THE CYCLE OF LIFE 417 



brush. Similar perfumes, almost always flower-like, are 

 well known in relatives of the conamon whites, and they are 

 almost invariably confined to the males and to the upper 

 surface of the wings. The cells that produce the scent — 

 which may be of the nature of a volatile oil — seem to lie 

 in the skin (or hypodermis) below the surface-membrane 

 of the wing, and the ' plume scales ' are only distributors. 

 There can be little doubt that Fritz Miiller's suggestion 

 is correct, that the pleasant flower-hke scents are useful to 

 the males in their courtship of the females, as auxiliary 

 means of attraction. It may also be that they help mem- 

 bers of the same species to recognize one another, for the 

 perfumes are often exceedingly distinctive or specific. 

 As to the repulsive scents, there is definite evidence that 

 they help to protect their possessors from insect-eating 

 enemies. 



Fire-Flies. — ^We have already referred to the court- 

 ship of the Itahan Fire-fly. The female, sitting among 

 the grass, signals to passing males, who respond and 

 settle down around her in a devoted circle. Flashes 

 of hght pass from the suitors to the object of their desire, 

 and from her to them, till the fire is sufficiently fanned, 

 a pairing takes place, and the party breaks up. Not less 

 refined is the approach that some male spiders make to 

 their somewhat explosive mates — ^vibrating with one of 

 their appendages one of the threads of the web on which 

 the exquisitely sensitive spinner sits. 



Audible Signals. — ^Dr. Karl Peters has given us a very 

 interesting picture of love-signalhng on the part of an 

 Alpine moth {Endrosa or Setina aurita, var. ramosa), which 

 he studied at AroUa. The males fly about actively, but 

 the females are sluggish and rest for the most part on 



BE 



