The cetaceans, or whale-like animals, which include the whale itself, the porpoise, the dolphin, the dugong, and the manatee, although they live entirely in the water, are all mammals. They bring forth their young alive, and suckle them just as the land mammals do; they are lung- breathing animals, and their blood is warm.
Nature, as we have seen, provides her various creatures with some sort of coat to prevent this bodily heat from being too rapidly dissipated, and modifies that covering to suit the requirements of each animal. The fur-animals of the frozen regions of the world are a striking example ofthis beneficent provision; some of them, such as the white bear, the otter, and the seals, which spend much of their lives in the icy water, have especially thick warm furs.
The animals we are about to consider now, however, never leave the water, and they are provided for in a different way; a thick coat of fur would not do in their case. Their skin is bare and naked on the outside, but immediately beneath it (in fact, forming part of it) is a thick under-coat of fat. Fat is a bad conductor of heat, sothat the under-coat of fat performs the same office forthese creatures as the thick fur covering does for the land mammals. It keeps their blood warm in those icy seas. But it does more than this; for being lighter than the water, it helps to keep the animals afloat.
It varies from 8 inches to 20 inches in thickness, according to the habitat of the animal. In the right whale of the frozen Arctic seas it is thickest, and is known as blubber; in the South Sea whale it is comparatively thin. The seals, because they live partly in the water, have a thin layer of this oily fat under their fur coat.
There are two kinds of whales-the baleen whale, which has no teeth, and the sperm whale, which has formidable teeth or tusks in the lower jaw.
The former class includes the Greenland, or right whale of the North Polar Seas; the South Sea or black whale of the Southern Ocean, especially round the Australian coasts and the extremities of Africa and America; and the Pacific or American whale of the north coast of America,round the neighborhood of Behring"s Straits. These whales are all very different in shape and size; the most valuable is the Greenland whale, an enormous creature, the largest of all the animals in the world, sometimes reaching 80 feet in length.
These whales have no teeth, but they have, hanging down from the upper jaw, on each side of the tongue, an extensive row of about 300 flat plates or blades of baleen or whalebone. These baleen plates are at right angles to the jawbone, and hang parallel to each other. They form, as they hang from the roof of the mouth, a transverse arch, the inner edge of each plate being fringed with stiff but flexible hairs. When the mouth is shut the fringed edges of the baleen plates rest on the upper convex surface of the tongue.
