They have evidently been very successful in exchanging flesh-feeding for fish-feeding, and if we consider for a moment what changes a four-footed land animal would wish to make in its body in order to swim and dive in the water, we shall see that these changes have taken place in the seals. First, a flexible body is required to wind and twist rapidly in the water, and this the seal arrives at by having the cushions of gristle between its joints very large and thick, while even its ribs are joined to its back by gristly rods, making its whole body very lissom. Next, a small head, offering little resistance to the water is an advantage, and this we find in all seals, while the short neck and extremely sloping narrow shoulders well encased in fat, make the body slope away gently with no jutting angles, but a round smooth surface from head to tail where it narrows like the tail of a fish. The next step is to do away with long angular arms and legs, which would impede it in diving and swimming, and here the seal meets the difficulty, not by losing its leg and arm bones, but by having them so shortened and encased in the skin that only the useful broad flippers are free, while the hind legs are set upon a very narrow hip joint (see Fig. 80), so that they bend backwards and work close to the body. Lastly, such a warm-blooded animal would want clothing to prevent it from being chilled in icy cold water, and here we find two protections. First, under the skin is a layer of oily fat, which, while it reminds us of the fat accumulated by bears before they settle down to their winter’s sleep, has become in the seals a dense oily mass, acting like a thick blanket in keeping up the warmth of the body; and secondly, the seal, like its distant relations the bears, has a dense furry covering, and over this a number of coarse long hairs, which give it that shining oily look we notice in all seals. No doubt every one has wondered, when watching seals in zoological gardens, where the fur can be which makes our sealskin muffs and jackets. The fact is, that this under fur is quite out of sight in the living seal, being covered by the coarse hairs; but if we could turn these aside, even in common seals, we should see the soft undergrowth beneath, and in the fur seals it is much thicker. Now the roots of these coarse hairs are deeper in the flesh than the roots of the soft undergrowth, and when the uppermost layer of the skin on which the fur grows is sliced off, the coarse hairs are cut away from their deep roots below, and can then be pulled out, leaving only the fur behind.