Spermatogenesis in liver flukes, C. sinensis, was investigated by using light and electron microscopes. The epithelium of the testis was composed of a basement membrane, numerous lamellae protuded from the membrance and large number of spermatogonia supported by the lamellae. The lumen of the testis was filled with numerous 8, 16 and 32-cell groups representing primary spermatocytes, secondary spermatocytes and spermatids respectively. None of cell groups with over 32 or under 8 cells was noticed. The process of spermatogenesis is presumably as follows; A cell group of 8 spermatogonia, attached together by a cytophore, is separated from the testis epithelium during the growth period, thus becoming primary spermatocytes. The primary spermatocytes divide to form a cell group of 16 secondary spermatocytes giving rise to a cell group of 32 spermatids through meiotic germ cell division. The spermatids begin to undergo a spermiogenesis. The newly formed sperms remain attached together in the lumen for a while before migrating through the vasa efferentia.
