238 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 



Birds. But the operation of the law does not stop here : 

 every thing yet known conspires to prove that, in the 

 animal creation at least, it is universal. The classes of 

 Birds and of Quadrupeds are each circular groups : their 

 minor divisions are, consequently, analogical ; hence it 

 follows, that if the types of a genus of birds represent 

 the primary divisions of the feathered creation, so also 

 must they represent the primary groups in the circle of 

 quadrupeds. The principle which regulates one extends 

 to all, or there would be no uniformity of plan or har- 

 mony of parts. This result, theoretically, or arguing 

 upon abstract reasoning, we should expect; and, ac- 

 cordingly, the more we study nature, the more is this 

 theory confirmed by analysis, and facts are explained 

 which by no other theory can be explained. Nor is this 

 principle of the natural system circumscribed to the 

 animal world ; although so little attention has been be- 

 stowed on the natural groups of plants, that, as yet, the 

 primary groups only of the vegetable kingdom have been 

 recently pointed out. We have elsewhere * illustrated 

 this theory in so many groups, of different denomina- 

 tions, in the class of Birds, and have shown its preva- 

 lence in others, that to go into further details, in this 

 place, would be superfluous. 



(294.) One of the most important results of the law 

 of representation is the clue that it affords to the location 

 of types, and to the determination of such chasms as 

 occur in imperfect groups. If the divisions of one 

 circle represent those of all others, it follows that each 

 of these divisions must have certain definite peculiarities, 

 either of structure or of economy, by which they can 

 be distinguished, and which belong only to them, and 

 the groups by which they are represented. If, there- 

 fore, a perfect group is compared with one that is im- 

 perfect, that is, with one whose affinities appear 

 broken and interrupted, we are materially assisted in 

 determining the nature of the missing types, and know, 

 with almost mathematical certainty, the true station 



* North. ZooL vol. ii. The Birds, 



