Normal upper arm blastemas and blastemas derived from double posterior or double anterior thighs of A. mexicanum were reciprocally exchanged either by autografting or homografting between dark and white animals. Those grafted blastemas which survived always regenerated a morphology and pigmentation characteristics of the donor limb. Thus, upper arm blastemas on double anterior or posterior thigh stumps regenerated normal forelimbs. Double anterior blastemas on normal upper arm stumps failed to regenerate, and double posterior blastemas on normal upper arm stumps regenerated posterior half hindlimbs. These results show that the morphogenetic field of the regenerate is reflected in the composition of the limb stump, and that its pattern is expressed autonomously.
Supernumerary limbs formed where posterior and anterior tissues of graft and host were opposed in 35–43% of cases where normal upper arm blastemas were grafted to symmetrical thighs. The morphology and pigmentation of the supernumeraries suggests that they are probably derived from both graft and stump, although a singular origin from either graft or stump is not ruled out in some cases.