In all important points of their structure the feathers of birds are similar to the hairs of animals, and are developed in a similar manner. They are all composed of a quill portion, in which the pith is contained, and of a shaft, which carries the vane, together with its barbs. The form of each of these portions varies much, even in different parts of the same bird, and the same feather has almost always two kinds of barbs; one close and firm, and the other loose, floating, and downy. If a small feather be plucked from the breast or back of a sparrow or any other small bird, the upper part of the feather is seen to be close and firm, while the lower is loose and downy, the upper part being evidently intended to lie closely on the body and keep out the wet, while the lower portion affords a soft and warm protection to the skin. Fig. 12, Plate X., shows the feather of a peacock, wherein the barbs are very slightly fringed and lie quite loosely side by side. Fig. 18 is part of the same structure, in a duck’s feather, wherein are seen the curious hooks which enable each vane to take a firm hold of its neighbour, the whole feather being thus rendered firm, compact, and capable of repelling water. The reader will not fail to notice the remarkable analogy between these hooks and those which connect the wings of the bee. Fig. 17 is a part of the shaft of a young feather taken from the canary, given for the purpose of showing the form of the cells of which the pith is composed. Fig. 20 is part of the down from a sparrow’s feather, showing its peculiar structure; and Fig. 21 is a portion of one of the long drooping feathers of the cock’s tail. Fig. 13 exhibits a transverse section of one of the large hairs or spines from the hedgehog, and shows the disposition of the firm, horn-like exterior, and the arrangement of the cells. Sections of various kinds of hair are interesting objects, and are easily made by tying a bundle of them together, soaking them in gum, hardening in spirit, and then cutting thin slices with a razor. A little glycerine will dissolve the gum, and the sections of hair will be well shown. Unless some such precaution be taken, the elasticity of the hair will cause the tiny sections to fly in all directions, and there will be no hope of recovering them. Several examples of the skin are also given. Fig. 27 is a section through the skin of the human finger, including the whole of one of the little ridges which are seen upon the extremity of every finger, and half of two others. The cuticle, epidermis, or scarf-skin, as it is indifferently termed, is formed of cells or scales, much flattened and horny in the upper layers, rounder and plumper below. The true skin, or “cutis,” is fibrous in structure, and lies immediately beneath, the two together constituting the skin, properly so called. Beneath lies a layer of tissue filled with fatty globules, and containing the glands by which the perspiration is secreted.