Chap. XIII. CLASSIFICATION. 433 



so perfect a collection : nevertheless, in certain classes, 

 we are tending in this direction ; and Milne Edwards 

 has lately insisted, in an able paper, on the high import- 

 ance of looking to types, whether or not we can separate 

 and define the groups to which such types belong. 



Finally, we have seen that natural selection, which 

 results from the struggle for existence, and which almost 

 inevitably induces extinction and divergence of character 

 in the many descendants from one dominant parent- 

 species, explains that great and universal feature in the 

 affinities of all organic beings, namely, their subordina- 

 tion in group under group. We use the element of 

 descent in classing the individuals of both sexes and of 

 all ages, although having few characters in common, 

 under one species ; we use descent in classing acknow- 

 ledged varieties, however different they may be from their 

 parent ; and I believe this element of descent is the hid- 

 den bond of connexion which naturalists have sought 

 under the term of the Natural System. On this idea of 

 the natural system being, in so far as it has been perfected, 

 genealogical in its arrangement, with the grades of differ- 

 ence between the descendants from a common parent, 

 expressed by the terms genera, families, orders, &c, we 

 can understand the rules which we are compelled to 

 follow in our classification. AVe can understand why we 

 value certain resemblances far more than others ; why 

 we are permitted to use rudimentary and useless organs, 

 or others of trifling physiological importance ; why, in 

 comparing one group with a distinct group, we summarily 

 reject analogical or adaptive characters, and yet use these 

 same characters within the limits of the same group. 

 We can clearly see how it is that all living and extinct 

 forms can be grouped together in one great system ; 

 and how the several members of each class are con- 

 nected together by the most complex and radiating 



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