206 AFFINITIES AND GEOGRAPHICAL 



mountain sheep. Asia and Africa have elephants, to which 

 the extinct mastodon of Northern Europe and the extinct 

 mammoth of North America are parallels ; and it now 

 appears that even the horse, of which there are several varie- 

 ties in the old world, was abundant in the new, at a period 

 long antecedent to the introduction of the present breed by 

 the colonists. Australia has its emeu, Africa its ostrich, and 

 America her rhea, all similar animals, though specifically 

 different. We find simiae planted in three great regions 

 Southern Asia, Western Africa, and equinoctial America, 

 but all of different character, those of America being pecu- 

 liarly distinct in their want of the opposable thumb and of 

 callosities in the seat, as also in the use of the tail as a pre- 

 hensile instrument. Australia has only a few very unim- 

 portant mammalian animals of her own besides the marsupials, 

 which are represented by a few species in America ; but to 

 the southern part of the latter continent are confined the 

 whole family of the sloths. Africa, in like manner, has exclu- 

 sive possession of the giraffe. To North America belongs a 

 great number of genera of birds quite peculiar to it, and also 

 a greater number and variety of the rodents than are found 

 in other parts of the earth. Similar facts could be stated 

 respecting other classes of animals ; but I limit attention to 

 the mammalia, as being the most restricted in number and 

 the best known. 



Some principles governing the parity and variation of the 

 organisms spread over different regions have been observed. 

 It is found, for instance, that there is more uniformity 

 between two continents which are both in the north or south 

 hemisphere, albeit divided by wide oceans, than between two 

 portions of one continent extending into both of these hemi- 

 spheres. North America is zoologically less allied to South 

 America than it is to Northern Europe. An island, however 

 far apart, is apt to show zoological features reflective of those 

 of the nearest continent. Two countries, again, divided only 

 by a narrow sea, have usually the same flora. 



Some principle affecting the development of the higher 

 animals can also be detected, in connexion with geological 



