470 Prof. E. B. Poulton mi the Mimetic N. American 



the liiud-wing upper surface in the tiirnus female is in 

 nearly the same position as the one conspicuous spot of 

 asterius and trmlus, while at the apical angle of the same 

 surface of the same wing, a large reel spot appears in turnus 

 and troilus. Red spots are not found in either position on the 

 upper surface of ])hilcno7\ These spots are certainly ances- 

 tral in the turnus female, inasmuch as they are present in 

 the non-mimetic female form and the non-mimetic male of 

 the same species, as well as in the allied non-mimetic species. 

 For the same reason the black-pupilled red spot at the anal 

 angle of asterius is ancestral. In troilvs, on the other 

 hand, both red spots are probably of recent origin on 

 the upper surface, and have been developed in relation 

 with the mimetic appearance. They are yellow in the 

 ancestral palamedes. It is probable that their red colour 

 in troilus has been developed in secondary mimicry of 

 asterius and the turnus female form of f/laucus. It is in 

 accordance with this interpretation that the red spot at 

 the anal angle of troilus, although without the black pupil, 

 bears considerable superficial resemblance to that o? asterius, 

 and that the red spot at the apical angle is especially well 

 developed in the female. 



The comparison of these three mimetic forms also yields 

 evidence of an approach towards the primary model, in 

 which the different species have made different rates of 

 progress, presumably determined in large part by the age 

 of the mimetic resemblance. 



Papilio troilus is evidently the oldest mimic. The 

 mimetic likeness, extending to both sexes, has been derived 

 from a very different appearance still preserved in imla- 

 medcs. The suppression in troilus of the fifth orange-red 

 spot of the inner row oi palamedes is apparently an advance 

 in the direction of the open loop of spots which is the 

 prominent feature in the hind-wing under surface of 

 phileno7\ Equally clear advance is seen in the bluish tint 

 which the submargiual yellow spots of the upper surface of 

 palamedes have gained in troilus. 



Fapilio polyxenes asterius is less perfect and presumably 

 less old as a mimic than troilus. The mimetic resemblance 

 is found on the under surface of both sexes, but on the 

 upper the male, if a mimic at all, has only reached an 

 early stage in the resemblance. The evolution of the 

 two rows of definite orange-red spots out of the ill-defined 

 elements found in the non-mimetic ancestors, was probably 



