Abstract
1. Some aspects of the influence of position on regeneration have been examined by comparing regeneration from two different levels along the newt forelimb. 2. We have defined a series of stages of forelimb regeneration in the newt,Notophthalmus viridescens, in order to facilitate this study. 3. Limbs amputated at either a proximal level (through the humerus) or a distal level (through the radius and ulna) pass through the same stages at the same times after amputation. 4. The histological sequence of events of digit regeneration was compared with that of limb regeneration from a proximal level of amputation and was found to be the same. 5. In limbs amputated at either proximal or distal levels, the rate of elongation of regenerates is the same during the phases of dedifferentiation, blastema accumulation, and blastema growth. 6. During the phase of differentiation and morphogenesis, the rate of elongation of regenerates from the proximal level is significantly greater than that of regenerates from the distal level. 7. The total length of regenerates from proximal and distal levels along the limb is significantly different. 8. The results indicate that positional information does not influence the developmental sequence of events of limb regeneration, but that it does influence the rate of growth of the regenerate and the specification of the structures to be replaced.
Highlights
A number of other factors, including temperature (Ellis, 1909; Maderson and Licht, 1968; Schmidt, 1968), light cycle (Maderson and Salthe, 1971), and season of the year (Schauble, 1972), have been shown to influence both the extent and the rate of regeneration in vertebrate appendages. It is unclear whether body size or ageing in adult urodeles has any influence on the rate of limb regeneration
According to Manner', Zapisek, and Vallee (1960), body size has no apparent influence on the rate of elongation of regenerate limbs; according to Goodwin (1946), ageing in adult urodeles has no apparent imfluence on the rate of regeneration
In the experiments reported in this paper, the temperature and light cycle were kept constant, all animals regenerated their limbs at the same time of the year, and all animals were within the smallest category used by Pritchett and Dent (1972)
Summary
Male and female adult newts, Notophtha~mus (Triturus) viridescent, were maintained in spring water at a constant temperature of 25~ C and a 12 hour light cycle. For the establishment of normal stages, forelimbs were bilaterally amputated through the distal third of the humerus. The external morphological changes taking place during forelimb regeneration of between 28 and 50 regenerating limbs were observed every other day; camera lucida drawings of another 28 regenerating limbs were made at foul day intervals. The limbs of 23 newts were amputated through the distal third of the humerus and between three and six limbs were placed in Bouin's fixative at each normal stage. Serial longitudinal sections of limbs were stained with either Maycr's hematoxylin and eosin or I-Ieidenhain's aniline blue
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