Ovarian primordial follicles. Light micrograph of a section through the cortex of a neonatal ovary, showing clusters of primordial follicles each containing a single oocyte (egg cell) surrounded by a layer of follicle, or granulose, cells. The oocytes are the female germline cells. At birth in humans there may be up to one million primordial follicles in a pair of ovaries. Primordial follicles remain arrested in development until activated to enter a prolonged growth and maturation phase called folliculogenesis. In postnatal and early adult life perhaps 10-20 primordial follicles are recruited each day to enter the follicular growth process resulting in the gradual decline in their number such that at menopause, only a few hundred remain. Magnification: