

DISTRIBUTION OF ORGANISMS. 225 



The two great continents of the earth are the first zoological 

 divisions of its surface. The animals as well as plants of the 

 old and new world are specifically different, with very few ex- 

 ceptions ; that is, they are different in the degree which 

 naturalists agree to consider as sufficient to establish distinct 

 species. But even North and South America present different 

 animals. We also find that the animals in the north and south 

 of Asia are different, and that most of the African species are 

 distinct from those of Asia. 



The differences are in some instances so great as to be held 

 by naturalists as generic. Beyond this point, however, there 

 are parities or identities. We see, for instance, in all these 

 various regions, feline animals, ruminants, pachyderms, rodents, 

 etc. Thus, for the lion and tiger of Asia, we have a different 

 lion and the panther in Africa, the jaguar in South America, 

 and the puma ranging from Brazil to Canada. Instead of the 

 elk of Northern Europe, and the argali of Siberia, we have, in 

 North America, the moose deer and mountain sheep. Asia 

 and Africa have elephants, to which the extinct mammoth and 

 mastodon of Northern Europe and North America are 

 parallels ; and it now appears that even the horse, of which 

 there are several varieties 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 

 peculiarly 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 unimportant 

 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 exclusive 

 possession of the giraffe. To Northern 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 

 any 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 



Q 



