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THE AMERICAN NATURALIST [Vol. XLVII 



Small-eyed flies were obtained from the same stock and further 

 work is now being done with these. 



The association of the differential factor between colored and 

 white eyes, w, with the differential factor between long and minia- 

 ture wings, m, was tested. Matings were made between white- 

 shorts and red-longs, and between white-longs and red-shorts and 

 in both cases the long-red female offspring were paired to short- 

 white males. In this way the F 2 progeny gave directly a meas- 

 ure of the classes of gametes produced by the long-red F 1 fe- 

 males, except as they may have been affected by differences of 

 viability. When white-shorts were mated with red-longs, the fe- 

 male offspring were of composition, wmx — x, giving excess of 

 white-shorts and red-longs over the other two possible combina- 

 tions : and when white-longs were mated with red-shorts, the fe- 

 male offspring were of composition, wx — mx, giving excess of 

 white-longs and red-shorts. 



Daughters of white-shorts by red-longs gave 3,371 red-longs, 

 1,136 red-shorts, 1,571 white-longs and 2,064 white-shorts. 



Positive association of w and m is given by the equation 



red-longs -f white-shorts 5,435 _ Q 



red-shorts + white-longs 2,707 ~~ ' 

 Greater viability of the longs is shown by the equation 

 longs _ 4,942 _ 

 shorts ~~ 3,200 ~~ ' ' 

 Greater viability of the reds is shown by the equation 



reds 4,507 



whites — 3,635 ~~ " ' 

 Daughters of white-longs by red-shorts gave 1,047 red-longs, 

 1,116 red-shorts, 1,651 white-longs, 671 white-shorts. 



Negative association of iv and m is given by the equation 

 red-longs -f white-shorts 1,718 ^ ^ 



According to previous work on these factors this equation 

 should have given O.50. and we may suppose that larger num- 



Greater viability of the longs is shown by the equation 

 longs 2,698 

 shorts 1,787 ' 



