egg. It lies on the nucleus and is sharply distinguished 

 from the yolk membrane by its non-transparency and by its 

 loose structure. By lifting the yolk membrane from the 

 yolk it remains lying there. The blastoderm grows hourly 

 under incubation. Later it is composed of three layers — the 

 serous, vascular, and mucous — and finally, after the dis- 

 appearance of the yolk membrane, it contains the yolk in 

 itself" (p. 514). Oken's response indicated that Pander's 

 clear description had reached his consciousness. "This 

 means that the blastoderm and cover do not have any 

 relationship to the yolk membrane. "34 



On Oken's question about the nature and destiny of the 

 nucleus, Pander answered that the nucleus is represented in 

 the form of a whitish cap and corresponds with the cover of 

 the non-incubated egg. At the time of incubation, along 

 with the growth of the blastoderm, it loses its regular 

 form. By the seventh day it gradually disappears. 



Oken asked what is situated between the blastoderm and 

 the yolk membrane. Pander's response was: "Nothing; they 

 are directly connected. "35 



Concerning the relationship of the primary folds to the 

 spinal cord, which Oken did not understand, Pander was not 

 able to give a satisfactory explanation. 



The next two questions, about the development of the 

 heart and the digestive organs, Pander answered together. 

 He noted Oken's mistaken idea about digestive canal formation 

 as a blowing tube with a gaping opening. He objected to 

 the non-empirical nature of Oken's stress on a sac-shaped 

 beginning stage of development. "In order to understand the 

 formation of the heart and the intestinal canal," Pander 

 wrote, "it must be considered that the blastoderm is composed 

 of three layers." 



The lower one, membrana pituitosa, takes upon 

 itself the formation of the intestinal canal ; 



34. Pander, "Entwickelung des Kuchels," p. 514. 



35. Ibid. 



265 



