Galvanotropic Orientation in Volvox l6l 



the plant is swimming toward the anode there is seen to be no 

 current at its anterior end while the current continues normally 

 posteriorly (Fig. 2). If, now, the current be reversed a violent 

 current is initiated at the anterior end and the current at the 

 posterior end stops (Fig. 2). After this reversal the plant usually 

 continues swimming straight forward to the cathode for a short 

 distance, but soon swerves a little to one side or the other and 

 rapidly orients itself to the anode again. 



If the colonies have been exposed to sunlight and made cath- 

 odally galvanotropic the behavior of the flagella is completely 

 reversed. Exactly the same pictures are presented to the observer 

 but the current now stops on the cathodal side of the organism 

 and the volvox colony becomes oriented toward the cathode. This 

 result is of some importance for it shows that in the case of volvox 

 the direction of migration has not been changed by some quanti- 

 tative changes in the action of a mechanism which remains funda- 

 mentally the same; as has been described by Wallengren ('02, '03) 

 for Opalina and Spirostomum. In the cases described by Wallen- 

 gren the forward stroke of the cilia was always produced by the 

 galvanic current at the cathode side of the animal no matter what 

 its orientation; and, as the forward stroke of the cilia is the best 

 criterion we have for stimulation of infusoria (Bancroft, '05), it 

 must be concluded that in all these cases the underlying nature of 

 the galvanic stimulation was the same. In the case of volvox, 

 however, the facts described indicate clearly that in the anodally 

 galvanotropic colonies the pole at which the constant current pro- 

 duces its characteristic effect is the anode, while in the cathodal 

 colonies the same effect is produced by the current at the cathode. 

 In other words the galvanotropism has been reversed by means 

 of a reversal of the pole at which the electric current produces its 

 characteristic effect. 



The only other case that I know of in which a reversal of the 

 galvanotropism has been shown to be brought about in this way 

 is that of Paramecium in which it w^as found possible to reverse 

 the galvanotropism by chemical means (Bancroft '06, '06a). In 

 this case it was made probable that the chemical conditions under- 

 lying galvanic stimulation were the same no matter whether that 



