[The effect of aphidicolin on trochoblast differentiation in the early ontogeny of polychaetes]

The differentiation of trochoblasts in Nereis virens and Platynereis dumerlii embryos was investigated during different periods of time after fertilization by means of the DNA replication block. It was shown that the quantal cycle of ciliogenesis is not connected directly with the time of primary trochoblast founder cell formation. Development of the cilia on trochoblasts in P. dumerlii needed normal DNA replication at the fifth cycle. Ciliogenesis in N. virens completely stopped after the inhibition of replication of the fourth cycle and only partly when the fifth and sixth rounds of DNA replication were affected. The data obtained are discussed from the standpoint of Newport and Kirschner's depletion hypothesis.