128 ON SYSTEMATIC ZOOLOGY. 
began, that as these mived methods of classification do 
not set out with aiming at that which alone bestows 
value upon an artificial system, so they do not answer 
the humble purposes of a catalogue or index ; we have, in 
fact, given an instance, from the most celebrated of their 
advocates, that they are at ‘‘ utter variance with natural 
affinities.” Of all systems, they are, consequently, the 
most objectionable. Having stated the theoretical dis- 
tinction between an artificial and a natural system, and 
dwelt more especially on the merits which should be 
apparent in the former, we shall now proceed to inves- 
tigate the essential requisites which must belong to the 
latter. ; 
(180.) It is essential to a natural system that it be 
based on certain fundamental principles, which, so far 
as the laws of nature are known, are found to be general 
throughout all her productions ; thus producing that 
uniformity of plan which every principle of sound rea- 
soning convinces us must belong to the system of the 
creation. Every one sees that there is a scale in nature: 
that animals and plants, by the intervention of an infinity 
of intermediate forms, gradually blend into each other, and 
are finally so united that we know not where to draw the 
line of demarcation. This is an acknowledged truth, 
known for centuries ; but whether this series was simple, 
or whether, in its progress, it branched off into other 
ramifications, and became complex, were questions which 
long engaged the attention of philosophers. The dis- 
coveries, however, of this century have at length set this 
question also at rest, and decided that the natural series 
is complex, forming in its progress certain deviations 
which resemble a series of circles.* It follows, there- 
fore, that no system which represents the natural series 
as simple, whatever excellencies it may possess in other 
respects, can be founded on nature, since we now know 
that such is not the natural series. 
(181.) A system can only claim to be natural when 
* The circularity of natural groups has been already dwelt upon in our 
Preliminary Discourse, p. 207. 
