Rheotaxis and chemoreception in the freshwater snail biomphalaria glabrata (say): estimation of the molecular weights of active factors.

1. Dilute solutions of lettuce and wheatgerm extracts trigger positive rheotaxis in the freshwater snail, Biomphalaria glabrata. This response can be used as the basis of a sensitive bioassay for characterizing and identifying the chemicals to which the snail is attracted. 2. Using ultrafiltration techniques a range of different molecular weight fractions could be attenuated or removed from these extracts. By comparing the activity of these solutions with that of the original extract an estimate of the molecular weight of the attractant could be made. 3. In both cases the molecular weights of the attractants were estimated as being greater than 1000. Those in the lettuce were estimated at lying between 1000 and 10,000; whereas for wheatgerm the values were slightly higher and lay between 10,000 and 40,000. The ecological significance of these results is discussed.