Regeneration

All animals and plants are capable of regeneration to some extent but, as a general rule, the more highly evolved an animal is, the less are its powers of regeneration. Humans, for example, are able to regenerate skin and bone tissue, but are unable to regrow a finger if one is lost. Some internal organs can be regenerated if a large enough part remains as a starting point. The replacement of worn-out tissues is a form of regeneration and goes on throughout life. The most obvious is the replacement of skin from below as the outer layers rub off.
Some animals are able to regenerate new limbs – in fact lizards may actually shed their tails to confuse enemies and later grow new ones. Planarians are flatworms with great powers of regeneration. …