Oogonium

An oogonium (plural oogonia) is a small diploid cell which on maturation forms a primordial follicle in a female fetus or the female gametangium of certain thallophytes.

In the mammalian fetus

Oogonia are formed in large numbers by mitosis early in fetal development from primordial germ cells. In humans they start to develop between weeks 4 and 8 and are present in the fetus between weeks 5 and 30.

Structure

Normal oogonia in human ovaries are spherical or ovoid in shape and are found amongst neighboring somatic cells and oocytes at different phases of development. Oogonia can be distinguished from neighboring somatic cells, under an electron microscope, by observing their nuclei. Oogonial nuclei contain randomly dispersed fibrillar and granular material whereas the somatic cells have a more condensed nucleus that creates a darker outline under the microscope. Oogonial nuclei also contain dense prominent nucleoli. The chromosomal material in the nucleus of mitotically dividing oogonia shows as a dense mass surrounded by vesicles or double membranes.