39r, 



THE AMEBIC AN NATURALIST [Vol. XLIX 



The other results were obtained in the following way: 

 The abnormal red eyed F 2 females obtained from the 

 first experiment are heterozygous for abnormal (AbN) 

 and white (RW), except in so far as this class may 

 contain cross-over flies that are heterozygous in white but 

 homozygous in abnormal AbWAbE. Except for these 

 flies, these F 2 females are like the F t females, and if 

 mated to abnormal white males will continue in each 

 successive generation to give the same linkage data as 

 do the F 2 classes above. If bred in pairs exceptional 

 females homozygous for abnormal will be at once de- 

 tected, and can be thrown out; but even if bred in small 

 batches of four or five females the chance is small of in- 

 cluding homozygous abnormal females. 



In these counts no separation of the normal red fe- 

 males (when they occurred) from the abnormal red females 

 was made but the red females were put into the latter 

 class. Since the females were not intended to be used 

 for comparison this grouping does not affect the prob- 

 lem involved. If we divide the cross-over red abnormal 

 males (20) by the abnormal white males (854) plus 20 

 abnormal red males, we get the per cent, of cross-overs 

 which is here 2.3. This is slightly lower than that ob- 

 tained for the preceding data. 



Black, Red, Abnormal by Gray, White, Normal 

 Another series of experiments, carried on for a some- 

 what different purpose, may be utilized here for further 

 data. Gray, white, normal females were mated to black, 

 red, abnormal males. The daughters were gray, red, 

 normal (or slightly abnormal), and the sons gray, white, 

 normal. Inbred they give the results shown in Table 

 IV. Since the factor for black is not sex-linked, the 

 gray and the black classes may be added together as 

 shown in Table V. 



The results differ from those of Table II in the follow- 

 ing points : There are relatively more red normals which 

 may be assumed to be due to the external condition pre- 



