This ability is widespread in the animal kingdom, but its distribution is spotty. Salamanders are the best-known regenerators, but cockroaches can regrow legs,
In such systems a wound forms a blastema, a recognizable clump of proliferating cells that gives rise to the new structure. The distal tip of the new structure is made first, and then the middle part is filled in.
Regenerating systems always make the correct structures. For example, says Sue Bryant of the University of California in Irvine, planarian can be cut into 280 bits; each bit can regenerate a new body that is spatially appropriate to the starter. Researchers think that regeneration is divided into at least two phases: an early one that is poorly understood, and a later stage that seems to mirror very closely (if not ...
