76 Heredity and Eugenics 



ordinary rcd-ej'cd animals yield different results. The 

 red- eyed female crossed with a wh i te-eyed male produce s 

 only redj^eyed offsprin g, but the red-eyed ma le_ crossed with 

 'a''wHTte^^e(rTemale~ produces offsp ring only_hidf_jj^jwhich 

 are red ej;;ed, viz., the females, whereas the males are 

 white "eye_d'.'^ ' "^ 



These different results in the two cases apparently come 

 about as follows: 



FIRST CASE 



Gametes of red-eyed female =X-R and X-R 



Gametes of white-eyed male =A' and — 



Zygotes = A' • X-R (red-eyed female), and — X-R (red-eyed male). 



SECOND CASE 



Gametes of white-eyed female =A' and X 



Gametes of red-eyed male =X-R and — 



Zygotes = A • X-R (red-eyed female), and — -A' (white-eyed male). 



A short condition of the wings in Drosopliila, which 

 renders the animal incapable of flight, is likewise sex 

 limited in heredity, as has been shown by Morgan. By 

 crossing two races of Drosopliila, each of which possessed a 

 different sex-limited character, Alorgan has been able to 

 combine the two characters in a single race. T hus was 

 obtained a race bot h white eyed and short winged. The 

 synthesis cannot be made originally in a male individual , 

 but onh' in a female. For only in the female can th e two 

 cKaxacters be brought together, each associat ed with a 

 differe nt A', since in the ma le only one A' is pr esen t. Al- 

 though each sex-limited character seems to be attached 

 to or bound up with an X structure, it evide ntly has a 

 material basis distinct from__^'. Otherwise it would not 



