56 ESSAY ON CLASSIFICATION. 



The number of animals wliicli have a wide distribution is 

 so great, as far at least as genera are concerned, that, 

 it may even fairly be said that the maj ority of them have 

 an extensive geographical range, This amounts to the 

 most complete evidence, that, as far as these genera ex- 

 tend in their geographical distribution, animals, the struc- 

 ture of which is identical within this range of distribution, 

 are entirely beyond the influence of physical agents, un- 

 less these agents have the power, notwithstanding their 

 extreme diversity, within these very same geographical 

 limits, to produce absolutely identical structures of the 

 most diversified types. 1 



It must be remembered here that there are genera of 

 Vertebrata, of Articulata, of Mollusks, and of Eadiata 

 which occupy the same identical and wide geographical 

 distribution ; and that, while the structure of their respec- 

 tive representatives is identical over the whole area, as 

 Vertebrata, as Articulata, as Mollusks, as Radiata, they 

 are at the same time built upon the most different plans. 

 I hold this fact to be in itself a complete demonstration 

 of the entire independence of the structure of animals of 



1 An example may serve to bring circumscribed within the narrowest 



this argument nearer to those not limits; although a large number of 



familiar with Natural History. From them have representatives in other 



the Arctic Ocean to Cape Horn, Ame- parts of the world. It is plain, there- 



rica embraces such a variety of phy- fore, that physical agents cannot be 



sical features, that we may well sup- the cause of the existence of any of 



pose all the natural causes to which them, unless these agents act with 



the origin of organized beings could discrimination, producing mammalia 



be ascribed, to be or to have been of the same genus over the whole 



active within this range. Now there continent, and by the side of them 



is a peculiar kind of fox in Arctic other animals belonging to the most 



America ; others occur in the tern- diversified types, and agreeing with 



perate zone of that continent, and the extra-American representatives 



others again in more southern lati- of these types in every essential fea- 



tudes. With them the most diversified tare. This is tantamount to assuming 



animals of every class are associated, that such an action is the work of a 



among which there are many types, rational being, 

 the geographical range of which is 



