NOMENCLATURE. 147 



red to form species without individuals, or genera where 

 there are no species ; but in a valuable work on fishes, fif- 

 teen orders may be observed, instituted and named, which 

 have no representatives in nature *. 



In consequence of adopting a single character, derived 

 from a particular organ, in the construction of subdivisions, 

 these will be found variously related to the different cate- 

 gories of animals in the system. Even the positive cha- 

 racter of a particular organ on which a division depends, 

 will, in many cases, be found so modified in some of the 

 subdivisions, by the intermixture with the characters of 

 other organs, as to intimate a resemblance to other groups, 

 having a rank depending on very different relations. Among 

 the Mammalia, the whale, by swimming, intimates its re- 

 semblance to fishes, and the bat, by flying, makes an ap- 

 proach to a bird, although vast differences exist in other 

 characters. However numerous the relations of a group 

 may appear to be with many others, it is not practicable to 

 make these follow one another, in reference to such gra- 

 dations or transitions. When a group is constituted by the 

 help of a positive character, it is seldom expedient to con- 

 stitute the subdivision from its modification, a positive 

 character, furnished by some other organ, being preferable. 

 In like manner, a group with a negative character, will be 

 subdivided most suitably by the employment of a positive 

 one. 



Besides these remarks, which aie of a very general na- 

 ture, it is necessary here to take notice particularly of 

 those subdivisions which are employed in Zoology, the names 

 by which they are designated, and the rules which are ob- 

 served in their construction. 



* " Histoire Naturelle des Poissons," par le C,*^" Lacepede, Paris, 5 vols.' 

 4to. 1803. 



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