Ovarian follicles. Coloured light micrograph of a section through an ovary (orange), showing three primary follicles (pink). At the centre of each follicle is the large nucleus of the developing egg (oocyte, pale pink). Surrounding the egg are cuboidal follicular cells (dark pink). At birth there are tens of thousands of primordial follicles, the precursors to primary follicles, present in the ovaries. Once sexual maturity is reached, up to 20 primordial follicles are triggered to start developing into primary follicles every menstrual cycle. Only one will reach full maturity and release its egg (ovum) at ovulation. Magnification: x60 when printed 10cm wide