270 The Dancing Mouse 



made an ontogenetic study of the senses, and I am therefore 

 unable to describe in detail the course of their development 

 and decline. Of one important fact I am certain, that dis- 

 criminative sensitiveness increases up to a certain point with 

 age and with training. 



Differences in docility which are obviously to be correlated 

 with age abound. In the prime of its life (from the second 

 to the tenth month) the dancer is active, full of energy, quick 

 to learn ; in its senility (during the second year) it is inactive, 

 but at times even more docile than during the period of 

 greatest physical development. Frequently I have noticed 

 in connection with labyrinth tests that individuals of the age 

 of a year or more learn much more quickly than do individuals 

 of the age of two or three months. But, on the other hand, 

 I have contradictory observations, for now and then I ob- 

 tained just the opposite result in experiments to test docility. 

 Evidently this is a matter which demands systematic, quan- 

 titative investigation. Casual observation may suggest con- 

 clusions, but it will not justify them. 



Early in m/ investigation of the behavior of the dancer I 

 conceived the idea of determining the relation of modifiability 

 of behavior (docility) to age. The question which was fore- 

 most in my mind and for which I first sought an answer may 

 be stated thus : can the dancer acquire a given habit with 

 the same facility at different ages? Since the visual dis- 

 crimination experiment seemed to be well suited for the 

 investigation of this problem I planned to train, in the white- 

 black discrimination experiment, five pairs of dancers at the 

 age of one month, and the same number for each of the ages 

 four, seven, ten, thirteen, sixteen, and nineteen months. 1 



1 1 have not been able thus far to determine the average length of the 

 dancer's life. The greatest age to which any of my individuals has attained 

 is nineteen months. 



