NOMENCLATURE. 139 



and negative characters, with which to construct the pri- 

 mary divisions. In the first division, subordinate groups 

 may be formed, distinguished by the terms Pilose, Plu- 

 mose, Squamous, Testaceous and Crustaceous. Each group 

 might be farther subdivided by the numerous modifications 

 whicli these cuticular appendices exhibit. If we pursue the 

 same course with any of the other systems, — the motive, 

 sentient, nutritive or reproductive, each will exhibit peculi- 

 ar classes and orders. If we attempt, therefore, to classify 

 animals in this manner, we shall obtain as many Natural 

 Methods of classification as there are Systems of Organs. 



The advantages attending the classification of animals, 

 by the systems of organs they possess, are numerous. We 

 are able, in this manner, to comprehend all the modifica- 

 tions of form, structure, and function, of which an or- 

 gan is susceptible, and consequently to become better ac- 

 quainted with its relations and its uses. But, at the same 

 time, it would be inconvenient to have so many diiferent 

 primary divisions, and to have the cliaracters of a species so 

 divided and separated, that for the right understanding of 

 the whole, it would be necessary to consult the divisions of 

 eight or ten different classes. This mode of classifying 

 animals by their different systems of organs, though the 

 only one entitled to the appellation of a Natural Method, 

 has scarcely ever been practised by zoologists, unless in 

 detached physiological disquisitions. 



If w^e employ, exclusively, as the basis of our classi- 

 fication, any one of the systems of organs, we shall find, 

 that having formed a natural genus from the obvious 

 marks which it furnishes, it shall contain species differing 

 greatly from each other in the characters exhibited by one 

 or more of the remaining organs of the other systems. The 

 genus Helix of Linnaeus, is a natural genus in reference to 

 a portion of the cutaneous system, the shell, but it exhibits in 



