206 MIMICRY IN N. AMERICAN BUTTERFLIES 



a recent invader from the Old World tropics 

 the invader meanwhile retaining its original 

 characteristic pattern, is demonstrative of the 

 inadequacy of the theory which refers these 

 likenesses to the influence of soil, climate, &c. 



16. The poison-eating ' Aristolochia swallow- 

 tail' Pliarmacophagus (Papilio) philenor belongs 

 structurally to the American division of this 

 tropical section, and is probably an intruder into 

 North America from the south. 



17. Just as tropical species of Pliarmacophagus 

 are mimicked, especially by other sections of 

 swallow-tails, so the invading philenor is mimicked 

 by three species of the section * Papilio '. 



18. Of these three Papilio troilus, mimetic in 

 both sexes, is probably the oldest; P. asterius, 

 mimetic in female and on under surface of male, 

 the next ; and P. glaucus, mimetic in one out of 

 the two forms of female (the mimetic form be- 

 coming more numerous in the south of the range), 

 the youngest. 



19. The ancestors of these mimics persist with 

 little or no change in the two last-named species, 

 the non-mimetic sex or form ; in the first-named, 

 the allied palamedes. By their aid we can recon- 

 struct the history of the transformation. 



20. In asterius and glaucus partially melanic 

 forms of the female probably supplied a tinted 

 background on which the new and mimetic picture 

 was gradually built up by the modification of 

 elements in the original non-mimetic pattern. 



