Galvanotropic Oriejitation m Volvox 159 



the volvox w^hich I examined normally showed strong anodal gal- 

 vanotropism after an exposure to even bright diffuse daylight; 

 and exposure to the direct sunlight w^as required to change the 

 response to cathodal galvanotropism. 



BEHAVIOR OF THE FLAGELLA 



Volvox, as is well known, invariably swims with its anterior end 

 in advance. No one has described a backward swimming of the 

 colony as the result of any stimulus. It is accurately oriented by 

 both light (Holmes, '03, p. 320) and the electric current (Carlgren, 

 '00), but no one has worked out the mechanism of either of these 

 orientations. Holmes, however ('03, p. 321), states for the helio- 

 tropism that : "We are safe in saying that when volvox changes 

 its direction it is because the flagella on the two sides of the organ- 

 ism beat unequally." 



Fig. I Diagram of volvox, showing the currents in normal locomotion. The feathered arrow 

 indicates the direction of progression of the colony, the other arrows indicate the direction of the currents 

 in the water. 



If india ink be added to a preparation containing volvox cur- 

 rents are easily observed beginning at the anterior end and sweep- 

 ing backward to the posterior extremity on all sides with equal 

 intensity, as indicated by the arrows in Fig. i. I examined these 

 currents around volvox colonies that were in the act of orienting 

 themselves heliotropically but could make out no differences in 

 the currents on the two sides. I do not doubt, however, that 

 Holmes' statement is correct. 



In the case of galvanotropic individuals, however, differences 

 in the currents at the anode and cathode ends of the organisms 

 are easily detected. The most satisfactory way of studying these 

 differences is with volvox mounted in a sufficient thickness of fluid 

 so that it can swim freely. It swims so slowly that its motions 



