52 INDIVIDUAL DIFFEBENCES AND FAMILY BESEMBLANCES 



fore they could be tested, while No. 174 did not complete its record. 

 The ineompleted records of this mouse are given in Table III. The 

 one male that lived, No. 171, gave an average of 55 seconds and the 

 female made an average of 125 seconds. Their combined average 

 equalled 90 P.E. 29.7 seconds. Once again it may be noted that 

 the female was the one that made the comparatively poor time record. 

 The other litter of the seventh generation was obtained from mating 

 No. 123, whose average was 32 seconds, with No. 126, whose average 

 was 12 seconds. Their offspring, Nos. 150 to 154 inclusive, compose 

 a litter of one male and four females, one mouse, No. 153, did not 

 quite complete its record (see Table III.). The male of this litter, 

 No. 150, made a poor average record of 102 seconds, and it is worth 

 calling attention to the fact that its case is the only one, among all 

 the sixth, seventh, or eighth generations, where a male has made a 

 very poor record. Two females, Nos. 151 and 152, made good records 

 of 26 and 27 seconds each, while the remaining female made an aver- 

 age of 60 seconds. The family average in this case was 53.7 P.E. 

 13.4 seconds. The matings for the eighth generation have only just 

 been started ; one litter, however, Nos. 208, to 213 inclusive, has been 

 obtained by crossing No. 155, a male, with a time average of 62 sec- 

 onds, with No. 143, whose average was 100 seconds. Their offspring 

 were six in number, two males and four females. One male, No. 208, 

 died, but its incomplete records are given in Table III., and the re- 

 maining male, No. 209, made an average record of 36 seconds. One 

 female, No. 213, gave a good average of 13 seconds, while the other 

 three females ranged from 50 to 82 seconds. The average family 

 record amounted to 48.2 P.E. 8.0 seconds. 



The fourth .and last branch of the white family is given in Fig. 

 14. Here it may be seen that No. 91 was mated with another female, 

 No. 88, that made the very quick average record of 9 seconds. The 

 sixth generation litter of four males and two females that was ob- 

 tained from this mating made the best family record that has so far 

 been obtained, namely, 12 P.E. 1.0 second. None of the mice 

 made an average time record exceeding 20 seconds. It is an inter- 

 esting point that all but one of the 27 offspring of No. 91 made time 

 records considerably superior to the average. Three matings were 

 made from these sixth generation mice. No. 116, a male, was crossed 

 with No. 121, and these two mice made average records of 10 and 12 

 seconds respectively. Two seventh generation litters were obtained 

 from them. The first litter, Nos. 161 to 166 inclusive, was com- 

 posed of three males and three females, with a family average of 

 34.3 P.E. 7.4 seconds. Two of the males made good records of 14 



