ON THE PRINCIPLES OF CLASSIFICATION. 



IT may be said that investigations upon the structure of animals 

 have already yielded all the information coming from this source 

 which can serve to improve our classification of the animal kingdom. 



After the great natural divisions of the animal kingdom have 

 been circumscribed in accordance with their anatomical structure ; 

 after the classes of the animal kingdom have been characterized by 

 organic differences, it is hardly possible to expect that further inves- 

 tigations upon the structure of animals will afford the means of 

 establishing correctly the natural relations of the families. For it is 

 already seen that the amount of organic difference which exists be- 

 tween the different families is either too insignificant to afford a test 

 by which to settle their pre-eminence or inferiority, or so striking as 

 to impress us with an exaggerated idea of their indifference. Many 

 examples could be quoted to show, that, in this respect, from the 

 same identical facts, naturalists have arrived at very opposite conclu- 

 sions. And this diversity of opinion among investigators of equal 

 ability, leads me to think that comparative anatomy has done its 

 work in that direction, and that we must seek for another principle 

 in order to settle in a natural way the respective positions of the 

 minor divisions throughout the animal kingdom, and to set aside, 

 once forever, the arbitrary decisions which we are constantly tempted 

 to introduce into our classifications, whenever we attempt to arrange 

 all the families in natural groups. Before so much had been done 

 to improve the natural classification of the animal kingdom, it was 

 hardly possible to notice how much was, on every occasion, settled 

 by induction, and even arbitrary decision, beyond what the knowledge 

 of facts would justify for the brilliant results which the introduction 



