 Frog larvae are known as tadpoles and typically have oval bodies and long , vertically flattened tails with fins . The free @-@ living larvae are normally fully aquatic , but the tadpoles of some species ( such as Nannophrys ceylonensis ) are semi @-@ terrestrial and live among wet rocks . Tadpoles have cartilaginous skeletons , gills for respiration ( external gills at first , internal gills later ) , lateral line systems and large tails that they use for swimming . Newly hatched tadpoles soon develop gill pouches that cover the gills . The lungs develop early and are used as accessory breathing organs , the tadpoles rising to the water surface to gulp air . Some species complete their development inside the egg and hatch directly into small frogs . These larvae do not have gills but instead have specialised areas of skin through which respiration takes place . While tadpoles do not have true teeth , in most species , the jaws have long , parallel rows of small keratinized structures called keradonts surrounded by a horny beak . Front legs are formed under the gill sac and hind legs become visible a few days later . 
