Sex cells of most animals are either eggs in females (ova) or sperm in males. Eggs have the potential, when fertilized with the sperm of a male, to divide, form an embryo, and develop into an organism. In contrast to sperm, which are small, mobile, and produced in great numbers, eggs tend to be non-motile, larger, and produced in limited numbers.

Eggs are cells. That means that they contain a nucleus and cytoplasm and all of the other common cell structures. They differ from body cells, known as somatic cells, by the fact that they must eventually become haploid (having only one set of chromosomes) in preparation for fusion with the haploid sperm nucleus. The ovary is made up of diploid (having two sets of chromosomes) cells. The egg-forming ovarian cells are known as oogonia and are in fact stem cells that give rise to mature female gametes...