There are many differences between the marsupials and the eutherian mammals, but their reproduction most clearly distinguishes these two groups of mammals (Tyndale-Biscoe and Renfree 1987). The name marsupial, which derives from the Latin marsupium, meaning purse, refers to the pouch in which the young in many marsupial species develops. Although not all species of marsupial have pouches, other reproductive features are diagnostic – these include the structure of the internal genitalia of females, and the relative positions of the scrotum and penis in males. Unlike many eutherian species, where emphasis is on prolonged gestation and well-developed young at birth, all marsupials have rapid embryonic growth periods, and give birth to relatively undeveloped young that undergo much of their development to independence during the lactation period. This fundamental aspect has profound implications for marsupials' reproductive physiology, life history and development.
Male reproductive anatomy and function
Male marsupials are often larger than females and differ in body build and coloration (Strahan 1995). This is dramatically seen in red kangaroos, where the russet-coloured males may be twice the size of the blue-grey-coloured females.
Male reproductive systems of marsupials are like those of eutherian mammals in most respects (Setchell 1977, Tyndale-Biscoe and Renfree 1987). They consist essentially of the testes where the sperm are made, a specialised duct system that conveys the sperm to the outside, and a set of secretory glands that provide the bulk of the seminal fluid.