The germinal masses in the mother and daughter rediae of Triganodistomum mutabile were found to be unusually large and complex as compared with those in the other groups that have been studied. In this species the cercariae, which are without a tail and which have adult structures unusually well developed, are very large in proportion to the size of the daughter rediae, and only a comparatively few cercariae and developing embryos are present in these rediae. In spite of this, the large number of daughter rediae in an infected snail and the persistence of the large germinal masses provide for the production of large numbers of individuals. The large germinal masses attached at the posterior end of the rediae of this species resemble the floating germinal masses of the daughter sporocysts of the Plagiorchioidea, and add to the evidence that the Lissorchiidae are related to this group. The adult of T. mutabile resembles so closely that of Lissorchis fairporti Magath, 1917, that the two forms appear to be closely related. The fact that the larval stages described for these two species are so entirely different, suggests that the xiphidocercaria that Magath assigned to L. fairporti is not really the larval stage of this species.