54 DOCTRINE OF EVOLUTION 



and minor divisions of animals do not follow in the 

 order of the rungs of a ladder, even though they must be 

 assigned to different levels according to the complexity 

 of their construction. The summary given above, 

 namely, that the occurrence of lower and higher levels 

 reveals an order of evolution, is amplified and not con- 

 tradicted by the statement that the species of animals 

 are grouped in a treeHke arrangement. It is the task 

 of the evolutionist, provided with all the facts of com- 

 parative anatomy and deahng only with the various 

 species as separate leaves, so to speak, to reconstruct 

 the now invisible but not unreal twigs and branches 

 and limbs of the animal tree, and to show how they have 

 diverged at one time or another as they have grown 

 and spread to produce the species of the present day. 

 This he may do in so far as he may find sufficient 

 materials to enable him to employ the methods of 

 comparative anatomy and the great natural principle 

 established by this method that essential likeness 

 means consanguinity. 



No evidence of evolution could be more significant 

 and interesting than the results provided by the com- 

 parative study of development. In the first place it is 

 an obvious fact that every living thing changes in the 

 course of its life-history, and if as an adult it occupies 

 a high place in the animal scale, its embryological trans- 

 formation is more elaborate and intricate than in the 

 case of a lower form. Every one knows that organisms 

 do develop, and yet I believe that few appreciate the 

 tremendous significance of the mere fact that this is 



