REQUISITES OF A NATURAL SYSTEM. ]29, 



it attempts to explain the analogies or resemblances 

 between the individuals or divisions of one circular series, 

 when they are compared with those of another series. 

 It is evident that all natural objects possess two dif- 

 ferent sorts of relationship : one which is immediate., 

 and another which is remote. The goatsucker and the 

 swallow exemplify the first of these relations. These 

 genera are intimately connected by structure, habits, and 

 economy ; both fly nearly in the same manner, and both 

 live upon insects, captured in the same way : but the 

 goatsucker, besides this relation, has evidently another to 

 the bats, — by flying at the same hour of the day, and by 

 feeding in the same manner. The first relation is in- 

 timate — the latter remote. Hence arises the necessity, 

 imposed upon all who wish to develope the natural 

 system, of possessing clear perceptions of these two sorts 

 of relations ; and of becoming well acquainted with the 

 difierence between affinity and analogy.* The first is 

 exemplified by the swallow and goatsucker ; the latter 

 by the goatsucker and the bat. Now, as these varied 

 relations or resemblances are so universal throughout 

 nature, that they have been perceived since science first 

 dawned upon man, it is obvious that, a writer who makes 

 no effort to explain them, or to draw a just distinction 

 between such as are immediate and such as are remote, 

 neglects one of the most striking and wonderful pecu- 

 liarities of the natural system. Nor is a bare mention 

 of such relations the only notice which is required ; for 

 that carries with it no results : the accuracy of his series 

 must depend upon being able to prove that all these 

 resemblances follow each other in a uniform pro- 

 gression : because it has been repeatedly demonstrated 

 that the contents of one circular group represent the con- 

 tents of another circular group ; and this principle of the 

 natural system has been now so much developed, that not 

 a doubt can remain of its prevalence throughout nature. 

 Any system, therefore, which aims at being natural, must 



• Preliminary Discourse on Nat Hist. p. 182. 

 K 



