236 Dr. Cockayne on Intersexual forms of Plebeius argus. 



therefore heterozygous for sex, whereas in Droso'pliila 

 the reverse is the case. In Lepidoptera the male deter- 

 mining factor is carried by the X-chromosome and the 

 female determining factor appears to be carried by the 

 autosomal chromosomes. Nevertheless, it seems to me 

 likely that these Lycaenid intersexes possess an unusual 

 number of chromosomes and the number is probably an 

 uneven one. This would explain the restriction of male 

 characters to one side, and might also explain the origin 

 of the females with a different pattern on the two sides. 



Summary. 



Two kinds of female intersex are found in A. coridon 

 and P. argus, and in each the male characters are much 

 more often unilateral than bilateral. 



The first kind is much commoner than the second and 

 has blue scales, androconia, and other male characters. 

 The wings w^ith male characters are reduced in size. The 

 bluest bilateral ones look more like males than females. 

 The gonads and genitalia are female. 



The second kind has no androconia and no male 

 character except blue scales. The blue scales form streaks 

 or large patches, or may in coridon cover the whole of 

 both wings on one side except the margins. Very rarely 

 streaks of blue are found on the wings of both sides. A 

 specimen of coridon from Royston referred to ab. syngrapha 

 is more likely to be a completely blue intersex. 



Intersexes of the first kind may be fertile. Those of 

 the second kind have not been tested. There is a great 

 excess of females where these intersexes are found, and 

 females with a different upperside pattern on the two 

 sides have been met with in the same localities. Inter- 

 sexes in both species occur wild year after year in the 

 same localities, and the geographical range is wide. 



Bibliography. 



Bridges, C.B. Science, 1921, liv, p. 252. 



DE La Vaulx, R. Bull. Biol., 1921, Iv, pp. 1-86. 



Keilin, D., and Nuttall, G. H. F. Parasitology, 1919, 



xi, pp. 279—328. 

 Morgan, T. H., and Bridges, C. B. The Origin of 



Gynandromorphs, Carnegie, Inst, of Washington. 



1919, Publication No. 278. 

 Sturtevant. Science, 1920, liii, pp. 325-327, 



