56 



age except for the 65-day grouj, where again the loT/ering of the 

 average is due to the aui-eriority of males over those of the 

 25 day group, the females being auj-ericr in the 25 day grou; As 

 compared with the 65 day grouj . The difference between the two 

 younger groups a id the two older ones is not so marked as that 

 for trials or time but it in nevertheless apparent that the mem- 

 bers of tlie latter covered more ground than those of the former. 

 Yerkes found his older dancers somewhat superior to the younrer 

 ones in learning the labyrinth. The writer finds that the young- 

 er rats learn the maze in fewer trials, that their absolute time 

 is leso , their total time and distance are less, and that their 

 speed is greater than in the case of the older rats. His ten 

 month dancers were superior to those of one to two months while 

 the 25 and 65 day rats of this experiment formed the maze habit 

 more quickly than those 300 days old. 



The si,eed (which it will be remembered is the average 

 number of centimeters run per second throughout the learning 

 process, no distinction being made between early and late trials] 

 without exception decreases with increased age. The last group 

 is distinctly slower than any other and this to our mind is 

 again proof of the lessening of activity with age. 



The absolute time, which we have taken as the indication 

 of final efficiency, also diminishes with increasing age, and 

 is considerably lower at 300 days than at any previous age. Thus, 

 while at 2r days the average length of time required for the 

 execution of a peri^ect run was 5.7 seconds, at 300 days the very 

 best tine in which the food could be reached was 11.6 seconds, 

 more than twice the time of the youngest group. It follows that 



