146 MIMICRY IN N. AMERICAN BUTTERFLIES 



very simplest and sharpest pictures of organic 

 transformation presented for our investigation. 

 An effect — generally a strongly marked and con- 

 spicuous effect — has been brought about in those 

 elements which make up the superficial appear- 

 ance of a species, and this important change is 

 manifestly in the direction of only a minute 

 fraction of the infinitely complex organic environ- 

 ment, viz. that fraction contributed by the super- 

 ficial appearance of one or more very different 

 species, commonly indeed of but a single one. 

 When, as in North America, a recent invader 

 becomes the model determining the direction of 

 evolution in some constituent of the ancient 

 butterfly fauna, the case becomes especially 

 striking. 



The effects produced on the mimic are 

 generally sharper and more distinct than those 

 seen in the concealing resemblances to bark, 

 lichen, earth, &c., — the difference corresponding 

 to the more definite and individual appearance 

 usually presented by the pattern of the model 

 as compared with such elements in the vegetable 

 and mineral surroundings. There are also other 

 important differences. The models of Mimicry 

 are generally more restricted in their range, 

 and differ more widely in different areas and in 

 different parts of the same area than the models 

 of cryptic resemblance. Differences between the 

 local forms of the same model imply that the 

 mimicked species has itself been subject to rapid 



