Indicating that Tiedemann, in his manual of zoology, and 

 Meckel, in his translation of Wolff's work, had given credit 

 to Wolff, Pander remarked that Oken instead had attacked 

 Wolff sharply. Oken reproached Wolff for lack of clarity 

 and requested that Tiedemann "follow up completely the 

 development of the intestinal canal, or otherwise there will 

 be a gap ... in Wolff's descriptions. Now we must put an 

 end to all discrepancies. "25 Pander declared also that Oken 

 was not entirely correct in his complaints against Wolff's 

 lack of clarity and in indicating some of his mistakes. 

 "The reason for most of Wolff's mistakes," Pander wrote, "is 

 mainly ... in his assumption that the blastoderm is a 

 single layer . . . and that the origins of the developing 

 changes and their course are connected with it. "26 Pander 

 did not claim to have studied all the layers of the blastoderm 

 completely. He did, however, determine that "these layers, 

 either separated, or connected, are the only origin of the 

 different organs. "27 Pander concluded with a long quotation 

 from Wolff, in which he discussed the formation of the closed 

 intestinal canal from the original bifurcating layers, in 

 order to show his agreement with Wolff. 



Pander's observations on the development of the digestive 

 tract revealed the following. The heart depression (Wolff's 

 term, which Pander adopted) forms a wide cavity with a gaping 

 opening. The latter has an oval form; anteriorly it is 

 wider, and posteriorly the intestinal and mesenteric folds, 

 get lost in the posterior part of the tail covers. The colon 

 is formed when the walls of the tail portion move close to 

 each other. Concerning the mesenteric folds, Pander agreed 

 with Wolff that they are the rudiments not only of the 

 mesentery, but also of the kidneys. By the end of the second 

 day the heart bends more and more into the form of a horse- 

 shoe, or parabola," developing on the left side. 



Chapter 11 of Pander's dissertation is devoted to the 

 incidents of the third day. At that time the blastoderm 

 occupies half of the yolk surface; the form of the transparent 

 area loses its regularity, but in the anterior it remains 

 wider than posteriorly. The blood-carrying system emerges 



25. Ibid . , p. 42 (footnote). 



26. Ibid . 



27. Ibid. 



255 



