CHAPTER V. 



CLASSIFICATION. 



Classification is the arrangement of a number of diverse 

 objects into larger or smaller groups, according as they ex- 

 hibit more or less likeness to one another. The excellence 

 of any given classification will depend upon the nature of 

 the points which are taken as determining the resemblance. 

 Systems of classification, in which the groups are founded 

 upon mere external and superficial points of similarity, 

 though often useful in the earlier stages of science, are 

 always found in the long-run to be inaccurate.- It is need- 

 less, in fact, to point out that many living beings, the struc- 

 ture of which is fundamentally different, may, nevertheless, 

 present such an amount of adaptive external resemblance to 

 one another, that they would be grouped together in any 

 " artificial " classification. Thus, to take a single example, 

 the whale, by its external characters, would certainly be 

 grouped amongst the fishes, though widely removed from 

 them in all the essential points of its structure. " Natural" 

 systems of classification, on the other hand, endeavour to 

 arrange animals into divisions founded upon a due consi- 

 deration of all the essential and fundamental points of 

 structure, wholly irrespective of external similarity of form 

 and habits. Philosophical classification depends upon a 

 due appreciation of what constitute the true points of differ- 



