Germinal Beds, Oogenesis and Folliculogenesis

Abstract

In reptiles, oogenesis occurs throughout reproductively active life, which is not the case in birds. Reptiles and birds also differ from each other in regard to the presence or absence of germinal beds in the adult ovaries. The germinal bed(s), which constitute the sites for the multiplication of oogonia and formation of primordial oocytes, occur in the ovaries of reptiles. No such structures occur in the adult avian ovary which, however, shows primordial oocytes (oocytes in meiotic prophase) in its cortex. Actually, in birds, all oogonia are transformed into primordial oocytes during embryogenesis, leaving behind no stem germ cells (oogonia) for repeating the seasonal multiplication of oogonia by mitosis.