In attempts to arrange the digenetic trematodes into a natural classification, various workers have emphasized different aspects of the life history. Thus, in recent years major reliance has been placed on adult anatomy by Yamaguti, on details of germinal development in the germinal sacs by Cort, Ameel, and Van der Woude, on morphology of the body and host-parasite relationships of the cercarial stage by Cable, on embryology of the excretory bladder and ducts by LaRue, and on occurrence of sporocyst or redia stages in the first intermediate host by Odening. Although the miracidium is a relatively neglected stage in the life history of digenetic trematodes, as noted by Seitner, the detailed morphology of that stage is known for a representative number of species, and the use of miracidial epidermal cell patters in trematode taxonomy at or even above the familial level was suggested some time ago by Price and by Bennett.