This distinction of origin corresponds with a wide difference of both anatomical and chemical characteristics. A diagrammatic section of calf-skin is shown in Fig. 9, and a more correct representation of its actual appearance is given in Plate I. (Frontispiece). The _epidermis_ is very thin as compared with the true skin which it covers, and is entirely removed preparatory to tanning; it nevertheless possesses important functions. It is shown in Fig. 10 at _a_ and _b_, more highly magnified. Its inner mucous layer _b_, the _rete malpighi_, which rests upon the true skin _c_, is soft, and composed of living nucleated cells, which multiply by division and form cell-walls of keratin. These are elongated in the deeper layers, and gradually become flattened as they approach the surface, where they dry up, and form the horny layer _a_. This last is being constantly worn away, thrown off as dead scales of skin, and as constantly renewed from below, by the multiplication of the cells. It is from the epithelial layer that the hair, as well as the sweat and fat-glands, are developed. [Illustration: FIG. 9.--Vertical section of calf-skin, magnified about 50 diameters. _a_, epidermis; _b_, grain or papillary layer; _c_, fibrous layer of skin; _d_, hairs; _e_, fat-glands; _f_, sweat-glands; _g_, opening of ducts of sweat-glands; _h_, hair-muscles.] Each hair is surrounded by a sheath which is continuous with the epidermis, and into which the young hair usually grows as the old one falls out. The hair itself is covered with a layer of overlapping scales, like the slates on a roof, but of irregular form. These give it a serrated outline at the sides, and when strongly developed as in wool and some furs, confer the property of felting. Within these scales, which are called the “hair cuticle,” is a fibrous substance which forms the body of the hair; and sometimes but not always, there is also a central and cellular pith, which under the microscope frequently appears black and opaque, from the optical effect of imprisoned air. On boiling or long soaking in water, alcohol, or turpentine, the air-spaces become saturated with the liquid, and then appear transparent. [Illustration: FIG. 10.--Epidermis layer.] The fibrous part of the hair is made up of long spindle-shaped cells, and contains the pigment which gives the hair its colour. The hair of the deer differs from that of most other animals in being almost wholly formed of polygonal cells, which, in white hairs, are usually filled with air. In dark hairs, both the hair and sheath are strongly pigmented, but the hair is much the most so, and hence the bulb has usually a distinct dark form. The dark-haired portions of a hide from which the hair has been removed by liming still remain coloured by the pigmented cells of the hair-sheaths, which can only be completely removed by “bating and scudding.” [Illustration: FIG. 11.--_a_, sebaceous gland; _b_, hair; _c_, erector muscle. Mag. 200.]