48 INDIVIDUAL DIFFERENCES AND FAMILY RESEMBLANCES 



Nos. 86, 87, 88, and 89. These females had been previously tested 

 and found to give exceptionally good records as indicated in Table 

 II. Twenty-seven offspring resulted from these matings. Their rec- 

 ords are remarkably uniform and the family averages are among 

 the lowest so far obtained. The result of crossing No. 91 with No. 

 89, who made the quick average of 12 seconds, is shown as the sixth 

 generation in Fig. 14, which is composed of two males and two fe- 

 males. These mice were uniformly quick to learn, making averages 

 of 8, 12, 11 and 15 seconds, with a family average of 14 P.E. 0.6 

 seconds. 



Fig. 12 represents a continuation of the history of the white 

 family resulting from the mating of No. 91 with No. 87, that made a 

 good time record of 15 seconds. These mice produced, in the sixth 

 generation, two litters, the first of which was composed of five males 

 and two females that made exceptionally quick and uniform records, 

 and showed, as in the previous mating that we have just discussed, a 

 considerable amount of family resemblance. Their family average 

 amounted to 13.1 seconds with the low P.E. of 1.7. It is to be noted 

 that three of the mice of this litter made an average of eight seconds, 

 .two an average of twelve seconds, one an average of 16 seconds, 

 and another 28 seconds. The second litter of No. 91 X No. 87 gave 

 two males and two females, and again good records were made by all 

 but one of the mice, No. 138, that made an average of 76 seconds. 

 The other mice gave average time records of 23, 9 and 11 seconds 

 respectively, while the family average amounted to 29.7 P.E. 11.4 

 seconds. The seventh generation of this particular branch of the 

 white family was composed of three different matings of the sixth 

 generation mice. No. 115, with an average of 12 seconds, was crossed 

 with No. 118 that made a similar average. Their offspring are 

 shown at the left of Fig. 15, and two litters were obtained from the 

 same mice. The first litter gave a family average of 41.1 P.E. 7.5 

 seconds, and the members of this family made fairly low and uniform 

 records, except in the case of No. 143, that made a poor time average 

 of 100 seconds. Four of the other mice made records in the neigh- 

 borhood of 30 seconds and one took 16 seconds. It is a curious fact 

 that in each of the litters of the seventh generation of this branch of 

 ,the white family there was a single female that made time records 

 that were considerably poorer than any of the records made by the 

 males of the same litters. It will be also found that this condition 

 holds to a limited extent for the two other (branches of the strain that 

 will be given later in Figs. 13 and 14. This irregularity in the be- 

 havior of the females tended to increase the mean variations for the 



