THREE STAGES IN DEVELOPMENT. 36 1 



embryos of the lower and the higher Vertebrates ; as yet, 

 however, the embryo of Man is hardly distinguishable from 

 that of the higher Mammals. Finally, in the third stage 

 (lower row of Section III.), in which the gill-arches have 

 already disappeared and the face is formed, the differences 

 become more evident, and grow, henceforth, more and more 

 striking. The significance of such facts as these cannot be 

 over-estimated. ^*^^ 



If there exists an inner, causal connection between the 

 incidents of germ-history and those of tribe-history, as in 

 accordance with the law of heredity, we must assume then 

 these ontogenetic facts immediately afford most important 

 phylogenetic conclusions. For the wonderful and compre- 

 hensive harmony between the individual evolution of Man 

 and that of other Vertebrates is only explicable by assuming 

 the descent of these from a common parent-form. Indeed 

 this common descent is now granted by all able naturalists 

 who in place of a supernatural creation assume a non- 

 miraculous evolution of organisms. 



