[Temporary patterns in the embryonic development of the beluga].

The data concerning the absolute and relative duration of different periods of the beluga embryogenesis are obtained and the relative durations of the same periods of embryogenesis in beluga, sevryuga (Acipenser stellatus) and sturgeon (Acipenser güldenstädti) were compared. The relative durations of cleavage, gastrulation and early organogenesis in beluga are rather stable within the zone of optimal temperatures and similar to those in sturgeon and sevryuga. In beluga the relative duration of the period between the insemination and the appearance of the 1st cleavage furrow on the egg surface and the relative duration of the second half of embryogenesis (from the formation of heart rudiment till the hatching of single larvae) are somewhat less.