Regeneration of larval urodele limbs containing homoplastic transplants

Forelimbs of larval Ambystoma were amputated through the elbow. In many cases the humerus was partially or totally extripated. Homoplastic transplants, previously labeled with tritiated thymidine, were then inserted into the limb stump, which was re‐amputated through the graft. Experiments involving the addition of appendicular or visceral skeletal parts revealed fusion of the implant with the humerus and suggested interactions between skeletal components. The morphology of such regenerates was usually normal. The various skeletal elements exhibited a differential susceptibility to regression, Meckel's cartilage being particularly resistant. As a consequence, the distal blastema was often spatially removed from the proximal shoulder region. Nevertheless, reconstitution of the head of the humerus was always observed. The cellular origin of this portion of the regenerate was probably local connective tissue. Unlike Meckel's cartilage, the humerus released many cells to the accumulation blastema. These labeled cells may have divided at a higher rate than other blastemal cells, suggesting the possibility of tissue‐specific regeneration of cartilage. Transplanted muscle and connective tissue originating from either the jaw region or the limb behaved similarly to each other. Labeled connective tissue cells proximal to the amputation plane began dividing before the blastema was established, therefore the time of onset of cell division may vary according to the tissue involved and its location with respect to the blastema. A distinction between inductive phenomena and cell contributions was also made.