A tadpole (also called pollywog or porwigle) is the larval stage in the life cycle of an amphibian, particularly that of a frog or toad.
Most species of amphibians do not exhibit parental care. So, when they lay their eggs they do not care for their young. Some species of poison dart frogs, however, will allow their tadpoles to wiggle onto the back of the male frog and be carried about. There are also species that build foam nests in the tree branches overhanging ponds. When the tadpoles hatch they fall into the water below and are at that time large enough to avoid many more predators had they hatched in the pond.
As a tadpole matures, it most commonly metamorphosizes by gradually growing limbs (usually the legs first, followed by the arms) and then (most commonly in the case of frogs) outwardly absorbing its tail by apoptosis. Lungs develop around the time of leg development, and tadpoles late in development will often be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the tadpole’s mouth changes from a small, enclosed mouth at the front of the head to a large mouth the same width as the head. The intestines shorten to accommodate the new diet. Most tadpoles are herbivorous, subsisting on algae and plants. Some species are omnivorous, eating detritus and when available, smaller tadpoles.
[via x x x]