IMPORTANCE OF AFFINITIES 33 



We must then be guided everywhere by natural affinities in composing 

 the groups which result by dividing each kingdom into classes, each 

 class into orders, each order into sections or famihes, each family 

 into genera, and each genus into different species if there is occasion 

 for it. 



There is thorough justification for the belief that the complete series 

 of beings making up a kingdom represents the actual order of nature, 

 when it is classified with direct reference to affinities ; but, as I have 

 already pointed out, the different kinds of divisions which have to 

 be set up in that series to help us to distinguish objects with greater 

 ease do not belong to nature at all. They are truly artificial although 

 they exhibit natural portions of the actual order instituted by 

 nature. 



It should be added that in the animal kingdom, affinities should 

 be decided mainly from a study of organisation. The principles 

 employed for settling these affinities should not admit of the smallest 

 doubt. We shall thus obtain a solid basis for zoological philosophy. 



It is known that every science must have its philosophy, and that 

 it cannot make real progress in any other way. It is in vain that 

 naturalists fill their time in describing new species, in grasping all 

 the shades and small details of their varieties, in enlarging the immense 

 list of catalogued species, in establishing genera, and in making incessant 

 changes in the principles which they use. If the philosophy of science 

 is neglected her progress will be unreal, and the entire work will 

 remain imperfect. 



It is indeed only since the attempt has been made to fix the extent 

 of affinity between the productions of nature that natural science 

 has obtained any coherence in its principles, and a philosophy to make 

 it really a science. 



What progress towards perfection is made every day in our classi- 

 fications since they were founded upon the study of affinities ! 



It was through the study of affinities that I recognised that in- 

 fusorian animals could no longer be put in the same class as polyps ; 

 that radiarians also should not be confused with polyps ; and that 

 soft creatures, such as medusae and neighbouring genera, which 

 Linnaeus and even Bruguière placed among the molluscs, were essen- 

 tially allied to the echinoderms, and should form a special class with 

 them. 



It was again the study of affinities which convinced me that worms 

 were a separate group, comprising animals very different from 

 radiarians, and still more from polyps ; that arachnids could no longer 

 be classed with insects, and that cirrhipedes were neither annelids nor 

 molluscs. 



