In order to arrive at their definitions, we must first prove the existence of a real natural system, a subject which involves an enquiry into the designs of creative power, one of the most awful themes which the human intellect can attempt.

The most obvious and undeniable examples of design in the organised creation are seen in the adaptation of each species to the circumstances in which it lives.

Now, if this were the sole mark of design, if each species constituted a being per se, adapted to its peculiar condition of existence, but not allied in physiological structure to its fellow species, there would then be no natural system; man might indeed clas- sify such objects according to their accidental or fancied resemblances, but there would be none of those essential peculiarities of structure which we find to pervade vast groups of beings whose external forms are often widely dis- similar.

The existence then of a comparatively few grand types of structure, or " centres of creation," from the differ- ent modifications of which the innumerable species now existing derive their characters, may be taken as a proof that species were created not absolutely, but relatively, not merely with reference to their destined mode of life, but also with reference to other species whose destination was similar, though not identical with their own.

If these views be cor- rect, it results that the resemblances of different species in essential points of structure, furnish evidences of design, less obvious, perhaps, but not less certain, than the adaptation of any one species to its external condition of existence ; and the " natural system" thus acquires an air of truth not inferior to the ocular demonstrations of anatomy.