result of the closing and accretion of the spinal layers 

 ("primary folds" of Pander) . 



Concerning Pander's ideas for the period from the 

 twentieth to the thirtieth hour of incubation, Oken 

 accepted the description of blood vessels development and 

 asked only about how the heart develops. 



The most perplexing ideas for Oken related to the 

 forty- second hour of incubation. Giving a literal 

 description from Pander concerning the depression in which 

 the head of the embryo is submerged and also concerning the 

 folds forming the borders of this depression and represent- 

 ing the rudiment of the amnion, Oken said "We do not 

 understand that. Also, as with Wolff's description . . . 

 we want to know, can anybody understand that?" 



Further on, Oken referred to the following: "The 

 head portion extends to the place of the division of the 

 heart into two stems, and in this region forms the heart 

 depression which leads to the esophagus, the lateral angles 

 of this portion extending forward strongly to the tail." 

 It is not completely clear from the quotation why Oken 

 burst into this tirade: "It is impossible to understand 

 a single letter. All is stated as Wolff stated it, and 

 therefore it is completely unclear. How could the 

 digestive canal be, say, cut off downwards and have the 

 shape of a blowing tube with a gaping empty opening?" 

 Cp. 1535). 



Concerning the formation of the rectum from the walls 

 of the tail, Oken again said that this cannot be understood. 

 Then moving from the individual details of the formation of 

 the digestive canal to Pander's general ideas, he wrote: 

 "It cannot all occur like that. The body develops from 

 cavities or sacs, and generally not from layers." Pander 

 and his colleagues, Oken continued, "write as if t^hey 

 completely forget that the yolk and the yolk membrane 

 (which is a cavity or sac) represent an actual part of 

 the body, and that the embryo does not swim in the yolk, 

 as the fish in water." 



The source of these comments, freely expressed in a 

 controversial form characteristic of Oken, are the wrongly 

 interpreted observations on the development of mammals, 



262 



