26 



The first letter indicates the father, the second letter 

 the mother, of the litter. Indlviiual rats were distingruishable 

 fron each other by a convenient syatam of ear marks, and on every 

 cage was a tag showing the e>:j erimental number, parentage, late 

 of birth, dex and ear mark for each rat contained therein. Thus, 

 W M 1/9/14 H-± 4, would be deciphered, rat number four, female, 

 right ear straight, born January ninth, 1114, mother !', father 

 W. 



Tlie number of trials required by animals of this group 

 in learning the problem varied from fourteen to fifty-one, the 

 absolute time from four and nine-tenths seconds to nine and one- 

 tenth seconds, the total time from siity-four minutes to six 

 hundred forty -nine minutes; and the total distance from one 

 hundred thirty-nine meters to four hundred eighteen meters. 



The "absolute time" is the average time for the last six 

 trials, represents the limit of efficiency in speed for a given 

 group, and varies among individual rats ivithin the group as 

 well as for the groups themselves. Thus, the record time for 

 the twenty-five day group was made by a rat which could ruji 

 fron entrance to food box in four seconds, but no other rat at- 

 tained this speed, and one in particular could not make the run 

 in less than eight seconds. The last six trials were all with- 

 out err^ r and would seerr. to afford a fair basis for judging the 

 average final efficiency, which for thi.. group was five and 

 aeven-tenths seconds. The ab^^olute distance is the same for 

 each group, since the last six trials are errorless, and the 

 true pathway measure.: approximately four and five-tenths meters. 



