Gynandromorphous Lepidoptera. 331 



abruptaria bred by Simmons could not occur in the same 

 family, except in cases where both parents were heterozy- 

 gous for colour. In this case one parent was homozygous 

 and one heterozygous, and so Doncaster's explanation is 

 an unlikely one. 



Harrison has recently described a remarkable hybrid 

 Ennomos subsignaria $ X E. quercinaria 9. The individual 

 was a male with all the characters, external shape and 

 colour and structure of the external genitalia, on the left 

 side like the male parent, subsignaria, and on the right side 

 intermediate between the two parent species. To explain 

 its origin Harrison suggests that it arose from the entry 

 of two spermatozoa into a single ovum, and that the 

 nucleus of one of them fused with the nucleus of the 

 ovum and formed the right side with its mixture of ma- 

 ternal and paternal characters, whilst the other developed 

 independently and formed the left side, a purely paternal 

 product. 



The explanation is quite possible, since in most Lepido- 

 ptera it is the male which is homozygous for sex and the 

 female heterozygous. Had Harrison's hybrid been female 

 on both sides his explanation would have fallen to the 

 ground. 



Nevertheless, though it will fit in with Morgan's first 

 theory, it is susceptible of explanation on the theory 

 which Morgan put forward in 1914, and I advanced in 

 1915. 



Harrison says that though these hybrids show a mixture 

 of paternal and maternal characters with some preponder- 

 ance of the subsignaria features, the secondary hybrids 

 segregate on mendelian lines, subsignaria and quercinaria 

 characters behaving very much like single mendelian units. 

 Thus Harrison's specimen may be regarded as a case of 

 heterochroism without gynandromorphism, and it is almost 

 certain that ordinary heterochroic specimens arise from a 

 normal fertilisation between a single spermatozoon and a 

 single ovum, in which the mitosis in an early cleavage, 

 usually the first, is abnormal. 



Thus there are absolute proofs that gynandromorphs, 

 including heterochroic examples, do arise from a normally 

 fertilised ovum, and it is probable that examples of simple 

 heterochroism arise in the same way. The proofs are 

 three in number : first, the gynandromorph of Drosophila of 

 known parentage, bred by Morgan; secondly, the halved 



