Ovarian follicles. Light micrograph of a sectioned ovary, showing the egg-containing follicles (pink circles). In the foetal ovary, primary oocytes (eggs, small pink circles) begin division and are surrounded by a layer of granulosa cells (purple dots), forming primordial follicles (upper frame). No further development occurs until sexual maturity is reached. During each menstrual cycle around 15 primordial follicles are activated but usually only one matures fully, becoming a primary follicle (larger body, lower left) surrounded by several layers of follicular cells, and then a Graafian follicle, releasing the oocyte at ovulation. Magnification: x30 at 35mm size.