234 Dr. E. A. Cockayne on 



Genekal Kemarks. 



I think these insects must be regarded as intersexes 

 and not as true gynandromorphs or sex mosaics. Morgan 

 has proved conclusively that the latter are due nearly 

 always to the loss of an X-chromosome occurring usually 

 at the first division of the fertilised ovum. True gynandro- 

 morphs of both coridon and argus are known, and prove 

 that the secondary sexual characters in these species are 

 carried in the X-chromosome. If these insects were due to 

 an abnormality of the X-chromosome one would expect 

 to find male structures in their internal and external 

 genitalia and in their gonads. 



True intersexes in Lepidoptera are found in various 

 primary and secondary hybrids, of which a list is given 

 in my paper in the Journal of Genetics. All of them 

 replace females. Nuttall and Keilin have found inter- 

 sexes replacing females in lice, chiefly in hybrids or crosses 

 between head and body lice. 



Goldschmidt has studied intersexuality in Lynianlria 

 dispar in crosses between strong and weak races. In 

 the first cross between a male of a strong race and a female 

 of a weak race he obtained 50% males and 50% inter- 

 sexes or 100% males. Half the latter proved to be trans- 

 formed males and had only one X-chromosome like females 

 instead of two like normal males. Male intersexes, 

 individuals with two X-chromosomes but with some 

 female secondary sexual characters, appeared in later 

 generations. He considers that the intersexuality is due 

 to a difference of potency in the factors for maleness and 

 femaleness in different races of this species. 



Sturtevant has found large numbers of sterile inter- 

 sexes in a race of Drosophila simulans. He has given 

 convincing proof that they are females modified by a 

 recessive autosomal mutant gene, which causes them to 

 show male structures. Their sex glands are absent or 

 very minute. He has proved that the male parts have 

 two X-chromosomes in their cells like the female parts. 

 It is interesting that this gene or factor is carried not in 

 a sex chromosome but in an autosomal one. He has 

 shown also that in true gynandromorphs of D. simidans 

 the cells of the male parts contain only one X-chromosome. 



Bridges has found another kind of sterile intersex in 

 Drosophila melanogaster. In these the gonads are rudi- 



