EVOLUTION OF L. ASTYANAX 187 



that later, after the separation had become com- 

 plete, it spread northward over the whole range 

 of its parent. 



The evolution of astyanax from arthemis was far 

 simpler than that of arcMppus. The great 

 difference in appearance between parent and 

 offspring is brought about, as regards the upper 

 surface, by the disappearance of the broad white 

 band of arthemis together with all but a trace of 

 the sub-apical white markings of the fore wings. 

 Over and within the area formerly occupied by 

 the white band a bluish or greenish iridescence 

 spreads from the marginal region where it exists 

 in arthemis. This marginal iridescence — just as 

 in astyanax — is bluish in some individuals of 

 arthemis, greenish in others. Keddish sub- 

 marginal spots, although rarer in the hind wing 

 of astyanax, are actually commoner in the fore 

 wing than in arthemis. This curious fact, together 

 with the evidence that astyanax and archippus 

 may occasionally interbreed, suggests the pos- 

 sibility of some connexion between the origins 

 of the two mimics. 



The under surface of astyanax has not only 

 similarly lost the white markings, but the 

 chocolate-brown ground-colour of arthemis has 

 become transformed into a dark iridescent 

 greenish-brown. Against this background the 

 reddish spots near the margin and base of the 

 wings become far more conspicuous than in the 

 parent form. The material for this transforma- 



