FROG, Rana, a genus of batrachia, having in the adult state four legs and no tail, no gills, four toes on each of the fore-feet, five on each of the hind-feet, the feet more or less webbed; the head flat, the muzzle rounded; the mouth very large, a row of small teeth in the upper jaw, and an interrupted transverse row on the middle of the palate. The young (tadpoles) breathe by means of gills; external gills forming little fringes at the sides of the neck when they are very young, which, however, in a few days disap• pear; the gills, v.nich remain until the tadpoles undergo their final metamorphosis into frogs, being very numerous minute crests attached to four cartilaginous arches on each side of the neck, in a cavity to which the water enters from the mouth, and from which it is expelled by one or two small orifices. Tadpoles have no legs, and the body tapers into a tail, and thus has a fish-like form, very different from that of the mature F., the tail being furnished with a membranous border like a fin. The mouth of the tadpole is a horny beak, which falls off when it becomes a frog. When this metamorphosis takes place, the hind-legs grow first, and afterwards the fore-legs begin to appear, the tail being gradually absorbed. Tadpoles are capable of living in water only; but the mature F. visits the water only occasionally, although generally capable of remaining long imInersed, and always preferring moist places. In respiration, frogs draw in air through the nostrils, by movements of the muscles of the throat, and expel it by contraction of Those of the lower part of the abdomen. The thin smooth skin of frogs is also believed to be subservient to the aeration of the blood. The skeleton is destitute of ribs. The eye is large and very beautiful. The colors are often pleasing, and the general aspect agree able, in some species very much so, forming a strong contrast to the repulsive appear ance presented by toads, notwithstanding the close affinity between them both in struc ture and haoits. The greater proportionate length and strength of the hind-legs enables frogs to leap to a distance wonderful for creatures of their size, instead of crawling as toads do, and their activity and liveliness complete the contrast. The males have on
each side of the neck a delicate membrane, which becomes inflated with air when they croak. The power of voice in the females is much inferior. The croaking of numer ous frogs in marshy places, or around ponds and ditches, often makes an amusing and curious concert; but the powers of voice possessed by the frogs of Britain are not to be compared with those of the great bull-frogs (q.v.) of North America; whilst the neigh borhood of Rio Janeiro is enlivened as night comes on by the blacksmith F., which croaks so sonorously that the noise is like the clanging of a hammer on an anvil, the intermingled voices of some other kinds resembling the lowing of cattle at a distance; and in Peru, there is a F., of large dimensions, which has acquired the name of trapiehero, or sugar-miller, because its voice has a like that produced by a sugar-mill. The confused blending of the voices of different 'species of frogs, in these countries, destroying the stillness of night, is one of the things most certain to arrest the attention of the stranger. In colter climates, frogs usually bury themselves in mud, and spend the winter-in torpidity. In dry weather, they conceal themselves under shrubs and in tufts of herbage, from which rain quickly causes them to come forth, multitudes often . appearing where not one was to be seen before. They feed chiefly on insects, slugs, etc. The beaks of tadpoles are adapted to the eating of leaves and other vegetable food, on which Cuvier says they entirely subsist; but the younger Buckland, in his Curiosities of Natural _History (4th ed., Lond. 1859, pp. 2-4), in an amusing account of the habits of tadpoles, more correctly describes them as showing a great avidity for animal food, crowding round a dead kitten, and nibbling at the toes of little boys who wade in pools where they abound. The spawn of frogs is a gelatinous mass, in which the eggs are contained, and which swells greatly by imbibing moisture. Impregnation takes place after it is deposited, as with the spawn of fishes.