68 DWIGHT E. MINNICH 



producing an extension of the proboscis. Second, the same stim- 

 uU plus certain chemical stimuli will effect an extension of the 

 proboscis. Pyrameis must, therefore, discriminate through its 

 tarsi the presence of the chemical stimuli. Third, under certain 

 conditions, distilled water is one chemical stimulus which is very 

 efficient in evoking a response. Fourth, one condition which 

 determines the responsiveness to water is the degree of inanition 

 with respect to water. Satiety with respect to water inhibits the 

 responsiveness thereto. This response may, therefore, be con- 

 trolled, approaching 100 per cent or per cent, according as the 

 animal is or is not allowed access to water. Finally, although 

 Pyrameis fails to respond to water in a condition of satiety with 

 respect to the same, it, nevertheless, continues to respond vigor- 

 ously to a IM saccharose solution. The butterfly must, there- 

 fore, be able through its tarsi to distinguish sharply between 

 water and an aqueous solution of a non-volatile substance such 

 as saccharose. 



EXPERIMENTS WITH SIMULTANEOUS STIMULATION OF ALL 

 AMBULATORY TARSI 



Because of the mechanical difficulties involved in stimulating 

 individual tarsi, a more satisfactory method of experimentation 

 is to allow all the ambulatory tarsi to come in contact with the 

 stimulus at the same time. Experiments using this method were, 

 therefore, more generally employed. In these experiments the 

 wings of the butterfly were held in a spring clothes-pin, which was 

 manipulated by the hand. Upon removal from the cage, the 

 butterfly was first subjected to a preliminary trial of thirty 

 seconds, in which the feet rested on clean filter-paper. This 

 trial was carried out within 3 to 5 cm. of the place where the sub- 

 sequent trial with a given chemical stimulus was to be made, so 

 that the environment in the two trials was practically identical. 

 During the trial, the butterfly was gently lifted and let down 

 again at intervals of ten seconds, in order that it might become 

 thoroughly accustomed to this sort of manipulation. 



If there was no significant response during the preliminary 

 trial, as was usually the case, the butterfly was lifted from the 



