Studies on the germ cell cycle of the digenetic trematodeParorchis acanthusNicoll

Abstract

1. The anatomy of the adult miracidium of Parorchis acanthus is described.2. Development of the miracidium and of the succeeding larval stages has been followed.3. Cleavage of the fertilized egg gives rise to an ectodermal and a propagatory cell. The former gives rise to the soma, and the latter, after contributing a few small cells to the body of the miracidium, becomes the germ cell.4. This germ cell develops in the same way into the first generation redia while still in the body of the miracidium.5. The fully formed miracidium contains a single fully formed redia when it penetrates the intermediate molluscan host.6. In the intermediate host the miracidium disintegrates and second generation rediae are formed from the germ cells in the body cavity of the parent redia.7. The germ cells in the body cavity of the daughter redia give rise to cercariae by a similar process of embryonic development to that found in preceding generations.8. The germ cells in the cercariae become differentiated into the adult genitalia.9. No evidence has been found to show that rediae or cercariae are derived from cells in the wall of the redia.10. No ovary, maturation process, parthenogenesis, or fertilization takes place in any of the larval stages, but germinal lineage is apparent throughout the life cycle.