346 THORBORG MARIE BRUNDIN 



mere fact that 0. traskiana chooses its method of reaching the 

 light tends to the conclusion reached by Holmes in his work on 

 the phototaxis of fiddler crabs: "* * * that light is fol- 

 lowed much as an animal pursues any other object of interest, 

 such as prey or its mate * * *." Whatever internal con- 

 dition may have arisen in these forms or how it has arisen, the 

 more highly organized organism has some power of control 

 within it, which is lacking in the lower forms. 



Effect of blackening one eye. — 0. traskiana shows marked indi- 

 vidual variations of response to light when one eye is blackened. 

 In positive specimens of Ranatra and the eastern amphipods 

 studied by Holmes, and also in 0. pugettensis, there were circus 

 movements toward the normal eye when they were exposed to 

 light. In positive specimens of 0. traskiana, circus movements 

 will occur as often toward the blackened eye as toward the 

 normal eye. All specimens used for this experiment were strongly 

 positive. There is no way to account for this variability, except 

 that the animal might be made temporarily negative by having 

 one of the eyes covered over. The fact, however, that as soon 

 as the blacking is removed from the eye of one of these appar- 

 ently "temporarily negative" specimens, its reaction to the 

 light is decidedly positive, seems to throw considerable doubt 

 •upon this hypothesis. 



It is interesting to observe what looks very much like a case 

 of learning, or better perhaps, of control of the creature's move- 

 ments against the influence of external conditions, in the grad- 

 ual lengthening of the curve and the tendency toward traveling 

 to the light in a straight line. I started a specimen from a 

 point about eight inches from the light, placing it each time in 

 a position of facing it directly. I traced its path each time. 

 To avoid unnecessary handling, I picked up the specimen on 

 a piece of cardboard on to which it crawled, and put it back 

 to the starting point after each trial. The accompanying trac- 

 ing of successful paths represents the average series of paths, 

 showing the first uncontrolled circus movements, and the later 

 more direct course of travel. The eighth and ninth trials usually 

 show a straightening of the curved path. Holmes found the 

 same thing occurring in Ranatra. When one eye was black- 

 ened, there was a tendency to control the veering toward the 

 normal side, and to travel to the light in a more direct course. 



