Color enhanced scanning electron micrograph (SEM) of an ovarian follicle. A primary follicle contains chromosomes within which are surrounded by several layers of granulosa cells. Granulosa cells are glycoproteins, which help form the zona pellucida. The zona pellucida is penetrated by the sperm during fertilization and separates the oocyte from the granulosae. While many follicles mature with each ovarian cycle, only one becomes a Graafian follicle, releasing its oocyte during ovulation. Magnification: 90x.