Wikipedia
Epimorphosis
Epimorphosis is the regeneration of tissues or organs through the dedifferentiation of existing, differentiated adult tissues. Adult cells dedifferentiate (though not fully into embryonic stem cells) into a mass of cells that then re-differentiates into the new structure. This phenomenon is seen in frog, newt, and salamander limbs. Their limbs may be amputated, but the lost portions of the limb are able to grow back.