INTRODUCTION. 67 



eitlier of the parent species, if not among them- 

 selves ; thus implanting new forms and new charac- 

 teristics in a progeny, which may again and again 

 receive additional blood of the foreign stock, with 

 the more facility, since the hybrid conformation is 

 already prepared for further adulteration ; and, not- 

 withstanding the known tendency to sterility, obli- 

 terate specific distinctions, and form a homogeneous 

 race. 



The circumstances of the existence of dissimilar 

 forms of a common type, are parallel to those of the 

 Argali, (Ovis Ammon,) equally found identical or 

 different in Asia, Africa, and the islands of the 

 Mediterranean, which existed anciently in Spain, 

 and at this moment is spread over a great part of 

 western North America. In no case are these ani- 

 mals suspected to have been transported by human 

 intervention, and yet they are located in some places 

 where, without the aid of man, they cannot have 

 migrated, unless we admit of changes on the surface 

 of the earth since the present Zoology Mas in being, 

 of such magnitude, as to include the formation of 

 the Mediterranean — the separation of the British 

 Islands from the continent of Europe — of the Indian 

 Islands from that of Asia — and the formation of a 

 channel to cut America from connexion with the 

 Old World. How this genus Ovis could have re- 

 sisted the effects of extreme alterations of climate 

 such as then must have occurred under the two con- 

 ditions of existence before and after the great catas- 

 trophe, forms a further case of difficulty ; while to 



