Chap. YI. ORIGIN OF SPECIES. 263 



acting directly on individuals had originally produced 

 this race or species, they certainly would have caused 

 much modification of it in different parts of this region ; 

 for the upper Amazons country differs greatly from the 

 district near the Atlantic in climate, sequence of sea- 

 sons, soil, forest clothing, periodical inundations, and so 

 forth. These differences moreover graduate away, so 

 that the species is subjected to a great diversity of 

 physical conditions from locality to locality, and ought 

 in consequence to present an endless series of local 

 varieties, on the view mentioned, instead of one con- 

 stant form throughout. Besides, how should we ex- 

 plain the fact of H. Thelxiope and H. Melpomene 

 both existing under the same local conditions ; and 

 how account for the diversified modifications presented 

 in one and the same" locality as at Serpa and on the 

 Tapajos?* 



There is evidently therefore some more subtle agency 

 at work in the segregation of a race than the direct ope- 

 ration of external conditions. The principle of natural 

 selection, as lately propounded by Darwin, seems to 

 offer an intelligible explanation of the facts. According 

 to this theory, the variable state of the species exhibited 

 in the districts above mentioned would be owing to 

 Heliconius Melpomene having been rendered vaguely 

 instable by the indirect action of local conditions dis- 



* As the action of external influences would be on the early states 

 of the insects and not on the adults, it is well to mention that the 

 broods of the Heliconii appear to be social ; the larvfe feeding together 

 and undergoing their last transformation on the same tree. This I 

 observed with regard to the H. Erato, a species closely allied to H. 

 Thelxiope. 



