Structure of control and oestrogen-cultured gonads. Oestrogen-cultured XY gonads developed ovarian-like cortical and medullary structures with germ cells distributed at the periphery of the cortex (arrowhead), while control gonads developed normal testicular architecture with germ cells confined to testis cords. Gonad plus mesonephros (meso)complexes were sectioned at 8 μm and stained with Mallory's triple stain. Top: Gonads cultured in control media. Bottom: Gonads cultured in the presence of oestrogen. Control XY gonads have normal male development with the formation of seminiferous cords (SC; outlined by dashed line) delineated by a basal lamina (stained dense blue) with the germ cells contained within these structures. Oestrogen-treated XY gonads formed a cortex (C) which contained germ cells and a central medulla (M), resembling the normal ovarian architecture of equivalent stage XX gonads.