الفهرس 
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Abstract
The freshwater gastropod snails, especially these act as intermediate hosts of some species of trematodes or parasites represent the most obvious group of animals and became very important for many peoples care of different biological events due to their medical and economical importance.
The present work included some factors affecting some physiological and biological aspects of four species of freshwater gastropod snails in Egypt, these are Biomphalaria alexandrina the intermediate host of Schistosoma mansoni, Lymnaea natalensis which transmit fascioliasis; Physa acuta, which not affecting by any kind of trematodes or parasites and Lanestis carinatus snails which may infected by xiphidiocercariae. Physa acuta and L. carinatas snails were used as control snails for laboratory work conditions.
The effect of parasitism or infection on the physiological status of the snails was studied as count of heart beats under laboratory conditions. The current work indicated that:
1- Small freshwater snails more active and faster than large snails. Physa acuta snails the most active and the fastest snails.
2- The pattern of movement was studied for B. alexandrina snails, and it was considerably straight line with S-shape movement pattern at turns. While, the movement pattern of uninfected L. natalensis snails was more or less u shaped....