37^ 



PERMANENT HYBRIDS 



underlying haplo-diploid sex-differentiation in Habrobracon. In 

 this wasp diploid males are occasionally produced by fertilisation. 

 They arise particularly in inbred stocks. They are accompanied 

 by reduced, not increased, fertility of the parents. These diploid 

 males show that diploidy alone does not determine femaleness ; 

 particular genes must also be concerned. From the inheritance 

 of a character determined by genes linked with such hypothetical 

 sex-determinants. Whiting {1935) has shown that the males are 



PareDfs 



9^n 

 (AAXy) 



, ,, I (AAXFYAX 



f arberless : ^— ^ ^^ 



fafberei: 



(AAxX)(AAyy) (AAXy)(AAXY) 



Fig. 119. — Normal and abnormal (giving black symbols) methods of 

 sex-inheritance in Habrobracon. Non-reduction gives the 

 fatherless females. Non-selective fertilisation gives the fathered 

 males. 



of two kinds, which we may call X and Y, while the females are 

 produced by the combination X — Y. The regular femaleness of 

 diploids is due to the complementary products of meiosis being 

 present in the egg after fertilisation and the opposite type always 

 fusing with the sperm nucleus, which will be either X or Y, according 

 to the father. The biparental males are due to the breakdown of 

 this inhibition ; they are either XX or YY. Probably the products 

 of the second meiotic division are the alternative mates of the sperm, 

 and this would indicate that the second is regularly the reductional 



