12 THE ORIGIN OF GYNANDROMORPHS. 



DISTRIBUTION OF SEGMENTATION NUCLEI AS DEDUCED FROM DIS- 

 TRIBUTION OF THE CHARACTERS OF GYNANDROMORPHS. 



If the first division of the segmentation nucleus corresponds with 

 the right and left sides of the embryo, and if chromosomal elimina- 

 tion is more common at this tune or more easily detected, we should 

 expect most gynandromorphs to be roughly bilateral. We have found 

 that this is the most frequent type. If the first division were in the 

 antero-posterior direction and elimination were frequent at this time, 

 we should expect to find some gynandromorphs with the anterior end of 

 one sex and the posterior end of the other sex. This type also is fairly 

 frequent. 



If the first division were dorso-ventral we might expect correspond- 

 ing gynandromorphs, but, although more difficult to detect, they 

 appear almost never to be of this kind. 



If the second division were a time of elimination we would expect 

 quadrants instead of halves. Such cases are known. 



The striking fact about the gynandromorphs is that large regions 

 of the body are involved. Granting that later differences would be 

 less easily detected, in certain organs at least, the results are so em- 

 phatically in favor of large parts of the body being involved that we 

 think it highly probable that the elimination is most frequent in the 

 first division. 



The difficulty of reaching a decision is greatly increased when it is 

 recalled that from the ventral plate of the embryo the serosa is formed 

 by a folding upward of the sides of the plate. How much of the ventral 

 ectoderm is carried in this way to the dorsal surface is not known. 

 Should it replace the dorsal covering derived from the segmentation 

 nuclei (that goes then into the serosa which is later thrown off), the 

 results for ectodermal organs are restricted to the regions on each side 

 of the ventral plate. The mesoderm also grows from the ventral to 

 the dorsal surface, and presumably mesodermal dorsal structures have 

 come from ventral material. 



A further complication arises in connection with the imaginal plates 

 out of which many adult organs are produced. Unless the exact origin 

 of their cells is known, it is not possible to safely conclude at what time 

 the early elimination takes place. 



STARTING AS A MALE VERSUS STARTING AS A FEMALE. 



The evidence recorded in the preceding pages is analyzed on the 

 basis that the gynandromorph starts as an XX individual, or female, 

 and that the male parts arise by the elimination of an X from one 

 of the cells. The evidence from hybrid combinations shows very 

 clearly that practically all of our gynandromorphs have started as 

 XX individuals, as 19 are more female, 14 nearly equal, 6 more male. 



