(24.) _Wool-Bearing Animals._--In most dictionaries wool is defined as the fleece of sheep, as if, in fact they were the only animals which yield it, than which nothing can be more erroneous; since we are assured by the ablest naturalists, that almost every animal, from the butterfly up to man, possesses more or less of this covering, and that some indeed rival the sheep in the quantity they bear. Though wool is possessed in considerable quantity by carnivorous animals, especially bears, yet the herbivorous quadrupeds, never to mention the sheep, are principally noticed for its growth, and for affording a commodity which becomes an article of profit in the hands of some tribes. Heriot, in his travels through Canada, remarks, that "the savage women manufacture thread of the wool of the buffalo, and weave it into cloth. Most parts of the body are invested with a dusky wool, which is of a quality extremely fine--is much valued--and can with great facility be used in manufactures. The quantity usually contained on one skin is about eight pounds." So far from the sheep being invariably a wool-bearing creature, it would appear as liable to be entirely destitute of it as some other animals; for in Tartary, the eastern parts of India, China, and some parts of Africa, a hair of varying quality forms their sole covering; and Sir Joseph Banks imported three from Spain, which were smooth, sleek, and as short-haired as a horse. (25.) _Structure of the Skin._--The skin is composed of three coats, or layers; the outermost, the cuticle or scarf-skin, is a thin delicate membrane, devoid of feeling, and of a scaly texture, pierced by innumerable small holes, for the passage of the hairs, and perspiration, and covering the next, or mucous coat, so named from its pulpy appearance. In this resides the colouring matter, which imparts its peculiar tints to the hair, and which can only be satisfactorily demonstrated in the dark races. The existence of this coat has been by some denied; but it is probable that, though present in all, it can only be exhibited in such as have depth of tint, to admit of the display. It is here that sensation principally resides; the nerves, or rather their terminations, ramifying minutely in its substance, at which they have arrived by piercing the third tunic, or true skin, a dense firm elastic membrane, in which the roots of the hairs are imbedded, and from which, in fact, they take their origin. (26.) _Sebaceous Follicles._--The skin is studded over by small glands, or what, in anatomical language, would be called sebaceous follicles, which vary in number in different breeds, and different parts of the body, being most numerous on the breast and shoulders, and secreting a peculiar unctuous semi-solid matter, which, as we shall immediately see, possesses alkaline properties.