NATURAL SYSTEMS. 199 
or as if each had been created upon distinct plans. 
So in regard to fish, or reptiles, or insects; each is 
successively arranged independently of the others, 
as if they were so many isolated systems, and not 
merely portions of one. We may, perhaps, be cen- 
sured for dwelling upon the defects of some of the 
most influential authorities of the day ; but it should 
be remembered, that error must be removed before 
truth can be established. Natural history, like all 
other human knowledge, is progressive; nor does it at 
all follow, that, because our predecessors may have 
been mistaken on some points, we are to set aside their 
authority, or undervalue their labours, upon others. 
It has been well said of such men, that even thei 
errors are the errors of genius; and that they are 
calculated, if rightly used, to teach wisdom to such 
as come after them. Let it be remembered, also, 
that we are now investigating natural history as we 
would do any other of the physical sciences ; and that 
we can only hope to advance its interests by making it 
subject to the same general principles, and the same 
rules: of investigation, which are applicable to all. 
There cannot be a doubt, that mixed systems, how- 
ever objectionable upon the grounds we have stated, 
have done incalculable good, and have brought the 
science to such an advanced state, that, in these 
latter days, a glimpse of the natural system has at 
length opened upon us. 
(135.) We shall now shortly consider the nature 
of those classifications which aim at exhibiting uni- 
form principles and general results, and which we 
have consequently termed natural systems. The 
term, we before observed, is in some respects ob- 
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