9 



less movements made by rats at different ages. At thirty -five 

 dajj-s of age, when physical activity appears to have reached 

 its highest stage, the percentage of useless movements is larg- 

 est. As the rats grow older, this superabundant activity dis- 

 aipears, and in its place comes direction of activity." 



To summarize the main points in this brief historical sur- 

 vey, we may note-. 



First: - That there is disagreement as to the age of 

 greatest activity, Slonaker putting it first between eighty- 

 seven and one hundred twanty days, and later at ten months 

 for the males and twelve and five-tenths months for the females, 

 while Wataon believes it to be at about thirty-five days; 



Second: - That Yerkes finds the labyrinth habit more easily 

 learned by the old dancers than by the young, v.hile if Watson's 

 interpretation is correct the reverse should be true; 



Third: - Yerkes concludes that the fe[;:ale is superior 

 to the male in learning the labyrinth. 



APPARATUS AiJD lilOCEDlTRL. 



Albino rats were chosen as subjects in this investigation 

 for several reasons: Slonaker, rVatson and Yerkes v.-orked with 

 rodents, and we deaired to compare our results with theirs. 

 Nearly two hundred animals were required for actual experiment- 

 al work and many more than that had to be kept on hand to pro- 

 vide for replacing any who might become unfit for work, and to 

 allow for the usual liJSses through death and sickness. It has 



