Morphological examination of epididymal epithelium in the mule (E. hinnus) in comparison with parental species (E. asinus and E. caballus).

Following previous studies about the ultrastructure of male genital tract in parental species, a comparative study of epididymis of one of the possible hybrids, the mule, has been undertaken. Apart from small differences, general features of epididymal epithelium in the mule are similar to those of parental species. However, extension of our studies from the donkey to the horse to the hybrid permits a deeper insight into the morphology of this tract of excurrent duct. In the meantime, it is possible to evidence some features, sometimes shared with other species if taken separately, which in the whole characterize the epididymis in Equidae: the presence in principal cells of intranuclear inclusions and peculiar small granules in the basal cytoplasmic edge; the organization of groups of cells, likely to be principal ones, in such a way as to constitute intraepithelial crypts; a cumbersome presence of lipofuscinic matter all along the epithelium. Another interesting observation in the presence in the mule epididymis of well recognizable macrophages. All these data are discussed in comparison with parental species and with other species described in literature. Beyond any other consideration, it can be outlined that the complex morphology of the epithelium lining ductus epididymis in the mule is unaffected by the absence of spermatozoa, which are normally the target of the manifold functions of the epithelium itself.