364 



Classification. 



Chap. XIV. 



is supported by observing the great diversity of forms which, in any 

 small area, come into the closest competition, and by certain facts 

 in naturalisation. 



I attempted also to show that there is a steady tendency in the 

 forms which are increasing in number and diverging in character 

 to supplant and exterminate the preceding, less divergent and less 

 improved forms. I request the reader to turn to the diagram 

 illustrating the action, as formerly explained, of these several 

 principles ; and he will see that the inevitable result is, that the 

 modified descendants proceeding from one progenitor become broken 

 up into groups subordinate to groups. In the diagram each letter 

 on the uppermost line may represent a genus including several 

 species ; and the whole of the genera along this upper line form 

 together one class, for all are descended from one ancient parent 

 and, consequently, have inherited something in common. But the 

 three genera on the left hand have, on this same principle, much in 

 common, and form a sub-family, distinct from that containing the 

 next two genera on the right hand, which diverged from a common 

 parent at the fifth stage of descent. These five genera have also 

 much in common, though less than when grouped in sub-families ; 

 and they form a family distinct from that containing the three 

 genera still farther to the right hand, which diverged at an earlier 

 period. And all these genera, descended from (A), form an order 

 distinct from the genera descended from (I). So that we here have 

 many species descended from a single progenitor grouped into 

 genera ; and the genera into sub-families, families, and orders, all 

 under one great class. The grand fact of the natural subordination 

 of organic beings in groups under groups, which, from its famili- 

 arity, does not always sufficiently strike us, is in my judgment thus 

 explained. No doubt organic beings, like all other objects, can be 

 •classed in many ways, either artificially by single characters or more 

 naturally by a number of characters. We know, for instance, that 

 minerals and the elemental substances can be thus arranged. In 

 this case there is of course no relation to genealogical succession, 

 and no cause can at present be assigned for their falling into 

 groups. But with organic beings the case is different, and the 

 view above given accords with their natural arrangement in group 

 under group ; and no other explanation has ever been attempted. 



Naturalists, as we have seen, try to arrange the species, genera, 

 and families in each class, on what is called the Natural System. 

 But what is meant by this system ? Some authors look at it merely 

 -as- a scheme for arranging together those living objects which are 

 most alike, and for separating those which are most unlike; or as 



