Natural ability of living being to replace worn out parts, to repair damaged parts, to regrow cost off organs & to reform entire body from a small piece. Power of regeneration was first discovered in Hydra by trembley.
1. In amoeba each piece can form new amoeba if a part of nucleus present.
2. In sponges cells are loose, can form complete animal, described by H.V. Wilson.
3. In hydra a piece can form new animal if epidermis & dermis both layers present having interstitial cell which is totipotent in nature. Regeneration of a part of an organism by growth at the cut surface is known as epimorphosis.
4. In planaria compelte animals is developed from small fragment rate is high at head present and progressively decreases towards the tail end. This variation is called axial gradient.
5. In earthworm anterior end can regenerate posterior end.
6. Insects, crabs, lobester & spider can regenerate a lost leg. Cray fish can regenerate eyes too. Prawn breaks off the injured appendage i.e. autotomy.
7. Cephalopods can rejenrate arms.
8. In starfish tube feet is regenerated by autotomy.
9. Ammocoet larva of lamprey can regenerate lost tail.
10. Salamender, newt, axolotal larva can regenerate leg, tail, jaws, external gills, intestine and ratina.
11. Some lizards can regenerate the lost tail. The regenerated tail differs from the original one in shape, eg. absence of vertebrae and kinds of scales covered.
12. Certain birds can regenerate beak, feathers etc.
13. In mammals, in liver power of regeneration is maximum.
If one kidney is lost, the other compensate it. It is compensatory hypertrophy.