CHAPTER I. 
SYNTHETICAL GROUPING OF THE PLACENTAL ANIMALS. 
Any attempt to overthrow existing theories unanimously 
approved by men competent to decide on their merits — 
such for instance as Newton’s of the planetary movements 
— should not only be made with the greatest caution, but 
received with the greatest distrust. We learn to consider 
such theories higher than the result of human ingenu¬ 
ity, and to regard the men who have revealed them as 
distinct from speculators, however skilful. But when, 
as in the arrangements of Natural History, there exists 
no general plan, each systematist enjoying the exclusive 
monopoly of his own views, it must be obvious that the 
true arrangement — the theory we can regard as greater 
than resulting from human ingenuity—is yet undiscovered. 
In a work on Astronomy, if the theory be not Newtonian 
it is nothing; but when a systematic work on Zoology 
makes its appearance, we immediately enquire “what is 
the arrangement?” We compare its merits with those of 
other arrangements; and so unusual a thing is it for an 
author to adopt the theory proposed by a prior author that 
such a proceeding would be held a matter of literary pi¬ 
racy : and should both authors have their works in the 
B 
