[The relative duration of similar periods in the early embryogenesis of teleosts].

The absolute (in min.) and relative (in the number of tau0) duration of the periods of cleavage, epiboly and that between the onset of gastrulation and the stage of 10 pairs of somites were determined in Cyprinus carpio L., Misgurnus fossils L., Esox lucius L. and Coregonus peled Gmel. at different constant temperatures. The stability of the dimensionless characteristics for the duration of each of these periods in the species in question within the limits of optimum temperatures was shown. A comparison of the relative duration of the same periods of early embryogenesis in C. carpio, M. fossilis, E. lucius, Salmo trutta L. morpha fario and S. gairdneri Rich. has shown that in the species under comparison the relative durations of the period of synchronous cleavage divisions are similar, whereas those of the period of asynchronous cleavage divisions differ. The relative durations were found to be similar for the period between the onset of gastrulation and the stage of 10 pairs of somites in M. fossilis, E. lucius and 2 species of Salmo. Differences were revealed in the relative duration of the period of epiboly; the average relative rate of the movement of blastoderm cells toward the vegetative pole is similar in the species with the eggs of small size (C. carpio, M. fossilis, Coregonus peled) and increases with the egg size. The temporal relationships between the embryonic periods under study in the species in question and possible mechanism which determine these relationships are considered with respect to the data on egg structure, as well as on the stage when the isolated blastoderm acquires the capacity of differentiation in vitro.