A MAGNETIC COMPASS RESPONSE OF AN ORGANISM

¹ Department of Biological Sciences, Northwestern University, Sweet Briar College and Goucher College, and the Marine Biological Laboratory, Woods Hole, Mass.

1. The snail is able to differentiate between two weak magnetic fields, one oriented at right angles to the other.

2. The relative influence of experimental north-south and east-west oriented magnetic fields in producing dispersion of snail pathways, or effecting a magnetoklinokinesis, displays both solar- and lunar-day rhythms.

3. The relative influences of experimental N-S and E-W fields in effecting a predominantly counterclockwise snail-turning exhibits solor daily, lunar daily, and semi-monthly rhythms.

4. The solar and lunar clock-regulated discriminatory responses for magnetic fields indicate the snail to be significantly oriented as if by internal magnetic compass needles which in turn are hands of horizontal solar- and lunar-day "clocks."

5. Further arguments are advanced for concluding that organismic orientation to the earth's natural weak magnetic field is a normal organismic phenomenon.

6. Implications of this demonstrated solar and lunar "clock-compass" capacity for the well-known sun-compass" and "moon-compass" orientations of animals are discussed. Also, the insurance value of a "clock-compass" capacity as a potential navigational system for animals when deprived of celestial references, is pointed out.