Regeneration is a mode of asexual reproduction in some organisms. The process of getting back a full organism from its body parts is called regeneration. The simple multicellular animals like hydra and planaria show regeneration.
Regeneration in hydra:
If the body of hydra gets cut into a number of pieces, then each body piece can regenerate into a complete hydra by growing all the missing parts.
The regeneration of an organism from its cut body part occurs by the process of growth and development.
The cells of cut body parts divide rapidly to make a ball of cells.
The cells then become specialised to form different types of tissues which again form various organs and body parts.