The development of th emiracidium, three generations of rediae, and the cercaria was followed from a single germinal cell to fully developed individuals. The germinal cells in each stage were found to be in direct lineal descent from the fertilized ovum. The germ cells of the adult undergo maturation and fertilization in a manner similar to that found in other trematodes. A single germinal cell, lying in the posterior part of the developing miracidium, divides into an ectodermal cell and a propagatory cell. The cells resulting from the division of the ectodermal cell form the body of the single first generation redia which contains the descendants (germinal cells) of the propagatory cell. Each of these germinal cells gives rise toa second generation redia, and the germinal cells in the body cavity of the latter give rise to third generation rediae. The germinal cells in the third generation rediae form cercariae by a process of embryonic development similar to that found in the preceding generations. The propagatory cell in the cercarial embryo divides repeatedly to form the genital primordium of the adult. The germinal cells are distinguishable from the somatic cells by their slightly larger size, their clear nuclei which contain one or two large densely staining nucleoli and clumps of chromatin along the nuclear membrane. No structures which could be interpreted as ovaries or testes were found in any of the redial generations. In all generations, the diploid number of chromosomes, counted in the