Spermiogenesis in the brush-tailed possum, Trichosurus vulpecula (Marsupialia). The development of the acrosome.

Acrosome development in the Australian Brush-tailed possum, Trichosurus vulpecula, displays a number of extraordinary features. This is particularly evident in the later stages of spermiogenesis, when the area of the nuclear surface bounded by the nuclear ring, and covered by the acrosome, is reduced considerable. As a result, the acrosomal material becomes located over its definitive position on the anterior third of the dorsal nuclear surface; in this process it is thrown into a series of folds, and a wide subacrosomal space is formed. Further changes around the time of spermiation result in the release of a spermatozoon in which a thin layer of acrosomal material is closely applied to the nucleus over the area of the definitive location of the acrosome, whilst its margins are greatly extended and project freely away from the nucleus. The latter feature does not appear to have been reported for the sperm of other mammals.