Top: Bipotential gonads begin to form around E10.5 (in mouse), as paired structures, on the ventromedial sides of the mesonephroi. Sry expression in the E10.5–11.5 bipotential gonad initiates testis differentiation.
Left: By E13.5, the cells of the testis are organized into two functional compartments: testis cords and the interstitial space, outside the cords. Within the testis cords, Sertoli cells surround germ cells. A basal lamina is deposited between Sertoli cells and peritubular myoid cells. The interstitial compartment contains Leydig cells and the coelomic vessel with extending branches between the cords.
Right: By contrast, further differentiation of the XX gonad is delayed. germ cells enter meiosis at around E13.5, alongside vascularization and remodelling of the ovary to form germ cell cysts. Few morphological changes are apparent in the ovary until near birth (E18.5), when ovarian follicles begin to form in the ovarian cortex.