Development of the male urogenital system of the koala phascolarctos cinereus.

This paper described several developmental stages of the male urogenital system in the koala Phascolarctos cinereus, employing both light and scanning electron microscopy. There are few studies of the development of the urogenital system in male marsupials. Findings by White and Timms (1994) that male koalas can be infected with Chlamydia psittaci emphasise the importance of studies on male animals and in particular their reproductive system. Specimens in our study ranged in age from 15 days postnatal to adults. Due to the rarity of such specimens, details of each specimen are linked to the changes of the structures at each available stage. Light microscopy revealed that differentiation of the gonads had commenced by 15 days postnatal and that the cytological arrangements of the urogenital system are essentially the same as those of other mammals. Scanning electron microscopy revealed stereocilia and microvilli along the lumen of each ductus epididymis and cilia and microvilli along the lumina of the vasa deferentia and urethra. The development of these structures coincided with the onset of sexual maturation, sperm production and differentiation at about three years of age.