The Theory of Evolution 75 



group identical ; for with a sufficient knowledge of the devel- 

 opment it is always possible to distinguish between the em- 

 bryos of different species, as well as between the adults, only 

 it is more difficult to do so, because the embryonic forms are 

 simpler. 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 

 acceptance of this doctrine we have an interpretation of how 

 it is possible for the embryonic stages of most members of a 

 group to have the same form, although they are not identi- 

 cal. There has been a continuous, although divergent, stream 

 of living material, carrying along with it the substance out of 

 which the similar embryonic forms are made. As the stream 

 of embryonic material divided into different paths it has also 

 changed many of the details, sometimes even all ; but never- 

 theless it has often retained the same general method of 

 development that is associated with its particular composition. 

 We find the likeness, in the sense of similarity of plan, ac- 

 counted for by the inheritance of the same sort of substance ; 

 the differences in the development must be accounted for in 

 some other way. 



Among modern writers Hurst alone has advanced a view 

 that is similar in several respects to that which I have here 

 defended. It may be well to give his statement, since it 

 brings out certain points of resemblance with, as well as cer- 

 tain differences from, my own view. 1 He says : " Direct 

 observation has shown that, when an animal species varies 

 (i.e. becomes unlike what it was before) in adult structure, 

 those stages in the development which are nearest the adult 

 undergo a similar, but usually smaller, change. This is shown 

 in domestic species by the observations of Darwin, and the 



1 Hurst, C. H., "Biological Theories, III," "The Recapitulation Theory," 

 Natural Science, Vol. ii., 1893. 



