consists of various strata of complicated fibres, which admit of being separated from each other. It is from this skin that the hairs originate, and from which they derive their nourishment.
In regard to chemical composition, the external covering approaches to the nature of horn, but it differs from that substance by the admixture of a peculiar substance, viz. chitine or entomoline. Portions of phosphate of lime and magnesia are also constituent ingredients, although they exist in small quantities. One of the peculiar properties of chitine is its insolubility in potass. "Exhibited separately, which is very easy, by means of steeping horny parts in a solution of potass, it appears as an almost colourless transparent substance, which becomes brown in nitric acid, and in the dry distillation produces no carbonate of ammonia, and therefore appears to contain no azote; it burns without previously melting, but is soluble in boiling or heated sulphuric acid.
"Besides the above, small portions of albumen, a peculiar brown colouring matter, which dissolves in caustic potass, but not in boiling alcohol, as well as traces of phosphate of iron, have been found in the horny integument of insects, upon different analyses. The albumen belongs doubtlessly to the third tunic, as does the brown colouring matter to the mucous rete: to this, also, we attribute the chitine, where-by the true horny skin, namely, the epidermis, will
scales: yet even these scales, according to Cuvier, obtain their colour from being, in the chrysalis, in a state of mucosity, similar to that which is found under the skin of the caterpillar.
