Blastema



A blastema is a mass of undifferentiated cells capable of growth and regeneration into organs or body parts. Blastemata are typically found in the early stages of an organism's development such as in embryos, and in the regeneration of tissues, organs and bone.

"Primitive" Organisms such as salamanders can still produce blastema when adult; more developed organisms such as frogs can't. That's the reason why salamanders can regenerate an amputed leg and frogs aren't able to do so.