Eutherian or placental mammals have reproductive systems typified by that of the rabbit. The erectile penis (1) is inserted into the female vagina (2), and sperm is emitted from the testes (3). This enters the uterus (4) to fertilize ripe ova descended from the ovaries (5). Urinogenital tracts (2, 6), separate from the rectum (7), replace the primitive cloaca.
Eutheria, the placental mammals, is a subclass of the Mammalia except those classified in the Monotremata and Metatheria (marsupials) and in which the fetus is nourished in the womb attached to a highly organized placenta until a comparatively late stage in its development. Eutheria are included in the orders: Insectivora, Rodentia, Edentata (see edentate), Lagomorpha, Carnivora, Artiodactyla, Perissodactyla, Cetacea (see cetacean), Hyracoidea, Proboscidia, Sirenia, Chiroptera, and primates.