524 



Wilham Morton Barrows 



This reaction indicates that the flies respond to a difference in the 

 intensity of the stimulus on the two sides of their bodies. 



The following peculiar response was very often observed. After 

 flies had passed the traps they would often suddenly turn and run 

 back with a characteristic zigzag motion to the mouth of the 

 charged trap. While testing with 50 per cent alcohol, it was noted 

 that about one-third of the flies reacted in this manner. Evidently 

 they are able to follow the current of odor back to its source. 

 These responses will be further discussed in a subsequent part of 

 this paper. 



TABLE IV 



The numbers of fies 'j.'hich reacted positively to each of three di^erent strerjgthi of acetic ether in water. In 

 each experiment the number of fies used was one hundred 



Number of the 

 experiment 



Number of flies that 

 entered the 



Ether 

 trap 



Control 

 trap 



Number of flies that 

 turned toward but 

 did not enter the 



Ethei 

 trap 



Control 

 trap 



4^ «-' 



o >- 





I. 



2. 



3- 

 4- 

 5- 

 6. 



33 

 S 

 9 



7 



19 



II. 5 



It is plain from an inspection of Table III that the largest number 

 of positive reactions was produced by 5 per cent acetic acid. 

 Not only is this true, but, when the trap was charged with this 

 strength, about half of the flies which at first failed to respond 

 to the stimulus returned through the current of odorous material 

 from the far end of the trough back to the mouth of the trap. 

 These responses are not included in the table. 



Acetic ether is soluble in water only to the extent of about 8 

 per cent, and when used in such high concentration it affects the 

 flies in a singular manner. They show intense excitement and 

 struggle at the mouth of the trap for a chance to enter, yet when 

 one has succeeded in entering it backs out almost immediately. 



