IMPORTANCE OF ACQUIRING FIRST PRINCIPLES. — REASONS FOR 
SUPPOSING A PLAN IN CREATION. — OPINIONS THEREON. — 
THE CIRCULAR THEORY, AND THE DIFFERENT TESTS WHICH 
EVERY CIRCLE MUST UNDERGO, EXPLAINED AND ILLUSTRATED. 
(383.) In the foregoing chapter we have laid before 
the student the qualifications which should be possessed 
both by the practical and the scientific naturalist ; and, 
having stated the objects of the former, we must now 
turn to the latter ; with the hope that the reader has both 
the time and disposition to acquire more than a super- 
ficial knowledge of zoology ; and that he is more de- 
sirous of pursuing it as a science, than to rest contented 
with being a mere collector of objects and facts. It has 
hitherto been but little the custom, with the inventors of 
systems, to lay before their disciples the reasons which 
have guided them ; it being generally taken for granted 
that the reputation of the writer rendered such a step 
unnecessary. It seldom happens, indeed, that students 
desire such information ; for if, from whatever cause, 
they resolve to adopt any particular system not connected 
with general principles, they trouble not themselves with 
seeking to know and to criticise the reasons upon which 
a system is founded. It is received by them as a law, 
propagated by a ruler of science, which they have 
neither the disposition nor the knowledge to call in 
question. This feeling continues, until they acquire 
sufficient knowledge to discover the defects (real or 
imaginary) of their favourite oracle. Itis then that the 
desire arises to know the reasons which have influenced 
the author, and the principles, if any, upon which he has 
proceeded. The student, in the méan time, has probably 
become an adept, and feels himself qualified to criticise 
that which, at the commencement of his studies, he 
