XXIV INTRODUCTION. 



researches of the great Von Baer we are indebted 

 for the enunciation of this important principle.^ 



Since the number of animal beings is exceed- 

 ingly great, it seems needless to insist upon the 

 necessity of arranging them into groups, so that 

 they may be readily compared with one another* 

 But it must not be inferred that it is the sole or 

 even the chief end of classification, so to facilitate 

 reference that the relative position of any animal 

 may be at once determined by means of easily re- 

 cognisable external characters. Systems which 

 propose to effect this object alone are termed 

 artificial, and of such systems there may be se- 

 veral. True classification is contradistinguished 

 by the term natural, since it may be defined as 

 the right appreciatiooi of the mutual relations 

 of animals, as dependent upon those characters 

 and capacities tvhich they have received from 

 their Creator, And as there is but one Author of 

 Nature, so also there can be but one true interpre- 

 tation of that Author's plan, though from insuffi- 

 cient knowledge and other causes, the various 

 attempts to frame a natural classification which 

 have hitherto been proposed, all differ more or 

 less from one another in matters of detail. 



We have already seen that animals may differ 

 from one another in the varying complexity 

 of their organisation. Differences of this kind, 

 which are usually obvious, were supposed, by the 



