No. 592] INDIVIDUAL DIFFERENCES 



carried down through the sixth generation, and are still 

 being tested. As neither of the mice of the F 4 generation 

 mated with Xo. 91, the only individual of the F 5 genera- 

 tion. No. 91 was mated successively with four unrelated 



white females, Nos. 86, 87, 88 and 89. These females had 

 been previously tested and found to give exceptionally 

 good records as indicated in Table TL Twenty-three off- 

 spring resulted from these matings. Their records are 

 remarkably uniform and the family averages are the low- 

 est so far obtained. The records of these families are 

 graphically represented in Fig. 8, and here only the con- 

 tinuation of the white family is given showing, the F 5 and 

 F 6 generations separately for each individual family. It 



