Light microscopical structure of the excurrent ducts and distribution of spermatozoa in the Australian rodents Pseudomys australis and Notomys alexis.

The light microscopical structure of the male excurrent ducts and the distribution of spermatozoa were examined in two species of Australian rodents, the plains rat, Pseudomys australis, and the hopping mouse, Notomys alexis. In plains rats the microstructure of the ductus epididymidis and ductus deferens was similar to that of the common laboratory rodents, with the majority of the spermatozoa being found in the cauda epididymides. By contrast, in the hopping mouse, the structure of the cauda epididymidis differed significantly as the height of the epithelium and stereocilia did not decrease from the distal caput to the cauda region, and luminal diameter did not increase markedly along its length. In addition, few spermatozoa were stored in the cauda region of the tract, and as many as 60% were located in the ductus deferens, the distal portion of which displayed a highly infolded epithelium and underlying lamina propria. These differences in histological structure of the hopping mouse excurrent ducts presumably reflect divergence in function of the various regions of the tract. Although the functional implications of the present findings remain to be determined, this study demonstrates the considerable plasticity in the male excurrent ducts amongst the hydromyine rodents of Australia.