the specific. Baer distinguished three forms of transition 

 from the general to the specific in ontogenetic development, 

 or three forms of differentiation: the primary, histological, 

 and morphological differentiations. 



The first type, primary differentiation, comprises the 

 division of the blastoderm into layers, which Pander had 

 called plates. At first, two layers appear. The external 

 layer Baer called the animal layer, and the internal layer 

 he called the vegetative, or the plastic layer. In the animal 

 layer, a skin layer and muscular layer become differentiated; 

 they are composed of the spinal and abdominal plates "which 

 include in a nondifferentiated shape the bony, vascular and 

 muscular systems with the corresponding nerves." The 

 vegetative part also differentiates into two layers, the 

 vascular and the mucous. 



In an article supplementing the translation of the first 

 volume of UBER ENTWICKLUNGSGESCHICHTE, B. E. Raikov* 

 successfully compared the subdivision of the blastoderm into 

 embryonic layers as suggested by Pander, Baer, and later by 

 Remak; illustrating his comparison with a table^ (96) . The 

 comparison reveals that Baer's identification of the rudiment 

 layers with the embryonic layers, in the modern meaning of 

 that term, constitutes an incorrect interpretation of primary 

 differentiation. BischoffS and Filipchenko also discussed 

 this issue. 4 



It must be added that Baer's designation of two embryonic 

 layers between the skin layer (ectoderm) and the mucous layer 

 (endoderm) , and not only one "mobile-rudiment layer," as Remak 

 later identified it ("mesoderm," according to modern embryology), 

 indicate Baer's cleverness in y observation. He was capable of 



1. B. E. Raikov, "On the life of scientific activities of 

 K. M. Baer" (Ozhizni inauchnoi deyatelnosti K. M. Baer) , 

 in K. M. BAER (1950), pp. 383 - 438. 



2. Ibid ., p. 419. 



3. Theodore Bischoff. ENTWICKLUNGSGESCHICHTE DER 



SAUGETHIERE UND DES MENSCHEN (Leipzig: Voss, 1842) 

 (Vol. VII of "Anatomie" edited by Zemmering) . 



4. Translator's note: K. M. Baer, SELECTED WORKS, 

 translation with introduction and comments by 



Yu. A. Filipchenko. 



343 



