<P> The shape of the urethral grooves of the males' genitalia is used to distinguish between Monodelphis brevicaudata, Monodelphis domestica, and Monodelphis americana . The grooves form 2 separate channels that form the ventral and dorsal folds of the erectile tissue . Several species of dasyurid marsupials can also be distinguished by their penis morphology . </P> <P> The only accessory sex glands marsupials possess are the prostate and bulbourethral glands . There are no ampullae, seminal vesicles or coagulating glands . The prostate is proportionally larger in marsupials than in placental mammals . During the breeding season, the male tammar wallaby's prostate and bulbourethral gland enlarge . However, there does not appear to be any seasonal difference in the weight of the testes . </P> <P> Female marsupials have two lateral vaginas, which lead to separate uteri, but both open externally through the same orifice . A third canal, the median vagina, is used for birth . This canal can be transitory or permanent . </P> <P> Marsupials give birth at a very early stage of development; after birth, newborn marsupials crawl up the bodies of their mothers and attach themselves to a nipple, which is located on the underside of the mother, either inside a pouch called the marsupium, or open to the environment . There they remain for a number of weeks, attached to the nipple . The offspring are eventually able to leave the marsupium for short periods, returning to it for warmth, protection, and nourishment . </P>

All of the following refer to the period before birth​ except