138 SINGLE CENTRES OP CREATION. [Chap. XH, 



It would be hopelessly tedious to discuss all the excep- 

 tional cases of the same species, now living at distant 

 and separated points, nor do I for a moment pretend that 

 any explanation could be offered of many instances. 

 But, after some preliminary remarks, I will discuss a 

 few of the most striking classes of facts; namely, the 

 existence of the same species on the summits of distant 

 mountain ranges, and at distant points in the arctic and 

 antarctic regions; and secondly (in the following chap- 

 ter), the wide distribution of freshwater productions; 

 and thirdly, the occurrence of the same terrestrial species 

 on islands and on the nearest mainland, though sepa- 

 rated by hundreds of miles of open sea. If the exist- 

 ence of the same species at distant and isolated points 

 of the earth's surface, can in many instances be explained 

 on the view of each species having migrated from a 

 single birthplace; then, considering our ignorance with 

 respect to former elimatal and geographical changes and 

 to the various occasional means of transport, the belief 

 that a single birthplace is the law, seems to me incom- 

 parably the safest. 



In discussing this subject, we shall be enabled at the 

 same time to consider a point equally important for us, 

 namely, whether the several species of a genus which 

 must on our theory all be descended from a common 

 progenitor, can have migrated, undergoing modifica- 

 tion during their migration, from some one area. If, 

 when most of the species inhabiting one region are dif- 

 ferent from those of another region, though closely 

 allied to them, it can be shown that migration from the 

 one region to the other has probably occurred at some 

 former period, our general view will be much strength- 

 ened; for the explanation is obvious on the principle of 



