Fig. 377.—Molar Tooth of African Elephant.
The tusks are of use in uprooting trees for their foliage and in digging soft roots for food. Can the elephant graze? Why, or why not? There is a finger-like projection on the end of the snout which is useful in delicate manipulations. The feet have pads to prevent jarring; the nails are short and hardly touch the ground. Order ________. Why? ________. Key, page [193].
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]).
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 to 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?____.
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?