Germinal development was studied in the rediae of Euryhelmis monorchis Ameel, 1938, a representative of the Heterophyidae. In immature mother and daughter rediae of this species the body cavity ispacked with embryos in graded series with the germinal cells at its posterior tip. In most of the mature and old daughter rediae examined, all the germinal cells had developed into embryos. No complex germinal masses are present as in the rediae of the Echinostomata and certain other trematode groups which can produce new embryos throughout the life of the infection. This type of germinal development in E. monorchis, which is like that described by Cable for another heterophyid, C. lingua, indicates that the multiplication of germinal cells is limited to the early development of the rediae. This is also characteristic of the amphistomes and notocotylids. This similarity in germinal development, and the fact that the cercariae require a period of growth outside the rediae in the tissues of the snail to complete their development, suggests the possibility that the Heterophyidae may be a rather primitive group related to the amphistomes.