The structural organisation of sperm head components of the wombat and koala(suborder : Vombatiformes): an enigma amongst marsupials

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. Altho ugh alike in form between the 2 species, the sperm nucleus of the former, b ut not the latter, had nuclear vacuoles and appeared to be more easily disp ersed by the Triton X-100. The structure of the acrosome of the spermatozoo n was similar between the 2 species and, in both, previously undescribed th in posterior and lateral segments were found to be present. It is suggested that this thin segment may facilitate sperm-zona and/or sperm-oolemma bind ing and fusion.