IN RATS AND GUINEA-PIGS. 27 



nose spots, he produced four individuals with nose spots and fourteen with- 

 out nose spots, or 22.2 per cent of nose-spot (NS) young. When he was 

 mated with these nose-spot young (N S$) or with nose-spot individuals 

 produced in other experiments but not of nose-spot ancestry, and so desig- 

 nated NS , he produced a much higher percentage of nose-spot young, viz, 

 53.6 per cent by N So mothers, and 61.5 per cent by N S$ mothers. In 

 one case he was mated with his NS\ daughter by an N So mother, from which 

 mating there resulted three nose-spot young and two otherwise marked, or 60 

 per cent N S. The number of young in this last experiment is too small 

 to be very significant quantitatively, but those in the other matings are 

 large enough. They show an increase in the per cent of NS young with an 

 increase in the amount of NS ancestry, and strongly suggested the possi- 

 bility of a still further increase by continued selection. Such increase, 

 however, has not up to this time been realized. Five sons or grandsons of 

 c? 1989 have been quite extensively tested and the same is true of one 

 individual ( 6^5595, ATSi, table 29) descended from a brother of 1989". Of 

 these six males, two have records, about equaling in production of nose- 

 spot young the record of c? 1989", but the records of the remaining four 

 are inferior to his. The two males with the best records are 6^5652 (table 29), 

 a son of d* 1989, and c? 5669 (table 29), a grandson of c? 1989 and son of 

 6^5151 (table 29). Neither of these males, however, has produced a large 

 number of young (the former 16, the latter 10), and so too much importance 

 must not be attached to the per cent results. Of all the six males, 5151 

 alone has produced more than fifty young. By Af So and NS\ mothers alike, 

 about 40 per cent of his young bear nose -spots. His father's record by the 

 same group of mothers was about 15 per cent better (see table 28). 



The collective results given by the six males enumerated in table 29 are 

 shown in table 30. They indicate that in the long run a higher percentage 

 of AT 5 young is produced by NSi than by AT So sires, but neither group 

 gives as high a percentage as the original nose-spot male, 1989 (table 28). 



The nose-spot mothers employed in these experiments are much more 

 numerous than the males, but because the number of young produced by 

 any one of them is in no case greater than fifteen, the results are not given 

 for the mothers individually, but only in collective form (table 30, last part) . 



The collective results for the females, like those for the males, show an 

 increase in the percentage of nose-spot young with increase in the amount 

 of nose-spot ancestry. In other words, the character is apparently inherited 

 feebly through both the male and the female lines, and is being gradually 

 fixed by selection. The process, however, is a slow one. After two gener- 

 ations of selection, the inheritance coefficient is no higher than in the original 

 male, 1989. Whether it can ultimately be made higher remains an open 

 question. 



