“The transformation of negatively heliotropic animals (Gammarus pulex) into positively heliotropic animals by chemical means”

After it had been proved that the heliotropism of animals and plants is identical, it seemed desirable to find means by which positively heliotropic animals could be transformed into negatively heliotropic ones, and vice versa. Groom and Loeb found that such a transformation was possible in the nauplii of Balanus perforatus at Naples by the influence of light, inasmuch as these animals were positively heliotropic in very weak light and negatively heliotropic in strong light. 1 Later Loeb found that the marine Copepods and young larvas of Polygordius became positively heliotropic on lowering the temperature as well as on increasing the concentration of the seawater, while they became negatively heliotropic under the opposite influences. 2 Moreover Loeb observed that negatively heliotropic Copepods can be made positively heliotropic by mechanical agitation, 2 and Miss Towle showed that the sign of heliotropism in Cypridopsis can be reversed by contact with solid bodies. 3 Holmes made the discovery that the positively heliotropic terrestrial Amphipods, e. g., Orchestia agilis, become negatively heliotropic when thrown into water. 4

The author had tried in vain to change the sense of heliotropism in animals by chemical means, and this gap was felt the more keenly, inasmuch as he was led to believe that chemical changes might ultimately determine changes in the sense of heliotropism. Recently, however, the author succeeded in finding instances in which specific chemical substances were capable of transforming the sense of heliotropism in animals.

The experiments were made with a fresh water shrimp (Gammarus pulex), which can be obtained at any time in large quantities at Berkeley. If one puts a large number of these animals suddenly into distilled water or into common tap water, they all become at first very negatively heliotropic. It is possible that this is caused by the mechanical agitation, connected with the transferral of the animals from one vessel to another, but this has not yet been ascertained with certainty. Half an hour or an hour later, the negative gathering of the animals becomes less dense, and the animals are scattered in the vessel.