18 

 groups, yet ea®h rat seemingly reached the norm at the 



time experimentation with each group stopped, Of course, 

 some rats of a group finished learning sooner than others. 

 Both the number of trials and days required to learn the 

 problem are shown by small squares arranged on base lines. 

 Males are indicated by plain squares, and females by 

 squares with diagonal line in them. Those on the three 

 base lines on the lower half of the plate show the num- 

 ber of trials for each individual rat when one, three 

 or five trials were given, The upper half of the plate 

 shows the number of days. The rats which finished 

 learning the problem with a norm higher than one second 

 are indicated by a circle within the blocks. 



curve helps in understanding at a glance individ- 

 ual differences. It will be seen that rats with one 

 trial a day finished learning with fewer trials but usually 

 more days than those required in three or more trials. 

 In addition those given three trials required fer/er trials 



