46 NEW-WORLD MIMICS [ch. 



One of these resembles the male while the other is 

 darker and is said to mimic philenor. It is known 

 as the turnus form and is found more commonly in 

 the southern part of the range of the species, i.e. in 

 the country where philenor is more plentiful. The 

 third species, P. asterius, has a more southerly dis- 

 tribution. Its female is darker and nearer to philenor 

 than the male. It must, however, be admitted 

 that none of the three species bears a very close 

 resemblance to philenor. It is suggested that this 

 is because P. philenor is a tropical form which has 

 only recently invaded N. America. The crossing of 

 philenor has, as it were, induced the three mimicking 

 Papilios to turn dark, but the model has not been 

 long enough in contact with them for the Hkeness 

 to become a close one. The explanation, however, 

 hardly accounts for the fact that the best mimic 

 of the three, P. troilus, in which both sexes are dark, 

 is found far north of philenor. Either the dark colour 

 was estabhshed without the influence of the Pharma- 

 cophagus model, or else the species rapidly extended 

 its range northwards after having been modified 

 under the influence of philenor in the south. But 

 in that case the critic may ask why it does not revert to 

 the original pattern now that it has got beyond the 

 model's sphere of influence. On the whole it seems 

 at present quite doubtful whether any relation of 

 a mimetic nature exists between P. philenor and 

 these three species of Papilio. 



P. philenor is also regarded as serving as a model 



