What is oogenesis? Explain with the help of diagram.

Oogenesis: The process of the formation of egg within ovary is called as oogenesis. This process is also involved in the following three phases:
(1) Proliferation phase: The cells of generative layer of the ovary divides to produce follicle. A cell of the follicle enlarging to produce oogonium.
(2) Growth Phase: In this stage oogonia increase in size and form primary oocytes.
(3) Maturation phase: In this phase primary oocytes divide meiotically to produce one eggs and three polar cells.