CHEMICAL SENSITIVITY OF TARSI OF PYRAMEIS 



73 



Not only did the specimens always respond to IM saccharose, 

 but the extension of the proboscis was in every case a complete 

 one. The total weighted response of all four animals under 

 all conditions was, therefore, 100 per cent. Furthermore, the 

 responses were rapidly executed. As shown in table 2, the 

 average time required for this solution to produce a complete 

 extension of the proboscis was between 1.7 and 3.4 seconds. The 

 response to IM saccharose was thus characterized by absolute 

 constancy under all nutritional conditions, by maximum inten- 

 sity, and by rapidity of execution. These facts all indicate that 

 this stimulus must be a very powerful one. Indeed, it was by 

 far the most effective of the stimuli tested. 



TABLE 2 



Showing the average time in seconds required by different stimuli to effect a complete 



extension of the proboscis 



Unlike IM saccharose, the responsiveness to 2M NaCl was 

 characterized by extreme variability. One has only to examine 

 the curves in figure 3 to become convinced of this fact. Take, 

 for example, specimen 11. During the first three days of its 

 life, no trials were made. On the 4th, 5th, and 6th days, the 

 responses to this solution were 0. On the 7th, 8th, and 9th days, 

 there was a variable number of responses for each day. On the 

 10th day the number of responses again fell to 0. On the 11th 

 day it rose to 100 per cent, where it remained until the 16th day. 

 The 16th, 17th, and 19th days (no observations w^ere made on 

 the 18th) the responsiveness was a little less than 100 per cent. 

 On the 20th day it dropped to 0, only to rise to 100 per cent the 

 21st day, and again fall to the following day, where it remained 

 for the last two days of experimentation. The responses of this 



