ZOOLOGICAL CLASSIFICATIONS. 205 



The characters which distinguish animals from each other 

 are far from having the same value : some are of seemingly 

 little or no physiological importance, seeing that their varia- 

 tions do not draw after them differences in the rest of their 

 economy; others never vary without coinciding with pro- 

 found modifications in the whole of their organization ; hence 

 they are called dominating, since they seem in some measure 

 to regulate these modifications. It is evident, then, that divi- 

 sions of an inferior rank can alone he based on subordinate 

 characters, while those of a higher rank ought to be founded 

 on those called dominating. To arrive, then, at a natural 

 classification of animals, it is above all necessary to know the 

 structure, functions, and mode of development of these beings ; 

 next, to inquire into the dominating characters of the organi- 

 zation of each. This we arrive at sometimes by physiological 

 considerations, at other times by anatomy only. Fixity is an 

 index of an organic domination, whilst the characters which 

 vary from one small group to another, are generally but of 

 little* interest. The nature and the degree of development of 

 the faculties, of which the organ thus modified is the instru- 

 ment, enables us also to judge, to a certain point, of the 

 zoological value of a modification of structure. But in other 

 cases, the determination of dominating characters presents 

 considerable difficulties, and analogy is not always a safe 

 guide, for the importance of an organ may vary considerably 

 in passing from one animal to another, and a part which 

 dominates in some sort the whole economy in some species 

 may in others be found fallen from its rank, and reduced 

 to play a secondary part. 



368. Zoologists are far from knowing the anatomy and 

 physiology of all animals ; neither are they agreed on the 

 relative importance of a great number of modifications of 

 structure which animals present. It is evident, then, that in 

 the existing state of science there can be no natural classifica- 

 tion ; hence also the variety of methods adopted by different 

 authors, and the modifications these methods daily undergo. 

 But this mode of classification must of necessity become more 

 perfect as our knowledge extends, and its instability, far 

 from being a defect, is the necessary consequence of its 

 perfectibility. 



369. The introduction of natural methods of classifica- 

 tion of living beings is one of the greatest services rendered 

 to natural history ; it has changed the aspect of the science, 



