194 DIVERSITY OF THE SEXES 



scales. This patch itself, moreover, is a feature 

 of the males alone, and occurs in many hair- 

 streaks where the position of the vein is not 

 altered. 



One of the most curious patches of this kind is 

 found in the males of certain yellow butterflies, 

 although wholly absent from others intimately 

 allied to them ; it is a little patch of lustreless 

 scales which occurs at that part of the base of the 

 hind wings which is always covered by the 

 front wings, so that it is quite 

 concealed from sight. 



Patches of a different nature 

 also mark the male sex ; thus 



the costal fold opened ; . , . -. -, , ,-, -, 



nat. size. next the middle of the lower 



median vein of the hind wings of the Monarch [see 

 Fig. 106], and in some of its allies, we have a 

 thickening and inversion of the membrane, con- 

 spicuous from its covering of black scales. 



In very many males of the larger skippers 

 (Hesperides) the front edge of the fore wing is 

 abnormally expanded and folded compactly upon 

 the upper face of the wing, so snugly that often 

 it can be only discovered with the lens [Pig. 161] ; 

 moreover the scales within this fold have turned 

 to white silken floss, which, when the fold is 

 raised, contrasts conspicuously with the ordi- 

 narily dark surface of this part of the wing. In 

 certain swallow-tails, also, the inner border of the 



