Epimorphosis
Epimorphosis is a term put forth by Thomas Hunt Morgan to help differentiate between different regenerative phenomena observed in nature[1]. Epimorphosis refers to regeneration of a missing part that involves cell proliferation. This distinguishes epimorphosis from morphallaxis, where regeneration of a missing part occurs through cellular rearrangement without cell proliferation.
Epimorphosis in salamander limbs
Immediately after the limb is amputated, a plasma clot forms over the wound. Epidermal cells at the wound margins migrate to cover the wound and will become the wound epidermis.[2] No scar tissue forms, as it would in mammals.
An apical ectodermal cap (AEC) forms on the tip of the stump. This is similar to the embryonic apical ectodermal ridge, which forms during normal limb development. The AEC causes the progress zone to re-establish; this means the cells under the AEC dedifferentiate and become mesenchymal. The AEC releases factors that drives the development of the new limb. It is basically resetting the limb back to its embryonic development stage.
But even though some of the limb cells are able to dedifferentiate, they are not able to fully dedifferentiate to the level of multipotent progenitor cells. During regeneration, only cartilage cells can form new cartilage tissue, only muscle cells can form new muscle tissue, and so on. The dedifferentiated cells still retain their original specification.[2]