The female urogenital system of Trichosurus vulpecula (Marsupialia).

Abstract

This paper is based on measurements from 1000 female specimens. In a stable population, summer anoestrus was followed by oestrus in April-May. Post-partum oestrus did not occur. Juvenile females frequently came into oestrus at 12 months of age but they did not necessarily rear young. The septum which initially divides the vaginal sac is usually perforated shortly before sexual maturity is attained, but entire septa may be found in females of any age. The sac in trapped, wild animals is greatly enlarged during oestrus but it is small and apparently functionless during parturition. Formation of the median vaginal canal is commenced early in pregnancy. The median canal is usually unlined, but in some specimens (5 of 68) the canal carried a well-developed epithelium which was columnar anteriorly and stratified squamous posteriorly. The two types of lining originate as infundibula extending from the vaginal sac and the urogenital sinus respectively. The epithelium appears to organize canal formation, but it is not required in a protective capacity, and no evidence suggests that it facilitates parturition. Omission of the epithelium seems to be an evolutionary advance and, in the usual absence of median canal lining, canal organization is probably relegated to terminal epithelia of the median sac and the urogenital sinus. The lateral canals open widely during oestrus, providing for transmission of semen. During pregnancy they become constricted or sealed posteriorly, and are usually closed during dioestrus and anoestrus, separating the reproductive system from the urinary one. In principle, the lateral canals and the median canal are similar in their initiation (both types originating from evaginations of anterior and posterior epithelia) but their development differs through heterochrony, formation of the median canal being retarded. However, the canals differ also in their reactions during late pregnancy when the lateral canals close as the median one opens.