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THE LOWER AMAZONS 



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. Morphological 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 supposed parent also seems to 

 have been modified, and then the demonstration is not 

 so clear, for some of the links in the chain of variation 

 are wanting. The process of origination of a species in 

 nature, as it takes place successively, must be ever per- 

 haps beyond man's power to trace, on account of the 

 great lapse of time it requires. But we can obtain a 

 fair view of it by tracing a variable and far-spreading 

 species over the wide area of its present distribution ; 

 and a long observation of such will lead to the conclusion 

 that new species in all cases must have arisen out of 

 variable and widely-disseminated forms. It sometimes 

 happens, as in the present instance, that we find in one 

 locality a species under a certain form which is constant 

 to all the individuals concerned ; in another exhibiting 

 numerous varieties ; and in a third presenting itself as 

 a constant form, quite distinct from the one we set out 

 with. If we meet with any two of these modifications 

 living side by side, and maintaining their distinctive 

 characters under such circumstances, the proof of the 

 natural origination of a species is complete : it could 

 not be much more so were we able to watch the process 

 step by step. It might be objected that the difference 

 between our two species is but slight, and that by classing 

 them as varieties nothing further would be proved by 

 them. But the differences between them are such as 

 obtain between allied species generally. Large genera 

 are composed, in great part, of such species ; and it is 



