iv. The integument of insects is often clothed, either partially or generally, with _pubescence_, or hairs of various kinds--a circumstance which seems to have more than one object. In _Parnus_, _Heterocerus_, _Gerris_, _Argyroneta aquatica_, and some other aquatic insects, the end in view seems to be to keep the water from wetting the crust; and in this case the covering of hairs is dense, silky, and decumbent. Another object is preventing friction from being injurious: thus humble-bees, that from their mode of nidification[1159], are usually more particularly exposed to it, are well clothed with hair; and in those articulations of insects where much friction takes place, we may often observe a dense fringe or coating of the same substance. This you may see in the common stag-beetle (_Lucanus Cervus_), where the thorax receives the head; and very remarkably at the same point in the Hercules-beetle (_Dynastes Hercules_ MacLeay): but besides these uses, there is probably one more universal, which will apply as well to those thinly scattered bristles and hairs, here and there one, to be noticed in many insects: but concerning this I can only throw out a conjecture, as I do not recollect ever to have seen any experiments with regard to this use of animal hairs. But may they not act as conductors, either to introduce some invisible fluid into the body in a positive state, or to convey it out, when received by other means, in a negative state? Every one knows that the fur of a cat has electric properties, and there may be an important general use of this kind attached to the fur and hairs of animals[1160]. But, as I said, I give this as a mere conjecture; and only wish it may excite your attention to the subject, and put in exercise your natural tact for experiment.
M. Cuvier regards the hairs of insects as merely a continuation of the epidermis, with which they fall when the animal changes its skin[1161]; but this will apply only to the hairs of larvæ: for the hairs of perfect insects in many cases are implanted in a pore, and pass through epidermis or crust to the membrane that lines it, in which they terminate.
v. We are now to consider the _composition_ of the integument; under which term I would include the different layers of which it consists, and its articulation.