176 Animal Intelligence 



The subjects of the experiments were three South Ameri- 

 can monkeys of the genus Cebus. At the time of beginning 

 the experiment No. i was about half grown, No. 2 was about 

 one fourth full size and No. 3 was about half grown. No. i 

 was under observation from November, 1899, to February, 

 1900; No. 2 and No. 3 from October, 1900, to February, 

 1901. No. i was during the period of experimentation 

 decidedly tame, showing no fear whatever of my presence 

 and little fear at being handled. He would handle and 

 climb over me with no hesitation. No. 2 was timid, did 

 not allow handling, but showed no fear of my presence and 

 no phenomena that would differentiate his behavior in 

 the experiments discussed from that of No. i, save much 

 greater caution in all respects. No. 3 also showed no fear 

 at my presence. Any special individual traits that are of 

 importance in connection with any of the observations will 

 be mentioned in their proper places. No. i was kept until 

 June, 1900, in my study in a cage 3 by 6 by 6 feet, and was 

 left in the country till October, 1900. From October, 1900, 

 all three were kept in a room 8 by 9 feet, in cages 6 feet tall 

 by 3 long by 2.6 wide for Nos. i and 2, 3 feet by 3 feet by 20 

 inches for No. 3. I studied their behavior in learning to 

 get into boxes, the doors to which could be opened by 

 operating some mechanical contrivance, in learning to 

 obtain food by other simple acts, in learning to discriminate 

 between two signals, that is, to respond to each by a dif- 

 ferent act, and in their general life. 



Following the order of the ' Animal Intelligence,' I shall 

 first recount the observations of the way the monkeys 

 learned, solely by their own unaided efforts, to operate 

 simple mechanical contrivances. 



Besides a number of boxes such as were used with the 

 dogs and cats (see illustration on p. 30), I tried a variety 



