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To elucidate the changes and differences in Schistosoma mansoni infected snails, Biomphalaria glabrata, during the process of estivation, the growth rate, survival rate, and histopathological findings were observed during the 22 weeks experimental period. Two groups of snails, each group consisted of 36 snails, were used for the present experiment. One group of snails carrying S. mansoni infection (Group Ⅱ) was underwent 18 weeks of estivation while other group of S. mansoni infected snails was applied as control group (Group Ⅰ) and reared in the water. The results obtained were as follows: 1. The growth rates (increase in shall diameter and wet weight) of estivating snails (Group Ⅱ) were consistently lower than those of their control snails (Group Ⅰ) kept in water. 2. The growth rates rose rapidly when the estivating snails were put into water for 4 weeks, after 18 weeks of estivation. No shedding of cercariae was observed among those exposed, estivating snails, when they were put into water again. 3. The survival rate of estivating snails (Group Ⅱ) was lower than their control (Group Ⅰ) from the beginning to 13th week of experiment, but since then they showed little difference. 4. The histopathological changes were observed in the hepatopancreas, ovotestes, seminal vesicle, kidney and restal ridge of above snails which belong to both Group Ⅰ and Group Ⅱ. In general, the reduction of parenchyme and degenerative pictures were prominently observed during the estivation (Group Ⅱ), whereas destructive and degenerative pictures by the compression of invaded cercariae were monitored in control snails (Group Ⅰ).
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