=Whales, Porpoises, Dolphins.=--As the absurd mistake is sometimes made of confusing _whales_ with fish, the pupil may compare them in the following respects: eggs, nourishment of young, fins, skin, eyes, size, breathing, temperature, skeleton (Figs. 209, 379, and 397). [Illustration: FIG. 378.--HARPOONING GREENLAND WHALE (see Fig. 351).] _Porpoises and dolphins_, which are smaller species of whales, live near the shore and eat fish. Explain the expression “blow like a porpoise.” They do not exceed five or eight feet in length, while the deep-sea whales are from thirty to seventy-five feet in length, being by far the largest animals in the world. The size of the elephant is limited by the weight that the bones and muscles support and move. The whale’s size is not so limited. The _whale_ bears one young (rarely twins) at a time. The mother carefully attends the young for a long time. The _blubber_, or thick layer of fat beneath the skin, serves to retain heat and keep the body up to the usual temperature of mammals in spite of the cold water. It also serves, along with the _immense lungs_, to give lightness to the body. Why does a whale need large lungs? The _tail of a whale_ is horizontal instead of vertical, that it may steer upward rapidly from the depths when needing to breathe. The _teeth_ of some whales do not cut the gum, but are reabsorbed and are replaced by horny plates of “whalebone,” which act as strainers. Give evidence, from the flippers, lungs, and other organs, that the whale is descended from a land mammal (Fig. 397). Compare the whale with a typical land mammal, as the dog, and enumerate the specializations of the whale for living in water. What change took place in the general form of the body? It is believed that on account of scarcity of food the land ancestors of the whale, hundreds of thousands of years ago, took to living upon fish, etc., and, gradually becoming swimmers and divers, lost the power of locomotion on land. _Order_ ____. _Why?_ ____. [Illustration: FIG. 379.--DOLPHIN.] Elephants are rapidly becoming extinct because of the value of their ivory tusks. Whales also furnish valuable products, but they will probably exist much longer. Why? The =manatees and dugongs= (sea cows) are a closely related order living upon water plants, and hence living close to shore and in the mouths of rivers. _Order_ ____. _Why?_ ____. [Illustration: FIG. 380.--MANATEE, or sea cow; it lives near the shore and eats seaweed. (Florida to Brazil.)] =Hoofed Mammals.=--All the animals in this order walk on the tips of their toes, which have been adapted to this use by the claws having developed into _hoofs_. The order is subdivided into the _odd-toed_ (such as the horse with one toe and the rhinoceros with three) and the _even-toed_ (as the ox with two toes and the pig with four). All the even-toed forms except the pig and hippopotamus chew the cud and are given the name of _ruminants_.