inquire what are the biological ad-
vances of widest influence of the past century?

Many advanced students of zoology would be
puzzled if called on to separate the truly outstanding
events of zoological progress from those of subor-
dinate importance. There were so many biological
advances in "The Wonderful Century" that the
task of selecting those to stand in the front rank re-
quires much discrimination. The basis for selection
is not the brilliancy of individual discoveries, nor
unprecedented progress in special fields, but the
consequences that followed unique discoveries and
the extent to which they influenced the whole field of
biology.

Instances of notable advances will at once emerge
for consideration such as: the establishment of
embryology on modern lines by Von Baer (1828), the
discovery of the nucleus of plant cells by Robert

10

OUTSTANDING BIOLOGICAL ADVANCES n

Brown (1831), the work of Johannes Mliller in animal
physiology, the development of vegetable morphol-
ogy by Hofmeister and of vegetable physiology by
Sachs and Pfeffer. These are biological, but im-
portant as they were, they did not influence the whole
field of biological science as did those events now
referred to as the outstanding biological advances of
the century.

To avoid repeated explanation, it is to be under-
stood that the term "biological" is generic and im-
plies botanical as well as zoological advances, but it is
used here in the restricted sense of "biological"
from the animal side.

Considered from the standpoint of wide influence,
there are five biological advances of the nineteenth
century to which all others are subordinate. These
are: the discovery of protoplasm; the formulation of
the cell- theory; the establishment of the theory of
organic evolution; the demonstration of the germ-
theory of disease in connection with the rise of
bacteriology, and, fifth, the experimental study of
heredity. There was a parallel development of
these subjects but, for clearness, separate considera-
tion is necessary.

The Discovery of Protoplasm. — The scientific

12 THE MAIN CURRENTS OF ZOOLOGY

discovery of protoplasm came in 1835, though its
significance was not recognized until twenty-five
years later. This living substance, common to plants
and animals, had been casually observed, at inter-
vals, from 1755 onwards. Under the microscope its
movement had been detected in the proteus animal-
cule, by Roesel von Rosenhoff in 1755. Thereafter,
in plants, by Myen, in 1827, and by other observers.
But all these observations were substantially point-
ing out the existence of movements of a semi-trans-
parent jelly-like substance in animals and plants.

An important forward step came in 1835 when
Felix Dujardin (1801-1860), a French naturalist,
published discriminating observations on this living
substance in simple animals such as various protozoa
and worms. Not content with merely observing its
movements, he experimented with it, and by applying
tests as to its solubility and behavior towards differ-
ent reagents, he distinguished between it and gum,
gelatine, mucus and white of egg, with which it has
superficial resemblances. Finally, in 1835, he de-
scribed it as a "living jelly endowed with all the
properties of life." His predecessors had not ob-
served it in this way; consequently, it is proper to
designate Dujardin as the scientific discoverer of

OUTSTANDING BIOLOGICAL ADVANCES 13

protoplasm. He called it sarcode, from the Greek,
meaning flesh-like.

Although Dujardin pointed out that sarcode was a
different substance from any other known to science,
and that it was endowed with all the properties of
life, he was far from recognizing the distinctive r61e
it plays in nature. The conclusion prevailed that
it was confined to the lower animals, and this long
delayed the recognition that it is the living substance
of all organisms — including, of course, the human
body. To reach this point took twenty-five years of
investigation by various men.

The name sarcode was not retained and the cir-
cumstances under which the original name was
changed to protoplasm may be briefly stated. Eleven
years after Dujardin's discovery, the German botan-
ist, Hugo von Mohl (in 1846), described the same
slimy substance in plants under the name proto-
plasma. In the interval, it had been de cribed, in
1840, under the designation protoplasm, in mamma-
lian embryos, by the Bohemian anatomist Purkinje".

In 1846, after von MohPs publication, the scientific
world was in the position of knowing "sarcode" of
lower animals, and "protoplasm" in certain animal
embryos as well as in plants.

H THE MAIN CURRENTS OF ZOOLOGY

There now began to rise the suggestion that
sarcode and protoplasm were different names for
one and the same substance and, in 1850, Ferdinand
Cohn definitely maintained that protoplasm and
sarcode were identical substances. Later in life Cohn
became eminent for investigations in bacteriology
but, at this time he was a young man of twenty-two
years and his contribution was considered theoretical
and insufficiently supported by observation and ex-
periment.

With Max Schultze (1825-1874), came the summa-
tion of the accumulated knowledge regarding proto-
plasm and the final step in bringing it into full
recognition in the scientific world. After a long
series of observations and experiments he announced,
in 1861, that living substance, be it called sarcode or
protoplasm, is essentially alike in animals and plants.
He reached this conclusion largely upon physiological
resemblances, pointing out, especially, that the con-
tractility exhibited by all protoplasm is essentially
similar to the contraction of muscles.

One thing that had stood in the way of an earlier
recognition of the true nature of protoplasm was,
that for some years, it was supposed to be confined
to lower animals and it was necessary that observa-

OUTSTANDING BIOLOGICAL ADVANCES 15

tion should establish that it is universal in all or-
ganisms before the general conclusion could be
reached.

Let us now estimate the consequences of the dis-
covery of protoplasm. Here for analysis we have
disclosed the living substance of all animals and
plants. In this- physical substratum all vital ac-
tivities exhibit their manifestations. Now for the
first time was recognized the basis of physiological
activities. If the naturalist is ever to bring vital
activities under close analysis, he must do so by
hemming acquainted with the properties and the
behavior of protoplasm. Even in its simplest form
it exhibits the germ of all properties that appear
better developed in higher organisms.

The recognition of the nature of protoplasm, to-
gether with the adoption of the cell-theory, led to the
foundation of modern biology, and the progress of
biology, since 1861, has been largely a matter of
becoming better acquainted with protoplasm. By
means of these discoveries vital phenomena were seen
in a new light and progress was started.

It is to be remembered throughout this book that a
great scientific discovery is never the product of one
man, nor of two men. Although in bringing forward

16 THE MAIN CURRENTS OF ZOOLOGY

the protoplasm idea, Dujardin (Fig. i) and Max
Schultze (Fig. 2) occupy the foremost position, a
great many other investigators, as the botanists
De Bary, Nageli, Strassburger and others contrib-
uted to this end.

The Cell-Theory.— The cell-theory had a parallel
development with the protoplasm idea and, ulti-
mately, they fused as one. The cell-theory was an-
nounced in 1838-1839, a few years after Dujardin's
discovery of protoplasm.

The microscopic examination of a thin section of a
plant stem, a similar section of hardened liver,
scrapings from the inside of the human cheek, the
skin of a frog, the skin, or epidermis, of a plant, all
reveal similar units of organic architecture. Further
studies show that brain tissue, bone and cartilage, in
fact, all organic tissues are constructed by the union
of microscopic elements nicely fitted in together.
This is the basis of the cell-theory, but it is a long
step from mere observation of these elements to the
generalization that all animals and plants are com-
posed of a union of similar cells. The latter concep-
tion in its full sweep unites all living creations on the
broad plane of similarity of structure and, as we shall
soon see, of similarity of origin — since all organisms,

FlG> L —FELIX DUJARDIN (1801-1860) FIG. 2.— MAX SCHULTZE (1825-1874) *

FIG. 3. — THEODOR SCHWANN (1810-1882) FIG. 4. — THEODOR BOVERI (1866-1916)

OUTSTANDING BIOLOGICAL ADVANCES 17

no matter how complex, begin their existence in the
condition of a single cell.

This "master-stroke of generalization" had a
wonderful unifying effect in bringing all animals and
plants under one view as to origin and structure.

The names of two men, Schleiden and Schwann,
are associated with the launching of this theory.
Schleiden was a botanist, and Schwann, an anat-
omist— a happy combination in biological investi-
gation. They are commonly spoken of as the
co-founders of the cell-theory. This statement, how-
ever, requires qualification, for the part played by
the two men was very unequal. Schwann, so to
speak, was the star and Schleiden played a subordi-
nate part.

Schleiden's work was auxiliary. He had observed
cell formation and cell structure of plants and pub-
lished a small paper on this subject in 1838. In a
friendly conference, he assisted Schwann, whose
researches were already the more extensive, by sug-
gesting that the nucleus (cytoblast) of the animal
tissues, examined by Schwann, was the same as the
nucleus of plants and this, apparently, flashed into
the mind of Schwann, the identity of organization of
animals and plants.

i8 THE MAIN CURRENTS OF ZOOLOGY

Schwann (Fig. 3) in an extensive paper (215 octavo
pages, with four plates), published in 1839 first em-
ployed the term "cell- theory" and explained its
meaning. This treatise, which is a biological classic,
was his famous Microscopical Researches regarding
the Accordance in Structure and Growth of Animals and
Plants (Mikroscopische Untersuchungen uber die
Uebereinstimmung in der structur und dem Wach-
sthum der Thiere und Pflanzen).

Schwann's writing in the Microscopical Researches
is clear and philosophical, and is divided into three
sections, in the first two of which he confines himself
strictly to descriptions of observations, and in the
third part of which he enters upon a philosophical
discussion of the significance of the observations.
He comes to the conclusion that: "The elementary
parts of all tissues are formed of cells in an analogous,
though very diversified manner, so that it may be
asserted that there is one universal principle of devel-
opment of the elementary parts of organisms, how-
ever different, and that this principle is the formation
of cells."

It was in this treatise also that he introduced the
term cell- theory as follows: "The development of the
proposition that there exists one principle for the

OUTSTANDING BIOLOGICAL ADVANCES 19

formation of all organic products, and that this
principle is the formation of cells, as well as the con-
clusions which may be drawn from this proposition,
may be comprised under the term cell-theory, using
it hi its more extended signification, while, in a more
limited sense, by the theory of cells we understand
whatever may be inf erred from this proposition with
respect to the powers from which these phenomena
result."

Schleiden had not used the term cell-theory, nor
developed the ideas at the basis of it, accordingly it is
more proper to give the credit to Schwann for this
great generalization and to speak of it as the cell-
theory of Schwann rather than the cell-theory of
Schleiden and Schwann.

There were serious defects in the theory as it
existed in the minds of the early observers. Both
Schleiden and Schwann attached importance to the
cell-wall and had a wrong idea of the nucleus (called
cytoplast by Schleiden) and of the formation of cells.
But, as researches progressed, the theory was greatly
expanded and unproved.

One of the most helpful steps was the full recogni-
tion of the origin of cells in multicellular organisms.
The many-celled animals and plants begin then-

20 THE MAIN CURRENTS OF ZOOLOGY

existence in the condition of a single cell, and from
this primary condition, the many cells arise by
successive divisions of the original one. These many
cells become separated into different groups which
exhibit different properties, and, by the combination
of cells having similar properties, the tissues arise.
When, finally, about 1865, all eggs, as well as their
fertilizing agents, or sperms, were recognized as cells,
we had the logical explanation of the origin of cells,
and, also, an insight into the nature of tissues.

At the time of Schleiden and Schwann a cell was
thought of as a box-like compartment or a little space
surrounded by walls but, presently, this conception
was materially changed. The cell- wall was seen to be
formed by the living protoplasm within, and atten-
tion became directed to that substance as the essen-
tial part of the cell. Many animal cells were observed
without cell-walls and the conclusion was soon reached
that the cell-wall is unimportant and may be lacking.
Accordingly, about 1860, Max Schultze defined the
essential qualities of a cell as "A mass of protoplasm
containing a nucleus." Up to this time the cell-theory
was chiefly a morphological doctrine, but now com-
bined with the protoplasm idea, which was essentially
physiological, it assumed a wider significance.

OUTSTANDING BIOLOGICAL ADVANCES 21

From this point ideas began to broaden and other
new relations were discovered. The minute struc-
ture of the cell was investigated, the centrosome and
the chromosomes were discovered, the behavior of
these parts and of the nucleus were observed. The
phenomena of fertilization of the egg, the mechanism
of heredity and the seat of hereditary qualities were
studied as problems pertaining to cell life.

So many sweeping conclusions resulted that a
new branch of biology having to do with the phenom-
ena of cellular life was organized. This division was
called cytology and the late Theodor Boveri (1866-
1916) (Fig. 4), was perhaps its leading representative
on the zoological side.

In its modern statement the cell-theory has come
to embrace four aspects which successively have been
developed. These are : the conceptions of the cell as a
unit of structure; the cell as a unit of physiology; the
cell in development and in heredity. The title of
Wilson's, now classic, book on The Cell in Develop-
ment and Inheritance carries this idea. (For com-
ments on the cell in inheritance see p. 43.)

From these considerations it becomes evident
that the cell-theory and the protoplasm idea are
broad generalizations that influenced the entire

22 THE MAIN CURRENTS OF ZOOLOGY

field of biology and classes them as outstanding
advances.

The Doctrine of Organic Evolution. — The doc-
trine of organic evolution is so comprehensive in its
range that it has entered into the whole frame-work
of human thinking and its acceptance has so pro-
foundly changed conceptions of man and nature that
it has produced a great mental revolution. There is a
natural cleavage between thought before 1859 and
thought after that date regarding the biological
interpretation of the universe. The doctrine of
organic evolution has done more to enrich zoology
than any other advance. In its full sweep it is one of
the greatest acquisitions of human knowledge. Al-
though utilized in different departments of learning
it is a biological doctrine and receives its fullest
illustration in zoology. It is the recognition that the
higher animals have been derived by modification
from the simpler ones and it cleared up many of their
heretofore perplexing relations. It is the discovery of
the lineage of animals and plants.

Although it is commonly believed that Charles
Darwin (Fig. 5) was the founder of this doctrine it
was clearly expressed more than fifty years before
the publication, in 1859, of Darwin's Origin of

FIG. 5. — CHARLES DARWIN (1809-1882)
A few years prior to the publication of The Origin of Species

OUTSTANDING BIOLOGICAL ADVANCES 23

Species. The French zoologist, Lamarck (1744-
1829) was the first to announce, in 1801, a compre-
hensive theory of evolution that has lasted to the
present, while Darwin's especial contribution was
the designation of natural selection as the chief
agency in bringing about the evolution of animals and
plants. Besides these two, the theories of Weismann
and De Vries have attracted the most attention.

This doctrine is so important and so intricate that
in a later chapter it will be returned to for fuller ex-
position of the different theories.

CHAPTER III

THE OUTSTANDING BIOLOGICAL ADVANCES-
CONTINUED

AFTER such high praise of the theory of organic
evolution, what can remain to be said of the advance
resulting from the biological work of Pasteur, Koch
and Lister?

The theory of Organic Evolution is philosophical
and wide-reaching, but the results of the study of
micro-organisms, with which Pasteur and others were
concerned, had more immediate practical applica-
tions.

The science of bacteriology embraces several
general questions such as, the germ-theory of disease,
the nature of fermentation, of inflammations, the
spontaneous origin of life, immunity, etc. In this
group of topics certain animal and plant organisms
are so intertwined as to their aspects and effects that
it is artificial to attempt to draw a sharp line sep-
arating the bacteria from all other organisms. When
strictly limited, bacteriology should be confined to
bacteria, which are minute plants, but, as the experi-
mental study of these micro-organisms advanced, it

24

OUTSTANDING BIOLOGICAL ADVANCES 25

was inevitable that some minute animal organisms
also should become involved. This overlapping of
closely related fields of investigation is so common
that it may be accepted as characteristic.

For our present purpose we shall not take up
specifically the various topics, mentioned above,
but, under the general caption Bacteriology, treat
in a general way of the movement and its re-
sults.

Rise of Bacteriology. — The rise of bacteriology
with its germ-theory of disease had far-reaching
consequences for the benefit of mankind; there is,
in fact, no biological advance that has had more
important bearings on the welfare of the human
race.

The micro-organisms are so minute that one would
scarcely expect them to play an important part in
human affairs. The world of exceedingly minute
life was first exposed by the Dutch microscopist,
Leeuwenhoek, who, in 1675, discovered the protozoa
and, in 1683, the bacteria. The protozoa are micro-
scopic animals while the bacteria are microscopic
plants. The more general term micro-organisms is
convenient as it includes them both — and, of course,
other minute plants that are not bacteria. It was

26 THE MAIN CURRENTS OF ZOOLOGY

nearly two centuries after Leeuwenhoek's discovery
before these organisms began seriously to be con-
sidered as of practical interest.

We cannot assign a definite date as the time of the
beginning of bacteriology. It took form gradually.
The researches of Ferdinand Cohn on the bacteria,
published at various times between 1853 and 1872,
form an important preliminary preparation. This is
especially true of his classification of the bacteria
which in its larger features is essentially the one used
to-day. If, however, any single man is to be con-
sidered as the founder of bacteriology that man is
Louis Pasteur, while for Robert Koch we reserve the
distinction of having lifted it into the position of an
independent science.

For convenience we may arbitrarily adopt the
date 1877, as being the time when bacteriology
sprang into general recognition. In that year both
Pasteur and Koch demonstrated that splenic fever, a
specific disease of sheep and cattle, is owing to the
growth within the body of a specific micro-organism
called the anthrax bacillus (Bacillus anthracis).
Previously, Pasteur had shown the nature of fer-
mentations (1857) and discovered the connection
between microscopic particles and silk-worm diseases

OUTSTANDING BIOLOGICAL ADVANCES 27

(1865), while Robert Koch in 1876 had made a
study of the growth of the anthrax bacillus.

In the early days, the men chiefly concerned in
bringing bacteriology into practical use were Pasteur,
Koch and Lister— all great benefactors to the race.

Pasteur. — The brilliant work of Pasteur (1822-
1895), Fig. 6, belongs to all biology. Starting his
scientific career as a chemist, he was soon drawn into
the investigation of biological problems, and, through
his later work, came to be recognized as one of the
foremost men of biological history. He left a heritage
of priceless value which will make his fame as en-
during as that of Aristotle. His supreme service was
in applying the results of biological investigation to
the benefit of mankind.

In laying the foundations of micro-parasitology
(about 1877), Pasteur opened a subject that over-
laps the different conventional division of biology,
and his foundations have been built upon by bota-
nists, zoologists and physicians. His investigations
gave an immense impulse to the study of pathogenic
organisms; and while his researches supplied the
foundations of scientific medicine, at the same time
they opened investigations in the life-history of
micro-organisms that have been extensively devel-

28 THE MAIN CURRENTS OF ZOOLOGY

oped by zoologists — as in the notable work of Fritz
Schaudinn and others.

One of Pasteur's early triumphs was the demon-
stration of the nature of fermentation (1857). This
process, which is so important in physiology, was
declared to be due merely to chemical action, but
Pasteur showed that it depends on the growth of
living micro-organisms, and he won his case against
the great opposition of the chemist Liebig.

Against his inclinations Pasteur was forced into
the controversy (with Pouchet), concerning the
spontaneous generation of life, and, in 1862, made his
decisive and epoch-making demonstrations — that life
is formed in nutrient fluids only when living germs are
allowed to enter from the outside. All this directed
attention to the constitution of the floating matter of
the air. The impalpable dust that is always present
and that shows in the path of a sunbeam through a
darkened room is of complex composition — besides
particles of non-living matter there are living or-
ganisms of different kinds in a dried condition.
Some of these are harmless and others are disease
producing. When floating germs are introduced into
canned fruits and meats, they grow and cause them
to spoil. Other kinds entering wounds produce

FIG. 6. — Louis PASTEUR (1822-1895)

OUTSTANDING BIOLOGICAL ADVANCES 29

suppuration and other diseased conditions. Still
other kinds may produce diseases when breathed into
the lungs, or, introduced into the body through milk,
water and various kinds of food. These discoveries
are of the utmost importance.

Those micro-organisms that cause canned fruits
and tinned meats to decompose are killed by heating
and when, thereafter, the cans are securely sealed the
contents are preserved in a wholesome condition.
Even more important than this was the recognition
(1865-1867) of the Edinburgh surgeon, Lister
(Fig. 7) that to keep the floating germs from surgical
wounds would prevent gangrene and pus formation.
Against great ridicule and opposition, Lister made his
experiments, using carbolic acid dressings and great
cleanliness and, about 1867, established the method
of antiseptic surgery. This followed as a conse-
quence of Pasteur's studies but the credit for this
application belongs to Lister (1827-1912). At first
it made slow progress against the contemptuous
criticisms of medical men, but the successes that
accompanied its practice were so overwhelming
that this great advance in surgery became estab-
lished.

Pasteur was soon led to experiment with diseases of

30 THE MAIN CURRENTS OF ZOOLOGY

animals such as splenic fever of sheep, cholera of
swine and fowls, and, through his efforts, and those
of contemporary workers, it was repeatedly demon-
strated that a particular micro-organism is the cause
of a particular disease. That most disease organisms
produce poisons or toxins within the system was
demonstrated and, thereupon, Pasteur began success-
ful attempts to produce serums, vaccines and anti-
toxins to counteract the poisons produced by the
growth of disease germs within the body.

Progressing by a series of ascending steps he
finally (about 1880) turned his attention from
animal diseases to infectious diseases of the human
body, and there he applied the same principle in the
production of antitoxin injections.

Having proved the efficacy of vaccines in animal
diseases Pasteur devoted himself to the means of
combating diseases of the human body. He chose a
comparatively obscure human disease, hydrophobia,
but as results showed made a wise selection, and in
working it out to a successful conclusion he estab-
lished the principles on which future advances were
to be made. In 1880 he was already engaged in the
study of hydrophobia and in 1885 he made his first
treatment of a human being — a young boy from

OUTSTANDING BIOLOGICAL ADVANCES 31

Alsace. This treatment was successful as his in-
oculation of animals had been.

The time had now come for the establishment of
the Pasteur Institute which was opened in Paris in
1888. This, the first institute of its kind, became
the parent of numerous similar institutions that have
been established in many cities throughout the
civilized world.

As Frankland says in his Life of Pasteur: — "The
extraordinary enthusiasm which accompanied the
foundation of this great Institution has certainly
not been equaled in our time." This took popular
form. " Considerable sums of money were subscribed
in foreign countries whilst contributions poured in
from every part of France. Even the inhabitants of
obscure little towns and villages organized fetes and
clubbed together to send then- small gifts." With the
lively appreciation of the French for science and its
unselfish achievements the opening of the Institute
was regarded as of national importance. On Novem-
ber 14, 1888, it was opened with impressive cere-
monies presided over by the President of the French
Republic. Thus, after a long period of struggle and
strong opposition such as often falls to the lot of
innovators, Pasteur came to honor and recognition.

32 THE MAIN CURRENTS OF ZOOLOGY

The Pasteur Institute must not be thought of as
founded chiefly for the treatment of hydrophobia —
this is merely incidental. It is organized for the
complete investigation of bacteria and all manner of
serum injections and vaccines for the control of
diseases. In the Paris Institute, Emile Roux, the
present Director, perfected and proved the efficacy
of the antitoxin of diphtheria (independently dis-
covered by Behring in 1892) . From it has emanated,
directly or indirectly, such important procedure as
vaccination against typhoid fever, the serum treat-
ment of bubonic plague, etc. Without the superb
work of Pasteur these advances could not have taken
place.

Koch. — Robert Koch (Fig. 8) was born in 1843,
and for several years before his death in 1910, he was
the Director of the Institute for Infectious Diseases
in Berlin. His investigations were mainly those of a
medical man and were crowned with remarkable
success. In 1881, he discovered the bacillus of
tuberculosis, in 1883, the specific germ of Asiatic
cholera, and since that time his name has been con-
nected with many notable discoveries that are of
continuous practical application in the science of
medicine. He was so ingenious, so highly trained and

OUTSTANDING BIOLOGICAL ADVANCES 33

so incisive in analysis, that from time to time he was
called on by different countries to assist in the in-
vestigation of the causes and means of control of
infectious diseases — such as Asiatic cholera, the
bubonic plague and the sleeping sickness of Africa.
Koch was intimately concerned in establishing
bacteriology as an independent science. In 1882, he
introduced into bacteriological study the ingenious
method of employing solid culture media. Bacteria
are so minute that it was a perplexing problem to
separate the several forms that are commonly mixed
and to secure a pure culture of one kind. This was
made possible by placing a liquid culture of the mixed
bacteria in melted gelatine — and other media ren-
dered liquid by heat. This mixture was stirred with a
glass rod and by this means the bacteria were sep-
arated and distributed. The melted gelatine was
now allowed to flow over a sterilized glass plate,
making a thin film which hardened on cooling. In
this manner the separated bacteria were held in place
and as they grew in clusters, there were spots of pure
or nearly pure culture. These spots were observed
under the microscope, were picked off and planted
again in liquid gelatine and the process repeated
until pure cultures were secured.

34 THE MAIN CURRENTS OF ZOOLOGY

These methods so obscure, and, at first, so difficult
to ferret out are now commonly demonstrated in
schools and training institutions. Many simple
experiments are now tried which give evidence of
the presence of these very minute germs in the air.
By exposing plates of sterilized gelatine in shallow
dishes with glass covers to keep out germs, in a room
before and after sweeping, in crowded school rooms
and in open country air, by allowing tap water to
trickle across a sterilized gelatine film, by allowing a
fly to walk upon it, etc. By these means the sterilized
plates become infected, they are immediately covered
and set away in a warm place. The growth of bac-
teria on the gelatine produces easily seen patches
and give evidence of the existence of these germs
which, individually, can be detected only by high
magnification. It is obvious that the rise of bac-
teriology with its special problems exerted wide
influence on all biological science and this justifies
classifying it with the outstanding advances of the
century.

The Experimental Study of Heredity.— The in-
vestigation of heredity is of surpassing interest.
There are so many theoretical and practical questions
involved. Perennial is the wish to know the way in

OUTSTANDING BIOLOGICAL ADVANCES 35

which hereditary qualities are passed from genera-
tion to generation and the conditions under which
they are transmitted and by which they are qualified.
This has led to much speculation and the formulation
of various temporary theories of heredity that have
given way to better ones. It is a long and involved
story to trace the transformations of these theories,
but, it may be said in a word, that, in the last decade
of the nineteenth century, they were replaced by the
theory of germinal continuity — one of the most
fruitful ideas of nineteenth century zoology. This
idea will be returned to under the evolution theory of
Weismann.

The theories referred to were chiefly the result of
speculative thinking, and more promising avenue?*
were opened through the application of experiment.

The application of experimental and of statistical
methods to the study of heredity was brought about
chiefly by two men — Francis Galton, the English*
man, and Gregor Mendel, an Austrian monk.

Although Mendel conducted his experimental ob-
servations of heredity and published his results
(1866-1867) before Galton had fairly begun, we
shall see that Galton's results got into notice before
those of Mendel and began to influence progress.

36 THE MAIN CURRENTS OF ZOOLOGY

Accordingly, since his influence preceded Mendel's,
Galton is commonly recognized as the founder of
the scientific study of heredity. Observations of
"Mendelian inheritance" began to be active only
after the opening of- the twentieth century.

Galton. — Francis Galton (1822-1911) Fig. 9, by
directing attention to the inheritance of individual
characters made the subject of heredity manageable.
Previously, hereditary traits had been considered in
their entirety, and the resemblances and differences
of parents and their offspring had been averaged.
This method was too diffuse, since no one could
distinguish sharply among the multiplicity of char-
acters; greater definiteness was introduced when
Galton began to study hereditary characters sep-
arately.

Galton was the grandson of Doctor Erasmus
Darwin and the half cousin of Charles. After pub-
lishing books on his travels in Africa, he began the
experimental study of heredity, and in 1871, he read
before the Royal Society of London a paper on the
theory of inheritance. The observations upon which
he based his conclusions were made by the transfu-
sion of blood in rabbits and their after-breeding.
Later he observed the method of inheritance of spots

FIG. 7. — SIR JOSEPH LISTER (1827-1912) FIG. 8. — ROBERT KOCH (1843-1910)

FIG. 9. — SIR FRANCIS G ALTON
(1822-1911)

FIG. 10. — GREGOR MEXDFL
(1822-1884)

OUTSTANDING BIOLOGICAL ADVANCES 37

on the coat of certain hounds, investigated by statis-
tical methods the inheritance of stature and of genius
in human families, etc. He was led by his observa-
tions to formulate a law of ancestral inheritance
which received its clearest expression in his book,
Natural Inheritance, published in 1889.

He was so deeply interested in Eugenics — the
investigation of the conditions that improve, or
impair, the races of animals — that he is to be re-
membered as the founder of that branch of biological
knowledge.

Mendel. — The earliest experimental investiga-
tions of heredity were conducted with plants, and
the first epoch-making results were those of Gregor
Mendel (1822-1884) (Fig. 10), a monk and later
abbot, of an Augustinian monastery at Briinn,
Austria. In the garden of the monastery, for eight
years before publishing his results, he made experi-
ments on the inheritance of individual (or unit)
characters in twenty-two varieties of garden peas.
Selecting certain constant and obvious characters, as
color and form of seed, length of stem, etc., he pro-
ceeded to cross these pure races, thus producing
hybrids, and, thereafter, to observe the results of
self-fertilization among the hybrids.

38 THE MAIN CURRENTS OF ZOOLOGY

The hybrids were produced by removing the un-
ripe stamens of certain flowers and later fertilizing
them by ripe pollen from another pure breed having
a contrasting character. The results showed that
only one of a pair of unit characters appeared in the
hybrids of the next generation, while the other con-
trasting character lay dormant. Thus, in crossing a
yellow-seeded with a green-seeded pea, the hybrid
generation showed only yellow seeds. The char-
acter thus impressing itself on the entire progeny was
called dominant, while the other that was held in
abeyance was designated recessive.

That the recessive color was not blotted out was
clearly demonstrated by allowing the hybrid genera-
tion to develop by self-fertilization. Under these
circumstances a most interesting result was attained.
The filial generation, derived by self-fertilization
among the hybrids, produced plants writh yellow and
green seeds, but in the ratio of three yellow to one
green. All the green-seeded individuals and one-
third of the yellow proved to breed true, while the
remaining two-thirds of the yellow-seeded plants,
when self -fertilized, produced yellow and green seeds
in the ratio of three to one.

Subsequent breedings gave an unending series of

OUTSTANDING BIOLOGICAL ADVANCES 39

results similar to those obtained with the first filial
generation.

This great principle of alternative inheritance was
exhibited throughout the extensive experiments of
Mendel, and it is now recognized as one of the great
biological discoveries of the nineteenth century.
Mr. R. C. Punnett gives (1905) a remarkably clear
and terse statement of the facts as follows: "When-
ever there occurs a pair of differentiating characters,
of which one is dominant to the other, three possibil-
ities exist: there are recessives which always breed
true to the recessive 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 in-breeding 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."

The results of MendePs experiments are the con-
sequence of the fact that the germ-cells retain their
purity with respect to unit characters. That is, in
the combination of germ-cells by cross-breeding, the
hereditary qualities do not lose their individuality —
they are mixed but not blended. When the germinal

40 THE MAIN CURRENTS OF ZOOLOGY

elements are formed in these hybrid plants two
classes of germ-cells will arise in equal number, one
class carrying the dominant and the other the reces-
sive quality. Chance combinations of these germ-
cells will yield on the average, one union of dominant
with dominant, one union of recessive with recessive,
and two combinations in which dominant and reces-
sive are united. In the latter instance the dominant
will be the visible character, the recessive, though
present, being invisible. This segregation of the
gametes into two sets of "pure" gametes was recog-
nized by Mendel in an attempted theoretical explana-
tion of his observed facts, and, in view of the state of
knowledge at the time, showed remarkable analytical
ability.

MendePs papers were published in 1866 and 1867 in
the proceedings of the Natural History Society of
Briinn, but their importance was overlooked for
nearly thirty-five years. The periodical in which
they appeared was not widely known, and moreover,
the minds of naturalists at that time were largely
occupied with the questions of organic evolution
raised through the publications of Darwin. In the
year 1900, however, the great principle of heredity
worked out by Mendel was independently redis-

OUTSTANDING BIOLOGICAL ADVANCES 41

covered by the botanists De Vries, Torrens, and
Tschermak. By searching the literature for anticipa-
tions of their results, the unrecognized papers of
Mendel were brought to light and made generally
known to the scientific world.

Since 1900, extensive experiments by Bateson and
many others have served to confirm and extend
Mendel's discovery. In the United States the experi-
ments of Davenport and of Castle on inheritance in
poultry, the inheritance of fur in guinea-pigs, erect-
ness of ears of rabbits, etc., the far-reaching experi-
ments of Morgan with the fruit-fly, as well as the
experimental work of others, have extended our
knowledge of Mendelian inheritance. The combined
work on inheritance in animals and plants of all
observers has so thoroughly supported Mendel's
conclusions, that the principle of alternative in-
heritance is commonly spoken of as Mendel's law.1

Other investigations have led to the recognition of
the physical basis of heredity and to the idea of
germinal continuity. Within the nucleus of cells of
plants and animals there are certain very minute
bodies, the chromosomes (discovered 1883), which

1 The seven paragraphs above are quoted from the writer's Biology and
Its Makers.

42 THE MAIN CURRENTS OF ZOOLOGY

stain deeply with micro-chemical dyes. These are
believed to be the bearers of heredity.

Since the germinal cells of plants and animals
must be fertilized before they develop, we find in the
chromosomes the source of maternal and of paternal
qualities — because fertilization is essentially a union
of the chromosomes of egg and sperm. Eggs in
getting mature lose one-half their chromosomes,
sperms, or their fertilizing agents, also in course of
formation have their chromosomes reduced by one-
half. Now the egg is fertilized by the union of the
sperm with it, and the fertilized egg is bi-parental.
One-half the chromosomes of the fertilized egg come
from the mother and one-half from the father. The
maternal chromosomes (of the egg) and the paternal
(of the sperm) are the bearers of the hereditary
qualities of both parents. In considering the cell-
theory it was pointed out that the problems of he-
redity are at bottom cellular problems and the state-
ments just made will help to illustrate that point.

In closing this review we may re-affirm, that, on
account of their wide influence on the entire field of
biology, the five events designated all qualify as
outstanding biological advances of the nineteenth
century.

CHAPTER IV
ZOOLOGY EMERGES

AFTER analyzing its five outstanding advances and
before proceeding to discuss other steps of biological
progress we should make a digression to consider the
circumstances under which science developed, and, in
particular, those conditions that led to the emergence
of zoology as a separate science.

As in human affairs present conditions can be
understood only in the light of precedent conditions,
so hi zoology, a brief sketch of its rise is essential to an
intelligent comprehension of the subject.

It is not necessary to attempt to picture the crude
beginnings of observations of animated nature, and
the dawning of simple ideas regarding animals and
plants. The hunters, the poets, the artists of an-
tiquity and the primitive nature-searchers accumu-
lated facts of observation and invented many fables
about animals. Fact and fable were intermingled and
molded into a crude natural history of animals which
existed long before the advent of Aristotle.

Knowledge of nature among the ancients reached
its highest development in the Greek philosopher

43

44 THE MAIN CURRENTS OF ZOOLOGY

and naturalist Aristotle (384-322 B. C.) (Fig. n).
He was a man of vast intellect engaged in a variety of
intellectual occupations. In addition to writings on
metaphysics, rhetoric, etc., he wrote and lectured on
the natural history of animals (Historia Animalium)
as an independent subject. It is noteworthy that at
this early day, hi his scheme of zoology, he subor-
dinated the ideas of classification to his observations
on structure (De Partibus Animalium) and develop-
ment (De Generations Animalium). These are the
three books of Aristotle on zoology that have been
handed down to us. He made extensive studies of
life histories and recorded many facts that were re-
discovered only in the nineteenth century.

The circumstance that made Aristotle eminent in
science (outside his superb natural talents and his
industry) was his method. He was the greatest in-
vestigator of antiquity! While we commonly think
of him as standing at the beginning of science, he
was, in fact, preceded by a large number of observers
whose writings and verbal utterances are lost. Al-
though living in the fourth century before Christ he
speaks of "the ancients" in his writings and says
that he took into account their observations in estab-
lishing his natural history, but he says, further, that

ZOOLOGY EMERGES 45

his effort to organize the subject is the first attempt
and in that regard he had no forerunners.

The designation "the greatest investigator of
antiquity" is significant since it implies that the
notable development of science among the Greeks was
owing chiefly to their method of inquiry — the direct
observation of nature and the application of reason to
the data thus gathered. Had investigation remained
the method of ascertaining truth, the history of in-
tellectual development would have been far different.

The Arrest of Inquiry. — With the overthrow of
ancient civilization the conditions of mental life were
so altered that there came about an arrest of inquiry
that bred ignorance and led to the decline of science.
All independent observation ceased. Men no longer
interrogated nature by the method that had proved
so fruitful. This condition of human development
supplies an answer to the question continually
raised — "Why was there no direct development of
learning on the splendid Greek foundation? "

With the sweep of the barbarian hordes from the
north over the civilized people of the south, monu-
ments of civilization were destroyed, libraries were
pillaged and burned, books became scarce and, subse-
quently, were housed chiefly in the. monasteries.

46 THE MAIN CURRENTS OF ZOOLOGY

General ignorance prevailed. The means of dis-
semination of knowledge did not exist, but the chief
factor in the overthrow of learning was the arrest of
inquiry into natural phenomena and the substitution
therefor of a metaphysical method. The priesthood
had access to the manuscript writings, and they, with
the medical men of the period, became the educated
classes. Under these conditions the direction of
intellectual life was assumed by the theologians who
were chiefly interested in contemplation of the
spiritual and the supernatural and the medical men
were submerged by the general change in the in-
tellectual atmosphere.

A world-shunning spirit was engendered that was
hostile to scientific inquiry and observations of nature
came to be looked on as prompted by impious cu-
riosity, and as an attempt to pry into the secrets
of the Creator. Without the wholesome effect of
observation and experiment, mystical explanations
were invented for natural phenomena and ignorance
and superstition prevailed. To question the mystical
interpretations of nature was to invite theological
persecution. No science could prosper under these
conditions, and zoology languished in common with
the other sciences.

ZOOLOGY EMERGES 47

A barren period of intellectual life followed. Al-
though the intellectual life of the middle ages was
active among theologians, philosophers and other
educated classes it was so directed that for a period
of a thousand years, under the dominance of theolog-
ical authority, no really productive writings resulted.
The leading medical men kept alive some spirit of
investigation but it was confined to then: own craft
and was handed along by preceptor to pupil without
becoming common property. Their occupation
brought them into touch with natural phenomena.
They knew the properties of herbs and their effects
on the human body. They became acquainted to
a limited degree, with anatomy and physiology.
Finally, it was through the medical men that renewal
of observation on organic nature was brought about.

Renewal of Observation. — Nearly nineteen cen-
turies after Aristotle there occurred, as one of the
features of the Renaissance, a revival of the scientific
method bringing once more into human affairs the
indispensable conditions even for the existence of
science. As the decline of science had been largely
due to the arrest of inquiry, and the substitution of
authority for investigation as the method of ascer-
taining truth, so the renewal, so far as progress of

48 THE MAIN CURRENTS OF ZOOLOGY

zoology was concerned, was a return to the observa-
tion of nature.

This new movement was a revolt of the intellect
against existing conditions. In its entirety it is
called the Renaissance. It was several centuries in
gaining enough headway to break over the barriers
that had been stretched across the path of progress.
From time to tune the more independent thinkers and
the more gifted individuals had attempted to restore
the practice of independent observation and thought,
but, repeatedly, their efforts were suppressed by
theological opposition. Finally, in the sixteenth cen-
tury, through the efforts of men like Galileo, Des-
cartes and Vesalius the method of scientific investiga-
tion was established. The renovation of intellectual
life began as early as the thirteenth century and
involved an expression of the human spirit in various
directions — artistic, literary, scientific, etc. The
artistic and literary development preceded the
scientific, and it was not until the Renaissance was
well under way that the scientific revival took place.
In the latter was involved not only the progress of
zoology, but all the benefits that have accrued from
the development of modern science.

Among the actors in the scientific renaissance,

ZOOLOGY EMERGES 49

Andreas Vesalius (1514-1560), by reforming anatomy
and thus placing morphological study on a new plane,
stands closest related to zoology. His great illus-
trated work on the structure of the human body
(De Fabrica Humani Corporis} 1543), based entirely
on observation, not only restored anatomy but at
the same time laid the foundations for the structural
studies of animals. On account of the wide influence
of this book of Vesalius', published in 1543, we must
recognize it as one of the milestones of biological
progress. It was his method of direct investigation
that produced the greatest results.

Previous to Vesalius anatomy had been expounded
from the desk chiefly by readings from Galen, a
celebrated physician of the fourth century A. D.
The strict adherence of Vesalius to observations and
faithfully drawn sketches from actual dissections
not only corrected many of Galen's statements but
overthrew authority as a source of knowledge and
replaced it by observation.

Some years later (about 1619) William Harvey,
who is known for his discovery of circulation of the
blood (1628), introduced experimental observation
into scientific investigation. Thus the method of
science was reestablished and, on the basis of ob-

50 THE MAIN CURRENTS OF ZOOLOGY

servation and experiment, scientific knowledge began
to advance.

The zoology of the period was intermingled with
medical science, especially with anatomy and phys-
iology, and had no recognized existence as an in-
dependent subject. Although William Harvey in-
vestigated the structure of many animals, the
embryology of the chick and of some mammals,
zoology remained in the iatric condition of union with
medicine. Out of this condition zoology emerged, not
full fledged, but as a small offshoot of the medical
sciences.

It was not long, however, in arriving at an in-
dependent position but the zoology of the seven-
teenth and eighteenth centuries had few modern
aspects.

In the early years of the Renaissance Aristotle was
translated, and later small independent advances were
made by various writers as Wotton (1552), Jonston
(1549-1553) and Aldrovandi (1599-1606). The most
important zoological work between Aristotle and
John Ray (the immediate prececessor of Linnaeus),
was that of the Swiss, Conrad Gesner (1516-1565).
His Historia Animalium is a voluminous publica-
tion, four volumes appearing between 1551 and 1556,

ZOOLOGY EMERGES 51

and a fifth in 1587, twenty-two years after his death.
In some editions it contains 4500 folio pages and
nearly 1000 illustrations.

Through the renewal of observation the stream of
science, so long held in check by wrong methods, was
released, movement was started and the seventeenth
century was notable . for advance in independent
observation. The microscope was introduced as a
tool of investigation. The whole field of nature came
rapidly under examination. Structural studies were
applied to vegetables as well as to animals. Mal-
pighi (1628-1694), Swammerdam (1637-1680) and
Leeuwenhoek (1632-1723) investigated the structure
of insects and of other simple animals producing
valuable work on minute anatomy, on histology and
on embryology. To notice these really important
contributions in detail would unduly prolong the
story. Accordingly, we pass to Linnaeus (1707-
1778) with whom systematic zoology may be said to
have begun.

CHAPTER V
LINN^US AND HIS INFLUENCE

THE service of Linnaeus to natural history was
unique. He introduced clarity and system. The
known animals and plants, ever increasing in number
through the collections of travelers and naturalists,
were in a confused state. They were known by local
names in different sections of the same country and
were differently designated in various languages.
By adopting Latin as a uniform medium he elabo-
rated a system of naming every production of nature
in two words, a generic and a specific name, as Fells
domesticate) for the domestic cat and Canis familiaris
for the domesticated dog. The other members of the
cat family as the lion, tiger, leopard, etc., were given
the generic name of Felis and the specific name, in
each case, distinguished the particular kind of Felis.
In a like manner, the members of the dog family as
the wolf, the fox, etc., are of the genus Canis but the
specific attached to the generic name indicates the
particular kind of anmal. The cat family as a whole
was designated Felidae and the dog family Canidae.

Thus we have a simple and uniform system by

5*

LINN^US AND HIS INFLUENCE 53

which all animals may be named. This system was
adopted throughout the world, and by a happy stroke
Linnaeus gave to natural science a common language
that remains in use to-day. The influence of this may
be realized when we remember that the naturalists
of all countries use identical names for the same
animals and plants. He also simplified the problem
of identification by giving terse descriptions, involv-
ing only the salient points by which animals and
plants may be recognized.

His publication the Systema Natures which passed
through twelve editions (first edition in 1735) is by
no means a treatise on organization of annuals and
plants, but a methodically arranged catalogue with
brief descriptions and their new names. The Sys-
tema embraces also a consideration of minerals.

Linnaeus did not invent the binomial nomenclature
but brought it into general use, and by common con-
sent, zoologists accept as the starting point for
zoological names the tenth edition of the Systema
Natures published in 1758. The botanists frequently
use as a base line for names his Species Plantarum of

1753-
Although Linnaeus made a lasting impression, he

gave to natural history a one-sided development.

54 THE MAIN CURRENTS OF ZOOLOGY

His followers were chiefly collectors and classifiers,
who by interminable species-making brought zoology
into disrepute from which it was rescued by Cuvier
and others who emphasized structure, development,
and physiology rather than mere classification. ,

Linnaeus also defined species, which centered at-
tention on the distinguishing characters of animals,
and paved the way for the consideration of the origin
of species that became so significant, under Darwin
in the nineteenth century. In this particular Lin-
naeus was preceded by John Ray (1628-1705) who
was the first to introduce into natural history an
exact conception of what is species.

Linnaeus (Fig. 12) was born in Rashult, Sweden,
1707, the son of a poor Lutheran pastor. He was
inattentive to ordinary studies, being engaged with
his own thoughts and taking delight in collecting
natural objects. He was regarded as dull and un-
fitted for an intellectual career. His father, in
dispair, was about to apprentice him to a shoemaker
when a doctor of the town recognized his unusual
type of mind and pursuaded his father to promote his
education. After many struggles with poverty, he
was graduated from the University of Hardewyk in
Holland in 1735 with the degree of Doctor of Med-

FIG. ii. — ARISTOTLE
(384-322 B. C.)

FIG. 12. — CAROLUS LIXN.EUS
(1707-1778)

FIG. 13. — RUDOLPH LEUCKART

(1823-1898)

FIG. 14. — GEORGES CUVIER
(1769-1832)

LINN^US AND HIS INFLUENCE 55

icine. But he was destined for a university career,
and after a few years of wandering in which he visited
France and England, he was appointed professor at
the University of Upsala and became one of the most
widely recognized men of its faculty. His drawing
power was great, during his residence the attendance
at the University advanced from 500 to 1500 and his
classes were attended by several hundred students.
He sustained close personal relations with his stu-
dents and his teaching gave a great impetus to the
study of natural history. His disciples were for the
most part men of smaller type and in their hands the
study of zoology was lowered by their devotion to
species-making while observations of a more im-
portant character on animals were neglected. Ac-
cordingly, the influence of Linnaeus was not progres-
sive. His chief service was to reduce to systematic
form observations on the external and general char-
acter of animals and to supply the nomenclature that
is in use at the present day.

As to personal appearance and human qualities
this light-haired Swede was a short, thick man with
large limbs, affable and easy of approach. He was
vain and his self-esteem was greatly increased by the
widely extended praise that had been given to his

56 THE MAIN CURRENTS OF ZOOLOGY

work. He was impatient towards criticism and
adverse comment of his work often threw him into a
violent passion.

In 1907 occurred the two hundredth anniversary
of his birth which was celebrated by the University of
Upsala with appropriate ceremonies. At this time
many articles were published about Linnaeus that
supply abundant reading matter regarding his life
and work. To mark this celebration there was pub-
lished a facsimile reproduction of the first edition of
the Systema Natures — a folio of eight pages — con-
taining the systematic arrangement of the "three
kingdoms " of nature embracing minerals, plants and
animals. This interesting document is readily ac-
cessible in the book market.

A splendid offshoot of the natural history of
Linnaeus is Ecology — the study of organisms in
relation to their surroundings. This has wider
affinities but is related to natural history. For con-
venience we may also place in this wide territory the
Geographical Distribution of Animals.

The Linnaean system of classification had grave
defects. It was not founded on a knowledge of the
comparative structure of animals and plants, but in
many instances upon superficial features that were

LIN1SLEUS AND HIS INFLUENCE 57

not distinctive in determining their position and
relationships. His system was essentially an arti-
ficial one, a convenient key for finding the names of
animals and plants, but doing violence to the
natural arrangement of those organisms.

To do justice, however, to the discernment of
Linnaeus, it should be added that he was fully aware
of the artificial nature of his classification. A real
natural system, founded on the true affinities of
animals and plants as indicated by their structural
characters, he regarded as the highest ami of classifi-
cation. But, he never completed a natural system,
learning only a fragment.

Even the larger groups of animals were extended
and much modified by Cuvier, by von Siebold, by
Leuckart and by others. As to the larger divisions
of animals and plants, Linnaeus recognized only
classes and orders. Then came genera and species.
He did not use the term family in his formulae; this
convenient designation having been introduced, in
1780, by Batch.

The first modification of importance to the Lin-
naean system was that of Cuvier, who proposed
(1815) a grouping of animals based upon a knowledge
of their comparative anatomy. He declared that

58 THE MAIN CURRENTS OF ZOOLOGY

animals exhibit four types of organization (Verte-
brata, Mollusca, Articulata and Radiata) and his
types were substituted for the primary groups of
Linnaeus.

But naturalists were not long in discovering that
the primary divisions of Cuvier were not well bal-
anced, and, indeed, that they were not natural
divisions of the animal kingdom.

The group Radiata was the least sharply denned,
since Cuvier had included in it not only those animals
which exhibit a radial arrangement of parts, but also
unicellular animals that were asymmetrical, and
some of the worms that showed bilateral symmetry.
Accordingly, Karl Th. von Siebold, in 1845 separated
these animals and redistributed them. For the
simplest unicellular animals he adopted the name
Protozoa, which they still retain, and the truly
radiated forms, as starfish, sea-urchins, hydroid
polyps, coral animals, etc., were united in the group
Zoophyta. Von Siebold also changed Cuvier's
branch, Articulata, separating those forms, such as
Crustacea, insects, spiders, and myriopods, which
have jointed appendages, into a natural group called
Arthropoda, and uniting the segmented worms with
those worms that Cuvier had included in the radiate

LINNAEUS AND HIS INFLUENCE 59

group, into another branch called Vermes. This
separation of the four original branches of Cuvier
was a movement in the right direction, and was
destined to be carried still farther.

Rudolph Leuckart (Fig. 13), the distinguished
zoologist of Leipsic, following the lead of von Siebold
made further modifications. He split von Siebold's
group of Zoophytes into two distinct kinds of radiated
animals: the starfish, sea-urchins, sea-cucumbers,
etc., having a spiny skin, he designated Echinoderma;
the jelly-fishes, polyps, coral animals, etc., not posses-
sing a true body cavity, were also united into a
natural group, for which he proposed the name
Ccelenterata.

From all these changes there resulted the seven
primary divisions — branches, subkingdoms, or
phyla — which with small modifications are still in
use. These are Protozoa, Ccelenterata, Echino-
derma, Vermes, Arthropoda, Mollusca, Vertebrata.
These seven phyla are not entirely satisfactory and
there has resulted from more careful analysis a
multiplication of subkingdoms and a redistribution
of forms as in the case of the brachiopods, the
sponges, the tunicates, etc.

A tabular view showing the modifications made in

60 THE MAIN CURRENTS OF ZOOLOGY

the larger groups of animals will be helpful at this
point.

LINNAEUS
Mammalia (Mammals)

Aves (Birds)

Amphibia (Amphibia
and Reptiles)
Pisces (Fishes)
Insecta (Including
Crustacea, etc.)
Vermes (Including

CUVIER

Vertebrata (Embracing
five classes: Mam-
malia, Aves, Rep-

tilia Batrachia Pis-
ces)

Mollusca
Articulata

VON SIEBOLD

Vertebrata
(Embrac-
ing five
classes)

Mollusca
f Arthropoda

LEUCKAR

Vertebrata
(Five
classes)

Mollusca
Arthropoda

Mollusca and all
lower forms)

Radiata

\ Vermes
f Zoophyta

Vermes

f Echinodei
\ Ccelenter;

I Protozoa

Protozoa

Biological progress (outside the changes in classi-
fication) from Linnaeus to Darwin, although details
were greatly multiplied, proceeded by definite steps.
Linnaeus and his successors were concerned with the
organism as a whole, the external appearance, colors,
spots, the horns, the hoofs, etc. The next distinct
step was that taken by Cuvier and his school. In-
stead of the complete organism, the organs of which
it is composed became the chief subject of analysis.
The organism was dissected, the organs were exam-
ined and those of one kind of animal were compared
with another. This started the line of comparative
anatomy which played a much more important part
in the development of zoology than work of the
Linnaean type. After the organs were investigated
the tissues came under review and, then, with more

LINNJEUS AND HIS INFLUENCE 61

incisive inquiry, the cells composing the tissues
became the object of investigation. These progres-
sive steps of analysis, from the organism, to organs,
to tissues and cells finally culminated in the recogni-
tion of protoplasm the actually living substance of
all animal (and plant) organization.

Knowledge of the physiological side of animal life
had a parallel development. In the period of Lin-
naeus, the physiology of the organism was pursued
by Haller and his school; following this the physiol-
ogy of organs and tissues was advanced by J. Muller,
Bichat and others. Later, Virchow investigated the
physiology of cells, and Claude Bernard the chemical
activities of protoplasm.

CHAPTER VI
CUVIER AND STRUCTURAL ZOOLOGY

AFTER Linnaeus had founded natural history and
started activity in collecting and classifying animals
zoology was soon in ripe condition for a new depar-
ture. The method of Linnaeus brought about a
general familiarity with the animal kingdom, but so
long as studies were confined to externals and to the
organism as a whole no deep-seated advance could
be made.

Cuvier now came forward, and by a more incisive
analysis, he placed emphasis on the study of struc-
ture as the key to the knowledge of animal life.
When structure is pursued to its limit, by embracing
microscopic as well as gross anatomy and the process
of development, it makes a very important division of
zoological study. This is structural zoology or com-
parative anatomy. The combination of the various
studies that fall under this head are commonly
designated morphological studies and the term
morphology is used to embrace them all.

In order to complete the picture of animal life

there is needed the complementary division of

62

CUVIER AND STRUCTURAL ZOOLOGY 63

physiological studies. Thus Physiology and Mor-
phology are the two chief divisions of Zoology. We
must remember that there was concurrent progress
in these two departments but for clearness they must
be separately considered.

Cuvier (1767-1832), (Fig. 14), although he had his
forerunners, may be said to have founded compara-
tive anatomy about 1805, and his influence dom-
inated zoology for the first third of the nineteenth
century. After attendance at the Carolinian Acad-
emy, at Stuttgart, in order to add to his slender
purse, he accepted employment as private tutor to
the sons of the Count d'H6ricy. This took him to
the sea coast near Caen in northern France. Hav-
ing time at his disposal, with eager enthusiasm he set
himself to become acquainted with the structure of
marine animals (especially mollusca). The results
of his investigations were sent to Paris for publica-
tion and this served to bring him to the notice of the
working naturalists of the French metropolis. In
particular, Lamarck and Geoffroy Saint-Hilaire con-
nected with the Royal Garden (Jardin du Roi, later
the Jardin des Plantes) gave a hospitable reception to
his work and extended a helping hand. He was
invited to come to Paris to connect himself with the

64 THE MAIN CURRENTS OF ZOOLOGY

Jardin du Roi, and here he developed the Natural
History Museum and gained recognition. Paris was
thereafter his home and the scene of his triumphs.

His was an attractive personality and as he threw
himself into his work with enthusiasm and well-
directed industry, he gained power, and soon forged
ahead of his companions in research. He was a
favorite of the Emperor Napoleon and by him was
made head of the educational system of France. He
became a legislator and, finally, a Peer of France,
but with all his public duties he remained faithful to
his love of zoological science and continued to work
in that field.

After his extensive treatise on comparative anat-
omy (1805) he published, in 1815, his well-known
book on the Animal Kingdom (Le Regne Animal).
In this he divided the animal kingdom into branches
(embranchements) on the basis of their structure,
recognizing as stated in the previous chapter, four
great types of structure, the radiate, articulate,
molluscan and vertebrate. Although this classifica-
tion has been superseded by a better one, the basis of
structure employed by Cuvier was important and was
used in further advances.

Comprehensiveness of view was a distinguishing

CUVIER AND STRUCTURAL ZOOLOGY 65

feature of Cuvier's mind. In his investigations he
covered the whole field of animal organization from
the lowest to the highest, and combining his results
with what had been accomplished by earlier workers,
he established comparative anatomy on broad lines
as an independent branch of natural science.

Cuvier represents the beginning of that side of
zoology that reached its highest development in
Karl Gegenbaur (1826-1903) and Max Ftlrbringer of
Germany, in Owen (1804-1892) and Huxley (1825-
1895) of Great Britain, and in Joseph Leidy (1823-
1891) and E. D. Cope (1840-1897) of the United
States. His intellectual heirs in France were H.
Milne-Edwards (1800-1885) and Lacaze-Duthiers
(1821-1901).

Notwithstanding all his mental gifts, Cuvier was
not able to appreciate the most important contribu-
tion made to zoology in his period, by his distin-
guished contemporary and fellow-worker, Lamarck.
He became a strong opponent of the theory of organic
evolution of which Lamarck was the founder (1801
and 1809) in its modern sense. How completely
Cuvier's opposition served to hold in check the
progress of this fruitful idea in France is well recog-
nized.

66 THE MAIN CURRENTS OF ZOOLOGY

His famous debate with Saint-Hilaire, in 1830, on
the subject of unity of type involved the principles of
evolution. Cuvier won the debate largely from skill
as a debater and his personal magnetism. Posterity
views the matter in a different light and reckons this
opposition to Lamarck's views as one of the short-
comings of Cuvier.

His influence was so lasting that it prevented for
many years a respectful hearing of the evolutionary
idea in France, and she was the last of the highly
intellectual nations to harbor as true the ideas of
organic evolution. Frenchmen, however, have at-
toned for this to a degree by establishing in the
University of Paris a Professorship of Evolution
under the charge of Maurice Caullery, and have
given a cordial, if somewhat belated, recognition to
one of their foremost zoologists — Lamarck.

Comparative anatomy, the subject founded by
Cuvier, supplies some of the most obvious and con-
vincing evidences of organic evolution. Rightly
pursued it is a rich subject not only for facts but for
ideas. It is the division of zoology most commonly
used in the laboratory exercises of the present time.

Before leaving the consideration of Cuvier's con-
tribution to zoology, it should be pointed out that he

CUVIER AND STRUCTURAL ZOOLOGY 67

recognized the fossil vertebrates of the Paris basin as
being the remains of extinct animals, and he founded
the science of vertebrate paleontology. Lamarck,
whose researches were largely directed to the
analysis of the invertebrates, also investigated the
fossil remains of these lower animals and founded
invertebrate paleontology.

As we shall see in a future chapter the investigation
of fossil remains is a part of zoological study.

Histology. — The structure of organisms presents
two phases, that which is discernible to the unaided
eye and that revealed only by the microscope. The
former is gross anatomy and the latter rninute or
microscopic anatomy. The study of the micro-
scopic structure of the tissues is so important and
offers so many problems, that a new division of struc-
tural zoology (comparative anatomy) arose under the
name of histology.

This is the microscopic anatomy of the tissues.
The brilliant Bichat (1771-1801) was a pioneer in the
investigation of the tissues of animals but histology
did not take form until later. The establishment of
the cell- theory in 1839 gave a great impetus to this
study, and histology in the hands of Goodsir, of Eng-
land, Koelliker, of Germany, and Ranvier, of France,

68 THE MAIN CURRENTS OF ZOOLOGY

took on new and important aspects. It is a subject
in which all medical students are trained and reveals
what may be called the physiological anatomy of the
tissues. After the establishment of the cell-theory
it became clear that organs do not perform their
function as units but through their smaller ele-
ments— the cells.

The rise of histology is interesting, but to follow it
specifically would involve too great detail. Among
the many workers in this field we may select von
Koelliker (1817-1905), (Fig. 15), as the typical
histologist of the nineteenth century. He published
a text-book of Histology in 1857 and, thereafter, for
forty years he continued to make contributions to
this division of science. His great book on the tissues
(Handbuch der Gewebelehre) passed through several
editions from 1870 to 1897. It was thoroughly revised
and brought down to date in the years 1894-1897.

The plant histologists, Grew and Malpighi, of the
eighteenth century made interesting observations
and published many sketches of the microscopic ap-
pearance of plant tissues. These sketches, which
were faint foreshadowings of the cell idea, can be
examined by those sufficiently interested to look
up the works of Grew and Malpighi.

CUVIER AND STRUCTURAL ZOOLOGY 69

Leydig (1821-1908), in 1864, applied histology to
insects and other invertebrates.

Virchow developed a line of abnormal histology
which figures now under the name Pathology. Thus
structural studies of the tissues under the microscope
have given rise to normal histology and abnormal
(pathological) histology or pathology.

CHAPTER VII
THE RISE OF EMBRYOLOGY

AFTER the comparative anatomy of Cuvier was
well under way came the establishment of embryol-
ogy in which von Baer (1797-1876) was the central
figure. In 1828, by the publication of his detailed
observations on the development of the chick and
other animals (1834), he established the germ-layer
idea and carried the science of the development of
animals to a high level.

Embryology is supplemental to comparative anat-
omy and in its present stage of development is to be
classified as a morphological subject. It is not pos-
sible to appreciate in its full meaning any structural
problem of zoology without the assistance of em-
bryological study. The adult condition of an or-
ganism is the result of a series of changes, it is, in
fact, the last step in a long series of modifications
that have occurred in the process of building the
body from the single-celled condition of the egg to its
completed state. These modifications are so pro-
found that often the affinities of the animal can-
not be recognized in the modified state, and we

70

THE RISE OF EMBRYOLOGY 71

must go backwards and follow the embryological
record to see where the modifications of structure
occurred.

The most unexpected and most illuminating expe-
riences come from this source. In the embryos of
higher animals are found many traces of former
ancestral conditions. Evanescent organs as gill-
slits (with appropriate circulation) occur in all higher
animals including the human body. The gill-slits of
birds and mammals are transient and never come to
functional use. But their presence is indubitable,
and we begin to realize that they are clues to the
structural features of ancestral forms. They have
been handed along by heredity and although not
rising to a functional condition, they exist as hered-
itary survivals from the days when the ancestors of
birds and mammals were aquatic and had use for
gill-slits in respiration. The presence of rudimentary
teeth hi the jaws of the embryos of toothless whales
have the same significance.

Besides the transitory hereditary survivals, there
are many rudimentary organs such as rudimentary
ear muscles, tail muscles and the vermiform appendix
of the human body which are interpreted in a similar
way.

72 THE MAIN CURRENTS OF ZOOLOGY

It becomes apparent, that in the course of develop-
ment there is an embryological record impressed
upon the organism, embryological study reveals this
record and its interpretation is part of the task of the
anatomist. Embryology is of great importance in
zoology as giving clues to the relationship of animals
and affording data for the recognition of their line of
descent.

Von Baer (Fig. 16), the founder of modern em-
bryology, was a man of superb mental endowment,
unusual in the way in which he combined accurate
observations with sane and fruitful generalizations.
His "reflections" on the general features of the
development of animals are still of value. His book
on The Development of Animals (Entwickelungs-
geschichte der Tiere-Beobachtung und Reflexion) is one
of the great biological classics. He had finished his
embryological investigations in 1828, at the age of
thirty-one, and lived thereafter for forty-eight years.
At the time of the publication of his treatise on
embryology he was a professor in the University of
Konigsberg, but soon retired to look after his estates
in Russia. He made no further contributions to
embryology but became known for investigations in
meteorology, anthropology, etc. An autobiography,

FIG. 15. — ALBRECHT VON KOELLIKER
(1817-1905)

FIG. 16. — KARL ERNST VON BAER

(1792-1876)

FIG. 17. — FRANCIS M. BALFOUR
(1851-1882)

FIG. 1 8. — CLAUDE BERNARD

(1813-1878)

THE RISE OF EMBRYOLOGY 73

published in 1864, gives an interesting account of
his mental development.

Between von Baer and Balfour (1851-1882) under
whom embryology took on modern aspects, the
observations on the development of animals were
greatly multiplied. Activity was increased after the
announcement of the cell- theory (1839) and em-
bryologists began to see more clearly the significance
of the germinal elements and the germ-layers.

It was determined that the egg and the sperm are
single cells, the final step in reference to all eggs
being taken by Gegenbaur in 1865. The three germ-
layers common to all animals above the Ccelenterates
(Hydra, Hydroids, Jelly-fish, etc.) were shown to be
essentially alike as to origin and to give rise to the
same kind of tissues in the different animals. In the
light of embryology, all animals were seen to be
related through ancestral lines and to be united on the
broad plane of similarity of origin and development.
Von Baer had already indicated this, but it was in the
period between him and Balfour, that this great
truth became better illustrated and took hold on the
minds of embryologists and influenced their in-
vestigations.

Balfour (Fig. 17) now comes upon the scene and

74 THE MAIN CURRENTS OF ZOOLOGY

does eminent service. Up to this time the investiga-
tions of the embryology of animals, Both inverte-
brates and vertebrates, had resulted in a vast ac-
cumulation of monographs and scientific memoirs.
These publications were scattered in technical
periodicals, in the special publications of learned
societies, etc.

Balfour gathered these researches, read, digested
and published the results in a unified picture of the
science of embryology. He clarified as well as
unified the subject and produced a comprehensive
book on comparative embryology that contained the
substance of what was known regarding the develop-
ment of all animals from the lowest to the highest.
Balfour was especially gifted with the power of dis-
criminating analysis and charm of expression. His
book, of priceless value to embryologists, was pub-
lished in two volumes, 1880-1881, under the title of
Comparative Embryology.

Just after completing this monumental work while
on a journey to the Alps for recuperation he met his
death by slipping with his guide from one of the
Alpine passes.

Since 1881 the science of embryology has devel-
oped rapidly. There has been great refinement of

THE RISE OF EMBRYOLOGY 75

observation and of technique. Studies have become
more intensive such as following the cell-succession
from the egg step by step until the germ-layers are
established, further investigations into the mech-
anism of development, the nature of fertilization
and the study of the behavior of the chromosomes of
egg and sperm. The subject has also become ex-
perimental.

It has become too vast for a single publication to
embrace the embryology of invertebrates and verte-
brates, and, as a consequence, we have the standard
embryology of invertebrates by Korschelt and Heider
and many volumes on vertebrate embryology. There
are also those on a single animal, as Lillie's Develop-
ment of the Chick, and those on the development of the
Human Body such as the volumes by McMurrich,
Keibel and Mall, etc.

The great reference book on vertebrate embryology
as a whole is the comparative and experimental
embryology of Vertebrates, in six volumes, under the
editorship of Oskar Hertwig, assisted by a large
number of collaborators.

Among living and recent embryologists should be
mentioned: Oskar Hertwig (b. 1849) °f Berlin; Wil-
helm His (1831-1904) of Leipsic, whose researches on

76 THE MAIN CURRENTS OF ZOOLOGY

the development of the nervous system, the origin of
nerve fibers and the embryology of the human body
are important; and the late Charles Sedgwick Minot
(1852-1914) (Fig. 22). The last named biologist, of
dignified yet gracious personality, is remembered for
the wide and stimulating influence which he exerted
upon the development of biological research in the
United States. He was a prolific writer, his best
known books being Human Embryology and A Text
Book of Embryology, which take high rank. He
established at the Harvard Medical School a com-
prehensive collection of prepared sections of the
embryos of all classes of vertebrate animals. Under
the name of the Harvard Collection these are gen-
erously placed at the service of investigators and
have been the source of sketches for a large number
of embryological papers.

The notable collection of human embryos accumu-
lated on the Carnegie foundation by Professor
Franklin P. Mall (1862-1917), of John Hopkins
University is also available for reference and for the
use of investigators.

CHAPTER VHI

GENERAL PHYSIOLOGY AS A DIVISION OF
ZOOLOGY

THE study of structure and development is not
enough to acquaint us with the essential features of
an animal. The most significant thing about animal
mechanism is that it is endowed with life and we
should observe the principal activities of the mech-
anism along with its structure. As before indi-
cated, morphology and physiology represent the main
divisions of zoology. While physiology as a science
has advanced to great proportions and to a position
of independence, nevertheless general physiology of
animals is a part of zoology. It will, therefore, be
appropriate at this point to engage in a considera-
tion of the rise of physiology without attempting to
separate general physiology of animals from the main
current.

Morphology and physiology had a parallel devel-
opment. Just as Vesalius renovated structural
studies so Harvey by demonstrating the circulation
of the blood gave life to a new physiology.

This demonstration of the circulation had more

77

78 THE MAIN CURRENTS OF ZOOLOGY

far-reaching consequences than appear on the sur-
face. It was not merely showing that the blood
moves in a circuit, it also opened up the entire ques-
tion of the part played by the blood in the animal
economy. This is basal to the understanding of
physiology.

The tissues are bathed by the blood current. It is
the carrier of oxygen to the tissues of the body; into
its stream are diffused all the products of digestion, of
secretion, and of excretion; by its circulation it
distributes nourishment to the most remote parts of
the body and brings back the products of worn out
tissues for elimination by the kidneys, the lungs and
the skin. Accordingly, a proper conception of the
circulation was a necessary preliminary for the prog-
ress of physiology.

The classic book of Harvey (Fig. 30) on the cir-
culation of the blood (De Motu Cordis et Sanguinis)
was published in 1628, but he had been giving the
substance of it in his university lectures since 1619.

In the time of Harvey, however, physiology had
not fully emerged— it was still intermingled with
medical studies. It was not till the following cen-
tury, through the work of Haller, that it took its
place as an independent subject to be pursued for its

GENERAL PHYSIOLOGY 79

own sake and not necessarily for its applications to
medicine.

Haller's elements of physiology (Elementa Phys-
iologies) published in 1758 was the first comprehen-
sive treatise devoted exclusively to that subject.
After Haller physiology, now opened for investiga-
tion, grew rapidly. We must remember, however,
that Harvey was the pioneer who introduced experi-
mental study into biological science. The work of
Haller greatly broadened the field and encouraged
physiological experimentation.

From the time of Haller we pass to the nineteenth
century. In the opening year of that century was
born a man, Johannes M tiller, who exercised great
influence not only on physiology but upon the whole
field of biological science. Verworn says of him:
"He is one of those monumental figures that the
history of every science brings forth but once. They
change the whole aspect of the field in which they
work, and all later work is influenced by their
labors." Although Muller was professor of Phys-
iology at Bonn, and later at Berlin/he was also an
anatomist and, perhaps, more of a morphologist .in
his methods of investigation than physiologist. He
was great in his general influence. He had an un-

80 THE MAIN CURRENTS OF ZOOLOGY

usual faculty for inspiring enthusiasm in his students
and many of them, as Helmholtz and others, have
borne testimony of his immense influence in giving
them an outlook on life and inspiring them to their
highest endeavor.

Miiller (1801-1857) (Fig. 19) made physiology
broadly comparative. He brought into it all the
means of advancing the knowledge of animal or-
ganization— morphology, the microscope, chemis-
try, experiment, etc. He included psychology as a
new departure in the study of physiology.

But to the Frenchman Claude Bernard (1813-
1878) belongs the chief credit as the innovator of
experimental physiology. With the exception of
Ludwig, no other physiologist of his period can be
compared with him in the experimental field. In his
Introduction to the Study of Experimental Medicine
(Introduction a V etude de la Medecine Experimentale —
1865), ne summed up what he had for years been
teaching in his university lectures, and this remains
the standard contribution on the aims and methods
of experimental physiology.

Bernard's position in the history of physiology has
not been fully appreciated by biologists. He was the
foremost representative of physiology of his period.

FIG. 19. — JOHANNES MULLER (1801-1858)

GENERAL PHYSIOLOGY 81

Notwithstanding the overshadowing figure of M tiller
and his tremendous general influence, Bernard's
scientific contributions to physiology are of a higher
order. A careful reading of Bernard's investigations
and lectures are serving to advance him into the
foremost rank. Although his great skill as an exper-
imenter and his exposition of experimental phys-
iology in his Introduction entitle him to eminence, he
will be longest remembered for several epoch-making
discoveries.

Of these discoveries only two will be mentioned.
First the discovery of the occurrence of glycogen in
the liver — one of the first and most complete studies
of internal secretions. That the liver forms animal
starch (glycogen) as well as bile was a brilliant con-
clusion which was demonstrated by well thought-out
experiments. Bernard was notable for the way in
which he directed his experiments towards definite
ends. He was no blind experimenter who reached
into the unknown by tentative gropings, but first he
made a crucial mental analysis of his problem, and
then devised experiments for its investigation.

His discovery of vaso-motor nerves — both dilators
and constrictors — was another piece of experimenta-
tion of broad application in physiology.

82 THE MAIN CURRENTS OF ZOOLOGY

It will clear matters to remember that Bernard
used the designation experimental medicine as
synonymous with physiology, accordingly his Intro-
duction a r etude de la Medecine experimentale was a
treatise on experimental physiology.

It was Bernard (Fig. 18) who also gave a definite
position to general physiology which, as before
stated, is a division of biological study. His now
classic Phenomena Common to Animals and Plants
(Legons sur les phenomenes communs aux Animaux et
aux Vegetaux), published in 1878, was the first
treatise devoted to consideration of the vital ac-
tivities of plants and animals.

Physiology established on the broad foundations of
Bernard and M tiller developed along two independent
pathways — the physical and the chemical. We find a
group of physiologists, among whom Weber, Ludwig,
Du Bois, Reymond and Helmholtz were note-
worthy leaders, devoted to the investigations of
physiological facts through the application of meas-
urements and records made by mechanical means.
With these men came into use the time-markers, the
kymographs, and other ingenious methods that have
been adopted by Zoology, Physics and other sciences.
The investigation of vital activities by means of

GENERAL PHYSIOLOGY 83

graphic records made by instruments of precision has
come to represent one especial phase of modern
physiology.

The other marked line of physiological investiga-
tion has been in the domain of chemistry, where
Wohler, Liebig, Kiihne, and others have, through the
chemical changes occurring in its body, observed the
various activities that take place within the or-
ganism. Some of the more recent observations have
made a particular feature of the study of chemical
changes taking place within living matter. The
prodigious development of organic and biological
chemistry has shown the close interrelationship of
chemistry, physiology and biology.

The physiological method has been much applied
in zoological study. Besides the important investiga-
tions carried on by zoologists under the title of
"Experimental Morphology" there has arisen a
recognized division designated experimental zoology
which is chiefly physiological.

General physiology is so intimately related that all
students of zoology should take occasion to become
acquainted with Verworn's admirable treatise on
General Physiology.

CHAPTER IX
THE ANIMAL KINGDOM

IT is common phraseology to speak of the great
province embracing all animals as "The Animal
Kingdom." Linnaeus employed the designations
"Animal Kingdom," "Plant Kingdom" and "Min-
eral Kingdom" to indicate the three kingdoms of
nature; and the title of Cuvier's general zoology was
The Animal Kingdom Arranged According to its
Organization.

One phase of zoology has for its aim to give a
descriptive inventory of the animal kingdom. We
should remember, however, that this is merely one
aspect of zoology. In early times, it was the dom-
inate feature of zoological study, but it is now subor-
dinate in importance to those phases of the subject
that deal with structure, development, physiology,
habits, etc. The orderly arrangement of animals into
natural groups of different rank should be the out-
come of a study of their structure and life histories.

In the time of Linnaeus, the classification of
animals was based on observations of the external
resemblances and differences and, later, the internal

84

THE ANIMAL KINGDOM 85

structure was taken into account for the same pur-
pose. At the present time, however, and ever since
the doctrine of descent began to be accepted, nat-
uralists have had a better criterion for determining
relationships. Animals exhibit relationships because
they have sprung from a common stock. The mem-
bers of a natural group resemble each other in struc-
ture because they have a genetic relationship and
those that are closest allied have a closer kinship.
When the entire animal series is spoken of as the
Animal Kingdom, the large natural subdivisions of
the territory formerly were called subkingdoms, but,
at present, the designation commonly employed for
each subdivision is Phylum (from the Greek phylos,
a tribe). There is no agreement among zoologists as
to the number of phyla into which the animal king-
dom should be divided. " Some authorities recognize
only eight, while others maintain that there should
be as many as twenty or even more." Such extensive
subdivision of even the primary groups is probably
justified on technical grounds, but, as Richard
Hertwig has remarked: "In this way groups poor in
species and of little importance in a general account
of the animal kingdom are placed on the same basis
as the large and exceedingly important groups of

86 THE MAIN CURRENTS OF ZOOLOGY

vertebrates, arthropods and molluscs and thus ob-
tain, especially in the eyes of the beginner, an
importance which does not belong to them."

For our present purpose, it will be sufficient to
enumerate and briefly characterize the ten phyla
which embrace nearly all animals except those of
somewhat uncertain position. While merely the
phyla are mentioned here, it is to be understood that
the division of these large groups into classes, orders
and families brings us by groups of different rank to
genera and species. The latter divisions supplying
the generic and specific name by which individual
animals are known.

I. Protozoa. — The simplest microscopic, usually
aquatic, single-celled animals. In these animals, the
manifestations of life are reduced to their simplest
expression and a study of them is the best introduc-
tion to the more complex animals and also the best
introduction to general physiology. Certain forms
are disease-producing or pathogenic, as the germ of
malaria, of sleeping sickness, etc. Although very
minute, certain kinds of protozoa commonly occur as
fossils. Those producing shells of carbonate of lime
making beds of chalk, and those forming shells of
silica occurring in fossiliferous earths. The known

THE ANIMAL KINGDOM 87

Protozoa number about 8500 living and 200 fossil
species.

n. Porifera. — The sponges, chiefly marine an-
imals composed of many cells surrounding pores and
channels through which water circulates freely.
Besides budding, they are reproduced by eggs and
sperms. The soft living "sponge-flesh" is usually
supported by spicules and, in different varieties, by
skeletons of horny, calcareous or silicious material.
The horny sponges are of commercial importance.
The calcareous sponges and glass sponges are fre-
quently found as fossils. Fresh water sponges,
usually inconspicuous, are widely distributed but of
no commercial value. Approximately 2 500 living and
800 fossil species are known.

III. Coelenterata. — A group of slightly complex
animals embracing the fresh water hydra and nu-
merous salt water forms, as the polyps, jelly-fish,
coral-forming animals, etc. They exhibit a radial
arrangement of parts and most of them possess
peculiar stinging cells. The first distinctly developed
nervous system and sense-organs appear in this
group. Four thousand two hundred living and nearly
2000 fossil species are recognized.

The animals formerly grouped under the general

88 THE MAIN CURRENTS OF ZOOLOGY

heading Vermes present diverse and often puzzling
relations. It is now universally recognized that there
is no natural group or phylum "vermes" but the
title is often retained on account of its convenience.
The title is justifiable only as a popular name for
shape. The animals included under it do not form a
natural group of related species and the general
tendency is to split the group into at least three
phyla, — the flatworms, the roundworms and the
segmented worms or annelida. The brachiopod,
which are so abundant as fossils (500x3 species) are
frequently classified as shelled worms; at other
times, they are separated into an independent phy-
lum, or are united with the bryozoa into a phylum
molluscoida.

IV. Platyhelminthes. — This phylum of flatworms
includes fresh water, salt water and land planarians
and parsitic forms. The parasitic flatworms, such as
tapeworms, liver-flukes, etc., are responsible for
certain diseases of man and other animals. Four
thousand six hundred species are known.

V. Nemathelminthes. — The roundworms or thread-
worms are chiefly small parasitic worms, living in
the alimentary canal, the blood or the tissues of
man and other animals. The hookworm, respon-

THE ANIMAL KINGDOM 89

sible for much misery and shiftlessness among the
"poor whites" of the south, is an example. Other
common illustrations are: The harmless "Vinegar-
eel"; — the pin worm of the alimentary canal; the
Trichinella, which imbeds itself in the muscles and
comes from infected and imperfectly cooked pork;
the Filaria, a blood parasite, etc. One thousand five
hundred living species are recognized.

VI. Annelida. — The segmented worms embrac-
ing the earthworm, the leeches and others. Some
forms burrow in the earth, others inhabit fresh water
(leeches), and salt water (Nereis). About 4000
living species are known.

VH. Echinodermata. — Marine animals with a
spiny skin or a calcareous test covering the soft parts.
The sea cucumbers, the starfishes, sea urchins, sea-
lillies, etc., belong to this group. They exhibit a
radial arrangement of parts. Locomotion is usually
by tube-feet connected with a characteristic water
vascular system. There are known approximately
3000 living and 2600 fossil forms.

Vm. Arthropoda. — Contains the largest number
of species of any phylum. Separated from all forms
of worms by possessing jointed appendages. The
phylum embraces several large classes as: (i) Cms-

90 THE MAIN CURRENTS OF ZOOLOGY

tacea, lobster, crayfishes, shrimps, sow-bugs, etc.
(2) Insecta, an enormous group containing about
400,000 described living and 5000 fossil species.
Very interesting for exhibiting serial homology of the
appendages. These structures, although all equiva-
lent, and arising in the same manner, are, under
certain conditions, transformed into jaws, antennae,
walking-limbs, swimerets, etc. The insects exhibit
more clearly than any other animals the phenomona
of metamorphosis such as the development of a
worm-like larva through the chrysalis stage into the
winged insect. These animals are also immensely
interesting on account of their relation to the fer-
tilization of flowers, their habits, their communal
life and as disease carriers. (3) Myriopoda} centi-
peds, "thousand-legged worms," etc. (4) Arachnida,
or spiders, notable as web-spinners. This class in-
cludes scorpions, Limulus (the king-crab) and others.
IX. Mollusca. — Slugs, snails, clams, oysters,
squids, cuttle-fish, devil-fish, etc. Although the name
mollusca is from the Latin Mollis, meaning soft, this
applies only to the bodies of these animals; a large
number of them secrete shells which circumstance
makes them of frequent occurrence as fossils. About
60,000 living and 21,000 fossil forms are known.

THE ANIMAI^ KINGDOM 91

X. Vertebrate. — The most highly developed an-
imals, those above the simplest ones possessing ver-
tebrae, but this feature is not common to all. Ex-
cluding Tunicates and Amphioxus, five classes are
recognized: Fishes, Amphibia, Reptiles, Birds and
Mammals. The latter class including man. There
are about 30,000 living and a large number of fossil
species.

Intermediate between the molluscs and the
vertebrates are sea-squirts, or Tunicates. A phylum
Chordata is frequently made to include the Tunicates,
other primitive forms, and the vertebrates because
all these animals are alike in possessing a notochord, a
dorsal nerve-cord and gill-slits. The Tunicates num-
ber about 300 species.

There are several other groups of invertebrates of
uncertain position but which are often elevated into
the rank of phyla. If the Brachiopods are classed as
shelled worms, the most important of the remaining
forms are the Bryzoa. These are moss-like, incrusting
animals, inhabiting both salt and fresh water, and
numbering about 700 living and 1800 fossil species.

For a more detailed analysis of the animal kingdom,
with sketches and consideration of the structure of
types, consult the various manuals and text-books.

92 THE MAIN CURRENTS OF ZOOLOGY

The Animal Series. — In a certain sense animals
constitute a series, at the lower end of which are the
simple Protozoa and at the upper end the Mammals.
However graphic this conception may appear, it
needs to be taken with proper qualifications. An-
imals do not by any means form a connected series.
There is much overlapping of different groups and
there are various perplexing offshoots — as in the case
of the Echinoderms. Animals constitute a series in
the sense that they have a common ancestry and that
the higher forms are derived from the lower by a
process of descent, but adaptations to different con-
ditions of life have brought about many diversities.
The significant point is that they do not stand as
separate creations but are all related structurally,
physiologically and psychologically.

We may say, the most striking general feature of an
animal is that it has not arisen independently, but
that it exhibits a genetic similarity with other mem-
bers of the animal kingdom. The recognition of the
common genealogy of animals led to the doctrine of
organic evolution. It also prepares us to understand
that the study of a few selected types from the differ-
ent natural groups, with an analysis of their struc-
ture, their life histories and their relations to sur-

THE ANIMAL KINGDOM 93

rounding conditions, may serve to open the whole
field of zoology. Huxley attempted to do this by the
use of a single animal in his famous Introduction to
the study of Zoology based upon the study of the
Crayfish in all its essential relations to other animals
and to nature at large.

The study of types is a good procedure, but how
to avoid having this method lead merely to accumu-
lation of a certain set of facts regarding animals is a
matter of much concern, since that has been the
result, in so many cases, of holding exclusively to this
plan. As stated in an earlier chapter, what is lacking
in this method is concurrent attention to the back-
ground of the subject — information about the condi-
tions under which the subject developed, the cir-
cumstances that made possible its advances, the men
who accomplished results and an orderly though
brief account of the steps in its development.

The Number of Animals. — The number of known
animals is ever increasing by descriptions of new
species. Aristotle mentioned about 500 but probably
knew more. Linnaeus, in 1758, described 4236
species. About a hundred years later, Agassiz and
Brown listed 129,530. In 1886, Ludwig's revision of
Leunis's Animal Kingdom gives 273,220, and Pratt,

94 THE MAIN CURRENTS OF ZOOLOGY

in 1911, enumerates 522,400. This represents only
the named species of living animals and is far short
of the actual number. In Pratt's enumeration there
are 360,000 insects. We are to understand that the
number of living species is much larger since there
are many that have not been described and classified.

CHAPTER X
ZOOLOGY OF FOSSIL REMAINS

THERE is one large division of zoology not yet
touched upon — the study of the remains of extinct
animals. This is obviously a department of zoology
although it is more frequently placed with geology
under the name of paleontology. The extinct
animals were ancestors of those now living and many
revelations are found by studying their fossil re-
mains. The fossil remains of animals are so nu-
merous and cover such a long range of tune, that we
have preserved in the rocks not only a picture of the
succession of animal life on the globe for many cen-
turies, but, also, records of the transmutations or the
structural changes they have undergone. These open
such a wide sweep of observation that they are of
incalculable value in the study of zoology.

It is estimated that if the fossil bearing rocks were
accumulated in one series they would measure more
than forty miles in thickness and represent a period
of several millions of years in their formation. Exam-
ination of the fossils from the lower rocks shows that

for many aeons there were no vertebrate animals, and,

95

96 THE MAIN CURRENTS OF ZOOLOGY

that for the duration of many additional seons, the
only living vertebrates were Fishes. From the fishes
were gradually evolved the amphibians, the reptiles,
the birds and, finally, the mammals. All these
changes requiring immense stretches of time took
place before the advent of man.

From tune to time the fossil series exhibits interest-
ing connecting links such as the curious tailed and
toothed bird, the archaeopteryx, showing structural
relations between reptiles and birds.

The science of fossil remains is not only an off-
shoot of zoology but as before stated it was founded
by zoologists; Cuvier being the recognized founder
of vertebrate and Lamarck of invertebrate paleontol-
ogy. This science was extensively developed by
Zittel, the paleontologist of Munich, and by Cope
(Fig. 20), Leidy (Fig. 21), and Marsh in the United
States as well as by more recent workers.

Extensive progress has been made within the past
twenty-five years in observations of the fossil animals
and among other advances the genealogy of several
living families of mammals has been traced. Notable
studies have been made on the ancestry of Camels,
Elephants, etc. The most thoroughly known an-
cestral history is that of the horse. The zoological

F'G. 20. — E. D. COPE (1840-1897) FIG. 21. — JOSEPH LEIDY (1823-1891)

FIG. 22. — CHARLES SEDGWICK MINOT FIG. 23. — CHARLES OTIS WHITMAN

(1852-1914) (1842-1910)

ZOOLOGY OF FOSSIL REMAINS 97

history of this animal is a hackneyed theme but,
nevertheless, very convenient for reference. Al-
though not old hi comparison with the earlier animal
life, a quite close series of fossil remains shows the
development of the horse family through a period of
3,000,000 years. The earliest authenticated ancestor
of this race began in the Eocene period with an animal
having a four-toed limb in front and a five-toed one
behind. About the size of a fox, this eohippus was
the ancestor of the horse tribe. From this point, the
descendants of the original forms show the structural
modifications through which the family of horses
passed, until we arrive at the recent horse with a
single toe on both fore and hind feet, with the molar
teeth modified and fitted for its food of grass and
grain.

In the museum at Yale University and, notably,
in the American Museum of Natural History in New
York City, are preserved a large number of the fossil
remains of these animals. The development was not
that of a single kind of horse but parallel development
of several varieties some of which have become
extinct and others continued. It is a difficult
problem to keep separate the straight line of ancestry
of our modern horse, but the material now accu-

98 THE MAIN CURRENTS OF ZOOLOGY

mulated enabled Professor Henry F. Osborn, and
others, to separate the equus line from the other fossil
horses and to indicate the direct line of descent.

From the zoological standpoint especial interest
has centered about the fossil remains of man and of
pre-humans that are throwing light on the question
of human lineage.

The story of prehistoric man is imperfectly known,
although sporadic explorations have already accu-
mulated an interesting series of evidences bearing on
the subject, such as primitive stone implements of
human manufacture, crude sketches of extinct
animals by prehistoric artists, and fossil remains of
primeval man showing gradations in the shape and
the capacity of skulls. All these correlated sources
afford most convincing proofs of man's great antiq-
uity. He has left traces of his occupancy of the
earth, especially in central and southwestern Europe
and in England, long before the dawn of the historical
period.

The prehistoric stone implements are found asso-
ciated with the bones of extinct animals in caves, and
imbedded in the strata of soil and gravel that have
remained undisturbed for many centuries. The stone
implements are of three grades: Neoliths, the more

ZOOLOGY OF FOSSIL REMAINS 99

recent ones, carefully shaped with skill and artistic
feeling; Palaeoliths, very ancient, rude, but evidently
shaped by design; and Eoliths, rough stone chips
bearing evidence of use and indicating the existence
of man of less developed skill. These latter imple-
ments carry the trace of a tool-making creature back
into the Tertiary period.

Besides the stone implements there are many
sketches of extinct animals by prehistoric artists,
scratched on bone, ivory, horn, slate and on the walls
of caves. The inference to be drawn from these
sketches is that man was alive in Central and South-
western Europe when the hairy mammoth and the
reindeer occupied the same territory. The crude
sketches of palaeolithic man, just referred to, merge
by gradations into the more carefully drawn, and
sometimes colored sketches, of Neolithic man. Those
of the cave of Altimera, in Spain, are very notable
products of Neolithic artists.

The range of discovery of fossil human relics gives
evidence of a wide geographical distribution of
primitive races during palaeolithic times. Variations
in the degree of skill in the manufacture of stone
implements, as well as in other particulars, have
brought to archaeologists the recognition of different

ioo THE MAIN CURRENTS OF ZOOLOGY

culture periods, which are well exhibited in different
parts of France and Central Europe. No less than
six culture-periods of palaeolithic man are known,
indicating that the prehistoric period of human
development was far longer than the entire historic
period.

It is, however, to fossil remains of primitive man
that we must look for evidences of structural changes
that have taken place in the human frame.

Of all the bony parts, the skull is the most interest-
ing for comparison, since its size and configuration
indicate in a general way the degree of development
of the brain, and, as a consequence, the relative
grade of intelligence.

One of the most famous documents of man's an-
cestral history is the well-known Neanderthal skull,
discovered in a cave near Diisseldorf in the valley of
the Neander, in 1856 and first described in 1857. It
is now exhibited with other parts of the skeleton in
the provincial museum at Bonn on the Rhine. The
inferences drawn from this very ancient skull, with
its low receding forehead, showing small develop-
ment in the region of the higher mental faculties,
created a sensation, and great opposition was devel-
oped in allowing the discovery to rank as an evidence

ZOOLOGY OF FOSSIL :REA3AIN}} <-.] >oi

of primitive man. But its importance has been
enhanced by the discovery of a long series of similar
skulls.

In 1886, came the discovery in the Cave of Spy,
Belgium, of two skeletons with the same structural
features as those of the Neanderthal remains, and,
since that time, the discoveries of numerous similar
relics have established the existence of a Neander-
thal race living in the middle of the palaeolithic
period. The more notable members of the Neander-
thaloid series embrace: the human remains of
Krapina, in Croatia, found in 1899-1904, and con-
sisting of parts of the skeletons of ten persons from
infancy to old age; the skeletal remains of La Chapelle
aux-saints and of Le Moustier.

In August, 1908, there was discovered in South-
western France, by well directed efforts of French
archaeologists, a very interesting skeleton of the
Neanderthal type, and now known as the man of La
Chapelle aux-saints. This is the skeleton of an old
man with an almost complete skull, and a lower jaw
lacking some of the teeth. Since the comprehensive
analysis of these remains, published by Boule in 1913,
this is the most thoroughly known skeleton of the
Neanderthal race and may be taken as a type. Be-

102 THE MAJN CURRENTS OF ZOOLOGY

sides the structural features of the bony parts, it is
interesting to note that the casts of the interior of
the cranium show the surface features of the brain.
As compared with the brain of modern man, it is
small in the region of the frontal lobes and shows a
greater simplicity in the pattern of the convolutions.

A somewhat more primitive type was discovered a
few months earlier (March, 1908) at the famous
station of Le Moustier. It is the skull of a young
person and valuable for comparison.

These aboriginal people represent one link of the
chain of human ancestry, and they were followed by a
higher developed type of primitive man before the
dawn of history and the emergence of the modern
type.

A much more interesting circumstance is that
the Neanderthal people were preceded by more
primitive pre-humans. There are known at present
three examples of remains that are distinctly pre-
Neanderthaloid. The first to be discovered, and also
the most primitive pre-human species known, is
represented by portions of the skull, and of the leg
bones, found in Central Java by the Dutch surgeon,
Dubois, during the years 1891 and 1892, and made
known in 1894. These remains were found in Ter-

ZOOLOGY OF FOSSIL REMAINS 103

tiary deposits and were christened with the name of
Pithecanthropus Erectus. The capacity of the skull,
930 cubic centimeters, precludes the conclusion that
it belongs to the series of anthropoid apes — the
largest cranial capacity of apes, living or fossil, not
exceeding 600 cubic centimeters.

The second pre-Neanderthaloid is the perfect
lower jaw with all the teeth, discovered in 1907 in
the sands of Mauer, near Heidelberg. These de-
posits belong to the lower Quarternary, and since the
discovery of the Heidelberg jaw it is claimed that
Eoliths have been discovered in the same layer.
The jaw, while distinctly human as to characteristics
of the teeth, is very primitive. The creature to
which it belongs has been designated Homo Heidel-
bergensis.

The most recent discovery of pre-human remains
comes from England. At Piltdown Common, in
Sussex, in 1912, there was unearthed a skull, with
parts of the lower jaw and teeth, that fits into the
series of the pre-Neanderthaloids. It has been sug-
gestively named the dawn man (Eoanthropus Daw-
sonii).

Above the Neanderthal race come the numerous
fossil remains of Neolithic man, merging by struc-

104 THE MAIN CURRENTS OF ZOOLOGY

tural gradations into those of recent type. The
skeleton of Mentonne, that of Combe Chapelle (1909),
of Galley Hill (1895), the Cro-magnon race and other
representatives are forms that connect palaeolithic
with recent man.

Putting these discoveries together we have an
interesting series of gradations of skulls, leading one
into the other, and covering a range of cranial capac-
ity from 930 cu. cm., that of the Java man, to 1480-
1555 cu. cm. that of the average white European.
The Neanderthal skulls occupy an intermediate
position with a cranial capacity of approximately
1400 cu. cm.

In tracing backwards from recent man, it is not to
be assumed that the ancestral line breaks off ab-
ruptly. Even the Java man had antecedents, and
it is natural to assume his derivation from an extinct
Primate of the Earlier Tertiary deposits. Positive
evidences are lacking, but the known presence of
anthropomorphous Primates in the Miocene of
France offers a possible suggestion. Paleontological
discoveries have supplied the line of genealogy of
several families of mammals, and if, on this basis, we
assume that man and the anthropoid apes had a
generalized ancestor, it is nevertheless clear that the

ZOOLOGY OF FOSSIL REMAINS 105

human and the simian lines have had an independent
development for many centuries. There has been
no crossing of the lines since Tertiary times.

The derivation of man from an extinct Tertiary
Primate seems already to be well authenticated.
Furthermore, the fossil records give evidence of the
conditions under which the development of the
higher races of animals began. By making plastic
casts of the interior of the fossil skulls of Tertiary
mammals, it has been determined that there was in
that geological period a marked increase in the size of
the brain. This circumstance was of the greatest
importance both for progress and for perpetuity of
certain kinds of animals. Those, in particular, whose
increased intelligence enabled them to cope more
successfully with the conditions 'of their existence,
and to turn natural forces to their advantage, were
continued and unproved. In pre-humans the increase
in brain surface led to the power of storing up im-
pressions, and, finally, brought about a condition of
educability which formed the starting point for
marked improvement.1

1 The above 14 paragraphs quoted from the writer's Biology and Its

Makers.

CHAPTER XI

MAIN PATHWAYS AND RECENT TENDENCIES
OF ZOOLOGY

AT this point it will be convenient to indicate the
chief pathways by which the territory of zoological
study has been entered and explored. Broadly
speaking, the main highways of zoology are embraced
under the following designations: Structural Zoology
(Morphology), with its subdivisions — comparative
anatomy, histology, embryology, and the study of
fossil animals; Systematic Zoology (Natural History),
comprising classification, ecology (the relation be-
tween animals and their surroundings), study of
habits and geographical distribution of animals;
General Physiology of animals, with animal psychol-
ogy and animal behavior; Experimental Zoology,
(which is more a method of general application than
a subdivision), embracing Genetics, experimental
morphology and similar branches; and, Philosophical
Zoology, with organic evolution and related topics.
In addition there are some miscellaneous divisions of
smaller importance.

To bring these various subdivisions under bird's-

106

MAIN PATHWAYS AND TENDENCIES 107

eye view with brief comments will help mark the
pathways of the territory.

Structural Zoology. — The two broad aspects in the
investigation of animal forms are morphological and
physiological. Supplemental to one another, they
embrace the statics and the dynamics of animals—
the architecture and the function. Structural
zoology (or morphology) is fundamental in providing
a basis for physiological investigations. It includes
topics dealing with gross and minute anatomy, with
the process of building, or development of the body,
and the study of fossil animals. Accordingly, we
recognize its chief subdivisions as comparative
anatomy, histology, embryology and paleontology
(paleozoology).

Comparative Anatomy. — The study, broadly com-
parative, of the structure of animals, well adapted for
the early stages of laboratory observation, usually
pursued by an examination of types of animal life
from the lowest to the highest. The microscope is
necessary for the examination of the whole group of
protozoa and for other minute animals such as
rotifers, microscopic Crustacea, etc.

Comparative anatomy is chiefly the structural
study of animals as to their organs and systems of

io8 THE MAIN CURRENTS OF ZOOLOGY

organs, as the digestive system, the circulatory sys-
tem, the nervous system, etc. It aims to establish
homologies between organs by tracing the origin and
modifications of structures occurring in series of
animals.

Histology. — By the microscopic study of the
tissues composing the organs we come to histology.
This reaches a deeper level of morphological analysis
than comparative anatomy. In its full scope, it dis-
tinguishes the cells as well as the tissues, and cytology
is an offshoot of histology. The study of cells, how-
ever, has assumed such importance and opened so
many new questions that cytology stands out as
an independent division. The arrangement, the form
and staining qualities of cells often do much to show
the use of tissues, and, therefore, cytology has its
physiological side.

Embryology. — This likewise has become a broad
subject including observation of all stages of devel-
opment from the egg to hatching — or birth. Among
its especial topics come the analysis of the germinal
elements, the nature of fertilization, the formation of
the germ-layers, the physical basis of heredity, the
histological differentiation (histogenesis) of tissues,
etc.

MAIN PATHWAYS AND TENDENCIES 109

Paleontology. — The study of fossil animals (paleo-
zoology) is a division of morphology since the in-
vestigation of the physiology of fossil remains is not
practicable. That part of it that deals with animal
forms is zoological rather than geological. It is a
study of the succession of animal life on the globe.
In passing, it should be remarked that the succes5ion
of plant life (paleobotany) has been in recent years
the field of very notable advances.

Systematic Zoology. — Deriving its name from the
systematic arrangement of animals as first accom-
plished in the Systema Naturae of Linnaeus. Since
classification is based largely on structural features, it
would appear that in its recent scientific aspects, it
should be the outcome of morphological study — and
such is the case. But this was not so in earlier
times — Systematic Zoology had large development
before morphology pushed into prominence. It
arose out of the old natural history of Linnaeus. The
designation natural history is, however, more com-
prehensive than classification. It represents the
kind of study of animals to which the name zoology
was applied after the Renaissance. After the rise of
morphology, natural history continued to develop
and took on modern form. To this division belongs

i io THE MAIN CURRENTS OF ZOOLOGY

the classification of animals for which the modern
name is taxonomy. From it arose the study of field
zoology, with such offshoots as ecology, the study of
habits, and, of the geographical distribution of
animals.

Work in ecology — the study of the relations be-
tween animals and their surroundings — has been
very active in the last decade. There has been
developed an extensive technique for experimental
observation of animals, special societies have arisen,
text-books and periodicals for the publication of
results of ecological study have been started. Geo-
graphical distribution of animals is also allied to
natural history.

General Physiology. — The most significant thing
about an animal is that it is endowed with life and
the analysis of those vital processes that are an ex-
pression of its life, should go hand in hand with the
study of its structure. Zoology that is limited to
study of the architecture of animals manifestly is in-
adequate. General physiology of organisms is as much
a part of zoology as is morphology but it is not so
frequently utilized in courses of study. The subject
as related to zoology embraces a general considera-
tion of the principles upon which all physiological

MAIN PATHWAYS AND TENDENCIES in

operations depend — responses to stimuli, fermenta-
tion and digestion, circulation, secretion, excretion,
reproduction of animals, etc. But physiology is also
an independent science, pursued for its own sake, and
statements like those just made are not to be taken
even to imply that physiology in this sense is a part
of zoology. A parallel situation exists in reference to
anatomy, which is a separate science, whilst the
comparative anatomy of animals is a major subject
of zoology. Physiology, is broadly biological, and
this constant overlapping of closely related subjects is
to be expected.

The study of the reactions of the protozoa to va-
rious stimuli has been much cultivated — both in
zoology and in physiology — since these organisms
exhibit life in relatively simple expressions. The
illuminating quality of such experimental studies has
been so fully recognized, that modern text-books on
human physiology, in most cases, begin with an
analysis of the properties of protoplasm and the
physiological reactions of the protozoa. This is the
best means of introduction to the study of experi-
mental physiology.

Animal Psychology and Animal Behavior. — The
divisions of animal psychology and animal behavior

ii2 THE MAIN CURRENTS OF ZOOLOGY

may be considered as offshoots of general physiology.
In recent years, these subjects have become much
cultivated fields by zoologists and psychologists.
The results of these studies throw light on some of
the basal problems of the development of animal
intelligence and afford means of estimating the men-
tal equipment of different animals. A few suggestive
titles, taken at random, supply illustrations — The
Mental Powers of Spiders, by the Peckhams, a widely-
known study in comparative psychology; The Be-
havior of Lower Organisms, by H. S. Jennings; Ro-
mane's Starfish, Sea-urchins and Echinoderms, a
study of physiological response; Chapters on the
reactions of the Protozoa in the classical General
Physiology of Max Verworn.

The mental evolution of animals is extremely
interesting as affording illustrations, on another side,
of that oneness of nature, the recognition of which as
we have seen is one of the results of zoological study.
Just as there are gradations of structure connecting
the lower and the higher animals (the specialized
arising by modifications from simpler ones) so, in the
rise of animal intelligence, there is a graded series of
states keeping pace with the structural differentiation
of the nervous system.

MAIN PATHWAYS AND TENDENCIES 113

Investigations in these fields have become so
numerous that special periodicals have been estab-
lished for the publication of researches of animal
psychology and of animal behavior.

Experimental Zoology. — This is rather a method
of broad application than a subdivision of zoology,
and bearing this in mind, it forms a convenient cap-
tion under which to introduce several topics as Gen-
etics, Mendelian Inheritance, Experimental Morph-
ology, Experimental Embryology and Experimental
Cytology.

Genetics. — Genetics, or the science of inheritance,
has been the scene of great activity, has developed
until it stands as a much pursued independent divi-
sion of zoology. Experiments on the breeding of
plants (corn, wheat, flowers, etc.) and animals have
brought great extensions of knowledge regarding the
growth and the conditions of inheritance in or-
ganisms.

Mendelism. — The whole subject of heredity has
been pursued by experimental methods giving rise
to a large number of special researches too numerous
even to summarize. One feature that has occupied
the center of the field is the study of Mendelian
inheritance. This is properly a subdivision of

ii4 THE MAIN CURRENTS OF ZOOLOGY

Genetics, but owing to the great prominence of the
subject it is treated separately. Referring to Chap-
ter IV for a statement of Mendel's law of alternative
inheritance, we can say that it has been demon-
strated in poultry, guinea pigs, rabbits and other
animals. The fruit-fly which breeds rapidly and is
easily kept under observation, has proved an ex-
cellent subject for observations of the effects of
crossing and the study of unit characters. Morgan
and his students have made extensive contributions
to the study of heredity with this insect. They have
added much to support the conclusion that the
chromosomes are the normal mechanism for the
transmission of Mendelian characteristics.

Experimental Morphology. — The earlier experi-
ments of the last part of the nineteenth century were
carried on under the name of experimental mor-
phology— experiments on animals with a view to
determine the changes undergone by changed condi-
tions of life. Placing eggs and developing organisms
under different conditions of environment and ob-
serving the results. The eggs and larvae of aquatic
forms are especially adapted for experiments of this
nature — inasmuch as the chemical and thermal en-
vironment can be easily changed. The entire sur-

MAIN PATHWAYS AND TENDENCIES 115

roundings can be materially changed by dissolving
chemical salts not injurious to life in the water
inhabited by these organisms. Observations with
this kind of experimentation have been very helpful
in attacking problems of the life of organisms.

Experiments on regeneration and conditions of
growth have been numerous, and experiments on
fertilization, both with sperms and with chemical
salts, are among those which have yielded important
results. In this connection should be mentioned the
experiments of Loeb on artificial parthenogenesis and
of Lillie on the nature of the fertilization process.

Wilhelm Roux, who has done very notable work in
experimental morphology, has established a special
periodical (Archiv fur Entwickelungs Mechanik) for
the researches in this field.

Philosophical Zoology. — The profound changes in
thought produced by the establishment of the doc-
trine of organic evolution, and its effects upon our
interpretations of nature, gave rise to the division
of philosophical zoology. In this field are included
the rise of evolutionary thought and the formula-
tion of the different theories of organic evolution.
The latter are attempts to designate the physical
agency or agencies that have operated to bring about

n6 THE MAIN CURRENTS OF ZOOLOGY

organic evolution, the truth of which is so clearly
evidenced by the facts of comparative anatomy, of
embryology and of paleontology. Philosophical
interpretations of development, of heredity, and of
other zoological generalizations, also come under this
division of zoology.

Miscellaneous Divisions. — Zoology has been
broadened and enriched by the cultivation of especial
lines of interest and this has led to an arbitrary sub-
division of some of the larger provinces. The position
of some of these subjects is not clearly defined and
they owe their prominence to particular interest in
their applications. Others of the miscellaneous group
are clearly offshoots from the larger divisions.

Eugenics. — The subject of Eugenics (a subdivision
of Genetics) commands at present a large place.
This scientific study of the conditions that may im-
prove or impair the racial qualities is properly under-
taken only on a broad knowledge of biology and,
especially, of zoology. As previously stated it was
especially fostered by Francis Galton.

Protozoology. — In reference to unicellular organ-
isms, a department of protozoology has been created
with especial reference to pathogenic protozoa. But,
quite outside the question of disease-producing

MAIN PATHWAYS AND TENDENCIES 117

protozoa, it has long been recognized that in order to
understand the real nature of living organisms one
must first become acquainted with the phenomena of
the Protozoa. The study of this single group has
assumed so much prominence that, already there has
been established in several universities a professor-
ship of Protozoology.

The study of the lif e history of pathogenic protozoa,
of parasitic worms and of other disease-producing
and disease-carrying animal organisms has devel-
oped into a department of Parasitology.

The application of zoological facts to the benefit of
mankind is a considerable feature of present-day
work. This is a continuation and extension of the
work inaugurated by Pasteur. Under this general
head are included the demonstration of the connec-
tion between insects and the propagation of yellow
fever, malaria, sleeping-sickness, typhoid fever and
other disorders. Although still in their infancy
much benefit has already accrued from zoological
studies of this character.

Economic Entomology. — Investigations in economic
entomology have become very active. They have
been stimulated by the economic need of the control
of the ravages by insect pests that have attacked

n8 THE MAIN CURRENTS OF ZOOLOGY

crops, fruit and shade trees. In response to this
practical need, the researches on structure, habits,
life history, development, conditions of life, etc., of
insects have been greatly increased. A host of
specially trained observers, widely distributed over
the country, have produced important economic re-
sults which at the same time have greatly advanced
zoological knowledge. The Bureau of Entomology
at Washington has been the center promoting this
kind of investigation and the results have been
characterized by accuracy and scientific production
of a high order. Some states and cities have well-
organized departments for carrying on observations
of this nature.

Marine Zoology. — The investigation of marine life
has been greatly developed by exploring expeditions
and by the establishment of seaside stations. The
most famous of these is the international research
station at Naples (Stazione Zoologicd) founded by
Anton Dohrn in 1872. Tables and rooms for re-
search in this station are maintained partly by the
cooperation of universities and learned societies of
the world. Researches carried on at the station are
by no means confined to marine zoology, but the
marine forms that are so abundant in the gulf of

FIG. 24. — Louis AGASSIZ (1807-1873)

MAIN PATHWAYS AND TENDENCIES 119

Naples are used for the investigation of the widest
range of zoological problems.

In the United States, Louis Agassiz (Fig. 24) was
the pioneer with his marine station started in 1873
on the island of Penikese, Massachusetts. The
Marine Biological station at Woods Hole, Mass-
achusetts, is, in a sense, the successor of the Penikese
laboratory. It was chiefly developed by Whitman
(1842-1910) who had been a student under Agassiz.
The influence of Whitman (Fig. 23) on the develop-
ment of American zoology was very great. Besides
acting as Director of the station at Woods Hole for
nineteen years, he was a professor at Clark Univer-
sity and afterwards of the University of Chicago.
He founded the Journal of Morphology and carried it
through seventeen volumes. The greatness of Whit-
man was in his large noble spirit, his philosophical
cast of mind and the feeling of uplift which he im-
parted to his students and to other zoologists.

Other marine stations of the United States on the
Atlantic Coast as Cold Spring Harbor, New York,
South Harpswell, Maine, Dry Tortugas, Florida, and
Beaufort, North Carolina, are supplemented by
those of the Pacific Coast as the Puget Sound Station
at Friday Harbor, Washington, Ocean Grove, Cal-

120 THE MAIN CURRENTS OF ZOOLOGY

ifornia, La Jolla, California, and other places. In
Great Britain the leading station is at Plymouth,
while the marine stations of other European coun-
tries are numerous and important.

The explorations of the abysmal depths and the
survey of the sea bottom have resulted in extension of
zoological knowledge. These explorations of this
character have been carried on by various govern-
ment expeditions. The notable voyage of the Chal-
lenger (1872-1876), has led to the publication of
monumental reports written by the cooperation of
zoologists of the different parts of the world. The
recent Siboga expedition of Holland and the Harri-
man expedition of the United States brought much
additional information about sea animals. To this
class of voyages belong those on which Darwin (The
Beagle) and Huxley (The Rattlesnake) made their
trips as naturalists.

A department of oceanography has been created
as a division, chiefly of zoology, and in deep sea
investigations Sir John Murray of England and
Alexander Agassiz of the United States made notable
observations. Albert L, Prince of Monaco, main-
tains a station of oceanography on the French coast.
This station is splendidly equipped, and important

MAIN PATHWAYS AND TENDENCIES 121

contributions to knowledge have resulted from the
investigations which are published in periodicals of
the station.

Limnology. — Fresh water stations have been estab-
lished at many points in the United States and in
other countries in which the fauna of lakes and rivers
have been scientifically studied. The pioneer station
of this class was established by Zacharias at Plon,
Holstein. Investigation of the biology of lakes and
rivers is designated Limnology and work of this
nature has assumed considerable importance.

In connection with aquatic observations, there has
developed the plankton work, consisting of studies,
both qualitative and quantitative, of the minute
floating life of waters.

Certain Recent Tendencies. — The development
of the experimental method and its wide application
in the different departments of zoological investiga-
tion is the most characteristic recent tendency of
zoology. Zoological investigation has successively
advanced from the stage of mere observation to that
of comparison and, finally, to the method of experi-
mentation.

The greatest present activity is in some of the
more recent offshoots of zoology such as: cytology,

122 THE MAIN CURRENTS OF ZOOLOGY

the experimental study of heredity, including Men-
delism, neurology, protozoology and parasitology,
ecology, animal psychology and behavior, paleo-
zoology and economic entomology. Morphological
investigations on broad lines have been largely taken
over by the anatomists, while the zoologists are more
engaged with cytology, ecology, genetics, etc.

In the line of cellular studies (cytology) there has
been great refinement of technique and of observa-
tion. The minute constitution of the germinal ele-
ments and of the cellular phenomena of develop-
ment have been worked out, the physical basis of
heredity has been located in the chromosomes and,
more recently, partly within the cytoplasm of the
egg. These studies are closely allied with those of
experimental embryology in which so many advances
are being made — the nature of fertilization as a
physiological process, etc.

The theory of sex-determination and the biology of
twins have aspects of especial interest and, recently,
have been investigated by zoologists with important
results.

In morphology, studies in neurology have taken
the center of the field. Although there are many
individual pieces of morphological investigation car-

MAIN PATHWAYS AND TENDENCIES 123

ried out on a higher plane than that of previous
years, investigations of the architecture of the
nervous system in all its aspects is one of the obvious
recent tendencies of zoology.

Cooperation in neurological research is a promising
sign, made by the association of Neurological Insti-
tutes in a tacitly understood program of investiga-
tion. Some of the Institutes thus cooperating are
those of Ludwig Edinger at Frankfort on the Main,
of Ariens Kappers of Holland and of the Wistar
Institute of Philadelphia. In the United States the
Wistar Institute of Anatomy and Biology is especially
devoted to researches hi Neurology under the leader-
ship of Professor H. H. Donaldson.

Adjuncts. — Various adjuncts such as museums,
zoological gardens, special collections, etc., have
been helpful to the work of zoologists. These have
been of service in the dissemination of knowledge of
animals among the masses, but, most of all, they have
supplied facilities for the researches of specialists.
Among the institutions of this type in the United
States may be mentioned the Agassiz Museum of
Comparative Zoology at Harvard University, the
collections at Yale University, the American Mu-
seum of Natural History of New York City, the

i24 THE MAIN CURRENTS OF ZOOLOGY

Carnegie Museum at Pittsburgh, the collections of
the Philadelphia Academy of Sciences, the National
Museum and the Smithsonian Institution at Wash-
ington.

Zoological gardens exist in New York, Washing-
ton, Philadelphia, Chicago and at other places.

The embryological collection of the late Dr. Charles
Sedgwick Minot of Boston and of Dr. Franklin P.
Mall (died 1917) of Baltimore are of great service to
investigators in embryology.

The entomological bureau at Washington, D. C.,
and several of the State Entomologists have done
much to advance and to spread broadcast the
knowledge of Insects. The sumptuous publications
of the United States government have placed in hand
many valuable reports on animal life and animal in-
dustry. The activities and publications of the
United States Fish Commission are also notable.

CHAPTER XH
A CHAPTER ON INSECTS

INSECTS are so interrelated with general topics that
a chapter on insects will serve to further illustrate the
progress of zoological study.

This is the largest group of animals, there being
approximately 400,000 species described and classi-
fied and there are many not named. From whatever
point of view these animals have been studied, they
have awakened interest and enthusiasm among
naturalists. Those who devote particular attention
to this field of study are designated entomologists
and the great division of zoology thus set apart is
designated entomology.

From the time of Malpighi (1628-1694) and
Swammerdam (1637-1680) insects have been ob-
jects of interest and of especial consideration to the
minute anatomists.

In their life histories some insects, as the butter-
flies, bees, etc., exhibit hi the clearest fashion and in
the widest range the phenomena of metamorphosis.
Hatching from the egg in a form different from the

adult many of these annuals pass through various

125

126 THE MAIN CURRENTS OF ZOOLOGY

stages of moults as larvae, then enter the quiescent or
pupa stage and emerge from the cocoons, or cases, as
adults.

In reference to the fertilization of flowers insects
exhibit some of the most interesting relations of
nature. With remarkable adroitness they extract the
nectar of flowers, and at the same time carry pollen
from flower to flower, and further cross-fertilization.
Often there are especial adaptations in structure to
promote this end.

But it is in reference to their habits that they show
the most extraordinary display of instinctive in-
telligence and complex behavior. Those forms as
ants, bees and social wasps living in social com-
munities, that are well organized as to divisions of
labor and concerted action, may be properly re-
garded as animals of dominant intelligence.

The French entomologist J. H. Fabre (1823-1913)
devoted a long life to observation of insects showing
especial aptitude for searching out their habits.
He has related his observations in voluminous and
charming writings which reached the dimensions of
ten volumes under the title of Souvenirs Entomolo-
giques. These memoirs have been translated into
English and have had a wide circulation. Fabre

A CHAPTER ON INSECTS 127

(Fig. 25), on account of his talents as an observer, his
gifts as a writer and his direct appeal to a non-
technical audience is probably more widely known
than any other entomologist. Those who wish to
taste the flavors of this charming writer on natural
history are recommended to look into his volume on
The Hunter-Wasps.

Other entomologists, more important from the

%

scientific standpoint and who have addressed only a
scientific audience are less generally known.

Obviously it would be out of keeping to attempt
in a few pages to treat of the various aspects of the
large and complex group of insects. Accordingly,
only a few selected topics will be brought briefly un-
der consideration.

On account of their relation to the transmission of
diseases insects have become of world-wide interest,
and those topics are selected that best illustrate their
connection with human diseases. These are Malaria,
Yellow Fever and Sleeping-sickness. It is to be borne
in mind that there are other human diseases trans-
mitted through the agency of insects, as bubonic
plague, sometimes, typhoid fever, etc., and many
animal diseases of cattle, horses and lower animals.

Malaria. — Let us become acquainted with the

128 THE MAIN CURRENTS OF ZOOLOGY

circumstances under which was demonstrated the
transmission by insects of Malaria. Malaria is a
widely-spread infectious disease. This disease, char-
acterized by periodically recurring chills and fever
was called Malaria, which means bad air, from the
belief that the Malaria was due to miasmatic vapors
arising from swamps and marshes. The disease,
formerly called fever and ague, was observed to be
most prevalent in marshy districts and in places with
standing water. It is now known that this is owing to
the fact that wet places supply the conditions for the
nurture of the mosquitoes that transmit the disease.

That it is transmitted by a particular kind of
mosquito was well established by Ross in 1898.
There were several steps leading up to this final
demonstration each one of which is an interesting bit
of biological advance.

It was in 1880 that Laveran, a French military
surgeon, then serving in Algeria, made known the
presence of a micro-organism within the blood of
patients suffering from malaria. This so-called
plasmodium is a microscopic animal (protozoan)
parasite. In the blood of an infected person the
minute malarial parasite bores its way into a red
blood corpuscle and feeds and grows at the expense

A CHAPTER ON INSECTS 129

of the protoplasm of the corpuscle. It rapidly grows
and divides into a progeny of thirteen to eighteen
small spore-like individuals which are set free into the
blood by the bursting of the wall of the blood cor-
puscle. This sporulation occurs periodically and
corresponds to the attacks of chills followed by fever,
which attacks are intermittent, depending on the
life cycle of the parasite.

There are two varieties liberated into the blood
stream, those in largest number being able to mul-
tiply by direct division, while the other kind consist
of germinal elements that require a different host and
a different set of conditions in order to unite and
complete their life history. Their union is a process
of fertilization and is accomplished in the blood of a
mosquito, in which animal they undergo a compli-
cated development, resulting finally, in an immense
number of spore-like individuals.

The history of the first kind is more simple. They
bore their way into new corpuscles and repeat the
changes mentioned above. The number of corpus-
cles infested is continually multiplying so that soon
the blood becomes the seat of a prodigious number of
the malarial parasites.

The rate at which they are produced varies with

130 THE MAIN CURRENTS OF ZOOLOGY

different species. If they mature and produce spores
in thirty-six hours, the patient has chills and fever
every other day — for the chills and fever correspond
to the period of sporulation and bursting of the
corpuscles. There are other species with a different
period of growth giving rise to the different types of
malaria — the three-day, the four-day, etc. Minute
as they are these different varieties can be distin-
guished under the microscope.

The question of how the parasite gets into the
blood had now to be solved as a step in tracing the
infection to its source. Suspicion was fastened on
the mosquito and after observations by several in-
vestigators it was finally shown in 1898 that the bite
of a particular species of spot-winged mosquito
transmits Malaria. (Grassi had previously shown
that these parasites complete a part of their life
history in the body of the mosquito.) The scientific
name of the mosquito is Anopheles. The Culex or
common house mosquito is not a malaria carrier.
The Anopheles is widely distributed. It is a night-
flier, and only the female circulates, sucks blood, and,
when infected, transmits the disease.

In the most infected districts it was experimen-
tally demonstrated that to remain in well-screened

A CHAPTER ON INSECTS 131

shelters after sundown was sufficient to protect
against infection. Experiments on a large scale were
also carried on in the most infected districts of the
swampy campana of central Italy. Camps were
constructed in these unhealthy districts and the
persons experimented upon were divided into two
groups that lived under similar conditions — except
that one group was protected in well-screened rooms,
though freely exposed to the fogs and vapors from
the marshes. The other group was unprotected by
screens. The results were spectacular. Those pro-
tected from the bites of mosquitoes contracted no
fever while those that were exposed to mosquito bites
were stricken with malaria.

As a further experiment infected mosquitoes were
sent from Rome to London and there allowed to bite
healthy person who were by this means infected with
malaria fever. Thus was forged the last link in the
chain of evidence connecting the Anopheles mosquito
with the transmission of malarial fever.

This was the first demonstration of direct connec-
tion between insects and the transmission of a
specific disease. Although suggestions that insects
act as disease carriers are found scattered through
scientific literature for a number of years, neverthe-

132 THE MAIN CURRENTS OF ZOOLOGY

less, experimental evidence proving the truth of the
theory was lacking. Dr. Manson (later Sir Patrick)
in 1880 was the first to show that the blood of human
beings may become infected with a worm-like par-
asite (Filaria sanguinis) by the bites of a mosquito.
Others as Dr. A. F. A. King (1883) contended on
theoretical grounds that mosquitoes carry malaria
but adduced no experimental evidence. It was in
1894 that Manson communicated his theory con-
cerning mosquitoes to Major Donald Ross of the
British army and on this suggestion he began working
on malaria in India. For more than two years his
results were negative because he worked on the
mosquito Culex — but, turning his attention to
Anopheles, he was soon able to trace in this form part
of the life cycle of the malaria parasite. Many ob-
servers had a part in bringing the demonstration to a
conclusion. Grassi, the Italian, did important work
(1894), but Ross, with the assistance of suggestions
from the work of others, and utilizing their partial
results, was able to demonstrate so completely that
the malarial parasite is transmitted to human beings
through the bite of a particular kind of mosquito,
that credit for this great discovery is usually ac-
corded to him.

A CHAPTER ON INSECTS 133

His observations afford a typical example of the
method of zoological research — a combination of
observation, of experiment and of discerning deduc-
tion derived from the results of the complex and
involved relations. Several steps were necessary to
reach the final conclusion:

1. The discovery of the micro-organism in man by
Laveran in 1880.

2. Tracing the life history of this germ showing
that only a part of its life cycle is carried on in the
human body and that another part is in the body of
the Anopheles mosquito.

3. Demonstrating that the bites of an infected
Anopheles mosquito transmits the disease.

4. Camp experiments showing that it is not due to
other causes.

Malaria cannot be contracted by contact with an
infected patient, nor through the inhalation of va-
pors of swamps. The question now arises, how does
a mosquito become infected? When a mosquito
sucks blood from a person suffering from malarial
fever it draws into its body blood containing the
parasite (the second variety mentioned that repro-
duce by fertilization) some of which are in a con-
dition to conjugate. These forms conjugate and

134 THE MAIN CURRENTS OF ZOOLOGY

undergo a development in the walls of the stomach
of the mosquito. The conjugation is a sort of fer-
tilization such as occurs in all animals and plants, but
it will not take place in human blood. A " secondary
host" is necessary in which to complete the life
cycle. After fertilization the developing forms pro-
duce nodules on the walls of the stomach of the
mosquito and in these nodules takes place the
transformation into spindle-shaped forms which get
into the salivary ducts of the mosquito. When
biting, the mosquito injects some of these into the
blood of the victim and there they begin to multiply
rapidly by asexual budding.

Doses of quinine are used to kill the malarial
parasite.

Studies of the development of the mosquito soon
led to methods of protection. Mosquitoes breed in
water — a small quantity being sufficient . Protection
comes from draining marshes, getting rid of pools and
of containers of exposed water, and from spraying
with crude petroleum so that the wigglers which
hatch from the eggs can not get air, and conse-
quently, the mosquito can not come to its full devel-
opment. The use of screens and remaining indoors
after sundown are also wise measures of precaution.

A CHAPTER ON INSECTS 135

These methods have cleared malarial regions of
the sources of infection and, in particular, in the
Panama zone, conditions were established that made
possible the construction of the Panama Canal.

Yellow Fever. — There is no more interesting and
inspiring chapter of biological achievements than
that of the struggle and the triumph of demon-
strating the nature and the means of conveyance of
yellow fever. This is one of the greatest medical
discoveries of any century. It is usually designated
the greatest American medical discovery — but, it
stands in parity with another medical advance orig-
inating in the United States, viz., painless surgery, ac-
complished by means of the administration of ether.

Yellow fever is a rapidly spreading, most dreaded
and very fatal disease of tropical and sub-tropical
climates. Havana and Gulf ports have repeatedly
been the scene of this great scourge. Up to 1898 it
was believed to be communicated by infected articles
of clothing, bedding, furniture, etc., and, further,
that it was commonly introduced into the body
through respiration. But, thanks to the investiga-
tions of Walter Reed and his associates, it is now
thoroughly demonstrated that yellow fever is trans-
mitted through the bite of a mosquito and in no

136 THE MAIN CURRENTS OF ZOOLOGY

other way. Just as malaria is always transmitted by
mosquitoes of the Anopheles variety so also is yellow
fever carried by another mosquito of the genus
Stegomyia.

In the year 1900, President McKinley appointed
Dr. Walter Reed (Fig. 26) as chairman of a com-
mittee to proceed to Havana for the study of in-
fectious diseases — more especially yellow fever. In
about six months after his arrival he, with the
assistance of his associates, had shown that yellow
fever is transmitted only by the bite of a particular
kind of mosquito.

Some of his results summarized are as follows:

1. The virus or germ exists for the first three days
in the blood of the sick before it is capable of pro-
ducing infection.

2. A mosquito of a single species — Stegomyia
fasciata — becomes infected by sucking blood from a
sick person, and after twelve days have elapsed (and
thereafter) can carry the disease.

3. There is no other way of infection.

Reed's work is another illustration of the power of
applied intelligence guided by scientific observation.

The essential steps involved in this discovery are
similar to those in the investigation of malaria:

FIG. 25. — J. HENRI FABRE
(1823-1913)

FIG. 26. — WALTER REED (1851-1902)

From H. A. Kelly's Walter Reed and

Yellow Fever

FIG. 27.— W. T. G. MORTON (1819-1868)

From Camac's Epoch-Making Contributions

to Medicine

FIG. 28. — EDWARD JENNER
(1749-1823)

A CHAPTER ON INSECTS 137

1. The particular organism producing the disease
is not known — probably because it is too small for
microscopic observation. Nevertheless, it is demon-
strated that there is something in the blood that
produces the disease. This something is assumed to
be of animal nature — owing to the requirement of
two hosts and a relatively long tune to complete its
cycle. For want of a better name it is designated a
virus.

2. The demonstration that it can not be trans-
mitted by clothing, bedding, contact with the sick
nor through the atmosphere. Prior to 1898 it was
generally believed that these were sources of infection
but two young privates of the United States army —
John R. Kissinger and J. J. Moran — volunteered to
put the question to a practical test, and for twenty
nights they slept in contact with bedding and night
clothing removed from those sick and dying with
yellow fever. No contagion followed and thus it was
proved that the disease can not be conveyed in this
manner. This service to the cause of science by these
two men involved great courage and high devotion to
the cause of humanity.

3. Experimental evidence that, on the other
hand, yellow fever is transmitted by the bite of

138 THE MAIN CURRENTS OF ZOOLOGY

the mosquito Stegomyia. John Moran of the
United States army submitted to the bite of an in-
fected mosquito — as a result he was stricken with the
disease but recovered. Dr. Lazear, one of Reed's
assistants, was accidentally bitten by a mosquito and
died of yellow fever. The circumstances attending
both these cases were such that no doubt existed as
to the direct connection between the bite of the
infected mosquitoes and the disease.

Reed appreciated the significance of his discovery,
and in the first enthusiasm of the demonstration he
wrote this intimate estimate to his wife: "Rejoice
with me, sweetheart, as aside from the antitoxin of
diphtheria and Koch's discovery of the tubercule
bacillus, it will be regarded as the most important
piece of work, scientifically, during the nineteenth
century."

The results of the demonstration were immediate
and far reaching. Havana and Gulf ports were
practically freed from the disease. Indeed, since
1901, Havana, formerly the favorite home of this
deadly disease, has been exempt from its ravages.

Sleeping Sickness. — The third of these biological
studies of insects and transmission of diseases in-
volves the sleeping sickness. The sleeping sickness

A CHAPTER ON INSECTS 139

is a strange mysterious disease characterized, as the
disease progresses, by lethargy and a somnolescence
which terminates fatally.

It had long been known on the western coast of
Africa, but, in 1901 a virulent outbreak occurred in
central Africa, in the Uganda district and along the
shores of Lake Victoria Nyanza. The disease killed
so many that the British government undertook to
investigate the causes of the disease and to seek a
remedy. The wide-spread nature of this epidemic in
which 200,000 died in one year compelled notice.
Colonel Bruce of the British navy, who was expe-
rienced in the investigation of infectious diseases,
was sent there in 1903 to hives tigate the conditions
and the characteristics of the disease.

As in the case of malaria and yellow fever it took
the highest qualities of scientific observation to
discover the particular organism of the disease and
to find out the way in which it is transmitted.
Colonel Bruce had the problem to work out, of the
nature and the mode of infection of sleeping sickness.
He determined that as to its nature, it is produced by
the presence in the blood and the cerebro-spinal
fluid of a cork-screw shaped parasite — a minute
animal organism somewhat longer than the diameter

i4o THE MAIN CURRENTS OF ZOOLOGY

of a blood corpuscle. This organism is sharp pointed
at each end and is provided with a vibratile mem-
brane and a fiagellum which produce motion. This
parasite — called a trypanosome — was, by Bruce and
other observers, found in the blood and spinal fluid
as a constant concommitant of the disease.

Its mode of transmission was obscure and a
problem of great difficulty. Studies on the wild and
domesticated animals of the district were a means of
throwing light on the matter. Similar protozoan
parasites were known to infect domesticated animals
and to live in the blood of native wild animals such
as the antelope, buffalo, and others. These wild
animals having been long infested with these par-
asites had acquired a tolerance for them and re-
mained unharmed, but recently infected domesti-
cated animals were not immune. These parasites
were shown to be conveyed by the bite of a tsetse-fly
from the wild game inhabiting the district — in whose
blood they produce no deleterious result — to the
annuals that were susceptible to poisons produced
by the parasites. By analogy, suspicion was fastened
on the tsetse-fly as the probable source of transmis-
sion, but it was a very difficult matter to prove it. In
searching for the agent of the transmission of human

A CHAPTER ON INSECTS 141

sleeping sickness, Bruce had the help of many native
collectors who were paid to bring to his camp the
various flies and other insects of the district. Finally,
the source of transmission was fastened on a par-
ticular species of the tsetse-fly — Glossina palpalis.
The tsetse-flies are a genus of flies only found in
Africa. There are seven species known — the par-
ticular fly that transmits sleeping sickness in human
beings is a little bigger than the common house fly
and much like it in color.

To establish an undoubted connection between
the tsetse-fly and the transmission of sleeping sick-
ness came to Bruce as a triumph of scientific observa-
tion and deduction. Finding that monkeys also were
susceptible to the disease he caused infected flies to
bite monkeys, thus producing the disease and dem-
onstrating the mode of its transmission.

In 1906, a sort of arsenic aniline (Atoxyl) was
found by Thomas and Breinl to be helpful in some
cases. The suggestion of this substance as a possible
remedy was erroneously ascribed to Robert Koch
who merely confirmed the observations of the earlier
investigators.

To avoid a common confusion it may be well at
this point to emphasize the fact that the three

I42 THE MAIN CURRENTS OF ZOOLOGY

diseases spoken of above are all produced by animal
organisms. On the other hand, the bacteria whose
pathogenic qualities have been known so long are
plants. Thus, typhoid fever, tuberculosis, diphtheria,
etc., are produced by plant parasites and malaria,
sleeping sickness, and probably yellow fever are
produced by minute animal organisms.

Among other diseases transmitted by insects may
be mentioned the bubonic plague, by the bite of lice
of rats; many diseases of cattle, by bites of flies,
ticks, etc. These insects pass along the disease
germs which they have derived by blood sucking
from other animals.

CHAPTER Xin
THEORIES OF EVOLUTION

THE circumstances surrounding the rise of evolu-
tion theories in the nineteenth century are not gen-
erally understood. There is a wide-spread belief
that the theory of Charles Darwin was first in the
field, and, confusion on this point is so general that
whenever organic evolution is mentioned many peo-
ple conclude that the particular hypothesis of Dar-
win is always referred to, but such is by no means the
case. By organic evolution is meant the great nat-
ural process through which animals and plants have
come to be what they are — a purely historical ques-
tion of what has happened in the past to produce the
transmutation of animals and plants — in a word, the
discovery of the lineage of living organisms. Dar-
winism, on the other hand, is one explanation offered
to account for the evolution of animals and plants.
Darwin undertakes to designate the particular
agency that has been at work in nature to produce
the various kinds of organisms. Darwinism refers
specifically to the action of natural selection as the

chief agent in bringing about organic evolution.

143

144 THE MAIN CURRENTS OF ZOOLOGY

To Lamarck, the eminent French zoologist, be-
longs recognition as the founder of the doctrine of
organic evolution, fifty years before the publication
of Darwin's great book, The Origin of Species. It is
true, however, that the publication of Darwin's book
was the means that brought the matter prominently
before the world and started the vigorous contro-
versy regarding the truth or falsity of the theory.

There are four theories of organic evolution that
have received a large amount of attention from
naturalists in addition to several supporting and
some rival theories. No one can be adequately in-
formed on the matter who does not take the trouble
to get an idea of the prominent features of these
theories and their relation to one another. The four
theories referred to are those of Lamarck, Darwin,
Weismann, and De Vries.

Lamarck. — Although the evolutionary point of
view had been vaguely suggested at different times
prior to Lamarck, he was the first to announce a
comprehensive theory of organic evolution that has
maintained to the present time a creditable standing
in the intellectual world. His immediate predeces-
sors, Buffon, Goethe, and Erasmus Darwin (grand-
father of Charles Darwin), dealt with the same great

THEORIES OF EVOLUTION 145

theme but much less rigorously than Lamarck. The
earlier theories were either too vague and discursive
or too inadequate to serve as foundations. La-
marck's theory was so much more thoroughly thought
out that it completely superseded all earlier attempts
and marks the beginning of evolutionary thought in
its modern sense.

Lamarck (Fig. 29) first gave expression to his
evolutionary ideas in 1800, in an introductory lecture
to a course of instruction regarding the invertebrates.
This was published in 1801. The theory was some-
what elaborated in the years 1802, 1803, and 1806.
Finally, it was fully expounded in Philosophic
Zoologiquej in 1809, and that year marks the first
distinct epoch in the rise of evolutionary thought.

In this book he sets forth the basis of his con-
clusions. He ascribes to the effects of use and disuse
the various modifications of organic structures — use
tending to increase, and disuse to decrease the size
and efficiency of organs. The changes thus pro-
duced, by organisms adapting themselves to the con-
ditions under which they live, were supposed by
Lamarck to be directly inherited and improved (or
further decreased) in succeeding generations.

It appears, he says: "that time and favorable con-

146 THE MAIN CURRENTS OF ZOOLOGY

ditions are the two principal means which nature has
employed in giving existence to all her productions.'7
When surrounding conditions are stable the evolu-
tionary process reaches a stage of equilibrium, but,
when the environment varies (or new needs arise),
the new conditions of life impress themselves on the
plastic organisms and they become altered to better
adapt themselves to these new conditions. His
theory as set forth was comprehensive and included
the evolution of the human body as well as all other
organisms.

Adaptation of organisms to environment, in gen-
eral and in detail, producing changes of structure
through use and disuse of organs and the direct in-
heritance of the modifications is a simplified state-
ment of Lamarck's theory.

Until Lamarck was fifty years of age he was a
botanist and had secured a lasting reputation in that
field, but, in 1894, when the Jar dm des Plantes was
reorganized he was appointed to a position in Zoology
in charge of the invertebrates. Apparently, it was
the observations he made in connection with these
new duties that led to the formulation of his theory.
At this time the belief was current that species are
unalterable. The dogma of the fixity of species

FIG. 29. — J. B. LAMARCK (1744-1829)
From Thornton's British Plants, 1805

THEORIES OF EVOLUTION 147

prevailed. Linnaeus had announced himself in favor
of the idea, and, so generally was his authority recog-
nized, that scarcely anyone thought of bringing it
into question. But Lamarck saw that species vary
in a state of nature to such an extent that they pass
beyond the limits that can, in reason, be assigned to
species.

Lamarck's theory, although so definite, did not
find a foothold during his lif etime and the fifty years
between 1809, when his book was published, and
1859, when Darwin's Origin of Species appeared, was
characterized by the temporary disappearance of
the theory of organic evolution. His ideas were
ridiculed by Cuvier and were practically laughed out
of court. Charles Darwin also paid little heed to
Lamarck as a predecessor. But, it is a significant
circumstance that, nearly a century after being
promulgated, Lamarck's principle of use-inheritance
and the beginning of variations should have been
revived, and, under the title of Neo-Lamarckism,
should occupy such a prominent place in the discus-
sions regarding the factors of organic evolution that
are being carried on at the present time. The re-
vival of Lamarckism is especially owing to the
paleontological investigations of Cope, Hyatt and

148 THE MAIN CURRENTS OF ZOOLOGY

others. The work of E. D. Cope, in particular, led
him to attach importance to the effects of mechanical
and other external causes in producing variations in
animal structure, and he has pointed out many in-
stances of use-inheritance.

Lamarck's theory was founded on two sets of
facts — those of variation and heredity. These are
essential to any theory of transmutation of species.
Lamarck undertook to account for variation through
the influence of environment during the lifetime of
the individual, and the direct inheritance of these
purposeful variations was assumed. This is the in-
heritance of acquired characters which as we shall see
was vigorously opposed by Weismann.

Darwin. — Darwin's theory is based on three sets
of facts — variation, heredity, and natural selection.
Two of the factors are the same as those of Lamarck
but they were treated differently by Darwin. La-
marck undertook to assign causes for variation.
Darwin (Fig. 5) accepted variation and assumed that
there is continually occurring in living organisms
many small fluctuations in structures. Naturally
many of these small, fortuitous, variations would
be swamped, but, obviously, some of them are re-
tained and improved upon. His reply to the ques-

THEORIES OF EVOLUTION 149

tion: "What particular variations will be perpet-
uated?" was, "only those that prove of benefit to
the race in the struggle for existence and in adapting
themselves to environment. ' ' The chance inheritance
cf the multitudinous variations would produce
chaotic results unless directed by some agency and
this directing agency was designated by Darwin,
Natural Selection. This is the central idea of Dar-
win's theory and the essentially new factor that he
added tb the discussion. He observed the changes
produced by artificial selection under domestication
of animals and cultivation of plants. Certain varia-
tions are selected by breeders and agriculturalists to
be bred intensively, and, by this means, marked
changes are produced in pigeons, poultry, dogs, cat-
tle, flowers, etc. Now since these changes are
obviously the result of a process of selection on the
part of man, Darwin concluded that conditions exist
in nature which lead to the selection of certain
variations to survive and to the suppression of others.
Some such assumption is necessary, because there
is a tendency to overproduction in animals and
plants, leading to a struggle for existence, and, the
determination of survival, would scarcely be a matter
of chance. One illustration will suffice to carry the

ISO THE MAIN CURRENTS OF ZOOLOGY

idea. A single trout, for illustration, lays from
60,000 to 100,000 eggs. If the majority of these
arrived at maturity and gave rise to progeny, the
next generation would present a prodigious number,
and the numbers in succeeding generations would
increase so rapidly, that soon there would not be
room in the fresh waters of the earth to contain their
descendants. It is true that most animals produce
fewer eggs (some lay more), but observation estab-
lishes the truth that animals tend to multiply by
geometric progression, while as a matter of fact the
number of any one kind remain practically constant.

The agency that determines which organisms shall
be preserved in the struggle for existence is natural
selection. This agency will favor certain variations
in structure that may prove of advantage, so that,
in the long run, those best adapted to conditions of
life would survive.

Natural selection works in such a variety of ways
that a few illustrations are essential. Fleetness in
such animals as antelopes may be the particular
thing which secures their safety. In all kinds of
strain due to scarcity of food, inclemency of weather
and other rigorous conditions, those forms with the
best powers and physiological resistance will have

THEORIES OF EVOLUTION 151

the best chance to survive. The keen vision of birds
of prey, such as hawks, will be a factor in their
preservation. Those hawks that are born with weak
or defective vision cannot cope with the conditions
under which they get their food. Natural selection
compels the eye to come up to a certain standard and
the conditions of living maintains the standard.
Certain animals are protected from their enemies
by being inconspicuous — conforming to the colors
of the background on which they live — resembling
twigs and other natural objects. In other cases,
especially among insects, flaming colors give warning
that the animals are of noxious taste and their
pursuers learn to leave them alone. An illuminating
instance of the action of natural selection is the
production of weak-winged beetles from strong-
winged ancestors. In very windy islands the strong-
winged forms being more in the air and flying further
from protection are blown out to sea. The weak-
winged are better adapted to these particular con-
ditions, and, natural circumstances tend to favor
them and to operate against the strong-winged
individuals. This makes one point clear — natural
selection tends to adapt animals to their conditions of
life and results, not always, in the survival of the

iS2 THE MAIN CURRENTS OF ZOOLOGY

best, that is the ideally perfect, but in the survival of
the fittest. A similar instance is found in the sup-
pression of certain sets of organs in internal parasites.
The organs of digestion, not being necessary under
their condition of life, are suppressed, but the repro-
ductive organs, upon which continuance of the race
depends, are greatly increased. These illustrations
will assist in giving an idea of what Darwin meant by
natural selection.

One other point should be emphasized. Darwin,
who was one of the most candid, sincere and straight-
forward of men, did not claim that natural selection
was the only natural agency but merely the chief one
in bringing about evolution.

Darwin's theory met with a very different recep-
tion from Lamarck's. It received immediate atten-
tion. It was vigorously attacked and defended and
was ultimately accepted. The contrast was so
great that naturally the inquiry arises — Why? It
was promulgated more than fifty years after La-
marck's announcement and, in the meantime, the
way had been prepared by the publication of Lyell's
Principles of Geology (1830), by Chambers' Vestiges
of Creation (1844), by Herbert Spencer's writings
regarding the reasonableness of the hypothesis of

THEORIES OF EVOLUTION 153

development (1852) and by other writers. The times
were more favorable for launching the great idea of
evolution. But the wide currency which the idea
immediately attained was chiefly owing to Darwin's
exposition of the idea of natural selection. He
designated explicitly a natural cause for the changes
in animals that had heretofore been so perplexing.
Even the masses could understand his argument.
The character of his first publication (Origin of
Species, 1859) was also such as to attract attention
and secure respect. He had been at work on his
theory, experimenting and observing, for more than
twenty years, and his publication showed that
quality of thoroughness, fairness and ripeness that
commanded consideration.

Among those who assisted in the spread of the
Darwinian theory amongst English-speaking people,
Thomas Henry Huxley (Fig. 31) stood preeminent.
Darwin was of pacific disposition while Huxley was
aggressive and both ready and forceful in public
debate. He became the recognized champion of the
theory of descent, and vigorously and effectively de-
fended it against attack.

It is an interesting circumstance that Alfred Rus-
sell Wallace (1823-1913), by a flash of insight, had

154 THE MAIN CURRENTS OF ZOOLOGY

arrived independently at the idea of struggle in
nature, with the survival of the fittest through
natural selection. He communicated these ideas to
Mr. Darwin in 1858, and, with high-minded gen-
erosity, Darwin was disposed to allow the credit to
go to Mr. Wallace, withholding his own publication
upon which he had been working for so many years.
He was pursuaded to leave the matter in the hands
of two of his friends, Sir Charles Lyell and Joseph
Hooker, who arranged for the publication simulta-
neously, of manuscript sketches of Darwin, made in
1839, 1844 and 1857, and the essay of Wallace pre-
pared in 1858. Although Darwin was so punctilious
about having his friend, Wallace, receive a share of
the credit, Wallace himself has insisted, and the
world has recognized, that the credit for the natural
selection theory belongs essentially to Darwin.

Weismann. — The theory of Weismann is more
complex and is difficult to state with brevity and
lucidity. It will dispel a wide-spread" confusion
regarding his theory to say, at once, that he is a
Darwinian — the recognized leader of the Neo-
Darwinians. He carried the idea of natural selection
further than Darwin did, extending it to the tissues
and even to the minute vital elements of the cell. It

THEORIES OF EVOLUTION 155

is to be understood, therefore, that as regards Dar-
winism, his is a supplementary or supporting theory
and not a replacing theory.

It is complex and involves assumptions as to the
behavior of a number of hypothetical vital units,
designated by Weismann: idants (chromosomes); ids
(chromomeres), determinants, and biophors (the
elementary vital units). Two of these, the ids and
the idants are visible under the microscope, but the
determinants and the biophors are too minute to be
rendered visible.

His theory of evolution is in reality the outcome of
his theory of heredity, designated the "Continuity
of germ-plasm, " and to comprehend his reasoning it is
necessary to understand what is meant by the germ-
plasm and by its continuity.

As is well known, animals and plants arise from
germinal elements of microscopic size; these are, in
plants, the spores, the ovules and their fertilizing
agents; and, in animals, the eggs and the sperms.
Now, since all animals, even the highest, begin their
existence as a fertilized egg, that structure, minute as
it is, must contain all hereditary qualities, because
this is the only material substance that passes from
one generation to another. This formative sub-

156 THE MAIN CURRENTS OF ZOOLOGY

stance is the germ-plasm. It is the living vital sub-
stance of organisms that takes part in the develop-
ment of new generations.

Weismann (Fig. 32) points out that the many-
celled body was gradually produced by evolution, and
that in the transmission of life by the higher animals
the continuity is not between body-cells and their
like, but only between germinal elements, around
which in due course new body-cells are developed.
Thus he regards the body-cells as constituting a sort
of vehicle within which the germ-cells are carried.
The germinal elements contain the primordial sub-
stance around which the body-cells have developed,
and, since in all the long process of evolution the
germinal elements have been the only form of con-
nection between different generations, the substance
composing them has unbroken continuity.

This conception of the continuity of the germ-
plasm is the foundation of Weismann's doctrine.
It is one of the most fruitful biological ideas devel-
oped during the nineteenth century, and it replaced
as a basis all earlier theories of heredity. Although
Weismann was not the originator of the idea of
germinal continuity, he is nevertheless the one who
has developed it the most extensively.

FIG. 30. — WILLIAM HARVEY
(1578-1657)

FIG. 31. — THOMAS H. HUXLEY
(1825-1895)

FIG. 32. — AUGUST WEISMANX
(1834-1914)

FIG. 33. — HUGO DE VRIES

THEORIES OF EVOLUTION 157

In 1893 there was published an English translation
of his famous book The Germ-Plasm which stimulated
so much discussion among biologists. This sets
forth his theory of heredity. For many years Weis-
mann was a professor in the University of Freiburg,
and his lectures on the evolution theory were de-
servedly famous and well attended. The best
exposition in English of his theory is The Evolution
Theory, published in two volumes in 1904. In the
preface he says: "I make this attempt to sum up and
present as a harmonious whole the theories which for
forty years I have been gradually building up on the
basis of the legacy of the great workers of the past,
and on the results of my own investigations and
those of my fellow-workers."

Since we may assume that there has been unbroken
continuity of the germ-plasm from the beginning, we
may also assume that its organization has become
very complex. Protoplasm is impressionable, re-
sponding to various forms of stimuli and undergoing
modifications in response to environmental influences.
These subtle changes occurring within the proto-
plasm affects its organization, and, in the long run,
it is the summation of experience that determines
what a particular mass of protoplasm shall be and

158 THE MAIN CURRENTS OF ZOOLOGY

how it will behave in development. Two separate
masses of protoplasm differ in detail, as to capabili-
ties and potentialities, according to the experiences
through which they have passed, and no two will be
absolutely identical.

We have seen that variation and heredity are the
two primary factors of evolution. The way in which
Weismann accounts for variation among the higher
animals is both ingenious and interesting. In all
higher organisms the sexes are separate and repro-
duction of their kind involves the union of germinal
elements from both parents.

As previously stated, the germinal elements in-'
volved are ovules and pollen of plants and eggs and
sperms of animals. In animals, the egg bears all
hereditary qualities from the maternal side, and the
sperm those from the paternal side. The intimate
mixture of these in fertilization gives great possibil-
ities of variations arising from the different com-
binations and permutations of the vital units within
the germ-plasm.

The variations once started will be fostered by
natural selection.

It is now evident that if we follow Weismann's
conclusions logically, there can be no inheritance of

THEORIES OF EVOLUTION 159

acquired characters — that is, of acquisition made by
the body-cells, or changes arising in them, during the
lifetime of the individual. None of the body-cells are
transmitted and the hereditary qualities must all be
located within the plasms of the germ-cells.

The outstanding features of Weismann's theory
are as follows:

1. The germ-plasm has unbroken continuity from
the beginning of life.

2. Heredity is accounted for on the principle that
the offspring is composed of some of the same stuff
(germ-plasm) as its parents. The body-cells are not
inherited.

3. Consequently, there is no inheritance of ac-
quired characters.

4. Variations arise from the union of the germinal
elements, giving rise to varied combinations and
permutations of qualities of the uniting germ-plasms.

5. Weismann adopts and extends the principle of
natural selection.

De Vries. — Hugo de Vries (Fig. 33), director of
the Botanical Garden in Amsterdam, has experi-
mented widely with plants, especially the evening
primrose (CEnothera Lamarckiana) , and has shown
that different species appear to rise suddenly. These

160 THE MAIN CURRENTS OF ZOOLOGY

sudden variations that breed true, and thus give rise
to new forms, he calls mutations. This indicates the
source of the name applied to his theory.

In his Die Mutationstheorie, published in 1901, he
argues for the recognition of mutations as the
universal source of the variations that lead to species-
formation. Although he evokes natural selection
for the perpetuation and improvement of variations,
and points out that his theory is not antagonistic
to that of natural selection, it is nevertheless di-
rectly at variance with Darwin's fundamental con-
ception, that slight individual variations "are prob-
ably the sole differences which are effective in the
production of new species" and that "as natural
selection acts solely by accumulating slight, succes-
sive, favorable variations, it can produce no great or
sudden modifications."

The work of De Vries is a most important con-
tribution to the study of the origin of species, and is
indicative of the fact that many factors must be
taken into consideration when one attempts to
analyze the process of organic evolution. His ob-
servations widen the field of exploration. While he
has demonstrated that species may arise by muta-
tions, there is at the same time good evidence — from

THEORIES OF EVOLUTION 161

paleontology and other sources — that species may
also arise by slow accumulations of small variations.

One great value of his work is that it is based on
experiments and that it has given a great stimulus to
experimental studies. Experiment was likewise a
feature of Darwin's work, but that seems to have
been almost overlooked in the discussions aroused by
his conclusions. De Vries, by building upon exper-
imental evidence, has led naturalists to realize that
the method of evolution is not a subject for argu-
mentative discussion, but for experimental investi-
gation.

Other Theories. — In addition to the four theories
briefly outlined other theories have been advanced,
which, in their relation to the Darwinian hypothesis
of natural selection, fall into two categories. There
are competing theories designed to replace that of
natural selection, and there are auxiliary, or support-
ing theories, that are designed to throw new light on
the conditions of species-forming, and to strengthen
the natural selection theory by its more complete
elucidation. Such an extensive literature has grown
up in the discussion of these matters, that even
summaries would unduly prolong the subject of this
chapter. The entire case has been presented with

162 THE MAIN CURRENTS OF ZOOLOGY

remarkable clearness in Kellogg's Darwinism To-day,
to which volume the reader is referred for fuller
information.

There are, however, two ideas of fundamental im-
portance in post-Darwinian discussions that should
receive mention. These are designated respectively,
orthogenesis and isolation. Theodor Eimer, since
1888, has been the typical representative of the ideas
of orthogenesis — which means development in a
straight or definite direction. He maintains that
variations of organisms take place, not fortuitously
in radiating lines, but follow a few definite direc-
tions. He insists that variations are not preserved
on the basis of their utility, but as the result of the
direct inheritance of acquired characters. This is
intended as a replacing theory for that of natural
selection.

Isolation as a favoring condition of species-
formation has been championed by Moritz Wagner
(since 1868) and, more recently, by David Starr
Jordan, Gulick, Romanes and others. This is based
on the obvious fact that slight variations will be
more likely to persist if the species in which they
occur are segregated, or isolated, so that those ex-
hibiting similar variations shall be compelled to

THEORIES OF EVOLUTION 163

breed together. Slight variations before they be-
come fixed are very unstable, and they would very
likely disappear if the breeding were general with
species exhibiting counter variations. Isolation of
species, by geographical barriers or other natural cir-
cumstances, would lead to interbreeding and favor
the perpetuation and improvement of small varia-
tions. After the variations are started and lifted to
a plane where natural selection can take hold, then
the latter agent would become operative. Natural
selection originates nothing but guides the course of
evolution after variations are sufficiently developed
to make a difference in the struggle for existence.

Before closing this chapter a word regarding the
present status of the doctrine of organic evolution
will be in order. With so many discussions in
scientific circles regarding aspects of evolution there
is little wonder that the general public should be
confused, and that reports are often circulated that
there is a tendency on the part of the scientific world
to recede from the doctrine or even, to surrender it.
This vagueness regarding the present status of the
theory of organic evolution arises chiefly from not
understanding the nature of the points at issue.
Never before was the doctrine of organic evolution so

164 THE MAIN CURRENTS OF ZOOLOGY

thoroughly entrenched in the mind of the scientific
world. Never before was it so thoroughly supported
by such a wealth of compelling evidences which have
multiplied with the progress of biological investiga-
tion. The scientific discussions are no longer re-
garding the occurrence of evolution. The fact of
evolution is so widely recognized that it is regarded
in the light of a great truth of nature. But, regarding
the factors — the particular agencies that have been
at work in nature to bring about this recognized
development of life — there is much room for discus-
sion. The attempt to designate the particular factor,
or factors, has given rise to the different theories of
organic evolution. That natural selection is an
important agent at some stages of the process is
commonly conceded, but the factors — more primary
in nature — which produce variation and adaptation
are more obscure and will for a long time be subjects
of investigation.

CHAPTER XIV

SOME MISCELLANEOUS TOPICS. PAINLESS
SURGERY, ETC.

No student of biology should be unacquainted
with the circumstances leading up to the demon-
stration of the properties of anaesthetics and to
painless surgery. The discovery of the methods of
painless surgery was one of the greatest medico-
biological advances of all time, and the application of
these methods has conferred upon suffering hu-
manity one of the greatest blessings of science. It
was in a way a by-product of biological investigation,
and one of those advances so intimately connected
with the progress of biology that it is appropriate to
consider it within the scope of this book.

The first definite step that brought anaesthetics
into general use was the demonstration, in 1846, by
W. T. G. Morton, that ether is a safe, effective and
reliable agent for producing insensibility to pain
during a surgical operation.

Since there were anticipations of this discovery and
various claimants to recognition for the honor of the

important achievements, the story should be told in

165

166 THE MAIN CURRENTS OF ZOOLOGY

outline. Although the general use of anaesthetics in
surgery dates from 1846, there are scattered refer-
ences in classical writers, in mediaeval literature and
in other sources, to show that there was at least
occasional employment of hemp, of mandrake and
other opiates, to produce insensibility to pain during
surgical treatment. Vapors of a certain kind of
hemp were used in ancient times, Mandragora was
used in the thirteenth century in Italy, and it is
recorded that, in 1782, Augustus, King of Poland,
underwent an amputation while rendered insensible
by a narcotic. But these occurrences were inciden-
tal and led to no general use of pain-dispelling agents.

In 1787, Sir Humphrey Davy experimented upon
himself with the effects of nitrous oxide, commonly
called "laughing gas." His experiments were in-
teresting, and although he did not inhale the gas
to the point of complete insensibility, he made the
suggestion that it might be useful in surgical practice.

Again, in 1818, Faraday observed the pain-dis-
pelling effects of inhalation of the vapor of ether,
and in 1822, 1833 and 1834 similar observations were
reported by certain American physicians. But no
practical outcome resulted. These observations ap-
pear "to have been regarded in the light of mere

MISCELLANEOUS TOPICS 167

scientific curiosities and subjects for lecture-room
experiment." Had they been followed up by further
experiments and demonstrations the advent of pain-
less surgery would have been much earlier. They
were vague foreshadowings of this important event.

The demonstration, the earliest use and the com-
munication of the method of anaesthesia, is an Amer-
ican achievement. In 1844, Dr. Horace Wells of
Hartford, Connecticut, experimented with nitrous
oxide and began to use it for the painless extraction of
teeth in his dental practice; but, owing to an un-
successful experiment he became discouraged and did
not follow the matter very far. He also experi-
mented upon himself with ether but gave it up be-
cause he regarded its inhalation as too disagreeable.

Wells communicated his observations to the
Boston dentist, Dr. W. T. G. Morton, who acted
upon the suggestion with great enthusiasm and
energy. Dr. Morton thought that sulphuric ether
was probably a more promising agent than nitrous
oxide gas and experimented with it extensively.
After experiments on animals, and on patients in
his dental practice, he became convinced of its
reliability and, in September of 1846, he went to the
Boston surgeon, Dr. J. G. Warren, and requested

168 THE MAIN CURRENTS OF ZOOLOGY

opportunity to demonstrate his discovery on a
patient about to undergo a severe surgical operation
(removal of a tumor of the neck) at the Massachu-
setts General Hospital. In this case, the results of
the administration of ether were satisfactory and this
new method of painless surgery was communicated
to the medical world. It was at first received with
incredulity but speedily won recognition both in
America and in Europe. Dr. Oliver Wendell Holmes
supplied for the new method a singularly appro-
priate name, calling it anaesthesia, and the agents
producing this insensibility to feeling, anaesthetics.

The honor of this achievement belongs to Dr.
Morton (Fig. 27), but other claimants arose. The
bitter controversy over priority and credit for the
discovery was long drawn out. Dr. Charles T.
Jackson, the chemist of Boston, made a determined
effort to secure for himself credit for the discovery or,
at least, equal recognition with Morton. His ad-
herents got the matter considered by Congress and a
committee of the House of Representatives voted
him the credit. More judicious consideration of his
claims leads to the conclusion that his connection
with the discovery was incidental. It is true that he
experimented with ether, and, not knowing that

MISCELLANEOUS TOPICS 169

Morton had already experimented with it, he sug-
gested to Dr. Morton its pain-expelling effects.
Apparently, there floated in Dr. Jackson's mind
ideas regarding the employment of ether in surgery,
but Morton took the further step of extensive ex-
periment and use, and, above all, he demonstrated
in the Massachusetts General Hospital that it was
safe, effective and reliable. This brought it into
general use.

Another man, Dr. Crawford Long, nearly antic-
ipated the discovery of Morton. He was a practi-
tioner in a small town of Georgia, and in March,
1842, he had placed a patient profoundly under the
influence of ether and had painlessly removed a
tumor from the neck. He had also used ether in
other operations prior to 1846. In point of tune he
antedated Morton, but he had some misgivings as to
whether it was the effect of the ether that produced
insensibility, or a sort of hypnotic influence exerted
by himself, and his results were not published till
1849.

Although Jackson had vaguely divined the possi-
ble utility of ether in surgery, and Long had used it
in local country practice, it remained for Morton to
carry the matter to a practical conclusion. It re-

i yo THE MAIN CURRENTS OF ZOOLOGY

mained for him, on the basis of his own experiments,
followed by a hospital demonstration, to introduce
the method of anaesthesia to the medical world.
Morton's work was on a different plane from that of
his predecessors. Except for its practical use by
Long the work of others was merely anticipatory
glimpses, and Morton, by demonstrating the safety
and reliability of ether as an anaesthetic agent, in-
troduced the method into surgery.

The new method was put into immediate use. In
1847, after ether had been successfully used in
Europe, the Scottish surgeon, Sir James Simpson,
introduced the use of chloroform which had been
previously used in France by Flourens in experimen-
tation on animals. Since that time the methods of
administering ether and chloroform have been
greatly improved and they remain to-day the chief
agents used in anaesthesia.

Vaccination — Edward Jenner. — The method of
vaccination for small-pox was an original and unique
discovery, and antedated by more than three-fourths
of a century, the modern vaccinations and serum
inoculations devised by Pasteur.

Formerly, small-pox was a dreaded and highly
contagious disease. It was very prevalent, sweeping

MISCELLANEOUS TOPICS 171

as an epidemic over communities and carrying terror
and death in its path. Edward Jenner came from a
dairy county — Gloucestershire — of England where
a belief existed among the dairy people that persons
who had contracted cow-pox were immune from
small-pox. Cows are sometimes affected with a kind
of disease accompanied by watery pustules on the
udders, the hands of milkers become infected from
these, and, after a mild sickness, those individuals
were no longer susceptible to small-pox. It was the
quality of sagacity in Jenner that led him to make
use of this wide-spread belief and to investigate it
with the trained mind and the powers of a scientific
education. His discovery was a triumph of experi-
mental science.

Edward Jenner, the discoverer (1749-1823) (Fig.
28) went to London at the age of twenty-one, in
1770, to pursue medical studies and came under the
tutelage of the famous Dr. John Hunter. He was
broadened by his contact with Hunter and by
studies of comparative anatomy in his extensive
museum. He attempted to interest Hunter in the
question of immunity from small-pox, but Hunter,
his preceptor, was too busily engaged with other
matters to give it serious attention. Accordingly,

172 THE MAIN CURRENTS OF ZOOLOGY

Jenner went to work on his own account to investi-
gate the basis of the belief of the dairy people of his
native county.

After some experimentation he devised means of
vaccinating people with the relatively harmless virus
of cow-pox. In 1796, he made inoculations with
cow-pox material and after the recovery of his
patients from a mild sickness, in two months, he
inoculated the same individuals with small-pox
matter but they remained unaffected. This con-
vinced Jenner that this method was a protection
against the contagion of small-pox, and two years
after, in 1798, he announced his discovery to the
world.

It was immediately put into use and Jenner was
heralded as a great benefactor. Even before Jenner
the voluntary inoculation with the virus of small-pox
had been advocated. The disease was so prevalent
and the chance to escape the contagion was so small
that some were willing to run the risk of a voluntary
inoculation, under the belief that these inoculations
resulted in mild cases, but these were sometimes
fatal.

Jenner, however, investigated the matter with
scientific methods and devised a method of procuring

MISCELLANEOUS TOPICS 173

and using the virus of cow-pox so as to secure pro-
tection against the contagion of this most dreaded
disease. At the present time the use of his method is
so general — being at times prescribed by law — that
small-pox, from being one of the most common
diseases, is now comparatively rare.

The objections raised to vaccination are usually
based on the fear of communicating other serious
conditions. But this danger is reduced to a min-
imum by the production of pure and standard cul-
tures.

CHAPTER XV

THE TEN FOREMOST MEN OF ZOOLOGICAL
HISTORY. THE RANK OF DIFFERENT NA-
TIONS IN BIOLOGICAL PROGRESS

IT is a popular pastime to make out lists of the
foremost men in different lines of human achieve-
ment. In any subject it is natural to wish to settle
the question, Who were the great path-breakers?
It is a hazardous undertaking to attempt to designate
any particular number, and it would be wrong to
pretend, that there is an absolute standard upon
which the ten men of greatest distinction can be
selected. The formulation of such a tentative
group, for zoology, if not taken too seriously, will
serve some useful purpose. It will stimulate thought
and direct attention to some of the most eminent men
and to their contributions to zoological progress.
The point of view adopted will lead to divergent
results. Shall the foremost men be selected from the
standpoint of wide influence, or from that of intel-
lectual superiority of the individual and the quality
of his work? The former basis would give a different

group from the latter.

174

THE TEN FOREMOST MEN 175

The list of ten men given below is based on the
influence exerted by certain advances with which
they were prominently connected, rather than merely
on the high quality of their individual output as
scientific investigators. In some cases the highest
intellectual rank and the most eminent researches are
combined in one individual of wide influence, in
other instances, the influence of certain happy dis-
coveries (as in the case of Mendel) are out of pro-
portion to the relative rank of the man as a bi-
ologist.

1. Harvey. — Passing over Aristotle, who undoubt-
edly was the greatest scientific investigator of an-
tiquity, and beginning with the revival of science in
the sixteenth century, it seems to the writer that
the pioneer work of Wm. Harvey (1578-1657) re-
quires first recognition. He was at once observer and
experimenter. The influence of his work on the
circulation of the blood was profound and construc-
tive. It not only gave for the first time a rational
basis for the progress of physiology but also provided
biological science with a new method and stimulated
investigation. His book on the movement of the
heart and the blood (De Motu Cordis et Sanguinis)
published in 1628, is a biological classic. He also

1 76 THE MAIN CURRENTS OF ZOOLOGY

made the first (after the Renaissance) independent
advance in embryology (1651) and exercised consid-
erable influence on the progress of morphology.

Although Vesalius (1514-1564) before Harvey had
established the method of independent observa-
tion (human anatomy, 1543) he is subordinate to
Harvey.

2. Malpighi. — Our second selection in chron-
ological order is Malpighi (1628-1694). A careful
observer, making progress in Minute Anatomy of
animals, as in his famous monograph on the anatomy
of the silkworm (1670), in the anatomy of plants
(1671 and 1675), and, especially, in embryology
(1672). He was the first also (in 1661) to see the ac-
tual circulation of blood in the capillaries. Through
the exactness and the range of his observations, his
spirit and his teaching of anatomy, he was directly
connected with future progress.

Two of his contemporaries should be mentioned —
Leeuwenhoek and Swammerdam. Leeuwenhoek
was more discursive and less directly connected with
progress. Swammerdam was more exact in his
studies of insect anatomy, but the range of his work
was more limited and the publication of his complete
investigations was delayed till 1738. (During his

THE TEN FOREMOST MEN 177

lifetime, a small volume on the general history of
insects was published, in 1669.)

3. Linnaeus. — From the standpoint of wide in-
fluence Linnaeus (1707-1778) should be included in
our list. He was the man who brought the present
method of naming animals and plants into use and
thereby gave to natural history a new language. He
also introduced greater precision in the whole field of
description and classification. The stimulus im-
parted to natural history by the work of Linnaeus was
immense. Collection and classification of animals
and plants was carried on with enthusiasm and the
knowledge of the animals of the globe rapidly ex-
tended. Linnaeus also directed attention to species,
and thereby served to lay the foundation for the
question of the Origin of Species, which had such
important connection in the work of Lamarck and
Darwin.

4. Cuvier. — In the early years of the nineteenth
century this French legislator and zoologist gave
a new direction to zoological study. While Linnaeus
had given a great impulse to natural history and to
the study of the organism as a whole, Cuvier (1769-
1832) started a strong movement for structural
zoology. By extensive dissections he centered atten-

1 78 THE MAIN CURRENTS OF ZOOLOGY

tion on the structure of animals and founded com-
parative anatomy. He also laid foundations of the
science of Vertebrate Paleontology. On the whole,
his influence on the progress of zoology was so exten-
sive that he is to be heralded as one of the great path-
breakers.

5. Von Baer. — One of the great intellects of the
nineteenth century, von Baer (1792-1876), is to be
remembered for the great service of founding in
1828 embryology on modern lines. This has proved
to be one of the most helpful and illuminating lines
of zoological investigation. This supplemented the
work of Cuvier and from the two combined, compara-
tive anatomy and embryology of animals, for many
years proceeded the best results of zoological study.

6. Johannes Miiller. — Johannes Muller (1801-
1858) made physiology comparative, and stimulated
researches in both physiology and morphology.
Through his superb talents and extraordinary
qualities as a leader he helped in a signal way to
advance the standards of zoological investigation.
By appointment a professor of physiology, he was
also an investigator in zoological lines (morphology)
and promoted exactness of observation and high
quality of work. Considered strictly as a phys-

THE TEN FOREMOST MEN 179

iologist his contributions were less eminent than those
of Claude Bernard, but with a larger number of
disciples and with unusual gift for stimulating and
inspiring his students, he exerted a broad influence
for progress.

7. Pasteur. — From all points of view there can
be no doubt of the rank of Pasteur (1822-1895) as
one of the greatest biologists of the nineteenth cen-
tury. He is placed here as one of the men of greatest
influence on the progress of zoology because zoology
is the central subject of biology. There is continued
growth in the sum total of his influence. In close
relation with the influence of Pasteur should be men-
tioned the names of Koch and Lister.

8. Darwin. — Another, whose place is unquestioned
hi the rank of the foremost men of zoology, is
Charles Darwin (1809-1882). His theory of natural
selection as an agent of organic evolution has had the
most stimulating effect upon zoological progress of
any scientific advance. Although his predecessor,
Lamarck, is accorded high place at the present day,
no other man connected with the idea of organic
evolution has exerted the wide influence of Charles
Darwin.

9. Max Schultze. — This investigator embraced

i8o THE MAIN CURRENTS OF ZOOLOGY

in his work the summation of the protoplasm idea
and the reform of the cell-theory. The effect of
these two conceptions on zoology cannot be over-
estimated. Taking rank with the greatest dis-
coveries of the nineteenth century, their direct
application in zoology have been of supreme Value.
Schultze (1825-1874) also founded one of the most
influencial periodicals of zoological science, the
Archiv fur Mikroscopische Anatomie.

10. Mendel. — Since 1900, the date of the redis-
covery of alternative inheritance and purity of the
germinal elements, Mendelian inheritance has been
one of the most actively pursued of biological topics.
Mendel (1822-1884) made his chief observations on
plants and published the same in 1866-1867, but,
the study of Mendelian inheritance in animal forms
has exerted such a great influence, that his name is
properly embraced in this list. On the basis of
strictly scientific output and commanding intel-
lectuality there are other names that would contest
the position with Mendel, but, on the basis of the
wide influence of his happy discoveries, he is entitled
to rank with the men whose work has stimulated
zoological investigations and been of the widest
influence.

RANK OF DIFFERENT NATIONS 181

Rank of the Nations in Biological (Zoological)
Progress. — The relative position of the different
nationalities in biological progress from the zoological
side is a question that offers ground for conflicting
opinions. It is nevertheless of very great interest to
students of zoology and is an appropriate matter for
consideration in this connection. The general con-
clusion appears to me justified that no nation takes
absolute preeminence in originality and in quality of
investigation. Notwithstanding the brilliancy of the
French, the deep philosophical contributions of the
English, and the monumental industry of the Ger-
mans, not one of these nations can justly claim a
position of undisputed supremacy.

The fact should not be overlooked that there have
been notable pieces of zoological work from Italy,
from Ramon y Cajal in Spain, from Russia and from
the United States, but for the present inquiry, the
matter is chiefly conned to the highly developed
nations of Europe, the English, the French, and the
Germans.

Let us first examine the part played by these three
nations as path-breakers in the five outstanding
biological advances of the nineteenth century.

The advance of greatest importance, the theory of

1 82 THE MAIN CURRENTS OF ZOOLOGY

organic evolution, is to be credited in its inception to
the French (Lamarck) and the English (Charles
Darwin) . This is probably the greatest philosophical
contribution of the nineteenth century. After it was
well under way it was taken up by scholars of differ-
ent nationalities. Weismann, the German, De Vries,
the Hollander, have made notable contributions, and,
in America, Cope and others brought forward new
aspects of Lamarckism and established the school of
Neo-Lamarckism.

To the genius of Pasteur more than to any other
worker we owe the basis of the germ-theory of
disease with its concomitants as antitoxins, serum
injections and vaccines. The Englishman, Lister,
applied these to surgery and the German, Robert
Koch, (a student of Ferdinand Cohn), established
bacteriology (to which these matters belong) as an
independent science.

The discovery of protoplasm is credited to the
Frenchman Dujardin, but the great elaboration of
the idea to Max Schultze, the German.

The cell-theory is a product of German scholar-
ship— Schleiden and Schwann being founders and
Schultze developer of this important conception.

In the experimental study of heredity, while the

RANK OF DIFFERENT NATIONS 183

work of Francis Galton, the Englishman, was of high
quality and received earlier notice, it was over-
shadowed by the importance of MendeFs (Austrian)
results.

The encouragement of research in the German
universities — making results of investigations the
basis of recognition and advancement in scholarly
occupations — has had tremendous influence. The
degrees conferred by German universities require the
publication of a piece of research as a thesis, and if
merely volume of output is considered, the Germans
have been leaders — but for originality, quality and
philosophical insight the French and the English take
higher rank.

Turning from the outstanding advances we shall
consider who have been path-breakers in some of the
different divisions of zoological science — omitting the
mention of the living and most recent personalities.

In Physiology, if the Germans have their Haller
and Johannes Muller, so the English have their
William Harvey and Burdon-Sanderson and the
French their Magendie and Claude Bernard. The
latter occupies a unique position. He was the
veritable law-giver of experimental physiology. As
an investigator probably he was as Howell has said,

1 84 THE MAIN CURRENTS OF ZOOLOGY

"the greatest physiologist of all time." He is per-
haps better compared with Ludwig than with
Johannes Muller.

In Embryology while the Germans have Von Baer
(Russian) as founder, the Italians have Malpighi, as
forerunner, and the English have Francis M. Balfour,
as developer.

In Comparative Anatomy the French have Cuvier,
H. Milne-Edwards and Lacaze-Duthiers, the Eng-
lish, John Hunter, Richard Owen and Huxley to off-
set Meckel, Muller and Karl Gegenbaur.

The scientific output of a nation especially as to
quality, is largely an expression of national tempera-
ment.

The French are remarkable for lucidity, for in-
dsiveness, they are subtle and accurate in analysis
and exhibit great originality.

In zoology, the English are notable for philosoph-
ical grasp (Darwin) and have a passion for intel-
lectual honesty (Huxley).

The German mentality is more ponderous, less
original, but has been guided by great industry,
finding suggestions in the work of investigations of
other nations and elaborating these suggestions with
diligence and thoroughness. If other nations have

RANK OF DIFFERENT NATIONS 185

shown greater originality, and greater philosophical
grasp in zoological fields, the Germans have been
better developers of these new territories.

If we select the overshadowing contributions of
Darwin and Pasteur we might be inclined to place
English and French contributions to biological
thought above those of the Germans. This is, how-
ever, a too restricted view, and, broadly considered,
it appears that the different nations break about
even as regards eminent contributions to biological
progress. They constitute an international group of
peers among whom it is invidious to make distinc-
tions.

The fact that German contributions to scholarship
have been more energetically advertised and are
therefore more widely known, has given rise to a
wide-spread opinion that the Germans have been
unquestioned leaders hi biological progress. But,
this general impression gives way under a candid
consideration of the quality and the importance of
the scholarly output of other nations.

Zoology and Intellectual Progress. — Undoubtedly
the progress of zoology has played an important
part in the intellectual development of civilized
mankind, but the reason for this is only vaguely

1 86 THE MAIN CURRENTS OF ZOOLOGY

understood. That the progress of science, broadly
speaking, has been beneficial will not be disputed.
Manifestly it has been a powerful reconstructing
force. Wherever investigations of the phenomena of
nature have taken away old beliefs they have sub-
stituted something better and more consistent. But
zoology in particular, in the last half century, has
concerned itself with the investigation of the phe-
nomena of all living animals of the globe. This has
brought zoological investigation into a realm that
touches more closely than any other, the problems
of human origin and destiny.

The phenomena of life are so difficult of analysis
and apparently so mysterious that, naturally, there
was a great amount of metaphysical speculation re-
garding their interpretation, and many superstitions
and misconceptions arose. Zoology undertook to
investigate these problems and came into conflict
with traditional opinion. The atmosphere of thought
engendered by the progress of these studies of animal
life was broadening, and in its influence as wholesome
as it was stimulating. Wherever biological investiga-
tion prospered the results shed light and dispelled
error. There was progress -in straight thinking.

Immediately after the Renaissance these new

RANK OF DIFFERENT NATIONS 187

ideas began expanding the horizon of thought and
provoked many controversies, which for the time
were often bitter, but, in many instances, resulted
in freeing the mind from the bonds of inherited and
traditional superstitions.

Gradually all animal life came to be looked on as
the result of an orderly progress with no place for
the idea of chance. The idea of the constancy of
nature was established. Then arrived, in the last
half of the nineteenth century, largely as the result
of zoological progress, the doctrine of organic
evolution which produced a mental revolution. It is
generally recognized that from the time of the re-
vival of scientific learning to the present, while all
scientific study was making towards enlightenment,
still, the investigation of problems involving animal
life had unusually broad influence in promoting
intellectual progress.

The controversies engendered were often against
theological opinion, but these flashes of enlighten-
ment were by no means confined to that territory.
Scientific dogma (as that of the fixity of species) and
medical tradition (as to the source and the nature
of disease) also gave way to investigations of a
biological character.

CHAPTER XVI
SOME USEFUL BOOKS

THE books and periodical articles in the field of
zoology are so numerous and cover such a wide
range of topics that some sort of guide to the best
reading is nearly indispensable.

A continually increasing number of persons take
an interest in the larger ideas that have developed
from the critical investigation of animals, and this
class of readers often seek for palatable and satis-
fying literature on zoological subjects.

The writings appeal to various kinds of interest —
there are the more popular and the more technical.
In selecting reading we must recognize that refer-
ences which are good for one purpose often are not
good for another. Moreover, the focus of interest of
the reader varies with his mood as well as with his
purpose, and the selection of suitable reading for
different needs is a matter of no little difficulty.

There are informing books about insects, birds and
protozoa, but these will not be specifically adapted
to one whose chief interests are in evolution or
genetics.

188

SOME USEFUL BOOKS 189

The more technical publications are standardized
and are less difficult to indicate than good sources of a
popular character. For one whose interest in the
results of zoological studies is beginning to grow,
it is a great assistance to have some references to
reliable and trustworthy literature for fire-side
reading, in addition to the books of general reference
which will be consulted only at intervals.

There are books that supply stimulus and promote
a feeling for the work of the naturalist, such as Dar-
win's Voyage of the Beagle, Bates's A Naturalist on
The River Amazon, Wallace's Malay Archipelago and
those writings that bring us into contact with great
personalities such as the biographies of Darwin,
Pasteur, Huxley and Lister.

In the references indicated below attention has
been given to selecting sources of unquestioned merit
and reliability, but no claim is made to giving a
balanced list of reading. Assuming that a more
general interest exists in historical phases and in
biographies, I have cited a relatively larger number
of references of that nature.

The object of the reading lists is to supply — not in
too great number — reliable and trustworthy refer-
ences to a variety of zoological subjects. The more

190 THE MAIN CURRENTS OF ZOOLOGY

advanced student who has need of zoological refer-
ences on subjects not included will know how to go
about finding them. The general reader will also
find additional biographical sketches as well as
general topics referred to in the indices of the period-
ical literature with which nearly all libraries are
provided.

It has seemed desirable to give, first, a suggested
list of fifty books for the nucleus of a reference li-
brary, and to follow this list with additional titles of
books and articles in which the reader may find food
for various kinds of internal hunger which he may
feel from time to time for supplementary reading.

READING LISTS OF BOOKS AND PERIODICAL
ARTICLES ON ZOOLOGICAL SUBJECTS

(A) A REFERENCE LIBRARY OF FIFTY BOOKS

A suggested reference library of fifty titles including, be-
sides manuals and text-books, books on special topics of
zoological science. Among these special topics are biog-
raphies, historical phases, evolution, genetics, heredity,
cytology, ecology, birds, insects, protozoa, etc. The books
are arranged according to topics and not in the order of
preference.

HERTWIG, RICHARD. A Manual of Zoology, translated and
edited by J. S. Kingsley, 1902. Revised edition, 1912.
This is a standard reference, or PARKER and HASWELL'S
Text-Book of Zoology, 2 vols., 2nd edition, 1910, or
THOMSON'S Outlines of Zoology, 3rd edition, 1899.

WIEDERSHEIM, ROBERT. Comparative Anatomy of Verte-
brates, translated by W. N. Parker, 3rd edition, 1907.

MORGAN, THOMAS H. Experimental Zoology, 1907.

DARWIN, CHARLES R. A Naturalist's Voyage Round the
World. New edition, 1880. Also published under the
title The Voyage of the Beagle.

DARWIN, CHARLES R. The Origin of Species, 1859. Many
subsequent editions.

PACKARD, A. S. Lamarck, The Founder of Evolution, His
Life and Work, 1901.

WEISMANN, AUGUST. The Evolution Theory translated by
J. A. and Margaret Thomson, 2 vols., 1904.

DE VRIES, HUGO. Species and Varieties, their Origin by
Mutation, 1905.

191

192 THE MAIN CURRENTS OF ZOOLOGY

ROMANES, GEORGE J. Darwin and After Darwin, Vol. I,
1895. Or WALLACE, ALFRED R., Darwinism, 1889.

KELLOGG, VERNON L, Darwinism To-day, 1907.

JUDD, JOHN W. The Coming of Evolution, 1910.

JORDAN, DAVID S., and KELLOGG, VERNON. Evolution and
Animal Life, 1907.

LULL, R. S. Organic Evolution, 1917.

HUXLEY, T. H. Man's Place in Nature, in his Collected
Essays, 1900. Also published in many forms.

OSBORN, HENRY F. Men of the Old Stone Age, 1916.

FOSTER, MICHAEL. Lectures on the History of Physiology
During the i6th, i?th, and i8th Centuries, 1901.

THOMSON, J. ARTHUR. The Science of Life, An Outline of
the History of Biology and Its Recent Advances, 1899.

LOCY, WILLIAM A. Biology and Its Makers, 3rd edition,
1915. Historical phases.

DARWIN, F. Life and Letters of Charles Darwin, 2 vols., 1887.

HUXLEY, LEONARD. Life and Letters of Thomas Henry Hux-
ley, 2 vols., 1901.

FRANKLAND, PERCY and G. Pasteur, 1901.

PAGET, STEPHEN. Pasteur and After Pasteur, 1914.

WRENCH, G. T. Lord Lister, His Life and Work, 1913.

KELLY, HOWARD A. Walter Reed and Yellow Fever, 1906.

SEDGWICK, WILLIAM T., and WILSON, EDMUND B. General
Biology, revised edition, 1895.

DARWIN, CHARLES. Formation of Vegetable Mould through
the action of Worms, 1881.

WILSON, EDMUND B. The Cell in Development and Inheri-
tance, 1896.

WALTER, H. E. Genetics, 1913.

CONKLIN, E. G. Heredity and Environment in the Develop-
ment of Men, 1915.

DAVENPORT, CHAS. B. Heredity in Relation to Eugenics, 191 1.

BIBLIOGRAPHY 193

BATESON, W. Mendel's Principles of Heredity, with transla-
tions of his original papers on hybridization, 1902.

PUNNETT, R. C. Mendelism, 1911.

SHELFORD, VICTOR E. Animal Communities in Temperate
America, 1913.

CHAPMAN, FRANK M. Bird-Life, 1899.

BARROWS, WALTER B. Michigan Bird Life, Lansing, Michi-
gan, 1912.

COMSTOCK, JOHN H., and BOTSFORD, ANNA. A Manual for
the Study of Insects, 2nd Edition, 1899.

HOLLAND, W. J. The Butterfly Book, 1898.

FABRE, J. H. The Hunting Wasps, 1913.

HUXLEY, T. H. The Crayfish — An Introduction to Zoology,
1881, also 1906.

BAILY, F. R., and MILLER, A. M. Text-Book of Embryology,
3rd edition, 1916.

LILLIE, F. R. The Development of the Chick, 1908.

CALKINS, G. N. The Protozoa, 1901. Also, Protozoology,
1909.

JORDAN, DAVID S. A Manual of Vertebrates, new edition,
1916.

PRATT, HENRY S. A Manual of Common Invertebrate Ani-
mals— exclusive of insects, 1916.

HUXLEY, T. H. Lessons in Elementary Physiology, edited
and revised by Joseph Bancroft, 1915, or MARTIN, H. N.,
The Human Body, new edition, 1917.

HERRICK, C. J. An Introduction to Neurology, 1916.

VERWORN, MAX. General Physiology, translated by Fred-
erick S. Lee, 1899.

THOMSON, J. ARTHUR. The Study of Animal Life, 1892.

MARSHALL, J. MILNES. The Frog, new edition, 1916, or
HOLMES, Biology of the Frog, 1906.

BEDDARD, P. E. A Text-Book of Zoogeography, 1895.

194 THE MAIN CURRENTS OF ZOOLOGY

(B) SUPPLEMENTARY LISTS OF BOOKS AND
PERIODICAL ARTICLES

Embracing: (i) History and Biography; (2) Manuals and
Text-Books on Zoology; (3) Comparative Anatomy, Em-
bryology, etc.; (4) Books on special topics and (5) Mis-
cellaneous.

(i) HISTORY AND BIOGRAPHY
(a) History

CARUS, VICTOR. Geschichte der Zoologie, 1872. Also Histoire
de la Zoologie, 1880. A work of scholarship.

CUVIER, GEORGES. Histoire des Sciences Naturelles, 5 vols.,
1841-1845. Excellent. Written from an examination
of the original documents.

FOSTER, MICHAEL. Lectures on the History of Physiology,
1901. Fascinatingly written. Notable for poise and
judicial estimates, based on the use of the original
documents.

GEDDES, P. " A Synthetic Outline of the History of Biology."
Proc. Roy. Soc. Edinb., 1885-1886.

HERTWIG, OSKAR. "The Growth of Biology in the Nine-
teenth Century." Ann. Rept. Smithson. Inst., 1900.

LANKESTER, E. RAY. " The History and Scope of Zoology,"
in The Advancement of Science, 1890. Same article in
the Ency. Brit. Tenth edition.

LIBBY, WALTER. An Introduction to the History of Science,
1917. A small excellently written treatise, general in
scope.

LOCY, WILLIAM A. Article " Zoology," Cyclopedia of Educa-
tion, 1913. Also Biology and Its Makers. See list of
fifty books.

BIBLIOGRAPHY 195

MEDICINE. Related topics, dealing with the history of anat-
omy, embryology, physiology, etc., are treated in the
various Histories of Medicine.

MERZ. A History of European Thought in the Nineteenth
Century, vol. II, Scientific Thought, 1903.

MIALL, L. C. The Early Naturalists— Their Lives and Work
(1530-1789), 1.912. Good.

OSBORN, HENRY F. From the Greeks to Darwin, 1894. For
other references to the history of evolution see below,
under evolution.

THOMSON, J. ARTHUR. The Science of Life. See list of fifty
books.

WALSH, J. J. The Popes and Science, 1908.

WHITE, ANDREW, J. A History of the Warfare of Science with
Theology in Christendom, 2 vols., 1900. For Vesalius
and the overthrow of authority in science, etc.

WILLIAMS, HENRY SMITH. A History of Science, 5 vols.,
1904. Also The Story of Nineteenth Century Science,
1900. Good portraits.

(b) Biography

General Reference. RICHARDSON, B . W. Disciples of &scu-
lapius, 2 vols., 1901. Collected papers from the Ascle-
piad, containing accounts with portraits of Harvey,
J. Hunter, Malpighi, Vesalius and others.

Agassiz, Louis. Life and Correspondence, by his wife, 2
vols., 1885. Life, Letters and Works, Marcou, 2 vols.,
1896. " Agassiz at Peiukese," Amer. Nat., 1898. "What
we Owe to Agassiz," Wilder, Pop. Sci. Mo., July, 1907.

Aristotle. CUVIER on, a panegyric. GEORGE H. LEWES,
Aristotle — A Chapter from the History of Science, 1864,
a critical study. HUXLEY, On some Mistakes attributed
to Aristotle.

196 THE MAIN CURRENTS OF ZOOLOGY

Balfour, F. M. M. FOSTER, in Nature, vol. 29, 1882. Also,
Life with portrait in the Memorial Edition of Balfour's
Works. OSBORN, Recollections, with portrait, Science,
vol. 2, 1883. WALDEYER, Archiv fur Mikr. Anat., 1882.

Baer, Karl E. von. Leben und Schriften, his autobiography,
1864, 2nd edition, 1886. Life by STEIDA, 1886. Obituary,
Proceed. Roy. Soc. Lond., 1878. Nature, vol. 15, ELECKEL,
The History of Creation, vol. I, 1884. LOCY, "Von Baer
and the Rise of Embryology," Pop. Sci. Mo., 1905.
Rev. Scient., 1879. Fine portrait, as a young man, in
Harper's Magazine for 1899.

Bernard, Claude. Life by MICHAEL FOSTER. Excellent.

Bichat, Francois X. The Practioner, vol. 56, 1896.

Bois-Reymond, Emil Du. See Reymond.

Boveri, Theodor. Sketch in Science by RICHARD GOLD-
SCHMIDT, Feb. 25, 1915.

Brooks, William K. CONKLIN, J. Hop. Univ. Circulars.
The Century, vol. 25. A sketch of his life by some of
his former students and associates, three portraits,
Jour. Exp. Zob'L, vol. 9, 1910.

Burdon-Sanderson. Nature, vol. 73, 1905-06. A memoir,
Nature, vol. 89, 1912.

Cajal, Ramon y. See Ramon y Cajal.

Cohn, Ferdinand. Blatter der Erinnerung, with portrait,
1898.

Cope, E. D. aA Great Naturalist," H. F. OSBORN in The
Century, vol. 33, 1897. GILL, "Edward Drinker Cope,
Naturalist," Amer. Naturalist, 1897. Sketches of,
Amer. Journ. Sci., vol. 157, 1899. Nature, vol. 59,
1898-99. Pop. Sci. Mo., vol. 13, 1878. Ibid., vol. 19,
1881; Science, vol. 9, 1899. Obituary Notice, with por-
traits, Amer. Naturalist, 1897.

Cuvier, Georges. Life by FLOURENS. Memoires by MRS.

BIBLIOGRAPHY 197

LEE, 1833. BUCKLE, History of Civilization, vol. I,
pp. 633, et seq. LOCY, Biology and Its Makers, Chap-
ter VII.

Darwin, Erasmus. KRAUSE'S Life of E. Darwin, translated
into English, 1879. PACKARD, Life of Lamarck, chap-
ter XIV.

Darwin, Charles R. Life and Letters by his Son, 2 vols., new
edition, 1896. More Letters of Charles Darwin, 2 vols.,
1903. Chapter in MARSHALL'S Lectures on the Dar-
winian Theory. POULTON, Charles Darwin and the
Theory of Natural Selection, 1896. The original com-
munications of Darwin and Wallace, with letter of
transmissal signed by Lyell and Hooker, published in
the Trans. Linnaan Soc., 1858, were reprinted in the
Pop. Sci. Mo., Oct. n, 1912.

Dohrn, Anton. BOVERI in Science, Oct. n, 1912. Pop.
Sci. Mo., vol. 66, p. 99, portrait.

Dujardin, Felix. Notice Biographique by JOUBIN, with
portraits and illustrations, Archives de Parasitol, vol. 4,
1901. Dujardin's original description of Sarcode, Ann.
des Sci. Nat. (Botanique), vol. 4, p. 367, 1835.

Duthiers. See Lacaze-Duthiers.

Edwards. See Milne-Edwards.

Ehrenberg, Christian G. Life by LAUE, 1895. KENT,
Manual of Infusoria, vol. I.

Fabre, J. H. LEGROS, FABRE, Poet of Science, 1917.
MAETERLINCK, in Introduction to Fabre's Life of the
Spider. ELEANOR VAN HORN, American Magazine, 1907.
Literary Digest, 1907.

Foster, Michael. Nature, vol. 75, 1907, p. 345.

Galton, Francis. Memories of my Life, 1908. Sketches of,
Pop. Sci. Mo., vol. 29, 1886, Nature, vol. 70, 1907.

Gegenbaur, Karl. Erlebtes und Erstrebtest, portrait, 1901.

198 THE MAIN CURRENTS OF ZOOLOGY

Anat. Anzeiger, vol. 23, 1903. Ann. Rept. Smithson.
Inst., 1904.

Gesner, Conrad. BROOKS in Pop. Sci. Mo., 1885, illustra-
tions.

Haeckel, Ernst. His Life and Work by BOLSCHE, 1906.

Harvey, William. FOSTER, Lectures on the Hist, of Physiol-
ogy, Lecture II, Excellent. DALTON, History of the Cir-
culation. HUXLEY, William Harvey, a critical essay. Life
by D'ARCY POWER, 1898. BROOKS, "Harvey as Em-
bryologist," Bull. Johns Hop. Hospital, vol. 8, 1897.
Good. MORETON, An Anatomical Dissertation upon
the Movement of the Heart and Blood in Animals, a fac-
simile reproduction of the first edition of the famous
De Motu Cordis et Sanguinis, 1628, with English transla-
tion, 1894. Life by WILLIS in The Works of Harvey
rendered into English, Sydenham Soc., 1847.

His, Wilhelm. F. P. MALL in Amer. Journ. Anatomy, vol. 4,
1905. Sketch Anat. Anzeiger, vol. 26, 1904.

Hunter, John. The Scientific Works of J. Hunter, 2 vols.,
1 86 1 . RICHARDSON, Disciples of JEsculapius, vol. i , 1 901 .

Huxley, T. H. Life and Letters, by his son, 1901. Numerous
Sketches at the tune of his death, 1895. See Nature,
Pop. Sci. Mo., Nineteenth Century, etc.

Jenner, Edward. CAMAC, Epoch-Making Contributions to
Medicine, Surgery and the Allied Sciences, 1909.

Koch, Robert. Pop. Sci. Mo., vol. 36, 1889. Review of Re-
views, vol. 2, 1890. Ann. Rept. Smithson. Inst., 1911,
p. 651, with portrait. Sketches and references to his
discoveries numerous.

Kolliker, Albrecht von. His Autobiography, Erinnerungen
aus Meinem Leben, 1899, several portraits. WELDON,
"Life and Works," Nature, vol. 58, with fine portrait.
STERLING, Ann. Rept. Smithson. Inst., 1902.

BIBLIOGRAPHY 199

Lacaze-Duthiers, Henri de. Life with portraits in Archives
de Zool. Experiment, vol. 10, 1902.

Lamarck, H. B. A. S. PACKARD, Lamarck, the Founder of
Evolution, 1901. The best single reference on Lamarck.

Leidy, Joseph. Nature, vol. 44. Pop. Sci. Mo., vol. 28,
1891. A Tribute by A. S. Minot, Science, 1913. His
University Career, by W. Hunt, 1892.

Leuckart, Rudolph. Archives de ParasitoL, vol. i, no. 2.
Nature, 1898.

Leeuwenhoek, Antony van. New biographical facts hi
RICHARDSON, Disciples of dSsculapius, vol. i, p. 108.
LOCY, Pop. Sci. Mo., April, 1901.

Leydig, Franz. Brief sketch in his Horae Zoologicae, 1902.
Also in MIALL and DENNEY, The Cockroach, 1886.

Linnaeus, Carolus. CADDY, Through the Fields with Lin-
ntzus, 1887. "Jubilee at Upsala," Science, April 26,
1907. Many sketches and references in periodical lit-
erature in 1907 — the two hundredth anniversary of his
birth.

Lister, Joseph. WRENCH, G. T., Lord Lister, His Life and
Work, 1913. Pop. Sci. Mo., vol. 52, 1898. Rev. of
Reviews, vol. 14, 1896. Celebration of Lister's 8oth
birthday, Pop. Sci. Mo., 1907.

Ludwig, Carl. BURDON-SANDERSON, "Ludwig and Modern
Physiology," Ann. Rept. Smithson. Inst., 1896. LOM-
BARD, W. P., " The Life and Work of Carl Ludwig,"
Science, Sept. 15, 1916.

Mall, Franklin P. HUBER, In Memoriam, Anat. Record,
Jan. 1918; Flexner, An Appreciation, Sabin, Scientific
Achievements, Science, March 15, 1918.

Malpighi, Marcello. RICHARDSON, Vol. II. ATTI, Life and
Works, in Italian, 1847. Marcello Malpighi e I'Opera
Sua, 1897 — a collection of addresses at the unveiling

200 THE MAIN CURRENTS OF ZOOLOGY

of Malpighi's statue at Crevalcuore, that by Kolliker
excellent. LOCY, "Malpighi, Swammerdam and Leeu-
wenhoek," Pop. Sci. Mo., 1901. MACCALLUM, J. Hop.
Univ. Hospit. Bull.

Mendel, Gregor. BATESON, W., Mendel's Principles of
Heredity, 1902, also 1904. Contains biographical notice
and translation of the original papers on hybridization.
Ann. Kept. Smithson. Inst., 1901-1902. Pop. Sci. Mo.,
vol. 62, 1903; vol. 63, 1904. Science, vol. 23, 1903.

Milne-Edwards, H. Biographical sketch in Ann. Rept.
Smithson. Inst. for 1913.

Minot, C. S. Notice by H, H. DONALDSON, Science, Dec. 25,
1914; by C. W. ELIOT, Science, May 14, 1915. F. T.
LEWIS, with portrait.

Montgomery, Thomas H. CONKLIN, Science, Aug. 15, 1913.

Morton, W. T. G. CAMAC, Epoch-Making Contributions to
Medicine, Surgery and the Allied Sciences, 1909.

Muller, Johannes. VERWORN, General Physiology, 1899. His
life, complete list of works, etc., in Geddchtnissrede auf
Johannes Muller by Du BOIS-REYMOND, 1860. Eloge,
in English, by Virchow, Edinburg. Med. Jour., vol. 4.
Picture of his statue in Coblenz, Archivfur Mikr. Anat.,
vol. 55.

Owen, Richard. Life and Letters, 2 vols., 1894. CLARK,
Old Friends at Cambridge and Elsewhere, pp. 349 et seq.

Pasteur, Louis. Life by RENE VALLERY-RADOT, 2 vols.,
1894. Life by PERCY and G. FRANKLAND, 1901. Pasteur
and After Pasteur, STEPHEN PAGET, 1914. "Pasteur at
Home," illustrated, TARBELL in McClure's Mag., vol. i,
1893. Review of VALLERY-RADOT' s "Life of Pasteur,"
McClure's Mag., vol. 19, 1902. Nature, vol. 52, 1895.
Life by his son-in-law, translated by Lady Hamilton,
1886. Sketches of Pasteur very numerous.

BIBLIOGRAPHY 201

Ramon y Cajal, S. LOCY, Biology and Its Makers, portrait,
p. 176.

Reaumur, Rene A. Portrait and life in Les Savants Mo-
dernes, p. 332. MIALL, The Early Naturalists, p. 244,
1909.

Reed, Walter. H. A. KELLEY, Walter Reed and Yellow Fever,
1906.

Redi, Francesco. HUXLEY, " Spontaneous Generation,"
Scientific Memoirs, vol. 4, 1901. Same article, British
Assn. adv. Sci., 1870. Biographical sketch, Archives de
ParasitoL, vol. i, 1898. MAB BIGELOW, English transla-
tion of Redi's Esperienze Intorno Alia Generatione DegV
Insetti (1668), 1909.

Saint-Hilaire, Geoffroy. PACKARD'S Life of Lamarck, chap-
ter 13.

Schaudinn, Fritz R. Pop. Sci. Mo., vol. 70, 1907.

Schleiden, M. Sketch with portrait, Pop. Sci. Mo., vol. 22,
1882-1883. SACHS, Hist, of Botany, 1890. Translation
of his original paper of 1838 (Ueber Phytogenesis) — Illus-
trations, Sydenham Soc., 1847.

Schultze, Max. Sketch by SCHWALBE, with portrait, Archiv.
fur Mikr. Anat., vol. 10, 1874.

Schwann, Theodor. Sketch, Pop. Sci. Mo., vol. 37, 1000;
The Catholic World, vol. 71, 1900. Sa Vie et Ses Travaux,
FREDERACQ, 1884. LANKESTER, Nature, vol. 25, 1882.
Translation of his Microscopical Researches of 1839,
Sydenham Soc., 1847.

Spallanzani, Lazzaro. FOSTER, Lectures on the History of
Physiology, 1901. HUXLEY, "Spontaneous Generation,"
Scientific Memoirs, vol. 4, 1901. L'Abbato Spallanzani,
by PAVESI, 1901 — portrait.

Swammerdam, Jan. Life by BOERHAAVE in Biblia Natures,
also The Book of Nature, 1758. VON BAER, "Johann

202 THE MAIN CURRENTS OF ZOOLOGY

Swammerdam's Leben und Verdienste um die Wissen-
schaft," 1864, in Reden, vol. i, LOCY, Pop. Sci. Mo.,
April, 1901. MIALL, The Early Naturalists, 1912, p. 174.

Vesalius, Andreas. ROTH, Andreas Vesalius Bruxellensis,
the edition of 1892, the standard source of knowledge
of Vesalius and his times. FOSTER, Lectures on the His-
tory of Physiology, Lecture I. RICHARDSON, Disciples
of jEsculapius, vol. I.

Virchow, Rodolph. Celebration of the yoth birthday of
Virchow, addresses by OSLER, WELCH and others, J. Hop.
Univ. Circulars, vol. XI, 1891. JACOBI, Med. Record,
N. Y., vol. XX, 1881. Ann. Rept. Smithson. Inst., 1902.

Wallace, Alfred R. My Life, 2 vols., 1905. Lond. 111.
News, 1913 — large portrait.

Whitman, C. O. DAVENPORT, "The Personality, Heredity
and Work of Charles Otis Whitman," Amer. Naturalist,
vol. 41, Jan. 25, 1917.

Weismann, August. Sketch and brief autobiography, The
Lamp, vol. 26, 1903. CONKLIN, Science, Jan. 25, 1915.

Zittel, Karl von. SCHUCHERT, Biographical sketch with
portrait, Ann. Rept. Smithson. Inst., 1903-1904.

(2) MANUALS AND TEXT-BOOKS ON ZOOLOGY

(a) Larger publications

HERTWIG, RICHARD. A Manual of Zoology. See list of fifty

books.
PARKER, T. J., and HASWELL, W. A. A Text Book of Zoology,

2 VOls., 1910.

THOMSON, J. ARTHUR. Outlines of Zoology. See list of fifty

books.
The Cambridge Natural History, edited by S. F. HARMER and

A. E. SHIPLEY, ten volumes.

BIBLIOGRAPHY 203

A Treatise on Zoology, edited by E. RAY LANKESTER, ten

volumes, 1909.
The Riverside Natural History, edited by J. S. KINGSLEY, six

vols., 1884-1885. Also published under the title The

Standard Natural Hist.

BREHM, A. G. Tierleben, ten volumes, 1890-1893.
BRONN, H. G. Klassen und Ordnungen des Thier-reichs, 17

vols., 1880 , second edition in progress.

WEYSSE, ARTHUR W. A Synoptic Text-Book of Zoology,

1904.
JORDAN, DAVID S. A Manual of Vertebrates, 1916. See list

of fifty books.

PRATT, HENRY S. A Manual of Common Invertebrate Ani-
mals, 1916. See list of fifty books.
LEUNIS, JOHANNES. Synopsis der Thierkunde, 2 vols., 1883-

1886.
HOWES, G. B. Atlas of Practical Zootomy, 1902.

(b) Single volumes of medium size adapted for high school and
college classes

BIGELOW, M. A., and ANNA N. Introduction to Biology, 1913.

Also Applied Biology, 1911.
PEABODY, JAMES E., and HUNT, ARTHUR E. Elementary

Biology, 1912.
SEDGWICK and WILSON. General Biology, 1895. A classic.

See list of fifty books.

CALKINS, G. N. General Biology, 1914 and 1917.
NEEDHAM, JAMES G. General Biology, 1910.
MCFARLAND, JOSEPH. Biology, General and Medical, 3rd

edition, 1916.
HEGNER, ROBERT W. An Introduction to Zoology, 1910. Also

College Zoology,* 191 2. Practical Zoology, 1915.
ABBOTT, JAMES F. General Biology, 1914.

204 THE MAIN CURRENTS OF ZOOLOGY

GALLOWAY, T. W. Introduction to Zoology, 2nd edition, 1909.
KELLOGG, VERNON L. Animals and Man, 1911.
JORDAN, KELLOGG, and HEATH. Animal Studies, 1900.
HUXLEY, T. H. The Crayfish, 1881. See list of fifty books.
MORSE, E. S. A First Book of Zoology. An excellent simple

account of animals with unusually good sketches. Now

out of print.

PEARSE, A. S. A Text-Book of Zoology, 1917.
Other good single volumes by Davenport, Dougherty, Her-

rick, Hamaker, Hunter, Kellogg, Linville and Kelly,

Osborn.

(3) COMPARATIVE ANATOMY, EMBRYOLOGY, ETC.

WIEDERSHEIM, ROBERT. Comparative Anatomy of Verte-
brates, translated by W. N. Parker, 3rd edition, 1907.

KINGSLEY, J. S. Comparative Anatomy of Vertebrates, re-
vised edition, 1917.

WILDER, H. H. History of the Human Body, 1909.

LANG, ARNOLD. Text-Book of Comparative Anatomy (Inver-
tebrates) translated by H. M. and MATILDA BERNARD,
vol. i, 1892, vol. 2, 1896.

REIGHARD, JACOB, and JENNINGS, H. S. Anatomy of the
Cat, 1901.

(b) Embryology

HERTWIG, OSKAR. A Text-Book of Embryology, Man and
Mammals, translated by E. L. Mark, 1892.

HERTWIG, OSKAR, Editor. Lehrbuch der Vergleichenden und
Experimentellen Entwicklungslehre der Wirbeltiere, 6 vols.,
1902-1906.

KORSCHELT and HEIDER. Text-book of Embryology of Inverte-
brates, translated by Matilda Bernard, edited by Martin
Woodward, 4 vols., 1899.

BIBLIOGRAPHY 205

KELLICOTT, W. E. A Text-book of General Embryology, 1913.

Also Outlines ofChordate Development, 1913.
BAILEY and MILLER. See list of fifty books.
BALPOUR, F. M. Comparative Embryology, 2 vols., 1880-

1881.
FOSTER and BALFOUR. Elements of Embryology, 1874 and

1883.
KEIBEL, F., and MALL, F. P. Manual of Human Embryology,

2 vols., 1910.
McMuRRicn, J. P. Development of the Human Body, 5th

edition, 1915.

MINOT, C. S. Human Embryology, 1892.
MINOT, C. S. A Laboratory Text-Book of Embryology, 2nd

edition, 1910.
/ McBRiDE, E. W. Text-Book of Embryology, vol. i, Inverte-

brata, 1916.
PRENTISS, C. W., and AREY, L. W. A Text-book of Vertebrate

Embryology, 1917.
LILLIE, FRANK R. See list of fifty books.

(4) BOOKS ON SPECIAL TOPICS
Birds.

CHAPMAN, FRANK. Bird-Life. See list of fifty books.

BARROWS, WALTER B. See list of fifty books.

BAIRD, BREWER and RIDGWAY. Birds of North America,

1875-

KNOWLTON, FRANK H. Birds of the World, 1909.
REED, CHESTER A. Bird Guide, Part I, Water Birds, Game

Birds and Birds of Prey. Part II, Land Birds, 1908.

Cytology.

HERTWIG, OSKAR. The Cell, translated by Campbell, 1895.
v WILSON, E. B. The Cell. See list of fifty books. A classic.

206 THE MAIN CURRENTS OF ZOOLOGY

Genetics and Heredity.

CONKLIN. Heredity and Environment. See list of fifty books.
WALTER. Genetics. See list of fifty books.
BATESON. Mendel's Principles. See list of fifty books.
CASTLE, W. E. Genetics and Eugenics, 1916.
DAVENPORT, C. B. Heredity in Relation to Eugenics.
PUNNETT. Mendelism. See list of fifty books.
WILSON, JAMES. A Manual of Mendelism, 1916.
GUYER, M. F. Being Well Born, 1916.
THOMSON, J. ARTHUR. Heredity, 1908.

Evolution.

CLODD, EDWARD. Pioneers of Evolution, 1897.

COPE, E. D. Primary Factors of Evolution, 1896.

DARWIN, CHARLES. See list of fifty books, and Biography.

Fifty Years of Darwinism, Centennial Addresses (n Ad-
dresses), 1909.

JUDD, JOHN. The Coming of Evolution. See list of fifty books.

ROMANES, GEORGE J. See list of fifty books.

OSBORN, H. F. From the Greeks to Darwin.

KELLOGG, VERNON L. Darwinism To-Day. See list of fifty
books.

LULL, R. S. Organic Evolution. See list of fifty books.

SCOTT, W. B. The Theory of Organic Evolution, 1917.

WEISMANN, AUGUST. See list of fifty books.

PACKARD, A. S. Lamarck. See list of fifty books.

LAMARCK, J. B. Zoological Philosophy, translated by Hugh
Elliot, 1914.

DRUMMOND, HENRY. The Ascent of Man, 1894.

FISKE, JOHN. The Destiny of Man.

Insects.

DOANE, R. W. Insects and Disease. 1910.

FOLSOM, J. W. Entomology, 1909.

BIBLIOGRAPHY 207

KELLOGG, VERNON L. American Insects, 1904 and 1908.
HOWARD, L. O. Mosquitoes, 1901. Also, The Insect Book,

1905.
HOLLAND, W G. The Butterfly Book, 1898. Also, The Moth

Book, 1903.
REILEY, WILLIAM A., and JOHANNSEN, O. A. Handbook of

Medical Entomology, 1915.
WHEELER, WILLIAM M. Ants, 1910.

Protozoa.

BttTSCHLi, 0. Die Protozoa in Bronn's Klassen und Ord-

nungen des Thier-Reichs, vol. i, 3 parts, 1880-1889.
CALKINS, G. N. The Protozoa, 1901. Also Protozoology, 1909.
DOFLEIN, F. Lehrbuch der Protozoenkunde, 3rd edition, 1911.
CONN, H. W. A Preliminary Report on the Protozoa of Fresh

Water of Connecticut, 1905.
KENT. Manual of the Infusoria, 3 vols.
JENNINGS, H. S. Behavior of the Lower Organisms, 1906.
LEIDY, JOSEPH. Fresh Water Rhizopods of North America ,

1879.

(5) Miscellaneous

ADAMS, C. C. Guide to the Study of Animal Ecology, 1913.

BROOKS, W. K. The Foundations of Zoology, 1898.

NEEDHAM, J. G., and LLOYD, J. T. The Life of Inland Waters,
1916.

WARD, H. B., and WHLPPLE, G. C. Fresh-Water Biology, 1918.

CASTLE, CONKLIN, EAST, DAVENPORT and TOWER. Heredity
and Eugenics, 1912.

CHILD, C. M. Senescence and Rejuvenescence, 1915.

DRIESCH, HANS. The Science and Philosophy of the Or-
ganism, 1908.

GASKELL, WALTER. The Origin of Vertebrates, 1908.

208 THE MAIN CURRENTS OF ZOOLOGY^

HEILPRIN, A. Geographical Distribution of Animals.

HERRICK, FRANCIS H. Audubon, The Naturalist, 2 vols.,
1917.

JORDAN, D. S., and EVERMANN, B. W. American Food and
Game Fishes, 1902.

KEITH, ARTHUR. The Antiquity of Man, 1915.

LUCAS, F. A. Animals of the Past, 1902.

MORGAN, T. H. Evolution and Adaptation, 1903.

MORGAN, T. H., and others. The Mechanism of Mendelian
Heredity, 1915.

OSBORN, H. F. The Age of Mammals, 1910.

OSBORN, H. F. The Origin and Evolution of Life, 1917.

PATTEN, WILLIAM. The Evolution of the Vertebrates and their
Kin, 1912.

LANKESTER, E. RAY. The Kingdom of Man, 1907.

MARSHALL, C. E., and others. Microbiology, 1911.

MAST, S. O. Light and the Behavior of Organisms, 1911.

METSCHNIKOFF, ELIE. Inflammation. Also, The Prolonga-
tion of Life.

NEWMAN, H. H. The Biology of Twins, 1917.

THOMSON, J. ARTHUR. Darwinism and Human Life, 1911.

WILLISTON, S. W. Water Reptiles of the Past and Present,
1914.

HOWELL, WILLIAM H. A Text-Book of Physiology, 2nd edi-
tion, 1908.

STOHR, PHILIPP. Text-book of Histology, 1903.

JORDAN, H. E., and FERGUSON, J. S. A Text-book of Histol-
ogy, 1916.

EDINGER, LUDWIG. The Anatomy of the Central Nervous
System, translated by W. S. Hall, 1899. Several later
editions of this valuable work in German.

BURKHOLDER, J. F. The Anatomy of the Brain, 1912.

JOHNSTON, J. B. The Nervous System of Vertebrates, 1906.

INDEX

Acquired characters, inheritance
of, 159; nature of, 159; Weis-
mann on, 159

Adjuncts to the study of Zoology,
123

Agassiz, Louis, at Penikese, 119;
biographical references to, 195;
portrait, 118

Alternative inheritance, 39

Amphimixis, the source of varia-
tions, 158, 159

Anaesthetics, 168; Morton and
ether, 168, 170; and painless
surgery, 165, 168; O. W. Holmes
supplies the name, 168

Ancient science, 43

Anellida, 89

Animal behavior, studies of, in,
112

Animal kingdom, the, 84-94; psy-
chology and behavior, 112;
series, the, 92

Animals, classification of, 84-93;
the number of, 93; sub-kingdoms
or phyla, 86-93

Anopheles mosquito, the carrier
of malaria, 130

Antiquity of man, 98

Antiseptic surgery, 29

Aristotle, 44; biographical refer-
ences to, 195; greatest investi-
gator of antiquity, 44; influence
of, 45; portrait, 54

Arrest of inquiry, effect of, 45

Arthropoda, 89, 90

Artists, prehistoric, 98

B

Bacteria, and antiseptic surgery,
29; discovery of, 25; disease
producing, 28

Bacteriology, Cohn and, 26; Koch,
26, 33; Pasteur, 26, 27; rise of,
25-27

Baer, Karl von, biographical refer-
ences to, 196; and embryology,
72; his great classic on the de-
velopment of animals, 72; one
of the ten foremost men, 177;
portrait, 72

Balfour, F. M., biographical refer-
ences to, 196; masterly work
of, 74; portrait, 72; rank in
embryology, 73

Behavior, animal, 112

Bernard, Claude, biographical ref-
erences to, 196; discoveries, 81;
in physiology, 80; greatest
physiologist of all time, 184;
portrait, 72

Bichat, and investigation of the
tissues, 67

Binomial nomenclature of Lin-
naeus, 52, 53

Biographical references to the
eminent biologists, 195-202

Biological advances, the five
chief, ii ; the outstanding, 10-
42.

Biological laboratories, 118, 119;
Naples, 118; Woods Hole, etc.,
119

Biological progress, atmosphere
engendered by, 186; continuity

209

210

INDEX

of, 4; controversies produced
by, 187; of the nineteenth cen-
tury, 10

Biology, Zoology the central sub-
ject of, i, 6

Books, a suggested library of
fifty, 191-193; lists of the best
reading, 191-208; some useful,
188-190

Boveri, biographical references to,
196; eminence in cytology, 21;
portrait, 16

Brooks, biographical references to,
196

Brown, Robert, discovers nucleus
of plant cells, 10

Bruce, Colonel, and sleeping sick-
ness, 139; observations on sleep-
ing sickness, 138-141

Buff on, a forerunner of Lamarck,
144

Burdon-Sanderson, biographical
reference to, 196

Cajal, Ramon y, reference to por-
trait of, 201

Cell-Theory, The, 16-22; an-
nouncement of, 16; early de-
fects, 19, 20; formulation of,
18; Modifications of, 20, 21;
recent tendencies, 122; Schlei-
den, 17; Schwann, 17; Schwann's
treaties, 18; modern statement
of, 21

Chemistry, and biology, 8

Chordata, 91

Chromosomes, as bearers of hered-
ity qualities, 42; discovery of, 41

Circulation of the Blood, 78;

Harvey's demonstration of, 78;
ocular proof of, Leeuwenhoek,
176; Malpighi, 176

Classification of Animals, 53, 54;
tabular view of, 60

Ccelenterata, 87

Cohn, biographical reference to,
196; and bacteriology, 26

Comparative Anatomy, becomes
experimental, 114; rise of, 62-67;
recent tendencies of, 123

Continuity of the germ-plasm, 155

Cope, E. D., biographical refer-
ences to, 196; a great naturalist,
96; portrait, 96

Culture-periods, of palaeolithic
man, 99, 100

Cuvier, biographical references to,
196-197; debate with Saint-
Hilaire, 66; founder of com-
parative anatomy, 63; of struc-
tural zoology, 62-67; of verte-
brate paleontology, 67, 178;
one of the ten foremost men,
177; portrait, 54

Cytology,, Boveri and, 21; a de-
partment of biology, 21, 122;
recent tendencies of, 122, 123;
studies of, 122

Darwin, Charles, biographical ref-
erences to, 197; natural selec-
tion, 149, 150; one of the ten
foremost men, 179; origin of
species, 153; original draft of
his theory, 154; parallelism in
thought with Wallace, 153,
154; portrait, 22; reception of
his theory, 152

INDEX

211

Darwin, Erasmus, a forerunner of
Lamarck, 144

Darwinism, not the same as or-
ganic evolution, 143; vagueness
regarding, 143

De Vries, Hugo, mutation theory
of, 159-161; portrait, 156

Divisions of Zoology, the chief,
106

Dohrn, Anton, biographical refer-
ences to, 197; and the Naples
station, 118

Dujardin, Felix, 12, 13; biographi-
cal references to, 197; discoverer
of protoplasm, 12; portrait, 16;
sarcode, 13

E

Echinodermata, 89

Ecology, 56, no

Economic Entomology, 117

Edwards, Milne- , 65

Eimer, and orthogenesis, 162

Embryology, 70, 108; Balfour and,
73; chapter on, 70-76; impor-
tance of in zoology, 70, 72; rise
of, 70-76; Von Baer and, 72

Embryological Record, The, 72

English, The, rank of in biological
progress, 184, 185

Entomological Bureau at Wash-
ington, 118

Ether, in painless surgery, 165,
167, 169

Eugenics, 36, 116; books on, 206
Evolution, controversies regard-
ing, 163, 164; generalities con-
cerning, 143; the factors of, 164;

mental, of animals, 112; present
status of, 163

Evolution Theories, 22, 143-164;
Darwin's theory, 148-154; De
Vries, 159-161; Lamarck, found-
er of, 144; Weissman, 154-159;
replacing theories, 161; sup-
porting theories, 161

Experimental morphology, 114;
study of heredity, 35; zoology,

Fabre, biographical references to,
197; the Hunter- Wasps, 127;
portrait, 136; writings on in-
sects, 126

Factors of Evolution, 164

Fermentation, 28

Fossil remains, chapter on, 95-
105; collections in New Haven,
97; hi New York, 97; of man: —
Heidelberg jaw, 103; Java skull,
102; Neanderthal skull, 100;
Piltdown skull, 103; prehistoric
artists, 99; implements, 98

Fossil, bearing rocks, thickness of,
95; horses, 96, 97

Foremost Men of Biological His-
tory, the ten, 174-180

French, contributions to biological
progress, 184, 185; tempera-
ment, 184

Galton, biographical references
to, 197; portrait, 36; work on
inheritance, 36

Gegenbaur, 65; biographical refer-
ences to, 197

212

INDEX

Gelatine method of Koch, 33
General physiology, as a division

of zoology, 77-83
Genetics, the science of, 112, 113
German, contributions to biologi-
cal progress, 184, 185; mentality,
184

Germ-Cells, the, 156
Germ-Plasm, continuity of, 156,

157
Germ theory of disease, 24, 26, 29,

30; Koch and, 32, 33; Pasteur

and, 26
Gesner, 50, 51
Greatest men of biological history,

the ten, 174-180
Greek science, 43, 44, 45

Haller, 74

Harvey, 49, 78, 127, 128; bio-
graphical references to, 198;
book on the circulation, 78,
175; circulation of the blood,
78; in physiology, 78; one of
the ten foremost men, 175,
portrait, 156

Heredity, experimental study of,
35; Galton, 36; Mendel, 37;
material basis of, 41, 42

Hertwig, Oskar, 75

His, in embryology, 75, 76

Histology, 66, 67, 108

Holmes, O. W., names anaesthetics,
168

Human ancestry, 98, 99, 100

Huxley, 152; biographical refer-
ences to, 198; portrait, 156

Hybrids of plants, Mendel, 37

Hydrophobia, 30

Inheritance, alternative, 39; of
acquired characters, 159; ex-
perimental study of, 35; Galton,
36; Mendel, 37-41

Inoculation, Pasteur's methods,
30, 32; for smallpox, 170

Inquiry, the arrest of, 45

Insects, a chapter on, 125-142;
and disease, 127-142; and ferti-
lization of flowers, 126; habits
of, 126

Intellectual progress, Zoology and,
185-187

Isolation, a factor of organic
evolution, 162

Jardin, des plantes, 63; du Roi, 63
Jenner, and vaccination, 170-173;

portrait, 136
Jennings, on behavior of lower

organisms, 112

Koelliker, biographical references
to, 198; and histology, 68; por-
trait, 72

Koch, Robert, 32, 33; biographical
references to, 198; and germ
theory of disease, 32, 33; por-
trait, 36

Laboratories, marine, 118, 119
Lacaze-Duthiers, 65; biographical

references to, 199
Lamarck, the founder of evolu-
tion, 144; of invertebrate paleon-
tology, 67; biographical refer-

INDEX

213

ences to, 199; influence, 23; his
theory of evolution, 144-148;
neo-Lamarackism, 147; portrait,
146

Laveran, discovers micro-organism
of malaria, 128

Lazear, 138

Leidy, 96; biographical references
to, 199; portrait, 96

Leuckart, 59; biographical refer-
ence to, 199; and classification
of animals, 59, 60; portrait, 54

Leydig, 69

Limnology, 121

Linnaeus, 52, 57, 176; biographical
references to, 199; and his influ-
ence, 52-57; one of the ten fore-
most men, 176; portrait, 54;
his Systema Naturae, 53, 56

Lister, and antiseptic surgery, 29;
biographical references to, 199;
portrait, 36

Long, Crawford, and painless
surgery, 169

Ludwig, biographical reference
to, 199; hi physiology, 184

Lyell, influence on evolutionary
thought, 152

M

Main currents of zoology, 4, 5,
9; pathways of zoology, 106-
120

Malaria, parasite of, 128-134; pro-
tection against, 130, 131; trans-
mitted by mosquitoes, 127-135

Mall, F. P., biographical refer-
ences to, 199; his embryological
collection, 76, 124

Malpighi, 51; biographical refer-

ences to, 109; one of the ten
foremost men, 176

Man, the antiquity of, 98; fossil
remains of, 100-105

Men, the ten foremost of biological
history, 174-180

Manson, 132

Marine zoology, 118, 119; bio-
logical stations, 119, 120

Mendel, 37, 180; biographical
references to, 200; law of, 38-
41; one of the ten foremost men,
1 80; portrait, 36; rank of, 180

Mendelism, 40, 41, 113

Mental evolution of animals, 112

Micro-organisms, 25, 26, 27

Micro-parasitology, 27

Microscopic observation, 51

Microscopists, the pioneer, 51

Middle Ages, 46, 47; zoology of
the, 46

Minot, C. S., biographical refer-
ences to, 200; his embryological
collection, 124; influence on
biology, 176; portrait, 96

Miscellaneous divisions of zoology,
116

Mohl, and protoplasm, 13

Mollusca, 90

Morphology, experimental, 114;
and physiology, parallel de-
velopment of, 77

Morton, W. T. G., biographical
reference to, 200; and the dis-
covery of anaesthetics, 165,
167-169; portrait, 136

Mosquitoes, as disease carriers,
131, 132; transmit malaria, 130,
133; and yellow fever, 136

Miiller, Johannes, biographical

214

INDEX

references to, 200; in physiology,
79; as a teacher, 79, 80; makes
physiology comparative, 80; one
of the ten foremost men, 178;
portrait, 80
Mutation, the theory of, 159-161

N

Naples, biological station at, 118

National contributions to biologi-
cal progress, 181-185

Nations, rank of in biological prog-
ress, 181-185

Natural history, 52, 56, 106

Nature, the oneness of, 3

Natural selection, theory of, 149;
Darwin and, 149; illustrations
of, 150, 151

Neanderthal skull, 100

Nemathelminthes, 88

Neo-Lamarckism, 147

Neurology, 122

Nineteenth century, outstanding
biological advances of, 10-42

Nomenclature in zoology, 52, 53

Nucleus, discovery of in plants, 10

Number of animals, 93

O

Observation, arrest of, 45; the
method of science, 46, 47; the
renewal of, 47

Oceanography, 120

Oneness of nature, 3

Organic evolution, isolation a factor
of, 162; present status of, 163;
theories of, 143-164; Darwin,
148; De Vries, 159; Lamarck, 144;
Weismann, 154; rival theories,
161; supporting, or auxiliary, 161

Origin of species, 153
Orthogenesis, 162
Outstanding biological advances
of the nineteenth century, 10-42

Painless surgery, 165-170

Paleontology, Cuvier founds verte-
brate, 67, 178; Cope, and, 96; a
division of, zoology, 109; La-
marck founds invertebrate, 67;
Zittel and, 96

Parasitology, 117

Pasteur, 26-32; biographical ref-
erences to, 200; one of the ten
foremost men, 179; portrait, 28

Pasteur Institute, the, 31

Path-breakers of zoology, 183-
184

Pathology, 69

Philosophical zoology, 115

Physical basis of inheritance, 41

Physiology, general, a division of
zoology, 80, 82, no; Bernard,
81, 82, 178; Harvey, 78; Miiller,
79, 178; rise of, 78-83

Phyla of animals, 85

Physiological method, 83

Pithecanthropus erectus, 103

Platyhelminthes, 88

Porifera, 87

Prehistoric, artists, 99; man, 98

Progress of science, a reconstruc-
tive force, 1 86

Protoplasm, discovery of, 11-16

Protozoa, 86

Protozoology, 116, 117

Quinine, use of in malaria, 134

INDEX

215

Rank, of Mendel, 1 80; of the na-
tions in biological progress, 181-
185; of Pasteur, 179

Reading, comments on, 188-190;
lists of zoological, 191-208

Recent activity in zoology/i2i, 122

Recent tendencies of zoology, 121-
123

Redi, 201

Reed, Walter, 135; biographical
references to, 201; portrait, 136;
and yellow fever, 136-138

Reference books, 191-208; a sug-
gested library of fifty, 191-193;
and periodical articles, 191-208

References to biographical sketches
of biologists, 195-202

Sarcode, or protoplasm, 3

Schleiden, 17

Schultze, Max, 14, 79; biographical
references to, 201; and the cell-
theory, 20; one of the ten fore-
most men, 179-180; portrait, 16

Schwann, biographical references
to, 201; founder of the cell-
theory, 1 8; portrait, 16

Science, of the ancients, 43; of
the Middle Ages, 46, 47

Serum inoculations, of Pasteur, 30

Siebold, and classification of ani-
mals, 58, 60

Silk-worm, Malpighi's monograph,
176

Sleeping Sickness, 138-141, atoxyl
in, 141; Bruce and, 139; mode
of transmission, 140; parasite
of, 139

Small-Pox, Jenner and, 170, 173;

vaccination for, 170
Species, early views regarding,

146; fixity of, 146; the origin of,

147, i53
Spencer, Herbert, and organic

evolution, 152
Spontaneous generation, 28
Structural zoology, 107
Study of types, 93
Swammerdam, Jan, 51
Systema Naturae, of Linnaeus, 53, 56
Systematic zoology, 109

.Ten foremost men of biological
history, 174-181

Tsetse-fly, transmits sleeping sick-
ness, 141

Theory, the cell, 16-22; of organic
evolution, 22; the protoplasm,
14, 15. Theories of organic
evolution, 143-164; Darwin,
148; De Vries, 159; Lamarck,
144; Weismann, 154; other
theories, 161-163

Toxins and antitoxins, 30

Trypanosome, the parasite of
sleeping sickness, 139, 140

Types of animals, the study of, 93

Vaccinination, for small-pox, Jen-
ner and, 170-173; Pasteur, 30

Variation of animals, one of the
factors of evolution, 164

Vertebra ta, 91

Vesalius, biographical references
to, 202; and reform of anatomy,
48, 49, 176

216

INDEX

Virchow, 69; biographical refer-
ences to, 202

Virus, 137

Vries, Hugo, de, 159-160; muta-
tion theory of, 160; portrait, 156

W

Wallace, A. R., and Darwin, 153,

154

Weismann, 154; biographical ref-
erences to, 202; a nee-Darwin-
ian, 154; portrait, 156; his
theory of heredity, 154, 155;
of evolution, 156, outstanding
features of, 159

Whitman, C. O., biographical
references to, 202; influence on
biology, 119; portrait, 96

Yellow Fever, cause of, 135; the
Commission of, 136; trans-
mitted by mosquitoes, 137;
Walter Weed and, 136

Zittel, and paleontology, 96

Zoology, adjuncts to the study of,
123; aspects of, 3, 5; a subject
of general education, 1-8; as a
unified science, iv, 2; basal to
the study of medicine, 7; books
about, 191-208; the central
subject of biology, i, 6; emerges,
43-51; experimental, 113; the
foremost men of, 174-180; of
fossil remains, 95-105; greatest
present activity in, 121, 122;
and intellectual progress, 185-
187; the maul currents of, 4, 5,
9; main pathways of, 106-120;
miscellaneous divisions of, 116;
philosophical, 115; its position
in biology, 6; recent tendencies
of, 121-123; structural, 147

Zoological Progress, a system of
thought, iii

Zoological Thought, continuity
of, 4

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