APRiii 7, 1911] 



SCIENCE 



535 



pinks, males and females. The reciprocal 

 cross, viz., pink-eyed females and red-eyed 

 males, gives also in tiie first generation red- 

 eyed individuals only. These inbred have pro- 

 duced 1,133 reds, males and females; and 237 

 pinks, males and females. The results show 

 that pink is not sex limited. The simplest ex- 

 planation of the difference between the modes 

 of inheritance pf pink and white eyes is found, 

 I think, if we ascribe the factor involved in the 

 formation of pink eyes to some other part of 

 the mechanism than that involved in the 

 formation of white eyes. If I am right in 

 ascribing the sex-limited inheritance of white 

 eyes to some change in one of the sex chromo- 

 somes, then the factor for pink eyes must be 

 contained in some other part of the cell ; pos- 

 sibly in some other chromosome. That this 

 must be the correct interpretation is borne out 

 by the results of the second cross just given, 

 in which the male-producing sperm of the red- 

 eyed male produces red-eyed males. Evidently 

 this sperm adds the necessary factor to the 

 pink-bearing egg to produce red eyes, which 

 would not be the case if the factor in question 

 was present in the sex chromosome which is 

 assumed to be absent from this spermatozoon. 

 The hypothesis also makes clear how important 

 it may be to recognize that different parts of 

 the cell may be involved in producing such a 

 " unit character " as eye color. 



The relation of pink to white eyes is ex- 

 tremely interesting. When a pink-eyed female 

 is bred to a white-eyed male all of the off- 

 spring have red eyes. These inbred produce 

 red-, white- and pink-eyed offspring in the fol- 

 lowing proportions: 



Eed-eyed females 418 



Eed-eyed males 198 



White-eyed males 222 



Pink-eyed females 117 



Pink-eyed males 35 



White eyes appear again in this combina- 

 tion as sex limited. The pink eyes are rela- 

 tively few in number, and the females are 

 about three times as numerous as the males. 



The reciprocal cross, viz., white-eyed females 

 and pink-eyed males, gives in the first genera- 



tion red-eyed females and white-eyed males. 

 These inbred produce: 



Eed-eyed females 411 



Eed-eyed males 333 



White-eyed .females 377 



White-eyed males 365 



Pink-eyed females 76 



Pink-eyed males 94 



In this combination both males and females 

 with white eyes appear in the second genera- 

 tion in about the same proportion as the red- 

 eyed individuals. The pink eyes are again 

 fewer than the other classes, but now the 

 females are somewhat less numerous than the 

 males. These peculiar results can, I believe, 

 be accounted for theoretically, but the analysis 

 is too elaborate to give here. 



These results indicate that the white eye 

 lacks one factor for red and pink eye, another 

 factor for red. When combined all the ele- 

 ments for red are present. But the second 

 generation shows that the reds formed in this 

 way by recombination differ from the ordinary 

 reds in that they produce reds, pinks and 

 whites. The difference between these artificial 

 reds and the normal reds consists in the pres- 

 ence of one dose of red in the artificial and 

 two in the normal reds (at least in the female). 

 The segregation is a consequence of this 

 heterozygous condition. If this view is cor- 

 rect it should be possible to produce by the 

 proper combinations some pinks and whites 

 that when combined no longer produce reds, 

 but only pinks and whites. I have made such 

 races that have continued for several genera- 

 tions to produce pinks and whites only in very 

 large numbers. In order to discover whether 

 the induced change in this new race has taken 

 place in the white or in the pink, the following 

 experiment was carried out. One of the new 

 pink females was crossed to a white male of 

 the ordinary stock. This combination gave, it 

 will be recalled, with ordinary pinks, red males 

 and females, as stated above. The same thing 

 occurred in the new experiment, showing that 

 the pink had not been changed. On the other 

 hand, when a white male of the new " pink- 

 white " stock was crossed to an ordinary pink 



