Regeneration, in plants and animals, is the capacity to replace lost or damaged parts by growing new ones. Regeneration is common in plants. If a tree or shrub is cut off near the ground, new shoots may spring up from the stump. Among animals, the sponges, cnidarians, and the simpler worms show remarkable power of regeneration. They can be cut in pieces, and each piece can grow into a new animal. Starfishes can grow new arms. Crayfishes can grow new claws, eyes, and legs.
Animals with a backbone–called vertebrates–have only limited powers of regeneration. But a reptile called the glass lizard escapes from its enemies by breaking off the end of its tail. The glass lizard later grows a new one. Salamanders can regenerate lost limbs. People and other mammals can regenerate only hair, nails, skin, and a few other tissues. In some cases, a different sort of tissue grows over the damaged area and forms a scar.
