Tail Regeneration in the Geckonid Lizard,<i>Sphaerodactylus</i>

Abstract

ABSTRACT Tail regeneration in the Geckonid Lizards Sphaerodactylus goniorhynchus and argus is described. The rate of growth of a first regenerate, after a latent period of 10–12 days, is about 0·47 mm. per day. Subsequent regenerates grow more slowly. The tissues of the new tail are derived from a regenerative blastema which is formed beneath the epidermis covering the broken surface of the tail. A flaskshaped outgrowth of the ependymal epithelium is a centre for the proliferation of new cells. The outer part of the regenerative blastema is a zone of myogenesis, which becomes divided into the same number of muscle bands as in the original tail. Each muscle band becomes segmented, and motor nerves enter the intersegmental planes. At these sites a positive reaction for esterases is first seen. Multinucleate muscle fibres, which stretch from one intersegmental plane to the next, arise by the fusion of myoblastic cells. The regenerate is innervated by branches of the last three remaining pairs of spinal nerves. These branches keep pace with the growth of the regenerate, and form longitudinal nerves. Their terminal fibres enter the new ectoderm on the 4th day. Nitrogen mustard applied in solution to the outer surface of the regenerating area may inhibit, or slow down, the new growth. Degeneration of each type of cell within the regenerate is caused by nitrogen mustard, but melanocytes become more abundant than normal. A regenerate subsequent to one inhibited by nitrogen mustard grows as fast, or even faster, than a normal first regenerate, and again contains an excess of melanocytes.