in Zoology and Botany. 



185 



nervous system is superior in importance to the circulatory, 

 and the latter superior to the digestive sj^stem, yet this subject 

 is still in a very indeterminate state, and until our knowledge 

 of physiology is much further advanced, disputes will always 

 arise respecting the true position of certain species in the na- 

 tural classification. Such differences of opinion, however, will 

 continually diminish as our knowledge increases, and they are 

 even now very few in comparison with the numerous facts in 

 classification on which all naturalists are agreed. Much may 

 be effected by education and habit, which impart to the natu- 

 ralist a peculiar faculty (termed by Linnaeus a " latent in- 

 stinct") for appreciating the relative importance of physiolo- 

 gical characters to the satisfaction of himself and others, even 

 in cases where he is unable to explain the principles which 

 determine his decision. 



Granting, then, that by combining the number of points in 

 which any two species agree, with an estimate of the physio- 

 logical importance of those several points of agreement, the 

 naturalist may, in practice, form a tolerably exact conception 

 of the degree of resemblance between them ; he will proceed in 

 his construction of the natural system to place these species 

 at greater or less distance from each other, in proportion to 

 that degree of resemblance. If we suppose that by a repeti- 

 tion of this process every species is placed in its true position, 

 we obtain a definition of those much-disputed terms, affinity 

 and analogy, — the former of which consists in those essential 

 and important resemblances which determine the place of a 

 species in the natural system, while the latter term (analogy) 

 expresses those unessential and (so to speak) accidental re- 

 semblances which sometimes occur between distantly allied 

 species without influencing their position in the system. 

 With analogy, therefore, we have no further concern in the 

 present discourse, as it is a principle in no way involved in 

 the natural system. Affinity, on the contrary, forms the 

 chief element in this inquiry ; and to place species in the 

 order of their affinities is to construct the natural system*. 



It appears from the above views that the natural system 

 is an accumulation of facts which are to be arrived at only bv 

 a slow inductive process, similar to that by which a country 

 is geographically surveyed. If this be true, it is evident how 



* I am aware that by many naturalists analogy is considered to be as im- 

 portant an element in the natural system as affinity is. As the discussion 

 of this question would lead us away from the present object, 1 will not enter 

 upon it now, especially as my views respecting it are stated more at large 

 in the Mag. of Nat. liist. for May last, p. 222 et scq. 



