Differences in Behavior 275 



carefully sought out is to conceal or distort their meaning. 

 Too many of us, in our eagerness for quantitative results and 

 in our desire to obtain averages which shall justify general 

 statements, get the cart before the horse. 



Figure 33 presents the beginning of what I propose to call 

 plasticity curves. When these three curves are completed 

 on the basis of experiments with five dancers of each sex for 

 each of the ages indicated on the base line of the figure, they, 

 will indicate what general changes in plasticity, modifiability of 

 behavior, or ability to Jearn (for all of these expressions have 

 been used to designate much the same capacity of the organ' 1 

 ism) occur from the first month to the nineteenth in the male 

 and the female dancer, and in the race without respect to sex. 

 So far as I know, data for the construction of plasticity curves 

 such as I hope in the near future to be able to present for the 

 dancing mouse have not been obtained for any mammal. 



At present it would be hazardous for me to attempt to state 

 any general conclusion concerning the relation of docility 

 to age. 



The initiative of- the dancer certainly varies with its age. 

 In scope the action system rapidly increases during the first 

 few months of life, and if the animal be subjected to training 

 tests, this increase may continue well into old age. The ap- 

 pearance of noticeable quiescence does not necessarily indi- 

 cate diminished initiative. Frequently my oldest mice have 

 shown themselves preeminent in their ability to adjust their 

 behavior to new conditions. However, I have not studied 

 individuals of more than eighteen months in age. One would 

 naturally expect initiative to decrease in senility. All that 

 I can say is that I have seen no indications of it. 



We may now briefly consider the principal sex differences 

 which have been revealed by the experiments. In sensitive- 

 ness I have discovered no difference, but it should be stated 



