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THE AMERICAN NATURALIST [Vol. XLV 



LWFSRF— LWF 



LWFLWF Long-winged ? white eyes 



SBFLWF Long-winged $ red eyes 



SWFLWF Long-winged J white eyes 



LRFLWF Long-winged $ red eyes 



LWF Long-winged white eyes 



SEF Short-winged red eyes 



SWF Short-winged <$ white eyes 



LEF Long-winged red eyes 

 LEF LEF Long-winged, red $ 



SWF O Short-winged, white J 



LEFSWF^LEFO 



LEF SWF LWF SEF $ Gametes 

 LEF O ^ Gametes 



LRFLEF Long-winged 5 red eyes 



SWFLEF Long-winged $ red eyes 



LWFLEF Long-winged $ red eyes 



SBFLEF Long-winged $ red eyes 



LEF Long-winged red eyes 



SWF Short-winged J white eyes 



LWF Long-winged J white eyes 



SEF Short-winged <J red eyes 



In both eases the combination is possible because in 

 the female of the hybrid (P,) a shifting of the gene for 

 long and that for short wing (both carried by the X- 

 chromosome) takes place. This interchange is possible 

 during the synezesis of the two X-chromosomes. On the 

 other hand the male contains only one X-chromosome 

 which has no mate, hence the gene for long wings in the 

 hybrid (F,) can not leave that chromosome to pass into 

 the male-producing group. If it could do so short-winged 

 females would also appear, but as I have shown they are 

 not present in the second generation. 



Interpreted in terms of chromosomes these results can 

 have, in my opinion, but one meaning. During union of 

 homologous chromosomes (during synezesis, perhaps) 

 homologous genes pair and later separate to move to op- 



