Tadpoles are baby frogs that have the impressive ability to regenerate, or regrow, lost limbs. Adult frogs do not have this ability, and the reason why remains unknown.
Other animal species also have the ability to regenerate. Salamanders are amphibians, like tadpoles, that are able to regenerate parts of the spine. If the spinal cord is overly damaged or removed, the tail doesn't regenerate. Lizards are reptiles that are able to regenerate their tails after voluntarily disconnecting them from their bodies in response to a defense mechanism. During regrowth, bones are replaced with cartilage. Some species also have the ability to regenerate internal organs.