Reactions of the Pouiace Fly to Odorous Substances 533 



assumed by the tropism theory. Forward locomotion would be 

 called forth by an equal stimulation of the two antennae and lateral 

 movements by an unequal stimulation of these organs. If this 

 view is correct, circus movements ought to result after the removal 

 of one antenna even though the stimulating atmosphere contains 

 a uniformly distributed odorous substance. It was, therefore, 

 thought desirable to experiment upon flies from which one antenna 

 had been removed in order to produce excessive unilateral 

 stimulation. 



Before the operation the flies were tested for five minutes in 

 pure air and five minutes in an atmosphere with odor, to make 

 certain that they were normal, /. e., that they did not turn more 



TABLE viii 



Records of the times which six fies took to find food before and after the terminal segments of their antenna 



had been removed 



frequently to the right than they did to the left or vice versa. The 

 terminal segment of the right or the left antenna was then cut off 

 from each fly. After the removal of this segment, the flies were 

 fed and allowed to remain twenty-four hours, when they were 

 again hungry. They were then admitted singly to the cylinder 

 containing only pure air and watched for five minutes. Without 

 exception they reacted as they did under similar circumstances 

 previous to the operation. A little odor was now blown into the 

 cylinder from a wash bottle partially filled with fermenting banana 

 and the flies were again admitted singly and their movements 

 carefully watched. If the fly moved in a circular path, as was 



