A description is given of the development of the nucleoli of the ovarian nurse cells of Drosophila melanogaster during stages 7 through 10 of oogenesis. This developmental period lasts about a day, and during it the volumes of the nurse cell nucleolus, nucleus and cytoplasm all double once every 4–5 hours. The nucleolar bodies within the endopolyploid nurse cell nucleus grow until they form a thick network that is shaped like a shell whose outer boundary lies close to the inner surface of the nuclear envelope. RNA of nucleolar origin continually enters the cytoplasm. The nuclei of the nurse cells directly connected to the oocyte are most active in terms of DNA replication and RNA transcription. The nurse cells empty their cytoplasm into the oocyte which doubles its volume every 2 hours. The ribosomes stored in the ooplasm are derived almost exclusively from the nurse cell. The doubling time for the rDNA of the nurse cells is about 9 hours, and about 1,000 rRNA molecules are transcribed per rDNA cistron per hour during vitellogenesis.