166 MIMICRY IN N. AMERICAN BUTTERFLIES 



of arthemis, retaining unchanged every minute 

 part of the old markings that could be worked 

 into the new, and obliterating all the rest. Thus, 

 extending in this direction and wiping out in 

 that, the great transformation has been effected 

 and one of the most beautiful mimics in the 

 world produced. 



The evolution of the mimetic pattern on the 

 under surface has involved an even more elabo- 

 rate change than on the upper ; but it is not 

 necessary to repeat here the details which have 

 been only recently fully described.^ I will, how- 

 ever, allude to the fate of the most conspicuous 

 feature of arthemis, the broad white band crossing 

 both wings. Save for the traces mentioned below, 

 this marking has disappeared from both surfaces 

 of the hind wing of archippus, but its black outer 

 border is retained, and, cutting across the radi- 

 ate pattern formed by the strongly blackened 

 veins, detracts considerably from the mimetic 

 resemblance.^ On the under surface distinct 



' Trans. Ent. Soc. Lond. (1908), 454-60. 



' In the course of the address on December 31, 1908, 1 remarked 

 that if we could revisit the earth in a few hundred years we might 

 expect to find that this black line had disappeared from the hind 

 wing, and the mimetic resemblance correspondingly heightened. 

 Atthe conclusion, Mr. John H. Cook of Albany, N.Y., informed 

 me that he had discovered near his home many individuals in 

 which the black line was wanting from the upper surface. A few 

 days later he very kindly sent me a record of his observations, of 

 which an abstract is printed as a note at the end of this address 

 (see pp. 211-12). The study of Mr. Cook's facts shows that near the 

 city of Albany not only did the stripeless variety occur commonly 

 (1 in 14', during the three seasons in which the observations were 

 conducted, but also transitional forms with more or less broken 

 stripes were far commoner than the normal archippus (18 to 1). The 



