96 ROBERT M. YERKES 



to use the larger one, then he reached for the small one as though 

 to use both together. But the impulse died out and he turned 

 again to the larger box as usual, standing it on end, and per- 

 sistently trying to balance himself on it. Nothing else of special 

 interest happened during the interval of unaided effort. 



Similarly, I placed the boxes for the ape on April 19, allowed 

 him to get the banana and then gave him opportunity to try 

 for himself after the boxes had been displaced. This time he 

 immediately reached for the smaller box and moved it about 

 a little, thus indicating a new association. He next turned to 

 the larger box and worked with it persistently. Later, he once 

 more worked with the smaller box in an unusual manner. He 

 repeatedly stood on it, but made no attempt to lift it or to place 

 it on the larger box. Clearly the usually neglected smaller box 

 had become associated with the satisfaction of obtaining the 

 banana. The same method was carried out on April 20. As 

 I placed the boxes in position beneath the banana, Julius watched 

 with unusual intentness, and when it came his turn to try to 

 obtain the food by the use of the boxes, he began at once to 

 work with the smaller box, but as on April 19, he soon aban- 

 doned it and turned to the other. While I was making note of 

 this particular feature of his behavior, he suddenly seized the 

 smaller box by two corners with his hands and by one edge 

 with his teeth, and after a few attempts placed it on top of 

 the larger box, climbed up, and obtained the banana. 



Because of bad weather on April 21, the next test was made 

 on April 22, with everything as usual. Unaided, the ape was 

 given an opportunity to obtain the coveted reward, while I 

 stood ready to obtain records of his behavior with my camera. 

 He wasted no time, but piled the smaller box on top of the 

 larger one immediately, and obtained his reward. As soon as 

 opportunity was offered, he repeated the performance. The same 

 thing happened on April 23 and several succeeding dates. 



Julius had got the idea, and the only further improvement 

 possible was in skill in manipulating the boxes. 



One of the curious performances which appeared during the 

 imitative period is pictured in figure 26, plate V, where the 

 ape is seen lifting the smaller box into the air. This he did three 

 or four times one day, raising it toward the banana each time 

 as though he expected thus to obtain the reward. As he did 



