frog

frog Tailless amphibian, found worldwide. Frogs have long hind limbs, webbed feet, and external eardrums behind the eyes. Most begin life as tadpoles after hatching from gelatinous eggs, usually laid in water. Some frogs remain aquatic, some terrestrial living in trees or underground. Most have teeth in the upper jaw and all have long sticky tongues attached at the front of the mouth to capture live food, usually insects. Length: 2.5–30cm (1–12in). Subclass Salientia (or Anura), divided into 17 families; the most typical genus is Rana. See also toad

frog common name for an amphibian of the order Anura. Frogs are found all over the world, except in Antarctica. They require moisture and usually live in quiet freshwater or in the woods. Some frogs are highly aquatic, while others are better adapted to terrestrial habitats. Among the latter type, those with stout bodies and thick skins are often called toads , although the name toad is sometimes restricted to members of the most terrestrial family of the Anura, the Bufonidae.

Frogs lack tails in their adult stage. They have short, neckless bodies; long, muscular hind legs specialized for jumping; and webbed feet for swimming. The skin is smooth, usually some shade of green or brown, and often spotted. Frogs have no outer ears; their prominent eardrums are exposed on the sides of the head. The bulging eyes have nictitating membranes to keep the eyes moist. Adult frogs have lungs, but their breathing mechanism is poorly developed. At rest they breathe mainly through the mouth lining, filling the lungs only occasionally. When in wet places they also absorb much dissolved oxygen through their skins. Frogs have true voice boxes and are noted for their various sounds. Frogs capture insects and worms with their sticky, forked tongue, attached at the front of the lower jaw. Some large tropical species eat small mammals and snakes. A few frogs have skin glands that can produce irritating or poisonous secretions.

Most frogs hibernate in underwater mud and lay their eggs in early spring. With few exceptions fertilization is external. The eggs—up to 20,000 at one time—are fertilized as they are laid in the water and are given buoyancy and protection by a gelatinous covering secreted by the female. The gilled, aquatic larvae, or tadpoles , hatch after 3 to 10 days; by the end of their first summer most frogs have completed their metamorphosis to the air-breathing, tailless, carnivorous adult. In some species, however, eggs are laid on land, and the young hatch as tiny frogs. Growth to adult size usually takes several years.

There are over a dozen families of frogs; the term "true frog" is often applied to members of the family Ranidae. The cosmopolitan genus Rana belongs to this family and includes many of the commonest frogs of North America, such as the bullfrog, R. catesbeiana, and the leopard frog, R. pipiens. Species of Rana are important laboratory animals; they are readily available and easy to handle and maintain. Field biologists have in recent years noticed declines in the populations of frogs and other amphibians worldwide. Although pollution and habitat destruction are contributing causes, the main culprit is believed to be a fungus, Batrachochytrium dendrobatidis, that causes a skin infection. Research has suggested, however, that outbreaks of the fungus are due in part to climatic changes possibly linked to global warming.

Frogs are classified in the phylum Chordata , subphylum Vertebrata, class Amphibia.

Bibliography: See M. J. Tyler, Frogs (1983); C. Mattison, Frogs and Toads of the World (1987).

frog the word frog was used as as a general term of abuse in Middle English, and was applied specifically to the Dutch in the 17th century; its application to the French (late 18th century) is partly alliterative, partly from the reputation of the French for eating frogs' legs.

Allusions are also found to a traditional fairy story, recorded by the Grimm brothers, in which a frog in a pool returns a princess's lost golden ball in return for her promise that he may live with and be loved by her. When he claims the reward her father makes her keep her promise; the frog eats from her plate and sleeps in her room. In the original story it is when she has thrown him against the wall that he turns into his real shape, that of a handsome prince, who is now her lover and husband; the usual version is that it is when she kisses him that the enchantment is broken and he is restored.
have a frog in one's throat lose one's voice or find it hard to speak because of hoarseness. The expression dates from the early 20th century, but frog here relates to an earlier meaning of a soreness or swelling in the mouth or throat.