170 THE GENESIS OF SPECIES. [CHAP. 



matters, the appearance in Chile of frogs having close 

 genetic relations with European forms. But it is difficult 

 to understand the persistence and preservation of such 

 exceptional forms with the extirpation of all the others 

 which probably accompanied them, if so great a migration 

 of northern kinds had been occasioned by the cold of the 

 glacial epoch. 



Mr. Darwin candidly says/ " I am far from supposing 

 that all difficulties in regard to the distribution and 

 affinities of the identical and allied species, which now 

 live so widely separated in the north and south, and some- 

 times on the intermediate mountain-ranges, are removed." 

 ..." We cannot say why certain species and not others 

 have migrated ; why certain species have been modified 

 and have given rise to new forms, whilst others have re- 

 mained unaltered/' Again he adds, "Various difficulties 

 also remain to be solved ; for instance, the occurrence, as 

 shown by Dr. Hooker, of the same plants at points so 

 enormously remote as Kerguelen Land, New Zealand, and 

 Fuegia ; but icebergs, as suggested by Lyell, may have 

 been concerned in their dispersal. The existence, at these 

 and other distant points of the southern hemisphere, of 

 species which, though distinct, belong to a genera exclu- 

 sively confined to the south, is a more remarkable case. 

 Some of these species are so distinct that we cannot 

 suppose that there has been time since the commencement 

 of the last glacial period for their migration and subse- 

 quent modification to the necessary degree." Mr. Darwin 

 goes on to account for these facts by the probable exist- 

 ence of a rich antarctic flora in a M arm period anterior to 

 the last glacial epoch. There are indeed many reasons 



1 "Origin of Species," 5th edition, p. 459. 



