318 



THE EVOLUTION THEORY 



Fig. 54. A portion of the upper surface 

 of the wing of a male 'blue' {Lyccena 

 ■menalcas) ; after Dr. F. ICOhler. bl, ordin- 

 ary blue scales, d, scent-scales. Highly 

 magnified. 



scales, and it will have a delicate perfume of lemon or balsam, thus 



proving that the fragrance adheres to the scales. 



In the last ease, that is, among the Whites (Pieridse) (Fig. S3, a), 



the scent-scales are distributed fairly regularly over the upper surface 



of the wing, and the same is true 

 of our blue butterflies, the Lycaen- 

 nidse, whose minute lute-shaped 

 scales are shown singly in Fig. 



53, d, but in their natural position 

 among the ordinary scales in Fig. 



54. In many other diurnal, and 

 also in nocturnal Lepidoptera, the 

 fragrant scales are united into tufts 

 and localized in defi.nite areas. 



They then often form fairly large spots, stripes, or brushes, which 

 are easily visible to the naked eye. Thus the males of our 

 various species of grass-butterflies (Satyridse) have velvet-like black 

 spots on the anterior wings, while the fritillary, Argynnis 2Mphia, 

 has coal-black stripes on four longitudinal 

 ribs of the anterior wing which are absent 

 in the females, and which are composed of 

 hundreds of odoriferous scales. Certain large 

 forest butterflies of South America, resembling 

 our Apatura, bear in the middle of the 

 gorgeous green shimmering posterior wing a 

 thick expansible brush of long, bright yellow 

 scent-scales, and a similar arrangement obtains 

 in the beautiful violet butterfly of the Malay 

 Islands, the Zeuxidia wallacei depicted in 

 Fig- 55- In many of the Danaides, which 

 we have already considered in relation to 

 mimicry, the scent apparatus is even more 

 perfect, for it is sunk in a fairly deep pocket 

 on the posterior wings, and in this the scent- 

 producing, hair-like scales lie concealed until 

 the butterfly wishes to allow the fragrance to 

 stream forth. In many South American and 

 Indian species of Pcqnlio the fragrant hairs are disposed in a 

 sort of mane on a fold of the edge of the posterior wing, and 

 so on. The diversity of these arrangements is extreme, and they 

 are widely distributed among both diurnal and nocturnal Lepi- 

 doptera, in the latter sometimes in the form of a thick, glistening, 



Fie. 55. Zeuxidia wallacei, 

 male, showing four tufts 

 of long, bristle-like, bright 

 yellow scent-scales (d) on 

 the upper surface of the 

 posterior wing. 



