114 Studies in Animal Behavior 



needle is due to the contraction of the longitudinal 

 muscles of the opposite side of the body one would 

 naturally suppose that the avoidance of a light was 

 brought about in the same way. 



A few years ago I endeavored to study the pos- 

 sible inhibitory effect of light in the phototaxis of 

 Volvox. If the orientation of Volvox when swim- 

 ming toward the light is due to the fact that light 

 tends to inhibit the action of the flagella on the 

 more strongly illuminated side, we should expect 

 that, as the organism passed from a region of dim 

 light to where the light was more intense, its gen- 

 eral rate of locomotion would decrease, since both- 

 sides would be more strongly affected by the inhibi- 

 tory stimulus. Specimens of Volvox were placed 

 in a glass trough the bottom of which was marked 

 off into equal spaces. The time required for a speci- 

 men to traverse each space in its course toward the 

 light was noted in a number of cases, and it was 

 found that, on the average, the speed of the organ- 

 ism was quite uniform in the varying intensities of 

 light. The Volvox swam with much the same rapid- 

 ity until they came near the optimum when their 

 pace began to slacken. The results of the experi- 

 ments were therefore opposed to the view that orien- 

 tation is effected by the inhibitory effect of light on 

 the movements of the flagella on the more illumi- 

 nated side of the organism. Inhibition may function 

 in other ways in the orientation of Volvox and in 

 changing the sense of its reactions to light and other 



