DURATION OF AN AFTER-EFFECT IN PLANARIANS FOLLOWING A REVERSED HORIZONTAL MAGNETIC VECTOR

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

1. Planarians exhibit a significant difference between response to a reversed horizontal 0.05-gauss and a similarly reversed 4.0-gauss magnetic vector.

2. A difference between orientational behaviors in the natural field following 15-minute exposures of the worms to these two reversed field strengths persists for 20-30 minutes.

3. This after-effect decays exponentially with time.

4. Subjected to an abrupt reversal in horizontal magnetic field, an initial maximal response appears to be followed by a transient accommodation continuing for about 20 minutes. This partial accommodation is lost again completely by the end of 40 minutes. This transient accommodation appeared more evident for the weaker field during these studies.

5. It is shown that the response to the experimental magnetic field reversals varied substantially over the course of the 15-month period of the investigation, in a manner suggesting strongly the existence of relatively large influences of other uncontrolled geophysical variables, factors with biological influences of the same order of magnitude as those being investigated.