NOMENCLATURE. 143 



those modifications of character which constitute the pecu- 

 liarities of its vital principle. In giving the characters of 

 a species, we are apt to introduce those which are co-exten- 

 sive with the genus or order to which it belongs. In the 

 enumeration of the characters of what are falsely termed 

 by modern zoologists natural genera, such repetitions pre- 

 vail to a very inconvenient extent, aiid in some measure re- 

 tard rather than promote the interests of science. 



The employment of the twofold method of division, by 

 positive and negative characters, is so obvious in its expres- 

 sion, and so easy of application, that the reluctance which 

 many naturalists seem to display in using it, may well excite 

 our surprise. It would keep in check that rage for innova- 

 tion, which so peculiarly marks many modern cultivators 

 of the science, by assigning the limits within which it might 

 be exercised, and it would direct their efforts to fill up the 

 blanks which remain, instead of amusing themselves with 

 new systems, fabricated one day, and destroyed another. 

 This metliod, however, may be considered as yet in its in- 

 fancy, but its adoption appears to me to be the only re- 

 medy hitherto devised for checking those fluctuations which 

 have deservedly exposed the systems of natural history to 

 ridicule ; and for rendering the progress of zoology steady 

 and triumphant. 



In selecting the characters by which we are to be guided 

 in the formation of classes and orders, there will be some 

 room for difference of opinion. This, however, may be 

 considerably diminished, by considering that those charac- 

 ters which are of easiest detection, and which produce the 

 most equal division of species, in all cases, deserve the pre- 

 ference. Judging by these rules, the twofold division of 

 animals into vertebral and invertebral, is preferable to their 

 division into such as have the nervous matter apparent, 

 and such as have it concealed or disseminated, The one 



