Syntheses of nucleic acids during spermatogenesis in Nereis diversicolor (annelida polychaeta): a quantitative autoradiographic study. 
The development of DNA and RNA synthesis in the germ cell population was studied after a 3H-thymidine or 3H-uridine pulse at each stage of spermatogenesis.  The autoradiographic results show that the first sign (after 3 days in vitro) of cellular changes is an increase in RNA synthesis which reaches a maximum at day 5.  DNA replication (premeiotic S phase) occurred at day 7, then cells entered meiotic prophase (day 9).  Meiotic divisions and spermiogenesis occurred after 11 days.  Silver grain counts permit the conclusion that RNA synthesis is clearly higher during premeiotic interphase (days 3-7) than during spermatogonial proliferation (day 0).  It appears therefore that male meiotic differentiation in Nereidae is accompanied by increased RNA synthesis.