52 EVOLUTION 



of organogenesis (the development of organs) 

 some sort of repetition of the stages in the 

 evolution of organs. The embryo of a 

 higher Vertebrate has still in some measure 

 to recapitulate the steps taken by the devel- 

 oping embryo of a lower Vertebrate; and 

 though we may say that this is an architec- 

 tural necessity, that the end could be reached 

 in no other way, the facts seem to press us 

 to go further and say that something in the 

 inheritance, which is due to literal blood- 

 relationship, compels the repetition. 



Professor T. H. Morgan states the case as 

 follows: 'The most fundamental difference 

 between the view of von Baer and modern 

 views is due to our acceptation of the theory 

 of evolution, which seems to make it possible 

 to get a deeper insight into the meaning of 

 the repetition, that carries us far ahead of 

 von Baer's position. For with the accept- 

 ance of this doctrine we have an interpre- 

 tation of how it is possible for the embryonic 

 stages of most members of a group to have 

 the same form, although they are not 

 identical. There has been a continuous, 

 although divergent, stream of living ma- 

 terial, carrying along with it the sub- 

 stance out of which the similar embryonic 

 forms are made. As the stream of embry- 

 onic material divided into different paths it 



