VI 



SCALES 



331 



A. 



Socket holding the stalk in Galleria 

 mellonella ; B, insertion of the scale 

 of Polyommatus phloeas. b, Base of 

 scale ; ;, holding-ring ; w, surface of 

 wing. (After Spuler.) 



giving rise to metallic " interference-colours." The walls of the 

 scales are themselves, in some cases, tinted with pigment. It is 

 said that some of the scales contain air, and that the glistening 



O O 



whiteness of certain scales is due to this. The exposed surface of 



the scale usually differs from the 



surface that is pressed down on 



the wing in being delicately and 



regularly striated ; the colours 



of the upper and under surfaces 



of a scale may also be quite 



different. Scales are essentially 



of the nature of hairs, and all 



the transitions between hairs and F IG> 179. insertion of scales. 



true scales may be found on the 



wings of certain Lepidoptera that 



baar both hairs and scales, e.g. 



Ithomia. It has been calculated 



that there are a million and a half of scales on the wings of an 



individual of the genus Moiylio. The scales are arranged on 



the wing in an overlapping manner, somewhat like slates on the 



roof of a house. Each scale has a short stalk, and is maintained 



in position by the stalk fitting into a cavity in a projection of 



the wing-membrane (Fig. 172). 



Androconia. - -The males of numerous butterflies possess 

 scales peculiar in kind and various in arrangement. They may 

 be either irregularly scattered over the w r ing, or they may form 

 very complex definite structures (Fig. 173). They were formerly 

 called " plumules," but Scudder has replaced this name by the 

 better one, " androconia." The function of the androconia is 

 still obscure. An odour is believed to be connected with them. 

 Thomas supposes l that these scales are hollow tubes in connec- 

 tion with glands at their bases, and that matter secreted by the 

 glands passes through the scales and becomes diffused. In 

 nearly all Lepidoptera it is the male that seeks the female ; if 

 therefore odorous scales were present in one sex only we should 

 have supposed that this would have been the female rather than 

 the male. As, however, the reverse is the case, the function of 

 the androconia is supposed to be that of charming the female. 

 Scudder considers that the covering part of the androconial 



1 Amer. Natural., xxvii. 1893, p. 1018. 



