254 A BOOK OF INSECTS 



ceremony the wonder arises as to how the moment is 

 determined, and why the pairing did not take place before. 

 All the males are evidently most eager to pair, and yet 

 when pairing takes place no opposition is offered by the 

 other males to the successful suitor. Proximity does not 

 decide the point, for long beforehand the males often 

 alight close to the female and brush against her with 

 fluttering wings. In watching this wonderful and com- 

 plicated courtship one is driven to the conclusion that the 

 female must signify her intention in some way unknown 

 to us, and that it is a point of honour with the males to 

 abide by her decision." 



Reference has already been made to the fact that 

 many insects produce scents. These may be divided into 

 two classes, viz. (1) repulsive or protective scents, usually 

 common to both sexes, but often stronger in the female, 

 and (2) alluring scents, which are generally confined to 

 one sex only. The first class has already been dealt with 

 in connection with warning coloration, but alluring scents 

 are germane to our present subject. It has long been 

 known that the males of certain butterflies exhale an 

 agreeable perfume. Thus, the scent of the male green- 

 veined white (Pie?is napi) has been compared to lemon 

 verbena, that of the small white (P. rapce) to sweet-briar. 

 These odours emanate from the wings, and are produced 

 by curiously shaped scales that arise from glandular cells, 

 by which a volatile fluid is secreted. Similar scales are 

 found on the wings of many other butterflies and moths, 

 and are confined to the male sex. In some species they 

 are scattered among the ordinary scales, in others they are 

 arranged in brand-like patches, or are hidden in a little 

 pouch or beneath a fold of the wing ; and there can be 

 little doubt that they are employed in courtship as a 

 means of attraction. This suggestion was first made by 



