48 G. V. HAMILTON 



than an adult macacque. The but slightly lower record of the 

 two half -grown monkeys is, therefore, of some interest. Here, 

 too, an explanation is to be found in differences of reactive 

 tendency which require, for genetic evaluation, more than a single 

 standard of measurement. 



Phylogenetic aspects of table 2. A comparison of the various 

 adult groups shows that in order of ability to avoid useless 

 efforts to open exit doors the older normal human subject stands 

 first, the mature monkeys second, the dogs third, the cats 

 fourth, and the horse fifth. Table i shows that the horse has 

 the highest individual record of efforts to open doors that is 

 manifested by any subject, regardless of age. 



It is of some interest that twenty-six-months-old-Boy i 

 made a greater number of efforts to open exit doors than did 

 any of the following subjects: All other human subjects, all 

 of the monkeys, and dogs 2, 3F1, 5F2, 12F1, 13F2. If mere 

 ability to avoid useless activities w^ere a measure of intelligence, 

 this finding would imply that my son was less intelligent at 

 twenty-six months than was one of my forty-three-days-old 

 puppies (Dog 13F2). In view of the fact that at the time of the 

 experiment Boy i gave unmistakable evidence of having " free 

 ideas" (5), this is an absurd implication. 



IV, DETERMINATION OF THE DIFFERENT MODES OF ADJUSTMENT 



MANIFESTED 



It will be remembered that the conditions of the experiment 

 require the subject who seeks escape from the apparatus merely 

 to search for an unlocked door until he finds one. The present 

 chapter seeks to classify the different modes of searching for 

 this ever-varying unlocked door. 



In order to facilitate the descriptions that follow, the value 

 of each of the four exit doors in a given trial-situation will be 

 designated by one of the following terms : 



The impossible door. For any present trial this is the un- 

 locked door of the immediately preceding trial; hence it is an 

 inferentially impossible door of exit during the present trial 

 for any subject who is able to appreciate that no one door is 

 ever an unlocked door in two successive trials. 



The possible doors. No subject is able, during a given trial, 

 to tell with certainty which one of three exit doors will yield 



