The Mental Life of the Monkeys 203 



' no ' signal the act of holding the food six inches above the 

 box instead of a quarter or a half an inch. The progress is 

 shown in Fig. 31, E and E v I then tried taking the food 

 from a saucer off the front of the box for the ' yes ' signal and 

 from a small box at the back for the ' no ' signal. ' Yes ' was 

 perfect from the start (10 trials given). 'No' was right 

 once, then wrong once, then right for the remaining eight. 



EXPERIMENTS WITH No. 3 



No. 3 was kept in a cage not half so big as those of i and 2. 

 Perhaps because of the hindrance this fact offered to forming 

 the habit of reacting in some definite way to ' yes ' signals, 

 perhaps because of the fact that I did not try hand move- 

 ments as signals, there was no successful discrimination by 

 No. 3 of the yellow from the black diamond or of a card with 

 YES from a card with a circle on it. I tried climbing up to 

 a particular spot as the response to the ' yes ' signal and stay- 

 ing still as the response to the ' no ' signal. I also tried in- 

 stead of the latter a different act, in which case the animal 

 was fed after both signals but in different places. In the 

 latter case No. 3 made some progress, but for practical 

 reasons I postponed experiments with him. Circumstances 

 have made it necessary to postpone such experiments in- 

 definitely. 



PERMANENCE OF THE ABILITY TO DISCRIMINATE 



No. i and No. 2 were tried again after intervals of 33 to 48 

 days. The results of these trials are shown in Fig. 32 . Here 

 every millimeter along the base line represents one trial with 

 the 'no' signal (the 'yes' signals were practically perfect), 

 and failure is represented by a column 10 mm. high while 



