Page:Natural History (1848).djvu/112

102 a conical stopper, somewhat resembling the cork of a bottle, but of so dense a texture, and so perfectly adapted to the orifice, that every drop of water is excluded. So closely interwoven are the fibres of this valve, that it can scarcely be cut with a knife.

There is another part of the structure of these interesting animals which has relation to the immense pressure to which they are subjected at great depths. It is the coating of elastic fat in which the whole body is enclosed. When we consider that the pressure is sometimes upwards of a hundred and fifty times as great as that of the atmosphere, we wonder that it does not crush the animal, by causing the collapse of every internal cavity. To sustain this pressure, the body is enveloped in a mantle of very peculiar elasticity; the skin itself is greatly thickened, but, by an open texture of its interwoven fibres, it is made to contain in its structure, a thick layer of oil or blubber. "A soft wrapper of fat, though double the thickness to that usually found in the Cetacea, could not have resisted the superincumbent pressure; whereas by its being a modification of the skin, always firm and elastic, and, in this case, being never less than several inches, and sometimes between one and two feet thick, it operates like so much india-rubber, possessing a density and resistance, which, the more it is pressed, resists the more."

Another important office is performed by this thick coat of superficial fat. The grand homes of the Whales are the icy oceans of the Polar regions, where warm-blooded animals, as all the