ii8 EVOLUTION AND NATURAL THEOLOGY. 



might fall back upon this explanation in lieu of 

 a better ; but the variety of the Large White 

 Butterfly (Pieris Brassicce), which is found in 

 Madeira, very closely resembles the Himalayan 

 variety of the same insect. 



Two other explanations may be suggested. 

 It is possible that in some rare cases, a species 

 may be exposed to such influences as to cause it 

 to vary in nearly the same manner in widely 

 separated countries ; or else that such cases 

 represent an old form of a widely distributed 

 species, which has remained unchanged in 

 some portions of its range, while it has become 

 either extinct or modified in other countries. 



