The Industries of Animals

Chapter 3

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The Myrmica also forms similar pasture lands; its system is rather less perfect than that of the Lasius, as it does not form covered galleries to reach its stables.

It is content to build large earth huts around a colony. A large hole, which allows the pa.s.sage of the ants, but not the escape of the flock, is formed so that they may come to milk their cows. They use the same methods we have seenpractised on the Claviger, caressing the insect with their antennae until the sugared drop appears.[68]

[68] In Central America, Belt has described how the Leaf-hoppers are milked for their honey by various species of Ants, and also by a Wasp. He considered that some species of Leaf-hopper would be exterminated if it were not for the protection they received from Ants.--Naturalist in Nicaragua, 1888, pp. 227-230.

An example is quoted which shows still greater intelligence and foresight in Ants.

They have been known to repopulate their territories after an epidemic, or at least after the destruction of their Aphides. The proprietor of a tree, finding it covered with these exploited beasts, cleared it of its inconvenient guests by repeated washes; but the dispossessed Hymenoptera, considering that this pasture close to their nest was very convenient for a flock, resolved to repopulate it, and for some time these tenacious insects could be seen bringing back among the foliage Aphides captured elsewhere.[69]

[69] P. Huber, Recherches, etc., pp. 210-250; Lubbock, "On the Habits of Ants,"

Wiltshire Arch. and Nat. Hist. Mag., 1879, pp. 49-62.

Slavery among Ants.--The custom of making slaves is widely spread in the ant world; I have already described the expeditions organised to obtain them. We will now consider the relations of these insects among themselves.

The Formica sanguinea takes possession of the eggs of the Formica fusca and rears them with its own. When the slaves reach the adult condition they live beside their masters and share their labours, for the latter work, are skilful in all tasks, and can by their own activity construct an ant-hill and keep it going. If they desire servants, it is not in order to throw all the work on them, but to have intelligent a.s.sistants. This is the primitive form of slavery as it first existed among men. It was not until later that it became modified, to become at last an inst.i.tution against which the sentiment of justice arose. Other species of Ants have pushed the exploitation of slaves to a point Man has never reached. But the Formica sanguinea are companions to their helpers rather than masters, and even show them great consideration. When the colony emigrates one may see the owners of the nest, who are of larger size than the Formica fusca, take these up in their jaws and carry them the entire way.The Amazons (Polyergus rufescens) act otherwise. Very skilful in obtaining slaves and powerfully armed for triumphant raids, their nests always contain legions of servants, and the custom of being waited upon has become so impressed on the race by heredity that it is an instinct stronger even than personal preservation. The master ant has not only lost the taste and the idea of work, but even the habit of feeding himself, and would die of hunger beside a pile of honey or sugar if a grey ant was not there to put it into his mouth. Thus Huber, the earliest accurate observer of these ants, enclosed thirty Amazons with several pupae and larvae of their own species, and twenty negro pupae, in a gla.s.s box, the bottom of which was covered with a thick layer of earth; honey was given to them, so that, although cut off from their auxiliaries, the Amazons had both shelter and food. At first they appeared to pay some little attention to the young; this soon ceased, and they neither traced out a dwelling nor took any food; in two days one-half died of hunger, and the other remained weak and languid.

Commiserating their condition, he gave them one of their black companions. This little creature, una.s.sisted, formed a chamber in the earth, gathered together the larvae, put everything into complete order, and preserved the lives of those which were about to perish.

All their industry is expended in the acquisition of captives. The Polyergus avoid introducing into their houses adults who would not become reconciled to the loss of liberty, and would prefer to die rather than work for others. They carry off the larvae of Formica fusca and Formica cunicularia. When brought into the ant-hill these larvae are placed in the jaws of slaves of their own species, who care for them; they are born captives, and have neither the regret nor the idea of a free life. Among the Amazons the slaves undertake every labour; it is they who build and who care for the larvae of their masters, as well as those carried away in expeditions. They have also complicated personal services towards the Polyergus. They bring them food, lick off the dust from their hairs, clean them, carry them from one place to another, if there is need to emigrate, although they themselves are much smaller. The masters, by force of losing interest in work, lose also their votes when it is a question of taking a resolution concerning the whole colony. The servants act on their own initiative and their own responsibility, direct constructions according to their own ideas, and even in grave concerns, such as emigration, the idle masters do not seem to be consulted. The workers deliberate among themselves, and having come to a decision, proceed to execute it. They transport the household goods, the eggs, the future of the city, and the Amazons who have become its parasites. It is a most curious fact that the slaves should submit to this precarious fate when their masters are absolutelydependent on them. It is just to add that the robust mandibles of the latter may contribute to preserve the position they enjoy.[70]

[70] Lubbock has a brief discussion on the relations of Ants to their domestic animals and to their slaves, Ants, Bees, and Wasps, chap. iv.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--CARCa.s.sES 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.

The preservation of the individual and the preservation of the species.--In the previous chapter we have seen animals preparing for the future, and ama.s.sing materials for their own subsistence. In other cases these provisions are destined to feed the young. It is the same industry, sometimes exercised for the preservation of the individual, sometimes for the perpetuation of the race. We must expect to find acts of the last kind more instinctive and less reflective than those of the first, and this agrees well with what we know of natural selection. If we now see living beings display so many resources and calculate with such certainty all that will favour the healthy development of their descendants, we must not necessarily conclude that the species possess these instincts from the beginning. They are not to be regarded as mechanisms artfully wound up and functioning since the appearance of life on the earth with the same inevitable regularity. The qualities which we find in them were weak at first; they have developed in the course of ages, and have finally, by heredity, been impressed upon the creatures to manifest themselves by necessary acts from which there is no longer any escape. There is no need for surprise if we meet to-day, I do not say among all, but among a very large number of animals, this foresight for offspring in a well-marked form. It is easy to understand that the species that first acquired and fixed an instinct propitious to the increase of the race has rapidly prospered, stifling beneath its extension those that are less favoured from this point of view, which is of capital importance in a struggle for a place beneath the sun. At the present day if the struggle of animal life offers few facts of lack of foresight for the rearing of young, it is because this defect has killed the races who were subject to it; they have disappeared, or have only been saved by qualities of another order.For the rest, if it is difficult to reconst.i.tute except in imagination the different stages through which, in time, and in a determined species, acts at first imperfect, but designed, have become perfect and instinctive, we can at least find in s.p.a.ce different degrees of the same instinct in allied genera which lead us by a succession of transitions from mechanical action to reflective action.

As I cannot quote all the facts showing this care for the future, I will select a few.

It must be said at first that a considerable number of animals show nothing of the kind. Let us leave aside all the inferior beings to speak of those among whom we may expect some degree of method. Crustacea, fish, Batrachians, and many others lay their eggs, are contented to conceal them a little so that they may not become a too easy prey, and are altogether indifferent as to what may happen afterwards. As soon as they come out, the young obtain their own food from day to day; myriads are destroyed, and if the races remain so strong numerically it is because they are saved by the innumerable quant.i.ty of eggs produced by a single female. If it were not for this prodigious fecundity these species would have disappeared. Birds make no provision for their young; but, on the other hand, as long as the latter are weak and unable to obtain their own prey, the parents feed them every day by hunting both for themselves and the brood.

I will not insist on those beings who, like mammals, produce physiological reserves, not for their own use, but for the profit of their young. The females of these animals elaborate materials from their own organism and store them up in the form of milk to nourish the young. This fact is related to foresight, with a view to offspring, exactly in the same way as the Honey Ants show a transformation of foresight for the individual. In both cases industry is replaced by the function of a specially adapted organ.

Foods manufactured by the parents for the young.--It is especially insects with whose industries we are here concerned, and they are more or less instinctive in various cases. Every one knows how the Hymenoptera prepare honey from the pollen of flowers, to some extent for themselves, but especially in order that their young may at the moment of appearance possess a food which will enable them to undergo their first metamorphosis sheltered from the inclemencies outside.

These foods are enclosed with great art, according to the species, either in skilfully-constructed cells of wax, as by Bees, or in nests of paper or cardboard which the Wasps fabricate, or again in huts built of earth in the manner of the Chalicodoma.Species which obtain for their larvae foods manufactured by others.--Other insects have not this taste for lengthy labours, and do not know how to execute them; but they do not intend that their young shall be the victims of maternal lack of skill, and they display marvellous resources to enable them to profit by the foresight of others.

[Ill.u.s.tration: FIG. 15.]

The Sitaris muralis, a beetle whose customs have been described by Fabre in a remarkable manner,[71] may be counted among the cleverest in a.s.suring to its larvae the goods of others. It puts them in a position to profit by it, and when they are installed they know sufficiently well what to do. The species has so long perpetuated itself by this process that it has become, both in mother and offspring, highly automatic. It is a hymenopterous insect which this family, whose first vital manifestation is theft, thus levies a contribution on. It is called the Anthophora pilifera, and during the fine weather it makes a collection of honey intended to be absorbed by its own larvae, if it had not the misfortune to be watched by one of these intriguing Coleoptera. Wherever in Provence there is a perpendicular wall, natural or artificial, a little cliff, a sloping ditch, or the wall of one of those caves which the people of the country use for putting their tools in, the Anthophora hollows out galleries, at the bottom of which he builds a certain number of chambers. He fills each of them with honey, places in it an egg which floats in the midst of this little lake of nectar, and closes it all up. The Sitaris covets this honey to nourish its offspring, and the chamber to shelter it. After having discovered one of the galleries of which I have spoken, the female Sitaris comes about the beginning of September to lay her eggs, which are numerous, being not generally fewer than two thousand. In the following month the larvae appear; they are black, and swarm in a little heap mixed up with the remains of egg-sh.e.l.ls. They vegetate in this condition for a long time, and may still be found there in May. At this period they have become more active, and, in order to complete their development, are thinking of profiting by their favourable situation near the entrance to a gallery of the Hymenoptera; when a male Anthophora comes within reach, two or three of them catch hold of him and climb on to his thorax. They maintain themselves there by clinging to the hairs. At the moment of fertilisation the male, thus burdened, comes in contact with the female; the coleopterous larvae then pa.s.s on to her, so that, according to Fabre"s expression, the meeting of the s.e.xes brings death and life to the eggs at the same time.

Henceforth fixed on this laying insect, the little Sitaris remain quiet, and have only to wait; their future is a.s.sured. The Anthophora has made her chambers, andwith the greatest care has filled each of them with honey. Then in the midst she deposits an egg, which remains floating on the surface like a little boat; when her task is accomplished, the mother pa.s.ses to a new cell to confide to it another of her descendants. During this time the parasite larva hastily descends the abdominal hairs and allows itself to fall on the egg of the Anthophora, to be then borne upon it as upon a raft; its fall must take place at the precise instant which will enable it to embark without falling into the honey, in which just now it would be glued fast, and perish. This series of circ.u.mstances results only in the introduction of a single Sitaris into a chamber; the moment which must be profited by is too short for many of them to seize. If the female Anthophora carries others hidden in her hairs, they are obliged to await a new hatching to let themselves glide off. Thus enclosed with the egg of the Anthophora and its provision of honey, the larva has no other rival to fear, and may alone utilise the whole store.

This parasitism has to such an extent become a habit with the species, that the larva"s organisation has become modified by it. At the moment when it falls into the cell it cannot feed on honey. It is indispensable for its development that it should first devour the egg on which it floats; it can at this period be nourished by no other food. In acting in this way it also frees itself from a voracious being who would require much food. This first repast lasts about eight days, at the end of which it undergoes a moult, takes another form, and begins to float on the honey, gradually devouring it, for at this stage it becomes able to a.s.similate honey.

Slowly its development is completed, with extremely interesting details with which we need not now concern ourselves. The larva of Sitaris is then in conditions exceptionally favourable for growth; but, in spite of appearances, there is no reason for admiring the marvellous foresight and extraordinary sureness of instinct; nearly everything depends on a fortuitous circ.u.mstance, a chance. This becomes very evident if we study another related beetle; it is called the Sitaris colletis, and lives at the expense of the hymenopterous Colletes, as its relative at the expense of the Anthophora. But these two species of the same genus are very unequally aided by chance. The one whose history we have just traced attaches itself to an insect whose egg floats above a store of honey; the second chooses a victim who attaches its egg to the walls of a chamber. (Fig. 15.) This almost insignificant difference has a considerable influence on the parasite"s evolution. In the first case it is alone, and may develop with certainty; in the second, on the contrary, several Sitaris penetrate the chamber and climb up to attack the egg, which in this case also must be their first food. This rivalry causes a struggle to the death. If one of the larvae is notably more vigorous than its rivals, it may free itself from them and survive. Let us consider the fate in store for the two species. The first is much more favoured, since a happy chance permits eachgerm to produce an individual; in the second, each individual which completes its evolution deprives several of its brothers of life. And even this only happens in the most favourable cases, for it may be that not one Sitaris in the chamber may reach the adult state. If the first arrival begins to absorb the egg of the Colletes, a second hungry one may kill it in the midst of its repast and take its place. But the conqueror finds the provisions already reduced and insufficient to enable it to reach the moulting stage, at the end of which it could profit by the honey.

Ill-nourished and weakened, it cannot support this crisis, and its corpse falls beside that of its fellow whom it had sacrificed. Three or four parasites may thus succeed to the same feast, and the victory of the last is useless to him. His first struggle for life and his first triumph are followed by irreparable defeat. These two examples show very well how a slight difference may favour a species, and how a happy quality is capable of being perpetuated by heredity, since by its very nature it is destined to be extended to more numerous beings.

[71] "Hypermetamorphoses et Moeurs des Melodes," Ann. Sc. Nat., iv. Serie, t.

7, 1857, p. 299; also "Nouvelles observations sur l"hypermetamorphose et les Moeurs des Melodes," ibid., t. 9, 1858, p. 265.

[Ill.u.s.tration: FIG. 16.]

Carca.s.ses of animals stored up.--These insects lay up for their offspring stores manufactured by themselves or by others. The cla.s.s we are now about to consider makes provision of animals either dead or in a torpid condition, with more or less art and more or less sure instinct. Most people have seen the Necrophorus or Burying Beetle working in fields or gardens. These are large Coleoptera who feed on abandoned carrion; everything is good to them--bodies of small mammals, birds, or frogs; they are very easy to please, and as long as the beast is dead that is all they require. When they have found such remains, and consider only how to satisfy their hunger, they do not take much trouble, and gnaw the prey on the spot where they have found it. They are not alone at the feast, and in spite of their diligence numerous rivals come up to dispute it; it is necessary to share with a great number of noisy and voracious flies and insects.

In the adult state they come out well from this compet.i.tion; but as good parents they wish to save their larvae from it, as in a feeble condition these might suffer severely. They desire to lay up a carca.s.s for their young alone, and with this object they bury it in the earth. The eggs also which will thus develop in the soil have more chance of escaping destruction by various insectivorous animals. If these diggers find a rat (Fig. 16) or a dead bird, three or four unite their efforts,glide beneath it, and dig with immense activity, kicking away with their hind legs the earth withdrawn from the hole. They do not pause, and their work soon perceptibly advances. The rat gradually sinks in the pit as it grows deeper. When they have the good fortune to find the earth soft they can sink the prey in less than two hours to a depth of thirty centimetres. At this level they stop, and throw back into the hole the earth they have dug out, carefully smoothing the hillock which covers the grave. Thus stored up, the carca.s.s is ready to receive the Necrophorus eggs. The females enter the soil and lay on the buried mammal; then they retire, satisfied to leave their little ones, when they appear, face to face with such abundant nourishment. When they emerge from the envelope the young larvae find themselves in the presence of this stored food, which has been softened by putrefaction and rendered more easy of digestion. If the treasure has not fallen on a spot easy to dig, the Necrophorus quickly recognise the fact, and do not waste time in useless labour. Endowed with considerable strength relatively to their size, three or four of them creep beneath the prey, and co-ordinating their efforts they transport it several metres off to a spot which they know by experience to be suitable for their labours. It may happen that soft earth is too far away, and transport becoming too difficult a task, they renounce it. But as good food should never be wasted, they utilise it by feeding themselves, awaiting a more manageable G.o.d-send for their offspring.

Many observers have studied these beetles, and all are surprised at their sagacity, and the way in which their various operations are adapted to circ.u.mstances; genuine reflection governs their acts, which are always combined to produce a definite effect.

Provision of paralysed living animals.--It is unnecessary to say how much better it would be for the young larva to have at its disposal instead of a carca.s.s a living animal, but paralysed and rendered motionless by some method. It is difficult to believe the thing possible, yet nothing is better established. There is a hymenopterous relative of the Wasp called the Sphex. Instead of laying up honey they store animal provisions for their larvae. Fabre has studied one of them, the Sphex flavipennis.[72] It is in September that this wasp lays her eggs; during this month to shelter her little ones she hollows out a dozen burrows and provisions them. She has then to devote about three days" work to each of them, for there is much to do, as may be imagined. For each of these hiding-places the Sphex first pierces a horizontal gallery about two or three inches long; then she bends it obliquely so that it penetrates deeply into the earth, and it is again continued in this direction for about three inches. At the end of this pa.s.sage three or fourchambers are made, usually three; each of these is meant to receive one egg.

The insect interrupts its mining task, not forming the three chambers consecutively; when the first is completed she provisions it--we shall soon see in what manner--and lays an egg there; then she blocks it up, suppressing all communication between this cell and the gallery; this done she bores a second pa.s.sage, provisions it, and lays another egg, closes up the orifice, and proceeds to prepare the third. This work is pushed on with great activity, and when completed the Sphex entirely fills up the subterranean pa.s.sage, and completely isolates the hope of the race at a depth sufficient to shelter it well. A last precaution is taken: before leaving, the rubbish in front of the obstructed opening is cleared away, and every trace of the operation disappears. The nest is then definitely abandoned, and another one prepared.

[72] "etude sur l"instinct et les metamorphoses des Sphegiens," Ann. Sci. Nat., 1856.

The chambers in which the larvae are enclosed--hastily made with little care, and with rough unsmoothed walls--are not very solid, and could not last long without slipping; but as they only have to last for a single season they possess sufficient resistance for the insect"s purpose. The larva also knows very well how to protect itself against the roughness of the walls, and overlays them with a silky secretion produced by its glands.

We have now to consider the nature of the provisions placed by the Sphex near the egg. Each cell must contain four crickets. That is the amount of food necessary for a larva during its evolution, and these insects are in fact large enough to supply a considerable amount of nourishment. When the Sphex interrupts digging operations it is to fly on a hunting expedition. It soon returns with a cricket it has seized, holding it by one antenna which it turns round in its jaws. It is a heavy burden for the slender Sphex to bear. Sometimes on foot, dragging its burden after it, sometimes flying, and carrying the suspended cricket always in a pa.s.sive condition, the burrow is gradually reached, not without difficulty. In spite of appearances, the cricket is not dead; it cannot move, but if kept for several days it will not putrefy, and its joints remain supple. It is simply the victim of a general paralysis.

The cause of the paralysis.--It was evidently of the greatest interest to know how the Sphex contrived this capture, and what method it used to suppress the movements of the prey. In order to obtain the solution of this problem, Fabreduring a long period acc.u.mulated experiments and observations, and at last discovered in every detail how the thing was done. In order to compel the Sphex to act in his presence, he placed himself in front of the orifice of a gallery in which the insect was working; he soon saw it returning with a paralysed cricket. Arrived at the burrow, the insect placed the prey on the ground for a moment and disappeared in the pa.s.sage to see that everything was in order, and that no damage had taken place since its departure. Everything was going well, and it reappeared, took up its burden, and again entered the subterranean pa.s.sage, drawing the victim along. It brought it into the chamber for which it was destined, placing it on its back, the head down and the feet towards the door. Then it set out hunting again until it had ranged four crickets side by side. Before attempting a decisive experiment, the observer felt his way. At the moment when the Sphex was buried in the earth examining the chamber, Fabre withdrew the prey a short distance and awaited events. Having made the domiciliary visit, the Sphex then went straight to the place where it had left its insect, but could not find it. It was naturally very perplexed, and examined the neighbourhood with extreme agitation, not knowing what had happened, and evidently regarding the whole affair as very extraordinary; at last it found the victim it was seeking. The cricket still preserved the same immobility; its executioner seized it by an antenna and drew it anew to the entrance of the hole. In the interior of the subterranean domain everything is in good order; the insect had just a.s.sured itself of the fact, and we should expect to see it enter with its prey; not at all, it entered alone, and only decided to introduce the prey after it had made a fresh inspection. This fact is surprising, and it is still more surprising that if the practical joke of removing the cricket is repeated several times in succession, the Sphex drags it anew every time to the entrance of the burrow and first descends alone; forty times over this experiment succeeded without the insect deciding to renounce the habitual manoeuvre. Fabre insists on this fact, and rightly, for nothing should be neglected; he makes it a text to show how automatic instinct is, and how the acts which proceed from it are invariably regulated so as to succeed one another always in the same order. In their nature these acts are quite indistinguishable from intelligent acts; only the creature is not capable of modifying them to bring them into harmony with unforeseen circ.u.mstances. All this is correct, but where it becomes excessive is in endowing animals alone with instinct and separating them from this point of view from Man. It is incontestable that the custom of visiting the burrow before introducing a victim into it has become so imperious in the Sphex that it cannot be broken, even when it is of no use. It is a mechanical instinct. But we may see an exactly parallel manifestation of human intelligence.

In face of danger man utters cries of distress; they are heard and a.s.sistancecomes. But these appeals are not intelligent and appropriate to the end; they are instinctive. Place the same individual in a situation where he knows very well that his voice cannot be heard; this will not hinder him from reproducing the same acts if he finds himself in the presence of danger. It is thus that the Sphex proceeds, guided by instincts, and it is no reason for despising it. And even in the course of this little experiment the insect gives proof of judgment. When it finds its cricket, it is perfectly aware that it is the same cricket which it brought, that there is no life in it, and that there is no need to re-commence the struggle; it sees too that it is not an ordinary corpse liable to putrefaction, but the very same cricket, and it does not hesitate to utilise it at once.

These habits being ascertained, Fabre proceeded to find out how the paralysis is produced. He awaited near a burrow the Sphex"s arrival, dragging a victim by an antenna, and while the insect was occupied in the subterranean survey he subst.i.tuted a living cricket for that which the Sphex had left, expecting to find it on the spot where it had been placed. On emerging it perceives the cricket scampering away; not a moment was to be lost, and without reflection it leapt on the refractory victim. A lively struggle followed, a duel to the death among the blades of gra.s.s; it was a truly dramatic spectacle, the agile a.s.sailant whirling around the Cricket, who kicked violently with his hind legs. If a blow were to reach the Sphex it would be disembowelled; but it avoids the blows skilfully without ceasing its own violent attack. At last the combat ends; the cricket is brought to earth, turned on to its back, and maintained in this position by the Sphex. Still on its guard, the latter seizes in its jaws one of the filaments which terminate the abdomen of the vanquished, placing its legs on the belly; with the two posterior legs it holds the head turned back so as to stretch the under side of the neck. The cricket is unable to move and the conqueror"s sting wanders over the h.o.r.n.y carapace seeking a joint, feeling for a soft place in which it can enter to give the finishing stroke. The dart at last reaches, between the head and the neck, the spot where the hard portions articulate, leaving between them a s.p.a.ce without covering. The joint in the armour is found. The Sphex"s abdomen is agitated convulsively; the sting penetrates the skin, piercing a ganglion situated just beneath this point; the venom spreads and acts on the nervous cells, which can no longer convey messages to the muscles. That is not all; the sting wanders over the cricket"s belly, this time seeking the joint between the neck and the thorax; it finds it, and is again thrust in with fury; a second ganglion of the nervous chain is thus perforated and poisoned. After these two wounds the victim is completely paralysed.As already mentioned, several facts enable us to recognise that the Cricket is by no means dead. It is simply incapable of movement, as would happen after an injection of curare. This poison kills a superior animal, for it hinders the muscular movements of the chest and diaphragm, necessary to respiration; but if a frog, which can breathe through its skin, is thus acted on it comes to life again at the end of twenty-four or forty-eight hours if the dose has not been too strong. The cricket is in a similar condition; it neither eats nor breathes; being incapable also of movement, there is no vital expenditure; it remains in a sort of torpor, or latent life, awaiting the tragic fate that is reserved for it. When it has been deposited in the little mortuary chamber the Sphex lays an egg on its thorax. The larva will soon come out to penetrate the body of the prey by enlarging the hole left by the sting. It thus finds for its first meals a food which unites the flavour of living flesh with the immobility of death. Nothing can be more convenient. When the first body is eaten it proceeds to the second, and thus devours successively the four victims stored up by maternal foresight.

In order not to interrupt the description and interfere with the succession of the acts, I have pa.s.sed without remark the experiment in which Fabre subst.i.tuted a living animal for the Sphex"s already paralysed captive. It seems to me, however, that in this circ.u.mstance the insect showed judgment, and knew how to act in accordance with new requirements. It was evidently the first time in insect memory in which so surprising a phenomenon had been seen as a victim at the last moment again taking the field. We cannot make instinct intervene here. If the Sphex"s acts are so automatic as we are sometimes led to believe, in accordance with facts which are perfectly accurate, we ought always to observe the following succession of acts: first, hollowing of the burrow; second, the chase; third, the blows of the dart; fourth, the different manoeuvres for placing the victim in the sarcophagus. Now in the present case the insect had accomplished the first three series of actions, and had even begun the fourth; it ought next to drag the cricket into the burrow without listening to the recriminations which the latter had no business to make, since it was to be regarded as having received the two routine doses of poison. But the Sphex sees its victim come to life, understands this fact, and without seeking to fathom the cause judges that a new struggle and new blows of the sting are necessary; he understands that it is necessary to begin afresh, since the usual result has not been attained. He is then capable of reflection, and the series of acts which he accomplishes are not ordained with such inflexibility that it is impossible for him to modify them in order to conform them to varying circ.u.mstances.The Sphex occitanica acts in the same manner as its relative in this complicated art of laying up provisions for the family. The differences are only in detail.

Instead of hollowing the burrow first and then setting out on the chase to fill it, it does not devote itself to the labour of digging until a successful expedition has already a.s.sured the victim. (Fig. 17.) Instead of attacking crickets it seeks a larger orthopterous insect, the Ephippigera. The struggle is no doubt more difficult, but the result is proportionately greater, and the pursuit does not need to be so often renewed; a single captive is sufficient for its larva.[73]

[73] For some remarks on the action of the Sphex, and for Darwin"s opinion on the matter, see Romanes" Mental Evolution in Animals, pp. 299-303.

[Ill.u.s.tration: FIG. 17.]

The sureness of instinct.--It is not doubtful that a sure inherited instinct conducts the Sphex to p.r.i.c.k its victim in the situation of the nervous ganglia, which will be wounded in the act. It may be said that the lesion results from the position in which the hymenopterous insect maintains its victim; for the sting is on the median line, and can only penetrate at the soft points; the two points attacked are then rigorously determined by physical circ.u.mstances. But these arguments have no bearing if we consider the method of procedure adopted by the Ammophila,[74] a hymenopterous insect related to the preceding, which paralyses caterpillars. It is free in this case to insert its sting at any portion of the body; yet it knows how to turn over and arrange the captive so that the dart shall penetrate both times at two points where ganglia will be poisoned and immobility without death be induced. It must then be agreed that there is here an instinct much too sure to be called mechanical; but these facts, which considered alone seem simply marvellous, become much less so, and lend themselves to evolutionary interpretation, when it is recognised that they are related by insensible degrees to other facts of the same order, much more intelligent and at the same time less sure.

[74] Paul Marchal, "Observations sur l"Ammophila affinis," Arch. de Zool. exp. et gener., ii. Serie, t. x., 1892.

Similar cases in which the specific instinct is less powerful and individual initiative greater.--Here is, for instance, the case of the Chlorion, where each animal possesses more considerable initiative.[75] It attacks the c.o.c.kroach. These insects are of an extremely varied size, according to age, and as they are alsovery agile the Chlorion is not certain of being always able to obtain victims of the same dimension. The orifice of its burrow, which it hollows in walls between the crevices of the stones, is calculated on the average size of its victims. It has also the habit of paralysing the c.o.c.kroach by stinging it on the nervous chain. These preliminary operations do not impede it, but it is embarra.s.sed when it wishes to introduce through the entrance of its gallery an insect which is too large. It pulls at first as much as it can, but seeing the failure of its efforts it does not persevere in this attempt, and comes out to survey the situation. Decidedly the victim is too large and cannot pa.s.s through. The Chlorion begins by cutting off the elytra, which maintain it rigid and prevent it from being compressed. This done, it harnesses itself anew and re-commences its efforts. But this is not sufficient, and the victim still resists. The insect returns, and again examines the situation. Now it is a leg which is placed cross-ways and opposes the introduction of the body; strong diseases need strong remedies, and our Chlorion sets itself to amputate this enc.u.mbering appendage. It triumphs at last; the c.o.c.kroach yields to its efforts, and little by little penetrates the hole. As may be seen, the labour is laborious and painful, and may present itself beneath various aspects which call for a certain ingenuity on the part of the animal.

[75] Reaumur, Memoires pour servir a l"histoire des Insectes, Paris, 1742, t. vi., pp. 282-284.

Up to recent years the Cerceris was considered to act with as much certainty as the Sphex, and to obey an infallible instinct which always guided it for the best in the interests of its offspring. The insects it attacks belong to the genus Buprestis.

It consumes them in considerable numbers. Its manner of action, as described by Leon Dufour,[76] much resembles that of the Sphex, and it would be superfluous to describe it. The only fact which I wish to mention, and which has been put out of doubt by the ill.u.s.trious naturalist, is this: the Buprestis are paralysed, not dead; all the joints of the antennae and legs remain flexible and the intestines in good condition. He was able to dissect some which had been in a state of lethargy for at least a week or a fortnight, although, under normal conditions, these insects in summer decay rapidly, and after forty-eight hours cannot be used for anatomical purposes. Another observer, Paul Marchal, took up this question afresh, and the results which he obtained seemed to indicate an instinct much less firm than earlier studies tended to show.[77]

[76] "Histoire des Cerceris," Ann. Sc. Nat., ii. Serie, t. xv., 1841, pp. 353-370.[77] Arch. de Zool. exp., 1887.

Genera less skilful in the art of paralysing victims.--These researches show us that in the Cerceris instinct is still subject to defect. In some neighbouring genera we can seize it, as it were, in process of formation. The way in which the Bembex, or Sand Wasp, provisions burrows by maternal foresight is much less mechanical than that of the Sphex. It is again Fabre who has described with most care the customs of this hymenopterous insect.[78] It hollows out for each egg a chamber communicating with the air by a gallery, and performs this work with little care and very roughly. Less skilful than the others, it does not ama.s.s at once all the provisions which its larvae will need during the period of evolution. When the offspring has absorbed the last prey brought, it is necessary to bring a new victim. This insect is scarcely more advanced than birds, who feed their young from day to day. And it is a great labour to re-open every time the gallery which leads to the nursery; on all these visits, in fact, the Bembex fills it up on leaving, and causes the disappearance of all revealing traces. It is obliged to take so much trouble, because it has not inherited from its ancestors the receipt for the paralysing sting; it throws itself without care on its victim, delivers a few chance blows, and kills it. Necessarily it cannot, under these conditions, lay up provisions for the future; they would corrupt, and the larvae would not be benefited; hence the obligation of frequently returning to the nest, and of a perpetual hunt to feed descendants whom nature has gifted with an excellent appet.i.te. According to the age of the offspring, the mother chooses prey of different sizes; at first she brings small Diptera; then, when it has grown, she captures for it large blow-flies, and lastly gadflies.[79] It will be seen, then, that if we suppose the instinct of the Sphex to be slowly developed by being derived from a sting given at random, we make a supposition which is quite admissible and rests on ascertained facts.

However this may be, the Bembex, returning to its burrow, is able to find it again with marvellous certainty, in spite of the care taken to hide it by removing every trace that might reveal its existence. It is guided by an extraordinary topographic instinct, which men not only do not possess, but cannot even understand the nature of.

[78] Souvenirs entomologiques, 1879, pp. 225 et seq.

[79] A Wasp found in La Plata, the Monedula punctata, as described by Hudson (Naturalist in La Plata, pp. 162-164), is an adroit fly-catcher, and thus supplies her grub with fresh food, carefully covering the mouth of the hole with loose earth after each visit; as many as six or seven freshly-killed insects may be found forthe use of one grub.

It would appear that certain Hymenoptera, fearing to kill their victim with the sting, and not knowing the art of skilful lesions, attempt to immobilise them by wounds of another sort. This is the case with the Pompilius, according to Goureau,[80]

who has studied it. This insect nourishes its larvae with spiders; it seems certain that in most cases the spider is not p.r.i.c.ked. Victims who have been taken from the interior of provision burrows can live for a long time in spite of their wounds; they cannot, therefore, have received venom by inoculation. The author already quoted believes that the Pompilius seizes its captive by the pedicle which unites the abdomen to the cephalothorax, and that it triturates this point between its jaws. From this either death or temporary immobility may follow. The Pompilius also makes up for its relative ignorance by considerable ingenuity. Thus sometimes, when it fears a return to life of the victim destined for its larvae, it cuts off the legs while it is still pa.s.sive. Goureau has found in the nest of this insect living spiders with their legs cut off.

[80] "Observations pour servir a l"histoire de quelques Insectes," Ann. Soc.

entomol. de France, t. 8, 1839, p. 541.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--CLa.s.sIFICATION 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 COa.r.s.eLY-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 a.s.sOCIATION--INDIVIDUAL SKILL AND REFLECTION--DWELLINGS BUILT OF HARD MATERIALS UNITED BY MORTAR--THE DAMS OF BEAVERS.

Animals construct dwellings either to protect themselves from the cold, heat, rain, and other chances of the weather, or to retire to at moments when the search for food does not compel them to be outside and exposed to the attacks of enemies.

Some inhabit these refuges permanently; others only remain there during the winter; others, again, who live during the rest of the year in the open air set up dwellings to bring forth their young, or to lay their eggs and rear the offspring.

Whatever the object may be for which these retreats are built, they const.i.tute altogether various manifestations of the same industry, and I will cla.s.s them, not according to the uses which they are to serve, but according to the amount of art displayed by the architect.

In this series, as in those which we have already studied, we shall find every stage from that of beings provided for by nature, and endowed with a special organ which secretes for them a shelter, up to those who are constrained by necessity to seek in their own intelligence an expedient to repair the forgetfulness of nature. These productions, so different in their origin, can only be compared from the point of view of the part they play; there are a.n.a.logies between them but not the least h.o.m.ology.Animals naturally provided with dwellings.--Nearly all the Mollusca are enveloped by a very hard calcareous case, secreted by their mantle: this sh.e.l.l, which is a movable house, they bear about with them and retire into at the slightest warning.

Caterpillars which are about to be transformed into chrysalides weave a coc.o.o.n, a very close dwelling in which they can go through their metamorphosis far from exterior troubles. It is an organic form of dwelling, or produced by an organ. It is not necessary to multiply examples of this kind; they are extremely numerous. In the same category must be ranged the cells issuing from the wax-glands which supply Bees with materials for their combs in which they enclose the eggs of the queen with a provision of honey.

I do not wish to insist on creations of this kind which are independent of the animal"s will and reflection. Near these facts must be placed those in which animals, still using a natural secretion, yet endeavour to obtain ingenious advantages from it unknown by related species.

[Ill.u.s.tration: FIG. 18.]

There is, for example, the Macropus viridi-auratus, or Paradise-fish, which blows air bubbles in the mucus produced from its mouth. This mucus becomes fairly resistant, and all the bubbles imprisoned and sticking aside by side at last form a floor. It is beneath this floating shelter that the fish suspends its eggs for its little ones to undergo their early development.

Animals who increase their natural protection by the addition of foreign bodies.--Certain tubicolar Annelids, whose skin furnishes abundant mucus which does not become sufficiently hard to form an efficacious protection, utilise it to weld together and unite around them neighbouring substances, grains of sand, fragments of sh.e.l.l, etc. They thus construct a case which both resembles formations by special organs and manufacture by the aid of foreign materials.

The larvae of Phryganea, who lead an aquatic life, use this method to separate themselves from the world and prepare tubes in which to dwell. (Fig. 18.) All the fragments carried down by the stream are good for their labours on condition only that they are denser than the water. They take possession of fragments of aquatic leaves, and little fragments of wood which have been sufficiently long in the water to have thoroughly imbibed it and so become heavy enough to keep themselves at the bottom, or at least to prevent them from floating to the surface.

It is the larva of Phryganea striata which has been best studied; those ofneighbouring species evidently act much in the same way, with differences only in detail. The little carpenter stops a fragment rather longer than his own body, lies on it and brings it in contact with other pieces along his own sides. He thus obtains the skeleton of a cylinder. The largest holes are filled up with detritus of all kinds. Then these materials are agglutinated by a special secretion. The larva overlays the interior of its tube with a covering of soft silk which renders the cylinder watertight and consolidates the earlier labours. The insect is thus in possession of a safe retreat. Resembling some piece of rubbish, it completes its metamorphosis in peace, undisturbed by the carnivora of the stream. There is here already a tendency towards the dwellings of which I shall speak later on, and which are entirely formed of the external environment.

Animals who establish their home in the natural or artificial dwellings of others.--Between the beings whom nature has endowed with a shelter and those who construct it by their own industry, we may intercept those who, deprived of a natural asylum and not having the inclination or the power to make one, utilise the dwellings of others, either when the latter still inhabit them, or when they are empty on account of the death or departure of the owner. In the natural sciences there is no group of facts around which may be traced a clear boundary; each of them is more or less closely related to a group which appears at first of an entirely different nature. Thus it does not enter into our plan to speak of parasites.

Yet, if among these some turn to a host to demand of him both food and shelter, if even they can come to be so modified and so marked by parasitism that they can live in no other way, there are others who ask for lodging only from an animal better protected than they are themselves. It is these whose customs we are called upon to consider. In the interior of the branchial chamber of many bivalvular Mollusca, and especially the Mussel, there lives a little crustaceous commensal called the Pea-crab (Pinnoteres pisum). He goes, comes, hunts, and retires at the least alarm within his host"s sh.e.l.l. The mussel, as the price of its hospitality, no doubt profits by the prizes which fall to the little crab"s claws. It is even said that the crab in recognition of the benefits bestowed by his indolent friend keeps him acquainted with what is pa.s.sing on around, and as he is much more active and alert than his companion he sees danger much farther away, and gives notice of it, asking for the door to be shut by lightly pinching the mussel"s gill. But this grat.i.tude of the Crustacean towards a sympathetic bivalve is merely a hypothesis; we do not exactly know what pa.s.ses in the intimacy of these two widely-differing natures.For birds like the Cuckoo and the Molothrus it is not possible to plead attenuating circ.u.mstances. They occupy a place in an inhabited house without paying any sort of rent. Every one knows the Cuckoo"s audacity. The female lays her eggs in different nests and troubles herself no further about their fate. She seeks for her offspring a shelter which she does not take the trouble to construct, and moreover at the same time a.s.sures for them the cares of a stranger in place of her own.

In North America a kind of Starling, the Molothrus pecoris, commonly called the Cow-bird, acts in the same careless fashion. It lives in the midst of herds, and owes its specific name to this custom; it feeds on the parasites on the skin of cattle. This bird constructs no nest. At the moment of laying the female seeks out an inhabited dwelling, and when the owner is absent she furtively lays an egg there. The young intruder breaks his sh.e.l.l after four days" incubation, that is to say, usually much before the legitimate children; and the parents, in order to silence the beak of the stranger who, without shame, claims his share with loud cries, neglect their own brood which have not yet appeared, and which they abandon. Their foster children repay them, however, with the blackest ingrat.i.tude.

As soon as the little Molothrus feels his body covered with feathers and his little wings strong enough to sustain him he quits his adopted parents without consideration. These birds show a love of independence very rare among animals, with whom conjugal fidelity has become proverbial; they do not unite in couples; unions are free, and the mother hastens to deliver herself from the cares of bringing up her young in the manner we have seen. Two other species of Molothrus have the same habit, as have the American Cuckoo and the Golden Cuckoo of South Africa.

The habits of the Molothrus bovariensis, a closely allied Argentine Cow-bird, have been carefully studied by Mr. W. H. Hudson, who has also some interesting remarks as to the vestiges of the nesting instinct in this interesting parasitical bird, which now is constantly dropping eggs in all sorts of places, even on the ground, most of them being lost. "Before and during the breeding-season the females, sometimes accompanied by the males, are seen continually haunting and examining the domed nests of the Dendrocolaptidae. This does not seem like a mere freak of curiosity, but their persistence in their investigations is precisely like that of birds that habitually make choice of such breeding-places. It is surprising that they never do actually lay in such nests, except when the side or dome has been accidentally broken enough to admit the light into the interior.

Whenever I set boxes up in my trees, the female Cow-birds were the first to visitthem. Sometimes one will spend half a day loitering about and inspecting a box, repeatedly climbing round and over it, and always ending at the entrance, into which she peers curiously, and when about to enter starting back, as if scared at the obscurity within. But after retiring a little s.p.a.ce she will return again and again, as if fascinated by the comfort and security of such an abode. It is amusing to see how pertinaciously they hang about the ovens of the Oven-birds, apparently determined to take possession of them, flying back after a hundred repulses, and yet not entering them even when they have the opportunity.

Sometimes one is seen following a Wren or a Swallow to its nest beneath the eaves, and then clinging to the wall beneath the hole into which it disappeared.

That it is a recurrence to a long-disused habit I can scarcely doubt. I may mention that twice I have seen birds of this species attempting to build nests, and that on both occasions they failed to complete the work. So universal is the nest-making instinct that one might safely say the M. bovariensis had once possessed it, and that in the cases I have mentioned it was a recurrence, too weak to be efficient, to the ancestral habit." Mr. Hudson suggests that this bird lost the nest-making instinct by acquiring the semi-parasitical habit, common to many South American birds, of breeding in the large covered nests of the Dendrocolaptidae, although, owing to increased severity in the struggle for the possession of such nests, this habit was defeated.[81]

[81] P. L. Sclater and W. H. Hudson, Argentine Ornithology, 1888, vol. i. pp.

72-86. A brief summary of the facts regarding parasitism among birds will be found in Girod"s Les Societes chez les Animaux, 1891, pp. 287-294.

The Rhodius anarus, a fish of European rivers, also ensures a quiet retreat for his offspring by a method which is not less indiscreet. At the period of sp.a.w.ning, a male chooses a female companion and with great vigilance keeps off all those who wish to approach her. When the laying becomes imminent, the Rhodius, swimming up and down at the bottom of the stream, at length discovers a Unio.

The bivalve is asleep with his sh.e.l.l ajar, not suspecting the plot which is being formed against him. It is a question of nothing less than of transforming him into furnished lodgings. The female fish bears underneath her tail a prolongation of the oviduct; she introduces it delicately between the Mollusc"s valves and allows an egg to fall between his branchial folds. In his turn the male approaches, shakes himself over it, and fertilises it. Then the couple depart in search of another Unio, to whom to confide another representative of the race. The egg, well sheltered against dangers from without, undergoes development, and one fine day the little fish emerges and frisks away from his peaceful retreat.Other animals, more respectful of property, avoid using another"s dwelling until it is abandoned by its proprietor, and no reproach of indelicacy can be addressed to the Gobius minutus, a fish which lives on our coasts at the mouth of rivers. The female lays beneath overturned sh.e.l.ls, remains of Oysters, or Cardium sh.e.l.ls.

The valve is buried beneath several centimetres of sand, which supports it like a vault. It forms a solid roof, beneath which the eggs undergo their evolution.

Sometimes the male remains by the little chamber to watch over their fate. It is possible to distinguish the two holes of entrance and exit which mark his habitual pa.s.sage.

[Ill.u.s.tration: FIG. 19.]

The Hermit-crab perhaps knows best how to take advantage of old clothes. (Fig.

19.) He collects sh.e.l.ls of Gasteropods, abandoned flotsam, the first inhabitant of which has died. The Hermit-crab (Pagurus Bernhardus) is a Decapod Crustacean--that is to say, he resembles a very small Crab. But his inveterate habit during so many generations of sheltering his abdomen in a sh.e.l.l prevents this part from being encrusted with lime and becoming hard. The legs and the head remain in the ordinary condition outside the house, and the animal moves bearing it everywhere with him; on the least warning he retires into it entirely. But the Crustacean grows. When young he had chosen a small sh.e.l.l. A Mollusc, in growing, makes his house grow with him. The Hermit-crab cannot do this, and when his dwelling has become too narrow he abandons it for one that is more comfortable. At first enclosed in the remains of a Trochus, he changes into that of a Purpura; a little later he seeks asylum in a Whelk. Beside the shelter which these sh.e.l.ls a.s.sure to the Crustacean, they serve to mask his ferocity, and the prey which approaches confidently what it takes to be an inoffensive Mollusc, becomes his victim.

The Great Horned Owl likewise does not construct a nest; but takes possession of the dwellings abandoned by others. These birds utilise for laying their eggs sometimes the nest of a Crow or a Dove, sometimes the lair which a Squirrel had considered too dilapidated. The female, without troubling about the bad state of these ruins, or taking pains to repair them, lays her eggs here and sits on them.

Cla.s.sification of artificial shelters.--It is time to turn to animals who have more regard for comfort, and who erect dwellings for themselves or their offspring.

These dwellings may be divided into three groups: (1) Those which are hollowed in earth or in wood; (2) those which in the simplest form result from the division ofmaterial of any kind; then, as a complication, of materials bound together; then, as a last refinement, of delicate materials, such as blades of gra.s.s or threads of wool woven together; such are the nests of certain birds and the tents of nomads; (3) those which are built of moist earth which becomes hard on drying; the perfection of this method consists of piling up hard fragments, pieces of wood or ashlar, the moist earth being only a mortar which unites the hard parts together.

Animals exercise with varying success these different methods, all of which Man still practises.

Hollowed dwellings--Rudimentary burrows.--We will first occupy ourselves with the dwelling hollowed in the earth. It is the least complicated form. The number of creatures who purely and simply bury themselves thus to obtain shelter is incalculable; I will only mention a few examples, and pa.s.s on from simple combinations to the more perfected industries, of which they present the first sketch.

It is known that at a certain epoch of the year Crabs abandon their hard carapaces. This phenomenon is known by the name of the moult; they remain in this condition for some time; it is the period during which they grow; then their integuments are encrusted anew with lime and again become resistant. While they are thus deprived of their ordinary protection they are exposed to a crowd of dangers, and they are so well aware of this that they remain hidden beneath rocks and pebbles. A crab of Guadeloupe, called Gecarinus ruricola, escapes the perils of this situation, thanks to its kind of life and its habit of hollowing out a burrow to live in while it is deprived of its habitual defence. This Crustacean lives on the earth, at a distance of about ten or twelve kilometres from the sea-sh.o.r.e, and nourishes itself on animal and vegetable remains. It approaches the water only at the period of laying eggs, turning towards the coast in the months of February and March. This migration does not take place, like some others, in compact bands; each follows the road in independence, and preserves a certain amount of liberty with regard to the path and the epoch of the journey. They lead an aquatic life till May or June; then the female abandons her little ones, who had begun their development attached to her claws, and they return to land. The moult takes place in August. At the approach of this dreaded crisis each hollows a hole between two roots, supplies it with green leaves, and carefully stops up the entrance. These labours accomplished, the crab is entirely sheltered; it undergoes the moult in safety, and does not emerge from its retreat until it is again capable of facing enemies, and of seizing food with its claws, which have become hard again. This seclusion appears to last a month. Here is, then, anexample of a temporary dwelling rendered necessary by special conditions of defect for external life. We are here still in the infancy of the art.

Speaking generally, birds are accomplished architects. Certain of them are, however, content with a rudimentary cavern. There is no question here of those who retire to clefts in the rock or in trunks of trees, for in these cases the cavity is only the support of the true house, and it is in the construction of this that the artist reveals his talent. I wish to speak of animals which remain in a burrow without making a nest there. A Parroquet of New Zealand called the Kakapo (Strigops habroptilus) thus dwells in natural or hollowed excavations. It is only found in a restricted portion of the island and leads a miserable life there, habitually staying in the earth and pursued by numerous enemies, especially half-wild dogs. It tries to hold its own, but its wings and beak do not suffice to protect it, and the race would have completely disappeared if these birds were not able to resist, owing to the prudence with which they stay within their dwellings. They profit by a natural retreat, or one constructed in rocks or beneath roots of trees; they only come out when impelled by hunger, and return as soon as they can in case of danger.

A large number of animals also hollow out shelters for their eggs, with the double object of maintaining them at a constant temperature and of concealing them.

Most reptiles act in this manner. The way in which a Tortoise, the Cistudo lunaria, prepares its nest is extremely curious. When the time for this labour arrives, the tortoise chooses a site. It commences by boring in the earth with the end of its tail, the muscles of which are held firmly contracted; it turns the tail like a gimlet and succeeds in making a conical hole. Gradually the depth of the hole becomes equal to the length of the tail, and the tool then becomes useless. The Cistudo enlarges the cavity with the help of its posterior legs. Using them alternately it withdraws the earth and kicks it away, then piles up this rubbish on the edge of the hole, arranging it so as to form a circular rampart. Soon the posterior members can take nothing more from the too distant bottom. The moment for laying has now come. As soon as the egg arrives at the cloac

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