258 Dr. E. A. Cockayne on 



PL xxii, fig. 14a). A second was captured by Mr. H. B. 

 Williams at Royston, in 1915, and has androconia on both 

 wings on the right side (PI. LXX, fig. 2), and a third, 

 taken by Mr. F. W. J. Jackson at the same time and 

 place, also has androconia on the small misshapen side 

 (PI. LXX, fig. 1). 



Theoretical Discussion. 



A good deal of evidence has accumulated to prove that 

 sex and secondary sexual characters are Mendelian unit 

 characters, and that although closely linked they are 

 probably separable. There is even some evidence to 

 show that the secondary sexual characters themselves 

 may be separable into more than one unit character. It 

 is thought that the character for sex is carried by a special 

 chromosome sometimes recognisable microscopically, and 

 that secondary sexual characters are probably carried by the 

 same chromosome. It is probable that ordinary gynandro- 

 morphs are produced by unequal chromosome divisions at 

 the first cleavage of the normally fertilised ovum, and 

 that in this unequal division both the units for sex and 

 for secondary sexual characters participate. Hence such 

 individuals are likely to be true genetic hermaphrodites, 

 having the gonad, external genitalia and secondary sexual 

 characters peculiar to one sex on the one side, and those 

 peculiar to the other on the other side. 



In the Royston gynandromorphs the condition found 

 is quite different from this. In the considerable number 

 examined the gonads, internal and external genitalia have 

 always proved to be female. The dissimilarity on the 

 two sides is confined to certain secondary sexual char- 

 acters, male scent scales or androconia, coarse blue hair 

 scales and blue scales of ordinary shape, all of which 

 together may perhaps be a single Mendelian character. 

 The irregular division, which I suppose to be the cause 

 of this, must be confined to that part of the chromosome 

 bearing this character. The factor for sex in the chromo- 

 some must be unaffected because both gonads are female 

 and are invariably equal in size on the two sides. There 

 is some evidence that the unit for the accessory internal 

 genitalia and for the external genitalia is independent of 

 that for the gonads and it must also be unaffected; for, 

 although the internal organs are occasionally imperfectly 



