Explanation

No more oogonia are formed and added after birth. Oogonia (egg mother cells) divide by mitosis forming primary oocyte. Each primary oocyte then gets surrounded by a layer of granulosa cell called primary follicle. A larger number of these follicles degenerate during the phase from birth to puberty. Therefore, at maturity only 60,000-80,000 primary follicles are left in each ovary