RECENT ORIGIN OF MIMICS 178 



Papilionine models, and until certain general 

 conclusions have been discussed in the following 

 section. 



It has been shown that the Danaine models 

 invaded America from the Old World tropics, 

 probably following a northward route. Their 

 patterns are but little changed in the new sur- 

 roundings, and they still keep the characteristic 

 appearance of Old World Danaidas. Furthermore, 

 such changes as have taken place in the older 

 invader, D. plexippus, during its residence in the 

 New World, are also retained in those colonies 

 which, during the past half-century, have been 

 re-establishing themselves in the Old World. 

 These facts support Darwin's conclusion that the 

 physico-chemical influences of soil, climate, &c., 

 are of comparatively slight importance, a conclu- 

 sion which made him feel ' inclined to swear at 

 the North Pole, and ... to speak disrespectfully 

 of the Equator V 



The mimics on the other hand are derived from 

 characteristic and ancient inhabitants of the 

 northern land-belt. If, as the followers of the 

 theory of External Causes (see p. 148) maintain, 

 species are the expression of the physical and 



1 In a letter to Sir Charles Lyell, Oct. 11, 1859. Life and 

 Letters, ii. 212. 



