64 THE ORIGIN OF GYNANDROMORPHS. 



were half and half, the left half bearing a female type anal prominence with 

 forked bristles. Sections showed that ovaries were present with well-devel- 

 oped eggs, which account for the large size anteriorly of male-type abdomen. 

 The male parts, as distinguished by the normal bristles, included the whole 

 dorsal surface of the thorax, the two wings, which were of equal size (male), 

 the abdomen (except for half the genitalia), all the right legs, and somewhat 

 more than the right side of the head. The right foreleg bore a sex-comb. 

 The right eye was bar (male type), not vermilion in color. 



Explanations. On the theory that two nuclei were present in the egg, one 

 nucleus contained after reduction a cross-over forked X, the other nucleus a 

 bar X chromosome. The former fertilized by a vermilion forked X sperm 

 gave rise to the female parts on the left side, the latter fertilized by a Y 

 sperm gave rise to the left male side, with the bar eye, etc. 



Left side. Right side. 



f B 



v f 



On the assumption of a single nucleus in the egg a possible explanation is as 

 follows: The male parts show the character bar, and since bar was present 

 only in the mother, they are known to have been derived from the maternal 

 bar X, which was a non-cross-over X, since the eye did not show the character 

 vermilion. The female parts were forked, but since the eye was not vermilion, 

 one of the forked X's must have been a cross-over between vermilion and 

 forked. Crossing-over takes place only in the female and not in the male, 

 wherefore this X also is known to have come from the mother. One cross- 

 over and one non-cross-over X is the general rule for eggs produced by primary 

 equational non-disjunction. The other forked X must have come from the 

 father and therefore carried the gene for vermilion; but vermilion is recessive 

 and its effect is hidden by the normal allelomorph in the cross-over X from 

 the mother. The gynandromorph, as in cases 192 and 1333, started as a 

 XXX zygote which was saved from death and at the same time converted 

 into a mosaic by double elimination or somatic reduction at the first cleavage 

 division. 



Zygote. Left side. Right side. 



B f B 



v f 

 No. 4241. May 15, 1916. C. B. Bridges. Text-figure 53 (diagram). 



Parentage. One of the X chromosomes of the mother carried the genes for 

 lethal 7 and ruby eye-color, the other X the genes for yellow, eosin, and 

 forked. The X chromosome of the father carried the genes for yellow, eosin, 

 and forked. 



Description. The right side was male throughout, except that in the head 

 the female part (bordered by the dashed line in the diagram) extended nearly 

 to but did not include the right eye. The right eye was smaller and ruby. 



