In the course of a study on the life cycle of the mammalian lung fluke (Paragonimus), the meat of some fresh-water crabs, Potamon (Potamon) sp., collected in Naga, Camarines Sur, Luzon, in July, 1941, and found harboring encysted Paragonimus metacercariae, was fed to six white laboratory rats. Two of the rats were killed nine weeks after infection and on autopsy they were found to be infected not only with lung flukes but also with adult trematodes which have been identified as belonging to the genus Plagiorchoides Olsen, 1937. Control rats that were not given any crab meat remained free of trematode parasites, thus proving that the experimental animals derived their fluke infections from the crustaceans.