1909] Mimicry in the Butterflies of North America 215 



includes the well-known British "White Admiral" (L. sybilla) . 

 The example is unusually instructive, because the non-mimetic 

 ancestor of the mimic is still very abundant in Canada and the 

 north-eastern States, and we thus possess the material for recon- 

 structing the history by which the one form originated from the 

 other. We know that this ancestor, Limenitis arthemis, has per- 

 sisted almost unchanged, because of the resemblance between its 

 pattern and that of the other species of Limenitis (using the name 

 in the broad sense) from all parts of the circumpolar land-belt, 

 including North America itself. The difference between the pat- 

 tern of the mimic and that of its non-mimetic parent is enormous 

 — probably as great as that between any two butterflies in the 

 world; l)ut the steps by which the transition was effected were 

 long ago suggested by S. H. Scudder,^\ and have recently been 

 worked out in considerable detail by the present writer.'' 



L. arthemis exhibits the characteristic "White Admiral" 

 pattern — possessing on the upper surface a dark ground-colour 

 with a broad white band crossing both wings, and white markings 

 within the apex of the fore wing. Reddish or orange spots be- 

 tween the white bands and the margin are found in the hind 

 wings of many individuals, more rarely in the fore wings. These 

 latter markings are of the utmost importance, for, as Scudder 

 long ago pointed out (1. c, 714), they undoubtedly provided the 

 foundation for the change into the mimetic archippus. 



A careful comparison between arthemis and archippus reveals 

 the most conclusive evidence of selection. The one species has 

 become changed into the other precisely as if an artist were to 

 paint the pattern of archippus upon the wings of arthemis, retain- 

 ing 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 trans- 

 formation 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 elaborate change than on the upper; but 

 it is not necessary to repeat here the details which have been onh' 

 recently fully described.'" I will, however, allude to the fate of 



^^Butterflies of the Eastern United States and Canada, Cambridge, Mass. 

 <1889), 278, 714. 



'5 l^rans. Ent. Soc. llond., (1908), 454-460. 



»'• Trans. Ent. Soc. Loud. (1008), 454-400). 



