Ovum

An ovum is single cell released from either of the female reproductive organs, the ovaries, which is capable of developing into a new organism when fertilized with a sperm cell.

The outer surface of each ovary is covered by a layer of cells (germinal epithelium); these surround the immature egg cells, which are present in the ovaries from the time of birth. A hollow ball of cells, the follicle, encompasses each ovum. Within the follicle the ovum gradually matures. This process is called oogenesis.