Читать книгу The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers - Various - Страница 288

The amphibians hold a middle position between the reptiles and fishes. The name, Amphibia, means “double-lifed” or living on both land and water. The larvæ, after leaving the eggs, live in the water like fishes; they gradually accustom themselves to live in the air, and when their metamorphosis is complete they breathe by means of lungs.

They have red, cold blood, and are enveloped in a smooth, often slippery, skin. Some have tails, like the newt and salamander, and others are tailless, like the frog and toad.

Frog (Rana temporaria) is familiar all over America, and is found in the early spring in all our ponds, ditches, and lakes, in which also large quantities of frog’s eggs can be seen. When fully developed, frogs have a short, tailless body, a large head, and four legs, the toes being frequently joined together by a membrane.

They deposit their eggs (a) in the water, either in masses or in strings. The larvæ (called tadpoles) have a long, flattened tail (c); they have no legs, and breathe through gills (b), and are therefore very different from the fully developed frog. The gills gradually disappear, and lungs are developed; the fore legs make their appearance, the hind pair developing first (d and e); the tail gradually diminishes, and finally disappears (f). The change, is then complete, and the young frog leaves the water to begin its life upon land. The common frog leaves the water immediately after spawning, and makes itself very useful by destroying numerous injurious insects and snails.

In this country the commoner species of frogs embrace the Bull Frog (R. catesbiana), which is the largest, sometimes being eight inches long. Its sonorous bass notes are familiar to the ear, and to the eye it presents a greenish appearance, brightest on the head; with faint spots on the back and blotches on the legs. It occurs from Kansas eastwards, and its hind-legs fried are considered a delicacy.

The Spring Frog (R. clamatans) is widespread, about three inches in length, green and black spotted above and white below.

The common Green Frog (R. virescens) has irregular black blotches, and is paler beneath. Both average about three inches in length.

DEVELOPMENT OF THE FROG—FROM THE EGG TO THE FULL-GROWN ANIMAL (See Page 223).

The Pickerel Frog (R. palustris) is light brown in color, with two rows of large oblong blotches of dark brown on the back and spots elsewhere. It is smaller in size and less aquatic than most other kinds.

The Wood-Frog or Tree-Frog (R. sylvatica) is more closely related in structure to the toads than to the frogs proper. The tree-frogs show various interesting adaptations to their arboreal life. The last joint of each toe bears a claw, on which is supported a disc or sucker by means of which the animals can cling to a perfectly perpendicular surface. Most of them also exhibit in a greater or less degree the power of color-change, where the color varies from a dark brown to a lichen-like gray or a brilliant green.

Newts are separated from the lizards on account of their changes while young. Like the frogs, they are first tadpoles, and do not assume their perfect shape until six weeks after their exclusion from the eggs. The common Newt is a beautiful inhabitant of the ponds, ditches, and still waters.

The male newt is distinguished by a beautiful crimson tipped wavy crest of loose skin, that extends along the whole course of the back and tail, and which, together with the rich orange-colored belly, makes it a most beautiful creature. The female has a singular habit of laying her eggs upon long leaves of water-plants, and actually tying them in the leaf by a regular knot.

Salamander (Salamandra maculata) is a nocturnal animal, and found in woods and hedges under decayed leaves and similar matter. Their bodies are longer and similar to the lizard. Most of the species lay eggs, usually in the water. From these the gilled young hatch out. They are carnivorous or insectivorous. In the adult stage, some are aquatic, but more live on the earth burrowing beneath the soil or under stones, seeking their prey at night. None are poisonous, except that they have glands in the skin which secrete an acrid juice. Our largest species is the mud puppy (Necturus) of the Mississippi basin; the largest living species is the giant salamander of Japan, three feet in length.

Toad (Bufo).—Toads are distinguished from frogs by the absence of teeth, by the roughness of the skin, by peculiarities in the breastbone, and by the shorter hind-legs.

The common toad is a shy, nocturnal animal, hiding during the day in dark, damp places, crawling about at night in search of insects, grubs, slugs, worms, and the like. Its appearance is familiar—a dirty brownish-gray color, a warty skin, a flat head, swollen parotid glands above the ears, bright jewel-like eyes with a transverse pupil, slightly webbed toes. They are heavier and clumsier than frogs, and cannot leap nearly so far. During the winter they live in the mud or in holes. In spring they pair, and the females lay in the water-pools their numerous eggs in strings about three or four feet in length. The tadpoles are smaller and darker than those of frogs, and do not accomplish their transformation into toads until autumn.

Toads are widely distributed over most parts of the continents, but are most abundant in tropical regions. The common toad of North America ranges everywhere east of the Rocky Mountains. In the Southern States another very similar species is numerous, and other species are found in the West. The largest toad of tropical America measures eight inches in length.