Oogonium

Overview
An oogonium (plural oogonia) is an immature ovum. It is a female gametogonium. They are formed in large numbers by mitosis early in fetal life from primordial germ cells, which are present in the fetus between weeks 4 and 8.

Oogonia are present in the fetus between weeks 5 and 30.

Oogonia are also the female reproductive structures in certain thallophytes, and are usually rounded cells or sacs containing one or more oospheres.

Further development
Once the primordial germ cells have gotten to the ovary, they develop into oogonia. During week 6 of development, oogonia migrate from the yolk sac to the genital ridge ( site of the future gonads-ovaries in this case) located on the posterior abdominal wall. Oogonia develop by mitosis. However, some of them become primary oocytes, which begin meiosis which is halted in prophase I. When they have entered Prophase I of meiosis they become primary oocytes; it is important to note that this process is complete before birth, in contrast to spermatogenesis. Primary oocytes are present from week 10 until menopause at ~53 years

Oogamy
Oogamy may be spelt oögamy with a diaresis (or umlaut). The link with other articles may depend on this symbol.

Algae
This term is used in [phycology] (the study of algae) to refer to the union of the male (motile or non-motile) with the female gamete. The female oogonium is usually enlarged and develops a single ovum. The male (antheridium) usually produces many cells with flagella except in the Rhodophyta which have no flagella. There is no evidence that the red algae ever had flagella, or cilia and it is suggested that they are the most primitive eukaryotes.

Fungi
Oogonia also occur in the fungi.