CHEMICAL SENSITIVITY OF TARSI OF CERTAIN FLIES. 



pan b, where they were subjected to the contact stimulus of 

 paraffin oil and the distance stimulus of water vapor; .(3) a 

 position similar to 2, and far enough above pan b to prevent 

 contact of the tarsi with the oil, in which position they were 

 subjected to the distance stimulus of water vapor only. Posi- 

 tions i and 2 differed only in the nature of the contact chemical 

 stimulus afforded the tarsi, the tactile stimuli afforded by water 

 and paraffin oil and the distance stimulus from water vapor 

 being nearly identical in the two cases. Position 3 differed from 

 i and 2 in lacking any contact tarsal stimulation, either tactile 



or chemical. 



TABLE I. 



SHOWING THE RESULTS OBTAINED WITH Two SPECIES OF Phormia UNDER THE 

 FOLLOWING CONDITIONS OF STIMULATION: A, WATER VAPOR PLUS TARSAL CON- 

 TACT WITH WATER; B, WATER VAPOR PLUS TARSAL CONTACT WITH PARAFFIN OIL. 



1 4cf and 19 9 , P. regina; id\ P. terras novas; lo 71 and 49 belonging to these 

 two species but not specifically identified. 



The first set of experiments was carried out on twenty-nine 

 individuals belonging to the two species of Phormia. The results 

 (Table I.) showed 100 per cent, response in position i, and but 20 

 per cent, response in position 2. The animals were not tried in 

 position 3. In some of the trials in these experiments, however, 

 a source of error was discovered. The cotton pad in the oil 

 pan became accidentally contaminated with watei. 



In the second set of experiments, carried out on Lucilia 

 sericata, care was taken to avoid the sources of error in the first 

 group of experiments. In position I (Table II) Lucilia gave 95 

 per cent, response, in position 2, n per cent., and in position 3, 

 13 per cent. These animals, therefore, actually responded more 

 to water vapor than they did to water vapor plus contact of the 

 tarsi with oil. 



