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THE AMERICAN NATURALIST [Vol. XLVIII 



In the cross of Beaded by Maroon-eyed flies, 1,369 flies 

 were raised in the F 2 generation. Fifty-seven of these 

 flies had Beaded wings ; only one of the Beaded-winged 

 flies had Maroon eyes, while fifty-six were red-eyed. (See 

 Table XXI.) 



TABLE XX. 



Back-crosses of F x Females of the Cross Pink Beaded <J X Black ? 



Fj males of the cross Sepia by Beaded were back- 

 crossed to normal Sepia females. Inasmuch as cross- 

 overs probably do not occur in the male (Morgan, 1912c), 

 no Beaded Sepia flies should occur in the offspring of this 

 cross. Table XXII shows that none occurred. The num- 

 bers are not large, but since they are entirely in accord 

 with the other third chromosome results, it was not 

 thought worth while to increase them. That apparent 

 cross-overs may very rarely occur will appear possit 

 when we consider the results of crossing Beaded by Pir 

 and the probable significance of the phenomenon will 

 considered. 



TABLE XXI 

 F, Results of the Cross Beaded 5 X Maroon 



In F 2 counts of the crosses involving Beaded and the 

 body color Ebony, totaling 4,417, in which 1.205 Beaded- 

 winged offspring occurred, not one had the body color 

 Ebony, and only eleven had Pink eye-;. Eepeated attempts 



