Active snails (Lymnaea stagnalis appressa) were put into fully insulated vials after their temps. had been adjusted to room conditions and were covered with water of the same temp. After an hour the temp. of the therojackets was taken. The snails were then weighed and inspection for parasitism made. On the ave. the parasitized snails raised the temp. of a small amount of water 2.7 times as high as did the healthy snails.