In embryogenesis, the sex cords (primitive sex cords, primitive seminiferous cords, or gonadal cords) are structures that develop from the genital ridges that further differentiate based on an embryo's sex. After sexual differentiation, at day 49, the sex cords in females become the cortical cords, also called secondary cords. After further development, they become the ovarian follicles. The sex cords in males become the testis cords by the action of the testis-determining factor protein, which helps to develop and nourish the Sertoli cells.