tadpole

tadpole, larval, aquatic stage of any of the amphibian animals. After hatching from the egg, the tadpole, sometimes called a polliwog, is gill-breathing and legless and propels itself by means of a tail. During the period of metamorphosis it develops the lungs, legs, and other organs of the adult and, in the frog and the toad, loses the tail.

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tadpole

 or polliwog

Aquatic larval stage of frogs and toads. Tadpoles have a short, oval body, broad tail, small mouth, and no external gills. Most are herbivorous, but those of some species are predatory or even cannibalistic. Tadpole metamorphosis follows a pattern of gradual development of forelimbs and hind limbs, resorption of the tail, shortening of the intestine, disappearance of the gills, and development of the lungs. On completion of metamorphosis, the young frog or toad emerges onto land.