This research analyzes the nature of the morphogenetic field of the regenerating amphibian limb, and the cellular rules which govern the specification of new patterns of spatial organization within the regeneration blastema. The following hypotheses are to be tested: (1) the mesodermal tissues represent a continuous gradient of positional values from the proximal to the distal end of the limb; (2) blastema cells can undergo only distal transformation along the proximal-distal axis; (b) the anterior posterior and dorsal-ventral patterns of the blastema can be directly altered by stump-blastema interactions when blastema and stump are disharmonious in these axes. These hypotheses will be tested by a series of transplantation experiments.