CHEMICAL SENSITIVITY OF TARSI OF CERTAIN FLIES. 173 



TABLE III. 



SHOWING THE RESULTS OBTAINED FROM TWENTY-FOUR FEMALES OF Phormia 

 regina UNDER THE FOLLOWING CONDITIONS OF STIMULATION: A, WATER VAPOR 

 PLUS TARSAL CONTACT WITH WATER; B, TARSAL CONTACT WITH PARAFFIN OIL; 

 C, WATER VAPOR ONLY; D, SAME AS B. THE LAST SET OF TRIALS WAS MADE 

 AS A CHECK. 



1 Confined to 3 of the 24 animals. 



2 Two of the animals were unfit for further experimentation after the first two 

 sets of trials and had to be discarded, hence the number of animals here represented 

 is only twenty-two. 



3 Trials in which water vapor called forth a complete extension of the proboscis 

 could not be followed immediately by another trial. This explains why there were 

 only 58 instead of 66 trials. 



First, animals which gave about 100 per cent, response when 

 their tarsi were brought in contact with water gave much less 

 than 20 per cent, response when their tarsi were brought in 

 contact with paraffin oil. Second, the response to water vapor 

 alone was sufficient to account for at least part of the responses 

 obtained with paraffin oil. In other words, in animals which 

 were about 100 per cent, responsive to tarsal contact with dis- 

 tilled water, the response to contact with paraffin oil was very 

 small. The response to the oil was not zero, however, as the 

 results of the third set of experiments show. Since the tactile 

 stimuli of water and oil are nearly alike, the great difference in 

 response can only be due to the difference in the contact chemical 

 stimulation afforded the tarsi. The tarsi of these flies must, 

 therefore, possess contact chemoreceptors. 



