A COMPASS DIRECTIONAL PHENOMENON IN MUD-SNAILS AND ITS RELATION TO MAGNETISM

Abstract

Nasaarius obsoletus in an unvarying field of illumination distinguished between geographic directions as the field was rotated to the various directions. This was shown by quantifying their tendency to alter their initial path direction. A comparable change with direction of a rotating horizontal 5-gauss field, while geographic direction remained constant, was also obtained. In each instance this latter change with simulated magnetic directional change was the opposite of that seen for the equivalent geographic direction. It is postulated that the sign of the natural magnetic response is reversed by the stronger experimental field as has been reported elsewhere for planarians. A conclusion that geomagnetism is a major element in this directional response was given strong support by finding a characteristic monthly modulation in the directional response pattern, and then discovering that a fully comparable monthly modulation occurred for the magnet-simulated directional changes.