The female gamete, required for reproduction. The ovum develops from an oogonium within the graafian follicle of the ovary and matures through the meiotic process of oogenesis. A mature ovum is about 0.13 to 0.14 mm (0.0051 to 0.0055 in) in diameter. At ovulation, the ovum is bounded by a translucent cellular membrane (the zona pellucida), which is connected to a layer of follicular cells (the corona radiata); these cells enclose the cytoplasm, nuclei, and chromatin material. The exact time during which a human ovum is capable of fertilization and further development before degenerating is not known; however, it is probably 24 hr.