MENTAL LIFE OF MONKEYS AND APES 37 



may be described as follows: (a) choice of the first box at the 

 left; (b) random choice with tendency to choose first, a box 

 near the middle of the group; (c) choice of first box at the right 

 followed by the one next to it on the left ; (d) direct choice of 

 the right box. 



The method of choosing the first box at the right end and 

 then the one next to it developed in the case of all except two 

 of the ten settings. The time of appearance is worth noting. 

 In setting 1, it failed to appear; in setting 2, it developed early, — 

 after about one hundred trials; in setting 3, after about one hun- 

 dred and fifty trials; in setting 4, after about one hundred and 

 fifty trials; in setting 5, after about one hundred and seventy 

 trials; in setting 6, after about one hundred trials; in setting 7, 

 after about fifty trials; in setting 8, it never developed; in setting 

 9, after about fifty trials; and in setting 10, it developed very 

 late, — after about four hundred and seventy trials. 



This method of reaction, although inadequate, proved remark- 

 ably persistent, and it is doubtful whether it had been wholly 

 overcome at the conclusion of the experiment. In the case 

 of the series of trials given on June 8, numbered 191 to 200, the 

 method used was either that of the first at the right and then 

 the next, or direct choice of the right box. 



Throughout the trials with this problem, the end boxes, num- 

 bers 1 and 9, were avoided. This is at least partially explained 

 by the fact that they never existed, and obviously never could 

 appear, in problem 2, as right boxes. In trials 601 to 610, given 

 on July 7, there occurred partial return to the formerly estab- 

 lished method of choosing the first door at the right. This 

 relapse was characteristic of what happened during the many 

 days which intervened between the definite appearance of this 

 habit and the final solution of the problem. 



Especially in connection with such relapses, Skirrl showed 

 extreme fatigue or ennui and often would refuse to work and 

 simply sit before the open doors yawning. This happened even 

 when he was extremely hungr\^ and evidently eager enough for 

 food. 



From July 12 on the hunger motive was increased by feeding 

 the monkey only in the apparatus and by so regulating the 

 amount of food given in each trial that he should obtain barely 

 enough to keep him in good physical condition. An increase 



