The animals of which I have thus far been writing are classified in the suborder _Mystacoceti_, or whalebone whales, and are distinguished from the suborder _Odontoceti_, or toothed whales, by the possession of two parallel rows of thin, horny plates which hang from the roof of the mouth. These plates, commercially called whalebone but properly known as baleen, are growths from the skin much like the claws, finger or toenails of land mammals and are not composed of bone but of a substance called “keratin.” Each plate is roughly triangular, being wide at the base and narrow at the tip, and has the inner edges frayed out into long fibers; these hairlike bristles form a thick mat inside the mouth and thus the small shrimps and other minute food upon which the baleen whales feed are strained out and eaten. The development of whalebone is one of the most remarkable specializations shown by any living mammal. The baleen is, in reality, merely an exaggeration of the cross ridges found in the roof of the mouth of a land mammal and a somewhat similar straining apparatus is present in a duck’s bill. The great majority of people believe that all large whales eat fish whereas none, except the sperm whale, does so when other food is to be obtained. All the baleen whales eat small crustaceans and especially the little red shrimp (_Euphausia inermis_), which is about three-quarters of an inch long. These minute animals float in great masses, sometimes near the surface but often several fathoms below it, and the movements of the whales are very largely determined by their position and abundance. [Illustration: The tongue of a humpback whale, which has been forced out of the animal’s mouth by air pumped into the body to keep it afloat. ] The feeding operations are most interesting to watch, and if the shrimps happen to be but a short distance under water, as often happens during the morning and evening or just before a storm, they can be easily seen. The whale starts forward at good speed, then opens its mouth and takes in a great quantity of water containing numbers of shrimp, turns on its side and brings the ponderous lower jaw upward, closing the mouth. The great soft tongue, filling the space between the rows of baleen, expels the water in streams, leaving only the little shrimp which have been strained out by the bristles on the inner side of the whalebone plates.