74 • D WIGHT E, MINNICH 



specimen were thus extremely variable, and specimens 12, 13, and 

 22 showed essentially similar conditions. A careful stud}^ of each 

 of these cases fails to show any apparent relationship between 

 the nutritional condition of the animal and its response to the 

 stimulus under consideration. Doubtless this response is very 

 definitely determined, but the determining conditions are not 

 evident from the present data. For the present, therefore, the 

 outstanding characteristic of the response to 2M NaCl is its 

 variabihty. It may be added that . this variability is very 

 great not only from one specimen to another, but also from 

 time to time in the same specimen. 



The variabihty of response to 2M NaCl means, of course, that 

 the total amount of response to this substance was much less than 

 to IM saccharose. Considering the weighted responses of all 

 four specimens collectively, the sodium chloride produced but 

 51.6 per cent response, as compared with 100 per cent for the 

 sugar solution. On comparing the curves of the two responses, 

 we find some days when specimens responded indistinguishably 

 to both stimuli. But we also find days when there was a clear- 

 cut difference of response. With every specimen there were 

 periods, ranging from two to seven days, during which the animal 

 gave 100 per cent response to IM saccharose solution, and yet 

 failed to evince even the slightest indication of response to 2M 

 NaCl. The only plausible explanation of these facts is that the 

 animal discriminated clearly between the stimuli. The fact that 

 it responded at times to both is in nowise incompatible with this 

 interpretation, while the fact that at other times it responded 

 100 per cent to one and per cent to the other can hardly be 

 explained in any other way. Clearly, therefore, the tarsi enable 

 Pyrameis to distinguish a 1]M saccharose solution from a 2]M 

 sodium-chloride solution. 



There remains for consideration the response to quinine hydro- 

 chloride. In certain specimens, for example, no. 12 and to a 

 slight extent no. 11, the curve of response to this substance 

 (fig. 3) also shows some variation from day to day, though much 

 less than with sodium chloride. No. 22, however, responded with 

 a complete extension of the proboscis in ei^ery trial, and no. 13 



