90 ON THE VARIATION OF SPECIES. 



a form which will not interbreed with the one from which it 

 was derived, although given. am }3le opjDortunities of doing 

 so, and does not exhibit signs of reverting to its parent form 

 when placed under the same conditions with it. Morpho- 

 logical 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 

 wdiich clearly appears to be the parent, coexists with one that 

 has evidently been derived from it. Generally, the supposed 

 parent also seems to have been modified, and then the de- 

 monstration 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 

 perhaps 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 observa- 

 tion of such will lead to the conclusion that new species in 

 all cases must have arisen out of variable and widely dis- 

 seminated 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 pre- 

 senting itself as a constant form, quite distinct from the one 

 we set out with. If we meet with any two of these modifi- 

 cations living side by side, and maintaining their distinctive 



