68 



THE ORIGIN OF GYNANDROMORPHS. 



sharp, the eye was red and the bristles wild-type; below the line the eye- 

 color was eosin (male type) and the bristles were clearly forked. It is pos- 

 sible that the not-eosin, not-forked part, described above as female, was 

 really male, in which case the fly would be a male mosaic. The fly, bred 

 as a male to an eosin-crimson female, produced 143 wild-type daughters and 

 151 eosin crimson sons. Two pairs of these were inbred and produced: 



Explanations. On the assumption that two nuclei were in the egg and that 

 the fly was entirely male, one nucleus contained an eosin forked X and the 

 other nucleus a wild-type X; each nucleus having been fertilized by a Y 

 sperm, the former gave rise to the eosin forked male parts and the latter to 

 wild-type male parts. In case the red parts were female the corresponding 

 nuclei must have come from an XX egg produced by primary non-disjunction, 

 and likewise fertilized by a Y sperm. 



Left side. 



W e f 



If male. 



Right side. 

 w e 



If female. 



On the view that only one nucleus was present in the egg, the possible 

 explanation is as follows: On the assumption that the wild-type parts were 

 female, both of the X's present must have come from the mother, since the 

 eye was not-bar, as would have been the case if the X of the father were present. 

 Moreover, that the sperm was the Y sperm is known from the fact that the 

 mother had no Y to contribute and yet the fly was fertile. The egg was there- 

 fore XX, one X being eosin forked and the other wild-type, and was pro- 

 duced by direct primary non-disjunction. Elimination of the wild-type X 

 occurred and the male cell gave rise to most of the body, including the gonads. 



Left side. 



Right side. 



w e 



f 



On the assumption that the wild-type parts were male, the zygote must 

 have had the same origin as above, but double elimination (or somatic re- 

 duction) occurred, so that one cell received a single eosin forked X and the 

 other a single wild-type X. 



Left side. Right side. 



iv e 



