272 



ADA W. YERKES 



TABLE 1 



the tendency merely to sit still without effort to solve the prob- 

 lem was very marked, the animal was given a chance on at 

 least three successive days, and showing no improvement, was 

 discarded. Fifteen rats, seven stock and eight inbred, were 

 discarded on this basis. Sixteen rats completed the training, 

 nine stock and seven inbred, and a seventeenth (stock) whose 

 timidity and wildness had made her exceptional throughout the 

 experiments, was discarded after the one hundred and tenth 

 trial, as she showed little sign of improvement. 



The rats with which the first tests were made were eight to 

 ten weeks old. The later ones were younger, for the effort was 

 made to start them at seven weeks (later at five weeks). The 

 nine rats used in the short maze were all born on the same day 

 and were thirty -five days old when the experiments were begun. 

 Not all were started on the same day. 



In table 1 is presented a list of the rats used in the maze ex- 

 periments, their sex, strain, generation, age, preliminary train- 

 ing, number of trials required for learning the maze and for 

 re-learning after an interval of twenty-eight days, and the 



