Effects of light on the orientation of the snail Physa pomillia in a weak magnetic field
1. The orientation of fresh-water snails (Physa pomillia) in a symmetrical magnetic field was studied from February to March and from September to October, 1965, during the hours 8:30 to 17:30. 2. The orientation of the snails was studied in an augmented magnetic field, 9 times that of the earth's field at Gainesville, Florida, with a bar magnet aligned parallel and at right angles to the earth's magnetic field. Control experiments were performed with the bar magnet removed from the apparatus. Possible effects of the magnetic field were tested under two different light conditions, using a window centered above the orientation platform, and one placed above and ahead of it. 3. Under the given experimental conditions the snails showed no significant right- or left-turning. 4. The time of year did not appear to affect the behavior of the snails in the arena. 5. Snails moving in the uniformly diffuse light from the centered window scattered over the whole range of the arena. Snails in the light gradient caused by the eccentric window oriented toward the point on the floor of the arena at which the light intensity was greatest (positive phototaxis). 6. Physa pomillia did not orient with respect to the direction and strength of the magnetic fields used.
