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_THE CONTEMPORARY SCIENCE SERIES._
EDITED BY HAVELOCK ELLIS.
THE INDUSTRIES OF ANIMALS.
THE INDUSTRIES OF ANIMALS.
BY
FREDERIC HOUSSAY.
WITH 44 ILLUSTRATIONS.
LONDON:
WALTER SCOTT, LTD.,
24 WARWICK LANE, PATERNOSTER ROW.
1893.
NOTE.
The English edition of this book has been revised throughout and
enlarged, with the author's co-operation. Numerous bibliographical
references have also been added. The illustrations, when not otherwise
stated, are in most cases adapted from Brehm's _Thierleben_.
CONTENTS.
CHAPTER I.
INTRODUCTION
The naturalists of yesterday and the naturalists of to-day--Natural
history and the natural sciences--The theory of Evolution--The chief
industries of Man--The chief industries of Animals--Intelligence and
instinct--Instinctive actions originate in reflective actions--The
plan of study of the various industries.
CHAPTER II.
HUNTING--FISHING--WARS AND EXPEDITIONS
The Carnivora more skilful hunters than the Herbivora--Different
methods of hunting--Hunting in ambush--The baited ambush--Hunting in
the dwelling or in the burrow--Coursing--Struggles that terminate the
hunt--Hunting with projectiles--Particular circumstances put to
profit--Methods for utilising the captured game--War and
brigandage--Expeditions to acquire slaves--Wars of the ants.
CHAPTER III.
METHODS OF DEFENCE
Flight--Feint--Resistance in common by social animals--Sentinels.
CHAPTER IV.
PROVISIONS AND DOMESTIC ANIMALS
Provisions laid up for a short period--Provisions laid up for a long
period--Animals who construct barns--Physiological reserves--Stages
between physiological reserves and provisions--Animals who submit food
to special treatment in order to facilitate transport--Care bestowed
on harvested provisions--Agricultural ants--Gardening ants--Domestic
animals of ants--Degrees of civilisation in the same species of
ants--Aphis-pens and paddocks--Slavery among ants.
CHAPTER V.
PROVISION FOR REARING THE YOUNG
The preservation of the individual and the preservation of the
species--Foods manufactured by the parents for their young--Species
which obtain for their larvae foods manufactured by others--Carcasses
of animals stored up--Provision of paralysed living animals--The cause
of the paralysis--The sureness of instinct--Similar cases in which the
specific instinct is less powerful and individual initiative
greater--Genera less skilful in the art of paralysing victims.
CHAPTER VI.
DWELLINGS
Animals naturally provided with dwellings--Animals who increase their
natural protection by the addition of foreign bodies--Animals who
establish their home in the natural or artificial dwellings of
others--Classification of artificial shelters--Hollowed
dwellings--Rudimentary burrows--Carefully-disposed burrows--Burrows
with barns adjoined--Dwellings hollowed out in wood--Woven
dwellings--Rudiments of this industry--Dwellings formed of
coarsely-entangled materials--Dwellings woven of flexible
substances--Dwellings woven with greater art--The art of sewing among
birds--Modifications of dwellings according to season and climate--Built
dwellings--Paper nests--Gelatine nests--Constructions built of
earth--Solitary masons--Masons working in association--Individual
skill and reflection--Dwellings built of hard materials united by
mortar--The dams of beavers.
CHAPTER VII.
THE DEFENCE AND SANITATION OF DWELLINGS
General precautions against possible danger--Separation of females while
brooding--Hygienic measures of Bees--Prudence of Bees--Fortifications
of Bees--Precautions against inquisitiveness--Lighting up the nests.
CHAPTER VIII.
CONCLUSION
Degree of perfection in industry independent of zoological
superiority--Mental faculties of the lower animals of like nature to
Man's.
APPENDIX
INDEX
THE INDUSTRIES OF ANIMALS.
CHAPTER I.
INTRODUCTION.
THE NATURALISTS OF YESTERDAY AND THE NATURALISTS OF
TO-DAY--NATURAL HISTORY AND THE NATURAL SCIENCES--THE THEORY
OF EVOLUTION--THE CHIEF INDUSTRIES OF MAN--THE CHIEF
INDUSTRIES OF ANIMALS--INTELLIGENCE AND INSTINCT--INSTINCTIVE
ACTIONS ORIGINATE IN REFLECTIVE ACTIONS--THE PLAN OF STUDY OF
THE VARIOUS INDUSTRIES.
_The naturalists of yesterday and the naturalists of to-day._--The
study of animals, plants, rocks, and of natural objects generally, was
formerly called "natural history"; but this term is tending to
disappear from our vocabulary and to give place to the term "natural
sciences." What is the reason of this change, and to what does it
correspond? for it is rare for a word to be modified in so short a
time if the thing designated has not itself varied.
Exterior forms have certainly changed, and the naturalist of yesterday
makes upon us the impression of a legendary being. I refer to the
person described in George Sand's romances, marching vigorously over
hills and valleys in search of a rare insect, which he pricked with
delight, or of a plant difficult to reach, which he triumphantly dried
and fixed on a leaf of paper bearing the date of the discovery and the
name of the locality. A herbarium became a sort of journal, recalling
to its fortunate possessor all the wanderings of the happy chase, all
the delightful sounds and sights of the country. Every naturalist
concealed within him a lover of idylls or eclogues. Assuredly all the
preliminary studies which resulted from these excursions were
necessary; we owe gratitude to our predecessors, and we profit from
their labours, sometimes regretting the loss of the picturesque
fashion in which their researches were carried out.
The naturalist of to-day usually lives more in the laboratory than in
the country. Occasional expeditions to the coast or dredgings are the
only links that attach him to nature; the scalpel and the microtome
have replaced the collector's pins, and the magnifying glass gives
place to the microscope. When the observer begins to pursue his
studies in the laboratory he no longer cares to pass the threshold. He
has still so much to learn concerning the most common creatures that
it seems useless to him to waste his time in seeking those that are
rarer, unless he takes into account the unquestionable pleasure of
rambling through woods or along coasts;--but such a consideration does
not belong to the scientific domain.
A change of conditions of this nature does not suffice to create a
science. To take away from a study all that rendered it pleasant and
easy, and to make it the property of a small coterie, when it was
formerly accessible to all, is not sufficient to render it scientific.
It is a fatality rather than a triumph to have undergone such a
change. The change is an effect rather than a cause.
When little or nothing was known it was necessary to begin by
examining the phenomena which first met the eyes of the observer, such
as the customs of animals and the characters which distinguished them
from each other. Their differences and resemblances were studied; they
were formed into groups, classed and arranged in an order recalling as
much as possible their natural relations. In classifying it is
impossible to consider all the facts or the result would be chaos; it
is necessary to choose the characters and to give preponderance to
certain of them. This sorting of characters has been executed with the
sagacity of genius by the illustrious naturalists of the last century
and the beginning of the present. But the frames which they have
traced are fixed and rigid; nature with her infinite plasticity
escapes from them. We render a great homage to the classifiers when we
say that they have confined the facts as closely as it is possible to
do. The catalogues which they have prepared are of a utility which is
unquestionable, although their _role_ is to be useful only; we cannot
pretend to make them the expression, the symbol, the formula in which
all natural phenomena are to be enclosed. To confound classification
with science is to confound the lever with the effect which we expect
from it.
Curiosity, moreover, always impels towards that which is least known.
External appearances having been studied, the form and function of
internal organs were investigated. Physiology and comparative anatomy
were born and developed; researches abounded and observers abandoned
the field for the laboratory.
The difference in methods of research and the pushing of precision to
its extreme limits--an inevitable result of the different nature of
the observations to be made--did not however yet render legitimate the
claim for natural studies to be called "science."
_Natural history and the natural sciences._--A more important event
has taken place. The ancient naturalists, like their contemporaries,
had firm beliefs which they used as unquestionable principles for the
comprehension of all facts. The explanation of an observation was
ready in advance. The study of facts invariably brought to the pen of
the writer the same enthusiastic admiration of the marvellous part
played by Providence in nature.[1] The phenomena in which this action
was not strikingly apparent were merely described without any attempt
to relate them with each other, or with the other facts. A hypothesis
which left a great number of facts without explanation was necessarily
insufficient. The descriptions, in spite of all their individual
interest, did not constitute a homogeneous whole, a science. They were
merely a collection of more or less natural histories.
[1] See, for example, Reaumur, _Memoires pour l'histoire
des Insectes_, t. i., pp. 23-25.
Science only begins on the day when we have found the simple theory
which binds together all the facts at that time known, without of
course prejudicing the future. As the number of acquired facts
increases, if the theory in question continues to explain the new as
it explained the old, the science becomes more firmly established. If
we can imagine a time arriving when all the possible phenomena are
known, and the existing hypothesis still explains them, nothing
henceforth can overturn it, the science is completed. That is the
simple case in which a theory has been victorious; but if it is
contradicted by a single well-authenticated fact it must fall or
become modified. The more things a theory explains in the present the
more chance it has of success in the future. It is still only a matter
of chances, for the theory is always at the mercy of unforeseen
observation, which may rudely overthrow it.
There is no theory which must not be modified constantly, at least in
its details. To render it more and more general by successive
improvements is the aim to be pursued. A collection of studies
constitutes a science when a hypothesis has arisen already
sufficiently strong to oblige us to refer to it all new acquisitions,
and to compel us to see if they fortify or oppose it.
It would indeed be a narrow conception if we were to consider as
scientific the partisans of the theory alone; more than anywhere else
discussion is fruitful in the natural sciences; and if it is necessary
to be constantly preoccupied with the general ideas of the day, it is
not at all necessary to adhere to them servilely. The naturalists of
to-day are in possession of a formula with which we must always
preoccupy ourselves; in other words, there are natural sciences.
_The theory of Evolution._--This hypothesis which comes before all
others is the theory of evolution. This is not the place to expound
it, to go over the proofs which have been amassed to build it up, nor
the criticisms which have been directed against it. It has to-day come
out of the struggle victoriously. A prodigious quantity of facts, of
comparative anatomy and of embryology, inexplicable without it, emerge
from the chaos and constitute a whole, truly and marvellously
homogeneous. Issued from the natural sciences, the doctrine of
evolution now overflows them and tends to embrace everything that
concerns man: history, sociology, political economy, psychology. The
moralists seek, and will surely find, compromises permitting ethical
laws to endure the rule of this overwhelming hypothesis.
Without going too far back into history, let us look towards the end
of the last century and the beginning of this. Cuvier, Lamarck,[2] and
Geoffroy Saint-Hilaire,[3] all preoccupied with general ideas, were
each trying to build up a doctrine. The theory of evolution was born
beneath the pen of Lamarck, but immediately fell under the attacks of
Cuvier.[4] It is to Darwin that the honour belongs of having rescued
it from oblivion and of having initiated the movement which to-day
rules the natural sciences. Studies in embryology and anatomy are
rising without number beneath this impulse; and perhaps it may be said
that these new sciences, so fruitful in results, absorb a little too
much attention and leave in the shade subjects longer known, but
which, however, gain new interest by the way they fit into present
scientific theories.
[2] _Philosophie zoologique_, 2e edition, Paris, 1830;
_Histoire des Animaux sans Vertebres_, Introduction, 1835.
[3] _Philosophie anatomique_, 1818; _Zoologie generale_, 1841.
[4] _Le Regne Animal_, 1829; _Lecons d'Anatomie comparee_,
2e edition, 1835-46.
I wish to speak of the manners of animals; the facts regarding them
are of sufficient interest if we consider them one by one, and they
become much more interesting when we attempt to show the close way in
which they are bound together. Volumes would not suffice to exhaust
the subject; but if the entire task is too considerable, I may at
least hope to accomplish a part of it by treating of those facts which
may be brought together under the common title of Animal Industries.
Taken separately, they may be reproached with a certain anecdotal
character, but we cannot fail to agree that taken altogether they
constitute an important chapter in the sciences of life.
_The chief industries of Man._--Let us first throw a rapid glance at
the various stages which the civilisation and industry of Man have
gone through before arriving at their present condition. To make clear
these phases we might either follow the state of civilisation in any
given country by tracing back the course of centuries, or else at a
given epoch find out in different parts of the earth all the stages of
human evolution. The savage men of to-day are not further advanced in
their evolution than our own ancestors who have now gone to fossil.
However it may be, Man, at first frugivorous, as his dentition shows
as well as his zoological affinities, in consequence of a famine of
fruit or from whatever other cause, gradually began to nourish himself
with the flesh of other animals. To search for this fleeing prey
developed in him the art of hunting and fishing. His intelligence,
still feeble, was entirely concentrated on this one point: to seize on
an animal and to feed on it, although neither his nails nor his teeth
nor his muscles make it natural to him. To hunt, to fish, to defend
his territory against the wild beasts who attacked it and himself, to
drive back tribes of his fellows who would diminish his provisions,
these were the first rudiments of the industry of Man. Having become
more skilful, he obtained in an expedition more game than he could
consume at once; he then kept near him living beasts in order to
sacrifice them when hunger came. His reserve of animals increased;
they became accustomed to live near him; and he took care of his
larder. A flock was gradually constituted, and the owner learnt to
profit from all the resources which it offered him, from milk to wool.
Henceforth he became economical with his beasts, and moved about in
order to procure for them abundance of grass and water. He was still
always hunting and fighting; but there were now accessory industries,
and he was especially occupied in the domestication of animals. Then
it happened that he acquired a taste for a graminaceous grain--corn.
To seek the blades one by one is not a very fruitful labour, and
decidedly troublesome. Man collected a supply of them, cultivated
them, possessed fields which he sowed and harvested. He was henceforth
obliged to renounce his herds, which had become immense; for he could
not leave the soil where his corn was ripening, if he wished to gather
it himself, and his cattle were lacking pasture. The number of beasts
diminished; bread had killed milk. Man only kept near him a small
flock capable of feeding on a moderate territory. He abandoned his
temporary shelters, tents of skin or of woven wool, and since he must
henceforth live on the same piece of land, he constructed there a
fixed dwelling. Such is, taken altogether, the genesis of the industry
of the dwelling connected with the culture of the soil; to earlier
periods corresponded the natural or hollowed cave and the woven tent.
_The chief industries of Animals._--In a more or less perfect degree
we find the same industries among animals generally. In order to make
just comparisons, we ought especially to consider the methods of those
who are not endowed with specially appropriated organs, for in this
case their task is rendered too simple. To take an example. The Lion
is certainly an incomparable hunter; but his whole organisation tends
to facilitate the capture of living prey. His agility and the strength
of his muscles enable him to seize it at the first leap before it can
escape. With his sharp claws he holds it; his teeth are so keen and
his jaw so strong that he kills it immediately; with such natural
advantages what need has he of ingenuity? But in the case of the Wolf
or the Fox it is quite another matter; they hunt with a veritable art
which Man himself has not disdained, since he has taken as his
associate their relative, the Dog. It is the same with the Eagle and
the Crow. The latter, in order to seize the prey which he desires,
needs much more varied resources than the great bird of rapine for
whom nature has done everything.
We find among animals not only hunting and fishing but the art of
storing in barns, of domesticating various species, of harvesting and
reaping--the rudiments of the chief human industries. Certain animals
in order to shelter themselves take advantage of natural caverns in
the same way as many races of primitive men. Others, like the Fox and
the Rodents, dig out dwellings in the earth; even to-day there are
regions where Man does not act otherwise, preparing himself a lodging
by excavations in the chalk or the tufa. Woven dwellings, constructed
with materials entangled in one another, like the nests of birds,
proceed from the same method of manufacture as the woollen stuffs of
which nomad tribes make their tents. The Termites who construct vast
dwellings of clay, the Beavers who build huts of wood and of mud, have
in this industry reached the same point as Man. They do not build so
well, no doubt, nor in so complex a fashion as modern architects and
engineers, but they work in the same way. All these ingenious artisans
operate without organs specially adapted to accomplish the effect
which they reach. It is with such genuine industries that we have to
deal, for the most part neglecting other productions, more marvellous
in certain ways, which are formed by particular organs, or are
elaborated within the organism, and are not the result of the
intelligent effort of the individual. To this category belong the
threads which the Spider stretches, and the cocoon with which the
Caterpillar surrounds himself to shelter his metamorphosis.
_Intelligence and instinct._--By attentive observation it is possible
to find in animals all the intermediate stages between a deliberate
reflective action and an act that has become instinctive and so
inveterate to the species that it has re-acted on its body, and thus
profoundly modified it so as to produce a new organ in such a way that
the phenomena are accomplished as a simple function of vegetative
life, in the same way as respiration or digestion.
If an individual is led to reproduce often the same series of actions
it contracts a _habit_; the repetition may be so frequent that the
animal comes to accomplish it without knowing it; the brain no longer
intervenes; the spinal cord or the chain of ganglia alone govern this
order of acts, to which has been given the name of _reflex actions_. A
reflex may be so powerful as to be transmitted by heredity to the
descendants; it then becomes an _instinct_.
Thus by its nature instinct does not differ from intelligence, but is
intimately connected with it by a chain of which all the links may be
counted. The most intelligent of beings, Man, performs actions that
are purely mechanical; many indeed can with justice be called
instinctive; and, on the other hand, an animal for whom an innate
hereditary instinct is sufficient in ordinary life will give proof of
intelligence and reflection if circumstances in which his instinct is
generally efficacious become modified so that he can no longer profit
by them. Among other ingenious experiments to show the supposed
difference between instinctive and reflective acts, Fabre brings
forward the following[5]:--The _Chalicodoma_, a hymenopterous relative
of the Bees, constructs nests composed of cells formed of mud
agglutinated with saliva. The cell once constructed, the insect begins
to fill it with honey before laying an egg there. He returns with his
booty and wishes to disburse himself in the nest, finds the cellule
which he has to fill, and proceeds always in the same order: first, he
plunges his head in the cell and disgorges the honey which fills his
crop; secondly, he emerges from the cell, turns round, and lets fall
the pollen which remains attached to his legs. Suppose that an insect
has just disgorged his honey, the observer touches his belly with a
straw; the little animal, disturbed in his operation, returns to it
having only the second act to perform. But he re-commences the whole
of his operations though having nothing more to disgorge; he again
plunges his head into the cell and goes through a pretence of
disgorging, then turns round and frees himself from the pollen.
Although touched twice, thrice, or more frequently, he always repeats
the first action before executing the second. It is, says Fabre,
almost like the movement of a machine of which the wheelwork will not
act until one has begun to turn the wheel which directs it.
[5] J. H. Fabre, _Souvenirs entomologiques_, Paris, 1879,
pp. 275 _et seq._
It is incontestable; but I would add, as this conscientious observer
does not, that that does not prove that the intelligence of the insect
differs essentially from ours; it is a simple question of degree. Look
at a boy who is going to jump over a ditch: he begins by spitting into
his hands and rubbing them one against the other before taking his
spring. In what has this served him? It is not more intelligent than
the gesture of the bee who first plunges his head in the cell before
freeing his claws, although the first gesture is useless.[6]
[6] It should perhaps be added that while the boy's action
is not consciously intelligent, it is by no means
purposeless, and is therefore not quite parallel with the
insect's. By vigorously irritating the sensory nerves of the
hand the boy imparts a stimulus to his muscular system. His
act belongs to a large group which has been especially
studied by Fere. See his _Sensation et Mouvement_ (1887),
and _Pathologie des Emotions_ (1892).
And, from another side, if nothing is more instinctive than the manner
in which domestic Bees construct their cells of wax with geometric
regularity, there are other circumstances in which these same insects
give proof of remarkable reflection, sagacity, and intelligence in
co-ordinating their actions in the presence of an event to which they
are not accustomed, and in attaining an end which has presented itself
by accident. Such are, for example, the arrangements which they make
to defend their honey against the attacks of a great nocturnal Moth,
the Death's Head. I shall have to revert to these facts.
We must not then regard instinct, as has often been done, as a
rudiment of intelligence, susceptible or not of development; but much
rather as a series of intelligent acts at first reasoned, then by
their frequent repetition become habitual, reflex, and at last, by
heredity, instinctive.
What the individual loses in individuality and in personal initiative,
heredity restores to him in the form of instinct which is, as it were,
the condensed and accumulated intelligence of his ancestors. He
himself no longer needs to take thought either to preserve his life or
to assure the perpetuation of his race. The qualities which he
received at birth render reflection less necessary; thus species
endowed with some powerful instinct seem not to be intelligent when
they live sheltered from unforeseen events.
From one point of view instinct appears to be a degradation rather
than a perfecting of intelligence, because the acts which proceed from
it are neither so spontaneous nor so personal; but from another point
of view they are much better executed, with less hesitation, with a
slighter expenditure of cerebral force and a minimum of muscular
effort. A habitual act costs us much less to execute than a deliberate
and reflective act. It is thus that the constructions of bees are more
perfect than those of ants; the former act by instinct, the latter
reason their acts at each step.
_Instinctive actions originate in reflective actions._--No doubt it
may be said: It is a pure hypothesis thus to consider instinct as
derived from intelligence; why not admit as well that instinctive acts
have been such from the beginning--in other words, that species have
been created such as we see them to-day? The preceding explanation,
however, has the advantage of being in harmony with the general theory
of evolution, which, whether true or not, so well explains the most
complicated facts that for the present it must be accepted. For the
rest, if it is not possible to appraise the psychic faculties
possessed by the ancestors of existing animals we may at least observe
certain facts which put us on the road of explanation.
An interesting member of the Hymenoptera, the _Sphex_, assures food
for the early days of the life of its larvae in a curious way.[7]
Before laying its eggs it seizes a cricket, paralyses it with two
strokes of its sting--one at the articulation of the head and the
neck, the other at the articulation of the first ring of the thorax
with the second--each stab traversing and poisoning a nervous
ganglion. The cricket is paralysed without being killed; its flesh
does not putrefy, and yet it makes no movement. The _Sphex_ places an
egg on this motionless prey, and the larva which emerges from it
devours the cricket. Here assuredly is a marvellous and certain
instinct. One cannot even object that the strokes of the sting are
inevitably directed to these points because the chitinous envelope of
the victim offers too much resistance in other spots for the dart to
penetrate, because here is the _Ammophila_, a near relative of the
_Sphex_, which chooses for its prey a caterpillar. It is free to
introduce its sting into any part of the body, and yet with extreme
certainty it strikes the two ganglions already mentioned.[8]
[7] "Etude sur l'Instinct et les Metamorphoses des
Sphegiens," _Ann. Sc. Nat._, iv. Serie, t. 6, 1856.
[8] P. Marchal, "Observations sur _l'Ammophila affinis_,"
_Arch. de Zool. exper. et gener._, ii. Serie, t. 10, 1892.
We cannot suppose that the insect has anatomical and physiological
knowledge to inform it of what it is doing. The act is distinctly
instinctive, and seems imprinted by a fatality involving no possible
connection with intelligence. But let us suppose that the ancestors of
these Hymenoptera have thus attacked crickets and killed (not
paralysed) them with one or more wounds at any point. By chance some
of these insects, either in consequence of their manner of attacking
the prey or from any other cause, happen to deliver their blows at the
points in question. Their larvae on this account are placed in more
favourable conditions than those of their relatives whom chance has
less well served; they will prosper and develop sooner. They inherit
this habit, which gradually becomes through the ages that which we
know. It is possible; but why, it may be asked, this hypothesis,
apparently gratuitous, of strokes of the sting given at random? Are
there any facts which render this explanation plausible? Assuredly.
Thus the _Bembex_, which especially attacks Diptera to make them the
prey of its larvae, throws itself suddenly on them and kills them with
one blow in any part of the body. It is unable in this way to amass in
advance sufficient provision for its larvae; the corpses would putrefy.
It is obliged to return from time to time bearing new pasture.[9]
Again, M. Paul Marchal, taking up the study of instinct in the
_Cerceris ornata_,[10] has shown that in this species at least of
_Sphegidae_ the stings have not so considerable an effect. This insect
attacks a wild bee, the _Halictus_. He strikes his victim with two or
three strokes of the sting beneath the thorax, but the paralysis is
not definite, perhaps on account of the nature of the venom, which is
not identical in all species. The tortured creature may regain life at
the end of some hours. Thus the _Cerceris_ is obliged to destroy the
upper part of the neck by repeated malaxation of that part for several
minutes at a time. The effect of this second act, by injuring the
cerebroid ganglia, is to render impossible the return of action;
moreover, it permits the aggressor to satisfy personal gluttony, and
to feed on the liquids of the organism of the vanquished, which is
easy, because the dorsal blood-vessel passes at this level. It can
thus satisfy a personal need while thinking of the future of the race.
[9] J. H. Fabre, _Souvenirs entomologiques_, pp. 225 _et seq._
[10] "Etude sur l'Instinct du _Cerceris ornata_," _Archives
de Zoologie experimentale_, ii. Serie, t. 5, 1887.
It has been said in this connection that in such cases the sure
instinct with which these species were originally endowed has been
distorted, but that is to admit some degree of variation; the
hypothesis of degeneration is as gratuitous as the other, and if we go
so far as to risk a hypothesis, it would be better to use it to
explain facts and not to entangle them.
_Plan of study of the various industries._--The different industries
carried on by animals may be divided into a certain number of groups.
In the case of each of these categories I propose to arrange the facts
in such a way as to bring forward first those animals which, having no
special organs, are obliged to exercise the greatest ingenuity, and
then to indicate the facts which show how variations have arisen which
enable other species to accomplish these acts with marvellous ease.
We will first examine the simplest industries: hunting and fishing,
those industries of which the object is the immediate search for prey;
and to these may be added those which are related to them as re-action
is to action--that is to say, the industries of which the effect is to
provide for the immediate safety of the individual.
Then in an exposition parallel to the march of progress followed by
human civilisations, we shall study among animals the art of
collecting provisions, of domesticating and exploiting flocks, of
reducing their fellows to slavery.
Finally, we shall investigate the series of modifications which the
dwelling undergoes, and we shall see how certain species, after having
constructed admirably-arranged houses, know how to make them healthy,
and how to defend them against attacks from without.