A polytrophic ovariole of the fleshfly, Sarcophaga tibialis Macquart, is composed of two successively maturing egg chambers, each consisting of an oocyte, an interconnected cluster of 15 nurse cells, and an enveloping layer of follicle cells. The oocyte is established at the posterior end of the egg chamber. Nurse cell differentiation is characterized by nucleolar multiplication. At 25°C the first egg generation took approximately 8 days to develop. During this period, the growth rate of the egg chamber increased with time. A dramatic increase occurred during days 4–6, and was associated with the formation of large intercellular spaces between the follicle cells as well as an accumulation of numerous yolk globules. Completion of egg-chamber development was marked by the degeneration of the cluster of nurse cells and that of follicle cells.

By employing histological techniques, it was possible to identify 11 stages of oocyte development in adult female Sarcophaga tibialis (Diptera: Sarcophagidae). Stages 1–4 were represented by the differentiation of the oocyte and the acquisition of the follicular envelope. Stages 5–9 were characterized by a considerable growth of the oocyte which occurred due to an enormous deposition of yolk in the cytoplasm, while the follicle cells were typified by large intercellular spaces. Descriptions are given of the follicle cell degeneration during stages 10 and 11, which end with membrane formation around the mature egg.