14- THEORY OF EVOLUTION 



in the general relation of the parts to each 

 other. 



It is in this sense that the evidence from 

 comparative anatomy can be used 1 think as 

 an argument for evolution. It is the resem- 

 blances that the animals or plants in anj^ group 

 have in common that is the basis for such a con- 

 clusion; it is not because we can arrange in a 

 continuous series any particular variations. In 

 other words, our inference concerning the com- 

 mon descent of two or more species is based on 

 the totality of such resemblances that still re- 

 main in large part after each change has taken 

 place. In this sense the argument from com- 

 parative anatomy, while not a demonstration, 

 carries with it, I think, a high degree of 

 probability. 



The Evidence from Embryology 



In passing from the egg to the adult the 

 individual goes through a series of changes. 

 In the course of this development we see not 

 only the beginnings of the organs that gradu- 

 ally enlarge and change into those of the adult 

 animal, but also see that organs appear and 



