INVESTIGATING the cause of the deaths of practically 100 per cent of the freshwater trout in an open storage reservoir in South Wales in 1942, J. B. Duguid and Edith M. Sheppard (J. Path, and Bact., 56, 73; 1944) found that they were due to general peritonitis caused by the plerocercoids of a tapeworm belonging to the family Diphyllobothridæ. Hundreds of these flatworms, 1–10 cm. long, were found burrowing in the peritoneal tissues. The sticklebacks (Gasterosteus aculeatus) in the same reservoir were also infested.