英文科學(xué)讀本 第四冊(cè)·Lesson 43 Reptiles

Lesson 43 Reptiles

The reptiles are the creeping or crawling animals. They produce their young from eggs, and do not suckle them. Although they breathe through lungs they have cold blood, and the heart has three chambers instead of four. The animals belonging to this class, like the mammals and the birds, are divided into different orders. Our earlier lessons have made us familiar with one of these orders— the snakes. It includes large serpents, that crush and mangle their prey within the large folds of their bodies before swallowing them, and venomous snakes, which kill their victims by means of their poisonous fangs.

Next to these we have the order of lizards. These include a large variety of animals, from the pretty harmless little lizard, a few inches in length, which frequents the heaths and sunny banks in our own country, to the enormous and powerful crocodiles and alligators of the tropics, many of which attain the length of 20 feet.

The body, which is long and covered with scales, is supported on four short legs, and there is generally a great length of tapering tail.

They are all armed with teeth. Some of the smaller varieties live on insects, some on vegetable food, but the giant members of the order live mostly in the water, and prey upon fish and other water animals. They also lie in wait for animals that come down to the water to drink.

The chameleon is a curious member of the order. It lives mostly in trees, has the singular-power of changing its color, and preys on insects. There are full twenty different varieties of this peculiar animal. The tortoises form the next order of reptiles. These animals have their bodies enclosed in a sort of double shell. There is a flattened under-shell or breast-plate, upon which the animal rests on the ground. This is made of hard thickened skin, and is known as the plastron. It is joined at its edges by a broad rounded shield, the carapace, which covers the animal. This carapace is really part of the bony skeleton of the animal. All the vertebrate animals we have hitherto examined possess an internal bony skeleton, but here we have a creature with its bony skeleton on the outside of its body. The carapace is really nothing but the vertebral bones and the ribs, with the spaces between them filled up with horny plates, the whole grown together into the hard solid shell. The head, neck, and limbs are not joined immovably to this solid outer skeleton. They are free to move, and they contain all the chief bones found in other animals. The front and hinder parts of both carapace and plastron are left open, for the head and limbs.

The head is very peculiar in form, and in place of teeth these animals are provided with a hard horny mouth. The smaller members of the family feed on vegetables and insects, but there are others, which measure upwards of 3 feet across, and prey upon crocodiles’ eggs, fish, and many kinds of water animals.