CHEMICAL SENSITIVITY OF TARSI OF CERTAIN FLIES. 



These results on flies are similar to those obtained by the 

 author on nymphalid butterflies (Minnich, '220). In both cases 

 the response to water can be completely controlled, while that to 

 saccharose can not. In butterflies, however, the administration 

 of iM saccharose fails to alter the response to this solution at all 

 while in flies, it causes a drop of about 20 per cent. In flies, 

 further, the period required for the response to water to become 

 100 per cent, is measured in hours, while in butterflies it is meas- 

 ured in days. This is another indication of what is evident in 

 many other ways, viz., that the metabolism and activity of the 

 fly are much more intense than those of the butterfly. 



Barrows ('07) observed that when one foot of a fruit fly touched 

 food or a small drop of water the proboscis was immediately 

 extended. He suggested that the two transparent hairs found 

 beneath the claws of each front foot might contain the sense 

 organs involved. B. M. Patten ('17) noted that the modified 

 anterior pair of legs of the whip tail scorpion were sensitive to 

 chemical stimulation including water. Similar observations 

 showing the sensitivity of the walking legs to contact with food 

 and other chemical stimuli in various Crustacea have been 

 made by a number of investigators: Herrick (1895) for the 

 lobster; Bell ('06) and Holmes and Homuth ('10) for the cray- 

 fish; and Balss ('13) for the prawn, Palaemon treillanus. 



These observations together with the past and present observa- 

 tions of the author cover species from three classes of Arthropoda, 

 viz., Crustacea, Insecta and Arachnida. The presence of contact 

 chemoreceptors, serving as organs of taste, in the distal ends of 

 thoracic legs must, therefore, be considered to be of general 

 occurrence among arthropods. 



GENERAL SUMMARY AND CONCLUSIONS. 



1. The muscid flies, Phormia regina Meigen, Phormia terrx- 

 nov3& R.D., and Lucilia sericata Meigen, extend the proboscis 

 upon appropriate contact chemical stimulation of the tarsi. 



2. The response to water varies from o to 100 per cent., and 

 the response to I M saccharose from 80 to 100 per cent, depending 

 upon the nutritional state of the animal. 



3. By means of these reactions, it can be shown that the 

 chemoreceptors in the tarsi serve as organs of taste. 





