The smallest North American toad is the oak toad of the Southern States, which is only an inch long. When, in the breeding season, these diminutive toads flock to the pools in great numbers, they keep up an ear-splitting chorus of shrill peeps, like so many young chickens.
FROGS AS NURSERY MAIDS AND WEATHER PROPHETS
The tree frogs are a very large family (Hylidæ) distributed all over the world, except Africa, but most of the species belong to the steamy forests of tropical America. All are of small size, have smooth skins, normally greenish, but very changeable in color to adapt the creatures to the hue of their surroundings, as a protective device; and most of them inhabit trees. To enable them to do this the toes end in expanded, padlike disks, the contraction of which, when the foot is pressed against a surface, produces one or more furrows and, in addition, causes the exudation of a little mucilaginous liquid. The foot pressed against the surface expels the air, and this fact, aided by the stickiness of the pad, enables the frog to hold on to even a vertical plane of glass. All Hylidæ have a voice, often very loud, and enhanced by membranous sacs under or on each side of the throat, or in some cases internal; this sac, when blown out may be almost as large as the creature's body, as may be seen in our common gray tree frog when "singing." This species, like most others, becomes very noisy in the evening, in cloudy weather and before rain, with its not unmusical croaking; and a similar European species is kept in confinement by some people as an interesting pet and weather prophet.
The most interesting thing about the Hylidæ is their various methods of breeding, for while most of them lay their eggs, up to a thousand in number, in the water, many produce but a few, and attach them to the body.
A large tree frog called in Brazil "ferreiro" (smith), makes a sound like a mallet slowly and regularly struck on a metal plate. This frog actually builds a nursery in the shallow edge of a pond, where a basin-shaped hollow, with a rim, is formed by the broad-handed female. Here she leaves her eggs, safe from egg-eating fishes or insects, as the rim forms a wall higher than the surface of the water. A Japanese frog makes a similar basin, then produces a liquid which she kicks into a froth, and into the midst of this the eggs are dropped, and there the hatched larvæ develop, and remain until the gradual collapse of the mud rim sets them free.
In these and similar cases the eggs and tadpoles are abandoned by the parents; but many frogs watch over and care for their young. Some carry the young in a pouch on the back, but how it is accomplished is not known. A West African species carries its eggs in its mouth; and the male of Darwin's frog, of Chile, carries the eggs in a great vocal pouch beneath its throat, which subsequently forms a nursery for the tadpoles until they emerge as young frogs.
It must be noted, however, that some of these examples belong to the related family Cystignathidæ—a very extensive family largely represented in Central and South America.
The remainder of the tailless amphibians are assembled in the numerous and widely distributed family Ranidæ, which is that of the "true" frogs. The typical subfamily, Raninæ, is cosmopolitan, except as to Australia and South America south of the Amazon basin; but some less typical forms are confined to the tropics, and include several strange species, such as the little arboreal Dendrobates frogs of Brazil, one of which is famous for furnishing in the secretion of its skin a dye that when properly applied turns the green plumage of tame parrots into yellow—a fashionable tint. These small and pretty frogs are noted for their solicitude for their young, carrying baby tadpoles on their backs—where the infants creep and become attached—from place to place, as safety or better water conditions suggest.
The North American frogs are good examples of the ranine race, and those more commonly seen are the following:
Leopard frog (Rana pipiens), green with irregular black blotches, mostly in two rows on the back; legs barred above; belly pale. Eastern specimens are more olive than bright green.