development very little. The spinal cord, curved at a 

 straight angle, continues in the medulla oblongata. As a 

 result of the divergence of the lateral parts of the latter, 

 the opened fourth ventricle is formed. The four hillocks 

 are seen in the form of a divided sac. Pander was not sure 

 whether what he had seen was brain material or its membranes. 

 It is difficult to know, he wrote, because "the brain mass 

 even on the sixth day of incubation is still so soft that 

 it flows like tears. "29 



At the end of 1817, in Oken's journal I sis, 30 there 

 appeared an extensive review of Pander's dissertation. The 

 review was not signed, but there is reason to believe that 

 it came from Oken himself. The review first of all expressed 

 satisfaction that the publication of these long-awaited 

 investigations was "accomplished with unprecedented diligence, 

 monetary expenditure, and talent." Oken, if indeed he is the 

 author, implied that Pander was not the sole author of his 

 work, but only a participant in a collective with Dollinger 

 and d'Alton. Baer decisively disproved this interpretation. (72) 



Oken quite fairly and in detail reviewed the dissertation, 

 alternating statements and extracts with his notes and 

 questions. First he wanted to know what the chalazae are. 

 He expressed the idea that they are tubes through which the 

 food materials pass into the yolk, because, in his opinion, 

 during incubation the albumin and not the yolk diminishes; 

 but it is not directly connected with the embryo. This 

 fantastic assumption is confirmed, in Oken's opinion, by 

 turning the eggs many times. This twists the chalazae, and 

 their assumed pathways close; hence those long-living eggs, 

 i.e. turned many times, do not hatch. 



Oken rightly indicated the novelty and importance of the 

 discovery of the embryonic layers. He was only unsatisfied 

 with the description of their development and did not under- 

 stand how they connect with the yolk membranes. In this 

 respect Oken suggests three possibilities: 1) The layers are 

 mechanically connected with each other, "as drops of wax on 

 paper"; such structures, in his opinion, do not correspond 

 with the nature of living substances, 2) The yolk membrane 



29. Pander, DISSERTATIO, p. 68. 



30. ISIS (1817), No. 192, pp. 1529 - 1540. 



260 



