THEORY OF EVOLUTION 23 



of cleavage, possessed by their common 

 ancestor. 



Accepting this view, let us ask, does the evi- 

 dence from embryology favor the theory of 

 evolution? I think that it does very strongly. 

 The embryos of the mammal, bird, and lizard 

 have gill slits today because gill slits were pres- 

 ent in the embryos of their ancestors. There is 

 no other view that explains so well their pres- 

 ence in the higher forms. 



Perhaps someone will say, Well! is not this 

 all that we have contended for! Have you 

 not reached the old conclusion in a roundabout 

 way? I think not. To my mind there is a 

 wide difference between the old statement that 

 the higher animals living today have the origi- 

 nal adult stages telescoped into their embryos, 

 and the statement that the resemblance be- 

 tween certain characters in the embryos of 

 higher animals and corresponding stages in the 

 embryos of lower animals is most plausibly ex- 

 plained by the assumption that they have 

 descended from the same ancestors, and that 

 their common structures are embryonic sur- 

 vivals. 



