446 DWIGHT E. MINNICH 



Pyrameis alone (Minnich, '22) I have shown further some of 

 the substances which can be differentiated through the tarsal 

 organs. These substances consist of distilled water and several 

 aqueous solutions, including a solution of IM saccharose. In 

 the course of this investigation two facts were discovered which 

 have made possible a quantitative study of the tarsal sensitivity 

 to saccharose solutions. First, contact of the four ambulatory 

 tarsi with a IM saccharose solution will always effect an extension 

 of the proboscis, irrespective of the nutritional condition of the 

 animal. From the time of its emergence from the pupa until 

 its death, whether starved or abundantly fed, the butterfly will 

 continue to respond with the utmost constancy to this stimulus. 

 Second, contact of the tarsi with distilled water alone will also 

 effect an extension of the proboscis, but only after a prolonged 

 period of inanition with respect to water. Thus, a butterjfly 

 deprived of water for a sufficient number of days, generally 

 four to seven, will finally become 100 per cent responsive to 

 water. This response, however, ceases at once if the animal be 

 allowed to drink water. By the mere adixiinistration of water, 

 therefore, Pyrameis can be maintained in a state of per cent 

 responsiveness to water, but of 100 per cent responsiveness to 

 IM saccharose. Under these conditions, the minimal concen- 

 tration of saccharose necessary to effect a response is readily 

 determined. It is the purpose of the present paper to report the 

 data obtained in this fashion. 



METHODS 



All butterflies were hatched in captivity. Upon hatching they 

 were kept without food or water until they became 100 per cent 

 responsive to w^ater. They were then placed on a diet of distilled 

 water which was administered morning and evening. Although 

 some individuals appeared quite weak after the period of total 

 inanition, they generally revived after their first access to water, 

 and for some days the w^ater diet was sufficient to maintain them 

 in a normal condition. Sooner or later, however, the butterflies 

 began to show signs of weakness which gradually increased until 

 further trials became impossible. At this point IM saccharose 



