Page:Jardine Naturalist's library Entomology.djvu/103

Rh understood in what its peculiar characters and attributes consist. The external integument, or crust of insects, occupies the place of the skin in higher animals, as it forms a general envelope for all the parts; but, unlike the skin, it is of a rigid and horny consistency. In the latter particular it is liable to a good deal of variation, being sometimes horny and inflexible, (as in beetles,) at other times comparatively soft, and yielding to the slightest pressure. In all cases, however, it has sufficient strength to give effectual support to the muscles, which are attached to its interior surface, thus serving the same purpose as the bones of the vertebrata; on this account, insects have been sometimes described as bearing their skeleton externally. Besides resembling the true skin in its situation, it is found to display further conformity to it, in consisting of three principal layers, viz. the epidermis or exterior layer, the rete mucosum, and lastly, the leathery tunic, sometimes called the dermis or corium. The first of these is smooth, shining, and generally uncoloured, for the most part thickly perforated with small holes, through which the hairs rise to the surface. The mucous tissue (rete mucosum) consists, according to Strauss, of two layers, the upper of which is closely attached to the epidermis, and in this reside the brilliant colours with which so many insects are adorned. The third layer is without colour, and