128 ON SYSTEMATIC ZOOLOGY. 



began, that as these mixed 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. 



( 1 80.) 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. 



