132 ROBERT M. YERKES 



used by other observers. The box stacking experiment has, 

 according to my private information, been used by Koehler. 

 It is obviously important that such tests be applied in the same 

 manner to individuals not only of the different genera of anthro- 

 poid apes, but of different ages, sex, and condition of training. 



The box stacking experiment, although it yielded complete 

 success only as a result of suggestion on my part, proved far 

 more interesting during its progress than any other portion of 

 my work. In connection with it, the orang utan exhibited 

 surprisingly diverse and numerous efforts to meet the demands 

 of the situation. It is fair to characterize him as inventive, 

 for of the several possible ways of obtaining the banana which 

 were evident to the experimenter, the ape voluntarily used all 

 but two or three, and one of these he subsequently used on 

 the basis of imitation. 



Had Julius been physically and mentally mature, my results 

 would undoubtedly have been much more impressively indica- 

 tive of ideas, but even as matters stand, the survey of my ex- 

 perimental records and supplementary notes force me to con- 

 clude that as contrasted with the monkeys and other mammals, 

 the orang utan is capable of expressing free ideas in considerable 

 number and of using them in ways highly indicative of thought 

 processes, possibly even of the rational order. But contrasted 

 with that of man the ideational life of the orang utan seems 

 poverty stricken. Certainly in this respect Julius was not above 

 the level of the normal three-year-old child. 



In common with other observers, I have had the experience 

 of being profoundly impressed by the versatility of the ape, 

 and however much I might desire to disprove the presence of 

 free ideas and simple reasoning processes in the orang utan, 

 I should feel bound to accept many of the results of my tests 

 as evidences of such experience. 



I have attempted to indicate briefly the historical setting of 

 my investigation. I propose, now, in the concluding section, 

 to look forward from this initial research and to indicate as 

 well as I may in a few words the possibilities of results im- 

 portant for mankind from the thorough study of the monkeys 

 and anthropoid apes. 



