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, itis universal. Thi 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. yol. ii, The Birda 
