10 



INSTINCT. 



bubble of air, and appears like a globe of quick- 

 silver; with this she enters her cocoon, and 

 displacing an equal mass of water, again 

 ascends for a second lading, till she has suffi- 

 ciently filled her house with it, so as to expel 

 all the water. The males construct similar 

 habitations by the same manoeuvres. How 

 these little animals can envelope their abdomen 

 with an air-bubble, and retain it till they enter 

 their cells, is still one of Nature's mysteries 

 that have not been explained.'' 



We need say nothing of the habitations 

 formed by solitary animals of the higher tribes, 

 chiefly by burrowing under ground, for their 

 own protection and comfort; but the most curi- 

 ous of such solitary habitations on the earth's 

 surface are also furnished by the tribe of 

 spiders. 



" Some species of spiders, M. Audouin re- 

 marks, are gifted with a particular talent for 

 building : they hollow out dens ; they bore 

 galleries ; they elevate vaults ; they build, as it 

 were, subterranean bridges; they construct also 

 entrances to their habitations, and adapt doors 

 to them, which want nothing but bolts, for 

 without any exaggeration, they work upon 

 a hinge and are fitted to a frame. The 

 interior of these habitations is not less 

 remarkable lor the extreme neatness which 

 reigns there; whatever be the humidity of the 

 soil in which they are constructed, water never 

 penetrates them ; the walls are nicely covered 

 with a tapestry of silk, having usually the lustre 

 of satin, and almost always of a dazzling white- 

 ness. 



" The habitations of the species in question 

 are found in an argillaceous kind of red earth, 

 in which they bore tubes about three inches in 

 depth and ten lines in width. The walls of 

 these tubes are not left just as they are bored, 

 but are covered with a kind of mortar, suffi- 

 ciently solid to be easily separated from the 

 mass that surrounds it." " The door that closes 

 the apartment is still more remarkable in its 

 structure. If the well were always open, the 

 spider would sometimes be subject to the intru- 

 sion of dangerous guests. Providence has there- 

 fore instructed her to fabricate a very secure 

 trap-door which closes the mouth of it. To 

 judge of this door by its outward appearance, 

 it appears to be formed of a mass of earth 

 coarsely worked, and covered internally by a 

 solid web, which would be sufficiently wonder- 

 ful for an animal that seems to have no special 

 organ for constructing it ; but when divided 

 vertically, it is found to be a much more com- 

 plicated fabric than its outward appearance in- 

 dicates, it being formed of more than thirty 

 alternate layers of earth and web emboxed, as 

 it were, in each other, like a set of weights for 

 small scales. 



"If these layers of web are examined, it will 

 be seen that they all terminate in the hinge, so 

 that the greater the volume of the door the more 

 powerful is the hinge. The frame in which the 

 tube terminates above, and to which the door 

 is adapted, is thick, arising from the number 

 of layers of which it consists, and which seem 

 to correspond with those of the door; hence 



the formation of the door, the hinge, and the 

 frame, seem to be a simultaneous operation ; 

 except that in fabricating the first, the animal 

 has to knead the earth as well as to spin the 

 layers of web. By this admirable arrangement 

 these parts always correspond with each other, 

 and the strength of the hinge and the thickness 

 of the frame will always be proportioned to the 

 weight of the door. 



" The interior surface of the cover to the 

 tube is not rough and uneven like its exterior, 

 but perfectly smooth and even like the walls of 

 the tube, being covered with a coating of white 

 silk, but more firm, and resembling parchment, 

 and remarkable for a series of minute orifioes 

 placed in the side opposite the hinge, and ar- 

 ranged in a semicircle ; there are about thirty 

 of these orifices, the object of which, M. Au- 

 douin conjectures, is to enable the animal to 

 hold her door down in any case of emergency 

 against external force, by the insertion of her 

 claws into some of them."* 



But the most extraordinary habitations formed 

 by the instincts of animals are those which are 

 the joint result of the labours of communities; 

 and here we observe the same difference as has 

 been already noticed, between the inhabitants 

 of the air and of the ocean. Many of the ani- 

 mals that inhabit the latter are formed by na- 

 ture, as Mr. Kirby expresses it, (and evidently 

 with a view to the rude shocks to which they 

 are exposed,) " into a body politic, consisting 

 of many individuals, separate and distinct as 

 inhabiting different cells, but still possessing a 

 body in common, and many of them receiving 

 benefit from the systole and diastole of a com- 

 mon organ ; thus by a natural union is symbo- 

 lized what in terrestrial animal communities re- 

 sults from numerous wills uniting to effect a 

 common object. The land, as far as I recol- 

 lect, exhibits no instance of an aggregate animal, 

 nor the ocean of one which, like the beaver, 

 lemming, bee, wasp, &c. forms associations to 

 build and inhabit a common house. "f 



And there is a curious family, named Salpa, 

 in which the individuals are attached to each 

 other almost like bees in their cells at birth, 

 and are afterwards separated when they have 

 acquired strength; thus forming the link be- 

 tween the aggregated sea animals (such as Co- 

 rals, Madrepores, Sertularia, Flustra, &c.) and 

 the associated land animals. 



The habitations that are formed by animals 

 of the latter description, although in very diffe- 

 rent parts of the scale of beings, afford equally 

 curious evidence of skill and contrivance, and 

 of the wills of numerous individuals, bound 

 together by a common instinct, as surely as the 

 materials of which the aggregate animals are 

 composed. Take, for example, the houses of 

 beavers. 



" Beavers set about building some time in 

 the month of August: those that erect their 

 habitations in small rivers or creeks in which 

 the water is liable to be drained off, with won- 

 derful sagacity provide against that evil by 



* Kirby, vol. ii. p. 287, et scq. 

 t Kubj, vol. i. p. 222. 



