Write a note on regeneration.

Explanation

(i)Regeneration is regrowth in the injured region. Regeneration was first studied in Hydra by Abraham Trembley in 1740.
(ii) Regeneration is of two types morphallaxis and epimorphosis. In morphallaxis the whole body grows from a small fragment. E.g. Hydra and planaria.
(iii) When Hydra is accidentally cut into several pieces, each piece can regenerate the lost parts and develop into a whose new individual.
(iv) The parts usually retain their original polarity, with oral ends, the developing tentacles and aboral ends, by producing basal discs.
(iv) Epimorphosis is the replacement of lost body parts. It is of two types, namely reparative and restorative regeneration.
(vi) In reparative regeneration, only certain damaged tissue can be regenerated, whereas in restorative regeneration several body parts can develop. E.g. star fish, tail of wall lizard.