Primary nucleolus and amphinucleoli in the oocytes of Patella coerulea L. (Moll. Gast.).

Electron microscope observations show in the primary nucleolus some granulations with dimensions less 70 A than those of the amphinucleoli (90 A). Even though the primary nucleolus has a high RNA content, this has not a very active turnover except at the periphery, probably in relation to the emission of 'daughter-nucleoli'. The amphinucleoli, even though they do not have RNA which is cytochemically discloseable, possess, however, RNA at a very high rate of turnover.