Maturation of the oocyte in the polytrophic ovariole of the flesh fly, Sarcophaga ruficornis was subdivided into 12 growing stages. The nurse cells increasing in volume during initial stages 1-6, shrink sharply in size from stage 7 onwards and finally disintegrate in stage 12. The oocyte continues to increase in volume till it reaches 1.2×1077 μ3 in stage 12 before ovulation. The onset of vitellogenesis is marked by the appearance of protein-containing granules in the peripheral ooplasm in stage 7. The follicular epithelial cells around the oocyte exhibit changes in their shape in different stages and perhaps facilitate as well as stop the transport of yolk precursors to the ooplasm. Finally, after the formation of egg membranes around the yolk-filled oocyte, the follicular epithelium is sloughed off in stage 12.