VON BAER AND RISE OF EMBRYOLOGY. in 



His ' Formatione Intestinorum ' embodies his greatest contribu- 

 tion to embryology rather than his { Theoria Generationis ' ; not only 

 is it a more fitting model of observation, but in it he foreshadows the 

 idea of germ-layers in the embryo, which, under Pander and Von 

 Baer, became the fundamental conception in structural embryology. 

 Throughout his work, both early and late, he likens the embryonic rudi- 

 ments, which precede the formation of organs, to leaflets. In his 

 work of 1768, he describes in detail how the leaf-like layers give rise 

 to the systems of organs: Showing that the nervous system arises 

 first from a leaf-like layer, and is followed, successively, by a flesh- 

 layer, the vascular system and, lastly, by the intestinal canal — all 

 arising from original leaf -like layers. 



In these important generalizations, although they are verbally in- 

 correct, he reached the truth as nearly as it was possible at the time, 

 and laid the foundation of the germ-layer theory. 



Wolff was a man of great power as an observer, and although his 

 influence was for a long time retarded, he should be recognized as 

 the foremost investigator in embryology before Von Baer. 



The little known of his life is gained through his correspondence 

 and a letter by his amanuensis. Through personal neglect, and 

 hostility to his work, he could not secure a foothold in the universities 

 of Germany, and, in 1764, on the invitation of Catharine of Eussia, he 

 went to the Academy of Sciences at St. Petersburg, where he spent >the 

 last thirty years of his life. 



His sincere and generous spirit is shown in his correspondence with 

 Haller, his great opponent. " And as to the matter of contention be- 

 tween us, I think thus: For me, no more than for you glorious 

 man, is truth of the very greatest concern. Whether it chance that 

 organic bodies emerge from an invisible into a visible condition, or 

 form themselves out of the air, there is no reason why I should wish 

 the one were truer that the other, or wish the one and not the other. 

 And this is your view also, glorious man. We are investigating for 

 truth only: we seek that which is true. Why then should I contend 

 with you?" 



I have not been able to locate a portrait of Wolff, although I have 

 sought one in various ways for several years. The Secretary of the 

 Academy of Sciences at St. Petersburg writes that no portrait of 

 Wolff exists there, and that they will gratefully receive information 

 regarding any existing portrait of the great academician. 



The Period of Von Baer. 



What Verworn says of Johannes Miiller's position in physiology, 

 may with equal appropriateness be applied to Von Baer in the science 

 of embryology. He was : " One of those monumental figures that the 

 history of every science brings forth but once. They change the whole 



