Tadpole

Tadpole, or polliwog, larval amphibian hatched from transparent, jellylike eggs laid on the water. Tadpoles have the physical characteristics of fish (tail and gills). Through metamorphosis (a stage that can last from 10 days to 2 years, depending on the species) legs appear, the digestive system develops, the tail begins to shrink, and lungs develop as the gills disappear. In the adult frog or toad, the tail also disappears.