I'rZ'f 



nent, fifteen were from the 7th t.ener».ti on, fourteen fron the 

 6th and one from the 9th. In Table XH 1h shown a conparative 

 8ununaj-y consistint;, of the daily averat'eB of all the 7th and 

 all the 8th t^enerations (inclucint, with the 8th the one 9th 

 {generation rat). The table shows that four of the 7th tjenera- 

 tion and seven of the 8th tieneration failed to learn the in- 

 clined plane. The 7th t^eneration required, on the avera^^e, 

 59.60 days to learn; the Bth (generation, 86.53 . The absolute 

 retention of the 7th generation was, on the average 44.945 

 seconds; of the 8th generation, 13.8?5 seconds. All the 7th 

 generation had relearned at the end of the twenty-fourth day; 

 but all the eth generation had relearned by the end of the 

 eighth day. The 7th generation required, en the average, 8 . no 

 days to relearn; the Eth generation but 5.00 days. 



In these criteria of ability the 7th generation ex- 

 celled in learning; the Sth in absolute retention and relearn- 

 ing. But seven of the Sth generation as against but four of 

 the 7th had failed to learn, and for that reason not tested 

 for relearning. There eeerriS, on the v/hole but little differ- 

 ence, but in the learning v/here all were used the advantage 

 lies V7ith the 7th generation. 



The body length and body rveight of the 7th ^^enera- 

 tion at^erage greater than those of the 6th. The average actual 

 brain weight of the 7th generation is greater than that of 

 the eth. The relative brain weight of the 7th generation (in 

 reference to body length) is 5.20^j less than that of the 8th 

 generation. The relative brain weight ( in reference to body 

 weight) of the 7th generation is 13.93'' less than that of the 

 8th. The relative brain v/eights of the inbred rats used in 

 the inclined plane has not deteriorated fron one generation 

 to another, but has increased. The percentage of water in brain 



