GROWTH OF IDEAS 269 



scheme to that of the other higher mammals, was 

 not discovered in 1868 by the wicked Haeckel, but 

 in 1827 by the great master of embryological 

 research, Carl Ernst von Baer. The considerable 

 external resemblance, at certain stages of develop- 

 ment, between the embryos of reptiles, birds, and 

 mammals, including man, was decisively established 

 by the same great scientist. These really remark- 

 able stages in the development of the human 

 embryo, during which, in accordance with the 

 biogenetic law, it shows clear traces of the gill-slits 

 of its fish-ancestors, and has a corresponding fin- 

 like structure of the four limbs and a very con- 

 siderable tail, can be seen by the general reader at 

 any time in the illustrated works of His, Bcker, and 

 KoUiker (Haeckel's chief opponents) or in any 

 illustrated manual of embryology, and their full 

 force as evolutionary evidence can be appreciated. 

 Any man that constructs his philosophy in such a 

 way that, in his conviction, it stands or falls with 

 the existence of these embryonic phenomena, is in 

 a very delicate position, apart altogether from 

 Haeckel. His philosophy will collapse, even if the 

 History of Creation had never been written. 



These curious discussions did not seriously inter- 

 fere with the success of the book. In thousands 

 and thousands of minds, in 1868, this little work 

 proved the grain of seed that led on in time to 

 serious thought. From that time onward Haeckel 

 knew that he had not only scientific colleagues and 

 academic pupils, but a crowd of followers. When 

 he made an excursion into the northern part of the 



