REESE LIBRARY

OK THK

UNIVERSITY OF CALIFORNIA.

L

Accessions No.

, I&Q7-

THE

METHOD OF DARWIN

g>tufip fa Scientific

BY

FRANK CRAMER

€p
ERSITY
i

OF THE

E

.--

CHICAGO

A. C. McCLURG AND COMPANY
1896

COPYRIGHT

BY A. C. MCCLURG AND Co.
A.D. 1806

TO

MY FRIEND AND TEACHER,
BRADFORD PAUL RAYMOND.

PREFACE.

/TVHIS attempt to analyze the method em-
*• ployed in the biological sciences arose
from the belief that the direct study of scientific
method, as it is illustrated by the works of the
accepted masters, is worthy of far more careful
attention than is usually accorded to it. As a
rule, scientific men are so deeply engrossed in
their investigations that they rarely undertake
to discuss method. The logical processes in-
volved and the nature of the difficulties met
writh in scientific investigation are the same as
in the practical affairs of life. The fundamental
processes of reasoning are the same everywhere ;
and it cannot but be helpful to study those pro-
cesses as they are actually applied by master
minds in fields where precision of method is
peculiarly essential. Even though there may
be grave question concerning the practical value
of the study of formal logic, there can be no

viii PREFACE.

question concerning the importance of attention
to the best practice in matters of reasoning.

Some of the reasons which induced me to
select Darwin's works as a basis for an analysis
of scientific method were: (i) the desire to
confine the discussion to the writings of a single
author, in order to concentrate the reader's at-
tention upon a model; (2) the fact that his
works cover a wide range of subjects, and can
be read and understood by those who have had
only a moderate amount of scientific training;
and (3) above all, the fact that Darwin's inves-
tigations, and the reasoning based upon them,
have furnished the biological sciences with their
dominant principles.

To facilitate the study of his works from the
point of view of method, references have been,
added to nearly all the examples drawn from
them. A few examples have been mentioned
or briefly discussed several times, and this may
detract slightly from the freshness of some parts ;
but a partial compensation may be found in the
fact that the repetition of the same example,
under different divisions of the subject, will
emphasize more strongly the complex inter-

PREFACE. ix

dependence of the various logical processes. In
several instances, particularly those of radicles,
climbing plants, and electric organs, the discus-
sions have been carried into considerable detail:
this has been done for the purpose of show-
ing what an actual course of investigation and
reasoning is like, — how results, whether true or
false, are worked out.

At the same time, no effort has been made to
make the treatment of Darwin's method exhaust-
ive, nor has any formal explanation of the vari-
ous logical processes been made. Those who
are likely to read this book are already suffi-
ciently familiar with the terminology of logic and
the practice of science to understand it easily;
and extended explanations would require an ex-
cursion into the domain of formal logic, which
is not a part of the purpose of the present
work.

Some of the most important processes have
been selected, and Darwin's applications of
them illustrated, in such a way as to confine
the whole discussion within the narrowest pos-
sible limits. It is an easy matter to provoke
differences of opinion in discussing either the

X PREFACE.

nature or the names of the logical processes;
but as far as it lay in my power I have avoided
setting my foot on controversial ground. There
are in the book, no doubt, many errors in
detail, but it is hoped that no serious ones have
crept in.

I wish to thank Professor Francis Darwin of
Cambridge, England, and President David Starr
Jordan of Stanford University, both of whom
made important suggestions, and Professor H.
B. Lathrop of Stanford University, who care-
fully revised the manuscript.

FRANK CRAMER.
MANZANITA HALL.

CONTENTS.

CHAPTER PAGE

I. EDUCATION AND THE ART OF REASONING . . 15

II. DARWIN'S VIEW'S OF METHOD 25

III. STARTING POINTS. — METHOD OF STARTING

INVESTIGATIONS. — ISOLATED PHENOMENA . 47

IV. EXHAUSTIVENESS. — TlME GIVEN TO INVESTI-

GATIONS.— TREATMENT OF OBJECTIONS . . 60

V. NEGATIVE EVIDENCE 82

VI. CLASSIFICATION 88

VII. ANALOGY 95

VIII. INDUCTION 107

IX. DEDUCTION. — EXPLANATION OF KNOWN FACTS.
— IMPORTANCE OF- THEORY TO GOOD OB-
SERVATION 121

X. DEDUCTION. — ANTICIPATION 133

XI. DEDUCTION. — GENERAL INSTANCES . . . . 160

XII. UNVERIFIED DEDUCTIONS 178

XIII. ERRONEOUS DEDUCTION 192

XIV. GENERAL DISCUSSIONS . . 207

XV. LOGICAL HISTORY OF THE PRINCIPLE OF NAT-
URAL SELECTION 212

XVI. CONCLUSION 229

LIST OF DARWIN'S WORKS REFERRED TO
IN THE FOOT-NOTES.

Origin of Species, Sixth Edition, 1872.

Descent of Man and Selection in Relation to Sex, 1871.

Variation of Animals and Plants under Domestication,
Second Edition, 1875.

Expression of the Emotions in Man and the Lower Ani-
mals, 1872.

A Monograph of the Cirripedia, Vol. I., 1851 ; Vol. II.,
1854-

The Formation of Vegetable Mould through the Action
of Earthworms, 1881.

Naturalist's Voyage around the World, 1860.

Geological Observations on Volcanic Islands and on

Parts of South America, Second Edition, 1876.
Structure and Distribution of Coral Reefs, Third Edition,

Fertilization of Orchids, Second Edition, 1877.

Effects of Cross- and Self-Fertilization, 1876.

Different Forms of Flowers on Plants of the same Species,

1877-

Insectivorous Plants, 1875.
Climbing Plants, 1875.
Power of Movement in Plants, by Charles and Francis

Darwin, 1881.
Life and Letters of Charles Darwin, by Francis Darwin,

two vols., 1887.

A SCIENTIFIC discovery is the outcome of an interesting
process of evolution in the mind of its author. When we are
able to detect the germs of thought in which such a discovery
has originated, and to trace the successive stages of the rea-
soning by which the crude idea has developed into an epoch-
making book, we have the materials for reconstructing an
important chapter of scientific history. — PROF. J. W. JUDD,
Critical Introduction to Bettany's Edition of Darwin's "Structure
and Distribution of Coral Reefs"

UNIVERSITY

THE METHOD OF DARWIN.

i.

EDUCATION AND THE ART OF REASONING.

TT is an opinion not uncommon among educa-
tors that a definition of education which
would cover all kinds of training is an impossi-
bility. Such a definition, as it widens for the
reception of manual training and the study of
Greek, kindergarten work and the post-graduate
course, certainly threatens to become " like a
circle in the water, which never ceaseth to
enlarge itself till by broad spreading it dis-
perse to naught." The difficulty in framing it
ha's apparently increased in recent years, since
the old standards of value in education have
had to struggle for existence with all the other
college and university studies. The old defini-
tion, "to lead out and train the mental powers,"
is comprehensive enough for all purposes, for
it tells neither what the mental powers to be
trained are, nor how they are to be trained ;

1 6 THE METHOD OF DARWIN.

by the change of a word or two it would apply
equally well to the art of breaking colts. If
the definition is stated more in detail, it is
found to lie entirely in the domain of applied
logic; and education of the intellect, in the
only sense in which it can cover the whole
field, is the process of training the intellect in
the art of reasoning.

If there is or ever shall be a common aim in
all phases of education, it will be based upon
this common element. However important the
information may be which is conveyed to the
student in any department of study, his ability
to retain it and use it for further acquisition
depends entirely on the method by which he
acquired it, and the degree to which he has be-
come master of that method. The facts neces-
sary for a new investigation are easily brought
to hand if the intellect has been trained to
work independently. One of the most strik-
ing things in Darwin's Autobiography is the
relative importance, to be mentioned again
hereafter, which he assigns, in his analysis
of his own education,1 to the accumulation of
facts and to the development of mental habits.
Probably few minds ever possessed in a higher

1 Life and Letters of Charles Darwin, by Francis Darwin,
Vol. I. pp. 51, 52.

EDUCATION AND ART OF REASONING. I/

degree the power to collect and utilize facts.
He said the real education of his mind began
on the Beagle voyage. And yet he gave a
very subordinate place to the vast number of
facts with which he became acquainted on the
voyage, and assigned supreme importance to
the habits of incessant industry and concen-
trated attention which were developed in him,
and to the necessity of reasoning in the solution
of geological problems.

If the most important and only common ele-
ment in education is the development of the
power of reasoning, it may seem strange that
logic, proudly called the science' of sciences,
should play so obscure a role that in many
institutions it is practically ignored, and in
the rest it is tolerated in a very brief course.
The two most probable reasons for this are,
first, the general notion that the human mind
learns to reason as the human body learns to
walk, that there is no need of teaching; that
as training in the latter can only produce a
Delsartean gait, which for practical purposes is
little superior to an awkward wabble, so train-
ing in the art of reasoning is likely to produce
nothing but over-refinement, which accepts
indifferently postulates foolish and wise, and
seeks only to draw out their consequences into
2

I fr THE METHOD OF DARWIN.

gossamer threads. The second reason is, that
the logic usually taught is not the logic of
common life refined by successful scientific
experience, but "formal logic," emptied of all
-— ^ contents and divested of all covering. Every
fool can walk, and, as Darwin truly said, any
fool can generalize and speculate. But the
secret of originality, ingenuity, skill to seize
facts, grasp their significance, and anticipate
consequences, is not hidden here. Not the
power to reason, but the power to reason
quickly and unerringly and doggedly and im-
partially is the basis of success alike for the
business man and for the man of science.

If skilful and accurate reasoning constitutes
so essential an element of education, and if
logic, as formally taught, is, for the mass of
students, so barren of results, it is pertinent
to inquire what provision for logical training
is made in the general instruction of colleges
and universities. In the evolution of the col-
lege curriculum the individuality of the student
has finally been recognized and provided for,
and the dignity of the sciences, as subjects
conducive to mental discipline, has become an
accepted fact. The material of education has
by this been both increased and improved.
Method has also undergone profound changes.

EDUCATION AND ART OF REASONING. K)

The laboratory for science, sources of informa-
tion for history, inventional work in mathe-
matics, all bear witness that the student has
been brought into direct contact with the mate-
rial by means of which his intellect is to be
trained. The best laboratory hand-books are
no longer books of directions, but of sugges-
tion and question ; these books constitute a
distinct recognition that the art of reasoning is
the heart of education, that the true student is
from first to last a discoverer, and that any
method which makes the discoveries for him is
wrong.

There are, however, two very distinct orders
of reasoning: the order of discovery, which the
mind follows as it winds its way among facts,
adopting tentatively hypotheses which are after-
wards rejected, and groping along the border
of the unknown in the pursuit of knowledge;
and the order of proof or argument, used by
the investigator in his effort to convince his
hearer or reader of the truth of his results.
The order of proof may ignore entirely the
steps by which the discoveries were made, the
materials collected, and the conclusions drawn.
The aim is conviction, and the evidence is
arranged in the most lucid order to support the
conclusions established at the end of an inves-

2O THE METHOD OF DARWIN.

tigation. It is true that sometimes the order
of discovery is the best for purposes of proof;
but unless it happen to be so, it is ignored
after the investigation is completed.

Logicians insist that their science is the
science of proof ; that it does not furnish truth,
but tests by which to determine whether or not
a supposed discovery is truth. Books and lec-
tures are invariably built up on the plan of
proof. In them the question how a conclusion
was reached is rarely presented, and when it
does occur, pains is seldom taken to provide
for its answer. So far, then, as these ele-
ments of education are concerned, the student
is made a recipient. He is struck by the lucid
arrangement of facts, the majestic sweep of the
argument, and wonders why the world did not
sooner get hold of truth that seems so conclu-
sive to him. In the laboratory, the hand-books"
tell him what to look for and where to find it ;
and in the lecture-room the facts are arranged
and the theoretical explanations are made for
him. Thus in neither of the two practical
divisions of the art of reasoning is he allowed
to follow even the untrained impulses of his
intellect. The average student knows next to
nothing of the science of reasoning, and is
largely prevented from practising the art of

EDUCATION AND ART OF REASONING. 21

reasoning either from the standpoint of dis-
covery or from that of proof.

This general indictment against the college
curriculum needs to be hedged in by many
qualifications; but there are none which seri-
ously break its force. The graduate student is
left largely to his own resources, and must do
his own reasoning or go without any. A few
of the best laboratory hand -books question and
suggest to the student, so that he is kept from
dissipating his energy; but they largely compel
him to make his own discoveries and develop
independence. ' A few teachers habitually, and
many teachers occasionally, compel their stu-
dents to cast their materials into the order of
proof or argument in topical reports ; but those
very reports are, as a rule, the best illustra-
tion of the utter lack of logical insight on the
part of students.

Before applied logic secures general recog-
nition proportionate to its importance, it will
have to demonstrate its ability to lay in the
mind of the student the foundation of accurate
thinking, to furnish him with analyses of mod-
els of successful reasoning, and criteria by which
to detect false reasoning.

It is strange that while the study of our
mother tongue and of all the sciences has

22 THE METHOD OF DARWIN;

undergone so great a revival, the science of
reasoning should still be lying in the valley of
dry bones. Fate may have decreed that its
revival should be the crowning phase of modern
progress in educational methods. Slowly but
very surely these methods are drifting in the di-
rection of a more extended and a more profound
recognition of the importance of reasoning.

When educational practice shall have demon-
strated the importance of the art of reasoning,
scientific models of the art, for purposes of logi-
cal study, will be found to be rare, especially
those that reveal the order of discovery. The
scientist, after establishing a conclusion to his
own satisfaction, is not concerned with telling
other people how he reached it, but with con-
vincing them of its truth. For this purpose
he throws his conclusions and facts into the.
order best suited to form a compact argument.
In the vast majority of cases it is impossible to
follow out the original course of thought by a
study of the results as they are embodied in a
book. It would probably be difficult for an
author himself to trace again the windings of
his thought. Therefore, while there is a fair
number of models for the study of argument,
the writers who habitually take their readers
so far into their confidence as to tell them by

EDUCATION AND ART OF REASONING. 2$

what steps they arrived at facts and conclusions,
are extremely rare.

Several reasons have led to the following
study of Darwin's method: first, conviction of
the supreme practical importance of the direct
study of scientific method; secondly, the fact
that logicians and scientific philosophers draw
their illustrations of scientific method almost
exclusively from the physical sciences; thirdly,
while those illustrations are fascinating on
account of their brilliancy and their approach
toward mathematical certainty, the biological
sciences are much better adapted to furnish
models for the average student, because in the
nature of their logical difficulties they approach
more nearly to the experiences of common
life; fourthly,f Darwin's custom of presenting
all sides of a case very frequently led him to
expose the original course of his thought and
the order of his discoveries so clearly as to
make the reader almost feel that he and Dar-
win are making the discovery together. Dar-
win consciously recognized or unconsciously
felt that there was considerable power to pro-
duce conviction in an understanding of the
particular way in which the truth was first
reached. He so habitually took the reader
into his confidence that he will probably always

24 THE METHOD OF DARWIN.

remain the clearest model in the biological
world for the study of applied lo^kT^)

There are two ways open for the logical
study of Darwin's works: one in which the
methods of handling material and the differ-
ent logical processes would be illustrated by
examples from different parts of his works;
and the other in which each of his investiga-
tions would be studied apart from the rest for
the purpose of noting the part which induc-
tion, deduction, analogy, and verification play
in producing the results. The former was
chosen, because in that way the best examples
of each of the logical processes could be
brought together in the smallest compass,
while the latter would require an elaborate
summary of the works themselves before their
logic could be discussed. No epitome, much
less selected examples, can be made a substi-
tute for a logical study of the works them-
selves; it can at most serve as a guide to
further study.

II.

DARWIN'S VIEWS OF METHOD.

IT is necessary to inquire briefly into Dar-
win's own views of scientific method.
He has given us the data for the inquiry, both
in direct statements and indirectly by his
opinions of the work and ability of other men.
In connection with this inquiry must be con-
sidered the intellectual and moral qualities of
the man himself, and the external influences
that bore upon him.

In some quarters the notion is entertained
that the scientific method leads infallibly to
the truth, and that it is something quite dis-
tinct from the logical method of every-day
life; and yet there is a general haziness as to
what the scientific method is. The aim of the
scientist is truth, but he has no special mental
faculty with which to discover scientific truth.
He approaches his problem, equipped with the
same logical processes that the common man
uses in arriving at facts that are important to
his success in life. Neglect in applying those

26 THE METHOD OF DARWIN.

processes strictly, in either case, results in
failure, and fidelity to them is the measure of
success. There is something more than merely
a weak analogy between the very small pro-
portion of successful business men and the
similarly small proportion of really successful
creative scientific men. The failures on both
sides are clue to the same kind of intellectual
errors. Nor are the principles of the scien-
tific method less clearly understood by success-
ful business men than by successful scientific
investigators.

Darwin has said that the training which he
got on the Beagle voyage was the first real ed-
ucation of his mind.1 His University course
at Cambridge had been mechanical. He de-
clared that the study of Paley's ''Evidences"
and "Natural Theology " gave him as much,
delight as did Euclid.2 And he believed at
the time, and to the end of his life, that the
study of these works was the only part of his
academic course that contributed to the educa-
tion of his mind. He got no inspiration, and
very little knowledge, from his medical course
at Edinburgh ; one of the principal records of
that course is his opinion that there are no

1 Life and Letters, Vol. I. pp. 51, 52.

2 Ibid., p. 41.

DA R WIN'S VIE WS OF ME TIIOD. 2 /

advantages and many disadvantages in lectures
compared with reading.1

He has given in his Autobiography the vari-
ous special subjects that occupied his attention
on the Beagle voyage. He attended to Zool-
ogy, Botany, and Geology. After mentioning
the others, he said that Geology " was far more
important, as reasoning here comes into play.
On first examining a new district, nothing can
appear more hopeless than the chaos of rocks;
but by recording the stratification and nature
of the rocks and fossils at many points, always
reasoning and predicting what will be found
elsewhere, light soon begins to dawn on the
district, and the structure of the whole becomes
more or less intelligible."2 It is interesting
to recall that he finally committed the shooting
of birds to his servant in order that he might
devote himself to the geology of the districts
in which he worked. The zoological and
botanical materials which he collected were
largely worked up by other scientists after his
return. On these subjects he collected a vast
amount of information, which gave birth to
his great biological theories, and was indis-
pensable in the work of his later life. But he

1 Life and Letters, Vol. I. p. 33.

2 Ibid., pp. 51, 52.

28 THE METHOD OF DARWIN.

did not work this information into a system
and bend his energies upon it. He devoted
himself to the solution of .geological problems
in the field; while the biological problems
only arose in their early shadowy outlines
during the voyage, and remained in the form
of questions till long after his return. Thus
it came about that from an educational point
of view his biological work was secondary and
the geological work pre-eminent. Had his
life-work ended with the reports of the Beagle
voyage, he would have been rated as a geol-
ogist. But after his return he exercised upon
great biological problems the intellectual
strength and vigor which had been developed
by the solution of geological problems in the
field. " The above various special studies were,
however, of no importance," he said, "compared
with the habit of energetic industry and of con-
centrated attention to whatever I was engaged
in which I 'then acquired. Everything about
which I thought or read was made to bear
directly on what I had seen or was likely to
see." He had problems constantly before him,
and the time allowed for their solution was
always limited by his own movements and
those of the ship; so that energy and concen-
tration became habitual in a mind already

DARWIN'S VIEWS OF METHOD. 29

strong by nature. His isolation from other
scientific men and from books doubtless also
developed in him the habit of using all the
facts that presented themselves, and directly
and indirectly getting at their significance.
He could not lay his hands on ready-made
explanations of the facts that came before him,
and was compelled to explain them himself.
He said of himself, " I think I am superior to
the common run of men in noticing things
which easily escape attention, and in observ-
ing them carefully. . . . From rny earliest
youth I have had the strongest desire to under-
stand or explain whatever I observed, — that
is, to group all facts under some general laws." 1
These natural traits were of necessity strength-
ened and developed by their incessant exercise
on the voyage.

Another prominent trait in Darwin was the
accuracy with which he made his observations
and experiments. " He saved a great deal of
time through not having to do things twice."
And he always "wished to learn as much as
possible from an experiment, so that he did
not confine himself to observing the single
point to which the experiment was directed,
and his power of seeing a number of things

1 Life and Letters, Vol. I. p. 83.

UNIVEHSIT

30 THE METHOD OF DARWIN.

was wonderful." 1 Both his accuracy of obser-
vation and his grasp of all the facts connected
with an experiment were doubtless made hab-
itual on the voyage by the never absent con-
sciousness that there was only one opportunity
to do whatever he did.

During that memorable voyage Darwin's
education went on, unhampered by laboratory
hand-books with directions for finding the
facts, or by professors to do the reasoning for
him either before or after the facts were found.
In all his work there was the complex and
incessant interplay of observation, induction,
deduction, and verification which constitutes
the scientific method. The necessity of work-
ing rapidly, accurately, and thoroughly forced
upon him by the consciousness that his time
was limited, and that the work could not be
done over again, coupled with his native energy
and independence, accounts for the character
and quantity of his scientific work.

The mental traits alluded to were coupled
with remarkable conscientiousness. In the
long run it pays the scientist to be honest, not
only by not making false statements, but by
giving full expression to facts that are opposed
to his views. Moral slovenliness is visited

1 Life and Letters, Vol. I. pp. 121, 122.

DARWIN'S VIEWS OF METHOD. 31

with far severer penalties in the scientific than
in the business world. Scientific results are
used as foundations for further investigations,
and for this reason they are tested again and
again; and if any man's work is unreliable
it is done over by some one else, who reaps
the permanent credit. But the temptations to
make statements too broad, to neglect objec-
tions, to smooth over difficulties superficially,
are almost infinite. There is apparent through-
out all of Darwin's work much more than the
intellectual uprightness that is due to a belief
in " reward and punishment. " The very grain of
his scientific character was conscientiousness.

His educational history, his thoroughness, his
scientific honesty, his logical power, his power
of minute observation and broad generaliza-
tion, the greatness of the problems with which
he dealt, and the profound influence of his
views upon the thought of the world, all con-
spire to make him a model in the study of
scientific method. Some of his views have
been rejected, and many may be profoundly
modified by more accurate knowledge, but
these things will in no way affect the value
of Darwin as a type of what education should
accomplish, and how it must accomplish it.

Darwin appreciated the humblest scientific

32 THE METHOD OF DARWIN.

work, and listened with deference to the sug-
gestions of others. He never dealt out primi-
tive justice to his opponents on the principle
of an eye for an eye and a tooth for a tooth.
He is morally famous for the forbearance that
he exercised toward those who attacked him.
This fame is heightened by the fact that he
was an acute judge of mental quality. His
investigations made it necessary for him to
collect information from all sorts of sources,
— not only at first hand, from Nature herself,
but at second hand, from many kinds of books,
made by many kinds of men. He has com-
plained that it was exceedingly difficult to find
out what and whom to trust.1 But his criti-
cisms of certain kinds of work show how
definite were his standards of value in measur-
ing scientific results.

Perhaps the most savage things Darwin ever
wrote are contained in letters to Hugh Strick-
land, and relate to the nomenclature of sys-
tematic zoology and botany.2 He expressed
freely his contempt for describers of species
who think the honor consists in having one's
name appended to that of a newly described
species, and whose work is generally so inac-

1 Life and Letters, Vol. II. p. 75.

2 Ibid., Vol. I. pp. 334, 338> 344-

DARWIN'S VIEWS OF METHOD. 33

curate or imperfect, or both, as to be practi-
cally worthless for any of the higher purposes
of science. Nor was he satisfied with mere
details even when they were accurate. In his
reminiscences of Robert Brown he said that
Brown seemed to him "to be chiefly remark-
able for the minuteness of his observations,
and their perfect accuracy."1 Darwin often
took breakfast with Brown, and on those occa-
sions the latter, according to Darwin, "poured
forth a rich treasure of curious observations
and acute remarks; but they almost always
related to minute points, and he never with
me discussed large or general questions of
science."

He has given us an interesting example of
his opinion of the opposite tendency toward
speculation, to the neglect of facts. During
his career as a medical student he admired
greatly his grandfather Erasmus Darwin's
" Zoonotnia."2 "But on reading it a second
time," he said, "after an interval of ten or
fifteen years, I was much disappointed, the
proportion of speculation being so large to the
facts given." These criticisms of the work
and methods of others are in perfect accord

1 Life and Letters, Vol. I. pp. 57, 6b.

34 THE METHOD OF DARWIN.

with his own practice. He combined in him-
self the qualities of both Brown and his own
grandfather. His works are a series of models
of the scientific method, because of the rare
and happy combination of minute and accurate
observation and daring speculation followed by
ruthless testing and pruning of his hypotheses.
He thought it worth while to notice and pene-
trate into the meaning of the most insignifi-
cant fact, and was capable of sweeping the
whole earth for evidence in support of his
largest theories. He could take the time to
count twenty thousand seeds of Ly thrum sali-
caria; 1 and his prophetic philosophical eye
led him to exclaim, "What a science Natural
History will be when we are in our graves,
when all the laws of change are thought one of
the most important parts of Natural History ! ".2
At various times and under various circum-
stances Darwin expressed fragmentary opinions
concerning what constitutes scientific method,
but never tried to make a complete statement of
it. His notion of what the method is, is shown
mostly by what he said concerning "deduc-
tion." For instance, concerning Bastian's
work, he said, in a letter to Wallace, "I am

1 Different Forms of Flowers, etc., p. 189.

2 Life and Letters, Vol. I. p. 439.

DARWIN'S VIEWS OF METHOD. 35

not convinced, partly, I think, owing to the
deductive cast of much of his reasoning; and
I know not why, but I never feel convinced by
deduction, even in the case of H. Spencer's
writings";1 and in a letter to John Fiske, "I
find that my mind is so fixed by the inductive
method, that I cannot appreciate deductive
reasoning; I must begin with a good body of
facts, and not from principle (in which I always
suspect some fallacy), and then as much deduc-
tion as you please." 2

Now deduction means, in one of its* senses,
reasoning from the general to the particular,
from a law, principle, or general fact to a
particular fact. But in the above quotations
Darwin meant by deduction, and the deductive
method, reasoning from postulates the truth of
which is accepted as beyond dispute. Induc-
tion, as a logical process, means reasoning
from particular to general, from facts to laws
or principles. But induction, or inductive
method, when used in a sense synonymous
with scientific method, includes all the logical
processes, induction, deduction, analogy, veri-
fication, — every way in which the intellect
passes from fact to fact. This is widely differ-
ent from what Bacon originally meant by induc-

1 Life and Letters, Vol. II. p. 346. 2 Ibid., p. 371.

36 THE METHOD OF DARWIN.

tive method; but practically no scientific man
has ever followed Bacon's method.

The inductive method, as illustrated by Dar-
win's own work, and as understood by all who
think clearly on the subject, consists in the
formation of an hypothesis from the facts by
induction at the earliest possible moment in
an investigation, deductive application of the
hypothesis to known facts, and in the search
for others that ought to exist if it is true, until
it proves itself imperfect. By the help of the
new facts the hypothesis is improved (by in-
duction) and again applied, until by successive
approximations it reaches the truth. So that
in the so-called inductive or scientific method
deduction is far more extensively used than
induction. But to say that one of the processes
is more important than the other would be like
saying that the female element, for example,
is more important for reproduction than the
male element. It is interesting to note in
this connection that John Stuart Mill, the
modern logician who has stood out as the
champion of the inductive method, has incon-
sistently described the combination "hypoth-
esis, deduction, and verification," as the
deductive method.1

1 Mill, System of Logic, People's Edition, p. 304.

DARWIN'S VIEWS OF METHOD. 37

The scientific or inductive method as under-
stood and practised by Darwin begins and
ends with facts. It takes nothing for granted
that relates to the matter under investigation,
and assumes as true only such things as the
law of causation and the validity of the reason-
ing processes; while the deductive method, as
understood by him, starts from principles
whose truth is not questioned. Regarded
simply as a logical process, however, deduc-
tion is equally valid whether the premises are
assumed to be true or admitted to be hypo-
thetical.

The ideal attitude of the scientific mind is
beautifully described in Darwin's own words
concerning himself: "I have steadily endeav-
ored to keep my mind free so as to give up any
hypothesis, however much beloved, (and I can-
not resist forming one on every subject,) as
soon as facts are shown to be opposed to it.
Indeed, I have had no choice but to act in this
manner, for, with the exception of the Coral
Reefs, I cannot remember a single first -formed
hypothesis which had not after a time to be
given up or greatly modified. This has natu-
rally led me to distrust greatly deductive
reasoning in the mixed sciences."1 *j> ^

1 Life and Letters, Vol. I. p. 83.

38 THE METHOD OF DARWIN.

It has been said that deduction, regarded
merely as a logical process, is equally valid
whether the premises are assumed to be true
or are admitted to be hypothetical. If the
premises are true, the conclusion must be true.
What brought the old deductive process into
so general disrepute was not its inadequacy,
but the using as premises in the process prin-
ciples that were held to be beyond dispute.
To this end the a priori reasoner went farther
and farther back in his philosophical repertory,
until he reached principles or axioms that he
felt could not be denied. Then by an irre-
sistible deductive swoop he reached conclu-
sions that must likewise be true. In such
philosophy there is little need of verification.

In science, and therefore also in the reason-
ing of practical life, the great question always
is whether the premises are true, or partly
true, or false. The old notion was that deduc-
tion led to certainty, and induction did not.
But in the scientific method the object is not
merely to deduce consequences from laws or
principles, but to establish the truth or falsity
of those laws or principles themselves. Hence
there is an incessant interplay of induction
and deduction. Darwin's distrust of deductive
reasoning was due to his fear of the premises.

DARWIN'S VIEWS OF METHOD. 39

But he said that all his hypotheses had to
be abandoned or modified, and they were the
conclusions of inductions; so that inductive
reasoning by itself is also absolutely worth-
less. The truth is, Darwin trusted nothing.
Induction furnished him hypotheses, and de-
duction interpreted known facts and led to new
ones under those hypotheses; but verification
of his deductions was as indispensable to him
as sunshine to a plant.

Darwin himself said, "Any fool can gen-
eralize and speculate." There has always been
an over-abundance of reasoning, both inductive
and deductive. Untrammeled induction is
largely responsible for the wild and worthless
beliefs that have burdened the world; and
untrammeled deduction is as largely respon-
sible for the dogmatic dry-rot that has pre-
vented progress in human discovery and beliefs.
Darwin was one of the most powerful deductive
reasoners that ever lived; and he was perfectly
fearless in making inductions, for, as he said
himself, he made an hypothesis on every sub-
ject. But the illustrations of the various logi-
cal processes that have been drawn from his
works show that even he — with his almost
superhuman powers of observation, his innate
desire to refer every fact to a general law, his

40 THE METHOD OF DARWIN.

rare ability to reason out the consequences of
his hypotheses, and his unbending determina-
tion to test his reasoning by ruthless investiga-
tion — made important inductions, deductions,
and analogies that were not true, and failed to
make deductions that should have thrust them-
selves upon him. He rarely, however, fell
into the old and vicious error of thinking that
reasoning of any kind is final proof.

He built up a large inductive structure in
pangenesis only to see it rejected; he went
wrong in his deduction concerning the relation
between high degree of specialization and the
chances in favor of preservation of a species;
and was prevented by a bad analogy from
investigating the effects of cross- and self-fer-
tilization in plants until the subject was thrust
upon him by empirical observation. He was
as productive of hypotheses as Nature is of liv-
ing things, and, like her, he subjected them
all to the principle of natural selection. His
mind was so fertile in guesses and so quick in
testing them that he called much of his work
"fool's experiments. " But in this way nothing
escaped him.

In recent years there has been made a for-
mal statement of the reasons why fertility in
hypotheses should be cultivated, and how they

DARWIN'S VIEWS OF METHOD. 41

should be used.1 The principle of multiple
hypotheses is urged, because in the sciences
it is not generally possible to hit at once upon
a cause from a study of the facts. As many
hypotheses as possible should be invented to
explain the facts under investigation, and as
fast as possible, as new light comes, other
hypotheses should be added, in order that the
mind may, as far as possible, put itself in
possession of all the possible causes of the
phenomena. By keeping them all constantly
before it, it can consider every fact from many
points of view; and each hypothesis will fur-
nish its own clews to further evidence. In
this way, also, the mind can more easily keep
itself in a judicial attitude. With the increase
of knowledge some of the hypotheses are shown
to be inadequate, and by the process of exclu-
sion their number is reduced until the inves-
tigation ends in the establishment of the true
theory of the cause of the facts under inves-
tigation.

In actual practice a good many difficulties
are connected with this method of using
hypotheses. Among a number of hypotheses
one will almost invariably have a somewhat
higher degree of probability than the rest; the

1 T. C. Chamberlain, in Science, Feb. 7, 1890.

42 THE METHOD OF DARWIN.

mind, working along the lines of least resist-
ance, follows the clews it offers to the neglect
of the other hypotheses. The more usual prac-
tice is typified in Darwin's method. He made
an hypothesis at the earliest possible moment,
and began to work with it. With increasing
knowledge it was modified, or rejected and
replaced by a more likely one. So that there
was a succession of hypotheses or of improve-
ments of the original one.

The method of multiple hypotheses is com-
mon enough, if it be made to include not only
the instances in which the same individual
entertains several hypotheses, but also those
in which different hypotheses are entertained
by different people. There are few questions
on which there are not several opinions; and
one approaching the subject impartially con-
siders them together in order to adopt the most
likely one. The process of exclusion works
admirably, and the result amounts to demon-
stration when all the possible hypotheses are
known, and one needs only to show that one
of them agrees with the facts and the others
do not. Newton, in establishing the law of
gravitation, showed that the orbits and veloci-
ties of the planets would be what they are if
the attractive force resided at the centre of the

DARWIN'S VIEWS OF METHOD. 43

system or in the sun, and acted with a force
varying inversely as the square of the dis-
tance; and that they could not be what they
are if the force were located anywhere except
at the centre. In this instance Newton was
able to exclude mathematically every theory
except the true one; and the demonstration
was made complete by the positive proof that
the facts accorded with the one hypothesis and
were at variance with every other.

Darwin used the principle of exclusion in
one of his early scientific efforts. There were
two hypotheses to account for the existence of
the great terraces called benches, or parallel
roads, of Glen Roy, in Scotland. It was evi-
dent enough that they had been formed by the
action of water; and they must either have
been formed by the sea, in which case the
uppermost, for example, must have been after-
wards elevated more than one thousand feet;
or they must have been the ancient shores of
a lake formed by the blocking up of the
open side of the now empty lake bed. Darwin
studied the region, and concluded that the
benches were of marine origin. He could not
conceive them to be due to barriers of rock or
detritus. He was then fresh from his studies
on the geology of South America. On the

44 THE METHOD OF DARWIN.

coasts of that continent he had grown familiar
with the immense scale on which elevations
take place, and had many opportunities to
study marine sand and gravel formations that
are now hundreds of feet above sea level. It
was therefore as easy for him to conceive a
marine origin of the terraces of Glen Roy as
it was difficult for him to believe that they
were the old shores of an elevated lake that
had been blocked in. He adopted the method
of exclusion, proved the one hypothesis prob-
able and the other improbable.

But this instance of the principle of exclu-
sion illustrates well the danger to which the
investigator is exposed in its use. In geology,
zoology, etc., — in what Darwin calls the mixed
sciences, — one can rarely know whether all
the possible hypotheses are known. Newton
could make a rigid demonstration, not simply
because he could treat his problem mathe-
matically, but because he was able to treat
all the possible hypotheses. When the gla-
cial theory was introduced into the geological
world the ancient terraces high above sea
level in the colder temperate zone were ac-
counted for. Then it was plain that the ter-
races of Glen Roy had been the shores, not
of the sea, nor of a lake dammed up by rock

DARWIN'S VIEWS OF METHOD. 45

or detritus, but of a lake dammed up by gla-
cial ice.

Darwin was ashamed of his arguments and
conclusions about Glen Roy. "My error," he
said, "has been a good lesson to me never to
trust in science to the principle of exclusion." l
But it is inevitable that apparently definite
views should receive just such shocks upon
the introduction of a great new principle in a
science. The facts that find their explanation
under the single newly discovered cause are
necessarily referred, before the advent of the
new hypothesis, to very various and unrelated
causes.

On the question of the origin of species
there were really two hypotheses, creation and
descent, when Darwin took hold of it; and he
adopted the process of exclusion in treating
them. The evidence was all in favor of descent
by natural selection and opposed to creation.
But he was himself emphatic in the declaration
that the origin of species by natural selec-
tion was not demonstrated. Belief in it must
be based on general considerations, — that
natural selection is an actually existing cause,
and that it explains a host of facts and brings
them under one point of view. One hypothesis

1 Life and Letters, Vol. I. p. 57.

46 THE METHOD OF DARWIN.

was excluded and the other adopted. And the
one that was accepted was based, not on direct
proof, but on one of the most magnificent series
of deductions that the world has ever seen.

The further discussion of this subject will
be deferred for the present. In the following
chapters Darwin's method of treating the prob-
lems that presented themselves to his mind
will be analyzed in some detail, and the clos-
ing chapter will deal with the logical history
of the principle of natural selection.

III.

STARTING POINTS. — METHOD OF STARTING IN-
VESTIGATIONS.— ISOLATED PHENOMENA.

THE starting points of many of Darwin's
researches were furnished him by other
intelligent men. In many cases these men not
only were in possession of the facts, but had
hit upon their true explanation. With the
facts thrust upon them, with enough reasoning
ability to pursue them, they gave away their
heritage, — luckily to one who knew its value.
In his frank but modest analysis of his own
mental qualities he said of himself, as already
quoted, " I think I am superior to the com-
mon run of men in noticing things which
easily escape attention, and in observing them
carefully. . . . From my earliest youth I have
had the strongest desire to understand or ex-
plain whatever I observed, . . . that is, to group
all facts under some general laws."1 There
can be no doubt that his great interest in
apparently little things, and his efforts to make

1 Life and Letters, Vol. I. p. 83.

48 THE METHOD OF DARWIN.

the most of them, were due to his conviction
that important things were hidden behind them,
that they were illustrations of general laws.

Lawson, Vice-Governor of the Galapagos
Islands at the time of Darwin's visit, knew
that the tortoises of the different islands dif-
fered from one another, and even declared to
Darwin that he could tell from which island
any tortoise came.1 He had the time, and
the material lay at his feet ; but he left it for
Darwin to make the Galapagos Islands famous
as illustrations of the local variations of
species. Darwin himself had to have the evi-
dence thrust upon him from several directions
before he grasped its significance, but his
greater appreciation of the nature and value
of the facts made him their master.

After his return from the Beagle voyage,
Mr. Wedgwood of Maer Hall suggested to
him that the apparent sinking of superficial
bodies, ashes, marl, cinders, etc., into the
earth is due to the action of earth-worms.2
Both the facts and the theory were ready at
hand. To the one man they were probably
interesting as intellectual playthings; to the
other they became the starting point for a

1 Naturalist's Voyage around the World, pp. 393-398.

2 The Formation of Vegetable Mould, etc., p. 3.

STARTING POINTS. 49

long investigation. Darwin read one of his
first papers, " On the Formation of Vegetable
Mould," before the Geological Society of Lon-
don, November 1, 1837; and on the same ap-
parently insignificant subject he published the
last book of his life.

While collecting in the Chonos Archipelago,
Southern Chile, he found numbers of an insig-
nificant little cirriped, none more than one
tenth of an inch long, embedded in the shell of
Concholepas peruviana.1 The zoological mate-
rial of his trip was turned over to specialists
for description, he furnishing the field notes
and editing the publications. Much zoological
information was thus given to the world, but
none of all that material ever served as a start-
ing point for a great investigation. The little
abnormal cirriped was left to Darwin himself;
probably because it was too small an affair to
be taken charge of by others. In his hands it
became the germ of a monograph on the Cirri-
pedia, which is still the classical literature
of the group. To determine its position he
studied the structure of as many genera as
possible. Dr. J. E. Gray, who had already
collected a large amount of material for a mon-

1 A Monograph of the Cirripedia, Vol. I., Preface, p. 5 ;
Vol. II. pp. 566-586.

4

$O THE METHOD OF DARWIN,

ograph of the group, turned it over to Darwin.
Gray did many things, but none well enough
to make what he wrote indispensable in the
study of any subject; he will be remembered
chiefly as a keeper of the zoological depart-
ment of the British Museum, and as a bitter
opponent of Darwin's theory of descent, while
the latter' s monograph heads the list of cirri-
ped literature.

Boitard and Corbie" merely made the obser-
vation that, when they crossed certain breeds
of pigeons, birds colored like the Columba
livia, or common dove-cot, were almost inva-
riably produced.1 It drew Darwin's attention
and led to numerous experiments on rever-
sion due to crossing. Certainly some, perhaps
many, scientific men had known that the species
of sundew (Droserd) catch insects. Darwin
himself had heard as much. Exhausted by
his long labors on the Origin of Species, he
was resting near Hartfield during the summer
.of 1860, and "was surprised by finding how
large a number of insects were caught by the
leaves of the common sundew (Drosera rotundi-
folid) on a heath in Sussex." 2 The right mind

1 The Variation of Animals and Plants under Domestica-
tion, Vol. II. p. 14.

2 Life and Letters, Vol. I. p. 77.

STARTING POINTS. 51

had been impressed, and away the giant intel-
lect started on another long and weary, but suc-
cessful, search after truth. Mr. W. Marshall
knew that in the mountains of Cumberland
many insects adhered to the leaves of Pin-
guicula; he told Darwin, and Darwin told the
world.1 Mr. Holland's statement that water
insects are often found imprisoned in the
bladders of Utricularia is interesting, chiefly
because it led Darwin to investigate the
genus.2

The most fertile suggestions, however, came
to him from the facts brought out by his own
work. He did not record the hundredth part
of the tentative notions that entered his mind;
but many of the most important and lasting
had their rise in what to most other men is the
refuse heap of curious and exceptional little
facts. Perhaps one of the noblest lessons he
left to the world is this, — which to him
amounted to a profound, almost religious con-
viction, — that every fact in nature, no matter
how insignificant, every stripe of color, every
tint of flowers, the length of an orchid's nec-
tary, unusual height in a plant, all the infinite
variety of apparently insignificant things, is

1 Insectivorous Plants, p. 369.

2 Ibid., p. 395.

52 THE METHOD OF DARWIN.

full of significance. For him it was a histor-
ical record, the revelation of a cause, the lurk-
ing place of a principle.

A typical example of his treatment of little
exceptional facts is that of "Hero, "the un-
usual plant in one of the later generations of
self -fertilized plants of Ipomoea purpurea.^ It
was a little -larger than the crossed seedlings
of the same generation, and the first exception
that had arisen, in his many experiments, to
the rule that the crossed are superior to the
self-fertilized seedlings in size and vigor. It
was a little thing, even for an exception, and
had occurred only after a very long series had
established the rule. It was very fit to suffer
the common fate of exceptions, and to be
deliberately choked for the benefit of the rule
to which it was so inconveniently related. By
other hands it would probably have been re-
corded and then ignored. Darwin made it the
parent of a whole race of exceptions. He
found "Hero" to be exceptional, not only in
being unusually tall, but in its being highly
self -fertile, in its great powers of growth, and in
its descendants which were crossed having no
advantage over its self-fertilized descendants.

His aim, as soon as he hit upon a line of
1 Effects of Cross- and Self-Fertilization, p. 60.

METHOD OF STARTING INVESTIGATIONS. 53

investigation, was to reach as quickly as pos-
sible a crucial test or a crucial observation
that would enable him to determine positively
whether or not his beliefs were justified. As
soon as the idea of descent of species took
definite shape in his mind, he determined,
after deliberation, to take up the study of
domestic pigeons.1 He selected these because
the variations were more numerous and plainer,
more of them had arisen in the historical period
than is usual with animal groups, the material
was abundant and easily accessible, etc. He
cnose for his investigation the conditions most
favorable to success.

When he discovered that insects are caught
in large numbers by the common sundew, he
gathered a number of plants, counted the leaves
and the number that had caught insects ; and
compared the results with the accidental de-
struction of insects by the viscous buds of the
horse-chestnut, etc.2 Similar results were pro-
duced by somewhat similar means; but by the
comparison he secured preliminary evidence
that the leaves of the sundew, unlike the buds
of the horse-chestnut, were excellently adapted

1 Origin of Species, p. 15; Variation of Animals and
Plants under Domestication, Vol. I. p. 137.

2 Insectivorous Plants, pp. 1-3, 63-76.

54 THE METHOD OF DARWIN.

for catching insects. To him adaptation for
insect catching meant that this habit was
advantageous to the plant; and that it must
derive nourishment from the captured insects.
He knew what elements plants required for
nourishment, and immediately set about mak-
ing another crucial test. When led to believe
that the leaves absorbed nutritious matter from
the insects, he made a crucial experiment by
immersing numbers of the leaves in nitro-
genous and non-nitrogenous fluidsW the same
specific gravity to find whether they would
act differently in the two cases, taking care
that the two sets of conditions should be the
same except in the presence of nitrogenous
matter in the one and its absence in the other.
The test confirmed his belief, and is an
example of the most rigid type of reasoning
and experiment, — a combination of positive
and negative evidence which Mill called the
Method of Difference. Darwin's clear notion
of what constitutes good evidence led him to
seek demonstrative evidence by the shortest
way. In the case just described he secured it
at once, and might have rested content with
having established the principle; but as soon
as he found that the nitrogenous fluid alone
excited energetic movements " it was obvious

ME THOD OF STAR TING INVES TIG A TIONS. 5 5

that here was a fine new field for investiga-
tion." His crucial tests only gave him confi-
dence that there was more beyond; then he
began the long series of observations and
experiments which resulted in the charming
volume on "Insectivorous Plants."

It is told elsewhere how he was deterred by
theoretical considerations from experimenting
on the effects of cross- and self-fertilization,
and how the expectation of early results was
fairly thrust upon him by the difference in size
and vigor between crossed and self-fertilized
seedlings.1

When once his attention was fixed, he made
a preliminary experiment on two plants, with
the effects of cross- and self-fertilization as the
principal object of investigation. The results
corroborated his previous observations, and
he was in possession of the principle. Such
simple preliminary experiments are interest-
ing, since, if they do not establish a principle
fully, they raise up for it a higher degree of
probability than any succeeding experiments,
and make it possible to work deductively with
considerable confidence.

The introduction of the principle of con-
tinuity into general scientific thinking has

1 Effects of Cross- and Self-Fertilization, pp. 6-8.

56 THE METHOD OF DARWIN.

made it a normal intellectual process to look
upon exceptional and isolated phenomena as
merely extreme instances of much larger
groups. One of the marked characteristics of
Darwin's work is that he selected such extreme
instances, and sought to connect them with the
more common facts to which they were related,
by proving, or at least suggesting, their deri-
vation from the latter. Wherever it was pos-
sible in his experiments, he varied the amount
of a cause in order to note the proportionate
variation in the amount of the effect; and
where he had to depend upon observation alone,
he made strenuous efforts to connect extreme
instances by gradations of character.

Thus, he and his son Francis, by continuous
attention to the sleeping movements of plants,
were able to show that it is not true, as is gen-
erally supposed, that the leaves move only in the
evening when going to sleep, and in the morn-
ing when awaking ; for they found no exception
to the rule that leaves which sleep continue to
move during the whole twenty-four hours, only
moving more quickly when going to sleep and
awaking than at other times.1 They were able
to show that sleeping movements are only
liighly specialized and exaggerated modifica-

1 Power of Movement in Plants, p. 403.

ISOLATED PHENOMENA. 57

tions of the universal movement of circumnu-
tation. In his experiments on insectivorous
plants with phosphate of ammonia he varied
the proportion of the latter to determine how
small an amount would affect the tentacles of
Drosera.1 He found that excessively minute
quantities of the latter would produce reac-
tion. His results were so astonishing that in
1873 he doubted his own experiments of 1872,
and in 1874 he again thought that some mis-
take must have been made, and again repeated
the experiments, but always with the same
results. He discussed these remarkable facts
at some length, tried to make them more cred-
ible by comparing them with similar cases that
are equally astonishing but are known to be
true; and expressed the hope that his experi-
ments would be repeated, at the same time
laying down the conditions of success.

While studying the power of circumnutation
in plants the Darwins accidentally left some
of their specimens in several cases exposed to
oblique light. Before they "knew how greatly
ordinary circumnutation was modified by a
lateral light, some seedling oats, with rather
old and therefore not highly sensitive cotyle-
dons, were placed in front of a northwest win-

1 Insectivorous Plants, pp. 154-173.,

58 THE METHOD OF DARWIN.

dow, towards which they bent all day in a
strongly zigzag course. On the following day
they continued to bend in the same direction,
but zigzagged much less. The sky, however,
became, between 12 140 and 2 135 P.M., overcast
with extraordinarily dark thunder-clouds, and
it was interesting to note how plainly the
cotyledons circumnutated during this inter-
val."1 These observations they considered of
some value from their having made them while
they were not attending to heliotropism ; and
they were led by them "to experiment on
several kinds of seedlings, by exposing them
to a dim lateral light, so as to observe the gra-
dations between ordinary circumnutation and
heliotropism." An accidental observation led
to variations in the experiments, which re-
sulted in demonstrating continuity between two
apparently distinct classes of movements.

In some of his remarkable studies on grada-
tions of characters, where it was impossible to
make experiments, he sought out and observed
Nature's own variations. Perhaps the most
striking instance of the study of gradations of
character is that connected with the "ocellus "
on the tail coverts of the peacock.2 This

1 Power of Movement in Plants, p. 421.

2 Descent of Man, Vol. II. pp. 132-145

ISOLATED PHENOMENA. 59

feather-mark was properly considered a serious
difficulty to Darwin's theory because of its
remarkable character. But with consummate
ingenuity he undertook to connect it by a
series of less and less remarkable markings
with the ordinary feather-markings of the
group to which the peacock belongs. It is
impossible to exaggerate the importance of
studying phenomena in their quantitative and
qualitative variations, for on it depends the
establishment of continuity between phenom-
ena apparently widely separated, and it fre-
quently leads to results that can be reached in
no other way.

IV.

EXHAUSTIVENESS. — TIME GIVEN TO INVESTI-
GATIONS.—TREATMENT OF OBJECTIONS.

THE theories with which Darwin dealt were
so general, and the facts that had to be
handled as evidence were so vast in number,
that probably no man was ever exposed to
greater temptation to collect his evidence pro-
miscuously from all quarters, picking up in
each field what was already known, and sup-
plementing it by a few test observations. But
he never contented himself with sketching
theories and adorning them with dashes of
evidence.

He made himself invincible by the exhaust-
iveness with which he determined the quality
of his evidence. The great confidence which \
scientific men have had in him has been due |
to the fact that he did not leave it to them to . ,
test the theories which he presented. He con-
vinced the world of the truth of a doctrine
which others had striven in vain for fifty years
to establish. To my mind one of the chief

EXHA US TIVENESS. 6 1

characteristic differences between his work
and that of Lamarck and others, apart from
differences in the explanations offered, is its
superb exhaustiveness. It is as impossible
now to take the ideas of descent and of natural
selection out of the world as to take a star out
of the sky. The firm establishment of these
ideas was due to the quality and quantity of
Darwin's work, and both of these were deter-
mined by the same exhaustiveness in method.

When he started out to describe the single
little abnormal cirriped from the west coast
of South America, he was characteristically
led, as he said, for the sake of comparison, to
examine the internal parts of as many genera
as he could procure. This untamed determina-
tion to find out all there was to know about
what he was describing was associated with a
fine contempt for the kind of work that merely
describes new things without showing all their
connections. One of the greatest and most
constant obstacles to his progress was that this
intellectual quality was so rare or so little cul-
tivated in other naturalists; so much of the
scientific material with which he had to deal
was so superficially or carelessly worked out
that he never knew what to trust.

Among the best examples of this spirit of

62 THE METHOD OF DARWIN.

exhaustiveness is his study of pigeons.1 As
usual, he knew clearly what he was after, and
this gave him the power of selecting judiciously
the lines along which to make investigations
and of using to the best advantage the materials
he worked on. In his remarks on the search
for the cause of the modification of species, he
said, " Believing that it is always best to study
some special group, I have, after deliberation,
taken up domestic pigeons." With other ends
in view, pigeons might be studied in different
ways. But remembering his purpose, his work
on pigeons is a model of exhaustiveness as well
as of reasoning. He not only studied the vari-
ation of breeds, but sought its explanation by
a minute study of individual differences. He
considered the skeleton as well as the feathers,
and gathered facts and specimens from all over
the world.

What is true of his study of pigeons is true
of his work on orchids. The adaptation of
flowers for cross-fertilization had interested him
for many years, and he had collected a large
mass of observations; but he was true to his
instinct : " It seemed to me a better plan to
work out one group of plants as carefully as I

1 Variation of Animals and Plants under Domestication,
Chaps. V. and VI., pp. 137-235.

EXHAUSTIVE NESS. 63

could rather than publish many miscellaneous
and imperfect observations." Orchids furnished
an extreme case ; and his work on them is fas-
cinating from the nature of the subject, the end
aimed at, and the ingenuity of the reasoning
employed. He showed "how admirably these
plants are constructed so as to permit of, or to
favor, or to necessitate cross-fertilization " ; but
the way in which he did it is as admirable from
a logical point of view as the flowers them-
selves are in their peculiar adaptation. By
thus selecting judiciously the most extreme
special cases for exhaustive examination, he
threw the strongest light on all the collateral
evidence, and made it easy for him to under
stand its significance. On the shoulders of
such work his theories sat firmly, and it made
it easy for those who came after him to work
out the classes of facts which he was not able
to exhaust.

In each of the many special studies which he
carried on there are many models of method in
the pursuit of details. The following case is
especially interesting because it illustrates both
the habitual care of the authors in their experi-
ments on the movements of plants and the ex-
treme liability to error that results from a
wrong start. Since the book on the " Power of

64 THE METHOD OF DARWIN.

Movement in Plants " was written, it has been
shown that the conclusion of the authors that
"an object which yields with the greatest ease
will deflect a radicle " is wrong. The whole
superstructure of reasoning which resulted in
the notion that the tips of radicles are sensitive
to contact was therefore built on sand. The
experiments and reasoning will be discussed
from the point of view of the authors at the
time they were made, and afterwards attention
will be called to the corrections that have since
been made by others. In their work on the
movements of radicles, Charles and Francis
Darwin found that "an object which yields
with the greatest ease will deflect a radicle."
Extremely thin tin-foil on soft sand was not at
all impressed, and deflected the root at right
angles. Hence, they reasoned, the cause "of
the deflection could not be mechanical contact.
A conceivable hypothesis was that " the gentlest
pressure might arrest growth and the apex grow
only on one side; but this view leaves unex-
plained the curvature of the upper part, extend-
ing for a length of 8-10 mm. . . . We were
therefore led to suspect that the apex was sen-
sitive to contact, and that an effect was trans-
mitted from it to the upper part."1 By the

1 Power of Movement in Plants, pp. 131-140.

EXHAUSTIVE NESS. 65

exclusion of the other two hypotheses — me-
chanical contact and arrest of growth — they
confined themselves to the last one, sensitive-
ness to contact. This would have been a fine
field for a discussion of the known facts fol-
lowed by a necessary inference. Of the three
possible hypotheses, two had been excluded,
and the third must be true. It would seem
quite clear that the case was logically proved.
But instead of making this the end, they made
it the beginning of their work.

They "thought that any small hard object
affixed to the tip of a radicle freely suspended
and growing in damp air, might cause it to
bend if it were sensitive, and yet would not
offer any mechanical resistance to its growth."
The results of their experiments proved remark-
able. When approaching the subject they made
a preliminary trial with seven beans at a rather
cool temperature, and six radicles curved. To
quote again, "These six striking cases almost
convinced us that the apex was sensitive, but
of course we determined to make many more
trials." As they had noticed that radicles grew
much more quickly when subjected to con-
siderable heat, and as they imagined that heat
would increase their sensitiveness, they made
five or six dozen trials on more than two dozen
5

66 THE METHOD OF DARWIN.

beans at a temperature of 69°-72° F. The
result was moderately distinct deflection in only
one radicle; in five other cases slight and
doubtful deflection. "We were astonished at
this result, and concluded that we had made
some inexplicable mistake in the first six experi-
ments. But before finally relinquishing the
subject, we resolved to make one other trial,
for it occurred to us that sensitiveness is easily
affected by external conditions, and that radi-
cles growing naturally in the earth in the early
spring would not be subjected to a temperature
nearly so high as 70° F." In the vast num-
ber of successful trials that they made they
allowed the radicles to grow at a temperature
of 55°-6o° F.1

Had they stopped with the first trial, they
would have hit the explanation which they
finally adopted, and missed the effect of varia-
tions in temperature. Had they stopped with
the second, the question would have hung in
the balance between contradictory results. It
was very feasible to reason that the results of
the older experiment were due to some error of
observation or manipulation. Nothing would
have been known concerning the effect of tem-
perature, and nothing concerning the original

1 Power of Movement in Plants, pp. 141, 142.

EXHAUSTIVENESS. 6/

question. Their imagination had led them to
introduce a new element into the second experi-
ment; then reason prevented them from suc-
cumbing before the disturbance in the results,
and led them to recognize it as a determining
factor and treat it as such in their subsequent
experiments.

The contradictory state in which things would
have been left at the end of their second experi-
ment is neatly illustrated by another case in
connection with the same subject.1 Ciesielski
had shown, in his study of geotropic move-
ments, that roots extending horizontally with
their tips cut off did not grow downward. " He
further states that, if the tips are cut off after
the roots have been left extended horizontally
for some little time, but before they have begun
to bend downwards, they may be placed in any
position and yet will bend as if still acted on
by geotropism ; and this shows that some influ-
ence had been already transmitted to the bend-
ing part from the tip before it was amputated."
Sachs repeated these experiments, but denied
the conclusions, because in his experiments
the roots became distorted in all directions.
The Darwins undertook to learn the cause of
the contradiction in the results. After describ-

1 Power of Movement in Plants, p. 523.

68 THE METHOD OF DARWIN.

ing unsuccessful efforts based on reasoning,
they go on to say, " We next thought that, if
care were nat taken in cutting off the tips
transversely, one side of the stump might be
irritated more than the other, either at first, or
subsequently during the regeneration of the
tip, and that this might cause the radicle to
bend to one side." They amputated some
radicles obliquely and some transversely, and
allowed them to grow perpendicularly. There
was little or no distortion at first; but after
two or three days, when the new tips began to
form, the distortion of the obliquely amputated
radicles became very conspicuous. The new
tip was probably formed obliquely, causing the
bending. Sachs probably " unintentionally am-
putated the radicles not strictly transversely " ;
and by not attending to this apparently insig-
nificant condition he produced confusion and
failed to make a discovery.

This case is interesting not only because it
illustrates the difficulties that are met by the
individual investigator, but because it is a typ-
ical example of a very large proportion of con-
tradictions in results with which the literature
of science is burdened. The contradiction in
the results obtained by the two men was due,
not to errors of observation, but to neglect of

EX HA US TIVENESS. 69

the various conditions under which the experi-
ments were made. As I have elsewhere shown
for another more involved case, the disputant
observers were both right.1 It was lack of
exhaustion of the logical conditions of the
problem that led to the contradiction. Total
exclusion of error requires that every move-
ment of the experimenter be fraught with in-
tention. It is fairly safe to assume that, if two
observers are competent and upright, their con-
tradictory results, no matter on what subject,
will prove essential to the final solution of the
problem.

The publication of the " Power of Movement
in Plants " was followed by several years of
active investigation on and discussion of the
"Darwinian curvature" of radicles. It has
been shown that radicles, instead of being
deflected by tin-foil on soft sand, will pene-
trate mercury and pierce tin-foil even when
they strike it at a quite high angle. In expla-
nation of the initial error of the Darwins it has
been suggested that the radicles upon which
they experimented were wilted. It has been
further shown that in the experiments in which
they attached small hard objects to the tips of
the radicles to induce them to curve, the curva-

1 Popular Science Monthly, January, 1894, pp. 373~376«

7O THE METHOD OF DARWIN.

ture was not due to sensitiveness, but to the
action of the shellac by means of which the
objects had been attached. Microscopic exam-
ination of radicles to which the materials used
for attachment had been applied showed that
the cells were affected. In short, the curvature
of radicles ascribed to sensitiveness to touch
has been shown to be due to pathological con-
ditions brought into existence by the experi-
ments themselves. The reasoning was correct
enough, but the premises were false. Initial
errors led to a false conclusion, but the experi-
ments were all valuable as starting points for
more searching investigations. The hypothesis
of sensitiveness has been proved by Wiesner 1
and others to be untenable, but much more is
known of the Darwinian curvature now than
when the Darwins published their conclusions.
All Darwin's works on plants furnish ex-
amples of the practically complete develop-
ment of the conditions of the problem. In
the opening of the chapter on " Illegitimate
Offspring of Heterostyled Plants," he said, "I
give the results of my experiments in detail,
partly because the observations are extremely

1 Wiesner, J., Untersuchungen liber die Wachsthumsbewe-
gungen der Wurzeln (Darwinische und Geotropische Wurzel-
Kriimmung). Sitz. Akad. Wien, V. 89, I. pp. 223-302.

EXHA USTIVENESS. 7 1

troublesome and will not probably soon be
repeated, — thus I was compelled to count under
the microscope above twenty thousand seeds of
Lythrum salicaria. "* The whole of his work
on the same subject is on the same scale, vast
numbers of observations being condensed into
each of numerous tables.

It is elsewhere described how he had fore-
seen the importance of making comparative
observations on the effects of cross- and self-
fertilization in plants; and how he had been
deterred by a bad analogy, and had finally had
the subject thrust upon him while making
experiments on Linaria vulgaris and the carna-
tion with another end in view.2 There are
extant in all biological literature few equally
fine examples of the clear comprehension of
the conditions of a problem and of untiring
attention to them.3 He began by making a
preliminary experiment with two plants, and,
finding that, as in his previous accidental
observations, the cross-fertilized seedling was
in every respect superior to the self-fertilized,
he proceeded to experiment on a very large
scale.

1 Different Forms of Flowers on Plants of the same Species,
p. 189.

2 Effects of Cross- and Self-Fertilization, p. 8.
8 Ibid., pp. 10-27.

72 THE METHOD OF DARWIN.

He covered the plants with nets, and cross-
and self-fertilized them artificially without cas-
tration, so as to make the cases parallel in all
respects. The seeds were thoroughly ripened;
the cross- and self-fertilized seeds were chosen
in pairs that had germinated simultaneously,
and were planted on opposite sides of the same
pot. When one of a pair t became sickly or
injured, both were thrown away. All the
seeds which remained after a number of pairs
were thus planted were sown and left to grow
up crowded on opposite sides of the same pot.
The soil was carefully made uniform ; the
plants on the two sides of a pot were always
watered at the same time and as equally as
possible. The plants on the two sides of a pot
were separated by a partition, but the pot was
turned so that the two sides would be equally
lighted. In this way the cross- and self-fer-
tilized seedlings that competed with each other
were subjected to as nearly similar conditions
as human ingenuity could produce. Different
sets of competing plants were subjected to
different conditions, to determine whether the
inequality between the cross- and self-fertilized
seedlings would show itself only under favor-
able, or unfavorable, or under all circumstances.

In making the comparisons the eye alone

EX HA US TIVENESS. 7 3

was never trusted. Many plants were measured
while young, when nearly full grown, and when
matured. Equal numbers of the two kinds
were cut down and weighed. Records were
kept of the rate of germination, of the periods
of flowering, and of productiveness both as to
the number of capsules produced and as to the
average number of contained seeds. Finally,
the tables of measurements were submitted to
Francis Galton in order to insure against error
and to have them examined by the best statis-
tical methods. Darwin intended at first to
raise only one generation of crossed and self-
fertilized seedlings of each kind, but in many
cases he went as high as ten generations.
Plants of different generations were exposed to
different conditions in successive years. He
started crossed seeds of Ipomcea purpurea (third
generation) forty-eight hours later than the
self-fertilized; seeds were sown outdoors late
in the season, and only one stick given to each
set to climb on ; two lots were sown in a shady
and weedy part of the garden ; two other lots
were sown in a bed of candytuft; seeds from
the same plant were sown, the crossed in one
corner and the self-fertilized in another corner
of a tub in which a Brugmannia had been grow-
ing, and in which the soil was excessively

74 THE METHOD OF DARWIN.

poor; others were transferred from the hot-
house to the coldest part of the greenhouse; —
all to test the relative vigor of the crossed and
self-fertilized seedlings.

He considered the possible sources of error,
and showed that accidental cross-fertilization
of plants intended for self-fertilization, and
accidental self-fertilization of plants intended
for cross-fertilization, would diminish rather
than exaggerate his results. It having been
said that an excess of pollen was injurious, two
sets of sixty-four each of Ipomcea purpurea
were tested to find whether the quantity of
pollen applied to the stigma made any differ-
ence, and the statement was proved untrue.
He published the details of his experiments,
because they extended over eleven years and
"are not likely soon to be repeated." When
Darwin said in his conclusion that cross-fertil-
ized plants are superior to self-fertilized plants
and have a permanent advantage over them in
the struggle for existence, and that nature
abhors perpetual self-fertilization, there was
no man to gainsay it; his ingenuity had spent
itself in exhausting the conditions of the prob-
lem. He could have reached the same conclu-
sion from his two accidental observations and
his first direct experiment on the two plants.

EX HA USTIVENESS. 7 5

In this way he could have secured for himself
the priceless gem of "priority of discovery "
without the tedious years of work; he could
then have produced what so many scientists in
prominent positions produce on subjects fit to
occupy one mind for years, — a few pages of
general discussion and desultory reference to
scattered and long-known facts.

The characteristic of exhaustiveness and its
consequences is well illustrated in his "detail
work " in the Monograph of Cirripedia. By the
examination of an enormous number of speci-
mens he showed how very variable are the spe-
cies of the genus Balanus, and how, through
imperfect examinations and want of caution,
so many nominal species of fossil Balani have
been described. Discussing dubious species,
he said, " Bronn does not seem to have been
aware of the absolute necessity of giving
minute details in his descriptions of fossil
cirripeds."1 Probably in no department of
the biological sciences has there been more
superficial and worthless work done than in
the description of species. This is doubtless
due to the fact that a spurious fame could be
acquired by the connection between the author's
name and that of the species he described.

1 Monograph of the Cirripedia, Vol. II. pp. 173, 184.

76 THE METHOD OF DARWIN.

Even good naturalists have frequently regarded
a short description sufficient for ordinary pur-
poses of identification as even preferable to a
minute enumeration of details. Darwin not
only gave an example of the permanent worth
of the latter method of specific description in
his "Monograph of the Cirripedia," but his
book on the " Origin of Species " is one of the
finest examples extant of the fact that a short
statement of any subject to be valuable and
forcible must be an abridgment of and be
based upon a vast mass of details. In a corre-
spondence with Hugh Strickland he expresses
himself almost savagely in condemnation of
the wretchedly poor work of species describers;
he had unusually good reason to feel aggrieved
because the nature of his work compelled him
to use so much of the work of others. But he
did far less for the improvement of specific
description by personal example in the Mon-
ograph of Cirripedia, and by personal condem-
nation of the poor work of others, than he did
indirectly by his general theories of descent
and natural selection. The doctrine that species
had their origin in varieties and in individual
variations has changed the purpose of specific
description. Identification and classification
have been made processes subsidiary to some-

TIME GIVEN TO INVESTIGATIONS. //

thing higher. The establishment of a new
standard of value for specific work has not only
directed this work into new channels and the
careful study of details, but has made many old
descriptions valueless.

Intimately connected with the thoroughness
with which scientific work is done is the length
of time spent on it. One of the serious objec-
tions to waiting for better facilities, more evi-
dence, etc., when the question of closing up an
investigation arises, is the probability of loss
of interest in the subject. Promptness in com-
pleting any line of work seems commendable
on account of the economy of time, the greater
certainty of recording results to date, and the
importance of keeping the coast clear for new
work. But work "completed" in a short time
suffers from incompleteness, from whatever
point of view it is regarded. Nothing can be
so demonstrative as the relative permanence of
work that has been done slowly and work that
has been done with promptness and apparent
vigor. The latter almost invariably takes a
very subordinate place in the literature of the
subject when once that subject is competely
worked out.

In these days of competition, when every
field of biology is ferreted for new subjects of

78 THE METHOD OF DARWIN.

investigation, and others are likely to secure
priority of publication, there is every tempta-
tion to publish prematurely. Priority having
been gained by a so called preliminary notice,
a large proportion of the subjects are dropped
by the original investigators, and let alone by
others because they are "old." Time makes
investigation easier. Where speed is felt to be
necessary, a vast outlay of energy is frequently
required to discover what with more time would
almost come of itself. With the attention
steadily fixed, time brings to bear multitudes
of facts that would otherwise be lost. Gaps in
the evidence, if filled at all, are too often filled
with "necessary inferences" instead of facts.

There is perhaps no better case on record to
illustrate the effect of time on the develop-
ment of theory than the " Origin of Species/'
Darwin had already long reflected on the sub-
ject when he opened his first note-book for
facts in 1837; and for more than twenty years
thereafter he labored in analyzing and inter-
preting the facts of nature by the help of his
theory in order to test the latter in all its rela-
tions. By carrying on simultaneously several
investigations bearing on the general subject,
he could let each of his studies drag through
many years, and yet was able to accomplish

TIME GIVEN TO INVESTIGATIONS. 8 1

much. Some of the most important explana-
tions under his theories did not occur to him
until years after he had begun their study. It
will be pointed out later that after he once got
possession of a working hypothesis his work
was largely deductive; and it will be shown
how extremely difficult it is to work out all the
important consequences of such a hypothesis
even in many years. After it is once done the
task seems so easy that the wonder is that it
was not done sooner. But the contemplation
of the development of a great theory soon re-
veals the enormous difficulties in the way of
one or many who seek to work out its conse-
quences. Darwin did in each of his investiga-
tions what is usually done for a subject by a
number of successive workers ; each makes an
important contribution to the subject, removes
a serious objection to a theory, explains a sec-
tion of the evidence, points out an important
consequence, or modifies the statement of it
to bring it more clearly in harmony with the
greater knowledge on the subject. By succes-
sive approximations many men, working toward
the same end, originate, build up, and improve
a theory until it takes its place among perma-
nently established truths. As far as it was
possible for one man to do so Darwin did all

-g THE METHOD OF DARWIN,

this for his subjects before he gave them to the
world. His work on the " Expression of the
Emotions" began in 1838 and closed in 1872;
"Insectivorous Plants," 1860-1876; "Vegetable
Mould and Earthworms," 1837-1881. One of
the most notable legacies that he left to the
ambitious student is his example of great energy
and great patience, his incarnation of the truth
that time, as well as reason, is the handmaid of
science.

Coupled with the habit of treating exhaust-
ively the subjects with which he dealt, and
the willingness to bide his time for publication
until his views had reached their full maturity,
was his extreme conscientiousness in giving
full force to the objections against his. general
results. The habit of pursuing all the facts to
their meaning made it possible for him to say
that he had been able to consider in advance
all the objections that were afterwards made
to any of his views. The summing up of his
experiments on Adonis czstivalis, in the " Effects
of Cross- and Self-Fertilization," is an example
of the great length to which he went in record-
ing facts, especially if they were in any way
opposed to his conclusions. He said, "The
results of my experiments on this plant are
hardly worth giving, as I remarked in my notes

TREATMENT OF OBJECTIONS. 8 1

made at the time, * seedlings from some un-
known cause, all miserably unhealthy, ' nor did
they ever become healthy; yet I feel bound to
give the present case, as it is opposed to the
general results at which I have arrived."1

He did not hesitate to diminish the positive
results of his experiments or the effect of his
views by incorporating all exceptions, unless
they were clearly due to some known extra-
neous cause. But his inability to leave any
thing unexplained was so great that he rarely
left exceptional facts without at least sugges-
tions of possible explanations. He was ex-
tremely ingenious in guessing explanations for
facts that could not be brought under the same
general explanation as the other facts of their
class. A good instance of this art of wriggling
is his attempt to explain the sloping terraces
of Coquimbo.2

1 Effects of Gross- and Self-Fertilization, p. 128.

2 Geological Observations, etc., pp. 256-258.

V.

NEGATIVE EVIDENCE.

IT would naturally be expected, from Dar-
win's clear notions of evidence in gen-
eral, and the necessity that he was under all
his life of handling vast bodies of complicated
evidence, that his work would furnish examples
for the treatment of negative evidence. His
estimate of its value is well shown by his treat-
ment of the question whether Primula veris,
P. vttlgaris, and P. elatior are different forms
of the same species.1 After discussing the
evidence in favor of this view he said, " Nega-
tive evidence is of little value; but the follow-
ing facts may be worth giving." Then follows
the recital of his efforts to determine whether
the cowslip varies enough to justify the belief.
He transplanted cowslips from the fields into a
shrubbery, and then into highly-manured land;
the next year they were protected from insects,
artificially fertilized, and seed grown, which

1 Different Forms of Flowers on Plants of the same
Species, p. 62.

NEGATIVE EVIDENCE. 83

was sown in a hot-bed. The young plants
were set out, some in very rich soil, some in
stiff, poor clay, some in old peat, and others in
pots in the greenhouse, — seven hundred and
sixty-five in all. Though they and their parents
were subjected to all this diversity of treat-
ment, "not one of them presented the least
variation except in size." Negative evidence
is indeed of little value, unless it can be shown
that it covers the whole ground. In order to
transform these experiments into proof it would
be necessary to show that, if the three forms
belong to one species, the cowslip should have
varied under the conditions to which it was
subjected. It is far more difficult to disprove
a proposition by negative evidence than by
proving the truth of its contradictory. Darwin
accordingly demonstrated what several other
botanists had surmised: that the oxlip is a
hybrid between the cowslip and the primrose.

His efforts to determine whether Orchis morio
secretes nectar also furnish a good illustration
of his treatment of negative evidence.1 A
nectary implies nectar, but Sprengel had thor-
oughly searched many flowers of O. maculata
and morio, and could not find a drop. Of
his own efforts in this direction, Darwin said,

1 Fertilization of Orchids, pp. 36-41.

84 THE METHOD OF DARWIN.

" I have looked to all our common British
species and could find no trace of nectar; I
examined, for instance, eleven flowers of O.
maculata, taken from different plants growing
in different districts, and taken from the most
favorable position on the spike, and could not
find under the microscope the smallest bead of
nectar." Sprengel believed that these plants
exhibit an organized system of deception, "for
he well knew that the visits of insects were in-
dispensable for their fertilization " ; but Darwin
could not believe in so gigantic an imposture.
"Notwithstanding these several facts," he went
on, " I still suspected that nectar must be
secreted by our own orchids, and I determined
to examine O. morio rigorously. As soon as
the flowers were open I began to examine them
for twenty-three consecutive days; I looked at
them after hot sunshine, after rain, and at all
hours; I kept the spikes in water and examined
them at midnight and early the next morning."
He irritated the nectaries with bristles and ex-
posed them to irritating*vapors. He examined
flowers whose pollinia had been removed, and
others which would probably have them soon
removed. But the nectary was invariably dry.
Only after he had made the negative evidence
as complete as it could be made, by examining

NEGATIVE EVIDENCE. 85

the nectaries of very many flowers from differ-
ent places under all the possible circumstances
in which nectar might be secreted, did he feel
justified in saying, "We may therefore safely
conclude that the nectaries of the above named
orchids neither in this country nor in Germany
ever contain nectar." Even then he restricted
the negative conclusion to the two countries
in which the exhaustive examinations had been
made.

But he did not rest with this negative evi-
dence. It was strong enough to convince him
that there was no ordinary nectar, but the
further evidence that he presents shows how
quickly negative evidence falls into the back-
ground in the presence of even the most indirect
positive evidence. He was thoroughly con-
vinced that these orchids require the visits of
insects for fertilization, that insects visit flowers
for the attractions offered in the way of nec-
tar, pollen, etc. ; that nature could not deceive
insects by a permanent imposture, and yet that
in these orchids the ordinary attraction was
absent. It was as if a crime had been com-
mitted, and he were asked to believe there was
no criminal.

In examining the nectaries of the several
species of orchids he was "surprised at the

86 THE METHOD 'OF DARWIN.

degree to which the inner and outer membranes
forming the tube or spur were separated from
each other, also at the delicate nature of the
inner membrane, . . . and, lastly, at the quan-
tity of fluid contained between the two mem-
branes." He found the space between the
membranes of other nectaries quite dry. He
then examined other forms that do secrete nec-
tar in the ordinary way, and found the mem-
branes closely united, instead of separated by
a space. "I was therefore led to conclude," he
said, " that insects penetrate the lax membrane
of the nectaries of the above named orchids and
suck the copious fluid between the two mem-
branes. This was a bold hypothesis, for at the
time no case was known of insects penetrating
with their proboscides even the laxest mem-
brane." He afterwards learned that at the
Cape of Good Hope moths and butterflies pene-
trate peaches and plums, and in Queensland,
Australia, a moth penetrates the rind of the
orange. These facts merely proved his antici-
pation less anomalous than it had seemed.
The bees which he saw visiting Orchis morio
kept their proboscides inserted in the nectaries
for some time. He opened several nectaries,
and found brown specks, due, as he believed,
to punctures made some time before. Herman

NEGATIVE EVIDENCE. 87

Miiller has since corroborated Darwin's inter-
pretation, saying, " My own observations have
confirmed this view, as well as every detail of
the rest of Darwin's account."1 The nega-
tive evidence was, by its very completeness, a
stumbling-block to Darwin's beliefs. As must
sooner or later be done with all instances of
negative evidence, he again set about replacing
it by positive evidence, which removed the
necessity of the belief which the negative evi-
dence destroyed. Until that was done the neg-
ative evidence increased rather than diminished
the mystery that needed solution.

1 H. Miiller, Fertilization of Flowers, pp. 535-538.

VI.

CLASSIFICATION.

T)ERFORMED consciously or unconsciously,
•*- the act of classification is indispensable
to and accompanies every scientific inference.
A mind is orderly or slovenly, according as it
does or does not habitually and accurately
classify the facts with which it comes in con-
tact. The success of an investigation, the
worth of a conclusion, are in direct proportion
to the fidelity to this principle and the exhaust -
iveness with which the process is carried out.

In nature, constant forces at work upon vary-
ing materials necessarily produce segregation;
the like are brought together, and the unlike
separated. The result is a literally "natural
classification." This simple result is rarely
realized. The forces at work are so numerous,
and have acted so long, that, especially with
reference to living things, Nature's serial clas-
sifications in space and time have been broken
up and thrown into confusion to such an extent
that they are seldom recognizable. The result

CLASSIFICATION. 89

is a superficial chaos of phenomena. The
recognition of natural classifications was an
excessively slow growth; they were finally
worked out by the slow collection of material
and successive attempts at a natural arrange-
ment. In nature's arrangement of living things
over the earth it has been very difficult to recog-
nize law, and at first it was possible only where
isolation has been long continued and the forces
at work upon living things have been few and
steady in their action. Even then the recog-
nition has required extensive travel and a power-
ful inclination to classify and recognize the
relations of distant facts to each other.

It was the recognition of several such arrange-
rrients or classifications in Nature that first led
Darwin to reflect on the Origin of Species.
What immortalized his observations is not the
simple fact that they were made, but that by
their cumulative presentation they led Darwin
to seek an adequate cause for these natural
arrangements.

After pointing out, in the narrative of his
voyage, the striking relation between the fossil
and the living animals of South America, he
said : " This wonderful relationship in the same
continent between the dead and the living will,
I do not doubt, hereafter throw more light on

go THE METHOD OF DARWIN.

the appearance of organic beings on our earth,
and their disappearance from it, than any other
class of facts."1 In passing southward over
the continent of South America, he recognized
another of Nature's classifications: he noticed
the frequent recurrence of the fact that a species
occupying a given region was replaced to the
southward by a closely related species, and this
serial arrangement impressed itself strongly
upon him. His visit to the Galapagos Islands
gave him an almost perfect example of sim-
plicity in the working of Nature's forces. The
conditions for one of Nature's classifications
were perfect. When Lawson, the Vice Gover-
nor, had declared to him that the tortoises from
the different islands differed from one another,
Darwin did not see the significance of the fact.
He mixed up his collections from the various
islands, and did not dream that there lay before
him one of the most remarkable facts that
Nature ever revealed to a naturalist. By some
happy accident he compared the many speci-
mens of mocking thrushes shot on Charles
Island with those from Albemarle Island, and
was astonished to find that they belonged to
different species. It was not the fact that
there were two species of mocking thrush liv-

1 Naturalist's Voyage around the World, p. 173.

CLASSIFICA TION. 9 1

ing together on the two islands, but that they
lived apart, each on its own island, and that
they were closely instead of distantly related,
— that several islands were stocked, each with
its own species, or perhaps variety, of the same
kind of animal, — that struck him with wonder.
These facts haunted him, and drove him to look
for others like them. Upon his arrival at home
his insect collection proved the same law. He
had fortunately kept the plants of the different
islands separate, and Hooker, at Darwin's re-
quest to see whether the law held good for them,
found it to be so.1 Darwin had unwittingly
carried one of Nature's beautiful classifications
home to England with him. Keen insight into
the relation of facts to one another had enabled
him to recognize three striking examples of
Nature's arrangements.

The habit of grouping facts to extract the
truth from them was indispensable to Darwin's
work, for he constantly dealt with large bodies
of facts that were manageable in no other way.
It will be seen how difficult it is even for a
powerful observer to see facts for which he is
not looking, even though they lie under his
feet. An act of classification, to be worth
much, must usually be an effort to answer

1 Naturalist's Voyage around the World, pp. 393-398.

92 THE METHOD OF DARWIN.

a direct question. Science has derived very
little or no benefit from the miscellaneous col-
lecting and grouping of facts without any pre-
vious notion of what they are likely to reveal.
An investigation is usually made for the pur-
pose of answering a definite question, or of
verifying an anticipation. With some such
end in view, with some principle by which the
classification is guided, the result usually re-
veals not only what was looked for, but fre-
quently still more fundamental characteristics ;
for it is impossible to throw facts into any
order which reveals one truth without dragging
others into the light with it. The character of
Darwin's work required constant recourse to
lists and tables; he appreciated fully both their
value and their treachery, and his great ability
to recognize all the points brought out, no mat-
ter whether he was looking for them or whether
they bore directly on the subject which he hap-
pened to be investigating or not, made them
enormously useful to him.

Darwin's original purpose in measuring the
heights of the gravel-capped plains of Patagonia
was to ascertain the heights at which recent
fossil shells occurred. These measurements
gave him all he sought, — a notion of the amount
of elevation in the recent period. On compar-

CLASS 'IFICA TTON. 93

ing his measurements with those of the Beagle
survey, he was struck with their uniformity.
He tabulated all the measurements represent-
ing the summit edges of the plains; and the
tabulation proved to him that the elevation of
the land had gone on at a remarkably equable
rate over a north and south distance of at least
five hundred miles.1 There is comparatively
little danger of throwing away effort in a well
directed classification. The danger lies in not
comprehending the vast significance of the
process both in actual investigation and in the
presentation of results, and in the lack of per-
sistent determination to exhaust its resources.
Darwin himself sometimes owed it to happy
accident that he did not overlook this powerful
instrument.

Guided by deduction to the probable relation
of the distribution of volcanoes to that of coral
islands, and to the distribution of fringing and
barrier reefs and atolls in relation to each other,
he spent months in mapping them from the
descriptions of voyagers, surveying vessels, etc.
From the classification of a vast chaotic mass
of facts scattered throughout geographic and
geological literature, he extracted some of the
most important conclusions of his whole work

1 Geological Observations, etc., p. 211.

94 THE METHOD OF DARWIN.

on coral islands.1 Time has shown that the
conclusions reached from this mapping of facts
is too general. The conclusions that volcanoes
are invariably absent from the areas which have
recently subsided or are still subsiding, and are
commonly present in areas that are rising or
have recently risen, that fringing reefs lie in
the areas of elevation and atolls in the areas
of subsidence, may not be accepted without im-
portant reservations. But whether time shall
ultimately substantiate or correct Darwin's con-
clusions, or shall even destroy some of them,
his classifications will always remain essential
to the study of coral islands.

1 Structure and Distribution of Coral Islands, p. 189.

VII.

ANALOGY.

A NALOGICAL reasoning plays a very im-
<L± portant part in all scientific work; and
Darwin frequently availed himself of its help
in making discoveries and establishing conclu-
sions. He used every logical device to estab-
lish and extend his theories, and there is no
lack of material from which to choose exam-
ples. But analogy, when used on a large scale,
proves so treacherous, that it is useful for the
most part only in giving clues to discoveries.
There are but few examples of analogical rea-
soning on a large scale in Darwin's works.
The most important, perhaps, is his work on
Insectivorous Plants.

It has already been told how, while resting
at Hartfield after years of labor on the Origin
of Species, he was struck by the number of
insects caught by the leaves of the common
sundew. It soon became evident to him that
" Droseraw&s excellently adapted for the special
purpose of catching insects, so that the subject

96 THE METHOD OF DARWIN.

seemed well worthy of investigation."1 As
soon as he began to work on Drosera, and was
led to believe that the leaves absorbed nutri-
tious matter from the insects, he began to
reason by analogy from the well understood
digestive capacity of animals. One needs but
to imagine an attempt to do the work without
any knowledge of animal digestion to under-
stand at once its impossibility under such con-
ditions. By connecting his observations with
the well known animal processes he proceeded
on a course of rapid discovery that must other-
wise have remained entirely closed to him. At
almost every step he drew suggestions from
and checked his results by reference to animal
digestion. He made preliminary "crucial"
experiments by immersing some leaves of
Drosera in nitrogenous and others in non-
nitrogenous fluids of the same density to deter-
mine positively whether the former affected
the leaves differently from the latter.2 The
discovery that Drosera detects "with almost
unerring certainty the presence of nitrogen "
in various fluids "led me to inquire," he said,
''whether Drosera possessed the power of dis-
solving solid animal matter; the experiments
proving that the leaves are capable of true

J Insectivorous Plants, p. 2. 2 Ibid., p. 76.

ANALOGY. 97

digestion, and that the glands absorb the
digested matter."1 "These are, perhaps, the
most interesting of all my observations on
Drosera, as no such power was before distinctly
known to exist in the vegetable kingdom."
Having by analogy established the power of
true digestion in plants, analogy led him to
seek in plants the elements that do the work
of digestion in animals. Bringing together
what was known of plants, he pointed out that
the juices of many plants contain an acid, and
so one element of a digestive fluid was at hand;
and that all plants possess the power of dis-
solving albuminous or proteid substances, pro-
toplasm, chlorophyll, etc., and that "this must
be effected by a solvent, probably consisting
of a ferment together with an acid."2 After
writing the last quoted sentence he learned
that a ferment which converted albuminous sub-
stances into true peptones had been extracted
from the seeds of the vetch.

Sachs mentioned the discovery of the fer-
ment, recorded the fact that peptones had
themselves been actually found in the seeds of
the lupine, and added "as we come to know
the proteinaceous reserve materials of plants
better, and if we follow their behavior in the

1 Insectivorous Plants, p. 268. 2 Ibid., p. 362.

7

98 THE METHOD OF DARWIN.

animal body also, it can scarcely be doubtful
that, in spite of incomplete knowledge, the
assumption is nevertheless warranted that pep-
tonizing ferments are perhaps universally dis-
tributed in plants."1 "Attention was first
drawn to the occurrence of peptonizing fer-
ments in the vegetable kingdom by the re-
markable phenomena observed in the so called
insectivorous plants." By analogical reasoning
a whole new field of study was opened ; a new
view of the powers of plants was gained, and a
much closer analogy between plant and animal
functions was established. But if recent studies
are taken into account, the question may be
raised whether this stupendous analogical struc-
ture has not been undermined. Tischutkin
contends that the "digestion" of insectivorous
plants is not accomplished in the same way as
in animals, but is due to bacteria; that the
pepsin of the leaves is not a secretion of the
plant, but a by-product of the activity of the
bacteria.2 He proves that bacteria capable of
dissolving egg albumen are always present in
the secretion of the leaves; that they come
principally from the air, that the plant only
furnishes a medium for them to live in, that

1 Sachs, Physiology of Plants, p. 344.

2 Berichte der Deutschen Botanischen Gesellschaft, 1889.

ANALOGY. 99

disintegration of albuminous substances begins
only after enough micro-organisms are devel-
oped to do the work, and that the plant simply
assimilates what these lower organisms have
set free. The relation between the insectiv-
orous plants and the bacteria is one of genuine
symbiosis.

If the whole of Tischutkin's contention is
true, the great body of facts brought out by
Darwin must still be placed to the credit of
analogical reasoning. The facts concerning
plant and animal digestion would still remain
parallel, both in the succession of the phenom-
ena and in the results. It would be another
illustration of the vast importance of analogy
in scientific method, and of the fact that every
analogy, the strongest as well as the faintest,
will sooner or later fail.

In another instance, analogical reasoning
from animals to plants actually deterred him
from discovering the truth to which other logi-
cal processes might have led him. He states
the case so clearly himself that it will almost
suffice to quote him.1 "The adaptation of
flowers for cross-fertilization is a subject
which has interested me for the last thirty-
seven years. . . . From my own observations
1 Effects of Cross- and Self-Fertilization, pp. 6-8.

100 THE METHOD OF DARWIN.

on plants, guided, to a certain extent, by the
experience of breeders of animals, I became
convinced many years ago that it is a general
law of nature that flowers are adapted to be
crossed, at least occasionally, by pollen from
a distinct plant." It was a direct deduction
from his theory of natural selection that, since
they are adapted for cross-fertilization, cross-
fertilization must be advantageous to them.
Hence it was perfectly natural that he should
like to verify it. "It often occurred to me,"
he said, "that it would be advisable to try
whether seedlings from cross-fertilized flowers
were in any way superior to those from self-
fertilized flowers. But as no instance was
known with animals of any evil appearing in
a single generation from the closest possible
interbreeding, that is, between brothers and
sisters, I thought that the same rule would
hold good with plants, and that it would be
necessary, at the sacrifice of too much time, to
self-fertilize and intercross plants during sev-
eral successive generations, in order to arrive
at any results. I ought to have reflected that
such elaborate provisions favoring cross-fertili-
zation as we see in innumerable plants would
not have been acquired for the sake of a dis-
tant and slight advantage, or of avoiding a

ANALOGY. 10 1

distant and slight evil. Moreover, the fertili-
zation of a flower by its own pollen corresponds
to a closer form of interbreeding than is pos-
sible with ordinary bisexual animals; so that
an earlier result might have been expected."

He had carried the deduction far enough to
warrant an effort to verify it, but was deterred
by analogical reasoning from pursuing the
matter further. Had he clung to his general
theory and the special facts to be explained
under it, he would, as he said himself, have
reached an early result. The analogy, if it
had served a good purpose, ought to have led
him to reason that since continuous interbreed-
ing is harmful among animals, although there
are no special adaptations to prevent it, or to-
encourage the opposite, then, surely, the harm-
ful effects of close breeding and the benefits of
cross-fertilization ought to be very marked in
plants, with their striking adaptation for cross-
fertilization. The analogy had clearly led him
astray ; and he was finally brought back to the
subject by a different route.

" I was at last led to make the experiments
recorded in the present volume from the follow-
ing circumstance. For the sake of determin-
ing certain points with respect to inheritance,
and without any thought of the effects of close

102 THE METHOD OF DARWIN.

interbreeding, I raised, close together, two
large beds of self -fertilized and crossed seed-
lings from the same plant of Linaria vulgaris
(common Toad Flax). To my surprise, the
crossed plants, when fully grown, were plainly
taller and more vigorous than the self-fertilized
ones.

"Bees incessantly visit the flowers of this
Linaria, and carry pollen from one to the
other; and if the insects are excluded the
flowers produce extremely few seeds, so that
the wild plants from which my seedlings were
raised must have been intercrossed during all
previous generations. It seems therefore quite
incredible that the difference between the two
beds of seedlings could have been due to a
single act of self-fertilization; and I attributed
the result to the self-fertilized seeds not hav-
ing been well ripened, improbable as it was
that all should have been in this state, or to
some other accidental and inexplicable cause."
During the next season he raised two beds of
carnations (Dianthus caryophyllus) in the same
way and for the same purpose; the preceding
generations in this case also must have been
continuously cross-fertilized; again "the self-
fertilized seedlings were plainly inferior in
height and vigor to the crossed."

ANALOGY. IO3

" My attention, " he said, " was now thoroughly
aroused, for I could hardly doubt that the dif-
ference between the two beds was due to the
one being the offspring of crossed and the other
of self-fertilized flowers." After the effects
of cross- and self-fertilization had been thus
thrust upon him, he proceeded to make the
exhaustive examination that ran through many
years, and finally filled a volume. He foresaw
the meaning of the adaptations for cross-fer-
tilization and the character of the results, but
was deterred by a false analogy from making
the observations to which a careful study of the
facts by themselves would have infallibly led
him; and was finally driven to the subject
again by the empirical observation of the facts
that he had anticipated by reasoning. It may
seem strange that the very consequences which
theory led him to expect had to be twice forced
upon the attention of one who was so quick to
seize Nature's suggestions, before he could be
brought to investigate them. But the strange-
ness of such an intellectual phenomenon is all
due to the afterthought. Even in the sciences
that are most rigidly deductive it is a common
thing for the investigator to stumble indirectly
upon results which he might have foreseen or
often did more or less perfectly foresee.

104 THE METHOD OF DARWIN.

In a more complex case, analogy led to a con-
clusion which, although it could not be verified,
possesses great importance in relation to one of
the principal difficulties in the way of the gen-
eral theory of natural selection. In the course
of the investigation on " Different Forms of
Flowers on Plants of the same Species," he
noticed the striking parallelism between the
phenomena of hybridism and those of the
heterostyled plants which he was studying.1
When once the parallelism was established,
the remarkable and puzzling facts of hybridism
doubtless furnished a solid analogical basis
from which to foresee and scrutinize the results
of crossing the different forms of heterostyled
plants.

Difficulty in uniting two forms and sterility
of their offspring had been almost universal-ly
regarded as a test of specific distinctness.
Darwin showed clearly that this belief, al-
though very generally true, is by no means
universally so; and his work on heterostyled
plants showed that all the phenomena of hy-
bridism were displayed among forms that
certainly belonged to the same species. He
triumphantly overthrew the doctrine that

1 Different Forms of Flowers on Plants of the same
Species, pp. 242, 243.

ANALOGY. 105

mutual sterility is a mark of specific distinct-
ness. But Huxley, in his essay on the "Com-
ing of Age of the ' Origin of Species,' " said:
" In my earliest criticisms of the ' Origin' I
ventured to point out that its logical founda-
tion was insecure so long as experiments in
selective breeding had not produced varieties
which were more or less infertile; and that
insecurity remains up to the present time."1
Such was the serious nature of the facts of
hybridism which needed explanation. And it
was the close parallelism between hybridism
and heterostylism that led Darwin to seek in
the latter an explanation of the difficulties pre-
sented by the former. From the study of the
illegitimate offspring of heterostyled plants he
drew the conclusion that the sterility is due,
not to structural differences, but to functional
differences between the sexual elements; and
that it is not due directly to natural selection,
but is an incidental result accompanying the
adaptation of the sexual elements of the dif-
ferent forms of plants of the same species to
fertilize each other. By inverting the analogy
he transferred the conclusion to the facts of
hybridism. He said that it was this consider-
ation, that the sterility of species when first

1 Life and Letters, Vol. I. p. 551.

106 THE METHOD OF DARWIN.

crossed, and of their hybrid offspring, is due
to functional differences of the sexual elements,
and not to structural differences between the
species, that led him to make the many experi-
ments on the illegitimate offspring of hetero-
styled plants, and that made the results worthy
of publication. The great strength of the
analogy in his mind was doubtless due to the
fact that the parallelism was so very close as to
force the conclusion that the two sets of results,
one within a species, the other between species,
are due to the same cause.

VIII.

INDUCTION.

A T 7HEN Darwin had once grasped the idea
* * of the descent of species, and natural
selection as the cause determining modifica-
tion, it was inevitable that he should look upon
all classes of biological facts as consequences
of these. Accordingly, nearly all the investi-
gations which he carried on were pursued as
deductions from his general principles. But
although the larger outlines and a large part
of the details of his work were deductive, he
was frequently obliged to pass by induction
from facts to the subordinate principles which
he established

One of the earliest of the many instances in
which he felt compelled to re-interpret whole
groups of facts was that relating to human ex-
pression. When, in 1838, he read Sir Charles
Bell's great work on the "Anatomy of Expres-
sion," the view of the latter that man had been
created with certain muscles especially adapted
for the expression of his feelings struck him

108 THE METHOD OF DARWIN.

as unsatisfactory. As a deduction from his
general theory, he believed that the habit of
expressing our feelings by certain movements
had been somehow gradually acquired. This
view required that the whole subject of expres-
sion should be studied under a new aspect, and
each expression be given a rational explana-
tion.1 This led him to undertake his work on
the " Expression of the Emotions in Man and
the Lower Animals." Deduction pointed out
that expression must fall under the general
explanation; but it was impossible to foresee
the principles which governed the develop-
ment of the various expressions. From 1838
to 1872 he toiled away at the mass of complex
facts, and slowly overcame the difficulty of
bringing the different expressions together
under one or a few points of view. At last' he
was able to educe three principles of expres-
sion, which seemed to him to account for most
of the expressions and gestures involuntarily
used by man and animals under the influence
of various emotions and sensations. These
principles he arrived at, as he himself says,
only at the close of his observations.2 They

1 Expression of the Emotions in Man and the Lower
Animals, p. 19.

2 Ibid., p. 27.

INDUCTION. IC>9

are: (i) the principle of serviceable asso-
ciated habits; (2) the principle of antithesis;
(3) the principle of actions due to the constitu-
tion of the nervous system, independently from
the first of the will, and independently to a
certain extent of habit. It is to be remarked
of these three principles that they are induc-
tions, and that they are vague on two accounts:
they are in part so general that it might prove
difficult to bring them to a crucial test with
the hope of proving or disproving them; and
the only test to which they have been put is
that of explaining the very facts from which
they were drawn. They have not been used to
make further discoveries; they represent well
the type of inductions based on many carefully
studied facts, but unsupported by a subsequent
deductive research.

A simpler case of induction is his inference
concerning the age at which characters appear
which are inherited by one or both sexes. " It
is in itself probable," he said, "that any char-
acter appearing at an early age would tend to
be inherited equally by both sexes, for the
sexes do not differ much in constitution, before
the power of reproduction is gained"; and
went on to point out that characters appearing
late in one sex would tend to be restricted to

110 THE METHOD OF DARWIN.

that sex. " I was led to infer that a relation of
this kind exists from the fact that whenever
and in whatever manner the adult male has
come to differ from the adult female, he differs
in the same manner from the young of both
sexes." 1

The principle that characters appearing at an
early age are inherited by both sexes, and char-
acters appearing late in one sex are restricted
to that sex, is an induction from certain strik-
ing differences between the adult males and
females, and between the adult male and the
young of both sexes in many species. By
itself, without verification or other deductive
bracing, it would have been an interesting gen-
eralization. But Darwin sought to strengthen
it both by observing whether it held true in
particular cases, and by deducing it from more
general laws. In the first of the two quotations
given above, he pointed out the probability
that the truth of the principle depends on the
known changes that take place in the constitu-
tion of the sexes on approaching maturity. It
occurred to him to put the principle to a crucial
test, and to rely on the result. Thereupon fol-
lowed the investigation on the deer family,
described elsewhere in more detail.

1 Descent cf Man, etc., p. 276.

INDUCTION. Ill

Inductions are easily made; the test of a
good investigator, however, is not the number
of inductions he makes, but his subsequent
treatment of them. In his study of the amount
of material brought to the surface of the ground
by earthworms, Darwin noticed that the sur-
faces of old worm-castings were often studded
with coarse particles; and was thence led to
infer that a good deal of the finest part of
worm-castings was washed away by the rain.
Such an induction is so nearly self-evident that
it would seem superfluous to verify it. Darwin
.thought otherwise; he mixed fine precipitated
chalk with the castings, or gently stuck it on
to them ; the rain washed it away and proved
him correct. By this little induction, and a
verification almost childish in its simplicity
and apparent insignificance, he was able to show
that the amount of material brought to the
surface by earthworms is much greater than at
first appears.1 It is probably safe to say that
the majority even of investigators would have
regarded the induction sufficient unto itself,
and would not have hesitated to use it without
verification as evidence in proof of their views.
We here get a glimpse of how sharply Darwin
caught the significance of the minutest indica-

1 The Formation of Vegetable Mould, etc., p. 272.

112 THE METHOD OF DARWIN.

tions, and of the patience with which he made
experiments to prove things which to others
would seem so simple and self-evident as to
need no proof. Like his great contemporary,
Faraday, he " could trust a fact, and always
cross-examined an assertion." It was his con-
scientious verification of even his smallest
inductions that gave the scientific world its
great confidence in his work.

Darwin's greatest induction has yet to be con-
sidered, and will be discussed at some length ;
because, as well as being his greatest induc-
tion, it is his most notable speculative failure,
and will give an opportunity to study the char-
acteristics of false and true hypotheses. The
problem of inheritance, the transmission of
qualities from parent to offspring, had weighed
upon him during all the years of his work on
the theories of descent and natural selection.
Almost at the very start we find him making
experiments on beds of self- and cross-fertilized
plants to determine questions of inheritance.
These experiments possess their greatest inter-
est, not from having furnished any important
data for the solution of the problem of inherit-
ance, but from having finally impressed him
with the importance of cross-fertilization in
the plant kingdom. They show how early he

INDUCTION. 113

appreciated the connection between inheritance
and his general theories, and tried to get an
experimental basis for inference.

Darwin, as he himself confessed, had to make
a theory on every subject, and the intimate
relation between inheritance and his other
theories led him irresistibly to form a theory
on inheritance. Like Newton, he established
the best of theories, and, like him, "was also
capable of proposing one of the worst." He
finally published the hypothesis under the
title uPangenesis," in Volume II. of "Varia-
tion of Animals and Plants under Domestica-
tion." 1 The reason he gave for forming it was
to bring the vast number of perplexing facts of
inheritance together under a single intelligible
point of view. To do this he assumed the
existence of minute bodies called gemmules,
which are cast off by all the living cells of the
animal or plant body at all stages of its exist-
ence, and which multiply by division, have the
power of remaining dormant through an in-
definite number of generations, possess certain
remarkable affinities, etc. They were sup-
posed to collect in the reproductive elements,
and determine the character of the offspring.
Darwin endeavored to make the assumption

i Pages 349-399-
8

114 THE METHOD OF DARWIN.

reasonable by pointing out analogies between
the gemmules and the reproductive elements,
between their affinities and those of pollen,
etc. ; and rebutted the objection of excessive
minuteness by a comparison with molecules.
Doubtless the gemmules were a development
of the idea of reproductive elements, or blood-
corpuscles, or both ; and their peculiar origin,
powers, and hypothetical history were deter-
mined by the various facts that had to be
explained. It was a clear case of pure induc-
tion, untainted by any direct or indirect evi-
dence of the existence of the gemmules, or any
glimpse of the process by which characters are
transmitted. Darwin knew how speculative
the hypothesis was, and justified it because it
brought all the facts of inheritance together
under one point of view.

In his discussion of it he first stated the
facts to be brought together, and then the
hypothesis with a working explanation of it,
and finally tried to show, by reasoning deduc-
tively from the hypothesis to the facts in which
it had originated, that it explained them.

Usually during the effort to reach a cause by
the road of induction the cause itself is caught
sight of, either directly or indirectly, and it is
then possible to formulate at once at least a

INDUCTION: 115

provisional hypothesis. In the case of Pan-
genesis this was not true. Darwin gave the
following as the principal reasons for believing
in natural selection : " (i) It is a true or recog-
nized cause; (2) from the analogy of change
under domestication by man's selection, and
(3) chiefly from this view connecting under an
intelligible point of view a host of facts." To
this may be added a fourth, which he men-
tioned to Huxley in connection with the third,
as being the reasons why younger scientists
would choose his theories rather than the doc-
trine of creation; namely, that it would enable
them to search out new lines of investigation.

Let Pangenesis be tried by these four tests.
In the first place, it was not even claimed that
there was any proof, either direct or indirect,
of the existence of the gemmules. As a cause
which had been actually observed, they had no
existence. Secondly, while analogy is often a
strong collateral argument, and was so in the
case of natural selection, it was a treacherous
support in the case of Pangenesis. Perhaps as
many analogies were violated, as was pointed
out by Delpino and others, by the conception
of the gemmules as it could muster to its sup-
port; and one of the first essentials of an
argument from analogy is that the points of

Il6 THE METHOD OF DARWIN.

similarity shall be more numerous than the
points of difference. The third and chief
reason which Darwin gave for belief in natural
selection, that it connected under an intel-
ligible point of view a host of facts, is identi-
cal with the reason which he gave for forming
and so tenaciously clinging to the hypothesis
of Pangenesis. And this condition the latter
fulfilled. It was bound to do so by the very
terms of its origin. A hypothesis was not
likely to leave Darwin's hands until it did
harmonize with the facts from which it had
taken its rise.

The fourth reason for belief in a theory,
namely, that it leads deductively to new inves-
tigations, and through them to new facts, brings
up the hypothesis of Pangenesis against a wall.
A cause may be recognized as a working force";
its claim to having produced known effects may
be supported by analogy; and a vast body of
phenomena that must be effects of some cause
may be brought together into harmony under
it. But it must also be possible to work out
other consequences of the theory.

Francis Galton made a determined effort to
test the hypothesis. He felt the pressing
importance of doing so, for, as he said, "Its
postulates are hypothetical and large, so that

INDUCTION. II/

few naturalists seem willing to grant them."1
He reasoned that, if the gemmules or bearers of
inheritable qualities existed in such enormous
numbers in the body, they must be borne from
place to place and to the reproductive organs
by the blood. If this were true, then by inject-
ing blood from one variety of rabbit into the
blood-system of rabbits of another variety, the
gemmules introduced with the foreign blood
would pass with those proper to the animal
itself into the repVoductive elements, and
would modify the character of the offspring.
He foresaw the practical importance of such a
result. Slight dashes of blood could be intro-
duced by breeders to modify a variety; for
example, greyhounds could have a little of the
bull-dog instilled into them. At the end of
his investigation he said, " I have now made
experiments of transfusion and cross-circulation
on a large scale in rabbits, and have arrived
at definite results, negativing, in my opinion,
beyond all doubt, the truth of the doctrine of
Pangenesis." Thus ended the only effort ever
made to test the hypothesis deductively by
reasoning out its consequences and trying to
establish them by experiment.

1 Proceedings of the Royal Society, 1871, Vol XIX. p. 394
et seq.

Il8 THE METHOD OF DARWIN.

It would seem as if Galton's experiments had
proved the hypothesis false. Darwin, how-
ever, met the criticism, and slipped away from
the results by admitting that he would have
expected gemmules in the blood; but showed
that their presence there was no necessary part
of his hypothesis, because the latter applied
to the lower animals and to plants, which do
not have blood.1 Darwin's modest defence of
his hypothesis swept away not only Galton's
experiments, but the possibility of proving or
disproving it. Lionel Beale remarked, sarcas-
tically, that it might still be possible to test it
by cutting out a mass of an animal's flesh, and
grafting in its place a piece from an animal of
another variety.2 Darwin's rejoinder to Galton
was sound from the former's point of view.
But the hypothesis was incapable of definite
proof or disproof. There was no set of facts
left that could be appealed to as a test. A
good induction will not only be in harmony
with and bring under one point of view a host
of facts, but is likely to be supported by one or
more of the following lines of proof: (i) inde-
pendent direct evidence of the existence of the
cause involved in the induction ; (2) strong and

1 Nature, April 27, 1871, Vol. III. p. 502.

2 Nature, May u, 1871, Vol. IV. p. 25.

INDUCTION. 119

independent analogies; (3) the possibility of
deducing consequences from the hypothesis,
and verifying them by observation or experi-
ment; (4) the possibility of deducing the cause
or principle as an effect of another still more
general.

Huxley advised Darwin not to publish his
doctrine of Pangenesis ; but he nevertheless did
publish it, and gave as his reason the pressing
importance of co-ordinating the inexplicable
facts of inheritance. Other hypotheses have
followed Darwin's with as little success. Dar-
win did not formulate his hypothesis to support
his other theories, but its character was at least
in part determined by the latter. It is interest-
ing to note that the latest hypothesis of inherit-
ance, the most aggressive that has yet arisen,
has been developed as a special support for the
belief that natural selection acting upon con-
genital variations is the sole cause in the pro-
duction of species, and that acquired characters
are not inherited. The principal evidence on
which the hypothesis relies for support, apart
from the refutation of the direct evidence ad-
duced to support the belief in the inheritance
of acquired characters, are the karyokinetic
processes in cell division, and the early stage
in development at which, in some animals, the

120 THE METHOD OF DARWIN.

reproductive elements become distinct from the
parts which develop into the other organs of
the body. In this respect Weissmann's hypoth-
esis has an additional logical support. It has
provoked earnest discussion, and naturalists
have taken sides on the subject. Although
the germ plasm is itself an assumption, and
the hypothesis owes its existence to the known
facts of karyokinesis, it has led to further
investigations in some directions with fruitful
results. Darwin's hypothesis opened the ques-
tion under the new light that he had shed upon
nature, and the more recent hypotheses, like
his own, owe their existence to the " impelling
force " of his general theories of descent and
natural selection.

IX.

DEDUCTION. -EXPLANATION OF KNOWN FACTS.

—IMPORTANCE OF THEORY TO GOOD

OBSERVATION.

DARWIN fell upon the true cause of the
modification of species so early, that the
greater number of his special investigations
took on a deductive cast.1 His reflections upon
the known facts and principles of biology took
the form of efforts to explain them as deduc-
tions from his theory; and many of his new
discoveries were foreseen as consequences of
it. Hence the inductive process does not play
so important a part in his work as does the
inverse process of deduction.

It will not be necessary to dwell long upon
his success in giving the proper theoretical ex-
planations to already known facts and empirical
laws. It had required centuries of painstaking
research and numberless efforts at classification
before anything like a natural classification was

1 See the Chapter on the Logical History of the Principle
of Natural Selection,/^/, p. 212.

122 THE METHOD OF DARWIN.

reached. When, at the beginning of this cen-
tury, it was finally approached, and the natural
affinities of plants and animals were brought
out by it, the doctrine of descent was inevitable;
and it came. When Darwin had once become
impressed with its truth, and had found the
cause of modification, it was first of all neces-
sary to show that the great bodies of known
facts harmonized with his doctrines. The facts
of distribution, palaeontology, embryology, rudi-
mentary organs, etc., were all reduced. Each set
of facts presented its own difficulties.

Up to the present century it was regarded as
an axiom in taxonomy that the structures of
most importance to the animals possessing
them must be of most importance for the pur-
poses of classification. It is worth while to
note that this was accepted as self-evident, as
being beyond the necessity of proof. Systema-
tists were approaching the "natural arrange-
ment," and De Candolle discovered empirically
the rule that there is usually an inverse ra-
tio between the taxonomic and the functional
value of a structure ; but he could suggest no
reason for the paradox. Darwin's theory fur-
nished the philosophical explanation.1 The

1 Origin of Species, pp. 362-373. Romanes, Darwin and
After Darwin, pp. 34-37-

DEDUCTION. 123

organs of the highest functional value are
under the constant and pressing necessity of
changing with changes in the environment;
while those of least functional value remain
undisturbed, and pass, little or not at all modi-
fied, from generation to generation. The same
explanation holds for the rule concerning the
importance of "aggregates of unimportant char-
acters " in determining the affinities of animals
and plants.

In some parts of the natural system, there
are what are called "chains of affinities." A
group, instead of being broken up into well
separated sub-groups, consists of a chain in
which the adjacent parts are closely related,
but the more distant parts have comparatively
few points in common. It is impossible to
break up the group without violating the affini-
ties of adjacent parts, and it is difficult to define
it in such a way as to include the extremes.
The Crustacea furnish an example. What was
a special difficulty under the old views of clas-
sification is explained under the doctrine of
descent.1

One of the most important principles that
had been established empirically was the tree-
like arrangement of species and higher groups

1 Origin of Species, p. 368.

124 THE METHOD OF DARWIN.

in the natural classification. The recognition
of the principle came only after centuries of
efforts at classification; and after it was dis-
covered, no reason could be given for it. Al-
though so helpful and striking, it remained a
profound enigma, for there was nothing in the
nature of the things classified that required this
peculiarly complex arrangement rather than one
of several conceivable simpler ones. Darwin's
explanation of this principle under his theory
illustrates not only the explanation of empirical
laws, but the difficulty of doing what, after it
is done, seems very simple.

It was not until after he had been at work
upon the principle of natural selection for
many years, that the true explanation of this
law under his principle occurred to him. He
said, " I suppose I must be a very slow thinker,
for you would be surprised at the number of
years it took me to see clearly what some of
the problems were which had to be solved;
such as the necessity of the principle of diver-
gence of character, the extinction of inter-
mediate varieties, on a continuous area, with
graduated conditions," etc.1 After describing
his earlier sketches of his theory he said, "At
that time I overlooked one problem of great im-

1 Life and Letters, Vol. I. pp. 68, 524.

DEDUCTION. 125

portance, , . . the tendency in organic beings
descended from the same stock to diverge in
character as they become modified." That they
have thus diverged was proved by their arrange-
ment into groups within groups. "I can re-
member," he went on, "the very spot in the
road, whilst in my carriage, when to my joy
the solution occurred to me; and this was long
after I had come to Down." 1 The solution was
this, — "that the modified offspring of all
dominant and increasing forms tend to become
adapted to many and highly diversified places
in the economy of nature."

It seems very simple now to understand that
the tree-like arrangement of species must be
regarded as a direct consequence of the prin-
ciple of natural selection. It might even seem
easy to infer the tree-like arrangement as a de-
duction from the principle, and to discover it, if
it had not already been discovered empirically.
It is not because Darwin was so slow a thinker
that it took him so long to discover the relation
of cause and effect between natural selection
and the tree-like arrangement of species; but
it was because he was a strong and persistent
thinker that he discovered it at all. The think-
ing out of such connections is always a slow

1 Life and Letters, Vol. I. pp. 68-70.

126 THE METHOD OF DARWIN.

process. The final mental act may come like
a flash, as it did in Darwin's case, and be fol-
lowed by a very rapid and fruitful explanation of
details ; but such triumphs do not come to the
mind that will not serve the apprenticeship.1

It has been often declared that the work of
biologists since 1860 has consisted in explain-
ing known facts as deductions from Darwin's
theories, and further investigating the conse-
quences of those theories. The more exten-
sively a theory has been successfully applied,
the more easy it is to do what still remains to
be done. There is profound philosophy in the
saying, "To him that hath shall be given." It
was a comparatively easy matter to apply Dar-
win's theories to all sorts of facts and lines of
investigation after he had so thoroughly tested
and illustrated them ; but even then the scien-
tific world was very long in working out some
of their striking consequences. It is not to be
wondered at that Darwin was slow to under-
stand many things, or that he overlooked others
entirely. It is rather to be wondered at that
he accomplished so much single-handed. One

1 My friend, Prof. G. C. Price, has called my attention to
the fact that Lincoln was marvellously like Darwin in many
respects. The former was noted for his efforts to reach funda-
mental principles in thinking, and was also noted for the
" slowness " of his mental action.

OF THE

EXPLANATION OF KNOWN

of the hardest and most important lessons for
the majority of investigators to learn is that
the chances are all against their exhausting
their subjects, or even putting them into such
shape that the work will not all have to be
done over again, unless their work is done
slowly and continued persistently through long
periods of time.

Darwin's great logical power was fortified by
another rare quality of mind, — unusual acute-
ness in observing all collateral facts that came
out in his observations or experiments, whether
they seemed to bear directly upon the subject
of investigation or not. He was thus put in
possession of many facts that afterwards proved
valuable in ways that he could not foresee.
But with all his ability in these directions he
experienced difficulty in grasping the full
significance of facts.

In discussing Cleistogene flowers, near the
end of his work on the " Effects of Cross- and
Self-Fertilization," 1 after giving the reasons for
the belief he is about to express, he said, "I
must believe that plants now bearing small and
inconspicuous flowers profit by their still re-
maining open, so as to be occasionally inter-
crossed by insects. It has been one of the

1 Page 387.

128 THE METHOD OF DARWIN.

greatest oversights of my work that I did not
experimentize on such flowers, owing to the
difficulty of fertilizing them and to my not
having seen the importance of the subject."

Although it is clear that the possession of a
theory is no guaranty that all its consequences
will be foreseen, or, if foreseen, observed, or
even that, if they are both deductively foreseen
and empirically observed, they will be brought
into connection with the theory; nevertheless,
the importance of theory for accurate observa-
tion cannot be overestimated. However cau-
tious Darwin was about committing himself
unreservedly to a hypothesis, he never really
dispensed with one if he could find one.
Though he subdued his tendency to speculation
in the interest of observation, he did not dis-
pense with at least provisional hypotheses, even
in accumulating his facts. He felt the want
when he could not find one, and made it his
first task to establish some degree of probability
in favor of one.

One of his early experiences is a good illus-
tration of how even trained observers could not,
without the help of a theory, observe phenom-
ena on which they actually walked, and which
obstructed their progress.1 He has said, "I

1 Life and Letters, Vol. I. pp. 48, 49.

IMPORTANCE OF THEORY. I2Q

had a striking instance of how easy it is to
overlook phenomena, however conspicuous, be-
fore they have been observed by any one. We
spent many hours at Cwm Idwal, examining
the rocks with extreme care, as Sedgwick was
anxious to find fossils in them, but neither of
us saw a trace of the wonderful glacial phe-
nomena all around us; we did not notice the
plainly scored rocks, the perched boulders, the
lateral and terminal moraines, yet these phe-
nomena are so conspicuous that, as I declared
in a paper published many years afterwards in
the Philosophical Magazine (1842), a house
burnt down by fire did not tell its story more
plainly than did this valley. If it had been
filled with a glacier, the phenomena would have
been less distinct than they now are."

It may seem strange that two men, one already
a famous geologist and the other soon to be-
come one, should have overlooked such evi-
dence, which has since become so interesting,
so widely known, and so well understood. The
secret of their failure is that they were not
looking for it. It is usually the things that
men look for that they see; and to look for
things as yet unseen requires a theory as a
headlight. Even if they had noticed the mate-
rial of the moraines, the perched boulders, and
9

130 THE METHOD OF DARWIN.

the parallel scratches, they would certainly not
have been deeply impressed by them, because
they become impressive only when their rela-
tion to one another is understood, and this
could only be when the glacial theory had
been imported from a glacier country.

The importance of the discovery of the theory
of natural selection to the work of Darwin's life
will be dwelt upon later. A sigh of relief is
embodied in the declaration, " Here, then, I
had at last got a theory by which to work."1
Facts cannot be seen without some notion of
the relation they will bear to each other when
they are found. The stupendous importance
of theory for observation is illustrated by the
effect of Darwin's theories on biological inves-
tigation in all its phases. Huxley put it thus :
"The ' Origin' provided us with the working
hypothesis we sought."2 The whole biological
world was waiting for it; and when it came it
carried the biological sciences into the deduc-
tive stage, and opened an era of investigation
unprecedented in the rapidity with which dis-
covery advanced, and in the accuracy of the
results reached.

There are scattered throughout Darwin's

1 Life and Letters, Vol. I. p. 68.

2 Ibid., p. 551.

IMPORTANCE OF THEORY, 131

works numerous illustrations of the importance
of theory in the investigation even of matters
of detail. Writing of the trimorphic Lythrum
salicaria, he said, "The existence of the three
forms was first observed by Vaucher, and sub-
sequently by Wirtgen ; but these botanists, not
being guided by any theory or even suspicion
of their functional differences, did not perceive
some of the most curious points of difference
in their structure."1 MM. Boitard and Corbie,
in their study of pigeons, had seen and recorded
many facts which they could not use, simply
from lack of a theory. They had stated that
when they crossed certain breeds of pigeons,
birds colored like the Columba livia, or the
common dove-cot, were almost invariably pro-
duced.2 Darwin gave significance to these facts
and many others by the theory of descent.

In spite of his unusual power of seeing facts
apparently unconnected with the subject under
investigation, and his persistent habit of record-
ing results, whatever they might be, Darwin
himself, sometimes " not foreseeing the result,
did not keep a memorandum of all the facts,"
which would afterwards have proved useful.

1 Different Forms of Flowers on Plants of the same
Species, p. 138.

2 Variation of Animals and Plants under Domestication,
Vol. II. p. 14.

1 3 2 THE ME THOD OF DAR WIN.

No one was more thoroughly convinced of the
necessity of clear-cut theory for accurate obser-
vation; and he frequently expressed himself to
that effect. His son says of him, "He often
said that no one could be a good observer unless
he was an active theorizer. " 1 He said him-
self, " I am a firm believer that without specula-
tion there is no good and original observation." 2
" It is an old and firm conviction of mine that
the naturalists who accumulate facts and make
many partial generalizations are the real bene-
factors of science. Those who merely accumu-
late facts I cannot very much respect." 3

1 Life and Letters, Vol. I. p. 126.

2 Ibid., p. 465.

8 Ibid., Vol. II. p. 21.

X.

DEDUCTION. — ANTICIPATION.

A VERY few negative instances have been
•**• given to show the importance of theory
for accurate observation. They illustrate how
the absence of theory led to the oversight or
neglect of facts which later, under the sway
of theory, have become important. Darwin's
works are full of instances in which he was led
by his theory to anticipate the facts of nature.
It was inevitable that, having so early dis-
covered the theories which covered the whole
territory in which he worked, he should be
guided by them in the search for facts, and
that his work should thenceforth be deductive
in its character. Examples of this character-
istic method range from the great deductions
which led to nearly all his important special
investigations, and which illustrate the sweep-
ing consequences of his general theories, to the
little deductive details which show how swift
and accurate his prevision became even in the
matter of minute consequences of these theories.

134 THE METHOD OF DARWIN.

The minor instances will be given first, and
will be followed by the more general ones.
Then will follow deductions which he made,
but which are still unverified, or have been
verified by others; and lastly will be given
some of the instances in which he went clearly
wrong in his deductions.

The instance about to be given may well be
placed first, for the purpose of raising a mooted
question in logic. Mill took the position that
typically the process of inference consists in
reasoning directly from one particular case to
another; whereas the older and more generally
accepted view is that inference must pass by
induction from particulars to a general law, and
then by deduction from the general law to other
particulars. Darwin had found silicified wood
in certain tufaceous formations in Patagonia
and on the island of Chiloe on the west coast
of South America. He afterwards crossed the
Andean Cordillera in an east and west direc-
tion, and again found tufaceous formations.
In his description of the geological section of
the Uspallata range he said: "Many of these
tufaceous beds resemble, with the exception of
being more indurated, the upper beds of the
great Patagonian Tertiary formation, especially
those variously colored layers high up the river

DED UCTION. — ANTICIPA TION. 1 3 5

Santa Cruz, and in a remarkable degree the
tufaceous formations at the northern end of
Chiloe. I was so much struck with this re-
semblance, that I particularly looked out for
silicified wood, and found it under the follow-
ing extraordinary circumstances." 1

We are not told whether he gained his first
knowledge of the connection between silicified
wood and tufaceous formations from his geo-
logical researches in South America; nor if he
did, whether he had come to the general con-
clusion that silicified wood is likely to be found
in tufaceous formations, and therefore it ought
to be found in the beds of the Uspallata range,
or whether he simply reasoned that because
silicified wood is found in the tufaceous beds of
Chiloe, therefore it will be found in the very
similar tufaceous beds of the Uspallata range.
It is known that the two are found in connec-
tion in different parts of the world, and there
is a causal connection between them. The
peculiar conditions under which tufaceous beds
are deposited, and the subsequent processes of
mineral solution, etc., are such that, if wood
was present at the time of the deposition
of such beds, it would probably be silicified.
Whether Darwin knew of this causal connec-

1 Geological Observations, etc., p. 526.

136 THE METHOD OF DARWIN.

tion or only knew empirically that the two are
often found in connection, if he reasoned from
a belief that the two are likely to be found
together, the Uspallata case is one of deduc-
tion. It would be interesting to have a com-
plete record of the mental operations in this
case; but from Darwin's mental habit of leap-
ing quickly to hypotheses, even where the
connection between facts appeared altogether
empirical, there cannot be much doubt about
the deductive character of the process, even
if it be held that the process of inference is
typically from one particular case to another.

In his studies of coral islands he laboriously
gathered information concerning the distribu-
tion of atolls, barrier reefs, and fringing reefs,
and indicated each kind by a different color on
the map, distinguishing fringing reefs with red.
He had reached the conclusion that atolls and
barrier reefs lie in areas of subsidence, and
fringing reefs in areas of elevation. So far as
he could learn from records, Banks Islands and
some others apparently had no fringing reefs,
although they lie in what he had designated
the zone of elevation. He pointed out the
fact that most of the information concerning
coral reefs and islands had been collected and
recorded in the interests of navigation, and

DED UC TION. — ANTTCIPA TION. I 3 /

from this point of view narrow fringing reefs
would be insignificant, and likely to be over-
looked. He said, " I do not doubt that several
of these islands, now left uncolored [on his
map], ought to be red." Bonney, in his revised
edition of Darwin's "Coral Reefs," says, on
the authority of Captain Wharton, that Banks
Islands are fringed in parts.1

The data from which he had compiled the
map of the distribution of coral reefs and
islands had been recorded for a purpose entirely
different from that for which he wished to use
them ; hence much information that was impor-
tant for him was left out. The imperfect data
verified his principle of distribution; and he
was able to infer deductively that there were
small fringing reefs in existence where they
had not been observed or recorded.

In pursuit of the same subject he studied
carefully the charts of the Great Chagos Bank,
which he had not seen himself. He saw from
a study of the chart that, as he said, " On the
eastern side of the atoll some of the banks are
linear and parallel, like islets in a great river,
and they pointed directly towards a great breach
on the opposite side of the atoll. I inferred
from this that strong currents sometimes set

1 Structure and Distribution of Cpral Reefs, p. 220.

138 THE METHOD OF DARWIN.

directly across this great bank; and I hear
from Captain Moresby that this is the case."1
The causal relation between currents of water
and linear parallel islets was known to him;
from this law and the particular arrangement
of the banks he deduced the existence of cur-
rents, and verified the anticipation.

Some of these instances are so simple as
almost to require apology for their insertion ;
but their very simplicity makes them typical
of the most common of the logical processes.
The variety of consequences to be deduced
from principles or laws is so great, that induc-
tions by which those laws or principles are
reached are few compared with the deductions
by which their consequences are developed.

Darwin's studies of the fertilization of flowers
are full of examples of deduction and verifica-
tion ; and some of these are very curious. The
principle of advantage from cross-fertilization
lay at the root of these deductions; and it was
by incessant application of it that he was able
to interpret the most complex arrangements in
orchidaceous flowers. He studied the structure
of Listeraovata, and experimented on the action
of its parts, until he felt sure that he under-
stood the manner in which insects enter the

1 Structure and Distribution of Coral Reefs, p. 150.

DED UC TIO N. — A NTICIPA TION. 1 3 9

flower and free the pollinia. After watching
flowers for hours to see Nature at work, he was
rewarded with a verification of his interpreta-
tion.1 In the description of another case he
said, " From the large size of the flower, more
especially of the viscid disk, and from its won-
derful power of adhesion, I formerly inferred
that the flowers were visited by large insects,
and this is now known to be the case." 2 He
was well acquainted with the general interaction
of the parts and their relation to visiting insects.
From this and the size, etc. of the parts, he
was able to deduce the size and strength of the
insect. He had been convinced by theoretical
considerations that the pollen of Hedychium is
removed by the wings of hovering butterflies,
and wrote to India to have the butterflies ob-
served in action. Two years later Fritz Miiller
observed the process itself.

Probably no other of Darwin's works illus-
trates so well the variety of results which may
be deduced from a general principle by inge-
nuity and skill in interpretation as does that on
the " Fertilization of Orchids." When once
he had laid down the proposition that the
flowers of many plants are adapted for cross-

1 Fertilization of Orchids, pp. 119, 120.

2 Ibid., p. 190.

140 THE METHOD OF DARWIN,

fertilization, he set himself the task of inter-
preting the complex arrangement of parts in
orchidaceous flowers in relation to the visiting
insects in accordance with that proposition.

One of the most interesting and successful
applications of this principle is the following.
He has described various excrescences, warts,
ribs, ridges, etc. on the labellum, or large odd
petal of different orchids, the flowers of which
do not secrete nectar. He was haunted by
the question of the meaning of these absurdly
insignificant and irregular things, — their rela-
tion to the other parts and to the visiting in-
sects. He said, " From the position relatively
to the viscid disk [by means of which the pol-
len is removed by visiting insects] which these
excrescences occupy, and from the absence of
any free nectar, it formerly seemed to me higlrly
probable that they afforded food, and thus
attracted either Hymenoptera or flower-feeding
Coleoptera. . . . Nevertheless it was a bold
speculation that insects were attracted to the
flowers of various orchids in order to gnaw the
excrescences or other parts of the labella; and
few things have given me more satisfaction
than the full confirmation of this view by Dr.
Cruger, who has repeatedly witnessed in the
West Indies humble-bees of the genus Euglossa

DED UC TION. — A NTICIPA TION. 1 4 1

gnawing the labellum of Catasetum, CoryantJius,
G angora, and StanJiopea. " 1

When his attention was first attracted to the
cowslip (Primula veris), and he noticed the
different forms of flowers on different plants,
some with longer pistils, rougher stigmas, and
smaller pollen grains, and some with shorter
pistils, longer stamens, and larger pollen grains,
he inferred that the species was tending to
become dioecious. Later he became convinced
that the differences between the forms were for
the purpose of securing cross-fertilization, and
proved this to be the case. In his discussion
of the positions of the flower organs in the long-
styled and short- styled forms he said: "The
anthers in the one form stand nearly, but not
exactly, on a level with 'the stigma of the
other. ... It follows from the position of the
organs that if the proboscis of a dead humble-
bee, or a thick bristle, or a rough needle be
pushed down the corolla, first of one form and
then of the other, as an insect would do in visit-
ing the two forms growing mingled together,
pollen from the long-stamened form adheres
around the base of the object, and is left with
certainty on the stigma of the long-styled form ;
whilst pollen from the short stamens of the

1 Fertilization of Orchids, pp. 269, 270.

142 THE METHOD OF DARWIN.

long-styled form adheres a little way above the*
extremity of the object, and some is generally
left on the stigma of the other form. In ac-
cordance with this observation I found that
the two kinds of pollen, which could easily be
recognized under the microscope, adhered in
this manner to the proboscides of the two
species of humble-bees and of the moth which
were caught visiting the flowers." l

From these apparently insignificant deduc-
tions and verifications he passed on to show
that the short-styled form was far more likely
to be self-fertilized than the long-styled form.
For when he inserted a bristle or other object
into the corolla of the short-styled form, he
had to pass it between the anthers seated round
the mouth of the corolla, and some of the
pollen was almost invariably carried down arid
left on the stigma. His inferences concerning
adaptation for cross-fertilization in these forms
were completely verified, so far as it could be
done from a study of the relative positions of
the parts of the flowers and the action of insects
upon them. The proof was strong enough to
support the principle. But for Darwin it was
merely made the starting point for further
verification from the physiological side. "The

1 Different Forms of Flowers, etc., pp. 18-24.

DED UCTION'. — ANTICIPA TION. 1 43

several foregoing facts led me to try the effects
of the two kinds of pollen on the stigmas of
the two forms." This "trial" consisted of a
long series of experiments to establish the
effects of legitimate and illegitimate unions of
the two forms. The reward of this effort to
establish the principle by physiological evi-
dence is summed up in his own words: "From
the facts now given the superiority of a legiti-
mate over an illegitimate union admits of not
the least doubt ; and we have here a case to
which no parallel exists in the vegetable, or
indeed in the animal kingdom."1

It had long been known that if pollen from
a distinct species is placed on the stigma of a
plant, and afterwards (sometimes many hours
afterwards) pollen from its own species is
placed on the same stigma, the latter obliter-
ates the effects of the former, and the plant
will be fertilized by the pollen of its own
species. He had shown that the two forms of
flowers of the cowslip were beautifully adapted
in structure for cross-fertilization, and that it
was essential to the vigor of the species that
there be cross-fertilization between the two
forms, and that cross-fertilization between
flowers of the same form, or fertilization of a

1 Different Forms of Flowers, etc., p. 28.

144 THE METHOD OF DARWIN.

flower by its own pollen, should be prevented.
But he had also shown that there is a mechan-
ical liability to self-fertilization in the short-
styled form by the pollen being carried down
from the stamens to the pistil. These facts
led him to the belief that the pollen of the
other form is prepotent over the pollen of the
same form as that to which the stigma belongs,
when they are placed on it together. He said,
" There can hardly be a doubt that with hetero-
styled dimorphic plants, pollen from the other
form will obliterate the effects of the pollen
from the same form, even when this has been
placed on the stigma a considerable time before.
To test this belief I placed on several stigmas
of a long-styled cowslip plenty of pollen from
the same plant, and twenty hours later pollen
from a short -styled dark red polyanthus" (va-
riety of cowslip). Of the thirty seedlings, all
bore reddish flowers, showing that they were
the result of the cross.1

It is not surprising that, after he had verified
his general inference concerning prepotency in
heterostyled dimorphic plants by the experi-
ments with the highly specialized flowers of
the cowslip, he should take another step and
test the inference by a species in which there

1 Different Forms of Flowers, etc, p. 31.

DED UC TION. — A NTICIPA TION. 1 4 5

was much less difference between the two
forms. After describing the two forms of
Linum grandiflorum, which differ only in the
length of their pistils, he said that he had in
his garden two fine long-styled plants, sep-
arated by a considerable distance and some
evergreens from plants of the other form. He
marked twelve flowers on these two long-styled
plants, and put some short-styled pollen on
them ; but they, and the rest of the vast num-
ber of flowers on these two plants, had their
stigmas already covered with their own pollen,
and it was late in the season (September 15).
The pollen of the two forms could not be distin-
guished under the microscope. "Altogether,"
said Darwin, "it seemed almost childish to
expect any result. Nevertheless, from my ex-
periments on Primula I had faith, and did not
hesitate to make the trial, but certainly did
not anticipate the full result that was obtained.
The germens of the twelve flowers swelled, and
bore six good capsules (the seed of which germi-
nated) and two bad ones; only four falling off.
All the other flowers were absolutely barren;
not even their germens swelled."1 Not con-
tent with this striking result, he hunted down
this absolute sterility of the long-styled plants

1 Different Forms of Flowers, etc., p. 83.

146 THE METHOD OF DARWIN.

with their own form pollen, which his experi-
ments of 1 86 1 had brought out, by carrying
through a long series of experiments which, as
he said, were so curious that he gave them in
detail. His conclusion from the experiments is
that although the pollen of the two forms is iden-
tical under the microscope, "taking fertility as
a criterion of distinctness, it is no exaggeration
to say that the pollen has been brought to a de-
gree of differentiation, with respect to its action
on the stigma of the same form, corresponding
with that existing between the pollen and stigma
of species belonging to distinct genera." l

An excellent illustration of the relation
between induction and deduction in the scien-
tific method is furnished by Darwin's study of
the expression of grief. During several years,
he said, no expression seemed to him so utterly
perplexing as this one. Why should the inner
ends of the eyebrows be raised when a person
feels the emotion of grief? Or, in other words,
what is the cause of the obliquity of the eye-
brows under suffering? "Why should grief or
anxiety cause the central fasciae alone of the
frontal muscle, together with those round the
eyes, to contract?"2 Here was a little induc-

1 Different Forms of Flowers, etc., pp. 87-90.

2 Expression of the Emotions, etc., pp. 188-192.

DED UCTION. — ANTIC IP A TION. 1 47

tive problem: the effects given, to find the
cause, without any hint as to its nature. Sev-
eral years would seem long enough for a mind
like Darwin's.

He had seen Duchenne's photograph of a
young man contracting the grief-muscles while
looking up at a strongly illuminated surface,
but had entirely forgotten the picture. The
problem remained unsolved. One day while
on horseback, with the sun behind him, he met
a young girl whose eyebrows as she looked
up at him became extremely oblique, with the
proper furrows on her forehead. He had been
unable to reach the cause by contemplation
of the effects. Now he had observed a cause
producing effects identical with those which
puzzled him. There was now a basis for ex-
periment He went home and caused three of
his children, without their knowing why, to
look up at the top of a tall pine against a
bright sky. "With all three," he said, "the
orbicular, corrugator, and pyramidal muscles
were energetically contracted, through reflex
action " to protect the eyes against the light.
But they wanted to see, and a " curious struggle
arose between these muscles, that tended to
lower the brows and close the lids and all or
only the central fasciae of the frontal muscle,

148 THE METHOD OF DARWIN.

causing obliquity of the brows with puckering
and swelling of their inner ends, so that the
exact expression, in every detail, of grief or
anxiety was assumed "

"When children scream they contract the
orbicular, corrugator, and pyramidal muscles,
primarily for the sake of compressing their
eyes, and thus protecting them from being
gorged with blood." By observation on the
little girl and his own children he found that
the peculiar expression characteristic of grief
was the combined result of the reflex contrac-
tion of the muscles around the eye to protect it
by closing it, and the voluntary contraction of
other muscles to keep it open. In children the
unrestrained expression of suffering called into
action only one set of these muscles. These
were the factors in his possession for the solu-
tion of the problem. He knew that the eleva-
tion of the inner ends of the eyebrows was due
to the effort to keep the eyes open. " I there-
fore expected to find with children," he said,
"that when they endeavored either to prevent
a crying-fit from coming on, or to stop crying,
they would check the contraction of the above-
named muscles, in the same manner as when
looking upwards at a bright light; and conse-
quently that the central fasciae of the frontal

DEDUCTION. — ANTICIPA TION. 149

muscle would often be brought into play." He
himself observed children with reference to
this point, and had others, including physi-
cians, do so. He soon found that the "grief-
muscles " were very frequently brought into
very distinct action, and has given a number
of cases. The crying-muscles act in children,
and have acted for countless generations. The
pyramidal muscles are least under the control
of the will, and can be counteracted only by
the voluntary contraction of the central fasciae
of the frontal muscle ; and that is the expression
of grief.

This instance of the solution of an inductive
problem is by its apparent smallness a striking
example of the difficulties of scientific investi-
gation, and of the necessity of appealing to all
the logical processes. After the explanation is
once made, it would seem an easy matter to ana-
lyze the complex effect called the expression
of grief, and discover its causes in the involun-
tary contraction of one set, and the voluntary
contraction of another set of muscles; but the
apparent simplicity is all due to the explana-
tion itself. It will be remarked, in the discus-
sion of the logical history of the principle of
natural selection, that the causes of any set of
facts are rarely discovered by a direct study

I5O THE METHOD OF DARWIN.

of the effects. Sooner or later a cause is ob-
served to produce the effect of which an ex-
planation is desired; then by an induction the
cause is applied to the whole class of effects,
and the induction is established by subsequent
deduction and verification.

One of the most interesting examples of
reasoning recorded in Darwin's works is that
concerning the colors of caterpillars. Although
Darwin put the problem and Wallace solved it,
it is inserted here because it illustrates the
devices used to secure explanations of facts.
Darwin had undertaken to explain the beauty
of butterflies by the principle of sexual selec-
tion, but knew that it was foolish to think that
the beauty of the mature animal was thus ex-
plained unless the equally beautiful colors of
many caterpillars, in whose case sexual selec-
tion certainly could not act, were explained in
some special way.1 Here was another set of
facts that could not be reduced under his
theory; and again appears the almost insuper-
able difficulty of passing directly from facts to
their causes. He whom many regarded as a
master in the art of "wriggling" was unable to
devise an explanation, and appealed to Wallace,

1 Descent of Man, etc., Vol. I. pp. 202-204 ; Life and Letters,
Vol. II. p. 276.

DED UC TION. — A N TIC IP A TION. 1 5 I

who, he said, had an innate genius for solving
difficulties. Wallace, by a pretty paradox, re-
ferred this anomalous set of facts to the well
known principle of protective coloring. He
said most caterpillars require protection, as
may be inferred from some kinds having spines
or hairs, others being colored like leaves and
twigs. But in known cases in which the color-
ing served to protect the larva it did so by con-
cealing the animal from its enemies. Gaudy
colors would expose it to the sharp sight of
every foe ; how, then, could they serve to pro-
tect it? By reasoning from these considera-
tions "Mr. Wallace thought it probable that
conspicuously colored caterpillars were pro-
tected by having a nauseous taste." But as
they are tender, a peck from a bird's beak
would be fatal. "Distastefulness alone," said
Wallace, "would be insufficient to protect a
caterpillar unless some outward sign indicated
to its would-be destroyer that its -prey was
a disgusting morsel." Darwin presented the
reasoning to the Entomological Society, and
it was supported by statements of the members,
and afterwards verified by Jenner Weir's ex-
periments with his birds. The smooth green
and twig-like larvae were devoured by the
birds; and the spinous and brightly colored

152 THE METHOD OF DARWIN.

ones were rejected with signs of distaste-
fulness.

The correlation of brilliant colors and dis-
tastefulness was thus anticipated as a conse-
quence of natural selection, the principle of
protective coloring and the belief that animals
so protected by obscure colors are attractive to
their enemies. Darwin immediately seized on
this result as an opening for further investiga-
tions, and said : " This view will, it is probable,
be hereafter extended to many animals which
are colored in a conspicuous manner." The
study of animal coloration under Darwin's
principle of natural selection and the subordi-
nate principles of mimicry, etc., has been car-
ried to such a length, or rather the effort to
explain coloration under these and similar prin-
ciples has been carried to such a length, that
one prominent zoologist has felt justified in
characterizing the speculations of recent years
on the coloration of animals as a mild form of
scientific lunacy. There has been an enormous
amount of wild deduction and half-digested
observation ; but what is most needed is more
light on the physiological causes at work within
the animal and producing and determining the
distribution of colors.

It has been mentioned in another place that

DED UCTION. — ANTICIPA TION. 1 5 3

Darwin had concluded that characters inherited
by both sexes appear early in life, and that char-
acters restricted to one sex appear late. He
said, " I was led to infer that a relation of this
kind exists, from the fact that whenever and in
whatever manner the adult male has come to
differ from the adult female, he differs in the
same manner from the young of both sexes."
This induction he proceeded to strengthen by
deduction at both ends. He deduced the law
from a still more general one, as follows : " It
is in itself probable that any character appear-
ing at an early age would tend to be inherited
equally by both sexes, for the sexes do not
differ much in constitution, before the power
of reproduction is gained " ; and in the same
way characters appearing late in one sex would
tend to be restricted to that sex. l

From the other side, he sought to test the
law by an examination of its consequences; and
chose the deer family as a crucial instance, upon
which he felt he could rely.2 In some species
of this family the males alone have horns, and
in one species both sexes have them. If the
law were true, horns should appear late in
the species in which they are restricted to the

1 Descent of Man, etc., Vol. I. p. 276.

2 Ibid., p. 278 et seq.

154 THE METHOD OF DARWIN.

males, and early in the species of which both
sexes have horns. He found that in seven
species with horns only on the males the horns
appear late, — at nine months, or even later.
In the reindeer, which alone has horns on both
sexes, the horns appear in both sexes at the age
of four or five weeks. His investigations took
a somewhat wider range, and he gave other
illustrations and some exceptions to the law
among horned animals.

One of the most striking of his minor efforts
was his explanation of the origin of the remark-
able color patterns called " ocelli " on the tail
of the peacock.1 He had adopted the theory
of sexual selection for the explanation of the
beauty of birds, etc., which did not seem to
him to admit of explanation under natural selec-
tion. There are other naturalists who do not
believe that sexual selection plays the part in
nature which Darwin ascribed to it. But what-
ever view is taken of it, it furnished him with
the indispensable working hypothesis by means
of which to explain known facts and search for
others that ought to follow as consequences of
the hypothesis. It was characteristic of Dar-
win to select for investigation and explanation
extreme instances that would put his beliefs to

1 Descent of Man, etc., Vol II. pp. 132-145.

DED UCTION. — ANTIC IP A TION. I 5 5

the most rigorous test. The ocelli on the tail
of the peacock furnished such an instance. The
problem was how to explain the origin of these
ocelli from the ordinary feather markings of
the group to which the peacock belongs.

First, his belief that the colotf patterns of
many birds are due to sexual selection led him
to explain the absence of ocelli from the tail-
feathers of the two species of peacock by the
fact that these feathers are covered up and con-
cealed by the long tail-coverts. The theory
required that the patterns due to sexual selec-
tion should be exposed to the gaze of the
females. "In this respect," he said, "they
differ remarkably from the tail-feathers of Poly-
plectron, which in most of the species are orna-
mented with larger ocelli than those on the
tail-coverts." According to theory, the ocelli
had disappeared from the tail-feathers and
been remarkably developed on the tail-coverts
because the latter by enormous development
had covered the former. In Polyplectron, in
which the tail-coverts are not so enormously
developed, the ocelli were larger on the tail-
feathers than on the coverts. By the theory,
however, the markings of the Polyplectron are
more generalized, and some indications of
gradations between these two extremes ought

156 THE METHOD OF DARWIN.

to exist. " Hence," he said, " I was led to care-
fully examine the tail-feathers of the several
species of Polyplectron in order to discover
whether the ocelli in any of them showed any
tendency to disappear, and, to my great satis-
faction, I was successful." His whole study of
these ocelli is remarkable for the ingenuity
with which he worked out the consequences of
his theory and verified them ; and explained the
intricate pattern as a modification and speciali-
zation of more general feather-marking.

Darwin's theory of descent led him to regard
species as only more strongly marked varieties.
"From looking at species as only strongly
marked and well defined varieties, I was led to
anticipate that the species of the larger genera
in each country would oftener present varieties
than the species of the smaller genera." He
tested this deduction by an extensive tabulation
of plants and Coleoptera; "and it has invariably
proved to be the case that a larger proportion
of the species on the side of the larger genera
presented varieties than on the side of the
smaller genera. " 1

When once he had got hold of natural selec-
tion as the cause that had brought about the
adaptations in nature, it was an essential part of

1 Origin of Species, p. 44.

DED UCTION. — A NTICJPA TION. 1 5 /

the doctrine that only variations favorable to
the species could be preserved. It was an
inevitable inference from the nature of the
cause of adaptations that there could be no
such thing in nature as an adaptation for the
exclusive benefit of any other species than the
one possessing it. Darwin was so confident
of this deduction, although it could never be
rigidly verified by observation, that he boldly
staked the fate of his whole theory on the
truth of the inference. " If it could be proved
that any part of the structure of any one species
had been formed for the exclusive good of
another species, it would annihilate my theory,
for such could not have been produced through
natural selection."1 He could never know
from direct observation that there were no such
cases in existence, but he was driven to the
assertion of their non-existence by the nature
of the cause of adaptations. Doubtless this
deduction gave the severest blow that was ever
dealt to the belief in general benevolence in
Nature, and it has proved the final blow. It
was the apparently awful consequences of this
inevitable deduction that roused the bitter
opposition of the religious forces of the world.
It seemed to establish forever the doctrine that

1 Origin of Species, p. 162.

158 THE METHOD OF DARWIN.

advantage to self is the only invariable motive
of all the striving in the universe. The moral
consequences of the theory seemed to outrage
all the noble ideals that had ever been cherished
in the world.

Since the time he made the declaration, there
have been up for discussion numerous cases of
adaptation which seemed of no value, or even
hurtful, to the species possessing them. These
difficulties have caused a vast amount of stren-
uous explanatory wriggling under the name
symbiosis; but there has as yet been no case
found which can be positively regarded as an
example of what Darwin said could not exist.
He had long studied adaptations carefully; but
the nature of the cause, after he had discovered
it, helped him to understand more clearly the
nature of adaptations.

Good testimony for the necessity of a theory
of some kind to enable him to work effectively
is what Darwin wrote to Asa Gray about
cleistogamic flowers, which are self-fertilized
and do not open at all. He said, "The tem-
porary theory which I have formed on this class
of dimorphism, just to guide experiment, is
that the perfect flowers can only be perfectly
fertilized by insects, and are in this case abun-
dantly crossed; but that the flowers are not

DED UCTION. — ANTICIPA TION. 1 5 9

always, especially in early spring, visited
enough by insects, and therefore the little
imperfect self-fertilizing flowers are developed
to insure a sufficiency of seed for present genera-
tions. " This temporary theory is now generally
accepted as the true one.1

1 Life and Letters, Vol. II. p. 482.

XL

DEDUCTION. — GENERAL INSTANCES.

IT has been said that a large proportion of
Darwin's special investigations were started
as deductions from the general theories of
descent and natural selection for the purpose
of corroborating or testing them, and otherwise
working out their consequences. But before
turning to these it will be well to notice a
piece of deductive work not connected with
those theories; for it is important, both on
account of his using it himself as an illustra-
tion of his method and on account of the more
recent views that have arisen in opposition
to it.

The hypothesis concerning the formation of
coral reefs took its rise as a special application
of the general rule that depositions are made
over sinking areas to the coral limestones of
the west coast of South America.

The main outlines of his work on coral
islands were deductive, and so were many of
the special investigations of details. He spoke

DEDUCTION. — GENERAL INSTANCES. l6l

of the theory of the formation of coral islands
as the only one of his many hypotheses which
he had not to modify afterwards, and asserted
that therefore his study of coral islands was
more deductive in spirit than any other of his
investigations.1 After the theory had held
sway for forty years in the geological world as
a complete explanation of coral reefs, it was
called in question by John Murray, who sought
to replace it by another which seemed to him
more reasonable. Murray has found some ad-
herents; the war of the two theories has been
waged more or less hotly ever since, and both
views are still in the field. Darwin's theory
is not superseded,2 nor is it likely to be; but
it will nevertheless be somewhat modified to
adjust it to the greater knowledge 'of the
present. Indeed, if Darwin had lived to issue
another edition of his book, he would have
taken the new facts into account, as he did in
his latest correspondence. Here, again, he had
considered in advance many of the objections
that have since been raised against his theory.
But the chief interest of this case is derived

1 Life and Letters, Vol. I. pp. 58, 83.

2 Structure and Distribution of Coral Reefs, 3d edition,
Appendix by Prof. T. G. Bonney; Ibid., Bettany's edition,
Critical Introduction by Prof. John W. Judd.

ii

1 62 THE METHOD OF DARWIN.

from the facts that he regarded it as the most
deductive in spirit of all his work, and as the
only hypothesis which he was not obliged to
modify, and that scientists have since attacked
it more severely perhaps than any of his other
theories.

Darwin's approach to the subject of the ex-
pression of the emotions has already been
described under Induction. He said, "When I
read Sir C. Bell's great work [On the Anat-
omy of Expression], his view, that man had
been created with certain muscles specially
adapted for the expression of his feelings,
struck me as unsatisfactory."1 This was be-
cause he had become convinced of the truth of
evolution, which required him to believe that
the habit of expressing our feelings by cer-
tain movements had been somehow gradually
acquired. This view required that the whole
subject of expression should be studied under
a new aspect; "and each expression," he said,
"demanded a rational explanation. This belief
led me to attempt the present work." In this
case the general theory led him only to the
conviction that there must be some rational
explanation for each emotional expression; and
left him to find out inductively the particular

1 Expression of the Emotions, p. 19.

DEDUCTION.— GENERAL INSTANCES. 163

nature of the explanations. It will be recalled
that he reached three principles of expres-
sion; but only when he had completed his
observations.

Darwin's botanical work was almost entirely
done under the influence of the theory of evolu-
tion. His special investigations in this field
were based on corollaries from the general
theory. Writing to Mr. Murray, his publisher,
concerning his book on the "Fertilization of
Orchids," he said, "It will perhaps serve to
illustrate how natural history may be worked
under the belief of the modification of species. " 1
Equipped with the belief that all adaptations
are useful to the species possessing them,
and that innumerable flowers, among them the
orchids, are adapted for cross-fertilization, he
studied orchids and the effects of cross- and
self-fertilization in the same spirit in which he
had studied coral islands.

One of the most interesting of the many
investigations that arose out of his general
theories was that on climbing plants. As has
been said, he selected as subjects for special
research some of the principal difficulties that
presented themselves for explanation. He did
this because, if the theories were true, they

1 Life and Letters, Vol. II., Letter to Murray.

1 64 THE METHOD OF DARWIN.

ought to lead to the right explanations, and
because he always regarded it as better to
work out a single typical case or a few typ-
ical cases thoroughly, in proof of his theories,
than to offer miscellaneous suggestions on
many cases.

Climbing plants offered a case of special
importance. When once the principles of
descent and natural selection are adopted as
working hypotheses, it is a comparatively easy
matter to explain how a group of closely related
animals or plants come to possess one or more
striking characteristics in common. In such a
case they are all supposed to have inherited the
characters in question from a common ancestor.
For example, all the woodpeckers, with their
peculiar feet and tail and tongue, the last
with its remarkable apparatus of hyoid-bone
and muscle, — or the various oaks with their
acorns and cupules, their flowers and leaves,
— are believed to have descended from a com-
mon stock. The individuals of these groups
have a great many characters in common. But
climbing plants are found throughout the plant
kingdom. Some families contain several or
many closely related climbers, and these offer
no special difficulty so far as their mutual pos-
session of the power to climb is concerned.

DEDUCTION.— GENERAL INSTANCES. 165

But other large families, normally composed of
non-climbers, contain one or a few climbing
species, as, for example, the hop in the nettle
family.

The power to climb is so striking a charac-
ter, and is so plainly useful to the plant pos-
sessing it, that Darwin's theories would be
taxed with failure if they did not explain its
origin. But climbing plants are found through-
out the plant kingdom ; and they are not
descended from a common climbing ancestor,
for they possess nothing in common except
this one power to climb. ''Plants, "he said,
"become climbers in order, it may be pre-
sumed, to reach the light, and to expose a
large surface of leaves to its action and to
that of the free air. This is effected by the
climbers with wonderfully little expenditure of
organized matter in comparison with trees,
which have to support a load of heavy branches
by a massive trunk. Hence, no doubt, it arises
that there are in all quarters of the world so
many climbing plants belonging to so many
different orders." The very great advantage
offered to the climber has acted as a powerful
premium for the development of the capacity

1 Journal of the Linnean Society, 1865; Botany, Vol. IX.
pp. 107, 108.

1 66 THE METHOD OF DARWIN.

wherever variation offered the materials out of
which natural selection could produce it.

The first thing to be established in proof of
the derivation of climbing plants from non-
climbers was the existence of gradations in the
power of climbing, and of intermediate stages
between the different methods of climbing, —
by twining of the stem, by leaf-stalks, and by
tendrils; just as he connected the ocelli of the
peacock's tail by a series of gradations with
the more ordinary feather-markings of related
birds. But another unknown element was the
source of the variations upon which natural
selection could work to produce climbers. In
his arguments to prove his theories of descent
and natural selection Darwin showed that
variations do occur, and that when they occur
natural selection will inevitably preserve the
favorable and destroy the unfavorable. But he
could do little or nothing in the direction of
pointing out the cause of variations. He has
been incessantly twitted about this by his
opponents, especially because of the false
notion that he ascribed to chance all variations
whose causes were not known. Ignorance of
the sources of variation is no obstacle what-
ever to belief in Darwin's theories; but this
is true only when the species having a certain

DEDUCTION. — GENERAL INSTANCES. 1 6?

character in common are proved by many other
characters to be descended from a common
stock. In the case of climbing plants the same
kind of variation must have occurred indepen-
dently in all parts of the plant kingdom, or
there must have been a common source or ten-
dency which served as a starting point for the
development of the power to climb.

In his work on climbing plants, first pub-
lished as a paper in the Linnean Journal,1 he
worked out in a masterly way the gradations in
the power to climb, and between the different
methods of climbing, showing that all are mod-
ifications of the method of climbing by twining
of the stem/ Near the end of his work he said,
"We have seen how diversified are the move-
ments of climbing plants. . . . They belong to
many and widely different orders. . . . When
we reflect on this wide serial distribution of
plants having this power, and when we know
that in some of the largest well defined orders,
such as the Compos itae, Rubiaceae, Scrophu-
lariaceae, Liliaceae, etc., two or three genera
alone out of a host of genera in each, have this
power, the conclusion is forced on our minds
that the capacity of acquiring the revolving

1 Journal of the Linnean Society, 1865, Botany, Vol. IX.,
" On the Movements and Habits of Climbing Plants."

1 68 THE METHOD OF DARWIN.

power on which most climbers depend is
inherent though undeveloped in almost every
plant in the vegetable kingdom."1

It will be interesting to try to analyze the
conditions under which he made this definite
prediction. In his work on climbing plants he
showed that the power to climb depends on two
quite distinct powers: (i) the power of spon-
taneous circumnutation, and (2) sensitiveness to
touch, and the consequent bending toward the
side touched.

Without the theory of descent, the question
of the origin of the above mentioned sensitive-
ness could never have arisen at all. With the
theory of descent, and with natural selection as
a cause, and a belief in the existence of varia-
tions for it to work upon, it might have been
possible to infer some general power or tendency
in plants as the source of that sensitiveness to
touch; but it was not done, and from what has
been said elsewhere it is not likely that it
would have been done, at least without great
difficulty, from a knowledge of the highly
specialized effects. Darwin said, " If we in-
quire how the petiole of a leaf, or the peduncle
of a flower, or a branch, first becomes sensitive,
and acquires the power of bending toward the

1 Journal, p. 117.

DEDUCTION. — GENERAL INSTANCES. 169

touched side, we get no certain answer. Nev-
ertheless, an observation by Hofmeister well
deserves attention, namely, that the shoots and
leaves of all plants, whilst young, move after
being shaken; and it is almost invariably young
petioles and young tendrils, whether formed of
modified leaves or flower-peduncles, which move
on being touched; so that it would appear as
if these plants had utilized and perfected a
widely distributed and incipient capacity, which
capacity, as far as we can see, is of no service to
ordinary plants." l

Darwin was in search of a source of the sen-
sitiveness of plants, and Hofmeister had pro-
vided it by empirical observation. Darwin's
relation to this explanation was exactly the
same as it was in the discovery of the principle
of natural selection. It will be seen that in
the latter case he had studied very carefully the
effects (adaptations) to be accounted for, and
variations as the material upon which the un-
known cause might act; then by accidental
reading of Malthus the cause was presented
to him, and he brought it and its effects into
relation with each other by interpreting the
latter as results of the action of the former. In
the case of the sensitiveness to touch in plants,

1 Journal, p. 112.

THE METHOD OF DARWTN.

he was in possession of the cause (natural selec-
tion), and the specialized effects and the belief
that these are the results of the action of natural
selection upon variations ; Hofmeister furnished
the material which natural selection could de-
velop, by the observation that all young plants
are slightly sensitive to disturbance.

Now what was the logical setting for Darwin's
prediction that the capacity of revolving would
be found inherent, though undeveloped in almost
every plant in the vegetable kingdom ? If there
were no evidence to the contrary, it would be
supposed that he had been able to make the
prediction from the knowledge that climbing
plants occur throughout the plant kingdom,
and that therefore the source of the variation
must be a general tendency in plants. Such an
inference seems easy enough to make, as has
been shown in other cases, after it has been
made. In this case Darwin had the help of an
analogy upon which he could depend with con-
fidence. Hofmeister had furnished, by obser-
vation, a general source of the sensitiveness of
climbing plants in the slight sensitiveness of
young leaves and shoots in general. Sensitive-
ness to touch and power of circumnutation are
inseparable in climbing plants; what was more
natural, therefore, than the inference that the

DEDUCTION.— GENERAL INSTANCES. 17 1

power to revolve had its source in an unknown
general tendency, just as sensitiveness to touch
had its source in a known slight general sen-
sitiveness, each power having been developed
and specialized in climbing plants by natural
selection? Such an inference would seem al-
most inevitable. But in addition he was in
actual possession of a case in which the power
of revolving was imperfect and functionless.

He said that when he made the prediction he
"knew of only one imperfect case, namely, of
the young flower-peduncles of a Maurandia^
which revolved slightly and irregularly, like
the stems of twining plants, but without mak-
ing any use of the habit." l In the discussion
of Maurandia semperflorens, in his original
paper on climbing plants, he gave the follow-
ing interesting bit of history : " I should not
have noticed the present species, had it not
been for the following unique case. Mohl says
that the flower-peduncles, as well as the petioles,
are wound into tendrils." Darwin proved that
the flower-peduncles do not act as tendrils ; but
that they nevertheless, whilst young, exhibit
feeble revolving powers, and are slightly sen-
sitive to a touch. He observed nine vigorous
plants, and it was certain to him that neither

1 Origin of Species, p. 197.

THE METHOD OF DARWIN.

the slight spontaneous movements nor the slight
sensitiveness of the flower-peduncles were of
any service to the plants in climbing. He
gave reasons for believing that these imperfect
powers are not relics of former functional power,
and that correlation of growth did not transfer
them imperfectly from the internodes and young
petioles to the flower-peduncles; and said that,
by whatever means acquired, the case was inter-
esting to him because these useless capaci-
ties, by being a little perfected, would make
the flower-peduncles of this plant as useful for
climbing as are those of Vitis and other plants.1
The important part which the case of Mau-
randia played in the reasoning is shown by
what he said concerning it. What he had said
of the source of sensitiveness to touch he almost
literally repeated of the power of circumnuta-
tion : " If we further inquire how the stems of
petioles, tendrils, and flower-peduncles of climb-
ing plants first acquire their power of spontane-
ously revolving, or, to speak more accurately,
of successively bending to all points of the
compass, we are again silenced, or at most can
only remark that the power of movement, both
spontaneous and from various stimuli, is far

1 Journal of the Linnean Society, 1865; Botany, Vol. IX.
pp. 38-40.

DEDUCTION. — GENERAL INSTANCES. 1/3

more common with plants, as we shall presently
see, than is generally supposed to be the case
by those who have not attended to the subject.
There is, however, the one remarkable case of
the Maurandia semperflorens, in which the
young flower-peduncles spontaneously revolve
in very small circles, and bend themselves when
gently rubbed to the touched side; yet this
plant profits in no way by these two feebly
developed powers. A rigorous examination of
other young plants would probably show some
slight spontaneous movements in the peduncles
and petioles, as well as that sensitiveness to
shaking observed by Hofmeister. We see, at
least in the Maurandia, a plant which might,
by a little augmentation of qualities which it
already possesses, come first to grasp a support
by the flower-peduncles, as with Vitis and Car-
diospermum, and then by the abortion of some
of its flowers acquire perfect tendrils."1 At
this point he made the prediction already
quoted.

To sum up, Darwin based his conclusions
concerning the source of the power of revolving
upon the following data: (i) detailed knowledge
of the nature and extent of the climbing power
in the plant kingdom ; (2) proof that there are

1 Journal, p. 113.

174 THE METHOD OF DARWIN.

many gradations of structure and function
between simple twiners and tendril bearers;
(3) the conviction that all such highly special-
ized functions and structures are extreme de-
velopments of more general but less obvious
phenomena, or of slight variations whose source
is unknown ; (4) the almost perfectly analogous
case of sensitiveness to touch in climbing plants,
which is inseparably connected with the power
of revolving, and which he had connected with
the general though slight sensitiveness of plants
observed by Hofmeister; (5) and one of the
most important of the data mentioned, the
actual case of imperfect and functionless power
of revolving in Maurandia semperflorens, which
might by a little augmentation become useful
in climbing.

The final verification of the prediction • is
embodied in the volume on the " Power of
Movement in Plants," by Charles and Francis
Darwin. The sweeping character of the verifi-
cation cannot be better indicated than by quot-
ing their own statement of what they intended
to show in that volume ; it will serve, too, as a
summary of results, for they completely estab-
lished what they claimed : " In the course of
the present volume it will be shown that ap-
parently every growing part of every plant is

DEDUCTION,— GENERAL INSTANCES. 175

continually circumnutating, though often on a
small scale. Even the stems of seedlings be-
fore they have broken through the ground, as
well as the buried radicles, circumnutate as far
as the pressure of the surrounding earth permits.
In this universally present movement we have
the basis or groundwork for the acquirement,
according to the requirements of the plant, of
the most diversified movements. Thus the great
sweeps made by the stems of twining plants and
by the tendrils of other climbers result from a
mere increase in the amplitude of the ordinary
movements of circumnutation. The position
which young leaves and other organs ultimately
assume is acquired by the circumnutating move-
ment being increased in some one direction.
The leaves of various plants are said to sleep
at night, and it will be' seen that their blades
then assume a vertical position through modified
circumnutation, in order to protect their upper
surfaces from being chilled through radiation.
The movements of various organs to the light,
which are so general throughout the vegetable
kingdom, and occasionally from the light, or
transversely with respect to it, are all modified
forms of circumnutation; as, again, are the
equally prevalent movements of stems, etc.
towards the zenith, and of roots towards the

1 76 THE METHOD OF DARWIN.

centre of the earth. In accordance with these
conclusions, a considerable difficulty in the way
of evolution is in part removed, for it might
have been asked, How did all their diversified
movements for the most different purposes first
arise ? As the case stands, we know that there
is always movement in progress, and its ampli-
tude or direction, or both, have only to be mod-
ified for the good of the plant in relation with
internal or external stimuli. " 1

Thus the great work of observation and rea-
soning began with an effort to explain the power
of climbing among plants under the theories of
descent and natural selection; passed on to the
prediction of the universal movement of cir-
cumnutation and its verification; and closed by
explaining all the other highly specialized and
remarkable movements 'of plants and plant or-
gans as modifications of the same general but
unapparent movement. The principal difficulty
at first was the fact that climbers were found
throughout the plant kingdom, and could not
have been descended from a common climbing
ancestor. By the investigations of Darwin and
his son, not only were the different methods of
climbing shown to be modifications of the twin-
ing movements of the stem, but it and all the

1 Power of Movement in Plants, p. 4.

DEDUCTION.— GENERAL INSTANCES.

other movements of plants were shown to be
modifications of a universal movement. What
was at first a difficulty in the way of evolu-
tion became, like the structure of the flowers
of orchids, the ocelli of the peacock,, and the ex-
pression of the emotions, one of the strongest
supports of the theory.

12

XII.

UNVERIFIED DEDUCTIONS.

EVERY apparently insignificant fact was
full of meaning to Darwin; and he made
it the occasion for what he used to call "fool's
experiments." His speculative powers em-
ployed themselves as actively and energetically
on the details of his investigations as on their
larger outlines; but he was as ruthless in test-
ing and rejecting his speculations as he was
facile in making them. When, however, he
had once established a principle, he followed
out the deductions from it with as much confi-
dence as if he had already secretly seen the
facts whose existence he suspected or thought
probable. It is important to note the caution
with which he usually stated his anticipations,
and to contrast with it the energy and confi-
dence with which he sought and worked out
the facts. He spent his life establishing the
consequences of his theories, but with all his
fidelity and persistence he had to leave many
things unproved; some for lack of time, others

UNVERIFIED DEDUCTIONS. 1 79

because of the inaccessibility of the facts. He
had the satisfaction of living to see the whole
biological world applying itself to the work of
bringing out the consequences of his theories.
It is not a part of the present purpose, even if it
were possible, to follow out the logical history
of the subsequent work based on those theo-
ries. But it will be of interest to notice a few
instances in which he made deductions which
he could not verify. Some of these have been
since verified by others, and some still remain
unverified. They vary all the way from confi-
dent predictions to vague expressions of a wish
that some one would make observations that he
thought would bear fruit.

There is one instance of a difficulty in the
way of Darwin's theories which is of especial
importance. He outlined a possible explana-
tion, but the difficulty has proved itself so stub-
born that even some of his adherents feel that
his theories could not face many of the same
kind. The problem is almost exactly similar
to that of climbing plants, and its interest is
increased by some recent work that has been
done towards its solution.

Electric organs occur in various unrelated
species of fishes, and differ so widely in their
position in the body, their mode of innervation,

ISO THE METHOD OF DARWIN.

etc., that they could not possibly have been
derived from a single primitive electric organ.
In this respect the difficulty was exactly similar
to that of the climbing power in plants. After
pointing out that the electric organs of the
different electric fishes are not homologous, —
that they occupy different parts of the body,
are differently innervated, etc., — Darwin said
that the problem which remains is "by what
graduated steps these organs have been devel-
oped in each separate group of fishes. " In the
case of climbing plants he had been able to
show many gradations of structure and function,
— that even when not fully developed the power
to climb was serviceable to plants. He said,
" The electric organs of fishes offer another case
of special difficulty; for it is impossible to con-
ceive by what steps these wondrous organs have
been produced. But this is not surprising, for
we do not even know of what use they are." l

Darwin mentioned, however, as factors for
the solution of the problem, the great differ-
ences in the strength of the shocks, the close
analogy, as he called it, between the electric
organs and muscular tissue, the electrical phe-
nomena of ordinary muscle; and called atten-
tion to our ignorance of the habits and structure

1 Origin of Species, pp. 150, 151.

UNVERIFIED DEDUCTIONS. l8l

of the progenitors of electric fishes, and added,
" It would be extremely bold to maintain that
no serviceable transitions are possible by which
these organs might have been gradually devel-
oped." Nevertheless, the subject was unap-
proachable for him; and his opponents have
used the electric fishes as one of the greatest
stumbling-blocks in the way of natural selec-
tion. Even Romanes felt that the electric
fishes present so serious an obstacle that if
there were many such he would have to hold in
abeyance his belief in the theory.1 Darwin
believed that the facts, because they could not
be explained, did not therefore militate against
the theory. The much greater difficulty of
explaining the case of the electric organs com-
pared with that of climbing plants is due to two
important facts. In the latter there were at
least some gradations of structure and function
known ; and even when both were imperfect, it
could be shown that they were useful, so that
natural selection could act upon them. But
there were no imperfectly developed electric
organs in fishes which could be appealed to as
the source from which the perfect organs might
be developed; and what was still more impor-
tant, in some of the electric fishes the organs,

1 Romanes, Darwin and After Darwin.

1 82 THE METHOD OF DARWIN.

though perfect in structure, were apparently
functionless; they were not known to give off
any electrical discharge.

Darwin left the problem unsolved except for
the suggestions he offered, and it still remains
unsolved in part. Among the reasons for this
state of the subject are these : that the habits of
the electric fishes have been but little known,
that the powers of the electric organs are but lit-
tle understood, and that both are very difficult
to investigate.

The present state of the subject is made
interesting by the recent studies of Professor
Fritsch.1 From the first the electric organs
have been regarded as modified muscular tissue.
They occupy the place of what in other fishes
is common muscle. The Pacinian law of the
direction of the current in electric organs -is
that at the instant of the shock the side of the
electric plate on which the nerve enters is neg-
ative, and the opposite side positive; and in
this important respect such of them as are of
undoubted muscular origin agree with the com-
mon muscular tissue and its electrical phenom-
ena. Fritsch' s interesting recent studies on

1 Gustav Fritsch, Archiv fiir Anatomic und Physiologic,
Supplement Band, 1892; Nature, Jan. 19, 1893, Vo1- XLVII.
p. 271.

UNVERIFIED DEDUCTIONS. 183

the Mormyrida of the Nile have removed the
objection based on the existence of structurally
perfect electric organs which do not give off
electric discharges. He showed that these deli-
cate little fishes, hitherto regarded as pseudo-
electric, are really capable of giving off shocks
that can be felt by the hand and can be easily
measured with instruments. He has also shown
that in these fishes a part of the organ is in
a state of transition from muscular to electric
tissue. At the posterior end the electric organ
is sharply set off from the muscular tissue;
but at the anterior end it graduates more or
less perfectly into the muscular tissue, and the
organ seems to be actually developing in that
direction.

A special difficulty lay in the fact that in
MalapteruruS) an African fish, in which the
electric organ lies beneath the skin and encases
the body like a sheath, the electric current does
not obey the Pacinian law, but takes the oppo-
site direction. Fritsch removed the whole diffi-
culty by giving reasons for the belief that in
this case the organ is not of muscular but of
cutaneous origin, and represents the cutaneous
glands that are so plentiful in some parts of
the body. Such an exception, without the ex-
planation of Fritsch, would confuse the whole

1 84 THE METHOD OF DARWIN.

problem of the relation between muscle and
the electric organs. With the explanation, it
furnishes a good example of how investigation
dissolves difficulties.

It is a common saying that the solution of
one problem leads to new and frequently more
difficult ones. It may almost be said an inves-
tigation should be viewed with suspicion if it
does not leave more new problems than it started
out to solve. The belief of Fritsch that the
electric organs of Malapterurus are homologous
with the cutaneous glands opened up a new
phase of the general problem of the origin of
electric organs. Another difficulty presented
itself to Fritsch in the process of solving the
original problem which he set before himself.
In his study of the innervation of the electric
organs of Mormyrus he found that the nerves
which supply the electric organs decussate, or
cross from one side of the body to the other,
after leaving the spinal cord as anterior roots,
— much as the optic nerves form the optic
chiasma within the brain-case. There is no
similar case known of nerve fibres crossing
from one side of the body to the other after
they have left the central nervous system ; and
Fritsch properly thinks it to be more difficult
to explain by gradual variation and natural

UNVERIFIED DEDUCTIONS. 185

selection than the origin of the electric organs
themselves. He has suggested that this re-
markable peculiarity has been developed to
insure perfect co-ordination between the elec-
tric organs of the two sides of the body, with-
out which there could not be perfect unity of
action in the electric discharge, whereas while
the tissue is merely muscular it is important
that the organs of the two sides should act
independently of each other.

Fritsch has also called attention to the fact
that the sluggish powerfully electric fishes are
carnivorous, and the active feebly electric spe-
cies are at least mostly herbivorous.

More recently still, Professor Engelmann,1
of Utrecht, in a histological study of the elec-
tric organs in embryos of Raja clavata, etc.,
has established in detail the genetic relations
between some of the elements of cross-striped
muscle-fibre and the lamellae of the so called
meandrine or striped layer which, lying be-
neath the nerve end-plate in most species of
Raja, forms one of the principal constituents of
the electric organs in the tail of these fishes.
Hitherto little more had been known than that

1 Th. W. Engelmann, Archiv fur die Gesammte Physiolo-
gic des Menschen und der Thiere, Band LVII. pp. 149-180,
June 1 6, 1894.

1 86 THE METHOD OF DARWIN.

such relations existed. The whole problem has
advanced much farther toward a solution on the
morphological than on the physiological side;
but, as might have been expected, the demon-
stration of the exact relations between the
various elements of muscle-fibre and those of
the electric organs has enabled Engelmann to
indicate some very important and fruitful lines
for physiological experiment.

Although the homology of cross-striped mus-
cle-fibre and the constituents of the electric
organ has been proved even to many histo-
logical details, and the morphological changes
by which the former has been transformed into
the latter have become quite clear, the diffi-
culty of explaining the development of electric
organs from muscular tissue by means of natural
selection is as great as ever. Engelmann has
significantly suggested the existence of func-
tions that we are entirely ignorant of; and
refers, by way of illustration, to the recent
remarkable discoveries of the effects of the
removal, partial and complete, and grafting of
the thyroid gland,1 and to Brown-Sequard's
demonstration of the existence of an extremely
important "internal secretion" in the renal and

1 Archives de Physiologic Normale et Pathologique, 1890-
1894, and elsewhere.

UNVERIFIED DEDUCTIONS. 187

other glands.1 He has marked out a new field
of physiological research on the problem of
electric organs by the suggestion that the
marine biological laboratories be taken advan-
tage of to study the effects which the partial or
total removal, or destruction, transplantation,
etc. of those organs in various stages of onto-
genetic and phylogenetic development will have
on the normal functions of the animal. He
believes that it might thus be quickly shown
that these so called useless organs do serve an
important function in the animal economy, and
that it might be made clear what that function
is ; or that it might at least be shown what injury
their absence entails upon the animal.

It must be remembered that the problem of
electric organs has not yet been attacked in any
such way as that in which Darwin attacked the
problem of climbing plants. Fritsch by two
brief visits brought to light many important
facts; on the morphological side contributions
are steadily made, but the knowledge on the
subject up to date has been brought out piece-
meal. Before the mode of development of elec-
tric organs can be fully understood, there will
have to be not only knowledge of the electrical

1 Ibid., Series V., Vol. V. pp. 778-786, October, 1893, and
elsewhere.

1 88 THE METHOD OF DARWIW.

phenomena of muscle in general, but a thorough
investigation of the normal electrical phenom-
ena of fish-muscle, and of the efficacy of slight
shocks in water; the habits and environments
of the electric fishes, their enemies and their
prey, need to be carefully studied. When the
investigation is set going on a large enough
scale, and along all the lines on which there
is at present little more than dense ignorance,
there will be in the minds of those who have
attended closely to the principal biological
investigations of recent years no doubt about
the outcome. The logical processes involved
in the solution of such problems under the
influence of a general theory are practically the
same, whether the work is done by one man or
by a number of men who attack the problems
simultaneously or in succession.

The unverified deduction in the following
example is interesting on several accounts,
(i) The prediction involved what seemed to
many entomologists an improbability. (2) The
prediction has not been verified, but the im-
probability has been removed. (3) It has been
often quoted even by naturalists as a case of
verified prediction. Angrczcum scsquipedale,
an orchid native to Madagascar, has a long
whip-like nectary. On several flowers -Darwin

UNVERIFIED DEDUCTIONS. 189

found it eleven and a half inches long, with
only an inch and a half of nectar at the bottom.
He proved to his own satisfaction, by a study of
the structure of the flower, that it is fertilized
by moths that thrust their proboscides and heads
down into the flower to the utmost, and declared
that moths with proboscides long enough to
reach the nectar must exist in Madagascar.
"This belief of mine," he said, "has been ridi-
culed by some entomologists ; but we now know
from Fritz Miiller that there is a sphinx moth
in South Brazil which has a proboscis of nearly
sufficient length, for when dried it was between
ten and eleven inches long. When not pro-
truded, it is coiled up into a spiral of at least
twenty windings." The moth with the long
proboscis has not yet been discovered in Mada-
gascar; but the fact that there are moths else-
where with proboscides as long as the one
required in- the case of Angrcecum has removed
the improbability from the prediction. But the
point to be borne in mind is this, that the firm
conviction that orchids are fertilized by insects,
and that the flowers and insects are co -adapted
in structure, led Darwin to believe firmly in an
" improbable thing.*' l

The questions raised in Darwin's mind by

1 Fertilization of Orchids, pp. 162-166.

I QO THE METHOD OF DARWIN.

his own theories were innumerable; some of
them he answered by the great investigations
already mentioned, others he left unanswered
for various reasons. Only about two months
before his death he pointed out new lines of
investigation. Among other things he said
that there were many inconspicuous flowers not
known to be visited by insects during the day,
and the natural inference is that they are self-
fertilized. And he pointed out the desirability
of finding out whether these flowers are visited
at night by the innumerable individuals of the
many species of minute moths. If they are not
so visited, why do they expand at all ? Why
are they not cleistogamic ? He suggested, as a
mode of procedure, smearing the flowers with
viscid matter and then looking for insect scales;
but gave the caution that it would be necessary
to prove that the matter employed was not in
itself attractive to insects.1

It is a fascinating study to follow out the
suggestions that came to him and that he made
to others, to note the various degrees of success
with which the investigations were made by
others, to compare the spirit and methods with
which they were made with Darwin's own spirit

1 Miiller, Fertilization of Flowers, Prefatory Note, by
Charles Darwin.

UNVERIFIED DEDUCTIONS. IQI

and method. He knew the importance of study-
ing the speech of monkeys in relation to his
belief in the descent of man, and expected valu-
able results from it. "I wish," he wrote to
Asa Gray, " some one would keep a lot of the
noisiest monkeys, half free, and study their
means of communication."1 Mr. Garner has
recently written magazine articles and a book
on the subject, and has even visited the ape
country in Africa with elaborate arrangements
for studying the speech of monkeys in their
native haunts. It is too early to forecast re-
sults, but this case illustrates well how different
phases of Darwin's theories have attracted dif-
ferent types of men, and how caution or the
want of it may make or break confidence in the
results of their investigations.

1 Life and Letters, Vol. II. p. 183.

XIII.

ERRONEOUS DEDUCTION.

CONSIDERED simply as a logical process,
^-^ deduction is no more interesting in the
hands of the modern investigator than it was
in the hands of the mediaeval schoolman. The
scientist uses it, apart from its importance in
proof, or effort to convince others, merely as an
instrument with which to test what is known,
and to develop its unknown consequences. The
infallibility of the process is altogether hypo-
thetical. The conclusion is true only if "the
premises are true; and since the truth of the
premises is oftener the matter in question than
even the investigator dreams, the effort to get
at new truth by anticipating the consequences
of theory often results in false conclusions.
This must especially be the case when there is
no apparent reason to question the truth of the
premises ; when they would seem to have been
permanently established by repeated crucial
tests. In a number of instances Darwin went

TNIVERSI
ERRONEOUS DEDUCTION-.

clearly wrong in his deductions. Some of them
he corrected himself, for some he accepted the
corrections of others ; and some have never yet
been corrected directly, but only by the adop-
tion of the contrary principle from a study of
facts similar to those on which Darwin went
wrong. When his attention had become fixed
upon the cowslip (Primula veris), he found that
there were two forms of flowers on plants of
this species. He said, "The first idea which
naturally occurred to me was, that this species
was tending towards a dioecious condition; that
the long-styled plants, with their longer pistils,
rougher stigmas, and smaller pollen grains, were
more feminine in nature, and would produce
more seed; that the short-styled plants, with
their shorter pistils, longer stamens, and larger
pollen grains, were more masculine in nature."1
Nothing would seem more natural than that the
structural differences between the flowers should
indicate differences in sexual function. The
knowledge of dioecious plants and belief in the
modification of species could plainly suggest but
one interpretation of the structural differences of
the two kinds of flowers. Either they indicated
what was inferred from them, or they could

1 Different Forms of Flowers on Plants of the same
Species, pp. 18-21.

13

194 THE METHOD OF DARWIN.

indicate nothing at all. Had his conclusion
been left at this point, it would probably have
been accepted as both interesting and quite cer-
tain. The degree of certitude with which such
an inference is received depends on the number
of facts involved, their relation to each other,
and the degree to which they act as convergent
evidence toward the one conclusion. In these
respects the facts were all that could be desired.
It would seem that, if it is possible to make any
inferences at all concerning function from the
structure of plants, it would have been so in this
case.

For Darwin, as for every true student of
nature, deductions exist only to be verified.
The indirect evidence from structure he supple-
mented by experiments on the actual produc-
tion of seed by the two forms. He might have
pointed with pride to the cowslip as a plant in
an actual state of transition, — as a fine illus-
tration of his theory. But after describing in
detail the differences of structure in the two
forms of flower in the cowslip, he said, "The
question seems well worthy of careful investi-
gation." He made preliminary experiments
which of themselves would have been conclu-
sive, but used them to lay a basis for his much
more extensive experiments; they suggested

ERRONEOUS DEDUCTION. 195

methods, furnished cautions, and brought out
facts enough to determine the most important
directions of investigation. He marked a few
plants of each form in his garden, in a field,
and in a shady wood, and gathered and weighed
the seed. In all the lots the short-styled plants
yielded, contrary to his expectation, most seed.
He gave tables of results, and added that "by
all these standards of comparison the short-
styled form is the more fertile." In 1861 he
made fuller and fairer trials, and found that
the same result also held good for some other
species of Primula. " Consequently my anticipa-
tion that the plants with longer pistils, rougher
stigmas, shorter stamens, and smaller pollen
grains would prove to be more feminine in
nature, is exactly the reverse of the truth."

The facts on which his first inference was
based were easy to observe; they corroborated
each other in a remarkable way, and harmonized
perfectly with what was well known concerning
dioecious plants. There was no reason to sus-
pend judgment, for there were no facts that
obtruded themselves as objections to the infer-
ence. Now if under such circumstances an
inference turns out to be exactly the reverse of
the truth, what guaranty is there that a conclu-
sion will be correct in any case ? The answer

196 THE METHOD OF DARWIN.

was given in Darwin's researches. The evi-
dence was not all in. The structural evidence,
instead of serving as a basis for a true inference
concerning the functions of the organs, was
found to be in contradiction with them. Darwin
showed that both sets of facts were dependent
on a hitherto altogether unknown phenomenon,
the differentiation of the flowers of a species
into distinct sets with marked structural differ-
ences for the purpose of making cross-fertiliza-
tion almost absolutely certain.

The following case is perhaps as interesting
as it could be made, to illustrate the danger of
accepting as truth inferences that fall short of
demonstration, and only represent a high degree
of probability. In all the books that Darwin
had consulted Enonymus Europeans (spindle-
tree) is called hermaphrodite. But he found
from an examination of the species that about
half of the individuals had both stamens and
pistils of normal size, and were therefore her-
maphrodite; and that the remaining half had
pistils of the normal size, but short stamens with
rudimentary anthers without pollen, and were
therefore properly females. The ovules were
of equal size in the two forms. There could
not possibly be any other conclusion from the
structure of the flowers than the one he sug-

ERRONEOUS DEDUCTION. 197

gested, — that half of the plants, with perfect
flowers, were hermaphrodite, and the other half,
with rudimentary stamens and anthers and no
pollen, were female. What were the centuries
of study on plant structure worth, if it was not
safe to accept the conviction that female organs
of normal size are present for the bearing of
seed? Darwin said, "The most acute botanist,
judging only from structure, would never have
suspected that some of the bushes were in func-
tion exclusively males."1 As in the previous
example, he sought to verify his inference by
watching the fruit. He watched thirteen bushes,
— eight females and five " hermaphrodites. "
The females yielded abundant fruit, and a
single branch two or three feet long from one
of them yielded more than any one whole bush
among the "hermaphrodites." The inference
from structure was almost completely reversed.
The species seemed to be practically dioecious,
with the stamens aborted in the females, but
the pistils apparently normal in the individuals
that were almost exclusively male in function.
He might here again have rested the case, and
recorded the spindle-tree as dioecious.

But hear him : " I now determined to observe
more carefully during successive seasons some
1 Different Forms of Flowers, etc., pp. 287-292.

198 THE METHOD OF DARWIN.

bushes growing in another place about a mile
distant." He did so, and found some variability
among the females in the power of producing
fruit and seed, and great variability in the
"hermaphrodites," the latter never producing
as much or as fine seed as the other. At this
third stage it was clear that the plants of the
spindle-tree are neither part of them female and
part hermaphrodite, nor part of them female and
the rest, with both sets of organs, practically
male in function. The truth lay between the
two extremes, the variations in the one or other
direction depending even on the character of
the season. He said, " This case appears to me
very interesting, as showing how gradually an
hermaphrodite plant maybe converted into a
dioecious one." The final result of the long
drawn out investigation was in harmony with
his general doctrine of the descent of species,
and is an illustration of some of the best evi-
dence that has yet been adduced in its support.
To him it was interesting, because it showed
how gradually an hermaphrodite plant may be
converted into a dioecious one. To the student
of scientific method it is interesting as an
example of how an investigation, by stopping
short of exhaustion of the field, may lead, not
only to imperfect, but to false conclusions.

ERRONEOUS DEDUCTION. 199

In the work on the Fertilization of Orchids
Darwin's sagacity found full play in the inter-
pretation of the structure of orchids in ac-
cordance with the principle of adaptation for
cross-fertilization. Confident that all the mar-
vellously complex structures of orchidaceous
flowers were adaptations for cross-fertilization,
he regarded each case only as presenting a
question with regard to the particular mode of
the mutual action of the insect and the flower
organs. He was frequently able to predict this
mutual action in the case of particular species.
He never for a moment lost faith in the prin-
ciple; but in at least one case he went wrong in
his interpretation by not applying the principle
rigorously enough.

In the Cypripediumt or Lady's Slipper, there
are two small orifices near the anthers and one
large opening in the labellum or odd petal.1
After discussing the structure of the flower he
said, " Formerly I supposed that insects alighted
on the labellum and inserted their proboscides
through either of the small orifices close to the
anthers " to extract the nectar. This inference
seemed plausible enough; the small orifices
seemed well adapted to accomplish cross-fertil-
ization because they were close to the anthers,

1 Fertilization of Orchids, pp. 229-231.

200 THE METHOD OF DARWIN.

and an insect would inevitably remove the pol-
linia if it inserted its head into one of them.
But he had not clung closely enough to his
general principle. Darwin himself accepted
the correction of his inference as follows :
"Delpino, with much sagacity, foresaw that
some insect would be discovered " to remove
the pollinia by entering the labellum by its
large opening, and crawling out through one of
the orifices near the anthers; "for he argued
that if an insect were to insert its proboscis, as I
fhad supposed, from the outside through one of
the small orifices, the stigma would be liable
to be fertilized by the plant's own pollen; and
in this he did not believe, from having con-
fidence in what I have often insisted on, —
namely, that all the contrivances for fertiliza-
tion are arranged so that the stigma shall
receive pollen from a distinct flower or plant.
But these speculations are now superfluous ; for,
owing to the admirable observations of Dr. H.
Miiller, we know that Cypripedium calceolus, in
a state of nature, is fertilized in the manner
just described."

Darwin's error in this case consisted in not
considering one of the important elements of
his principle of adaptation for cross-fertiliza-
tion, — namely, the importance, not only of

ERRONEOUS DEDUCTION. 2O1

favoring cross-fertilization, but of protecting
the stigma against self-fertilization. When this
is considered, the direction in which the insect
entered would appear much more important
than comparative ease in getting at the nectar
or proximity of the orifices to the stamens.

One of the most remarkable cases of over-
sight in Darwin's work occurred in connection
with the Venus' Fly-trap. This plant is re-
stricted to a very narrowly limited locality in
North Carolina, and its organs are highly differ-
entiated for the purpose of catching insects.
Darwin could not reconcile the very limited
range of so highly specialized an insectivorous
plant with his general belief that the best
adapted plants and animals spread over the
earth and survive. In his discussion of Dioncea,
(Venus' Fly-trap), he said, " It is a strange fact
that Dion&a, which is one of the most beauti-
fully adapted plants in the vegetable kingdom,
should apparently be on the high road to ex-
tinction. This is all the more strange as the
organs of Dioncea are more highly differentiated
than those of Drosera." l

All the studi^ of forty years had borne out
the conviction that the adaptations of animals
and plants to their environment were the result

1 Insectivorous Plants, p. 358.

202 THE METHOD OF DARWIN.

of natural selection acting upon variations, and
preserving those that conduced to the preserva-
tion of the species. Following this principle,
it seemed almost self-evident that the more
highly specialized the organs of a plant or
animal are, and the more minutely adapted to
its surroundings and mode of life they become,
the more certain would the species be of con-
tinued existence and of success in the race of
life. He never, so far as I know, recognized
the inevitable consequence of extreme special-
ization. Had he pursued the deduction to the
end, he must have recognized the fact that a
high degree of specialization for a particular
mode of life is the mess of pottage for
which the birthright of the species has been
surrendered.

Darwin was familiar with, and recognized
the value of Agassiz's generalization that the
progenitors of the greater animal and plant
groups have been generalized forms. He him-
self deduced from his general theory the prin-
ciple that the species of the larger genera,
the wide ranging, much diffused, and common
species vary most, that they are more closely
related to each other, and that in this respect
they more nearly resemble varieties than do the
species of the smaller genera with restricted

ERRONEOUS DEDUCTION. 2O3

distribution.1 It is clear that the wide range
of a species, instead of depending on a high
degree of specialization for any one environ-
ment, depends rather on the absence of it. He
clearly recognized and pointed out the danger
of extinction to a species of limited range, but
nowhere recognized explicitly the connection,
on the one hand, between a high degree of
specialization for a particular environment or
mode of life and restriction of the species to
that particular environment, or the relation, on
the other hand, between wide range over the
earth and generalized characters which give
some general advantage that would be useful
under all or nearly all circumstances into which
the species might be thrown.

He said: "If we ask ourselves why this or
that species is rare, we answer that something
is unfavorable in its conditions of life; but
what that something is we can hardly ever tell."
He insisted that the improved and modified
forms would crowd out and exterminate the less
well adapted forms; but did not hit upon the
truth that, the more beautifully adapted a
species is to a definite locality and set of con-
ditions, the less it is adapted to enter into a
general competition for the possession of the

1 Origin of Species, pp. 42-44.

204 THE METHOD OF DARWIN.

earth. Both Agassiz's empirical generaliza-
tion that the progenitors of the principal plant
and animal groups were generalized forms,
and the deductive consequences of Darwin's
own theory of natural selection would indicate
that the highly differentiated forms are forever
handicapped. They have a present advantage
in having intensified their adaptation to a cer-
tain environment; but in the long run they
are doomed because they have lost the power
of adaptability to new conditions in direct
proportion to their present gain.

It is curious that Darwin had before him,
and mentioned in the same sentence, a case of
each kind: Dioncea, with its extreme adapta-
tions for insect catching, with only a single
species in the genus, restricted to a very small
locality, on the verge of extinction ; and Drostra,
with the same general advantage of catching
insects, but with no extreme adaptations, with
a vast number of species in the genus, dis-
tributed all but everywhere over the earth. It
is as great a surprise that he did not see the
connection between extreme specialization and
extinction on the one hand, and general advan-
tage and wide distribution on the other, as he
says it was to him that Dioncza is on the verge
of extinction. It is clearly inferable from

ERRONEOUS DEDUCTION. 205

these cases and the general principle of natural
selection that Nature has pronounced the sen-
tence of death upon highly specialized forms;
that they have passed out of the royal line of
descent for a special advantage; that if they
vary at all it can only be within the restricted
lines along which they have already gone so
far; and that the birthright belongs to forms
which have some general advantage, but are
not hampered by special adaptations. These
spread over the earth and from them branch
off the numerous closely related and variable
species that occupy all the environments of the
earth. Thus Drosera, with its power to catch
insects, is yet a plant like others, and has gone
forth with its advantage to possess the earth.
Vitis, with its climbing power, has scattered
its species by the hundred over the earth. It
is the modification that opens up to the species
a large area, which makes it possible for the
species to send out its kind into the whole
earth to be everywhere modified by local influ-
ences.

The principle that has been discussed is now
one of the well understood corollaries of the
principle of natural selection. I do not know
who first called attention to it. It has prob-
ably occurred to many minds independently.

206 THE METHOD OF DARWIN.

Darwin, so far as I know, never recognized it.
The earliest clear statement of it that I have
seen is by Prof. Joseph Le Conte in an article
on "Instinct and Intelligence," 1 published in
1875, only a few months after the publication
of Darwin's " Insectivorous Plants. " He said,
"Instinct, therefore, is accumulated experi-
ence, or knowledge of many generations fixed
M permanently and petrified in brain-structure.
All such petrifaction arrests development, be-
cause unadaptable to new conditions. They are
J £ound, therefore, only in classes and families
J^jJjjy^ widely differentiated from the main stem of evolu-
tion, from the lowest animals to man. Instincts
are, indeed, the flower and fruit at the end of
these widely differentiated branches, but flower-
ing and fruiting arrest onward growth." In
1877, Marsh, in a discussion of the suilline
type, stated the true principle when he said
that ambitious offshoots have perished, while
the generalized or rather unspecialized forms
continue the line of life with true suilline
stubbornness.2

1 Popular Science Monthly, October, 1875, P- 664.

2 American Journal of Science, XIV. (III.), pp. 362-364.

XIV.

GENERAL DISCUSSIONS.

DARWIN'S general discussions of the
various subjects that he worked out in
such minute detail are models both of clearness
and of exhaustiveness. The reasoning of the
second volume of the "Variation of Animals
and Plants under Domestication " is long sus-
tained and characterized by the use of enor-
mous numbers of facts. The latter is one of
the chief characteristics of his reasoning. He
was frequently compelled, as in the case of
the "Origin of Species," by the limits within
which he was obliged to condense his materials,
to substitute general statements for long series
of facts. The generalizations were condensa-
tions of the detailed facts, which were too
bulky for his pages. This is the reason why his
discussions leave the impression of an almost
infinite reserve of evidence; and rightly seem
to convey much more to the reader than is
actually written on the page.

Among Darwin's many exhaustive discus-

208 THE METHOD OF DARWIN.

sions of the materials which he had collected,
some of the most striking are his chapters on
pigeons,1 in which he considered the variation
of breeds, individual differences, and skeletal
differences; the discussion in the second volume
of the "Variation of Animals and Plants under
Domestication " ; the exhaustive analysis of his
materials in reaching his general conclusions
on the effects of cross- and self-fertilization;
and his repeated discussions of the cement
glands of Cirripedia, and of the parasitic and
complemental males on the hermaphrodite
"females," and the reasons for regarding them
as such rather than as independent forms.2
But the general discussion that is typical both
from the general interest of the subject and
the compactness and symmetry of the argument
is the work on the " Origin of Species."" It
would be impossible to analyze such a far-
reaching argument without restating it. Doubt-
less criticisms could be made against the
arrangement of materials and the order of dis-
cussion, and against the nature of the evidence
adduced. It is not intended here to raise the

1 Variation of Animals and Plants under Domestication,
Vol. I. pp. I37-235-

2 Monograph of Cirripedia, Vol. I. pp. 38, 180-293, Vol. II.
pp. 23-30, 151.

GENERAL DISCUSSIONS. 2 09

question whether his argument as a whole is
sound and carries conviction with it, but simply
to repeat that, considering the materials that
Darwin had to work with and the difficulties
under which he labored, the argument is
finished, and will always serve as a type of
probable proof.

Darwin himself has given the reasons for
this state of his great discussion. He has com-
plained that he must be a very slow thinker;
and doubtless the truth in this complaint
accounts for the fact that his thinking was
always so thorough. He also bewailed the fact
that he experienced great difficulty in writing.1
He felt that he had great ability to get things
wrong end foremost in his expression, and said
that he spent a great deal of time in arranging
the matter in his larger works. From one
point of view it is a paradox that such a man
should accomplish so much that has proved
of permanent value. But the lack of natural
felicity of expression and inability to think
rapidly, together with his persistence, insured
him against the vice of saying things nimbly,
and furnished the guaranty that whatever he
did would be thorough. It is safe to say that
a far larger proportion of false and inaccurate

1 Lifs and Letters, Vol. I. p. 80.
14

210 THE METHOD OF DARWIN.

statements and arguments with fatal flaws in
them are made by writers who express them-
selves easily, than by writers whose rhetorical
inability compels them to be painstaking.
When the expression is laboriously evolved by
an intellect that is otherwise strong, the thought
comes during the process to be regarded from
more points of view. In details there is greater
assurance of accuracy, and the proper relative
importance is more likely to be assigned to the
different phases of the truth. Given two intel-
lects equally conscientious, the slower moving
and more deliberate one will always hit upon
more phases of the truth than the quicker one.
Darwin attributed the success of the " Origin
of Species" to the way in which it was devel-
oped. Only when he had spent a number of
years in investigation, after he had got hold of
the theory of natural selection, did he allow
himself, in 1842, to draw up a brief thirty-five
page sketch of it. In 1844 he wrote a larger
sketch of two hundred and thirty pages. Then
followed years of laborious investigation, the
vast results of which were cast into an abstract
which, if it had been published, would have
been a very large work. Upon the urgent
advice of his friends, Lyell and Hooker, he
decided not to delay publication any longer;

GENERAL DISCUSSIONS. 211

but the large work was not in condition for
publication. An abstract of it was made; and
this abstract was the " Origin of Species." He
had written two condensed sketches, and finally
abstracted a much larger manuscript which was
itself an abstract.1 Probably no work was ever
better tempered and tested before it reached
the public eye.

1 Life and Letters, Vol. I. p. 70.

XV.

LOGICAL HISTORY OF THE PRINCIPLE OF
NATURAL SELECTION.

T^vARWIN'S own views of method, his treat-
•L ^ ment of evidence, and some of the
various logical processes which he employed in
his investigations, having been discussed and
illustrated by examples from his many works,
it now remains necessary to trace the logical
history and examine the present logical status
of the principle of natural selection, which gave
inspiration to and lay at the basis of his life-
work. The theory of natural selection has per-
meated and colored modern thought more deeply
than perhaps any other scientific theory, and
this fact alone makes the study of its logical
history extremely interesting.

The scientific influences, both in the form
of teachers and of books, to which Darwin was
exposed during and after his university life,
were opposed to the already well known doc-
trine of the descent of species. Various reasons
have been assigned for the failure of the doc-

PRINCIPLE OF NATURAL SELECTION. 21$

trine to impress itself upon scientific men.
The difficulty did not lie in the circumstance
that the facts of botany and zoology were
opposed to it; for it first took its rise out of
them. The affinities of species and of the
higher groups, and the facts of embryology,
distribution, and palaeontology by themselves
were sufficient to force the conviction that
species are derived, and the doctrine would
doubtless have won its way at once had it not
had to make head against the imported belief
in creation. Had the doctrines of descent and
creation been for the first time presented to the
scientific mind as alternative beliefs, there can
be no doubt that the former would have been
chosen as the true explanation of the facts,
even though no force capable of producing the
effects had been assigned. The cause would
still remain to be investigated, while the facts
would be brought together under a single point
of view. With the adoption of creation as an
explanation, an efficient cause is provided, but
the facts remain worthless either to prove or
to disprove the doctrine. It is not enough that
a cause should be capable of producing given
effects, but it should produce the given effects
and be incapable of producing any other set
of effects. In short, by the former view the

214 THE METHOD OF DARWIN.

special character of the facts is accounted for,
but from the latter it is impossible to deduce
the specific character of any phenomena. Any
other set of facts exhibiting a plan or purpose
of any kind could be deduced with equal ease
from the doctrine of creation.

When Darwin started on the Beagle voyage
he was orthodox on the question of the ori-
gin of species. As he travelled, and as his
knowledge of zoology and palaeontology became
wider and deeper, the doctrine of descent began
to take hold of him. The relation of the liv-
ing animals to the fossil species in South
America, the manner in which closely allied
animals replaced one another as he proceeded
southward over the continent, the South Amer-
ican character of the productions of the Gala-
pagos archipelago, and especially the slight
but distinct differences of the flora and fauna
on neighboring islands of the archipelago, im-
pressed him so strongly with the peculiar char-
acter of the facts and the necessity of a definite
mode of origin that he began to see the differ-
ence in the logical characters of the doctrines of
creation and descent1 The facts were better
explained by the latter than by the former; and
he connected them at least tentatively with the

1 Life and Letters, Vol. I. p. 67 ; Origin of Species, p. 2.

PRINCIPLE OF NATURAL SELECTION. 21$

old doctrine of descent. But as he himself
remarked, a naturalist might be convinced by
affinities, embryology, distribution, etc., that
species are derived by descent; but the conclu-
sion, though correct, would be unsatisfactory
until it was shown how it was brought about.

Lamarck had assigned causes for the modifi-
cation of species ; but Darwin insisted positively
that he derived no help whatever from him.
Logically, the failure of the former's doctrines
to win over the scientific world was due to his
connecting the doctrine of descent, which had
strong evidence in its favor, with hypothetical
causes which he did not subject to rigid de-
ductive tests in explanation of the facts. What
kept Darwin longest orthodox were the facts
of adaptation. No cause could be considered
adequate which did not account for the exqui-
site adaptation to environment found through-
out the animal and plant kingdoms. As he
said himself, " I had always been much struck
by such adaptation, and until these could be
explained it seemed to me almost useless to
endeavor to prove by indirect evidence that
species have been modified."1 He distin-
guished clearly in his own mind between the
two propositions which he undertook to prove

1 Life and Letters, Vol. I. p. 67.

2l6 THE METHOD OF DARWIN.

in the " Origin of Species " : first, that species
are derived by modification from other species,
and, secondly, that Natural Selection is the
chief cause of this modification. He did not
originate the former; the logical relation of his
work to it is deductive, and largely took the
form of an answer to the question, Do the facts
of Nature harmonize with the hypothesis?

The cause of the modification of species could
not even be raised as a question until the fact
of modification had been accepted, at least ten-
tatively. He recognized the cause of specific
modification as a problem to be solved, a prin-
ciple to be discovered by induction from the
effects it produced in the form of adaptations.
To quote his own words: "My first note-book
was opened in July, 1837. I worked on true
Baconian principles, and without any theory
collected facts on a wholesale scale, more
especially with respect to domesticated pro-
ductions," etc.1 He had rejected Lamarck's
suggestions, and it would seem impossible to
imagine a more interesting or more purely
inductive problem than that which presented
itself to him. There was for him no clew to
the cause which he wished to discover except
in the vast wealth of material which he regarded

i Life*nd Letters, Vol. I. p. 68.

PRINCIPLE OF NATURAL SELECTION, 21 /

as its effects. To have discovered the cause
by an analysis of the effects would indeed have
been a triumphant inductive discovery.

He selected wisely the material on which
to concentrate the investigation ; he said : " I
soon perceived that selection was the keystone
of man's success in making useful races of
animals and plants. But how selection could
be applied to organisms living in a state of
nature remained for some time a mystery to
me." In his study of domestic races he ob-
served both the effects (races) and the cause
(selection), and did not, except perhaps in
details, reason deductively from the cause to
discover the effect, or inductively from the
effects to discover the cause. The effort to
extend the principle of selection by induction
to animals and plants in a state of nature failed
because it was impossible to see how the prin-
ciple could be applied. The inductive problem
was apparently as far from solution as at the be-
ginning; he was still groping in the dark. It
would be a bootless speculation to try to answer
the question whether Darwin could ever have
solved by a study of adaptations the problem
which he set for himself. It would be hardy
to hold that a man with Darwin's intellectual
and moral resources, with his clear conception

2l8 THE METHOD OF DARWIN.

of the problem and the data from which it was
to be solved, could not have derived the cause
from an analysis of the effects ; and yet very
few problems like this were ever solved by
pure induction. It may be possible to infer
the nature of a cause from the nature of the
effects, but nearly always observers manage to
catch a glimpse of the cause at work. Then,
by a generalization, the cause is extended to all
the other effects of the same kind.

In October, 1838, at the end of fifteen
months of work on Baconian principles, with-
out any theory, he read Malthus on Population
for amusement.1 There had been much dis-
cussion in the eighteenth century concerning
the vice and misery in human society. It
was quite commonly believed that they were
due to the organization of society, and tha-t
they could be eliminated by reorganization of
society according to some ideal. The father
of Malthus shared this view; but the son, in
discussion with him, took the position that, no
matter how society might be organized, vice and
misery would follow inevitably from the fact
that the human race naturally increases more
rapidly than the means of subsistence. This
notion was finally developed into the " Prin-

1 Life and Letters, Vol. I. p. 68.

PRINCIPLE OF NATURAL SELECTION. 2IQ

ciple of Population," which fell into Darwin's
hands. The purpose of Malthus in this work
was to investigate the causes that had hitherto
impeded the progress of mankind toward hap-
piness. After establishing the principle that
population has a tendency to increase in geo-
metrical ratio, while the food supply can at best
increase only in arithmetical ratio, he pointed
out that the ultimate check to the increase of
population is lack of food; and that all the
immediate checks could be included under three
heads, moral restraint, vice, and misery, — and
urged moral restraint as a check to population,
because by it alone could vice and misery be
driven out of the world.1

Malthus stated with perfect clearness "the
constant tendency in all animated life to in-
crease beyond the nourishment prepared for
it," and the consequent struggle for existence;
and insisted that in every country, speaking of
the human family, some of the checks to popu-
lation are, with more or less force, in constant
operation.2 He recognized both artificial and
natural selection as results of the struggle for
existence. In the chapter on the " Checks to
Population among the American Indians," he
said: —

1 Malthus, Principle of Population (gth edition), pp. 1-8.

2 Ibid., p. 9.

22O THE METHOD OF DARWIN.

"As the parents are frequently exposed to
want themselves, the difficulty of supporting
their children becomes at times so great that
they are reduced to the necessity of abandon-
ing or destroying them. Deformed children
are very generally exposed ; and among some
of the tribes in South America, the children of
mothers who do not bear their labors well ex-
perience a similar fate from a fear that the off-
spring may inherit the weakness of its parent.

"To causes of this nature we must ascribe
the remarkable exemption of the Americans
from deformities of make. Even when a mother
endeavors to rear all her children without dis-
tinction, such a proportion of the whole number
perishes under the rigorous treatment which
must be their lot in the savage state, that prob-
ably none of those who labor under any original
weakness or infirmity can attain the age of
manhood. If they be not cut off as soon as
they are born, they cannot long protract their
lives under the severe discipline that awaits
them. In the Spanish provinces, where the
Indians do not lead so laborious a life, and
are prevented from destroying their children,
great numbers of them are deformed, dwarfish,
mutilated, blind, and deaf."1

1 Principle of Population, Chap. IV. pp. 20, 21.

PRINCIPLE OF NATURAL SELECTION. 221

It seems almost astounding that Malthus did
not recognize the importance of this principle
of natural selection based on the struggle for
existence and develop it deductively. Had he
worked out the principle of the survival of the
fittest among human beings after he so clearly
recognized it, it would have borne rich fruit
for the happiness doctrine. It would have re-
moved much of the gloom from his principle of
population, by showing that much permanent
good — much more, in fact, than from moral
restraint — arises from the struggle for exist-
ence by its preserving those best fitted to enjoy
life. From another point of view, the fact that
he did not develop the principle of natural
selection, at least within the human race, after
he had so plainly recognized both its action
and its effects, is not even remarkable. When
one has once made a study of the deductive
powers of such a man as Darwin, and finds that
with his great logical strength he sometimes
failed altogether, and was often very long in
reaching deductively the consequences of his
theory, it is not to be wondered at that Malthus
did not grasp one of the most important features
of his principle.

Since he failed to apply the principle of
natural selection within the human species,

222 THE METHOD OF DARWIN.

after he had himself stated clearly its action
and results, there is no cause for wonder at his
not applying it to the derivation of species.
In fact, there was a good reason why he should
not do the latter. He expressed himself vigor-
ously in opposition to the belief that a species
can vary by an indefinite amount in any given
direction; and denied Condorcet's theory of
the indefinite perfectibility of the human race.1
He admitted only a limited amount of varia-
tion within a species. Malthus. had worked out
the struggle for existence and recognized its
selective action, at least within a limited range;
and as a natural theologian he must have been
acquainted with numerous adaptations. But
he did not connect them as cause and effect,
because he did not admit general variability
of species, without which there could be no
material for the cause to act upon.

When the work of Malthus fell into Darwin's
hands, the latter was in possession of the doc-
trine of descent, and many facts in harmony
with it, and hence the convi.ction in his mind
that there was an efficient cause for these facts.
The adaptations found in nature seemed the
most difficult facts to explain under the theory
of descent, and Darwin was already widely

1 Principle of Population, p 270.

PRINCIPLE OF NATURAL SELECTION. 22$

acquainted with these. He had recognized, as
did others before him, specific variations as
material out of which new species must be
made, and had gone to work systematically to
study variations, especially in domestic pigeons,
the most favorable group of animals that could
have been selected ; and had recognized selec-
tion as the key to man's success in the produc-
tion of races. His study hitherto had helped
him to a wider knowledge and clearer notion
of adaptations, —the effects that had to be
explained; and a better understanding of the
nature and range of variations, — the materials
upon which the cause must have acted to pro-
duce the effects. And in the case of domestic
productions he was in full possession of the
cause, the materials on which the cause acted,
and the results, in selection, variations, and
races. As he himself said, he had been fully pre-
pared by his long study of the habits of animals
to appreciate the struggle for existence which
everywhere goes on. " It at once struck me," he
said, "that under these circumstances favorable
variations would be preserved and unfavorable
ones destroyed. The result of this would be
the formation of new species. Here, then, I had
at last got a theory by which to work." 1

1 Life and Letters, Vol. I. p. 68.

224 THE METHOD OF DARWIN.

It is not recorded at what point in his read-
ing of Malthus it struck him that the struggle
for existence, by working upon variations, would
produce new species. Probably with his mind
so thoroughly imbued with the subject that
everything he read was made to bear upon the
problem he almost instantaneously caught the
significance of the principle. Malthus himself
stated the principle clearly in the first few
pages of the book, and already on pages 21, 22,
of the ninth edition stated its action and effects
upon the American Indians. The significance
of these details is great from the logical point
of view. All the years of the Beagle voyage
had prepared Darwin to appreciate the principle.
The time since his return had strengthened his
belief in the descent of species, and his efforts
to reach the cause of modification inductively
had brought him detailed knowledge of both
variations and adaptations. What he had not
hitherto been able to discover by induction
came to him by accident, if it can be said that
anything can come by accident to a mind so
much on the alert for it. It would have been
one of the most fascinating chapters in scien-
tific discovery if he had recorded in detail the
mental activity and the feelings that must have
flooded him from the moment the discovery was

PRINCIPLE OF NATURAL SELECTION. 22$

made. There was an intellectual explosion, a
flash of the mind, and from that moment his
life-work was devoted to elaborating the conse-
quences of the principle. The facts which he
had been gathering and reflecting upon were
explained as the effects of the cause which
Malthus presented, and gathered a new sig-
nificance from it.

" Here, then, I had at last got a theory by
which to work," he said. The groping was at
an end. His future work was outlined. The
confession in that sentence can be appreciated
only by one who has in his own experience
passed from the mental strain and perplexity
of a purely inductive effort to the solid ground
afforded by even a fairly probable hypothesis.
Doubtless his work was thenceforth many times
more rapid than it could otherwise have been;
for with so vast a number of facts to be con-
sidered the theory itself was the only pathfinder.
Only after the discovery of the principle could
the work of gathering up and classifying known
facts and of searching for new ones, of reducing
exceptions and apparently unexplainable groups
of facts, go on apace. The logical process by
which adaptations, variations, and the struggle
for existence were brought together into the
relation of cause and effect was deductive; and

226 THE METHOD OF DARWIN.

the principle of Natural Selection still de-
pends for its logical support upon that power of
deductive explanation which Darwin recognized
in it the day he read Malthus on Population.
It has penetrated every field of thought, but in
the field in which it first gathered strength it
is still without direct demonstration. It has
been made the basis for countless deductive
operations, but it leans for support on the very
structures thus erected. Writing to Bentham,
in 1863, concerning the proofs of natural selec-
tion and the descent of species, Darwin said,
"Belief in natural selection must at present be
grounded entirely on general considerations :
(i) on its being a vera causa from the struggle
for existence; ... (2) from the analogy of
change under domestication by man's selection;
(3) and chiefly from this view connecting
under an intelligible point of view a host of
facts. " 1 To Huxley he said, in December,
1860, "I can pretty plainly see that, if my
view is ever to be generally adopted, it will
be by young men growing up and replacing the
old workers, . . . and finding out that they can
group facts and search out new lines of inves-
tigation better on the notion of descent than on
that of creation."2

1 Life and Letters, Vol. II. p. 210. 2 Ibid., p. 147.

PRINCIPLE OF NATURAL SELECTION. 22 J

From a logical point of view the work of the
last thirty years in the various fields of biology
has been a series of deductions and verifica-
tions of the original propositions laid down
by Darwin. He saw from the beginning that
belief in his theory must rest on general con-
siderations, the chief of which was its power
to facilitate deductive investigation; and there
it still rests. At this late day the chief apostle
of natural selection says that it is really diffi-
cult to imagine the process of natural selection
in its details, and that it is impossible to this
day to demonstrate it in any one point.1 It
is the logical relation of the principle to the
facts that makes it invaluable in modern
thought. The whole logical history of Dar-
win's principles illustrates what Mill said of
the deductive method. "To the Deductive
Method thus characterized in its three con-
stituent parts, Induction, Ratiocination, and
Verification, the human mind is indebted for
its most conspicuous triumphs in the investiga-
tion of nature. To it we owe all the theories
by which vast and complicated phenomena are
embraced under a few simple laws, which, con-
sidered as the laws of these great phenomena,

1 Weissmann, Contemporary Review, September, 1893, Vol.
LXIV. p. 322.

228 THE METHOD OF DARWIN.

could never have been detected by their direct
study." Writing of the celestial motions as
an illustration, he continued, "How could we
ever have ascertained the combination of forces
on which the motions of the earth and planets
are dependent by merely comparing the orbits
or velocities of different planets or the different
velocities and positions of the same planet ? "

Darwin himself did not discover the cause by
the direct study of the effects ; but his efforts
to reach a cause inductively gave him such an
insight into variations and adaptations that he
could prosecute vigorously the other two steps,
deduction and verification, when once the cause
was given. What Mill said of celestial motions
could be almost literally quoted of adaptations.
It would hardly be going beyond the facts to
say that the history of theories proves that
usually not even preliminary hypotheses con-
cerning causes are worked out directly from an
analysis of effects; but the causes are usually
caught in action during the effort to discover
them inductively, or are reached in a round-
about way.

XVI.

CONCLUSION.

MUCH might be said concerning the per-
sonal qualities of the man that did so
much scientific work of such uniformly high
character. The moral force that overcame life-
long physical suffering, that stood through
many years of silent toil face to face with the
certainty of abuse for its reward, that never
knew defeat and remained calm during the
years of victory, has a powerful influence on
the student of Darwin. The utter lack of
partisanship for any idea, the rare judicial
temper that made truth seem better than any
theory, the penetration, the power of concen-
tration, the firm mental grasp, the inability to
leave anything unexplained, — all these high
qualities have their silent evidence in the char-
acter of Darwin's scientific work. But his
intellectual and moral traits have been touched
upon here only in so far as was necessary in
order to discuss clearly his use of the logical
processes. The effectiveness of these processes

230 THE METHOD OF DARWIN.

must always be entirely dependent on the char-
acter of the individual using them.

Darwin's views on method can be summed
up in the assertion that he was afraid of every
statement or hypothesis until it was tested,
and indeed regarded an unverified belief as
worthless. The starting points of his investi-
gations were frequently what seemed to other
men interesting, but unimportant or incon-
venient exceptional facts. When he sought
explanations he seemed to be trying to get a
conclusion by the shortest and easiest route,
with as little labor as possible. But when he
had once got an hypothesis he dragged it before
all the multitude of facts that could be made
to bear witness to its truth or falsity, until it
seemed as if he were trying to make the inves-
tigation last as long as possible. Time seemed
no longer worth considering. He always used
the isolated phenomena which were most diffi-
cult to explain as tests of the validity of his
hypotheses. )/ By considering all possible objec-
tions during the progress of the development
of his conceptions, he threw a merciless light
on the weaknesses of his theories, and thus
gave them, in their final form, as high a degree
of probability as was possible. In his treat-
ment of negative evidence he never lost sight

CONCLUSION. 231

of its comparatively small value, and continued
the investigation until, by careful observation
of all collateral facts, he was able to combine
them into a body of positive evidence in sup-
port of a different or supplemental theory.

Classification was with him an invaluable
instrument for extracting information from
bodies of facts. His works teem with compar-
ative tables and statements of results derived
from them. Analogical reasoning, with all its
strength and weakness, was utilized as a power-
ful instrument of suggestion. Induction was
constantly active in the formation of hypoth-
eses. He could leave nothing unexplained.
He made an hypothesis for everything, and
then tested it unmercifully by deduction. He
appreciated the immense importance of theory
to good observation, explained in the light of
his general theories great bodies of facts and
principles which had been discovered empiri-
cally, and anticipated many important conse-
quences of those theories. Whenever it was
possible he undertook to verify those anticipa-
tions ; but did not hesitate to make predictions
that he could not verify. And with all his
vast and accurate knowledge of facts and his
logical power, he frequently fell into erroneous
reasoning.

232 THE METHOD OF DARWIN.

The processes employed in scientific inves-
tigations, although some of them have been
treated in separate chapters, have a vital inter-
dependence. Darwin did not and could not use
one process until its resources were exhausted,
and then turn to another. It was the very
swiftness with which different processes were
successively brought to bear upon his problems
that made it possible to digest so thoroughly
every set of facts with which he dealt. What-
ever may be the future of the particular con-
clusions which Charles Darwin reached, the
general method which he employed and the
general drift of his conclusions will have a
permanent value. All his efforts tended toward
the unification of knowledge. All his induc-
tions became corollaries of one great theory;
all his deductions had to do with efforts "to
test and prove the truth of that theory. The
subordination of all the devices of the intellect
to one great comprehensive purpose has given
a unity of aim to all the great works of his life,
has made his general method conspicuously
lucid, and has knit the products of his intellect
into one great logical whole.

THE END.

EcfT!B^vN

IT KT T \r -r- T^ „ ^\

LAUREL-CROWNED LETTERS.

BEST LETTERS OF LORD CHESTERFIELD. With an Intro-
duction by EDWARD GILPIN JOHNSON.

BEST LETTERS OF LADY MARY WORTLEY MONTAGU,
With an Introduction by OCTAVE THANET.

,BEST LETTERS OF HORACE WALPOLE. With an Intro-
duction by ANNA B. MCMAHAN.

BEST LETTERS OF MADAME DE SEVIGNE. With an
Introduction by EDWARD PLAYFAIR ANDERSON.

BEST LETTERS OF CHARLES LAMB. With an Introduction
by EDWARD GILPIN JOHNSON.

BEST LETTERS OF PERCY BYSSHE SHELLEY. With an
Introduction by SHIRLEY C. HUGHSON.

BEST LETTERS OF WILLIAM COWPER. With an Intro-
duction by ANNA B. MCMAHAN.

Handsomely printed from new plates, on fine laid paper, i6mo,
cloth, with gilt tops, price per volume, $1.00.

In half calf or half morocco, per volume, $2.50.

Amid the great flood of ephemeral literature that pours from
the press, it is well to be recalled by such publications as the
" Laurel-Crowned Letters " to books that have won an abiding
place in the classical literature of the world. — The Independent ',
New York.

The " Laurel-Crowned Series" recommends itself to all lovers
of good literature. The selection is beyond criticism, and puts
before the reader the very best literature in most attractive and
convenient form. The size of the volumes, the good paper, the
clear type and the neat binding are certainly worthy of all praise.
Public Opinion, Washington.

These " Laurel-Crowned " volumes are little gems in their
way, and just the books to pick up at odd times and at intervals
of waiting. — Herald, Chicago.

Sold by all booksellers, or mailed, on receipt of price, by

A. C. McCLURG & CO., PUBLISHERS,
CHICAGO.

LAUREL-CROWNED VERSE.

Edited by FRANCIS F. BROWNE.

THE LADY OF THE LAKE. By SIR WALTER SCOTT.

CHILDE HAROLD'S PILGRIMAGE. A Romaunt. By
LORD BYRON.

LALLA ROOKH. An Oriental Romance. By THOMAS
MOORE.

IDYLLS OF THE KING. By ALFRED, LORD TENNYSON.

PARADISE LOST. By JOHN MILTON.

THE ILIAD OF HOMER. Translated by ALEXANDER POPE.

2 Vols.

Each volume is finely printed and bound ; i6mo, cloth, gilt tops,
price per volume, #1.00.

In half calf or half morocco, per volume, $2.50.

All the volumes of this series are from a specially prepared
and corrected text, based upon a careful collation of all the more
authentic editions.

The special merit of these editions, aside from the graceful form
of the books, lies in the editor's reserve. Whenever the author
has provided a preface or notes, this apparatus is given, and thus"
some interesting matter is revived, but the editor himself refrains
from loading the books with his own writing. — The Atlantic
Monthly.

A series noted for their integral worth and typographical
beauties. — Public Ledger, Philadelphia.

The typography is quite faultless. — Critic ^ New York.

For this series the publishers are entitled to the gratitude of
lovers of classical English. — Schooljournal, New York.

Sold by all booksellers, or mailed, on receipt of price \ by

A. C. McCLURG & CO., PUBLISHERS,
CHICAGO.

LAUREL-CROWNED TALES.

ABDALLAH; OR, THE FOUR-LEAVED SHAMROCK. By ED.

GUARD LABOULAYE. Translated by MARY L. BOOTH.
RASSELAS, PRINCE OF ABYSSINIA. By SAMUEL JOHNSON.
RAPHAEL; OR, PAGES OF THE BOOK OF LIFE AT TWENTY.

From the French of ALPHONSE DE LAMARTINE.
THE VICAR OF WAKEFIELD. By OLIVER GOLDSMITH
THE EPICUREAN. By THOMAS MOORE,
PICCIOLA. By X. B. SAINTINE.
AN ICELAND FISHERMAN. By PIERRE LOTI.
PAUL AND VIRGINIA. By BERNARDIN DE ST. PIERRE.

Handsomely printed from new plates, on fine laid paper, i6mo,
cloth, with gilt tops, price per volume, #1.00.

In half calf or half morocco, per volume, $2.50.

In planning this series, the publishers have aimed at a form
which should combine an unpretentious elegance suited to the fas-
tidious book-lover with an inexpensiveness that must appeal to the
most moderate buyer.

It is the intent to admit to the series only such tales as have
for years or for generations commended themselves not only to
the fastidious and the critical, but also to the great multitude of
the refined reading public, — tales, in short, which combine purity
and classical beauty of style with perennial popularity.

A contribution to current literature of quite unique value and
interest. They are furnished with a tasteful outfit, with jusv
the amount of matter one likes to find in books of this class, and
are in all ways very attractive. — Standard, Chicago.

Sold by all booksellers, or mailed, on receipt of price, by

A. C. McCLURG & CO., PUBLISHERS,
CHICAGO.

TALES FROM FOREIGN LANDS.

MEMORIES. A Story of German Love. Translated from

the German of MAX MULLER by GEORGE P. UPTON.
GRAZIELLA. A Story of Italian Love. Translated from

the French of A. DE LAMARTINE, by JAMES B. RUNNION.
MARIE. A Story of Russian Love. From the Russian of

ALEXANDER PUSHKIN, by MARIE H. DE ZIELINSKA.
MADELEINE. A Story of French Love (crowned by the

French Academy). Translated from the French of JULES

SANDEAU by FRANCIS CHARLOT.
MARIANELA. A Story of Spanish Love. Translated

from the Spanish of B. PEREZ GALDOS, by HELEN W.

LESTER.

COUSIN PHILLIS. A Story of English Love. By Mrs.
GASKELL.

Handsomely printed on fine laid paper, i6mo, gilt tops, per vol-
ume, $1.00. The six volumes in neat box, per set, $6.00; in
half calf or half morocco, gilt tops, #13. 50 ; in half call or
half morocco, gilt edges, $15.00; limp calf or morocco, gilt
edges, $18.00.

This series of volumes forms perhaps the choicest addition to
the literature of the English language that has been made
in recent years.

An attractive series of stories of love in different countries, — all
gems of literature, full of local coloring. — Journal of Education,
Boston.

The stories are attractive for their punty, sweetness, and
pathos. ... A rare collection of representative national classics.
New York Telegram.

A series especially to be commended for the good taste dis-
played in the mechanical execution of the works. Typo and
paper are everything that could be desired, and the volumes are
set off with a gilt top which adds to their general appearance of
neatness. — Herald, Rochester.

Sold by all booksellers, or mailed, on receipt of price, "by

A. C. McCLURG & CO., PUBLISHERS,
CHICAGO.

MASTERPIECES OF FOREIGN
AUTHORS.

DOCTOR ANTONIO. By GIOVANNI D. RUFFINI.

THE MORALS AND MANNERS OF THE SEVENTEENTH
CENTURY. Being the Characters of LA BRUYERE. Trans-
lated by HELEN STOTT. Portrait.

GOETHE'S WILHELM MEISTER'S APPRENTICESHIP AND
TRAVELS. Translated by THOMAS CARLYLE. With Critical
Introduction by EDWARD DOWDEN, LL.D. Edited, with
notes, by C. K. SHORTER. Portrait. 2 vols.

PORTRAITS OF MEN. By C. A. SAINTE-BEUVE. Trans-
lated by FORSYTH EDEVEAIN. With Critical Memoir by
WILLIAM SHARP. Portrait.

PORTRAITS OF WOMEN. By C. A. SAINTE-BEUVE. Trans-
lated by HELEN STOTT. Portrait.

NOVALIS (FRIEDRICH VON HARDENBERG). His Life,
Thoughts, and Works. Edited and Translated by M. J.
HOPE.

THE COMEDIES OF CARLO GOLDONI. Edited, with
Introduction, by HELEN ZIMMERN.

In uniform i6mo size, cloth binding, per volume, 75 cents; half
vellum, gilt top, per volume, $1.00.

This series comprises translations of single masterpieces by
some of the best-known European writers, some of which have
never before, been presented in an English dress. The volumes
are well printed on good paper, and very prettily bound.

The " Masterpieces of Foreign Authors" unite intrinsic value
with external attractiveness. — Public Ledger, Philadelphia.

The work of the translators is beautifully done, and the pub
lishers have made dainty little volumes sure to win the apprecia-
tive regard of every book-loving eye. — Chicago Times.

Sold by all booksellers, or mailed, on receipt of price, by

A. C. McCLURG & CO., PUBLISHERS,
CHICAGO.

14 DAY USE

RETURN TO DESK FROM WHICH BORROWED

LOAN DEPT.

This book is due on the last date stami

on the date to which
Renewed books are subje

REG P LD

2 7'64 -10 AM

APR 9

RECU

JAN -4 1969

LD 21A-50m-8,'61
(Cl795slO)476B

General Library

University of California

Berkeley

YB 12543