The determination of ectodermal derivatives in various species of amphibia

The process of labyrinth determination has been studied in amphibians (three Urodela and seven Anura species) using homoplastic transplantation of ear ectoderm, containing labyrinth material onto the abdominal wall of embryos of the same stage of development. The stage of appearance of organ-specific properties in ear ectoderm was determined and the increase of these properties in the course of development was observed. The frequency of ear vesicles formation, the level of their differentiation and their size served as criteria. These criteria allow to align the studied species into a row, where organ-specific properties appear earlier and most completely in representatives of Ranidae family and in Bufo viridis, and weakest, in smooth newt. A comparison of properties of labyrinth material and other areas of ectoderm allowed to conclude that specific differences in determination of different ectodermal primordia are based on specific peculiarities of the whole ectoderm. The appearance of these differences can be explained by the shift in the beginning of gastrulation towards later stages of cleavage during the evolution of amphibians.