The ovary develops from three major cellular sources:Primordial germ cells, which arise from the endoderm of the yolk sac and differentiate into the primary oogonia;Coelomic epithelial cells, which develop into granulosa cells; andMesenchymal cells from the gonadal ridge, which become the ovarian stroma.Primordial germ cells begin their migration into the gonadal ridge during the sixth week of gestation and generate the primary sex cords. Ref: Hoffman B.L., Schorge J.O., Schaffer J.I., Halvorson L.M., Bradshaw K.D., Cunningham F.G., Calver L.E. (2012). Chapter 15. Reproductive Endocrinology. In B.L. Hoffman, J.O. Schorge, J.I. Schaffer, L.M. Halvorson, K.D. Bradshaw, F.G. Cunningham, L.E. Calver (Eds), Williams Gynecology, 2e.