These whales are so called because their muzzles are produced into beaks shaped somewhat like bottles. Although they belong to the toothed whales they only have two teeth in the lower jaw, and even these are so small that they are completely buried in the gum. By the side of the cachalot the bottle-nosed whale seems quite a small animal, for even the full-grown male seldom exceeds thirty feet in length, while the female is quite six feet shorter. It yields, on an average, about two hundredweight of spermaceti and two tons of oil. Its color, strange to say, is continually changing all through its life, for the young animals are black above and the older ones brown, which grows lighter and lighter as time goes on, till at last it becomes almost yellow. These whales seem to be very sympathetic creatures, for if one of them is wounded, its companions generally swim round and round it, and will even allow themselves to be killed one after the other rather than take to flight. But they are also rather stupid animals, for if they happen to find themselves near the coast they seldom seem to realize that they can easily escape by turning round and swimming out to sea, but leap and tumble about in a state of great terror till at last a big wave comes and throws them up on the beach. WHALEBONE-WHALES The members of the other great group of these animals are called whalebone-whales, because they have whalebone in their mouths instead of teeth. Of course this substance is not really bone at all. It consists of a kind of horny material which grows all round the upper jaw in a series of flattened plates, which are usually very long, and hang downward from the edge of the palate. Each of these plates, at the tip, is broken up into a sort of hair-like fringe; so that when the jaws are partly closed there is a kind of sieve, or strainer, between them, through which everything must pass that goes in or out of the mouth. This sieve is used in feeding. It seems strange that an animal so huge as a whale should feed on some of the smallest creatures which live in the sea. Yet such is the case, for the throats of the whalebone-whales are so narrow that one of them would almost certainly be choked if it tried to swallow a herring. So these whales live upon very small jelly fishes, and the young of shrimps, prawns, tiny crabs, etc., which often swim about in such vast shoals that for miles and miles the sea is quite alive with them. When the whale meets with one of these shoals it opens its mouth wide and swims through it. Then it partly closes its mouth, and squirts out the water which it has taken in through the whalebone strainer, the little animals, of course, remaining behind. These are then swallowed, a few thousand at a gulp, and the whale opens its mouth and repeats the operation over and over again, until its enormous appetite is satisfied.