THEORY OF EVOLUTION 9 



the same genei-al arrangement is found in all. 

 Anyone familiar with the evidence will, I think, 

 probably reach the conclusion either that these 

 animals have been created on some precon- 

 ceived plan, or else that they have some other 

 bond that unites them; for we find it difficult 

 to believe that such complex, yet similar things 

 could have arisen independently. But we try 

 to convince our students of the truth of the 

 theory of evolution not so much by calling their 

 attention to this relation as by tracing each 

 organ from a simple to a complex structure. 



I have never known such a course to fail in 

 its intention. In fact, I know that the student 

 often becomes so thoroughly convinced that 

 he resents any such attempt as that which I 

 am about to make to point out that the evidence 

 for his conviction is not above criticism. 



Because we can often arrange the series of 

 structures in a line extending from the very 

 simple to the more complex, we are apt to be- 

 come unduly impressed by this fact and con- 

 clude that if we found the complete series we 

 should find all the intermediate steps and that 

 thev have arisen in the order of their complex- 



