No. 530] CONCEPTION OF PURE LINES 75 



the daughters will have long wings and all of the sons 

 will have small wings, like their mother. 



These cases conform to Mendel 's principle of segrega- 

 tion. Were there time I could show by an analysis of the 

 problem why these sex-limited characters behave in in- 

 heritance in a different way from secondary sexual 

 characters, although the results in both cases may be 

 accounted for on the assumption that there are genes in 

 the cells for both kinds of characters. In a word, this 

 difference exists because one of the factors for the sex- 

 limited characters in question is absent from one of the 

 female determining chromosomes, while the genes for the 

 secondary sexual characters of the male are contained 

 in other chromosomes, possibly in those that contain the 

 male determinants. 



This interpretation of the relation between the X- 

 chromosomes and sex-limited characters makes it now 

 possible to demonstrate a point of great theoretical im- 

 portance. I invite your serious attention for a few 

 moments longer to this question. Three other characters 

 have appeared in my cultures that are sex-limited; one 

 of these only I may now speak of. A male with wings 

 half the normal length suddenly appeared. He trans- 

 mitted his short wings to some of his grandsons, but to 

 none of his granddaughters. I tried to see if the other 

 sex-limited character, white eyes, could be combined in 

 the same individual with short wings. As the next dia- 

 gram shows a red-eyed short-winged male was bred to a 

 white-eyed female with normal wings. All of the off- 

 spring had long wings ; the female had red eyes and the 

 males white eyes. These were inbred and produced 

 white and red-eyed males and females with long wings, 

 red-eyed males with short wings, and white-eyed males 

 with short wings. In the last case the transfer had been 

 made. The reciprocal cross also given in the diagram is 

 equally instructive. 



