[Effect of actinomycin D and sibiromycin on the embryonic and larval development of Nereis virens (Sars.)].

The morphogenetic function of nuclear apparatus has been studied by means of "chemical enucleation" using actinomycin D (60 microgram/ml, 3 hrs) and sibiromycin (10--100 microgram/ml, 3 hrs) at different developmental stages of Nereis virens (Sars.). The embryos were subjected to the effect of the inhibitors at the successive stages every 6 hrs beginning from the fertilization. The development proceeded in the normal way til the throchophore stage in spite of the inhibition of DNA-dependent RNA synthesis what agrees with the concept of P. P. Ivanov on the existence in Polychaeta of a developmental tendency to trochophore. The first period of morphogenetic activity of the genome which ensures the transition from trochophore to metatrochophore coincides with the gastrula stage and the second period which ensures the transformation of metatrochophore into nectochaete with the final phases of the trochophore stage.