TAIL MELANOPHORES OF XENOPUS IN NORMAL DEVELOPMENT AND REGENERATION

¹ Department of Zoology, University of Arizona, Tucson, Arizona

1. The peculiar light-sensitive melanophores in the ventral fin of Xenopus larvae first appear about stage 47. Gradually, pigmentation increases in the distal half of the fin, but the proximal portion remains free of melanophores throughout the larval period. New melanophores first become visible at the fin edge, with an apparent gradient of melanophore differentiation from somite to edge. The young melanophores are thin and elongated, but as differentiation proceeds they add new projections and become stellate. Even the youngest melanophores exhibit some degree of tail darkening in the absence of light, but the strongest response is displayed by the fully formed melanophores.

2. Four days after tail extirpation, melanophores are seen in the regenerating ventral fin. Pigmentation returns to all of the ventral fin except for a margin along the fin edge, with a "somite-to-edge" gradient again apparent. The new melanophores are of the typical tail fin type and are fully light-sensitive.

3. Melanophores on the dorsal surface differ markedly from those on the tail. The former are heavily pigmented and are apparently more sensitive to the chromatotrophic hormone than the latter. Dorsal melanophores contract upon exposure to darkness and expand in the light. They are less reactive to changes in illumination than the tail fin melanophores.