If the normal molluscan host of Fasciola were a species of Lymnaea it should be possible readily to produce experimental infection in that species. Although adult flukes have been reared from larvae found naturally in different species of Lymnaea in various countries, great difficulty has been experienced in producing experimental infection of these same species of Lymnaea. In fact, although the factors governing the successful completion of the life cycle are not known, the ease with which, according to text-books, the cycle may be followed experimentally, is contrary to experience in both Europe and warmer climates.