Classification. 27 



This general principle of natural affinity, of which 

 all naturalists have seen more or less well-marked 

 evidence in organic nature, and after which they have 

 all been feeling, has sometimes been regarded as 

 natural, but more often as supernatural. Those who 

 regarded it as supernatural took it to consist in a 

 divine ideal of creation according to types so that the 

 structural affinities of organisms were to them expres- 

 sions of an archetypal plan, which might be revealed 

 in its entirety when all organisms on the face of the 

 earth should have been examined. Those, on the 

 other hand, who regarded the general principle of 

 affinity as depending on some natural causes, for the 

 most part concluded that these must have been utili- 

 tarian causes ; or, in other words, that the fundamental 

 affinities of structure must have depended upon funda- 

 mental requirements of function. According to this 

 view, the natural classification would eventually be 

 found to stand upon a basis of physiology. Therefore 

 all the systems of classification up to the earlier part 

 of the present century went upon the apparent axiom, 

 that characters which are of most importance to the 

 organisms presenting them must be characters most 

 indicative of natural affinities. But the truth of the 

 matter was eventually found to be otherwise. For it 

 was eventually found that there is absolutely no cor- 

 relation between these two things ; that, therefore, it 

 is a mere chance whether or not organs which are of 

 importance to organisms are likewise of importance as 

 guides to classification ; and, in point of fact, that the 

 general tendency in this matter is towards an inverse 

 instead of a direct proportion. More often than not, 

 the greater the value of a structure for the purpose of 



