ULTRASTRUCTURAL STUDIES ON PREOVULATORY FOLLICLE IN MOUSE OVARY

The preparation of the ovulation gap in the preovulatory follicle in the mouse ovary occurs within 1-2 hours before ovulation. The luteinization of the granulosa cells which starts about 1/2 hour before ovulation, includes changes of the E. R. from a granular to an agranular form. The mitochondrial cristae change from a laminar to a tubular form; accumulation of glycogen-like granules and intermingling of theca- and granulosa cells by cytoplasmic protrusions. The ovulation gap forms by a successive degeneration of the cell layers in the apex, except the granulosa layer, starting in the outermost layer, the epithelium. The cell degeneration is always proceeded by a marked bulging of the E. R. which results in the disintegration. The last event which must occur before the ovulation hole is formed is a separation of the cells in the single granulosa layer, which separates the follicle fluid from the peritoneal cavity. © 1969 Springer-Verlag.