c66 'Journal of Comparative Neurology and Psychology. 



As has already been mentioued, all visual difference between the 

 boxes was eliminated. The boxes were of the same size, both were 

 painted black and closed at the back by ground glass windows. 

 Behind these windows, 16 c. p. electric lights were placed in order 

 to prevent the possibility of unequal lighting (at times these lights 

 were interchanged). The food boxes were sunk into the bottom of 

 the passage way, and nut hulls and the kernels used for food could 

 not be seen from the upper part of the entrance. To prevent any 

 possibility of this, however, both food boxes were partly filled with 

 empty nut hulls, and toward the close of a series, with whole nuts 

 and pieces of nuts. In a control test, both lights behind the boxes 

 were turned off entirely, leaving both boxes in total darkness ; fi.nally, 

 first one light and then the other was turned off to determine the 

 firmness of the association. 



Smell was eliminated by rubbing the side and bottom of the five- 

 inch passage way with nut kernels and with other aromatic sub- 

 stances. Food was frequently placed in both food boxes, when the 

 discrimination had been established, to test thoroughly the absence 

 or presence of smell associations as well as visual. 



In order to be certain that all the factors other than temperature 

 were alike in both boxes, the box which was made the standard on one 

 day (40°) was used as the variable on the succeeding day. This al- 

 teration was not constant, i. e., not made every other day. It was 

 feared that even this regularity might be learned by the squirrel, so 

 that the change of the standard temperature from one box to another 

 was made quite frequently in the midst of a single day's series. 



To prevent discrimination in the runway on any basis whatever, 

 the sides were covered with asbestos. It was not particularly in- 

 tended that discrimination on the basis of temperature should not 

 take place here, but in order to eliminate secondary criteria, it 

 seemed better to eliminate differences in temperature as well. 



After the association had been formed, an effort was made to de- 

 termine how the squirrel detected the temperature of the box. This 

 was very incompletely done, for the reason that it was desired to 

 confuse the animal as little as possible in order that the later experi- 

 ments might proceed immediately. Asbestos pieces were prepared 



