CLASSIFICATION A TREE-LIKE STRUCTURE. 69 



will not be modified to suit the surroundings, but 

 will (until they finally disappear) retain something 

 of their primitive structure. The common posses- 

 sion of these organs is, therefore, an evidence of 

 common descent, and since they are slightly modi- 

 fied, they will be the most important features for de- 

 termining relations. It is seen, on the other hand, 

 why it is that adaptive likeness, such as that between 

 the fish and the whale, is of no use in classification. 

 It becomes evident why indeed it is that the rudi- 

 mentary teeth in the jaws of the embryo whale are 

 of more importance, as indicating relationship, than 

 the whole of the remarkable resemblance to the 

 fish. Nearly all of the somewhat intricate princi- 

 ples of classification, arrived at originally from 

 purely empirical grounds, can now be elucidated 

 by a clear understanding of this principle and expla- 

 nation of classification. In short, it becomes clearly 

 evident that the true classification of the organic 

 world is not in isolated parallel lines, as was pre- 

 viously believed, but after the form of a branching 

 tree. This sort of classification may therefore be 

 looked upon as definitely settled by the combined 

 aid of paleontology, embryology, and the compara- 

 tive study of adult anatomy, although it was origi- 

 nally the result of the conception of evolution. 



Although this conclusion may be regarded as set- 

 tled, it of course by no means proves the descent the- 

 ory. What it does prove is that the facts are in 

 harmony with the descent theory and are not in har- 

 mony with the older idea of types. It is perfectly 

 possible that the idea of types and of special creation 



