DEVELOPMENT OF THE TECTUM IN GYMNOPHIONES, WITH COMPARISON TO OTHER AMPHIBIANS

Tectal development in a number of caecilian (Gymnophiona: Amphibia) sp ecies was examined and compared with that in frogs and salamanders. Th e caecilian optic tectum develops along the same rostrocaudal and late romedial gradients as those of frogs and salamanders. However, differe nces exist in the time course of development. Our data suggest that, a s in salamanders, simplification of morphological complexity in caecil ians is due to a retardation or loss of late developmental stages. Dif ferences in the time course of development (heterochrony) among differ ent caecilian species are correlated with phylogenetic history as well as with variation in life histories. The most pronounced differences in development occur between the directly developing Hypogeophis rostr atus and all other species examined. In this species, the increase in the degree of morphological complexity is greatly accelerated. (C) 199 8 Wiley-Liss, Inc.