. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Vol. 128, No. 3 June, 1965. THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY DURATION OF AN AFTER-EFFECT IN PLANARIANS FOLLOWING A REVERSED HORIZONTAL MAGNETIC VECTOR1 FRANK A. BROWN, JR. AND YOUNG H. PARK Department of Biological Sciences, Northivestern University, Eranston, Illinois Responsiveness of the living system to very weak magnetic fields is well estab- lished. Studies have involved organisms ranging from the unicellular Pararneciuni (Brown, 1962), through Volvox (Palmer, 1963), Ditgesia (Brown
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Vol. 128, No. 3 June, 1965. THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY DURATION OF AN AFTER-EFFECT IN PLANARIANS FOLLOWING A REVERSED HORIZONTAL MAGNETIC VECTOR1 FRANK A. BROWN, JR. AND YOUNG H. PARK Department of Biological Sciences, Northivestern University, Eranston, Illinois Responsiveness of the living system to very weak magnetic fields is well estab- lished. Studies have involved organisms ranging from the unicellular Pararneciuni (Brown, 1962), through Volvox (Palmer, 1963), Ditgesia (Brown, 1962), Nas- sarius (Brown, Brett, Bennett and Barnwell, 1960; Brown, Webb and Brett, 1960; Brown, Bennett and Webb, 1960; Brown, Webb and Barnwell, 1964), Drosof>hila (Picton, 1964). and Cockchafers (Schneider, 1963), to birds (Eldarov and Kholodov, 1964). The nature and strength of the response have been found to vary as functions of such factors as orientation of the experimental horizontal magnetic vector, of geographic orientation of the organisms, and of phase angles of the natural solar and lunar cycles. It was recently demonstrated, furthermore, that the mud-snail, Nassarius, is able to distinguish strength differences of the horizontal magnetic vector at least within the range, to gauss, displaying a maximum in capacity to respond to an experimentally reversed horizontal magnetic vector when the directional change is effected with minimal simultaneous change in vector strength (Brown, Barnwell and Webb, 1964). Following subjection to horizontal vector fields differing from the earth's local one, the snails, upon return to the nat- ural field, continued to display an influence of the experimentally imposed field. The effect lasted for at least three to five minutes. An after-effect of experimental magnetic fields, with strikingly similar characteristics, was discovered also for the planarian, Dnycsia (Brown, 1965). An after-effect has also been
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