CHAPTER 18 



SECOND PART OF UBER ENTWICKLUNGSGESCHICHTE: 



SCHOLIA AND COROLLARIES TO THE HISTORY 

 OF CHICKEN DEVELOPMENT IN THE EGG 



Baer called the second part of the first volume of his 

 work "Scholia and Corollaries" (95). In spite of that name 

 familiar to medieval students, it does not contain dogmatism 

 originating from any preconceived point of view, but penetrat- 

 ing thoughts on the basic regularities of chick development. 

 These represent generalizations of those observations stated 

 in the first part. 



The first scholium, "On the certainty of observations on 

 embryos," poses a question basic to arguments by embryo logists 

 from the seventeenth century. Specifically, is it possible to 

 confirm that the embryo exists only from that time when it, as 

 a whole, and its component parts become accessible for observa- 

 tion? Because of the narrowness of investigative means, Baer 

 asked "whether all the embryo with all its parts can be there, 

 but so finely structured that it is not accessible to the knife 

 and microscope" (I 212 (143)). 



With the example of muscle development, Baer proved that 

 the embryo as a whole does not acquire parts with minute 

 structure? and dimensions are beyond the limits of microscopic 

 powers. While the muscular fibers of the adult chicken can be 

 split into very minute fibers, seen only at very high magnifica- 

 tion, the embryonic muscle fibers are accessible for observation 

 under lenses, although they are still not formulated and can be 

 separated from each other only with difficulty. The same thing 

 applies to the nerve fibers and other component structures of 

 the embryo. Baer's general conclusion opposed the opinions of 

 the preformationists, leading to the assumption that the large 

 size of the embryonic component elements "undoubtedly makes 



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