Abstract
Sperm morphology of Australian Vespertilionidae was investigated. A small spatulate-shaped head with a simple acrosome and constricted neck occurred in 6 spp. of Vespertilioninae and 2 spp. of Nyctophilinae. In sperm from a Murina spp. the sperm head was longer and a larger nucleus occurred; in Miniopterus schreibersii and even larger sperm was present in which there was a massive acrosome. The phylogenetic implications of these findings are briefly discussed.