Not all whales are big, of course; some are no more than four-and-a-half feet long. Of the 100-odd species, almost half are the relatively small dolphins and porpoises. There are two basic kinds of whales, into which all species fall: the baleen whales and toothed whales. Baleen whales, which are the biggest of all, have huge strainers of a tough and flexible stuff called whalebone, or baleen, in-side their mouths. The whales with teeth include the broad-domed 60-foot-long sperm whale, the killer whale and all the dolphins and porpoises.
The whale is so completely adapted to life in the sea that many people still think of it as a fish. It is easy to see why because, while it is warm-blooded and breathes air, the whale certainly looks like a fish and in many ways it lives like a fish. It has no need, as some other sea mammals do, to go on land to bear its young. It is marvelously stream-lined. Its neck bones have shortened so that the head merges with the trunk. Its forelegs have become fins and its hind legs have completely disappeared.
The only remains of the whale's external ear are openings on either side of the head no thicker than a pencil. Their nostrils have moved from the front to the very top of the head and have become one or two blowholes that enable the whale to breathe without raising itself more than a few inches above the water's surface. A thick layer of blubber, or fat, not only helps keep it warm in cold polar seas but also acts as a food reserve when the whale travels to warmer waters where the kind of food it likes may not be so abundant.
