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.