TARSAL SENSITIVITY IN PYRAMEIS 453 



10th and ITtli days, the threshold of response to saccharose again 

 fell to M/100. On the 18th, 19th, and 20th days the respon- 

 siveness to water gradually reappeared and prevented any 

 conclusive determinations with saccharose. 



At the close of the trials on the 20th day the second period of 

 water diet was begun, and on the following morning the respon- 

 siveness to water had completely disappeared once more. The 

 threshold concentration of saccharose on this the 21st day was 

 still M/100. The water diet was continued until the close of the 

 26th day, the threshold concentration of saccharose gradually 

 falling meantime until it reached M/6400. In the last two trials 

 of the 26th day the butterfly had become extremely weak — a 

 fact which may account for the negative results obtained. 



The physical condition of the animal on the evening of the 

 26th day necessitated the administration of saccharose, and 

 accordingly the second period of saccharose diet was begun. On 

 the morning of the 27th day the butterfly appeared greatly 

 revived. But tests with saccharose showed that the threshold 

 of response had again risen to M/10, precisely as it had done 

 at the beginning of the first period of saccharose diet. On the 

 evening of the 27th day the animal seemed quite as vigorous as 

 usual, but on the morning of the 28th day it was found dead. 



In figure 1 the threshold concentrations of saccharose for 

 butterfly no. 13 are represented graphically. A glance at the 

 curve shows that during periods of total inanition followed by 

 periods of water diet, i.e., during saccharose inanition, the 

 threshold of response gradually fell, while immediately a period 

 of saccharose diet was begun the threshold abruptly rose. Two 

 facts are thus brought out clearly. First, the minimal effective 

 concentration of saccharose for the tarsi varies directly with the 

 nutritional condition of the animal. During periods of saccharose 

 diet the threshold remained at M/10; during periods of com- 

 plete inanition and water diet, i.e., saccharose inanition, the 

 threshold gradually fell to M/3200 or M/6400. Second, the 

 minimal effective concentration after prolonged inanition with 

 respect to saccharose may be extremely low. At the close of 

 the first period it was M/3200 ; at the close of the second, M/6400. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 36, NO. 4 



