24 E. P. LYON. 



due to strong extension of the tail, the animal first bending the 

 body ventrally and then suddenly extending it. The jumping 

 reaction occurred on strong stimulation of any kind : for example, 

 on throwing light suddenly into the dish. The orientation with 

 the head away from the light was accomplished by one or more 

 leaps, but so accurately that one could hardly speak of trial and 

 error. When the animals in swimming backward toward the 

 light suddenly hit any obstruction, the springing reaction carried 

 them momentarily away from the light. But they immediately 

 began, under the influence of the swimmerets, to move back- 

 ward toward the light. So it would often happen that on reach- 

 ing the side of the vessel the larvae would strike, jump away, 

 swim back, jump away again, and so on many times without 

 losing their orientation in the direction of the light rays. 



It was therefore of some interest to know how these larvae 

 would behave if the sense of response to light could be reversed. 

 I have made only a beginning of this study. 



The effects of raising the temperature were not clear. For 

 the most part the leaping reaction predominated. The animals 

 darted rapidly about and lost their orientation to light. 



Better results were obtained by diluting the sea water. If the 

 larvae were placed in a mixture of 50 c.c. distilled water and 100 

 c.c. sea water, a considerable proportion of them went to the 

 negative side of the dish. This they did without changing their 

 orientation. In other words they now employed the forward 

 instead of the backward type of locomotion and thus arrived at 

 the side of the dish away from the light. Often there seemed to 

 be a conflict between the two methods of locomotion, the animals 

 oscillating back and forth like shuttles, but always with the heads 

 away from the light. Equal quantities of distilled and sea water 

 gave even more pronounced results. 



The responses were not always so regular and machine-like as 

 I have described. Some of the more pronounced "negative" 

 individuals moved by an irregular, mostly sidewise motion away 

 from the light. Taken as a whole the " negative " effect secured 

 by diluting the sea water was less precise and definite than the 

 " positive " reaction. Also most of the "negative" individuals 

 were only temporarily so. 



