118 " Gynandromorphism" and Kindred Problems 



simple one. It would explain the cases where one sex preponderates 

 by supposing that one half develops less rapidly than the other. It 

 explains the occurrence of heterochroic gynandromorphs. The two 

 nuclei of the ovum may be alike in constitution, but one spermatozoon 

 may differ from the other. One may carry a dominant Mendelian 

 character and the other a recessive. 



It also explains the partial or complete doubling of the genital 

 apparatus. 



Familial and hereditary cases would be caused by the familial and 

 hereditary production of binucleate ova. 



Doncaster himself points out an objection, and that is that no 

 gynandromorphs were produced from the broods in which he found 

 binucleate ova. He also states that in the one case, in which it could 

 be investigated, the two zygotes of the fertilised egg would both have 

 produced males. 



There are other difficulties. On his supposition one would expect 

 that in broods, where heterochroic gynandromorphs were produced, 

 there would be an equal number of individuals showing heterochroism 

 without any gynandromorphism. 



No such individuals were produced in these broods. 



Another objection which may be brought forward is the regular 

 occurrence of gynandromorphs in certain mixed races and hybrids. It 

 is certain that binucleate eggs do not occur in the parent species in any 

 numbers or gynandromorphs of pure race would be equally common. 



Ainorphu populi, for example, produces gynandromorphs quite 

 commonly, perhaps 1 in 5000, but they should occur in half the indi- 

 viduals to suit Doncaster's theory. But as will be seen later these 

 gynandromorphs probably arise in a different way from the halved 

 examples. 



More important is the objection that reduplications only occur in 

 the genital apparatus, whereas they should occur quite as often in other 

 parts formed near the mid-line, if a gynandromorph is really a fusion of 

 two potentially complete individuals. 



The halved gynandromorph of Thaumetopoea pinivora, Tr. (left male, 

 right female), whose abdomen bifurcated into two equal parts each with 

 a complete genital apparatus is probably an example of partial fission 

 of the embryo comparable to the abcaudal duplication in mammals, 

 which gives rise to dipygus and other monsters. 



The theories, which suppose that a gynandromorph develops from a 

 uninucleate ovum, differ in some respects. 



