Crypts of ovarian surface: false-colour scanning electron micrograph (SEM) showing two crypts (depressions) in the epithelium covering an ovary. The crypts are infoldings of the superficial epithelium into the cortex of the ovary, and are regarded as expressions of high mitotic activity (cell division) within the organ, under the influence of steroid hormones. The outer surface of the ovary is covered (in a young female) by a layer of cuboidal cells, which become flattened in later life. It is through this surface that a mature ovarian follicle ruptures at ovulation. Magnification: x570 at 6x7cm size.