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Activation of unfertilized Chaetopterus eggs by treatment with an excess of KCl may lead to the production of unicellular ciliated larvae (Lillie's differentiation without cleavage). The effects of a number of inhibitors of protein (puromycin, cycloheximide, emetin), RNA (actinomycin D), and DNA (hydroxyurea) synthesis of differentiation without cleavage and on normal development have been studied in Chaetopterus. Incorporation of radioactive leucine, uridine, and thymine has been followed by biochemical methods and by autoradiography. The DNA content of the large polyploid nucleus has been estimated by cytophotometry. The initial pseudocleavage period of differentiation without cleavage is characterized by a burst in DNA and protein synthesis; the inhibitors have little or no effect on this burst and on pseudocleavage itself. Protein and DNA synthesis levels off during the following phase (segregation), but the inhibitors become more effective. RNA synthesis is almost linear for 20 h. These results are compared with those obtained on eggs from other species.

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