INTRODUCTORY REMARKS. XV 



Amphibia, by the presence or absence of feet ; the 

 Fishes, by the structure of their gills, and the posi- 

 tion of their fins ; the Insects, by the number, 

 form, and structure of the wings ; but the Class 

 called Vermes, a confused assemblage of the most 

 diverse materials, was divided on no definite or 

 legitimate principle whatever. Each order was 

 distributed into subordinate groups, called Genera, 

 and each genus into Species. As this last term 

 is often somewhat vaguely used, it may not be use- 

 less to define its acceptation. It is used to signify 

 those distinct forms which are believed to have pro- 

 ceeded direct from the creating Hand of GOD, and on 

 which was impressed a certain individuality, destined 

 to pass down through all succeeding generations, 

 without loss and without confusion. Thus, the 

 Horse and the Ass, the Tiger and the Leopard, 

 the Goose and the Duck, though closely allied in 

 form, are believed to have descended from no com- 

 mon parentage, however remote, but to have been 

 primary forms of the original creation. It is often 

 difficult in practice to determine the difference or 

 identity of species ; as we know of no fixed princi- 

 ple on which to found our decisions, except the 

 great law of nature, by which specific individuality 

 is preserved, that the progeny of mixed species 

 shall not be fertile inter se. That animals of dif- 

 ferent species will breed with each other, as the 

 Horse with the Ass, is universally known ; and 

 the progeny have, in many instances, again bred 

 with either of the parental species : but there is 



