RESPONSES OF THE PLANARIAN, DUGESIA, AND THE PROTOZOAN, PARAMECIUM, TO VERY WEAK HORIZONTAL MAGNETIC FIELDS

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Abstract
Flatworms, Dugesia dorotocephala, initially directed northward in an unchanging light field display a monthly rhythm during fall and winter in their tendency to veer from this path. This rhythm gradually becomes transformed to semimonthly in spring and summer. The monthly rhythm is weakened by a right-angle horizontal magnetic field of 4 gauss, and abolished by a parallel 4-gauss field. The tendency to turn varies with both compass-direction the apparatus is directed and the direction an imposed horizontal 10-gauss field is oriented. The worms are demonstrated to possess the capacity to resolve small differences in orientation of a 5-gauss horizontal field. The response to an artificial field reverses sign in passing from a field of 5 or less gauss to one of 10 gauss. Briefer experiments suggest that the protozoan, Paramecium caudatum, similarly is highly sensitive to very weak magnetic fields and orientations of its horizontal vector. It is concluded that the living system is not only sensitive to geomagnetism, but possesses an astounding capacity to distinguish its vector direction.

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