TARSAL CHEMORECEPTORS OF BUTTERFLIES 201 



experiment 2g, a similar situation held. The butterflies of this 

 experiment were tested after sixty-five hours without food or 

 water, while in experiment 3g, the other experiment of the series, 

 they had been but forty-four hours without these. There was, 

 therefore, a difference of twenty-one hours of inanition in this 

 case also. The increased period of inanition together with the 

 great sensitivity of the tarsal receptors to water may perhaps 

 account in part for this uniformity of response to different solu- 

 tions and to distilled water. As previously pointed out, butter- 

 flies were found to become more and more responsive to the 

 stimulation of water, the longer the period of inanition was 

 prolonged. It is possible, therefore, that in the cases under 

 discussion, the response to water had become so strong that the 

 differential effects of the various solutes were somewhat obscured. 

 In conclusion a word may be said concerning the uses of the 

 tarsal chemoreceptors. From what has been shown in the 

 present paper, it is clear that one very important function, 

 perhaps the sole function, is in connection with food substances 

 and water. Not only does the butterfly detect the presence and 

 exact location of such substances through these organs, but it 

 also discriminates to some extent the nature of the substance. 

 Whether this discrimination is final or merely preliminary can- 

 not be stated at present. It would be interesting indeed to 

 know whether the proboscis, once it has been extended through 

 stimulation of the tarsal organs, ever refuses the intake of the 

 stimulating substance. This point I hope to settle in the course 

 of further work. Whatever other organs may assist in the final 

 discrimination of food substances, it is certain that they are 

 first passed upon by the tarsal chemoreceptors. These organs, 

 therefore, function somewhat as organs of taste, and P^'rameis 

 and Vanessa may be said to taste with their feet. 



2. Conclusions 



1. In Pyrameis the degree of responsiveness to contact chemi- 

 cal stimulation of the tarsi is different for different substances. 



2. By means of the tarsal organs, Pyrameis is able to dis- 

 tinguish a 1 M saccharose solution from distilled water, and 



