174 MIMICRY IN N. AMERICAN BUTTERFLIES 



chemical forces of the environment, then the 

 Danaidas express the Old World tropics and the 

 species of Limenitis the northern land-belt. We 

 might expect on this theory that the Danaidas, 

 when they invaded the northern zone, might come 

 to resemble the Limenitis ; but the transformation 

 that has actually occurred is entirely inconsistent 

 with any such hypothesis. Although the Danaidas 

 have undergone no important change in the new 

 environment, their presence has entirely trans- 

 formed and brought into a close superficial re- 

 semblance to themselves the descendants of a 

 member of an ancient group. Such a fact is in- 

 consistent with any interpretation as yet offered 

 except that which refers the change to the accu- 

 mulation by selection of variations which promote 

 a likeness to the Danaidas. 



The facts also bear upon the two theories of 

 Mimicry associated with the names of H. W. Bates 

 and Fritz Miiller. According to Bates's theory, 

 Mimicry is a special form of protective or cryptic 

 resemblance. In the ordinary examples of this 

 principle, species are aided hi the struggle by 

 concealment, by a likeness to some object of no 

 interest to their enemies (such as bark, earth, &c.) ; 

 in these special examples (called mimetic) species 

 are aided by resembling some object which is un- 

 pleasant or even dangerous to their foes. Fritz 

 Miiller's theory of Mimicry includes the cases 

 in which the mimics, as well as their models, 

 are specially defended, although generally to an 



