common to North America and Europe. 471 



1. Transportation. 



2. Former connection of the regions. 



3. Distribution from several original centres. 



4. Transmutation. 



Of these, the two first are the most obvious, but the third 

 requires to be admitted with great caution, in practice, at 

 least, if not in theory ; for, if we suppose that certain physical 

 conditions of the earth's surface require particular organic 

 forms to develop the great ends of creation, we may conceive 

 two distinct regions to exist, with physical characters so nearly 

 alike, as to be better suited for the habitation of some single 

 species than for two distinct ones ; and, in the production of 

 a new series of beings, after a geologic convulsion has swept 

 a multitude from existence, it is not impossible that certain 

 exterminated species may be revived, to demonstrate a partial 

 similarity between the two epochs, like that indicated by the 

 plentiful occurrence of genera, the identity of the members 

 of which we seldom have occasion to doubt. But, although 

 many animals are able to live under varying circumstances, 

 such a multitude of conditions are requisite to demand the 

 independent existence of the same species in the most distant 

 localities,^ that the probabilities against such an occurrence 

 cannot be less than the proportion of ten thousand to unity. 

 It remains to notice the hypothesis usually named after 

 Lamarck, certainly not because it owes its origin to him, but 

 doubtless on account of his lucid exposition of it. IMr. Lyell 

 gives a pretty full analysis of these views, for the purpose of 

 disproving them, and he has apparently succeeded in the at- 

 tempt ; but, as several zoological views have been advanced 

 since the publication of this philosopher's "Principles of 

 Geology," which tend to invalidate some of the arguments 

 brought forward, it is impossible to do justice to the hypothe- 

 sis in question without alluding to them. Thus the cat 

 mummies of Egypt were said to be indcntical with the mod- 



* See Dr. Weissenbora's remarks, iq Charlcsworlh's Mag. Nat. Hist. ii. p. 623. 



