J 

 quired, on the Hveratje, 32.93 days to le.-irn; the 7th jener;*- 

 tion, 44.00/. The absolute retention of the 6th tieneration 

 was, on the :a.veraije, 65.443 seconds; of the 7th tbcneration, 

 126.680 seconds. Two of the 6th generation failea to i-eleiirn; 

 all the 7th generation had relearned at the end of fourteen 

 days. The 6th tjeneration required, on the average, 14.14 ( days 

 to r el earn; the 7 th ^^eneration but 8.60. 



In these criteria of ability, the 6th (ieneration 

 excelled in learningi and absolute retention; the 7th in relearn- 

 ing. It nust be renenbered, however, that two rats of the 7th 

 generation, having failed to learn, were not tested for relearn- 

 ing. On the whole, the ability of the 7th generation inbreds 

 in learning the naze appears to be soi.iewhat inferior to that 

 of the 6th. 



The body length and body weight of the 6th genera- 

 tion average greater than those of tne 7th. The averat^e actual 

 brain weight of the 6th generation is greater than that of the 

 7th. The relative brain weight (in reference to body length) 

 of the 6th generation is .91^^ less than that of the 7th gen- 

 eration. The relative brain weight (in reference to body weight) 

 of the 6th generation is 1.50/" less than that of the 7th gen- 

 eration. The relative brain weight of the inbred rats used 

 in the maze has not deteriorated fron one generation to anoth- 

 er; however, the number of rats considered in each generation 

 is but few, and all from the 7th generation are females hav- 

 ing greater relative brain weights than males. The percentage 

 of water in brain n.nd cord is within .03;:^ of the 3:une figure 

 in the two generations. 



In Plate IV is shown the curve of learning (below) 

 and of relearning (above) of the 6th and 7th generations of 

 inbred rats. The 6th generation curve is aiiown oy the broken 



