THE ORIGIN OF GYNANDROMORPHS. 



67 



the mother, and could have been the non-cross-over cut vermilion forked X. 

 Neither cut nor vermilion would show in the female parts, since they would 

 be recessive to their wild-t^-pe allelomorphs in the rugose forked X; and like- 

 wise rugose would not show, for it would be recessive to its wild-type allelo- 

 morph in the cut vermilion forked X. Both of these X's could not have come 

 from the father, for in that case both eyes would have been rugose. One of 

 the forked X's therefore came from the mother. The left wing was cut, and 

 since cut was present only in the mother, this X also must have come from 

 the mother. Since the cut side did not show forked, this cut X must have 

 been a cross-over anywhere between cut and forked. Thus we see that the 

 egg contained two X's which were different, one being the non-cross-over cut 

 vermilion forked X and the other the cross-over cut X, which is the normal 

 condition of XX eggs produced by primary equational non-disjunction. 

 This XX egg was fertilized by the rugose forked X sperm of the father, giving 

 an XXX zygote. At the first segmentation division, double elimination or 

 somatic reduction occurred, thereby enabling the fly to survive, but only 

 at the price of becoming a gynandromorph. The paternal (rugose forked) 

 and one of the maternal X's (cut vermilion forked) entered one cell, from 

 which developed the female right side, which showed only one mutant char- 

 acter, namely, forked. The cross-over maternal X (cut vermilion? rugose? 

 not-forked) entered the other cell and gave rise to the male left side, showing 

 the mutant character cut only. 



It should be noticed that in all four of these cases it has been the paternal X 

 and one of the maternal X's that have come together into the female part, and 

 that the male part was in each case maternal. This suggests that the essential 

 feature of the reduction is the active separation of the two X's which ab- 

 normally came from the same individual and the passive inclusion of the 

 paternal X in the same cell with either separated maternal X. 



Zygote. 



Left side. 



Right side. 



d 



f 



ct 



f 



ct 



rg 



ct 



rg 



rg jf 



rg f 



No. 7730. October 24, 1917. C. B. Bridges. Text-figure 55 (drawing). 



Parentage. — The mother was a wild- 

 type regular XX female (from a strain 

 of high non-disjunction) carrying the 

 genes for eosin and forked in one X 

 and only wild-type genes in the other. 

 The father was bar. No exceptions 

 were produced other than the fol- 

 lowing gynandromorph. 



Description. — The gynandromorph 

 was almost entirely male. All parts, 

 except the head, were male and had 

 forked bristles. The head was mainly 

 female, having straight bristles and a 

 red (not-bar) eye on the right side, and on the left side a division-line which 

 ran forward through the eye. Above this line, which was perfectly clean and 



Text-figure 55. 



