[On the diversity of the primary steps of embryonic development in the caudate amphibians]

Literary data on the peculiarities of the egg cleavage process in various representatives of the order of caudate amphibians consisting of 10 families have been considered. It has been recognized that in considerable number of species of Plethodontidae, Cryptobranchidae, and some other families, the synchrony of divisions is lost already after the 8-celled stage of the cleavage in large, yolk-rich and unpigmented eggs. A"standard" cleavage of early embryos of caudate amphibians, which had been described in the text-books on developmental biology and consists approximately of 10 synchronous divisions of comparatively small eggs, is characteristic only of the families Ambystomatidae and Salamandridae including 19.3% of species within the order Caudata. However, within each of these families there seems to be a number of species with a "nonstandard" type of early cleavage. The evolutionary relationships between two main types of early embryogenesis within the order Caudata are discussed.