Abstract
Oncomelania (Katayama) nosophora, the first intermediate host of Schistosoma japonicum in Japan, has an amphibious habit and, as noticed early by Miyagawa (1914), Sugiura (1933) and others, rarely stays in deep water. These snails are usually found in or on the moist soil just above the water edge of the brook or on moist vegetable matter above the level of water. However, when they become infected with Schistosoma cercariae, the cercariae emerge from them only when they are in water. We do not know exactly whether they actively creep into water so frequently or not, but it seems such is rarely the case. They are submerged passively in water when the water level of the brooks comes up owing to rainfalls, irrigations of rice fields and other causes, and such would be a good chance for Schistosoma cercariae to emerge from them. In such cases, the time interval during which snails are submerged in water is important. The following experiments were conducted to know the behavior of Oncomelania nosophora when submerged in water.
