Even within 150 years after de Graaf ' s work, when Baer 



began to study the initial stages of development, nothing 



had been added to the understanding of the nature of the 

 ovum. 



As mentioned above, Baer's report DE OVI MAMMAL IUM 

 was published in 1827 in Latin (Figure 25) as a letter to 

 the Petersburg Academy of Science. The next year Baer 

 published it in a reworked form in German. 2 



In the introduction to the jubilee edition in 1927 } 

 the translator (Ed.: into Russian), B. Ottov, confirmed that 

 "among all the results of Baer's investigations, the dis- 

 covery of the mammal ium ovum occupies the most significant 

 position." It is impossible to agree with this contention 

 only because the classical work UBER ENTWICKLUNGSGESCHICHTE 

 has still more significance. In the latter work, Baer actually 

 established the basis for comparative vertebrate anatomy. 

 Yet this assessment, of course, does not in any degree 

 depreciate the value of the wonderful discovery of the true 

 ovum in the mammalian ovary. 



Baer gave a detailed account in his autobiography of the 

 history of his embryonic investigations, explaining how he 

 discovered the mammalian ovum. The main method of his work, 

 which he frequently substantiated in his reports, was to trace 

 the process of development in reverse chronological order; 

 that is, to work from the already formulated condition of 

 any system or organ back to its more primitive beginning. 

 With his approach to the whole embryo, he could detect in 

 the incubated bird egg the already developing rudiment, which 

 had been named by previous embryologists the cock's trace 

 or the cover (in recent terminology, the embryonic disk) . He 

 admitted that "how the cock's trace or rudiment is formed did 

 not become completely clear to me, and it is, so far as I 

 know, still not. "3 



Baer, "Commentar zu der Schrift De ovi animalium et 

 hominis genesi," ZEITSCHRIFT FUR ORGANISCHE PHYSIK, 

 v. 2, pp. 125-192. (85) 



Baer, NACHRICHTEN, p. 413 (309) (Ed.: p. 300 in 

 German 2nd ed.). 



286 



