英文科學(xué)讀本 第四冊·Lesson 35 More about the Mammals

Lesson 35 More about the Mammals

The hoofed animals are without doubt the most useful order of the mammals. The members of this very large group have their toes enclosed in hard horny cases, which we call hoofs. They are all vegetarians.

The number of toes varies in the different members of the family. It is usual to arrange them as odd-toed and even-toed animals.

The tapir has three toes on the hind foot and four on the front foot; the elephant has five toes on each foot.

The elephant's feet are most admirably adapted for supporting the enormous weight of body, and for transporting the ponderous mass lightly, easily, and without jarring. This is accomplished by means of a hoof, composed of separate horny plates, which seem to act on the principle of an ordinary carriage spring. Everyone who, for the first time, sees an elephant walking, is always struck with surprise that the foot does not fall heavily on the ground, but swings forward lightly with an easy sweeping step.

The horse, ass, zebra, and quagga belong to a group known as single-toed animals. The hoof encloses a single toe, and on this one toe the animal walks. The rhinoceros is an odd-toed animal, but his foot is in three pieces.

The largest group of this hoofed order are the eventoed animals. The camel and the giraffe have two toes; the hippopotamus, hog, sheep, goat, ox, deer, and antelope have four toes.

In all, except the hippopotamus and the hog, the two hinder toes are very small. The animals walk on the front two toes only, which form a hoof that is divided down the middle, which we call cloven.

Animals such as hog, sheep, and hippopotamus, form a distinct class—the cud-chewers. They are distinguished by the pad in the upper jaw in place of incisor teeth, and by having four stomachs which are constructed for chewing the cud.

The elephant, rhinoceros, hippopotamus, and tapir are sometimes classified by themselves as thick-skinned animals. They are distinguished the thickness of their skin and the bulkiness of their body.

The next order are the whale-like animals. This order includes the whale, porpoise, and dolphin. These animals live in the sea, have a fish-like form, with short fin-shaped fore-limbs, and the hind limbs are entirely wanting. They are mammals and not fishes. They suckle their young, they have warm blood, they breathe through lungs, and cannot breathe in the water.

The last order of the mammals are the pouched animals. We have hitherto taken the structure of the limbs or teeth as our guide in arranging the various orders. This order is formed on an entirely different basis of classification. The animals which comprise it have one common characteristic—a curious pouch in which the young are carried for some time after their birth. The kangaroo of Australia and the opossum of America belong to this order.