260 THE LOWER AMAZONS. Chap. VL 



mode in which they occur and their relative geogra- 

 phical positions being in favour of the supposition 

 that H. Thelxiope has been derived from H. Melpo- 

 mene. Both are nevertheless good and true species 

 in all the essential characters of species ; for, as 

 already observed, they do not pair together when 

 existing side by side, nor is their any appearance of 

 reversion to an original common form under the same 

 circumstances. 



In the controversy which is being waged amongst 

 Naturalists, since the publication of the Darwinian 

 theory of the origin of species, it has been rightly said 

 that no proof at present existed of the production of a 

 physiological species, — that is, a form which will not 

 interbreed with the one from which it was derived, 

 although given ample opportunities of doing so, and 

 does not exhibit signs of reverting to its parent form 

 when placed under the same conditions with it. Mor- 

 phological species, — that is, forms which differ to an 

 amount that would justify their being considered good 

 species, have been produced in plenty through selection 

 by man out of variations arising under domestication or 

 cultivation. The facts just given are, therefore, of some 

 scientific importance ; for they tend to show that a 

 physiological species can be and is produced in nature 

 out of the varieties of a pre-existing closely allied one. 

 This is not an isolated case ; for I observed, in the 

 course of my travels, a number of similar instances. 

 But in very few has it happened that the species which 

 clearly appears to be the parent coexists with one that 

 has been evidently derived from it. Generally the sup- 



