232 



THE AMERICAN NATURALIST [Vol. L 



We may now take up in more detail the family histories. 

 Fig. 6 gives a graphic representation of matings, from 



which there were selected two mice, No. 20 Y$ and No. 

 26 YJ\ which made unusually poor records, 115 and 183, 

 respectively, though the other mice in the same litters had 

 good records. The parentage of Nos. 20 and 26 was un- 

 known; they were mated and gave two litters, each com- 

 posed of three males and one female. Three mice in these 

 two litters gave unusually slow records and made con- 

 siderably more errors than normal. Two other mice gave 

 poor records; two gave good records, while one died be- 

 fore it was tested. It is unfortunate that both females 

 in these litters died before further offspring could be 

 obtained. Table I gives the complete record of both time 

 and error averages for these mice. It is a question 

 whether or not the selection of parents having poor rec- 

 ords tended to produce more than the normal number of 

 offspring slow to learn. Further investigation can alone 

 afford an answer. 



The mice whose records are given in Table II are 

 graphically represented in Figs. 7 and 8. They have been 



