Geographical Distribution. 223 



slight, because the time allowed for it has been so 

 short. But the longer the time that a colony of a 

 species is thus completely isolated under changed 

 conditions of life the greater, according to the evolu- 

 tion theory, should we expect the change to become. 

 Therefore, in all cases where we happen to know, 

 from independent evidence of a geological kind, that 

 an oceanic island is of very ancient formation, the 

 evolution theory would expect to encounter a 

 great 'wealth of peculiar species. On the other 

 hand, as I have just observed, the special-creation 

 theory can have no reason to suppose that there 

 should be any correlation between the age of an 

 oceanic island and the number of peculiar species 

 which it may be found to contain. 



Therefore, having considered the principles of geo- 

 graphical distribution from the widest or most general 

 point of view, we shall pass to the opposite extreme, 

 and consider exhaustively, or in the utmost possible 

 detail, the facts of such distribution where the con- 

 ditions are best suited to this purpose that is, as I 

 have already said, upon oceanic islands, which may be 

 metaphorically regarded as having been formed by 

 nature for the particular purpose of supplying natura- 

 lists with a crucial test between the theories of 

 creation and evolution. The material upon which my 

 analysis is to be based will be derived from the most 

 recent works upon geographical distribution espe- 

 cially from the magnificent contributions to this depart- 

 ment of science which we owe to the labours of Mr. 

 Wallace. Indeed, all that follows may be regarded as 

 a condensed filtrate of the facts which he has collected. 

 Even as thus restricted, however, our subject-matter 



