Particulars on the life history of fresh-water pulmonates are generally scarce, especially in Europe, notwithstanding the fact, that they can as a rule be collected without much difficulty. Most fresh-water snails act as the first intermediate hosts of digenetic trematodes, worms which may cause dangerous diseases like schistosomiasis and liverrot to man and cattle. Because of the direct interest for their object of study a number of parasitologists have traced the life cycles of the Lymnaeidae: Lymnaea truncatula (Müll.) (WALTON, 1918; WALTON & JONES, 1926), Lymnaea brazieri (Smith) (Ross & MCKAY, 1929), Fossaria modicella (Say) (VAN CLEAVE, 1935), Acella haldemani (Desh.) (MORISSON, 1935), Stagnicola emarginata angulata (Sow.) (CORT, MCMULLEN, OLIVIER, and BRACKETT, 1940), Lymnaea stagnalis var. lillianae F. C. Baker and var. sanctae mariae Walker and Stagnicola palustris elodes (Say) (BRACKETT, 1940), of the Planorbidae: Australorbis glabratus (Say) (LUTTERMOSER, 1943) and finally of the Physidae: Physa parkeri Currier (CORT, OLIVIER, and MCMULLEN, 1941).