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

¹ Department of Biological Sciences, Northwestern University, Evanston, Illinois

1. The orientational response of the planarian, Dugesia, at a given time of solar day undergoes what appears to be a semi-monthly or monthly fluctuation, probably a consequence of the possession of a lunar-day rhythm in response to some compass-directional factor.

2. The monthly rhythm in Dugesia is modifiable by a weak magnetic field.

3. The monthly rhythm appears to undergo an annual modulation.

4. Dugesia exhibits a response to weak magnetic fields in the range of 0.17 to 10 gauss.

5. Dugesia differentiates between a horizontal field parallel to the long axis of the body and a field at right angles, and between N and S poles, and, furthermore, is able to resolve intermediate angular orientations of field with remarkable precision.

6. The response of Dugesia alters its character in passing from a field close to the earth's strength to one as little as 10 gauss, suggesting the perceptive mechanism to be specifically adapted to such a weak field as the geomagnetic one.

7. There is suggestive evidence that the protozoan Paramecium also responds to very weak magnetic fields.

8. Some possible roles for organisms of such astounding responsiveness to very weak magnetic fields are discussed briefly.