[Characteristics of the uptake of precursors into the developing egg of Nereis virens Sars].

The incorporation of 3H-thymidine, 3H-cytidine, 3H-adenine and 3H-glycine in the egg prior to insemination, as well as during the period from insemination up to 16 blastomeres, was investigated in a polychaete Nereis virens. The above compounds were shown to accumulate in the egg against the concentration gradient. Following the insemination the egg permeability falls sharply. This phenomenon coincides in time with the massive transport of substances from the egg resulting in the formation of gelatinous envelope. Within 2 hrs following the insemination, the egg permeability is restored up to the initial level. During the first four cleavage divisions, the activity of transport of the above substances suffers periodical changes, the maximum level of transport being timed to telo- and early interphase.