THE INTERNATIONAL SCIENTIFIC SERIES.
VOLUME XLIV.
I HAVE recently learnt from the publishers of the 'International
Scientific Series' that they have made arrangements with Sir John
Lubbock to bring out in the same series a work of his on Ants and Bees.
Necessarily, therefore, the material to be dealt with in his work will
to a large extent overlap that which is presented by my chapters on the
same insects; but after consulting with the publishers, and also with
Sir John Lubbock, it has seemed to me undesirable to omit these chapters
on account of the circumstances here stated. For, on the one hand, the
facts will not lose their value from being twice told; and on the other,
it is desirable that the present member of the Series should form in
itself, so far as its Author can make it, a complete _résumé_ of all the
more important facts of _Animal Intelligence_.
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ANIMAL INTELLIGENCE.
BY
GEORGE J. ROMANES, M. A., LL. D., F. R. S.,
ZOOLOGICAL SECRETARY OF THE LINNEAN SOCIETY.
NEW YORK:
D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.
1884.
PREFACE.
WHEN I first began to collect materials for this work it was my
intention to divide the book into two parts. Of these I intended the
first to be concerned only with the facts of animal intelligence, while
the second was to have treated of these facts in their relation to the
theory of Descent. Finding, however, as I proceeded, that the material
was too considerable in amount to admit of being comprised within the
limits of a single volume, I have made arrangements with the publishers
of the 'International Scientific Series' to bring out the second
division of the work as a separate treatise, under the title 'Mental
Evolution.' This treatise I hope to get ready for press within a year or
two.
My object in the work as a whole is twofold. First, I have thought it
desirable that there should be something resembling a text-book of the
facts of Comparative Psychology, to which men of science, and also
metaphysicians, may turn whenever they may have occasion to acquaint
themselves with the particular level of intelligence to which this or
that species of animal attains. Hitherto the endeavour of assigning
these levels has been almost exclusively in the hands of popular
writers; and as these have, for the most part, merely strung together,
with discrimination more or less inadequate, innumerable anecdotes of
the display of animal intelligence, their books are valueless as works
of reference. So much, indeed, is this the case, that Comparative
Psychology has been virtually excluded from the hierarchy of the
sciences. If we except the methodical researches of a few distinguished
naturalists, it would appear that the phenomena of mind in animals,
having constituted so much and so long the theme of unscientific
authors, are now considered well-nigh unworthy of serious treatment by
scientific methods. But it is surely needless to point out that the
phenomena which constitute the subject-matter of Comparative Psychology,
even if we regard them merely as facts in Nature, have at least as great
a claim to accurate classification as those phenomena of structure which
constitute the subject-matter of Comparative Anatomy. Leaving aside,
therefore, the reflection that within the last twenty years the facts of
animal intelligence have suddenly acquired a new and profound
importance, from the proved probability of their genetic continuity with
those of human intelligence, it would remain true that their systematic
arrangement is a worthy object of scientific endeavour. This, then, has
been my first object, which, otherwise stated, amounts merely to passing
the animal kingdom in review in order to give a trustworthy account of
the grade of psychological development which is presented by each group.
Such is the scope of the present treatise.
My second, and much more important object, is that of considering the
facts of animal intelligence in their relation to the theory of Descent.
With the exception of Mr. Darwin's admirable chapters on the mental
powers and moral sense, and Mr. Spencer's great work on the Principles
of Psychology, there has hitherto been no earnest attempt at tracing the
principles which have been probably concerned in the genesis of Mind.
Yet there is not a doubt that, for the present generation at all
events, no subject of scientific inquiry can present a higher degree of
interest; and therefore it is mainly with the view of furthering this
inquiry that I have undertaken this work. It will thus be apparent that
the present volume, while complete in itself as a statement of the facts
of Comparative Psychology, has for its more ultimate purpose the laying
of a firm foundation for my future treatise on Mental Evolution. But
although, from what I have just said, it will be apparent that the
present treatise is preliminary to a more important one, I desire to
emphasise this statement, lest the critics, in being now presented only
with a groundwork on which the picture is eventually to be painted,
should deem that the art displayed is of somewhat too commonplace a
kind. If the present work is read without reference to its ultimate
object of supplying facts for the subsequent deduction of principles, it
may well seem but a small improvement upon the works of the
anecdote-mongers. But if it is remembered that my object in these pages
is the mapping out of animal psychology for the purposes of a subsequent
synthesis, I may fairly claim to receive credit for a sound scientific
intention, even where the only methods at my disposal may incidentally
seem to minister to a mere love of anecdote.
It remains to add a few words on the principles which I have laid down
for my own guidance in the selection and arrangement of facts.
Considering it desirable to cast as wide a net as possible, I have
fished the seas of popular literature as well as the rivers of
scientific writing. The endless multitude of alleged facts which I have
thus been obliged to read, I have found, as may well be imagined,
excessively tedious; and as they are for the most part recorded by
wholly unknown observers, the labour of reading them would have been
useless without some trustworthy principles of selection. The first and
most obvious principle that occurred to me was to regard only those
facts which stood upon the authority of observers well known as
competent; but I soon found that this principle constituted much too
close a mesh. Where one of my objects was to determine the upper limit
of intelligence reached by this and that class, order, or species of
animals, I usually found that the most remarkable instances of the
display of intelligence were recorded by persons bearing names more or
less unknown to fame. This, of course, is what we might antecedently
expect, as it is obvious that the chances must always be greatly against
the more intelligent individuals among animals happening to fall under
the observation of the more intelligent individuals among men. Therefore
I soon found that I had to choose between neglecting all the more
important part of the evidence--and consequently in most cases feeling
sure that I had fixed the upper limit of intelligence too low--or
supplementing the principle of looking to authority alone with some
other principles of selection, which, while embracing the enormous class
of alleged facts recorded by unknown observers, might be felt to meet
the requirements of a reasonably critical method. I therefore adopted
the following principles as a filter to this class of facts. First,
never to accept an alleged fact without the authority of some name.
Second, in the case of the name being unknown, and the alleged fact of
sufficient importance to be entertained, carefully to consider whether,
from all the circumstances of the case as recorded, there was any
considerable opportunity for mal-observation; this principle generally
demanded that the alleged fact, or action on the part of the animal,
should be of a particularly marked and unmistakable kind, looking to the
end which the action is said to have accomplished. Third, to tabulate
all important observations recorded by unknown observers, with the view
of ascertaining whether they have ever been corroborated by similar or
analogous observations made by other and independent observers. This
principle I have found to be of great use in guiding my selection of
instances, for where statements of fact which present nothing
intrinsically improbable are found to be unconsciously confirmed by
different observers, they have as good a right to be deemed trustworthy
as statements which stand on the single authority of a known observer,
and I have found the former to be at least as abundant as the latter.
Moreover, by getting into the habit of always seeking for corroborative
cases, I have frequently been able to substantiate the assertions of
known observers by those of other observers as well or better known.
So much, then, for the principles by which I have been guided in the
selection of facts. As to the arrangement of the facts, I have taken the
animal kingdom in ascending order, and endeavoured to give as full a
sketch as the selected evidence at my disposal permitted of the
psychology which is distinctive of each class, or order, and, in some
cases, family, genus, or even species. The reason of my entering into
greater detail with some natural groups than with others scarcely
requires explanation. For it is almost needless to say that if the
animal kingdom were classified with reference to Psychology instead of
with reference to Anatomy, we should have a very different kind of
zoological tree from that which is now given in our diagrams. There is,
indeed, a general and, philosophically considered, most important
parallelism running through the whole animal kingdom between structural
affinity and mental development; but this parallelism is exceedingly
rough, and to be traced only in broad outlines, so that although it is
convenient for the purpose of definite arrangement to take the animal
kingdom in the order presented by zoological classification, it would be
absurd to restrict an inquiry into Animal Psychology by any
considerations of the apparently disproportionate length and minute
subdivision with which it is necessary to treat some of the groups.
Anatomically, an ant or a bee does not require more consideration than a
beetle or a fly; but psychologically there is need for as great a
difference of treatment as there is in the not very dissimilar case of a
monkey and a man.
Throughout the work my aim has been to arrive at definite principles
rather than to chronicle mere incidents--an aim which will become more
apparent when the work as a whole shall have been completed. Therefore
it is that in the present volume I have endeavoured, as far as the
nature and circumstances of the inquiry would permit, to suppress
anecdote. Nevertheless, although I have nowhere introduced anecdotes for
their own sake, I have found it unavoidable not to devote much the
largest part of the present essay to their narration. Hence, with the
double purpose of limiting the introduction of anecdotes as much as
possible, and of not repeating more than I could help anecdotes already
published, I have in all cases, where I could do so without detriment to
my main object, given the preference to facts which have been
communicated to me by friends and correspondents. And here I may fitly
take the opportunity of expressing my thanks and obligations to the
latter, who in astonishing numbers have poured in their communications
during several years from all quarters of the globe. I make this
statement because I desire to explain to all my correspondents who may
read this book, that I am not the less sensible of their kindness
because its bounty has rendered it impossible for me to send
acknowledgments in individual cases. However, I should like to add in
this connection that it does not follow, because I have only quoted a
small percentage of the letters which I have received, that all of the
remainder have been useless. On the contrary, many of these have served
to convey information and suggestions which, even if not reserved for
express quotation in my forthcoming work, have been of use in guiding my
judgment on particular points. Therefore I hope that the publication of
these remarks may serve to swell the stream of communications into a yet
larger flow.[1]
In all cases where I have occasion to quote statements of fact, which in
the present treatise are necessarily numerous, I have made a point of
trying to quote _verbatim_. Only where I have found that the account
given by an author or a correspondent might profitably admit of a
considerable degree of condensation have I presented it in my own words.
And here I have to express my very special obligations to Mr. Darwin,
who not only assisted me in the most generous manner with his immense
stores of information, as well as with his valuable judgment on sundry
points of difficulty, but has also been kind enough to place at my
disposal all the notes and clippings on animal intelligence which he has
been collecting for the last forty years, together with the original MS.
of his wonderful chapter on 'Instinct.' This chapter, on being re-cast
for the 'Origin of Species,' underwent so merciless an amount of
compression that the original draft constitutes a rich store of hitherto
unpublished material. In my second work I shall have occasion to draw
upon this store more largely than in the present one, and it is needless
to add that in all cases where I do draw upon it I shall be careful to
state the source to which I am indebted.
[The above was written when I sent this work to the publishers several
months ago, and I have thought it best to leave the concluding paragraph
as it originally stood. But in making this explanation, I cannot allude
to the calamity which has since occurred without paying my tribute, not
alone to the memory of the greatest genius of our age, but still more,
and much more, to the memory of a friend so inexpressibly noble, kind,
and generous, that even my immense admiration of the naturalist was
surpassed by my loving veneration for the man.]
FOOTNOTES:
[1] Letters may be addressed to me directly at 18 Cornwall Terrace,
Regent's Park, London, N W.
CONTENTS.
PAGE
INTRODUCTION 1
CHAPTER I.
APPLICATION OF THE FOREGOING PRINCIPLES TO THE LOWEST ANIMALS 18
CHAPTER II.
MOLLUSCA 25
CHAPTER III.
ANTS 31
CHAPTER IV.
BEES AND WASPS 143
CHAPTER V.
TERMITES 198
CHAPTER VI.
SPIDERS AND SCORPIONS 204
CHAPTER VII.
REMAINING ARTICULATA 226
CHAPTER VIII.
FISH 241
CHAPTER IX.
BATRACHIANS AND REPTILES 254
CHAPTER X.
BIRDS 266
CHAPTER XI.
MAMMALS 326
CHAPTER XII.
RODENTS 353
CHAPTER XIII.
ELEPHANT 386
CHAPTER XIV.
THE CAT 411
CHAPTER XV.
FOXES, WOLVES, JACKALS, &C. 426
CHAPTER XVI.
THE DOG 437
CHAPTER XVII.
MONKEYS, APES, AND BABOONS 471
INDEX 499
INTRODUCTION.
BEFORE we begin to consider the phenomena of mind throughout the animal
kingdom it is desirable that we should understand, as far as possible,
what it is that we exactly mean by mind. Now, by mind we may mean two
very different things, according as we contemplate it in our own
individual selves, or in other organisms. For if we contemplate our own
mind, we have an immediate cognizance of a certain flow of thoughts or
feelings, which are the most ultimate things, and indeed the only
things, of which we are cognisant. But if we contemplate mind in other
persons or organisms, we have no such immediate cognizance of thoughts
or feelings. In such cases we can only _infer_ the existence and the
nature of thoughts and feelings from the activities of the organisms
which appear to exhibit them. Thus it is that we may have a subjective
analysis of mind and an objective analysis of mind--the difference
between the two consisting in this, that in our subjective analysis we
are restricted to the limits of a single isolated mind which we call our
own, and within the territory of which we have immediate cognizance of
all the processes that are going on, or at any rate of all the processes
that fall within the scope of our introspection. But in our objective
analysis of other or foreign minds we have no such immediate cognizance;
all our knowledge of their operations is derived, as it were, through
the medium of ambassadors--these ambassadors being the activities of the
organism. Hence it is evident that in our study of animal intelligence
we are wholly restricted to the objective method. Starting from what I
know subjectively of the operations of my own individual mind, and the
activities which in my own organism they prompt, I proceed by analogy to
infer from the observable activities of other organisms what are the
mental operations that underlie them.
Now, in this mode of procedure what is the kind of activities which may
be regarded as indicative of mind? I certainly do not so regard the
flowing of a river or the blowing of the wind. Why? First, because the
objects are too remote in kind from my own organism to admit of my
drawing any reasonable analogy between them and it; and, secondly,
because the activities which they present are of invariably the same
kind under the same circumstances; they afford no evidence of feeling or
purpose. In other words, two conditions require to be satisfied before
we even begin to imagine that observable activities are indicative of
mind: first, the activities must be displayed by a living organism; and
secondly, they must be of a kind to suggest the presence of two elements
which we recognise as the distinctive characteristics of mind as
such--consciousness and choice.
So far, then, the case seems simple enough. Wherever we see a living
organism apparently exerting intentional choice, we might infer that it
is conscious choice, and therefore that the organism has a mind. But
further reflection shows us that this is just what we cannot do; for
although it is true that there is no mind without the power of conscious
choice, it is not true that all apparent choice is due to mind. In our
own organisms, for instance, we find a great many adaptive movements
performed without choice or even consciousness coming into play at
all--such, for instance, as in the beating of our hearts. And not only
so, but physiological experiments and pathological lesions prove that in
our own and in other organisms the mechanism of the nervous system is
sufficient, without the intervention of consciousness, to produce
muscular movements of a highly co-ordinate and apparently intentional
character. Thus, for instance, if a man has his back broken in such a
way as to sever the nervous connection between his brain and lower
extremities, on pinching or tickling his feet they are drawn suddenly
away from the irritation, although the man is quite unconscious of the
adaptive movement of his muscles; the lower nerve-centres of the spinal
cord are competent to bring about this movement of adaptive response
without requiring to be directed by the brain. This non-mental operation
of the lower nerve-centres in the production of apparently intentional
movements is called Reflex Action, and the cases of its occurrence, even
within the limits of our own organism, are literally numberless.
Therefore, in view of such non-mental nervous adjustment, leading to
movements which are only in appearance intentional, it clearly becomes a
matter of great difficulty to say in the case of the lower animals
whether any action which appears to indicate intelligent choice is not
really action of the reflex kind.
On this whole subject of mind-like and yet not truly mental action I
shall have much to say in my subsequent treatise, where I shall be
concerned among other things with tracing the probable genesis of mind
from non-mental antecedents. But here it is sufficient merely to make
this general statement of the fact, that even within the experience
supplied by our own organisms adaptive movements of a highly complex and
therefore apparently purposive character may be performed without any
real purpose, or even consciousness of their performance. It thus
becomes evident that before we can predicate the bare existence of mind
in the lower animals, we need some yet more definite criterion of mind
than that which is supplied by the adaptive actions of a living
organism, howsoever apparently intentional such actions may be. Such a
criterion I have now to lay down, and I think it is one that is as
practically adequate as it is theoretically legitimate.
Objectively considered, the only distinction between adaptive movements
due to reflex action and adaptive movements due to mental perception,
consists in the former depending on inherited mechanisms within the
nervous system being so constructed as to effect _particular_ adaptive
movements in response to _particular_ stimulations, while the latter
are independent of any such inherited adjustment of special mechanisms
to the exigencies of special circumstances. Reflex actions under the
influence of their appropriate stimuli may be compared to the actions of
a machine under the manipulations of an operator; when certain springs
of action are touched by certain stimuli, the whole machine is thrown
into appropriate movement; there is no room for choice, there is no room
for uncertainty; but as surely as any of these inherited mechanisms are
affected by the stimulus with reference to which it has been constructed
to act, so surely will it act in precisely the same way as it always has
acted. But the case with conscious mental adjustment is quite different.
For, without at present going into the question concerning the relation
of body and mind, or waiting to ask whether cases of mental adjustment
are not really quite as _mechanical_ in the sense of being the necessary
result or correlative of a chain of physical sequences due to a physical
stimulation, it is enough to point to the variable and incalculable
character of mental adjustments as distinguished from the constant and
foreseeable character of reflex adjustments. All, in fact, that in an
objective sense we can mean by a mental adjustment is an adjustment of a
kind that has not been definitely fixed by heredity as the only
adjustment possible in the given circumstances of stimulation. For were
there no alternative of adjustment, the case, in an animal at least,
would be indistinguishable from one of reflex action.
It is, then, adaptive action by a living organism in cases where the
inherited machinery of the nervous system does not furnish data for our
prevision of what the adaptive action must necessarily be--it is only
here that we recognise the objective evidence of mind. The criterion of
mind, therefore, which I propose, and to which I shall adhere throughout
the present volume, is as follows:--Does the organism learn to make new
adjustments, or to modify old ones, in accordance with the results of
its own individual experience? If it does so, the fact cannot be due
merely to reflex action in the sense above described, for it is
impossible that heredity can have provided in advance for innovations
upon, or alterations of, its machinery during the lifetime of a
particular individual.
In my next work I shall have occasion to consider this criterion of mind
more carefully, and then it will be shown that as here stated the
criterion is not rigidly exclusive, either, on the one hand, of a
possibly mental element in apparently non-mental adjustments, or,
conversely, of a possibly non-mental element in apparently mental
adjustments. But, nevertheless, the criterion is the best that is
available, and, as it will be found sufficient for all the purposes of
the present work, its more minute analysis had better be deferred till I
shall have to treat of the probable evolution of mind from non-mental
antecedents. I may, however, here explain that in my use of this
criterion I shall always regard it as fixing only the upper limit of
non-mental action; I shall never regard it as fixing the lower limit of
mental action. For it is clear that long before mind has advanced
sufficiently far in the scale of development to become amenable to the
test in question, it has probably begun to dawn as nascent subjectivity.
In other words, because a lowly organised animal does _not_ learn by its
own individual experience, we may not therefore conclude that in
performing its natural or ancestral adaptations to appropriate stimuli
consciousness, or the mind-element, is wholly absent; we can only say
that this element, if present, reveals no evidence of the fact. But, on
the other hand, if a lowly organised animal _does_ learn by its own
individual experience, we are in possession of the best available
evidence of conscious memory leading to intentional adaptation.
Therefore our criterion applies to the upper limit of non-mental action,
not to the lower limit of mental.
Of course to the sceptic this criterion may appear unsatisfactory, since
it depends, not on direct knowledge, but on inference. Here, however, it
seems enough to point out, as already observed, that it is the best
criterion available; and further, that scepticism of this kind is
logically bound to deny evidence of mind, not only in the case of the
lower animals, but also in that of the higher, and even in that of men
other than the sceptic himself. For all objections which could apply to
the use of this criterion of mind in the animal kingdom would apply with
equal force to the evidence of any mind other than that of the
individual objector. This is obvious, because, as I have already
observed, the only evidence we can have of objective mind is that which
is furnished by objective activities; and as the subjective mind can
never become assimilated with the objective so as to learn by direct
feeling the mental processes which there accompany the objective
activities, it is clearly impossible to satisfy any one who may choose
to doubt the validity of inference, that in any case other than his own
mental processes ever do accompany objective activities. Thus it is that
philosophy can supply no demonstrative refutation of idealism, even of
the most extravagant form. Common sense, however, universally feels that
analogy is here a safer guide to truth than the sceptical demand for
impossible evidence; so that if the objective existence of other
organisms and their activities is granted--without which postulate
comparative psychology, like all the other sciences, would be an
unsubstantial dream--common sense will always and without question
conclude that the activities of organisms other than our own, when
analogous to those activities of our own which we know to be accompanied
by certain mental states, are in them accompanied by analogous mental
states.
The theory of animal automatism, therefore, which is usually attributed
to Descartes (although it is not quite clear how far this great
philosopher really entertained the theory), can never be accepted by
common sense; and even as a philosophical speculation it will be seen,
from what has just been said, that by no feat of logic is it possible to
make the theory apply to animals to the exclusion of man. The expression
of fear or affection by a dog involves quite as distinctive and complex
a series of neuro-muscular actions as does the expression of similar
emotions by a human being; and therefore, if the evidence of
corresponding mental states is held to be inadequate in the one case, it
must in consistency be held similarly inadequate in the other. And
likewise, of course, with all other exhibitions of mental life.
It is quite true, however, that since the days of Descartes--or rather,
we might say, since the days of Joule--the question of animal automatism
has assumed a new or more defined aspect, seeing that it now runs
straight into the most profound and insoluble problem that has ever been
presented to human thought--viz. the relation of body to mind in view of
the doctrine of the conservation of energy. I shall subsequently have
occasion to consider this problem with the close attention that it
demands; but in the present volume, which has to deal only with the
phenomena of mind as such, I expressly pass the problem aside as one
reserved for separate treatment. Here I desire only to make it plain
that the mind of animals must be placed in the same category, with
reference to this problem, as the mind of man; and that we cannot
without gross inconsistency ignore or question the evidence of mind in
the former, while we accept precisely the same kind of evidence as
sufficient proof of mind in the latter.
And this proof, as I have endeavoured to show, is in all cases and in
its last analysis the fact of a living organism showing itself able to
learn by its own individual experience. Wherever we find an animal able
to do this, we have the same right to predicate mind as existing in such
an animal that we have to predicate it as existing in any human being
other than ourselves. For instance, a dog has always been accustomed to
eat a piece of meat when his organism requires nourishment, and when his
olfactory nerves respond to the particular stimulus occasioned by the
proximity of the food. So far, it may be said, there is no evidence of
mind; the whole series of events comprised in the stimulations and
muscular movements may be due to reflex action alone. But now suppose
that by a number of lessons the dog has been taught not to eat the meat
when he is hungry until he receives a certain verbal signal: then we
have exactly the same kind of evidence that the dog's actions are
prompted by mind as we have that the actions of a man are so
prompted.[2] Now we find that the lower down we go in the animal
kingdom, the more we observe reflex action, or non-mental adjustment, to
predominate over volitional action, or mental adjustment. That is to
say, the lower down we go in the animal kingdom, the less capacity do we
find for changing adjustive movements in correspondence with changed
conditions; it becomes more and more hopeless to _teach_ animals--that
is, to establish associations of ideas; and the reason of this, of
course, is that ideas or mental units become fewer and less definite the
lower we descend through the structure of mind.
* * * * *
It is not my object in the present work to enter upon any analysis of
the operations of mind, as this will require to be done as fully as
possible in my next work. Nevertheless, a few words must here be said
with regard to the main divisions of mental operation, in order to
define closely the meanings which I shall attach to certain terms
relating to these divisions, and the use of which I cannot avoid.
The terms sensation, perception, emotion, and volition need not here be
considered. I shall use them in their ordinary psychological
significations; and although I shall subsequently have to analyse each
of the organic or mental states which they respectively denote, there
will be no occasion in the present volume to enter upon this subject. I
may, however, point out one general consideration to which I shall
throughout adhere. Taking it for granted that the external indications
of mental processes which we observe in animals are trustworthy, so that
we are justified in inferring particular mental states from particular
bodily actions, it follows that in consistency we must everywhere apply
the same criteria.
For instance, if we find a dog or a monkey exhibiting marked expressions
of affection, sympathy, jealousy, rage, &c., few persons are sceptical
enough to doubt that the complete analogy which these expressions afford
with those which are manifested by man, sufficiently prove the
existence of mental states analogous to those in man of which these
expressions are the outward and visible signs. But when we find an ant
or a bee apparently exhibiting by its actions these same emotions, few
persons are sufficiently non-sceptical not to doubt whether the outward
and visible signs are here trustworthy as evidence of analogous or
corresponding inward and mental states. The whole organisation of such a
creature is so different from that of a man that it becomes questionable
how far analogy drawn from the activities of the insect is a safe guide
to the inferring of mental states--particularly in view of the fact that
in many respects, such as in the great preponderance of 'instinct' over
'reason,' the psychology of an insect is demonstrably a widely different
thing from that of a man. Now it is, of course, perfectly true that the
less the resemblance the less is the value of any analogy built upon the
resemblance, and therefore that the inference of an ant or a bee feeling
sympathy or rage is not so valid as is the similar inference in the case
of a dog or a monkey. Still it _is_ an inference, and, so far as it
goes, a valid one--being, in fact, the only inference available. That is
to say, if we observe an ant or a bee apparently exhibiting sympathy or
rage, we must either conclude that some psychological state resembling
that of sympathy or rage is present, or else refuse to think about the
subject at all; from the observable facts there is no other inference
open. Therefore, having full regard to the progressive weakening of the
analogy from human to brute psychology as we recede through the animal
kingdom downwards from man, still, as it is the only analogy available,
I shall follow it throughout the animal series.
It may not, however, be superfluous to point out that if we have full
regard to this progressive weakening of the analogy, we must feel less
and less certain of the real similarity of the mental states compared;
so that when we get down as low as the insects, I think the most we can
confidently assert is that the known facts of human psychology furnish
the best available pattern of the probable facts of insect psychology.
Just as the theologians tell us--and logically enough--that if there is
a Divine Mind, the best, and indeed only, conception we can form of it
is that which is formed on the analogy, however imperfect, supplied by
the human mind; so with 'inverted anthropomorphism' we must apply a
similar consideration with a similar conclusion to the animal mind. The
mental states of an insect may be widely different from those of a man,
and yet most probably the nearest conception that we can form of their
true nature is that which we form by assimilating them to the pattern of
the only mental states with which we are actually acquainted. And this
consideration, it is needless to point out, has a special validity to
the evolutionist, inasmuch as upon his theory there must be a
psychological, no less than a physiological, continuity extending
throughout the length and breadth of the animal kingdom.
* * * * *
In these preliminary remarks only one other point requires brief
consideration, and this has reference to the distinction between what in
popular phraseology is called 'Instinct' and 'Reason.' I shall not here
enter upon any elaborate analysis of a distinction which is undoubtedly
valid, but shall confine my remarks to explaining the sense in which I
shall everywhere use these terms.
Few words in our language have been subject to a greater variety of
meanings than the word instinct. In popular phraseology, descended from
the Middle Ages, all the mental faculties of the animal are termed
instinctive, in contradistinction to those of man, which are termed
rational. But unless we commit ourselves to an obvious reasoning in a
circle, we must avoid assuming that all actions of animals are
instinctive, and then arguing that because they are instinctive,
therefore they differ from the rational actions of man. The question
really lies in what is here assumed, and we can only answer it by
examining in what essential respect instinct differs from reason.
Again, Addison says:--
I look upon instinct as upon the principle of
gravitation in bodies, which is not to be explained by
any known qualities inherent in the bodies themselves,
nor from any laws of mechanism, but as an immediate
impression from the first Mover, and the Divine energy
acting in the creatures.
This mode of 'looking upon instinct' is merely to exclude the subject
from the sphere of inquiry, and so to abstain from any attempt at
definition.
Innumerable other opinions might be quoted from well-known writers,
'looking upon instinct' in widely different ways; but as this is not an
historical work, I shall pass on at once to the manner in which science
looks upon it, or, at least, the manner in which it will always be
looked upon throughout the present work.
Without concerning ourselves with the origin of instincts, and so
without reference to the theory of evolution, we have to consider the
most conspicuous and distinctive features of instinct as it now exists.
The most important point to observe in the first instance is that
instinct involves _mental_ operations; for this is the only point that
serves to distinguish instinctive action from reflex. Reflex action, as
already explained, is non-mental neuro-muscular adaptation to
appropriate stimuli; but instinctive action is this and something more;
there is in it the element of mind. Such, at least, is instinctive
action in the sense that I shall always allude to it. I am, of course,
aware that the limitation which I thus impose is one which is ignored,
or not recognised, by many writers even among psychologists; but I am
persuaded that if we are to have any approach to definiteness in the
terms which we employ--not to say of clearness in our ideas concerning
the things of which we speak--it is most desirable to restrict the word
instinct to mental as distinguished from non-mental activity. No doubt
it is often difficult, or even impossible, to decide whether or not a
given action implies the presence of the mind-element--_i.e._, conscious
as distinguished from unconscious adaptation; but this is altogether a
separate matter, and has nothing to do with the question of defining
instinct in a manner which shall be formally exclusive, on the one hand
of reflex action, and on the other of reason. As Virchow truly observes,
'it is difficult or impossible to draw the line between instinctive and
reflex action;' but at least the difficulty may be narrowed down to
deciding in particular cases whether or not an action falls into this or
that category of definition; there is no reason why the difficulty
should arise on account of any ambiguity of the definitions themselves.
Therefore I endeavour to draw as sharply as possible the line which _in
theory_ should be taken to separate instinctive from reflex action; and
this line, as I have already said, is constituted by the boundary of
non-mental or unconscious adjustment, with adjustment in which there is
concerned consciousness or mind.
Having thus, I hope, made it clear that the difficulty of drawing a
distinction between reflex and instinctive actions as a class is one
thing, and that the difficulty of assigning particular actions to one or
the other of our categories is another thing, we may next perceive that
the former difficulty is obviated by the distinction which I have
imposed, and that the latter only arises from the fact that on the
objective side there is no distinction imposable. The former difficulty
is obviated by the distinction which I have drawn, simply because the
distinction is itself a definite one. In particular cases of adjustive
action we may not always be able to affirm whether consciousness of
their performance is present or absent; but, as I have already said,
this does not affect the validity of our definition; all we can say of
such cases is that if the performance in question is attended with
consciousness it is instinctive, and if not it is reflex.
And the difficulty of assigning particular actions to one or other of
these two categories arises, as I have said, merely because on the
objective side, or the side of the nervous system, there is no
distinction to be drawn. Whether or not a neural process is accompanied
by a mental process, it is in itself the same. The advent and
development of consciousness, although progressively converting reflex
action into instinctive, and instinctive into rational, does this
exclusively in the sphere of subjectivity; the nervous processes engaged
are throughout the same in kind, and differ only in the relative degrees
of their complexity. Therefore, as the dawn of consciousness or the rise
of the mind-element is gradual and undefined, both in the animal kingdom
and in the growing child, it is but necessary that in the early morning,
as it were, of consciousness any distinction between the mental and the
non-mental should be obscure, and generally impossible to determine.
Thus, for instance, a child at birth does not close its eyes upon the
near approach of a threatening body, and it only learns to do so by
degrees as the result of experience; at first, therefore, the action of
closing the eyelids in order to protect the eyes may be said to be
instinctive, in that it involves the mind-element:[3] yet it afterwards
becomes a reflex which asserts itself even in opposition to the will.
And, conversely, sucking in a new-born child, or a child _in utero_, is,
in accordance with my definition, a reflex action; yet in later life,
when consciousness becomes more developed and the child _seeks_ the
breast, sucking may properly be called an instinctive action. Therefore
it is that, as in the ascending scale of objective complexity the
mind-element arises and advances gradually, many particular cases which
occupy the undefined boundary between reflex action and instinct cannot
be assigned with confidence either to the one region or to the other.
We see then the point, and the only point, wherein instinct can be
consistently separated from reflex action; viz., in presenting a mental
constituent. Next we must consider wherein instinct may be separated
from reason. And for this purpose we may best begin by considering what
we mean by reason.
The term 'reason' is used in significations almost as various as those
which are applied to 'instinct.' Sometimes it stands for all the
distinctively human faculties taken collectively, and in antithesis to
the mental faculties of the brute; while at other times it is taken to
mean the distinctively human faculties of intellect.
Dr. Johnson defines it as 'the power by which man deduces one
proposition from another, and proceeds from premises to consequences.'
This definition presupposes language, and therefore ignores all cases of
inference not thrown into the formal shape of predication. Yet even in
man the majority of inferences drawn by the mind never emerge as
articulate propositions; so that although, as we shall have occasion
fully to observe in my subsequent work, there is much profound
philosophy in identifying reason with speech as they were identified in
the term Logos, yet for purposes of careful definition so to identify
intellect with language is clearly a mistake.
More correctly, the word reason is used to signify the power of
perceiving analogies or ratios, and is in this sense equivalent to the
term 'ratiocination,' or the faculty of deducing inferences from a
perceived equivalency of relations. Such is the only use of the word
that is strictly legitimate, and it is thus that I shall use it
throughout the present treatise. This faculty, however, of balancing
relations, drawing inferences, and so of forecasting probabilities,
admits of numberless degrees; and as in the designation of its lower
manifestations it sounds somewhat unusual to employ the word reason, I
shall in these cases frequently substitute the word intelligence. Where
we find, for instance, that an oyster profits by individual experience,
or is able to perceive new relations and suitably to act upon the result
of its perceptions, I think it sounds less unusual to speak of the
oyster as displaying intelligence than as displaying reason. On this
account I shall use the former term to signify the lower degrees of the
ratiocinative faculty; and thus in my usage it will be opposed to such
terms as instinct, reflex action, &c., in the same manner as the term
reason is so opposed. This is a point which, for the sake of clearness,
I desire the reader to retain in his memory. I shall always speak of
intelligence and intellect in antithesis to instinct, emotion, and the
rest, as implying mental faculties the same in kind as those which in
ourselves we call rational.
Now it is notorious that no distinct line can be drawn between instinct
and reason. Whether we look to the growing child or to the ascending
scale of animal life, we find that instinct shades into reason by
imperceptible degrees, or, as Pope expresses it, that these principles
are 'for ever separate, yet for ever near.' Nor is this other than the
principles of evolution would lead us to expect, as I shall afterwards
have abundant occasion to show. Here, however, we are only concerned
with drawing what distinction we can between instinct and reason as
these faculties are actually presented to our observation. And this in a
general way it is not difficult to do.
We have seen that instinct involves 'mental operations,' and that by
this feature it is distinguished from reflex action; we have now to
consider the features by which it is distinguished from reason. These
are accurately, though not completely, conveyed by Sir Benjamin Brodie,
who defines instinct as 'a principle by which animals are induced,
independently of experience and reasoning, to the performances of
certain voluntary acts, which are necessary to their preservation as
individuals, or to the continuance of the species, or in some other way
convenient to them.'[4] This definition, as I have said, is accurate as
far as it goes, but it does not state with sufficient generality and
terseness that all instinctive action is adaptive; nor does it clearly
bring out the distinction between instinct and reason which is thus well
conveyed by the definition of Hartmann, who says in his 'Philosophy of
the Unconscious,' that 'instinct is action taken in pursuance of an end,
but without conscious perception of what the end is.' This definition,
however, is likewise defective in that it omits another of the important
differentiæ of instinct--namely, the uniformity of instinctive action as
performed by different individuals of the same species. Including this
feature, therefore, we may more accurately and completely define
instinct as mental action (whether in animals or human beings),
directed towards the accomplishing of adaptive movement, antecedent to
individual experience, without necessary knowledge of the relation
between the means employed and the ends attained, but similarly
performed under the same appropriate circumstances by all the
individuals of the same species. Now in every one of these respects,
with the exception of containing a mental constituent and in being
concerned in adaptive action, instinct differs from reason. For reason,
besides involving a mental constituent, and besides being concerned in
adaptive action, is always subsequent to individual experience, never
acts but upon a definite and often laboriously acquired knowledge of the
relation between means and ends, and is very far from being always
similarly performed under the same appropriate circumstances by all the
individuals of the same species.
Thus the distinction between instinct and reason is both more definite
and more manifold than is that between instinct and reflex action.
Nevertheless, in particular cases there is as much difficulty in
classifying certain actions as instinctive or rational, as there is in
cases where the question lies between instinct and reflex action. And
the explanation of this is, as already observed, that instinct passes
into reason by imperceptible degrees; so that actions in the main
instinctive are very commonly tempered with what Pierre Huber calls 'a
little dose of judgment or reason,' and _vice versâ_. But here, again,
the difficulty which attaches to the classification of particular
actions has no reference to the validity of the distinctions between the
two classes of actions; these are definite and precise, whatever
difficulty there may be in applying them to particular cases.
Another point of difference between instinct and reason may be noticed
which, although not of invariable, is of very general applicability. It
will have been observed, from what has already been said, that the
essential respect in which instinct differs from reason consists in the
amount of conscious deliberation which the two processes respectively
involve. Instinctive actions are actions which, owing to their frequent
repetition, become so habitual in the course of generations that all
the individuals of the same species automatically perform the same
actions under the stimulus supplied by the same appropriate
circumstances. Rational actions, on the other hand, are actions which
are required to meet circumstances of comparatively rare occurrence in
the life-history of the species, and which therefore can only be
performed by an intentional effort of adaptation. Consequently there
arises the subordinate distinction to which I allude, viz., that
instinctive actions are only performed under particular circumstances
which have been frequently experienced during the life-history of the
species; whereas rational actions are performed under varied
circumstances, and serve to meet novel exigencies which may never before
have occurred even in the life-history of the individual.
Thus, then, upon the whole, we may lay down our several definitions in
their most complete form.
Reflex action is non-mental neuro-muscular adjustment, due to the
inherited mechanism of the nervous system, which is formed to respond to
particular and often recurring stimuli, by giving rise to particular
movements of an adaptive though not of an intentional kind.
Instinct is reflex action into which there is imported the element of
consciousness. The term is therefore a generic one, comprising all those
faculties of mind which are concerned in conscious and adaptive action,
antecedent to individual experience, without necessary knowledge of the
relation between means employed and ends attained, but similarly
performed under similar and frequently recurring circumstances by all
the individuals of the same species.
Reason or intelligence is the faculty which is concerned in the
intentional adaptation of means to ends. It therefore implies the
conscious knowledge of the relation between means employed and ends
attained, and may be exercised in adaptation to circumstances novel
alike to the experience of the individual and to that of the species.
FOOTNOTES:
[2] Of course it may be said that we have no evidence of _prompting_ in
either case; but this is the side issue which concerns the general
relation of body and mind, and has nothing to do with the guarantee of
inferring the presence of mind in particular cases.
[3] _I.e._, ancestral as well as individual. If the race had not always
had occasion to close the eyelids to protect the eyes, it is certain
that the young child would not so quickly learn to do so in virtue of
its own individual experience alone; and as the action cannot be
attributed to any process of conscious inference, it is not rational;
but we have seen that it is not originally reflex; therefore it is
instinctive.
[4] _Psychological Researches_, p. 187.
CHAPTER I.
APPLICATION OF THE FOREGOING PRINCIPLES TO THE LOWEST ANIMALS.
_Protozoa._
NO one can have watched the movements of certain Infusoria without
feeling it difficult to believe that these little animals are not
actuated by some amount of intelligence. Even if the manner in which
they avoid collisions be attributed entirely to repulsions set up in the
currents which by their movements they create, any such mechanical
explanation certainly cannot apply to the small creatures seeking one
another for the purposes of prey, reproduction, or, as it sometimes
seems, of mere sport. There is a common and well-known rotifer whose
body is of a cup shape, provided with a very active tail, which is armed
at its extremity with strong forceps. I have seen a small specimen of
this rotifer seize a much larger one with its forceps, and attach itself
by this means to the side of the cup. The large rotifer at once became
very active, and swinging about with its burden until it came to a piece
of weed, it took firm hold of the weed with its own forceps, and began
the most extraordinary series of movements, which were obviously
directed towards ridding itself of the encumbrance. It dashed from side
to side in all directions with a vigour and suddenness which were highly
astonishing, so that it seemed as if the animalcule would either break
its forceps or wrench its tail from its body. No movements could
possibly be better suited to jerk off the offending object, for the
energy with which the jerks were given, now in one direction and now in
another, were, as I have said, most surprising. But not less surprising
was the tenacity with which the smaller rotifer retained its hold; for
although one might think that it was being almost jerked to pieces,
after each bout of jerking it was seen to be still attached. This trial
of strength, which must have involved an immense expenditure of energy
in proportion to the size of the animals, lasted for several minutes,
till eventually the small rotifer was thrown violently away. It then
returned to the conflict, but did not succeed a second time in
establishing its hold. The entire scene was as like intelligent action
on the part of both animals as could well be imagined, so that if we
were to depend upon appearances alone, this one observation would be
sufficient to induce me to attribute conscious determination to these
microscopical organisms.
But, without denying that conscious determination may here be present,
or involving ourselves in the impossible task of proving such a
negative, we may properly affirm that until an animalcule shows itself
to be teachable by individual experience, we have no sufficient evidence
derived or derivable from any number of such apparently intelligent
movements, that conscious determination is present. Therefore, I need
not wait to quote the observations of the sundry microscopists who
detail facts more or less similar to the above, with expressions of
their belief that microscopical organisms display a certain degree of
instinct or intelligence as distinguished from mechanical, or wholly
non-mental adjustment. But there are some observations relating to the
lowest of all animals, and made by a competent person, which are so
remarkable that I shall have to quote them in full. These observations
are recorded by Mr. H. J. Carter, F.R.S., in the 'Annals of Natural
History,' and in his opinion prove that the beginnings of instinct are
to be found so low down in the scale as the Rhizopoda. He says:--'Even
_Athealium_ will confine itself to the water of the watch-glass in which
it may be placed when away from sawdust and chips of wood among which it
has been living; but if the watch-glass be placed upon the sawdust, it
will very soon make its way over the side of the watch-glass and get to
it.'
This is certainly a remarkable observation: for it seems to show that
the rhizopod distinguishes the presence of the sawdust outside the
watch-glass, and crawls over the brim of the latter in order to get into
more congenial quarters, while it is contented with the water in the
watch-glass so long as there is no sawdust outside. But to proceed:
On one occasion, while investigating the nature of
some large, transparent, spore-like elliptical cells
(fungal?) whose protoplasm was rotating, while it was
at the same time charged with triangular grains of
starch, I observed some actinophorous rhizopods
creeping about them, which had similarly shaped grains
of starch in their interior; and having determined the
nature of these grains in both by the addition of
iodine, I cleansed the glasses, and placed under the
microscope a new portion of the sediment from the
basin containing these cells and actinophryans for
further examination, when I observed one of the
spore-like cells had become ruptured, and that a
portion of its protoplasm, charged with the triangular
starch-grains, was slightly protruding through the
crevice. It then struck me that the actinophryans had
obtained their starch-grains from this source; and
while looking at the ruptured cell, an _actinophrys_
made its appearance, and creeping round the cell, at
last arrived at the crevice, from which it extricated
one of the grains of starch mentioned, and then crept
off to a good distance. Presently, however, it
returned to the same cell; and although there were now
no more starch-grains protruding, the _actinophrys_
managed again to extract one from the interior through
the crevice. All this was repeated several times,
showing that the _actinophrys_ instinctively knew that
those were nutritious grains, that they were contained
in this cell, and that, although each time after
incepting a grain it went away to some distance, it
knew how to find its way back to the cell again which
furnished this nutriment.
On another occasion I saw an _actinophrys_ station
itself close to a ripe spore-cell of _pythium_, which
was situated upon a filament of _Spirogyra crassa_;
and as the young ciliated monadic germs issued forth,
one after another, from the dehiscent spore-cell, the
_actinophrys_ remained by it and caught every one of
them, even to the last, when it retired to another
part of the field, as if instinctively conscious that
there was nothing more to be got at the old place.
But by far the greatest feat of this kind that ever
presented itself to me was the catching of a young
_acineta_ by an old sluggish _amoeba_, as the
former left its parent; and this took place as
follows:--
In the evening of the 2nd of June, 1858, in Bombay,
while looking through a microscope at some _Euglenæ_,
&c., which had been placed aside for examination in a
watch-glass, my eye fell upon a stalked and triangular
_acineta_ (_A. mystacina_?), around which an
_amoeba_ was creeping and lingering, as they do when
they are in quest of food. But knowing the antipathy
that the _amoeba_, like almost every other
infusorian, has to the tentacles of the _acineta_, I
concluded that the _amoeba_ was not encouraging an
appetite for its whiskered companion, when I was
surprised to find that it crept up the stem of the
_acineta_, and wound itself round its body. This mark
of affection, too much like that frequently evinced at
the other end of the scale, even where there is a mind
for its control, did not long remain without
interpretation. There was a young _acineta_, tender,
and without poisonous tentacles (for they are not
developed at birth), just ready to make its exit from
the parent, an exit which takes place so quickly, and
is followed by such rapid bounding movements of the
non-ciliated _acineta_, that who would venture to say,
_à priori_, that a dull, heavy, sluggish _amoeba_
could catch such an agile little thing? But the
_amoeba_ are as unerring and unrelaxing in their
grasp as they are unrelenting in their cruel
inceptions of the living and the dead, when they serve
them for nutrition; and thus the _amoeba_, placing
itself round the ovarian aperture of the _acineta_,
received the young one, nurse-like, in its fatal lap,
incepted it, descended from the parent, and crept off.
Being unable to conceive at the time that this was
such an act of atrocity on the part of the _amoeba_
as the sequel disclosed, and thinking that the young
_acineta_ might yet escape, or pass into some other
form in the body of its host, I watched the _amoeba_
for some time afterwards, until the tale ended by the
young _acineta_ becoming divided into two parts, and
thus in their respective digestive spaces ultimately
becoming broken down and digested.[5]
With regard to these remarkable observations it can only, I think, be
said that although certainly very suggestive of something more than
mechanical response to stimulation, they are not sufficiently so to
justify us in ascribing to these lowest members of the zoological scale
any rudiment of truly mental action. The subject, however, is here full
of difficulty, and not the least so on account of the _amoeba_ not
only having no nervous system, but no observable organs of any kind; so
that, although we may suppose that the adaptive movements described by
Mr. Carter were non-mental, it still remains wonderful that these
movements should be exhibited by such apparently unorganised creatures,
seeing that as to the remoteness of the end attained, no less than the
complex refinement of the stimulus to which their adaptive response was
due, the movements in question rival the most elaborate of non-mental
adjustments elsewhere performed by the most highly organised of nervous
systems.
_Coelenterata._
Dr. Eimer attributes 'voluntary action' to the Medusæ, and indeed draws
a sharp distinction between what he considers their 'involuntary' and
'voluntary' movements. In this distinction, however, I do not at all
concur; for although I am well acquainted with the difference between
the active and slow rhythm upon which the distinction is founded, I see
no evidence whatever for supposing that the difference involves any
psychological element. The active swimming is produced by stimulation,
and is no doubt calculated to lead to the escape of the organism; but
this fact certainly does not carry us beyond the ordinary possibilities
of reflex action. And even when, as in some species is constantly the
case, bouts of active swimming appear to arise spontaneously or without
observable stimulation, the fact is to be attributed to a liberation of
overplus ganglionic energy, or to some unobservable stimulation; it does
not justify the supposition of any psychical element being concerned.[6]
M'Crady gives an interesting account of a medusa which carries its larvæ
on the inner sides of its bell-shaped body. The manubrium, or mobile
digestive cavity of the animal, depends, as in the other Medusæ, from
the summit of the concave surface of the bell, like a clapper or tongue.
Now M'Crady observed this depending organ to be moved first to one side
and then to the other side of the bell, in order to give suck to the
larvæ on the sides of the bell--the larvæ dipping their long noses into
the nutrient fluids which that organ of the parent's body contained. I
cite this case, because if it occurred in one of the higher animals it
would probably be called a case of instinct; but as it occurs in so low
an animal as a jelly-fish, it is unreasonable to suppose that
intelligence can ever have played any part in originating the action.
Therefore we may set it down as the uncompounded result of natural
selection.
Some species of medusæ--notably _Sarsia_--seek the light, crowding into
the path of a beam, and following it actively if moved. They derive
advantage from so doing, because certain small crustacea on which they
feed likewise crowd into the light. The seeking of light by these medusæ
is therefore doubtless of the nature of a reflex action which has been
developed by natural selection in order to bring the animals into
contact with their prey. Paul Bert has found that _Daphnia pulex_ seeks
the light (especially the yellow ray), and Engelmann has observed the
same fact with regard to certain protoplasmic organisms. But in none of
these or other such cases is there any evidence of a psychical element
being concerned in the process.
_Echinodermata._
Some of the natural movements of these animals, as also some of their
movements under stimulation, are very suggestive of purpose; but I have
satisfied myself that there is no adequate evidence of the animals being
able to profit by individual experience, and therefore, in accordance
with our canon, that there is no adequate evidence of their exhibiting
truly mental phenomena. On the other hand, the study of reflex action in
these organisms is full of interest--so much so that in my next work I
shall take them as typical organisms in this connection.[7]
_Annelida._
Mr. Darwin has now in the press a highly interesting work on the habits
of earth-worms. It appears from his observations that the manner in
which these animals draw down leaves, &c., into their burrows is
strongly indicative of instinctive action, if not of intelligent
purpose--seeing that they always lay hold of the part of the leaf (even
though an exotic one) by the traction of which the leaf will offer least
resistance to being drawn down. But as this work will so shortly be
published, I shall not forestall any of the facts which it has to state,
nor should I yet like to venture an opinion as to how far these facts,
when considered altogether, would justify any inference to a truly
mental element as existing in these animals.
Of the land leeches in Ceylon, Sir E. Tennent gives an account which
likewise seems to bespeak intelligence as occurring in annelids. He
says:--
In moving, the land leeches have the power of planting
one extremity on the earth and raising the other
perpendicularly to watch for their victim. Such is
their vigilance and instinct, that on the approach of
a passer-by to a spot which they infest, they may be
seen amongst the grass and fallen leaves on the edge
of a native path, poised erect, and preparing for
their attack on man and horse. On descrying their prey
they advance rapidly by semicircular strides, fixing
one end firmly and arching the other forwards, till by
successive advances they can lay hold of the
traveller's foot, when they disengage themselves from
the ground and ascend his dress in search of an
aperture to enter. In these encounters the individuals
in the rear of a party of travellers in the jungle
invariably fare worst, as the leeches, once warned of
their approach, congregate with singular celerity.[8]
FOOTNOTES:
[5] H. J. Carter, F.R.S., _Annals of Natural History_, 3rd Series, 1863,
pp. 45-6.
[6] For an account of the natural movements of the Medusæ and the
effects of stimulation upon them, see Croonian Lecture in _Phil. Trans._
1875, and also _Phil. Trans._ 1877 and 1879.
[7] See Croonian Lecture, 1881, in forthcoming issue of _Phil. Trans._
[8] _Natural History of Ceylon_, p. 481.