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Title: Ants and Some Other Insects: An Inquiry Into the Psychic Powers of These Animals
Author: Forel, Auguste
Language: English
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  _Ants and Some Other Insects_

  _An Inquiry into_

  _The Psychic Powers of these Animals_

  _With an Appendix on_

  _The Peculiarities of Their Olfactory Sense_


  _Dr. August Forel_

  _Late Professor of Psychiatry at the University of Zurich_

  _Translated from the German_


  _Prof. William Morton Wheeler_

  _American Museum of Natural History, New York_


  _The Open Court Publishing Company_


  _Kegan Paul, Trench, Trübner & Co. Ltd._




When discussing the ant-mind, we must consider that these small
animals, on the one hand, differ very widely from ourselves in
organisation, but on the other hand, have come, through so-called
convergence, to possess in the form of a social commonwealth a peculiar
relationship to us. My subject, however, requires the discussion of so
many complicated questions that I am compelled to assume acquaintance
with the work of others, especially the elements of psychology, and in
addition the works of P. Huber, Wasmann, von Buttel-Reepen, Darwin,
Romanes, Lubbock, my _Fourmis de la Suisse_, and many others. Since
the functions of the sense-organs constitute the basis of comparative
psychology, I must also refer to a series of articles entitled
“Sensations des Insectes” which I have recently published (1900-1901)
in the _Rivista de Biologia Generale_, edited by Dr. P. Celesia.
In these papers I have defined my position with respect to various
authors, especially Plateau and Bethe.

Very recently Bethe, Uexkull, and others have denied the existence of
psychic powers in invertebrate animals. They explain the latter as
reflex-machines, and take their stand on the ground of the so-called
psycho-physical parallelism for the purpose of demonstrating our
inability to recognise mental qualities in these animals. They believe,
however, that they can prove the mechanical regularity of behavior,
but assume unknown forces whenever they are left in the lurch in their
explanations. They regard the mind as first making its appearance in
the vertebrates, whereas the old Cartesians regarded all animals, in
contradistinction to man, as mindless (unconscious) machines.

The Jesuit father E. Wasmann and von Buttel-Reepen are willing, on
the other hand, to accept the inductive inference from analogy as a
valid scientific method. Like Lubbock, the lecturer and others, they
advocate a comparative psychology of the invertebrates and convincingly
demonstrate the existence of psychic faculties in these animals.
Wasmann, however, puts a very low estimate on the mental powers of the
higher vertebrates and, in my opinion, improperly, denies to them any
ability of drawing inferences from experience when in the presence of
new conditions (this alone he designates as intelligence); he believes
that man alone possesses an immortal soul (independent of natural
laws?) in addition to the animal mind.

It is necessary, first of all, to arrive at some common understanding
concerning the obscure notion “psychic” in order that we may avoid
logomachy, and carrying on theology in the sense of Goethe’s
Mephistopheles. Two concepts are confounded in an obscure manner in
the word “psychic”: first, the abstract concept of introspection, or
subjectivism, i. e., observation from within, which every person knows
only, and can know only, in and by himself. For this let us reserve the
term “consciousness.” Second, the “activity” of the mind or that which
determines the contents of the field of consciousness. This has been
included without further ado with consciousness in the wider sense,
and thence has arisen the confusion of regarding consciousness as an
attribute of the mind. In another place I have designated the molecular
wave of activity of the neural elements as “neurocyme.”

We cannot speak of the consciousness of human beings other than
ourselves without drawing an inference from analogy; quite as little
ought we to speak of a consciousness of forgotten things. The field
of our consciousness is constantly changing. Things appear in it and
disappear from it. Memory, through association, enables us to recall,
more or less directly and with more or less difficulty, things which
appear to be momentarily absent from consciousness. Moreover, both the
experience of self-observation and the phenomena of hypnotism teach us
experimentally that many things of which we seem to be unconscious,
are nevertheless present in consciousness or have been. Indeed,
certain sense-impressions remain, at the moment of their occurrence,
unconscious so far as our ordinary consciousness or superconsciousness
is concerned, although they can be subsequently recalled into
consciousness by suggestion. Whole chains of brain-activities,
(dreams, somnambulism, or secondary consciousness) seem ordinarily
to be excluded from the superconsciousness, but may subsequently be
associated by suggestion with the remembered contents of consciousness.
In all these cases, therefore, what seems to be unconscious is after
all proved to be conscious. The above-mentioned phenomena have
frequently led to mystical interpretations, but they are explainable on
a very simple assumption. Let us assume--and this is quite in harmony
with observation--that the fields of the introspectively conscious
brain-activities are limited by so-called association or dissociation
processes, i. e., that we are unable actively to bring them all into
connection at the same time, and that therefore all that seems to us
unconscious has also in reality a consciousness, in other words, a
subjective reflex, then the following results: Our ordinary waking
consciousness or superconsciousness is merely an inner subjective
reflex of those activities of attention which are most intimately
connected with one another, i. e., of the more intensively concentrated
maxima of our cerebral activities during waking. There exist, however,
other consciousnesses, partly forgotten, partly only loosely or
indirectly connected with the contents of the superconsciousness, in
contradistinction to which these may be designated as subconsciousness.
They correspond to other less concentrated or otherwise associated
cerebral activities. We are bound to assume the existence of still
more remotely interconnected subconsciousnesses for the infra-cortical
(lower) brain-centers, and so on.

It is easy to establish the fact that the maximum of our psychic
activity, namely, attention, passes every moment from one perception
or thought to another. These objects of attention, as visual or
auditory images, will-impulses, feelings or abstract thoughts, come
into play--and of this there is no doubt--in different brain-regions or
neuron-complexes. We can therefore compare attention to a functional
_macula lutea_ wandering in the brain, or with a wandering maximal
intensity of neurocymic activity. But it is quite as satisfactorily
established that other psychic phenomena external to attention are
likewise present in consciousness, though in a feebler condition.
Finally, it is well known that all that has been in consciousness--even
that which is now more, now less, forgotten--is included in the
psychic, i. e., in the contents of consciousness. On superficial
consideration this appears to satisfy theoretical requirements. But
in fact and in truth there are innumerable processes of which we
are feebly conscious for only a scarcely appreciable instant and
which anon disappear from consciousness. Here and not in the strong
and repeated “psychomes”--I beg your indulgence for this word, with
which I would for the sake of brevity designate each and every
psychic unit--are we to seek the transition from the conscious to
the apparently unconscious. Even in this case, however, the feeble
condition of consciousness is only apparent, because the inner
reflex of these processes can merely echo faintly in the field of a
strongly diverted attention. This, therefore, in no wise proves that
such half conscious processes are in and for themselves so feebly
represented in consciousness, since a flash of attention is sufficient
subsequently to give them definite shape in consciousness. Only in
consequence of the diversion of the attention do they lose more and
more their connection with the chain of intensity-maxima which, under
ordinary circumstances, constitute the remembered contents of our
superconsciousness. The more feebly, however, they are bound to the
latter, with the more difficulty are such half-conscious processes
later associated anew through memory with the dominant chain. Of such a
nature are all dreams, all the subordinate circumstances of our lives,
all automatised habits, all instincts. But if there exists between the
clearly conscious and the unconscious, a half-conscious brain-life,
whose consciousness appears to us so feeble merely on account of the
deviation of our ordinary train of memories, this is an unequivocal
indication that a step further on the remaining connection would be
completely severed, so that we should no longer have the right to
say that the brain-activities thus fading away nebulously from our
superconsciousness do not have consciousness in and for themselves. For
the sake of brevity and simplicity we will ascribe subconsciousness to
these so-called unconscious brain-processes.

If this assumption is correct--and all things point in this
direction--we are not further concerned with consciousness. It does
not at all exist as such, but only through the brain-activity of which
it is the inner reflex. With the disappearance of this activity,
consciousness disappears. When the one is complicated, the other, too,
is complicated. When the one is simple, the other is correspondingly
simple. If the brain-activity be dissociated, consciousness also
becomes dissociated. Consciousness is only an abstract concept,
which loses all its substance with the falling away of “conscious”
brain-activity. The brain-activity reflected in the mirror of
consciousness appears therein subjectively as a summary synthesis,
and the synthetical summation grows with the higher complications and
abstractions acquired through habit and practice, so that details
previously conscious (e. g., those involved in the act of reading)
later become subconscious, and the whole takes on the semblance of a
psychical unit.

Psychology, therefore, cannot restrict itself merely to a study of the
phenomena of our superconsciousness by means of introspection, for
the science would be impossible under such circumstances. Everybody
would have only his own subjective psychology, after the manner of
the old scholastic spiritualists, and would therefore be compelled to
doubt the very existence of the external world and his fellow-men.
Inference from analogy, scientific induction, the comparison of the
experiences of our five senses, prove to us the existence of the outer
world, our fellow-men and the psychology of the latter. They also
prove to us that there is such a thing as comparative psychology, a
psychology of animals. Finally our own psychology, without reference
to our brain-activity, is an incomprehensible patchwork full of
contradictions, a patchwork which above all things seems to contradict
the law of the conservation of energy.

It follows, furthermore, from these really very simple reflections
that a psychology that would ignore brain-activity, is a monstrous
impossibility. The contents of our superconsciousness are continually
influenced and conditioned by subconscious brain-activities.
Without these latter it can never be understood. On the other
hand, we understand the full value and the ground of the complex
organisation of our brain only when we observe it in the inner light
of consciousness, and when this observation is supplemented by a
comparison of the consciousness of our fellow-men as this is rendered
possible for us through spoken and written language by means of very
detailed inferences from analogy. The mind must therefore be studied
simultaneously from within and from without. Outside ourselves the mind
can, to be sure, be studied only through analogy, but we are compelled
to make use of this the only method which we possess.

Some one has said that language was given to man not so much for the
expression as for the concealment of his thoughts. It is also well
known that different men in all honesty attribute very different
meanings to the same words. A savant, an artist, a peasant, a woman,
a wild Wedda from Ceylon, interpret the same words very differently.
Even the same individual interprets them differently according to his
moods and their context. Hence it follows that to the psychologist and
especially to the psychiatrist--and as such I am here speaking--the
mimetic expression, glances and acts of a man often betray his true
inner being better than his spoken language. Hence also the attitudes
and behavior of animals have for us the value of a “language,” the
psychological importance of which must not be underestimated. Moreover,
the anatomy, physiology and pathology of the animal and human brain
have yielded irrefutable proof that our mental faculties depend on the
quality, quantity, and integrity of the living brain and are one with
the same. It is just as impossible that there should exist a human
brain without a mind, as a mind without a brain, and to every normal or
pathological change in the mental activity, there corresponds a normal
or pathological change of the neurocymic activity of the brain, i. e.,
of its nervous elements. Hence what we perceive introspectively in
consciousness is cerebral activity.

As regards the relation of pure psychology (introspection) to the
physiology of the brain (observation of brain-activity from without),
we shall take the theory of identity for granted so long as it is in
harmony with the facts. The word identity, or monism, implies that
every psychic phenomenon is the same real thing as the molecular
or neurocymic activity of the brain-cortex coinciding with it, but
that this may be viewed from two standpoints. The phenomenon alone
is dualistic, the thing itself is monistic. If this were otherwise
there would result from the accession of the purely psychical to the
physical, or cerebral, an excess of energy which would necessarily
contradict the law of the conservation of energy. Such a contradiction,
however, has never been demonstrated and would hold up to derision
all scientific experience. In the manifestations of our brain-life,
wonderful as they undoubtedly are, there is absolutely nothing which
contradicts natural laws and justifies us in postulating the existence
of a mythical, supernatural “psyche.”

On this account I speak of monistic identity and not of psycho-physical
parallelism. A thing cannot be parallel with itself. Of course,
psychologists of the modern school, when they make use of this term,
desire merely to designate a supposed parallelism of phenomena without
prejudice either to monism or dualism. Since, however, many central
nervous processes are accessible neither to physiological nor to
psychological observation, the phenomena accessible to us through
these two methods of investigation are not in the least parallel, but
separated from one another very unequally by intermediate processes.
Moreover, inasmuch as the dualistic hypothesis is scientifically
untenable, it is altogether proper to start out from the hypothesis of

It is as clear as day that the same activity in the nervous system
of an animal, or even in my own nervous system, observed by myself,
first by means of physiological methods from without, and second, as
reflecting itself in my consciousness, must appear to me to be totally
different, and it would indeed be labor lost to try to convert the
physiological into psychological qualities or _vice versa_. We cannot
even convert one psychological quality into another, so far as the
reality symbolised by both is concerned; e. g., the tone, the visual
and tactile sensation, which a uniform, low, tuning-fork vibration
produces on our three corresponding senses. Nevertheless, we may infer
inductively that it is the same reality, the same vibration which is
symbolised for us in these three qualitatively and totally different
modes i. e., produces in us these three different psychical impressions
which cannot be transformed into one another. These impressions depend
on activities in different parts of the brain and are, of course, as
such actually different from one another in the brain. We speak of
psycho-physiological identity only when we mean, on the one hand, the
cortical neurocyme which directly conditions the conscious phenomena
known to us, on the other hand, the corresponding phenomena of

And, in fact, a mind conceived as dualistic could only be devoid of
energy or energy-containing. If it be conceived as devoid of energy
(Wasmann), i. e., independent of the laws of energy, we have arrived
at a belief in the miraculous, a belief which countenances the
interference with and arbitrary suspension of the laws of nature.
If it be conceived as energy-containing, one is merely playing upon
words, for a mind which obeys the law of energy is only a portion of
the cerebral activities arbitrarily severed from its connections and
dubbed “psychic essence,” only that this may be forthwith discredited.
Energy can only be transformed qualitatively, not quantitatively. A
mind conceived as dualistic, if supposed to obey the law of energy,
would have to be transformed completely into some other form of energy.
But then it would no longer be dualistic, i. e., no longer essentially
different from the brain-activities.

Bethe, Uexkull, and others would require us to hold fast to the
physiological method, because it alone is exact and restricts itself to
what can be weighed and measured. This, too, is an error which has been
refuted from time immemorial. Only pure mathematics is exact, because
in its operations it makes use solely of equations of abstract numbers.
The concrete natural sciences can never be exact and are as unable
to subsist without the inductive method of inference from analogy as
a tree without its roots. Bethe and Uexkull do not seem to know that
knowledge is merely relative. They demand absolute exactitude and
cannot understand that such a thing is impossible. Besides, physiology
has no reason to pride itself upon the peculiar exactitude of its
methods and results.

Although we know that our whole psychology appears as the activity of
our cerebrum in connection with the activities of more subordinate
nerve-centers, the senses and the muscles, nevertheless for didactic
purposes it may be divided into the psychology of cognition, of
feeling and volition. Relatively speaking, this subdivision has
an anatomico-physiological basis. Cognition depends, in the first
instance, on the elaboration of sense-impressions by the brain; the
will represents the psycho- or cerebrofugal resultants of cognition
and the feelings together with their final transmission to the
muscles. The feelings represent general conditions of excitation of a
central nature united with elements of cognition and with cerebrofugal
impulses, which are relatively differentiated and refined by the
former, but have profound hereditary and phylogenetic origins and are
relatively independent. There is a continual interaction of these three
groups of brain-activities upon one another. Sense-impressions arouse
the attention; this necessitates movements; the latter produce new
sense-impressions and call for an active selection among themselves.
Both occasion feelings of pleasure and pain and these again call
forth movements of defense, flight, or desire, and bring about fresh
sense-impressions, etc. Anatomically, at least, the sensory pathways
to the brain and their cortical centers are sharply separated from the
centers belonging to the volitional pathways to the muscles. Further
on in the cerebrum, however, all three regions merge together in many
neurons of the cortex.

Within ourselves, moreover, we are able to observe in the three
above-mentioned regions all varieties and degrees of so-called psychic
dignity, from the simplest reflex to the highest mental manifestations.
The feelings and impulses connected with self-preservation (hunger,
thirst, fear) and with reproduction (sexual love and its concomitants)
represent within us the region of long-inherited, profoundly
phyletic, fixed, instinct-life. These instincts are nevertheless
partially modified and partly kept within due bounds through the
interference of the higher cerebral activities. The enormous mass
of brain-substance, which in man stands in no direct relation to
the senses and musculature, admits not only of an enormous storing
up of impressions and of an infinite variety of motor innervations,
but above all, of prodigious combinations of these energies among
themselves through their reciprocal activities and the awakening of
old, so-called memory images through the agency of new impressions.
In contradistinction to the compulsory, regular activities of the
profoundly phyletic automatisms, I have used the term “plastic” to
designate those combinations and individual adaptations which depend
on actual interaction in the activities of the cerebrum. Its loftiest
and finest expression is the plastic imagination, both in the province
of cognition and in the province of feeling, or in both combined.
In the province of the will the finest plastic adaptability, wedded
to perseverance and firmness, and especially when united with the
imagination, yields that loftiest mental condition which gradually
brings to a conclusion during the course of many years decisions that
have been long and carefully planned and deeply contemplated. Hence the
plastic gift of combination peculiar to genius ranks much higher than
any simpler plastic adaptability.

The distinction between automatism and plasticity in brain-activity is,
however, only a relative one and one of degree. In the most different
instincts which we are able to influence through our cerebrum, i.
e., more or less voluntarily, like deglutition, respiration, eating,
drinking, the sexual impulse, maternal affection, jealousy, we observe
gradations between compulsory heredity and plastic adaptability, yes,
even great individual fluctuations according to the intensity of the
corresponding hereditary predispositions.

Now it is indisputable that the individual Pithecanthropus or allied
being, whose cerebrum was large enough gradually to construct from
onomatopœas, interjections and the like, the elements of articulate
speech, must thereby have acquired a potent means of exploiting his
brain. Man first fully acquired this power through written language.
Both developed the abstract concept symbolised by words, as a
higher stage in generalisation. All these things give man a colossal
advantage, since he is thereby enabled to stand on the shoulders of
the written encyclopædia of his predecessors. This is lacking in all
animals living at the present time. Hence, if we would compare the
human mind with the animal mind, we must turn, not to the poet or
the savant, but to the Wedda or at any rate to the illiterate. These
people, like children and animals, are very simple and extremely
concrete in their thinking. The fact that it is impossible to teach
a chimpanzee brain the symbols of language proves only that it is
not sufficiently developed for this purpose. But the rudiments are
present nevertheless. Of course the “language” of parrots is no
language, since it symbolises nothing. On the other hand, some animals
possess phyletic, i. e., hereditarily and instinctively fixed cries
and gestures, which are as instinctively understood. Such instinctive
animal languages are also very widely distributed and highly developed
among insects, and have been fixed by heredity for each species.
Finally it is possible to develop by training in higher animals a
certain mimetic and acoustic conventional language-symbolism, by
utilising for this purpose the peculiar dispositions of such species.
Thus it is possible to teach a dog to react in a particular manner to
certain sounds or signs, but it is impossible to teach a fish or an
ant these things. The dog comprehends the sign, not, of course, with
the reflections of human understanding, but with the capacity of a
dog’s brain. And it is, to be sure, even more impossible to teach its
young an accomplishment so lofty for its own brain as one which had
to be acquired by training, than for the Wedda or even the negro to
transmit his acquired culture by his own impulse. Even the impulse to
do this is entirely lacking. Nevertheless, every brain that is trained
by man is capable of learning and profiting much from the experience of
its own individual life. And one discovers on closer examination that
even lower animals may become accustomed to some extent to one thing
or another, and hence trained, although this does not amount to an
understanding of conventional symbols.

In general we may say, therefore, that the central nervous system
operates in two ways: _automatically_ and _plastically_.

The so-called reflexes and their temporary, purposefully adaptive, but
hereditarily stereotyped combinations, which respond always more or
less in the same manner to the same stimuli, constitute the paradigm
of automatic activities. These have the deceptive appearance of a
“machine” owing to the regularity of their operations. But a machine
which maintains, constructs, and reproduces itself is not a machine.
In order to build such a machine we should have to possess the key
of life, i. e., the understanding of the supposed, but by no means
demonstrated, mechanics of living protoplasm. Everything points to
the conclusion that the instinctive automatisms have been gradually
acquired and hereditarily fixed by natural selection and other factors
of inheritance. But there are also secondary automatisms or habits
which arise through the frequent repetition of plastic activities
and are therefore especially characteristic of man’s enormous

In all the psychic provinces of intellect, feeling, and will, habits
follow the constant law of perfection through repetition. Through
practice every repeated plastic brain-activity gradually becomes
automatic, becomes “second nature,” i. e., similar to instinct.
Nevertheless instinct is not inherited habit, but phylogenetically
inherited intelligence which has gradually become adapted and
crystalised by natural selection or by some other means.

Plastic activity manifests itself, in general, in the ability of
the nervous system to conform or adapt itself to new and unexpected
conditions and also through its faculty of bringing about internally
new combinations of neurocyme. Bethe calls this the power of
modification. But since, notwithstanding his pretended issue with
anthropomorphism, he himself continually proceeds in an anthropomorphic
spirit and demands human ratiocination of animals, if they are to
be credited with plasticity (power of modification),--he naturally
overlooks the fact that the beginnings of plasticity are primordial,
that they are in fact already present in the Amœba, which adapts itself
to its environment. Nor is this fact to be conjured out of the world by
Loeb’s word “tropisms.”

Automatic and plastic activities, whether simple or complex, are merely
relative antitheses. They grade over into each other, e. g., in the
formation of habits but also in instincts. In their extreme forms
they resemble two terminal branches of a tree, but they may lead to
similar results through so-called convergence of the conditions of life
(slavery and cattle-keeping among ants and men). The automatic may be
more easily derived from the plastic activities than _vice versa_. One
thing is established, however: since a tolerably complicated plastic
activity admits of many possibilities of adaptation in the individual
brain, it requires much more nervous substance, many more neurons,
but has more resistances to overcome in order to attain a complicated
result. The activities of an Amœba belong therefore rather to the
plasticity of living molecules, but not as yet to that of coöperating
nerve-elements; as cell-plasticity it should really be designated as
“undifferentiated.”[1] There are formed in certain animals specially
complex automatisms, or instincts, which require relatively little
plasticity and few neurons. In others, on the contrary, there remains
relatively considerable nerve-substance for individual plasticity,
while the instincts are less complicated. Other animals, again, have
little besides the lower reflex centers and are extremely poor in both
kinds of complex activities. Still others, finally, are rich in both.
Strong so-called “hereditary predispositions” or unfinished instincts
constitute the phylogenetic transitions between both kinds of activity
and are of extraordinarily high development in man.

[1] If I expressly refrain from accepting the premature and
unjustifiable identification of cell-life with a “machine,” I
nevertheless do not share the so-called vitalistic views. It is quite
possible that science may sometime be able to produce living protoplasm
from inorganic matter. The vital forces have undoubtedly originated
from physico-chemical forces. But the ultimate nature of the latter
and of the assumed material atoms is, of course, metaphysical, i. e.,

Spoken and especially written language, moreover, enable man to exploit
his brain to a wonderful extent. This leads us to underestimate
animals. Both in animals and man the true value of the brain is
falsified by training, i. e., artificially heightened. We overestimate
the powers of the educated negro and the trained dog and underestimate
the powers of the illiterate individual and the wild animal.

I beg your indulgence for this lengthy introduction to my subject,
but it seemed necessary that we should come to some understanding
concerning the validity of comparative psychology. My further task now
consists in demonstrating to you what manner of psychical faculties may
be detected in insects. Of course, I shall select in the first place
the ants as the insects with which I am most familiar. Let us first
examine the brain of these animals.

In order to determine the psychical value of a central nervous system
it is necessary, first, to eliminate all the nerve-centers which
subserve the lower functions, above the immediate innervation of
the muscles and sense-organs as first centers. The volume of such
neuron-complexes does not depend on the intricacy of mental work but
on the number of muscle-fibres concerned in it, the sensory surfaces,
and the reflex apparatus, hence above all things on the size of the
animals. Complex instincts already require the intervention of much
more plastic work and for this purpose such nerve-centers alone would
be inadequate.

A beautiful example of the fact that complex mental combinations
require a large nerve-center dominating the sensory and muscular
centers is furnished by the brain of the ant. The ant-colony commonly
consists of three kinds of individuals: the queen, or female (largest),
the workers which are smaller, and the males which are usually larger
than the workers. The workers excel in complex instincts and in clearly
demonstrable mental powers (memory, plasticity, etc.). These are much
less developed in the queens. The males are incredibly stupid, unable
to distinguish friends from enemies and incapable of finding their
way back to their nest. Nevertheless the latter have very highly
developed eyes and antennae, i. e., the two sense-organs which alone
are connected with the brain, or supra-oesophageal ganglion and enable
them to possess themselves of the females during the nuptial flight.
No muscles are innervated by the supra-oesophageal ganglion. These
conditions greatly facilitate the comparison of the perceptive organs,
i. e., of the brain (_corpora pedunculata_) in the three sexes. This
is very large in the worker, much smaller in the female, and almost
vestigial in the male, whereas the optic and olfactory lobes are very
large in the latter. The cortical portion of the large worker brain
is, moreover, extremely rich in cellular elements. In this connection I
would request you to glance at the figures and their explanation.

Very recently, to be sure, it has come to be the fashion to
underestimate the importance of brain-morphology in psychology and even
in nerve-physiology. But fashions, especially such absurd ones as this,
should have no influence on true investigation. Of course, we should
not expect anatomy to say what it was never intended to say.

In ants, injury to the cerebrum leads to the same results as injury to
the brain of the pigeon.

In this place I would refer you for a fuller account of the details of
sensation and the psychic peculiarities of insects to my more extended
work above mentioned: _Sensations des Insectes_.

It can be demonstrated that insects possess the senses of sight, smell,
taste, and touch. The auditory sense is doubtful. Perhaps a sense of
touch modified for the perception of delicate vibrations may bear a
deceptive resemblance to hearing. A sixth sense has nowhere been shown
to occur. A photodermatic sense, modified for light-sensation, must be
regarded as a form of the tactile sense. It occurs in many insects.
This sense is in no respect of an optic nature. In aquatic insects
the olfactory and gustatory senses perhaps grade over into each other
somewhat (Nagel), since both perceive chemical substances dissolved in
the water.

The visual sense of the facetted eyes is especially adapted for seeing
movements, i. e., for perceiving relative changes of position in the
retinal image. In flight it is able to localise large spatial areas
admirably, but must show less definite contours of the objects than
our eyes. The compound eye yields only a single upright image (Exner),
the clearness of which increases with the number of facets and the
convexity of the eye. Exner succeeded in photographing this image in
the fire-fly (Lampyris). As the eyes are immovable the sight of resting
objects soon disappears so far as the resting insect is concerned.
For this reason resting insects are easily captured when very slowly
approached. In flight insects orient themselves in space by means
of their compound eyes. Odor, when perceived, merely draws these
animals in a particular direction. When the compound eyes are covered,
all powers of orientation in the air are lost. Many insects can adapt
their eyes for the day or night by a shifting of the pigment. Ants
see the ultra-violet with their eyes. Honey-bees and humble-bees can
distinguish colors, but obviously in other tones than we do, since
they cannot be deceived by artificial flowers of the most skilful
workmanship. This may be due, to admixtures of the ultra-violet rays
which are invisible to our eyes.

[Illustration: Fig. _W._]

[Illustration: Fig. _F._]

[Illustration: Fig. _M._]


Brain (supra-œsophageal ganglion) of an ant (_Lasius fuliginosus_),
magnified 60 diameters, seen from above.

    Fig. _W._ Brain of the Worker.
    Fig. _F._ Brain of the Queen (Female)
    Fig. _M._ Brain of the Male.

_St._ = Brain trunk. _L. op._ = Lobus opticus (optic lobe). _L. olf._
= Lobus olfactorius sive antennalis (olfactory lobe). _N._ = Facetted
eye. _N. olf._ = Nervus olfactorius sive antennalis (olfactory nerve).
_O._ = Ocelli, or simple eyes with their nerves (present only in the
male and queen). _H._ = Cellular brain cortex (developed only in the
worker and queen). _C. p._ = Corpora pedunculata, or fungiform bodies
(developed only in the worker and queen). _R._ = Rudimental cortex of

The length of the whole ant is:

    in the worker 4.5 mm;
    in the queen 6.0 mm;
    in the male 4.5 mm.

N. B. The striation of the corpora pedunculata and their stems is
represented diagrammatically, for the purpose of indicating rather
coarsely their extremely delicate fibrillar structure.

The ocelli (simple eyes) play a subordinate rôle, and probably serve as
organs of sight for objects situated in the immediate vicinity and in
dark cavities.

       *       *       *       *       *

The olfactory sense has its seat in the antennæ, usually in the
club-shaped flagellum, or rather in the pore-plates and olfactory
rods of these portions of the antennæ. On account of its external
and moveable position at the tip of the antenna, the olfactory organ
possesses two properties which are lacking in the vertebrates, and
particularly in man. These are:

1. The power of perceiving the chemical nature of a body by direct
contact (contact-odor);

2. The power of space-perception and of perceiving the form of objects
and that of the animal’s own trail by means of odor, and the additional
property of leaving associated memories.

The olfactory sense of insects, therefore, gives these animals definite
and clear-cut perceptions of space-relations, and enables the animal
while moving on the surface of the ground to orient itself with
facility. I have designated this sense, which is thus qualitatively, i.
e., in its specific energy, very different from our olfactory sense,
as the topochemical (olfactory) sense. Probably the pore-plates are
used for perceiving odor at a distance and the olfactory rods for
contact-odor, but this is pure conjecture. Extirpation of the antennæ
destroys the power of distinguishing friends from enemies and deprives
the ant of the faculty of orienting itself on the ground and of finding
its way, whereas it is possible to cut off three legs and an antenna
without seriously impairing these powers. The topochemical sense
always permits the ant to distinguish between the directions of its
trail, a faculty which Bethe attributes to a mysterious polarisation.
The ability to sense different odors varies enormously in different
insects. An object possessing odor for one species is often odorless
for other species (and for ourselves) and _vice versa_.

The gustatory organs are situated on the mouth-parts. Among insects the
reactions of this sense are very similar to our own. Will accustomed
some wasps to look in a particular place for honey, which he afterwards
mixed with quinine. The wasps detected the substance at once, made
gestures of disgust, and never returned to the honey. Mixing the honey
with alum had the same result. At first they returned, but after the
disagreeable gustatory experience they failed to reappear. Incidentally
this is also a proof of their gustatory memory and of their powers of

Several organs have been found and described as auditory. But after
their removal the supposed reaction to sounds persists. This would seem
to indicate that a deceptive resemblance to hearing may be produced by
the perception of delicate vibrations through the tactile sense (Dugès).

The tactile sense is everywhere represented by tactile hairs and
papillæ. It reacts more especially to delicate tremors of the
atmosphere or soil. Certain arthropods, especially the spiders, orient
themselves mainly by means of this sense.

It may be demonstrated that insects, according to the species and
conditions of life, use their different senses in combination for
purposes of orienting themselves and for perceiving the external world.
Many species lack eyes and hence also the sense of sight. In others,
again, the olfactory sense is obtuse; certain other forms lack the
contact-odor sense (e. g., most Diptera).

It has been shown that the superb powers of orientation exhibited by
certain aerial animals, like birds (carrier-pigeons), bees, etc.,
depend on vision and its memories. Movement in the air gives this sense
enormous and manifold values. The semi-circular canals of the auditory
organ are an apparatus of equilibrium in vertebrates and mediate
sensations of acceleration and rotation (Mach-Breuer), but do not give
external orientation. For the demonstration of these matters I must
refer you to my work above-cited. A specific, magnetic, or other mode
of orientation, independent of the known senses, does not exist.

The facts above presented constitute the basis of insect psychology.
The social insects are especially favorable objects for study on
account of their manifold reciprocal relationships. If in speaking of
their behavior I use terms borrowed from human life, I request you,
once for all, to bear in mind that these are not to be interpreted in
an anthropomorphic but in an analogous sense.


Many insects (perhaps all, in a more rudimental condition) possess
memory, i. e., they are able to store up sense-impressions in their
brains for subsequent use. Insects are not merely attracted directly
by sensory stimuli, as Bethe imagines. Huber, myself, Fabre, Lubbock,
Wasmann, Von Buttel-Reepen, have demonstrated this fact experimentally.
That bees, wasps, etc., can find their way in flight through the air,
notwithstanding wind and rain (and hence under circumstances precluding
the existence of any possible odoriferous trail), and even after the
antennæ have been cut off, to a concealed place where they have found
what they desired, though this place may be quite invisible from their
nest, and this even after the expiration of days and weeks, is a fact
of special importance as proof of the above assertion. It can be
shown that these insects recognise objects by means of their colors,
their forms, and especially by their position in space. Position they
perceive through the mutual relations and succession of the large
objects in space, as these are revealed to them in their rapid change
of place during flight in their compound eyes (shifting of retinal
images). Especially the experiments performed by Von Buttel-Reepen
and myself leave no doubt concerning this fact. Additional proof of a
different nature is furnished by Von Buttel, who found that ether or
chloroform narcosis deprives bees of all memory. By this means enemies
can be converted into friends. Under these circumstances, too, all
memory of locality is lost and must be reacquired by means of a new
flight of orientation. An animal, however, certainly cannot forget
without having remembered.

The topochemical antennal sense also furnishes splendid proofs of
memory in ants, bees, etc. An ant may perform an arduous journey of
thirty meters from her ruined nest, there find a place suitable for
building another nest, return, orienting herself by means of her
antenna, seize a companion who forthwith rolls herself about her
abductrix, and is carried to the newly selected spot. The latter then
also finds her way to the original nest, and both each carry back
another companion, etc. The memory of the suitable nature of the
locality for establishing a new nest must exist in the brain of the
first ant or she would not return, laden with a companion, to this
very spot. The slave-making ants (_Polyergus_) undertake predatory
expeditions, led by a few workers, who for days and weeks previously
have been searching the neighborhood for nests of _Formica fusca_. The
ants often lose their way, remain standing and hunt about for a long
time till one or the other finds the topochemical trail and indicates
to the others the direction to be followed by rapidly pushing ahead.
Then the pupæ of the _Formica fusca_ nest, which they have found, are
brought up from the depths of the galleries, appropriated and dragged
home, often a distance of forty meters or more. If the plundered nest
still contains pupæ, the robbers return on the same or following days
and carry off the remainder, but if there are no pupæ left they do not
return. How do the Polyergus know whether there are pupæ remaining?
It can be demonstrated that smell could not attract them from such
a distance, and this is even less possible for sight or any other
sense. Memory alone, i. e., the recollection that many pupæ still
remain behind in the plundered nest can induce them to return. I have
carefully followed a great number of these predatory expeditions.

While Formica species follow their topochemical trail with great
difficulty over new roads, they nevertheless know the immediate
surroundings of their nest so well that even shovelling away the earth
can scarcely disconcert them, and they find their way at once, as
Wasmann emphatically states and as I myself have often observed. That
this cannot be due to smelling at long range can be demonstrated in
another manner, for the olfactory powers of the genus Formica, like
those of honey-bees, are not sufficiently acute for this purpose, as
has been shown in innumerable experiments by all connoisseurs of these
animals. Certain ants can recognise friends even after the expiration
of months. In ants and bees there are very complex combinations and
mixtures of odors, which Von Buttel has very aptly distinguished as
nest-odor, colony- (family-) odor, and individual odor. In ants we have
in addition a species-odor, while the queen-odor does not play the same
rôle as among bees.

It follows from these and many other considerations that the social
Hymenoptera can store up in their brains visual images and topochemical
odor-images and combine these to form perceptions or something of a
similar nature, and that they can associate such perceptions, even
those of different senses, especially sight, odor, and taste, with one
another and thereby acquire spatial images.

Huber as well as Von Buttel, Wasmann, and myself have always found that
these animals, through frequent repetition of an activity, journey,
etc., gain in the certainty and rapidity of the execution of their
instincts. Hence they form, very rapidly to be sure, habits. Von Buttel
gives splendid examples of these in the robber-bees, i. e., in some
of the common honey-bees that have acquired the habit of stealing the
honey from the hives of strangers. At first the robbers display some
hesitation, though later they become more and more impudent. But he who
uses the term habit, must imply secondary automatism and a pre-existing
plastic adaptability. Von Buttel adduces an admirable proof of this
whole matter and at the same time one of the clearest and simplest
refutations of Bethe’s innumerable blunders, when he shows that bees
that have never flown from the hive, even though they may be older than
others that have already flown, are unable to find their way back even
from a distance of a few meters, when they are unable to see the hive,
whereas old bees know the whole environment, often to a distance of six
or seven kilometers.

It results, therefore, from the unanimous observations of all the
connoisseurs that sensation, perception, and association, inference,
memory and habit follow in the social insects on the whole the same
fundamental laws as in the vertebrates and ourselves. Furthermore,
attention is surprisingly developed in insects, often taking on an
obsessional character and being difficult to divert.

On the other hand, inherited automatism exhibits a colossal
preponderance. The above-mentioned faculties are manifested only in an
extremely feeble form beyond the confines of the instinct-automatism
stereotyped in the species.

An insect is extraordinarily stupid and inadaptable to all things
not related to its instincts. Nevertheless I succeeded in teaching a
water-beetle (_Dytiscus marginalis_) which in nature feeds only in the
water, to eat on my table. While thus feeding, it always executed a
clumsy flexor-movement with its fore-legs which brought it over on its
back. The insect learned to keep on feeding while on its back, but it
would not dispense with this movement, which is adapted to feeding in
the water. On the other hand, it always attempted to leap out of the
water (no longer fleeing to the bottom of the vessel) when I entered
the room, and nibbled at the tip of my finger in the most familiar
manner. Now these are certainly plastic variations of instinct. In a
similar manner some large Algerian ants which I transplanted to Zurich,
learned during the course of the summer months to close the entrance of
their nest with pellets of earth, because they were being persecuted
and annoyed by our little _Lasius niger_. In Algiers I always saw the
nest-opening wide open. There are many similar examples which go to
show that these tiny animals can utilise some few of their experiences
even when this requires a departure from the usual instincts.

That ants, bees, and wasps are able to exchange communications that
are understood, and that they do not merely titillate one another
with their antennæ as Bethe maintains, has been demonstrated in so
many hundred instances, that it is unnecessary to waste many words
on this subject. The observations of a single predatory expedition
of Polyergus, with a standing still of the whole army and a seeking
for the lost trail, is proof sufficient of the above statement. But,
of course, this is not language in the human sense! There are no
abstract concepts corresponding to the signs. We are here concerned
only with hereditary, instinctively automatic signs. The same is true
of their comprehension (pushing with the head, rushing at one another
with wide-open mandibles, titillation with the antennæ, stridulatory
movement of the abdomen, etc.). Moreover, imitation plays a great
rôle. Ants, bees, etc., imitate and follow their companions. Hence it
is decidedly erroneous (and in this matter Wasmann, Von Buttel, and
myself are of but one opinion) to inject human thought-conception and
human ratiocination into this instinct-language, as has been done to
some extent, at least, even by Pierre Huber, not to mention others.
It is even very doubtful whether a so-called general sensory idea
(i. e., a general idea of an object, like the idea “ant,” “enemy,”
“nest,” “pupa”) can arise in the emmet brain. This is hardly capable of
demonstration. Undoubtedly perception and association can be carried on
in a very simple way, after the manner of insects, without ever rising
to such complex results. At any rate proofs of such an assumption are
lacking. But what exists is surely in itself sufficiently interesting
and important. It gives us at least an insight into the brain-life of
these animals.

Better than any generalisations, a good example will show what I mean.

Plateau had maintained that when Dahlia blossoms are covered with green
leaves, bees nevertheless return to them at once. At first he concealed
his Dahlias incompletely (i. e., only their ray-florets), afterwards
completely, but still in an unsatisfactory manner, and inferred from
the results that bees are attracted by odor and not by sight.

_a._ In a Dahlia bed visited by many bees and comprising about
forty-three floral heads of different colors, I covered first seventeen
and then eight at 2.15 P. M., September 10th, with grape-leaves bent
around them and fastened with pins.

_b._ Of four I covered only the yellow disc;

_c._ Of one, on the other hand, I covered only the outer ray-florets,
leaving the disc visible.

So many bees were visiting the Dahlias that at times there were two or
three to a flower.

Result: Immediately all the completely covered flowers ceased to be
visited by the bees. Dahlia (_c_) continued to be visited like those
completely visible. The bees often flew to Dahlias (_b_) but at once
abandoned them; a few, however, succeeded in finding the disc beneath
the leaves.

Then as soon as I removed the covering from a red Dahlia the bees at
once flew to it; and soon a poorly concealed specimen was detected and
visited. Later an inquisitive bee discovered the entrance to a covered
Dahlia from the side or from below. Thenceforth this bee, but only this
one, returned to this same covered flower.

Nevertheless several bees seemed to be seeking the Dahlias which had so
suddenly disappeared. Towards 5.30 o’clock some of them had detected
the covered flowers. Thenceforth these insects were rapidly imitated
by the other bees, and in a short time the hidden flowers were again
being visited. As soon as a bee had discovered my imposition and found
the entrance to a hidden flower, she flew in her subsequent journeys,
without hesitation to the concealed opening of the grape-leaf. As
long as a bee had merely made the discovery by herself, she remained
unnoticed by the others. When this was accomplished by several,
however, (usually by four or five,) the others followed their example.

Plateau, therefore, conducted his experiments in a faulty manner and
obtained erroneous results. The bees still saw the Dahlias which he at
first incompletely concealed. Then, by the time he had covered them up
completely, but only from above, they had already detected the fraud
and saw the Dahlias also from the side. Plateau had failed to take into
consideration the bee’s memory and attention.

September 13th I made some crude imitations of Dahlias by sticking the
yellow heads of Hieracium (hawkweed) each in a Petunia flower, and
placed them among the Dahlias. Neither the Petunias nor the Hieracium
had been visited by the bees. Nevertheless many of the honey and
humble-bees flew at first to the artefacts in almost as great numbers
as to the Dahlias, but at once abandoned the flowers when they had
detected the error, obviously by means of their sense of smell. The
same results were produced by a Dahlia, the disc of which had been
replaced by the disc of a Hieracium.

As a control experiment I had placed a beautiful, odorous Dahlia disc
among the white and yellow Chrysanthemums which had been neglected by
the bees. For a whole half hour the bees flew by only a few centimeters
above the disc without noticing it; not till then was it visited by
a bee that happened to be followed by a second. From this moment the
Dahlia disc which lay in the path of flight was visited like the
others, whereas on the other hand the Petunia-Hieracium artefacts, now
known to be fraudulent, were no longer noticed.

Plateau has demonstrated that artificial flowers, no matter how
carefully copied from the human standpoint, are not noticed by insects.
I placed artefacts of this description among the Dahlias. They remained
in fact entirely neglected. Perhaps, as above suggested, the bees are
able to distinguish the chlorophyll colors from other artificial hues,
owing to admixtures of the ultra-violet rays, or by some other means.
But since Plateau imagines that the artificial flowers repel insects, I
cut out, Sept. 19th, the following rather crude paper-flowers:

α. A red flower;

β. A white flower;

γ. A blue flower;

δ A blue flower, with a yellow center made from a dead leaf;

ε. A rose-colored piece of paper with a dry Dahlia disc;

ζ. A green Dahlia leaf (unchanged).

It was nine o’clock in the morning. I placed a drop of honey on each of
the six artefacts mounted among the Dahlias. For a quarter of an hour
many bees flew past, very close to my artefacts but without perceiving
and hence without smelling the honey. I went away for an hour. On my
return artefact δ was without honey, and must therefore have been
discovered by the bees. All the others had remained quite untouched and

With some difficulty I next undertook to bring artefact α very close
to a bee resting on a Dahlia. But the attention of the bee was so
deeply engrossed by the Dahlia that I had to repeat the experiment four
or five times till I succeeded in bringing the honey within reach of
her proboscis. The insect at once began to suck up the honey from the
paper-flower. I marked the bee’s back with blue paint so that I might
be able to recognise her, and repeated the experiment with β and ε. In
these cases one of the bees was painted yellow, the other white.

Soon the blue bee, which had in the meantime gone to the hive,
returned, flew at once to α, first hovering about it dubiously, then to
δ, where she fed, then again to α, but not to the Dahlias. Later the
yellow bee returned to β and fed, and flew to α and δ where she again
fed, but gave as little heed to the Dahlias as did the blue bee.

Thereupon the white bee returned seeking ε, but failing to find it, at
once went to feeding on some of the Dahlias. But she tarried only a
moment on each Dahlia as if tortured by the _idée fixe_ of honey. She
returned to the artefacts, the perception of which, however, she was
not quite able to associate with the memory of the honey flavor. At
last she found a separate piece of ε, which happened to be turned down
somewhat behind, and began lapping up the honey.

Thenceforth the three painted bees, and these alone, returned regularly
to the artefacts and no longer visited the Dahlias. The fact is of
great importance that the painted bees entirely of their own accord,
undoubtedly through an instinctive inference from analogy, discovered
the other artefacts as soon as their attention had been attracted by
the honey on one of them, notwithstanding the fact that the artefacts
were some distance from one another and of different colors. For were
not the Dahlias, too, which they had previously visited, of different
colors? Thus the blue bee flew to α, β, γ, and δ, the yellow to β, α,
δ, and γ, the white ε, α, β, and δ. Matters continued thus for half
an hour. The hidden green ζ was not found, evidently because it was
indistinguishable from the green foliage.

Finally one bee, by herself, having had in all probability her
attention attracted by the three others, came to δ and fed. I marked
her with carmine. Thereupon she flew to α and drove the blue bee away.
Another bee was attracted to ε of her own accord and was painted with
cinnobar. Still another bee came by herself to β and was painted green.
It was now 12.30 o’clock. The experiment had therefore lasted more than
three hours, and during this time only six bees had come to know the
artefacts, while the great majority still kept on visiting the Dahlias.
But now the other bees began to have their attention attracted by the
visitors to the artefacts. One, then two, then three, and finally more
new ones followed, and I had not sufficient colors with which to mark
them. Every moment I was obliged to replenish the honey. Then I went to
dinner and returned at 1.25. At this moment seven bees were feeding on
β, two on α, one on γ, three on δ, the white one alone on ε. More than
half of all these were new, unpainted followers. Now a veritable swarm
of bees threw themselves on the artefacts and licked up the last traces
of the honey. Then for the first time, after more than four hours, a
bee from the swarm discovered the honey on the artefact ζ, which on
account of its color had remained concealed up to this time!

As a pack of hounds throws itself on an empty skeleton, the swarm of
bees, now completely diverted from the Dahlias, cast themselves on the
completely empty artefacts and vainly searched every corner of them for
honey. It was 1.55 P. M. The bees began to scatter and return to the
Dahlias. Then I replaced α and β by a red and white paper respectively,
which had never come in contact with honey and could not therefore
smell of the substance. These pieces of paper, nevertheless, were
visited and examined by various bees, whose brains were still possessed
with the fixed idea of the flavor of honey. The white bee, e. g.,
investigated the white paper very carefully for a period of three to
four minutes. There could, of course, be no such thing as an unknown
force or attraction of odor, or brilliancy of floral colors. This fact
can only be explained by an association of space, form, and color
memories with memories of taste.

Thereupon I took all the artefacts in my left hand for the purpose of
carrying them away. Two or three bees followed me, hovering about my
left hand, and tried to alight on the empty artefacts. The space-image
had changed and only the color and form could any longer be of service
to the bees in their recognition of these objects.

This experiment is so clear and unequivocal that I mention it here
among many others. It demonstrates:

1. The space, form, and color perceptions of the honey-bee. That these
are possible only through the agency of the compound eyes is proved by
other experiments (varnishing the eyes, extirpation of the antennæ,
mouth-parts, etc.).

2. The memory of the honey-bee, in particular her visual and gustatory

3. Her power of associating gustatory with visual memories.

4. Her ability instinctively to draw inferences from analogy: If she
has once been offered honey in an artefact, she will investigate
others, even those of a different color and hitherto unnoticed. These
she compares by means of the visual sense, since they are relatively
similar, and recognises them as similar though such objects are most
unusual in the bee’s experience.

5. Her poor olfactory sense, which is useful only at very close range.

6. The onesidedness and narrow circle of her attention.

7. The rapid formation of habits.

8. The limits of imitation of bees by one another.

Of course, I should not allow myself to draw these conclusions from
a single experiment, if they had not been confirmed by innumerable
observations by the ablest investigators in this field. Lubbock showed
clearly that it is necessary to train a bee for some time to go to
a particular color if one wishes to compel her to pay no attention
to other colors. This is the only way in which it is possible to
demonstrate her ability to distinguish colors. My bees, on the
contrary, had been trained on differently colored objects (Dahlias and
artefacts) and therefore paid no attention to differences in color. It
would be a fallacy to conclude from this that they do not distinguish
colors. On the contrary, by means of other experiments I have fully
confirmed Lubbock’s results.

By 2.20 P. M. all of my bees, even the painted ones, had returned to
the Dahlias.

On September 27, a week later, I wished to perform a fresh experiment
with the same bees. I intended to make them distinguish between
differently colored discs, placed at different points on a long scale,
representing on a great sheet of paper, varying intensities of light
from white through gray to black. First, I wished to train a bee to
a single color. But I had calculated without the bee’s memory, which
rendered the whole experiment impracticable. Scarcely had I placed
my paper with the discs on the lawn near the Dahlia bed, and placed
one or two bees on the blue discs and marked them with colors, when
they began to investigate all the red, blue, white, black and other
discs with or without honey. After a few moments had elapsed, other
bees came from the Dahlia bed and in a short time a whole swarm threw
itself on the paper discs. Of course, those that had been provided with
honey were most visited, because they detained the bees, but even the
discs without honey were stormed and scrutinised by bees following one
another in their flight. The bees besieged even the paint-box. Among
these there was one that I had previously deprived of her antennæ. She
had previously partaken of the honey on the blue discs and had returned
to the hive. This bee examined the blue piece of paint in the color-box.

In brief, my experiment was impossible, because all the bees still
remembered from a former occasion the many-colored artefacts provided
with honey, and therefore examined all the paper discs no matter of
what color. The association between the taste of the honey and the
paper discs had been again aroused by the sight-perception of the
latter, and had acquired both consistency and rapid and powerful
imitation, because honey happened to be actually found on some of the

Together with the perceptive and associative powers, the power of
drawing simple, instinctive inferences from analogy is also apparent.
Without this, indeed, the operation of perception and memory would be
inconceivable! We have just given an example. I have shown on a former
occasion that humble-bees, whose nest I had transferred to my window,
when they returned home often confounded other windows of the same
façade and examined them for a long time before they discovered the
right one. Lubbock reports similar facts. Von Buttel shows that bees
that are accustomed to rooms and windows, learn to examine the rooms
and windows in other places, i. e., other houses. When Pissot suspended
wire netting with meshes twenty-two mm. in diameter in front of a wasp
nest, the wasps hesitated at first, then went around the netting by
crawling along the ground or avoided it in some other way. But they
soon learned to fly directly through the meshes. The sense of sight,
observed during flight, is particularly well adapted to experiments
of this kind, which cannot therefore be performed with ants. But the
latter undoubtedly draw similar inferences from the data derived from
their topochemical antennal sense. The discovery of prey or other food
on a plant or an object induces these insects to examine similar plants
or objects and to perform other actions of a like nature.

There are, on the other hand, certain very stupid insects, like
the males of ants, the Diptera and may-flies (Ephemerids) with
rudimental brains, incapable of learning anything or of combining
sense-impressions to any higher degree than as simple automatisms, and
without any demonstrable retention of memory-images. Such insects lead
a life almost exclusively dominated by sensory stimuli; but their lives
are adapted to extremely simple conditions. In these very instances the
difference is most striking, and they demonstrate most clearly through
comparison and contrast the _plus_ possessed by more intelligent


The notion of volition, in contradistinction to the notion of reflex
action, presupposes the expiration of a certain time interval and
the operation of mediating and complex brain-activities between the
sense-impression and the movement which it conditions. In the operation
of the purposeful automatisms of instinct which arouse one another
into activity in certain sequences, there is also a time interval,
filled out by internal, dynamic brain-processes as in the case of
the will. Hence these are not pure reflexes. They may for a time
suffer interruption and then be again continued. But their operation
is brought about in great measure by a concatenation of complicated
reflexes which follow one another in a compulsory order. On this
account the term automatism or instinct is justifiable.

If we are to speak of will in the narrower sense, we must be able to
establish the existence of individual decisions, which can be directed
according to circumstances, i. e., are modifiable, and may, for a
certain period, remain dormant in the brain to be still performed
notwithstanding. Such volition may be very different from the complex
volition of man, which consists of the resultants of prodigiously
manifold components that have been long preparing and combining. The
ants exhibit positive and negative volitional phenomena, which cannot
be mistaken. The ants of the genus Formica Linné are particularly
brilliant in this respect, and they also illustrate the individual
psychical activities most clearly. The above-mentioned migrations from
nest to nest show very beautifully the individual plans of single
workers carried out with great tenacity. For hours at a time an ant
may try to overcome a multitude of difficulties for the purpose of
attaining an aim which she has set herself. This aim is not accurately
prescribed by instinct, as the insect may be confronted with several
possibilities, so that it often happens that two ants may be working in
opposition to each other. This looks like stupidity to the superficial
observer. But it is just here that the ant’s plasticity reveals itself.
For a time the two little animals interfere with each other, but
finally they notice the fact, and one of them gives in, goes away, or
assists the other.

These conditions are best observed during the building of nests or
roads, e. g., in the horse-ant (_Formica rufa_) and still better in _F.
pratensis_. It is necessary, however, to follow the behavior of a few
ants for hours, if one would have a clear conception of this matter,
and for this much patience and much time are necessary. The combats
between ants, too, show certain very consistent aims of behavior,
especially the struggles which I have called chronic combats (_combats
à froid_). After two parties (two colonies brought together) have made
peace with each other, one often sees a few individuals persecuting and
maltreating certain individuals of the opposite party. They often carry
their victims a long distance off, for the purpose of excluding them
from the nest. If the ant that has been borne away returns to the nest
and is found by her persecutrix, she is again seized and carried away
to a still greater distance. In one such case in an artificial nest
of a small species of Leptothorax, the persecuting ant succeeded in
dragging her victim to the edge of my table. She then stretched out her
head and allowed her burden to fall on the floor. This was not chance,
for she repeated the performance twice in succession after I had again
placed the victim on the table. Among the different individuals of the
previously hostile, but now pacified opposition, she had concentrated
her antipathy on this particular ant and had tried to make her return
to the nest impossible. One must have very strong preconceived opinions
if in such and many similar cases one would maintain that ants are
lacking in individual decision and execution. Of course, all these
things happen within the confines of the instinct-precincts of the
species, and the different stages in the execution of a project are
instinctive. Moreover, I expressly defend myself against the imputation
that I am importing human reflection and abstract concepts into this
volition of the ant, though we must honestly admit, nevertheless,
that in the accomplishment of our human decisions both hereditary and
secondary automatisms are permitted to pass unnoticed. While I am
writing these words, my eyes operate with partially hereditary, and my
hand with secondary automatisms. But it goes without saying that only
a human brain is capable of carrying out my complex innervations and
my concomitant abstract reflections. But the ant must, nevertheless,
associate and consider somewhat in a concrete way after the manner of
an ant, when it pursues one of the above-mentioned aims and combines
its instincts with this special object in view. While, however,
the instinct of the ant can be combined for only a few slightly
different purposes, by means of a small number of plastic adaptations
or associations, individually interrupted in their concatenation or
_vice versa_, in the thinking human being both inherited and secondary
automatisms are only fragments or instruments in the service of an
overwhelming, all-controlling, plastic brain-activity. It may be said
incidentally that the relative independence of the spinal chord and of
subordinate brain-centers in the lower animals (and even in the lower
mammals) as compared with the cerebrum, may be explained in a similar
manner if they are compared with the profound dependence of these
organs and their functions on the massive cerebrum in man and even
to some extent in the apes. The cerebrum splits up and controls its
automatisms (_divide et impera_).

While success visibly heightens both the audacity and tenacity of
the ant-will, it is possible to observe after repeated failure or in
consequence of the sudden and unexpected attacks of powerful enemies
a form of abulic dejection, which may lead to a neglect of the most
important instincts, to cowardly flight, to the devouring or casting
away of offspring, to neglect of work, and similar conditions. There is
a chronically cumulative discouragement in degenerate ant-colonies and
an acute discouragement when a combat is lost. In the latter case one
may see troops of large powerful ants fleeing before a single enemy,
without even attempting to defend themselves, whereas the latter a
few moments previously would have been killed by a few bites from the
fleeing individuals. It is remarkable how soon the victor notices and
utilises this abulic discouragement. The dejected ants usually rally
after the flight and soon take heart and initiative again. But they
offer but feeble resistance, e. g., to a renewed attack from the same
enemy on the following day. Even an ant’s brain does not so soon forget
the defeats which it has suffered.

In bitter conflicts between two colonies of nearly equal strength the
tenacity of the struggle and with it the will to conquer increases till
one of the parties is definitively overpowered. In the realm of will
imitation plays a great rôle. Even among ants protervity and dejection
are singularly contagious.


It may perhaps sound ludicrous to speak of feelings in insects. But
when we stop to consider how profoundly instinctive and fixed is our
human life of feeling, how pronounced are the emotions in our domestic
animals, and how closely interwoven with the impulses, we should expect
to encounter emotions and feelings in animal psychology. And these
may indeed be recognised so clearly that even Uexkuell would have to
capitulate if he should come to know them more accurately. We find
them already interwoven with the will as we have described it. Most
of the emotions of insects are profoundly united to the instincts.
Of such a nature is the jealousy of the queen bee when she kills the
rival princesses, and the terror of the latter while they are still
within their cells; such is the rage of fighting ants, wasps, and
bees, the above-mentioned discouragement, the love of the brood, the
self-devotion of the worker honey-bees, when they die of hunger while
feeding their queen, and many other cases of a similar description. But
there are also individual emotions that are not compelled altogether
by instinct, e. g., the above-mentioned mania of certain ants for
maltreating some of their antagonists. On the other hand, as I have
shown, friendly services (feeding), under exceptional circumstances,
may call forth feelings of sympathy and finally of partnership,
even between ants of different species. Further than this, feelings
of sympathy, antipathy, and anger among ants may be intensified by
repetition and by the corresponding activities, just as in other
animals and man.

The social sense of duty is instinctive in ants, though they exhibit
great individual, temporary, and occasional deviations, which betray a
certain amount of plasticity.


I have rapidly reviewed the three main realms of ant-psychology. It
is self-evident that in this matter they no more admit of sharp
demarcation from one another than elsewhere. The will consists of
centrifugal resultants of sense-impressions and feelings and in turn
reacts powerfully on both of these.

It is of considerable interest to observe the antagonism between
different perceptions, feelings, and volitions in ants and bees, and
the manner in which in these animals the intensely fixed (obsessional)
attention may be finally diverted from one thing to another. Here
experiment is able to teach us much. While bees are busy foraging on
only one species of flower, they overlook everything else, even other
flowers. If their attention is diverted by honey offered them directly,
although previously overlooked, they have eyes only for the honey. An
intense emotion, like the swarming of honey-bees (von Buttel) compels
these insects to forget all animosities and even the old maternal
hive to which they no longer return. But if the latter happens to be
painted blue, and if the swarming is interrupted by taking away the
queen, the bees recollect the blue color of their old hive and fly to
hives that are painted blue. Two feelings often struggle with each
other in bees that are “crying” and without a queen: that of animosity
towards strange bees and the desire for a queen. Now if they be given a
strange queen by artificial means, they kill or maltreat her, because
the former feeling at first predominates. For this reason the apiarist
encloses the strange queen in a wire cage. Then the foreign odor
annoys the bees less because it is further away and they are unable to
persecute the queen. Still they recognise the specific queen-odor and
are able to feed her through the bars of the cage. This suffices to
pacify the hive. Then the second feeling quickly comes to the front;
the workers become rapidly inured to the new odor and after three or
four days have elapsed, the queen may be liberated without peril.

It is possible in ants to make the love of sweets struggle with the
sense of duty, when enemies are made to attack a colony and honey is
placed before the ants streaming forth to defend their nest. I have
done this with _Formica pratensis_. At first the ants partook of the
honey, but only for an instant. The sense of duty conquered and all of
them without exception, hurried forth to battle and most of them to
death. In this case a higher decision of instinct was victorious over
the lower impulse.

In _résumé_ I would lay stress on the following general conclusions:

1. From the standpoint of natural science we are bound to hold
fast to the psychophysiological theory of identity (Monism) in
contradistinction to dualism, because it alone is in harmony with the
facts and with the law of the conservation of energy.

Our mind must be studied simultaneously both directly from within and
indirectly from without, through biology and the conditions of its
origin. Hence there is such a thing as comparative psychology of other
individuals in addition to that of self, and in like manner we are
led to a psychology of animals. Inference from analogy, applied with
caution, is not only permissible in this science, but obligatory.

2. The senses of insects are our own. Only the auditory sense still
remains doubtful, so far as its location and interpretation are
concerned. A sixth sense has not yet been shown to exist, and a special
sense of direction and orientation is certainly lacking. The vestibular
apparatus of vertebrates is merely an organ of equilibration and
mediates internal sensations of acceleration, but gives no orientation
in space outside of the body. On the other hand the visual and
olfactory senses of insects present varieties in the range of their
competency and in their specific energies (vision of ultra-violet,
functional peculiarities of the facetted eye, topochemical antennal
sense and contact-odor).

3. Reflexes, instincts, and plastic, individually adaptive, central
nervous activities pass over into one another by gradations. Higher
complications of these central or psychic functions correspond to
a more complicated apparatus of superordinated neuron-complexes

4. Without becoming antagonistic, the central nervous activity in the
different groups and species of animals complicates itself in two
directions: (_a_) through inheritance (natural selection, etc.) of
the complex, purposeful automatisms, or instincts; (_b_) through the
increasingly manifold possibilities of plastic, individually adaptive
activities, in combination with the faculty of gradually developing
secondary individual automatisms (habits).

The latter mode requires many more nerve-elements. Through hereditary
predispositions (imperfect instincts) of greater or less stability, it
presents transitions to the former mode.

5. In social insects the correlation of more developed psychic powers
with the volume of the brain may be directly observed.

6. In these animals it is possible to demonstrate the existence of
memory, associations of sensory images, perceptions, attention, habits,
simple powers of inference from analogy, the utilisation of individual
experiences and hence distinct, though feeble, plastic, individual
deliberations or adaptations.

7. It is also possible to detect a corresponding, simpler form of
volition, i. e., the carrying out of individual decisions in a more
or less protracted time-sequence, through different concatenations
of instincts; furthermore different kinds of discomfort and pleasure
emotions, as well as interactions and antagonisms between these diverse
psychic powers.

8. In insect behavior the activity of the attention is one-sided
and occupies a prominent place. It narrows the scope of behavior
and renders the animal temporarily blind (inattentive) to other

Thus, however different may be the development of the automatic and
plastic, central neurocyme activities in the brains of different
animals, it is surely possible, nevertheless, to recognise certain
generally valid series of phenomena and their fundamental laws.

Even to-day I am compelled to uphold the seventh thesis which I
established in 1877 in my habilitation as _privat-docent_ in the
University of Munich:

“All the properties of the human mind may be derived from the
properties of the animal mind.”

I would merely add to this:

“And all the mental attributes of higher animals may be derived from
those of lower animals.” In other words: The doctrine of evolution
is quite as valid in the province of psychology as it is in all the
other provinces of organic life. Notwithstanding all the differences
presented by animal organisms and the conditions of their existence,
the psychic functions of the nerve-elements seem nevertheless,
everywhere to be in accord with certain fundamental laws, even in the
cases where this would be least expected on account of the magnitude of
the differences.



Our sense of smell, like our sense of taste, is a chemical sense. But
while the latter reacts only to substances dissolved in liquids and
with but few (about five) different principal qualities, the olfactory
sense reacts with innumerable qualities to particles of the most
diverse substances dissolved in the atmosphere. Even to our relatively
degenerate human olfactories, the number of these odor-qualities seems
to be almost infinite.

In insects that live in the air and on the earth the sense of taste
seems to be located, not only like our own, in the mouth-parts, but
also to exhibit the same qualities and the corresponding reactions. At
any rate it is easy to show that these animals are usually very fond
of sweet, and dislike bitter things, and that they perceive these two
properties only after having tasted of the respective substances. F.
Will, in particular, has published good experiments on this subject.

In aquatic insects the conditions are more complicated. Nagel, who
studied them more closely, shows how difficult it is in these cases
to distinguish smell from taste, since substances dissolved in water
are more or less clearly perceived or discerned from a distance by
both senses and sought or avoided in consequence. Nagel, at any rate,
succeeded in showing that the palpi, which are of less importance in
terrestrial insects, have an important function in aquatic forms.

In this place we are concerned with an investigation of the sense of
smell in terrestrial insects. Its seat has been proved to be in the
antennæ. A less important adjunct to these organs is located, as Nagel
and Wasmann have shown, in the palpi. In the antennæ it is usually the
club or foliaceous or otherwise formed dilatations which accommodate
the cellular ganglion of the antennary nerve. I shall not discuss the
histological structure of the nerve-terminations but refer instead to
Hicks, Leydig, Hauser, my own investigations and the other pertinent
literature, especially to K. Kraepelin’s excellent work. I would merely
emphasise the following points:

1. All the olfactory papillæ of the antennæ are transformed, hair-like

2. All of these present a cellular dilatation just in front of the

3. Tactile hairs are found on the antennæ together with the olfactory

4. The character and form of the nerve-terminations are highly
variable, but they may be reduced to three principal types:
pore-plates, olfactory rods, and olfactory hairs. The two latter
are often nearly or quite indistinguishable from each other. The
nerve-termination is always covered with a cuticula which may be never
so delicate.

Other end-organs of the Hymenopteran antenna described by Hicks and
myself, are still entirely obscure, so far as their function is
concerned, but they can have nothing to do with the sense of smell,
since they are absent in insects with a delicate sense of smell (wasps)
and occur in great numbers in the honey-bees, which have obtuse

That the antennæ and not the nerve-terminations of the mouth and palate
function, as organs of smell, has been demonstrated by my control
experiments, which leave absolutely no grounds for doubt and have,
moreover, been corroborated on all sides. Terrestrial insects can
discern chemical substances at a distance by means of their antennæ
only. But in touch, too, these organs are most important and the palpi
only to a subordinate extent, namely in mastication. The antennæ enable
the insect to perceive the chemical nature of bodies and in particular,
to recognise and distinguish plants, other animals and food, except
in so far as the visual and gustatory senses are concerned in these
activities. These two senses may be readily eliminated, however, since
the latter functions only during feeding and the former can be removed
by varnishing the eyes or by other means. Many insects, too, are blind
and find their way about exclusively by means of their antennæ. This is
the case, e. g., with many predatory ants of the genus Eciton.

But I will here assume these questions to be known and answered, nor
will I indulge in polemics with Bethe and his associates concerning
the propriety of designating the chemical antennal sense as “smell.”
I have discussed this matter elsewhere.[2] What I wish to investigate
in this place is the psychological quality of the antennal olfactory
sense, how it results in part from observation and in part from the
too little heeded correlative laws of the psychological exploitation
of each sense in accordance with its structure. I assume as known the
doctrines of specific energies and adequate stimuli, together with the
more recent investigations on the still undifferentiated senses, like
photodermatism and the like, and would refer, moreover, to Helmholtz’s
_Die Thatsachen in der Wahrnehmung_, 1879. Hirschwald, Berlin.

[2] “Sensations des Insectes,” _Rivista di Biologia Generale_. Como,
1900-1901. For the remainder see also A. Forel, _Mitth. des Münchener
entom. Vereins_, 1878, and _Recueil. Zool. Suisse_, 1886-1887.

When in our own human subjective psychology, which alone is known
to us directly, we investigate the manner in which we interpret our
sensations, we happen upon a peculiar fact to which especially Herbert
Spencer has called attention. We find that so-called perceptions
consist, as is well known, of sensations which are bound together
sometimes firmly, sometimes more loosely. The more intimately the
sensations are bound together to form a whole, the easier it is for us
to recall in our memory the whole from a part. Thus, e. g., it is easy
for me to form an idea from the thought of the head of an acquaintance
as to the remainder of his body. In the same manner the first note of
a melody or the first verse of a poem brings back the remainder of
either. But the thought of an odor of violets, a sensation of hunger,
or a stomach-ache, are incapable of recalling in me either simultaneous
or subsequent odors or feelings.

These latter conditions call up in my consciousness much more easily
certain associated visual, tactile, or auditory images (e. g., the
visual image of a violet, a table set for a meal). As ideas they are
commonly to be represented in consciousness only with considerable
difficulty, and sometimes not at all, and they are scarcely capable of
association among themselves. We readily observe, moreover, that visual
images furnish us mainly with space recollections, auditory images with
sequences in time, and tactile images with both, but less perfectly.
These are indubitable and well-known facts.

But when we seek for the wherefore of these phenomena, we find the
answer in the structure of the particular sense-organ and in its manner
of functioning.

It is well known that the eye gives us a very accurate image of the
external world on our retina. Colors and forms are there depicted in
the most delicate detail, and both the convergence of our two eyes and
their movement and accommodation gives us besides the dimensions of
depth through stereoscopic vision. Whatever may be still lacking or
disturbing is supplied by instinctive inferences acquired by practice,
both in memory and direct perception (like the lacunæ of the visual
field), or ignored (like the turbidity of the corpus vitreum). But the
basis of the visual image is given in the coördinated _tout ensemble_
of the retinal stimuli, namely the retinal image.[3] Hence, since the
retina furnishes us with such spatial projections, and these in sharp
details, or relations, definitely coöordinated with one another, the
sense of sight gives us knowledge of space. For this reason, also, and
solely on this account, we find it so easy to supply through memory by
association the missing remnant of a visual spatial image. For this
reason, too, the visual sensations are preëminently associative or
relational in space, to use Spencer’s expression. For the same reason
the insane person so readily exhibits hallucinations of complicated
spatial images in the visual sphere. This would be impossible in the
case of the olfactory sense.

[3] It is well known that in this matter the movements of the eyes, the
movements of the body and of external objects play an essential part,
so that without these the eye would fail to give us any knowledge of
space. But I need not discuss this further, since the antennæ of ants
are at least quite as moveable and their olfactory sense is even more
easily educated in unison with the tactile sense.

Similarly, the organ of Corti in the ear gives us tone or sound scales
in accurate time-sequence, and hence also associations of sequence much
more perfectly than the other senses. Its associations are thus in the
main associations of sequence, because the end-apparatus registers
time-sequences in time-intervals and not as space images.

The corresponding cortical receptive areas are capable, in the first
instance, merely of registering what is brought to them by the
sense-stimuli and these are mainly associated spatial images for sight
and tone or sound-sequences for hearing.

Let us consider for a moment how odors strike the mucous membranes of
our choanæ. They are wafted towards us as wild mixtures in an airy
maelstrom, which brings them to the olfactory terminations without
order in the inhaled air or in the mucous of the palate. They come in
such a way that there cannot possibly be any spatial association of the
different odors in definite relationships. In time they succeed one
another slowly and without order, according to the law of the stronger
element in the mixture, but without any definite combination. If, after
one has been inhaling the odor of violets, the atmosphere gradually
becomes charged with more roast meat than violet particles, the odor
of roast succeeds that of violet. But nowhere can we perceive anything
like a definitely associated sequence, so that neither our ideas of
time nor those of space comprise odors that revive one another through
association. By much sniffing of the surface of objects we could at
most finally succeed in forming a kind of spatial image, but this would
be very difficult owing to man’s upright posture. Nevertheless it is
probable that dogs, hedge-hogs, and similar animals acquire a certain
olfactory image by means of sniffing. The same conditions obtain in
the sphere of taste and the visceral sensations for the same reasons.
None of these senses furnish us with any sharply defined qualitative
relations either in space or time. On this account they furnish by
themselves no associations, no true perceptions, no memory images,
but merely sensations, and these often as mixed sensations, which are
vague and capable of being associated only with associative senses.
The hallucinations of smell, taste, and of the splanchnic sensations,
are not deceptive perceptions, since they cannot have a deceptive
resemblance to objects. They are simply paræsthesias or hyperæsthesias,
i. e., pathological sensations of an elementary character either
without adequate stimulus or inadequate to the stimulus.

The tactile sense furnishes us with a gross perception of space and of
definite relations, and may, therefore, give rise to hallucinations, or
false perceptions of objects. By better training its associative powers
in the blind may be intensified. The visual sensations are usually
associated with tactile localisations.

Thus we see that there is a law according to which the psychology
of a sense depends not only on its specific energy but also on the
manner in which it is able to transmit to the brain the relations
of its qualities in space and time. On this depends the knowledge
we acquire concerning time and space relations through a particular
sense and hence also its ability to form perceptions and associations
in the brain. More or less experience is, of course, to be added or
subtracted, but this is merely capable of enriching the knowledge
of its possessor according to the measure of the relations of the
particular sense-stimuli in space and time.

I would beg you to hold fast to what I have said and then to picture to
yourselves an olfactory sense, i. e., a chemical sense effective at a
distance and like our sense of smell, capable of receiving impressions
from particles of the most diverse substances diffused through the
atmosphere, located not in your nostrils, but on your hands. For of
such a nature is the position of the olfactory sense on the antennal
club of the ant.

Now imagine your olfactory hands in continual vibration, touching all
objects to the right and to the left as you walk along, thereby rapidly
locating the position of all odoriferous objects as you approach or
recede from them, and perceiving the surfaces both simultaneously and
successively as parts of objects differing in odor and position. It is
clear from the very outset that such sense-organs would enable you to
construct a veritable odor-chart of the path you had traversed and one
of double significance:

1. A clear contact-odor chart, restricted, to be sure, to the immediate
environment and giving the accurate odor-form of the objects touched
(round odors, rectangular odors, elongate odors, etc.) and further hard
and soft odors in combination with the tactile sensations.

2. A less definite chart which, however, has orienting value for a
certain distance, and produces emanations which we may picture to
ourselves like the red gas of bromine which we can actually see.

If we have demonstrated that ants perceive chemical qualities through
their antennæ both from contact and from a distance, then the antennæ
must give them knowledge of space, if the above formulated law is true,
and concerning this there can be little doubt. This must be true even
from the fact that the two antennæ simultaneously perceive different
and differently odoriferous portions of space.[4]

[4] It is not without interest to compare these facts with Condillac’s
discussion (_Treatise on the Sensations_) concerning his hypothetical
statue. Condillac shows that our sense of smell is of itself incapable
of giving us space knowledge. But it is different in the case of
the topochemical sense of smell in combination with the antennary
movements. Here Condillac’s conditions of the gustatory sense are

They must therefore also transmit perceptions and topographically
associated memories concerning a path thus touched and smelled. Both
the trail of the ants themselves and the surrounding objects must leave
in their brains a chemical (odor-) space-form with different, more
or less definitely circumscribed qualities, i. e., an odor-image of
immediate space, and this must render associated memories possible.
Thus an ant must perceive the forms of its trail by means of smell.
This is impossible, at least for the majority of the species, by means
of the eyes. If this is true, an ant will always be able, no matter
where she may be placed on her trail, to perceive what is to the
right, left, behind or before her, and consequently what direction
she is to take, according to whether she is bound for home, or in the
opposite direction to a tree infested with Aphides, or the like.

Singularly enough, I had established this latter fact in my “Études
Myrmécologiques en 1886” (_Annales de la Societé Entomologique de
Belgique_) before I had arrived at its theoretical interpretation.
But I was at once led by this discovery in the same work to the
interpretation just given. Without knowing of my work in this
connection, A. Bethe has recently established (discovered, as he
supposes) this same fact, and has designated it as “polarisation of
the ant-trail.” He regards this as the expression of a mysterious,
inexplicable force, or polarisation. As we have seen, the matter is
not only no enigma, but on the contrary, a necessary psychological
postulate. We should rather find the absence of this faculty

But everything I have just said presupposes a receptive brain. The
formation of lasting perceptions and associations cannot take place
without an organ capable of fixing the sense-impressions and of
combining them among themselves. Experience shows that the immediate
sensory centers are inadequate to the performance of this task. Though
undoubtedly receptive, they are, nevertheless, incapable of utilising
what has been received in the development of more complex instincts
and can turn it to account only in the grosser, simpler reflexes and
automatisms. To be sure, a male ant has better eyes than a worker ant,
and probably quite as good antennæ, but he is unable to remember what
he has seen and is especially incapable of associating it in the form
of a trail-image, because he is almost devoid of a brain. For this
reason he is unable to find his way back to the nest. On the other
hand, it is well known that the brain of a man who has lost a limb or
whose hearing is defective, will enable him to paint pictures with his
foot, write with the stump of an arm or construct grand combinations
from the images of defective senses.

I venture, therefore, to designate as topochemical the olfactory
antennal sense of honey-bees, humble-bees, wasps, etc.

Can we generalise to such an extent as to apply this term without
further investigation to all arthropods? To a considerable extent this
must be denied.

In fact, the multiformity in the structure and development of the
arthropod sense-organs is enormous, and we must exercise caution in
making premature generalisations.

It is certain that in some aerial insects the olfactory sense has
dwindled to a minimum, e. g., in those species in which the male
recognises and follows the female exclusively by means of the eyes, as
in the Odonata (dragon-flies). To insects with such habits an olfactory
sense would be almost superfluous. Here, too, the antennæ have dwindled
to diminutive dimensions.

But there are insects whose antennæ are immovable and quite unable to
touch objects. This is the case in most Diptera (flies). Still these
antennæ are often highly developed and present striking dilatations
densely beset with olfactory papillæ. By experiment I have demonstrated
the existence of an olfactory sense in such Dipteran antennæ, and I
have been able to show that, e. g., in _Sarcophaga vivipara_ and other
carrion flies, the egg-laying instinct is absolutely dependent on the
sensation of the odor of carrion and the presence of the antennæ. In
these cases the contact-odor sense is undoubtedly absent. More or
less of a topochemical odor-sense at long range must, of course, be
present, since the antennæ are external, but the precision of the
spatial image must be very imperfect, owing to the immobility of the
antennæ. Nevertheless, flies move about so rapidly in the air that they
must be able by means of their antennæ to distinguish very quickly
the direction from which odors are being wafted. These insects do, in
fact, find the concealed source of odors with great assurance. But
this is no great art, for even we ourselves are able to do the same by
sniffing or going to and fro. But the flies find their way through the
air with their eyes and not at all by means of their sense of smell.
Hence their olfactory powers probably constitute a closer psychological
approximation to those of mammals than to the topochemical odor-sense
of ants, for they can hardly furnish any constant and definite

Even in many insects with movable antennæ and of less ærial habits, e.
g., the chafers and bombycid moths, the antennal olfactory sense is
evidently much better adapted to function at a distance, i. e., to the
perception of odors from distant objects, than to the perception of
space and trails. Such insects find their way by means of their eyes,
but fly in the direction whence their antennæ perceive an odor that is
being sought.

A genuine topochemical antennal sense is, therefore, probably best
developed in all arthropods, whose antennæ are not only movable in
the atmosphere, but adapted to feeling of objects. In these cases
the still imperfect topochemical odor-sense for distances can be
momentarily controlled by the contact-odor-sense and definitively
fixed topographically, i. e., topochemically, as we see so extensively
practised in the ants.

It would be possible to meet this view with the objection that a
contact-odor sense could not accomplish much more than the tactile
sense. I have made this objection to myself. But in the first place it
is necessary to reckon with the facts. Now it is a fact that insects in
touching objects with their antennæ mainly perceive and distinguish the
chemical constitution of the objects touched and heed these very much
more than they do the mechanical impacts also perceived at the same
time. Secondly, the tactile sense gives only resistance and through
this, form. On the other hand, the multiplicity of odors is enormous,
and it is possible to demonstrate, as I have done for the ants, and
Von Buttel-Reepen for the bees, that these animals in distinguishing
their different nest-mates and their enemies, betray nothing beyond
the perception of extremely delicate and numerous gradations in the
qualities of odors.

In combination with topochemical space-perception, these numerous
odor-qualities must constitute a spatial sense which is vastly superior
to the tactile sense. The whole biology of the social Hymenoptera
furnishes the objective proof of this assertion.

It would certainly be well worth while to investigate this matter in
other groups of arthropods which possess complex instincts.

In conclusion I will cite an example, which I have myself observed,
for the purpose of illustrating the capacity of the topochemical
olfactory sense.

The American genus Eciton comprises predatory ants that build temporary
nests from which they undertake expeditions for the purpose of preying
on all kinds of insects. The Ecitons follow one another in files, like
geese, and are very quick to detect new hunting grounds. As “ants of
visitation,” like the Africo-Indian species of Dorylus, they often take
possession of human dwellings, ferret about in all the crevices of the
walls and rooms for spiders, roaches, mice, and even rats, attack and
tear to pieces all such vermin in the course of a few hours and then
carry the booty home. They can convert a mouse into a clean skeleton.
They also attack other ants and plunder their nests.

Now all the workers of the African species of Dorylus and of many of
the species of Eciton are totally blind, so that they must orient
themselves exclusively by means of their antennal sense.

In 1899 at Faisons, North Carolina, I was fortunate enough to find a
temporary nest of the totally blind little _Eciton carolinense_ in a
rotten log. I placed the ants in a bag and made them the subject of
some observations. The Eciton workers carry their elongate larvæ in
their jaws and extending back between their legs in such a position
that the antennæ have full play in front.

Their ability to follow one another and to find their way about rapidly
and unanimously in new territory without a single ant going astray,
is incredible. I threw a handful of Ecitons with their young into a
strange garden in Washington, i. e., after a long railway journey and
far away from their nest. Without losing a moment’s time, the little
animals began to form in files which were fully organised in five
minutes. Tapping the ground continually with their antennæ, they took
up their larvæ and moved away in order, reconnoitering the territory
in all directions. Not a pebble, not a crevice, not a plant was left
unnoticed or overlooked. The place best suited for concealing their
young was very soon found, whereas most of our European ants under such
conditions, i. e., in a completely unknown locality, would probably
have consumed at least an hour in accomplishing the same result. The
order and dispatch with which such a procession is formed in the
midst of a totally strange locality is almost fabulous. I repeated
the experiment in two localities, both times with the same result.
The antennæ of the Ecitons are highly developed, and it is obvious
that their brain is instinctively adapted to such rapid orientation in
strange places.

In Colombia, to be sure, I had had opportunities of observing, not
the temporary nests, but the predatory expeditions of larger Ecitons
(_E. Burchelli_ and _hamatum_) possessing eyes. But these in no
respect surpassed the completely blind _E. carolinense_ in their
power of orientation and of keeping together in files. As soon as
an ant perceives that she is not being followed, she turns back and
follows the others. But the marvellous fact is the certainty of this
recognition, the quickness and readiness with which the animals
recognise their topochemical trail without hesitation. There is none
of the groping about and wandering to and fro exhibited by most of our
ants. Our species of Tapinoma and Polyergus alone exhibit a similar but
less perfect condition. It is especially interesting, however, to watch
the _perpetuum mobile_ of the antennæ of the Ecitons, the lively manner
in which these are kept titillating the earth, all objects, and their

All this could never be accomplished by a tactile sense alone. Nor
could it be brought about by an olfactory sense which furnished
no spatial associations. As soon as an Eciton is deprived of its
two antennæ it is utterly lost, like any other ant under the same
circumstances. It is absolutely unable to orient itself further or to
recognise its companions.

In combination with the powerful development of the cerebrum (_corpora
pedunculata_) the topochemical olfactory sense of the antennæ
constitutes the key to ant psychology. Feeling obliged to treat of the
latter in the preceding lecture, I found it necessary here to discuss
in detail this particular matter which is so often misunderstood.

    [In his latest _Souvenirs entomologiques_ (Seventh Series) J.
    H. Fabre has recorded a number of ingenious experiments showing
    the ability of the males of Saturnia and Bombyx to find their
    females at great distances and in concealment. He tried in
    vain (which was to have been foreseen) to conceal the female
    by odors which are strong even to our olfactories. The males
    came notwithstanding. He established the following facts: (1)
    Even an adverse wind does not prevent the males from finding
    their way; (2) if the box containing the female is loosely
    closed, the males come nevertheless; (3) if it is hermetically
    closed (e. g., with wadding or soldered) they no longer come;
    (4) the female must have settled for some time on a particular
    spot before the males come; (5) if the female is then suddenly
    placed under a wire netting or a bell-jar, though still clearly
    visible, _the males nevertheless do not fly to her, but pass
    on to the spot where she had previously rested and left her
    odor_; (6) the experiment of cutting off the antennæ proves
    very little. The males without antennæ do not, of course, come
    again; but even the other males usually come only once: their
    lives are too short and too soon exhausted.

    At first Fabre did not wish to believe in smell, but he was
    compelled finally, as a result of his own experiments, to
    eliminate sight and hearing. Now he makes a bold hypothesis:
    the olfactory sense of insects has two energies, one (ours),
    which reacts to dissolved chemical particles, and another which
    receives “physical odor-waves,” similar to the waves of light
    and sound. He already foresees how science will provide us with
    a “radiography of odors” (after the pattern of the Roentgen
    rays). But his own results, enumerated above under (4) and (5)
    contradict this view. The great distances from which the Bombyx
    males can discern their females is a proof to him that this
    cannot be due to dissolved chemical particles. And these same
    animals smell the female only after a certain time and smell
    the spot where she had rested, instead of the female when she
    is taken away! This, however, would be inconceivable on the
    theory of a physical wave-sense, while it agrees very well with
    that of an extremely delicate, chemical olfactory sense.

    It is a fact that insects very frequently fail to notice odors
    which we perceive as intense, and even while these are present,
    detect odors which are imperceptible to our olfactories.
    We must explain this as due to the fact that the olfactory
    papillæ of different species of animals are especially adapted
    to perceiving very different substances. All biological
    observations favor this view, and our psycho-chemical theories
    will have to make due allowance for the fact.]


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