ADAPTATION OF THE MAGNETORECEPTIVE MECHANISM OF MUD-SNAILS TO GEOMAGNETIC STRENGTH

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Abstract
-Nassarius obsoletus, permitted to emerge from a South-directed narrow corridor into an unvarying pattern of illumination, were assayed for the effectiveness of an experimentally reversed horizontal magnetic vector in inducing an alterd mean path direction. Reversals were effected at a series of strengths, 0.04, 0.1, 0.2, 0.4, 0.8, 2, 5, and 10 gauss. A sharp maximum responsiveness of the snails occurred at 0.2 gauss, the strength closest to the geomagnetic horizontal vector, indicating adaptation of the magneto-receptive mechanism to geomagnetic strength. Also, a persistent effect of the experimental magnetic fields was disclosed, lasting at least 3 to 5 minutes after field removal. Following a 3- to 5-minute exposure of S-directed animals to reversed fields stronger than the earth''s the snails, returned the the earth''s field, turned more strongly clockwise than controls, and following fields weaker than the earth''s, turned more strongly counter-clockwise.