164 THE GENESIS OF SPECIES. [CHAP. 



All this being supplemented by the intercalation of 

 armies of enemies, multitudes of ancestors of all kinds, 

 and myriads of connecting forms, whose raison d'etre may 

 be simply their utility or necessity for the support of the 

 theory of " Natural Selection." 



Nevertheless, when brought in merely to supplement 

 and accentuate considerations and arguments derived from 

 other sources, in that case difficulties connected with the 

 geographical distribution of animals are not without signi- 

 ficance, and are worthy of mention even though by them- 

 selves they constitute but simple problems, the solution 

 or non-solution of which could not alone vitally affect any 

 theory of specific origination. 



Many facts as to the present distribution of animal life 

 over the world are very readily explicable by the hypo- 

 thesis of slight elevations and depressions of larger and 

 smaller parts of its surface, but there are others which it 

 is much more difficult so to explain. 



The distribution either of animals possessing the power 

 of flight, or of inhabitants of the ocean, is of course easily 

 to be accounted for ; the difficulty, if there is really any, 

 must mainly be with strictly terrestrial animals of mode- 

 rate or small powers of locomotion and with inhabitants 

 of fresh water. Mr. Darwin himself observes, 1 " In regard 

 to fish, I believe that the same species never occur in the 

 fresh waters of distant continents." Now, the author is 

 enabled, by the labours and through the kindness of Dr. 

 Glinther, to show that this belief cannot be maintained ; 

 that naturalist having called his attention to the follow- 

 ing facts with regard to fish-distribution. These facts 

 show that though only one species which is absolutely 



1 "Origin of Species, "5th edition, 1869, p. 463. 



