106 PROCEEDINGS OF THE AMERICAN ACADEMY. 



$ wh. 9 house mouse 



$ gr. 48 9 gr. 50, 51, 52 $ bl.-wh. 9 bl.-wh. 



S vvli. 152 9 wh. 132 S bl.-wh. 227 9 bl.-wh. 25 



^ wh. 254 9 house mouse J" bl.-wh. 303 



S gr. 381 9 gr. 378, 379 



From the union of these two sorts of heterozygotes ( ^ gr. 381 and 

 9 gr. 378, 37'J) there were obtained thirteen young, of which nine were 

 entirely gray and four were gray with small white flecks on the forehead, 

 tail, or belly, one having also white feet. According to the Mendel ian 

 principles of segregation, the unions taking place to produce these thir- 

 teen young are the following (using the letters D, DR, and R as before, 

 to express respectively total, partial, and no pigmentation) ; 



D + R = gametes of $ , 

 D + DR= " 9, 



D + DR + DDR + DRR = offspring 



No albinos should result in F^, nor were there any produced. It now 

 became necessary to test the individuals of this generation severally in 

 order to determine their nature. As previously stated, four of the young 

 had small flecks of white on their otherwise gray coats. One of these 

 slightly spotted mice was bred to an albino of spotted ancestry (the im- 

 portance of this latter fact is elsewhere pointed out), and six young 

 were produced, three of which were gray with white spots, and three 

 were albinos. Evidently, then, the pigmented animal being tested was 

 either of the class DRR, or D"R, these being the only two in which 

 complete albinism was present as a recessive allelomorph. That it was 

 actually of the class DR'R, however, is sufficiently shown from the 

 fact that it not only showed partial albinism in the soma, but its three 

 spotted young by the albino showed a still greater amount of white. It 



