104 ROBERT M. YERKES 



2. Skirrl, Pithecus irus 

 Box Stacking Experiment 



The monkey Skirrl was tested by means of the box stacking 

 experiment much as JuHus had been. On August 23, with a 

 carrot suspended six feet from the floor of the large cage and 

 three boxes in distant corners, the animal was admitted and 

 his behavior noted. 



The boxes, which were made of light, thin material, ranged 

 in size from one six inches in its several dimensions to one 

 twenty inches long, thirteen inches wide, and eleven inches 

 deep. Only by using at least two of these boxes was it pos- 

 sible for the animal to reach the carrot. 



Immediate^ on admission to the cage, Skirrl began to gnaw 

 at the boxes, trying with all his might to tear them to pieces. 

 After some thirty minutes of such effort, interrupted by wander- 

 ings about the cage and attempts to get at the other monkeys, 

 he suddenly went to the largest box of all, set it up on end 

 almost directly under the carrot, mounted it, and looked up 

 at the food. It was still beyond his reach and he made no 

 effort to get it, but instead, he reached from his perch on the 

 big box for the next smaller box, which was approximately 

 sixteen inches, by fourteen, by twelve. This he succeeded in 

 pulling toward him, at the same time raising it slightly from 

 the floor, but his efforts caused the large box to topple over 

 and he quit work. The experiment was discontinued after a 

 few minutes, the total period of observation having been thirty- 

 five minutes. 



Skirrl handled the boxes with ease and with evident pleasure 

 and interest. He also noticed the carrot at various times during 

 the interval, but his attention was fixed on it only for short 

 periods. 



The test was continued on August 24 when, instead of a 

 carrot, a half banana was used as bait. It was placed only 

 five feet from the floor, and three boxes were as formerly placed 

 in distant corners of the cage. When admitted, Skirrl looked at 

 the banana, then pulled one of the boxes toward it, but in- 

 stead of mounting, he went to the smallest box and began to 

 gnaw it. Shortly, he mounted the middle sized box and looked 

 up toward the banana, but the box was not directly under the 



