Experiments demonstrated that infestation with the oligochaete worm, Chaetogaster limnaei, afforded a degree of protection to the snail Australorbis glabratus when the snail was exposed to Schistosoma mansoni miracidia. To a lesser extent, the oligochaetes protected snails exposed to echinostome cercariae. The presence of C. limnaei within the kidney of the snail Physa heterostropha is reported. An intimate association between the oligochaete worm Chaetogaster limnaei von Baer and various species of aquatic snails has long been recognized (von Baer, 1827), yet the nature of this relationship has not been adequately defined. Early naturalists considered C. limnaei to be a true parasite which was thought to feed upon the "slime" produced by the host. However, Wagin (1931) and subsequent investigators demonstrated that the oligochaete fed principally on microorganisms, and thus the worm has been considered a commensal. Wagin also observed that the oligochaete ingested cercariae and suggested that C. limnaei might be of value in controlling trematode transmission. While Krasnodebski (1936) confirmed Wagin's field observations and experimentally demonstrated that the oligochaete would ingest various types of cercariae, he did not believe that Chaetogaster could play a significant role in the control of trematodes. Backlund (1949) observed that cercariae of Fasciola hepatica were ingested by Chaetogaster, and Ruiz (1951) later reported a similar observation with respect to Schistosoma mansoni. Coelho (1957) noted that Chaetogaster frequently ingested S. mansoni miracidia, but commented that the worms did not protect snails from infection. How

Although the biological control of medically important snails has been suggested from time to time during the past quarter of a century (Nagano, 1927; Bequaert, 1928; Mozely, 1939, 1951; McMullen, 1952), the subject has, as yet, received but little serious consideration. Upon the initiation of our studies (Chernin, Michelson & Augustine, 1956a, b) the literature was searched for references to predators, parasites and diseases of molluscs which might furnish leads for experimental investigation.

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