AN ORIENTATIONAL RESPONSE TO WEAK GAMMA RADIATION

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Abstract
The planarian worm, Dugesia dorotocephala. responds to gamma (Cs137) sources when the intensity is no greater than 6 times background. The worms turned away from the gamma sources, whichever side they were presented, when traveling north or south, but not when traveling east or west. The worms could also distinguish among four gamma strengths, 1 1/2, 3, 6, and 9 times background by showing graded degrees of turning from the sources. A monthly rhythm was apparent in the response, the worms turning from the sources for four days before new and full moons and toward them for two days afterwards. The relations of the response to geographic orientation and to lunar period suggest a possible role of this responsiveness for biological clocks and compasses.