90 G. CARL Hl'BER 



Sobotta's statement concerning this point, which, owing to its 

 importance, I quote in full, reads as follows: 



Man wird diese mikroskopisch erkennbaren Verhaltnisse nicht an- 

 ders deuten konnen als in folgender Weise: Die Hamoglobinschollen, 

 die durch die aussere Wand des Dottersackes in die Dottersackhohle 

 gelangt sind, werden von der Oberflache des zylindrischen, die ganze 

 Seitenflache des Eizylinders iiberziehenden visceralen Dottersack- 

 epithels aus resorbiert und zwar geschieht das in der Weise, dass die 

 Hamoglobinschollen ziinachst als solche in der Zelle selbst eintreten, 

 dann aber im vacuolisierten Teil der Zelle gleichsam verdaut werden, 

 wobei die einzelnen kleinen Schollen vorher zu grosseren Tropfen zusam- 

 men-fliessen scheinen. 



My own observations on the albino rat as concerns this phe- 

 nomenon, more particularly as concerns the structure of the 

 cells of the visceral entoderm in the region of the extraembryonic 

 ectoderm, corroborate Sobotta in many particulars. This 

 question will be again and more fully considered in a contemplated 

 later publication dealing with the implantation and decidua 

 formation in the albino rat. It could not be considered now 

 without a discussion of the changes involved in the development 

 of the decidua, a question which I am not prepared to consider 

 fully now. It may be stated, however, that judging from my 

 own preparations and the figures of Grosser, the extravasation 

 of blood into the egg chamber is not nearly so extensive in the 

 albino rat as is shown in the figures of Sobotta for the mouse. 



The thin membrane which surrounds the yolk-sac cavity, 

 which I have designated as the parietal or transitory ectoderm, 

 is derived in development from the parietal or transitory ecto- 

 derm, and the relatively few parietal entodermal cells, as de- 

 scribed and figured for younger stages. At the stage of egg-cylin- 

 der development under consideration — with continuous pro- 

 amniotic cavity — this structure appears as a thin, practically 

 homogeneous membrane with scattered, flattened nucleated 

 cells on its inner surface. Sobotta regards these cells as derived 

 from the parietal entoderm, the cells of the parietal ectoderm 

 having disappeared. As concerns this, I am unable to speak 

 with certainty, since the Congo red solution used as a double 

 stain is not particularly favorable in differentially coloring these 



