ESSAY ON CLASSIFICATION. 



divisions, Fitzinger employs those most generally in use. 

 His subdivisions or grades of these two primary groups 

 are based upon a repetition of the same differences within 

 their respective limits. The Invertebrata, in which the 

 vegetative organs prevail, are contrasted with those in 

 which the animal organs prevail; and the same distinc- 

 tion is again drawn among the Vertebrata. Each of these 

 embraces two circles, founded upon the development of 

 one particular system of organs, etc. It cannot be ex- 

 pected that the systems founded upon such principles 

 should present a closer agreement with one another than 

 those which are based upon anatomical differences; yet I 

 would ask, what becomes of the principle itself, if its ad- 

 vocates cannot even agree upon what anatomical systems 

 of organs their classes are founded 1 According to Oken, 

 the Mollusks (Acephala, Gasteropoda, and Cephalopoda) 

 represent the system of circulation ; at least, in the last 

 edition of his system, he views them, in that light, whilst 

 Fitzinger considers them as representing the system of 

 sensibility. Oken identifies the Articulata (Worms, Crus- 

 tacea, and Insects) with the system of respiration ; Fitz- 

 inger with that of motion, with the exception of the 

 Worms, including Radiata, which he parallelizes with the 

 system of reproduction, etc. Such discrepancies must 

 shake all confidence in these systems, though they should 

 not prevent us from noticing the happy comparisons and 

 suggestions to which the various attempts to classify the 

 animal kingdom in this way have led their authors. It 

 is almost superfluous to add, that, great as the disagree- 

 ment is between the systems of different physiophiloso- 

 phers, we find quite as striking discrepancies between the 

 different editions of the system of the same author. 



