62 ESSAY ON CLASSIFICATION. 



produced by physical agents is for ever set aside by the 

 fact that neither the birds nor the reptiles, nor, indeed, 

 any other animals of New Holland, depart in such a man- 

 ner from the ordinary character of their representatives 

 in other parts of the world ; unless it can be shown that 

 such agents have the power of discrimination, and may 

 produce, under the same conditions, beings which agree, 

 and others which do not agree, with those of different 

 continents ; not to speak again of the simultaneous occur- 

 rence, in that same continent, of other heterogeneous 

 types of Mammalia, Bats and Kodents, which occur there 

 as well as everywhere else in other continents. Nor is 

 New Holland the only part of the world which nourishes 

 animals highly diversified among themselves, and yet pre- 

 senting common characters strikingly different from those 

 of the other members of their type, circumscribed within 

 definite geographical areas. Almost every part of the 

 globe exhibits some such group, either of animals or of 

 plants, and every class of organized beings contains some 

 native natural group, more or less extensive, more or less 

 prominent, which is circumscribed within peculiar geogra- 

 phical limits. 



Among Mammalia we might quote the Quadrumana, 

 the representatives of which, though greatly diversified in 

 the Old as well as in the New World, differ and agree 

 respectively in many important points of their structure; 

 also the Edentata of South America. Among Birds, the 

 Humming Birds, which constitute a very natural, beauti- 

 ful, and numerous family, all of which are nevertheless 

 confined to America only, as the Pheasants are to the Old 

 World. 1 Among Eeptiles, the Crocodiles of the Old World 



1 What are called Pheasants in The American Pheasants, so called, 

 America do not even belong to the are genuine Grouse, 

 same family as the eastern Pheasants. 



