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As marsupials, female opossums have a reproductive system that includes a bifurcated vagina and a divided uterus; many have a pouch. [29] The average estrous cycle of the Virginia opossum is about 28 days. [30] Opossums do possess a placenta, [31] but it is short-lived, simple in structure, and, unlike that of placental mammals, not fully ...
Being a marsupial and at the same time an aquatic animal, the water opossum has evolved a way to protect its young while swimming. A strong ring of muscle makes the pouch (which opens to the rear) watertight, so the young remain dry, even when the mother is totally immersed in water. [6]
A pouch is present in most species. Many marsupials have a permanent bag, while in others such as the shrew opossum the pouch develops during gestation, where the young are hidden only by skin folds or in the maternal fur. The arrangement of the pouch is variable to allow the offspring to receive maximum protection.
The water opossum and the now extinct Tasmanian tiger are the only two marsupials where the male also has a pouch (in order to protect their genitalia while swimming). [ 7 ] Some marsupials (e.g. phascogales ) lack the true, permanent pouches seen in other species.
Females have a gestation period of 16–18 days, after which they give birth to single young. [7] [8] A newborn brushtail possum is only 1.5 cm (0.6 in) long and weighs only 2 g (0.07 oz). As usual for marsupials, the newborn may climb, unaided, through the female's fur and into the pouch and attach to a teat.
Big lutrine opossums have two breeding periods per year resulting in litters of 7–11 offspring. Like most marsupials, litters are born into a pouch and are fed via lactation until the offspring is developed enough to leave the pouch. Gestation lasts approximately two weeks and young are weaned off mother's milk at around three months.
The common opossum (Didelphis marsupialis), also called the southern or black-eared opossum [2] or gambá, and sometimes called a possum, is a marsupial species living from the northeast of Mexico to Bolivia (reaching the coast of the South Pacific Ocean to the central coast of Peru), including Trinidad and Tobago and the Windwards in the Caribbean, [2] where it is called manicou. [3]
Like several other marsupials, they do not have a pouch, and it appears that females do not carry the young constantly, possibly leaving them in the burrow. [4] Largely because of their rugged, inaccessible habitat, they are very poorly known and have traditionally been considered rare.