Regeneration from different levels along the tail of the newt, Notophthalmus viridescens.

Some aspects of the influence of position on regeneration have been examined by comparing regeneration from different levels along the newt tail. Tails amputated such that either three-fourths one-half or one-fourth of the tail was removed pass through the same morphological and histological stages at the same times after amputation. In tails amputated at these three different levels, the rate of elongation of regenerates from more proximal levels is greater than that of regenerates from more distal levels. The total lengths of regenerates from different levels are proportional to the lengths of tail removed by amputation. Furthermore, the number of vertebrae formed in a tail regenerate is directly proportional to the number of vertebrae removed by amputation. When a tail blastema is transplanted to a more proximal level tail stump, intercalary regeneration between the stump and transplant occurs and the resulting regenerate has a complement of vertabrae appropriate to its new level along the tail. The results indicate that position along the appendage does not influence the developmental sequence of events of regeneration, but that it does influence the rate of growth and the structures to be replaced.