°卵黄囊→原始生殖细胞→初级性索 Foregut Hindgut Genital Allantois lGti Genital Hindgut Primordial ridge Heart germ cells Mesonephros Cloaca Yolk sac B Aort Meso Primordial Proliferating Paramesonephric duct Primitive coelomic epithelium sex cords•卵黄囊 → 原始生殖细胞 → 初级性索