The sperm head structural organisation of the koala and hairy-nosed wombat, and the effects of varying
concentrations of the ionic detergent, Triton X-100, on its component parts, were determined by electron
microscopy. Although alike in form between the 2 species, the sperm nucleus of the former, but not the
latter, had nuclear vacuoles and appeared to be more easily dispersed by the Triton X-100. The structure of
the acrosome of the spermatozoon was similar between the 2 species and, in both, previously undescribed
thin posterior and lateral segments were found to be present. It is suggested that this thin segment may
facilitate sperm-zona and/or sperm-oolemma binding and fusion.
