IN NATURAL HISTORY. 13 
Many modifications of Cuvier’s great divisions 
have been attempted ; but though some improve- 
ments have been made in the details of his 
classification, all departures from its great funda- 
mental principle are errors, and do but lead us 
away from the recognition of the true affini- 
ties among animals. Some naturalists, for in- 
stance, have divided off a part of the Radiates 
and Articulates, insisting upon some special fea- 
tures of structure, and mistaking these for the 
more important and general characteristics of 
their respective plans. Subsequent investiga- 
tions have shown these would-be improvements 
to be retrograde movements, only proving more 
clearly that Cuvier detected in his four plans 
all the great structural ideas on which the vast 
variety of animals is founded. This result is 
of greater importance than may at first appear. 
Upon it depends the question, whether all such 
classifications represent merely individual im- 
pressions and opinions of men, or whether there 
is really something in Nature that presses upon 
us certain divisions among animals, certain affin- 
ities, certain limitations, founded upon essen- 
tial principles of organization. Are our systems 
the inventions of naturalists, or only their read- 
ing of the Book of Nature? and can that book 
have more than one reading? If these clas- 
sifications are not mere inventions, if they are 
