THE TROPHOBLAST AND ITS SURROUNDING BLOOD SPACES. 55 



BLOOD SPACES TO THE CONFLUENT CAPILLARIES 

 IN THE SURROUNDING TISSUE. 



ad. 1. In Figs. 16, 17 & 18 (Plates IX & X), the ectoblast 

 cover and the trophoblast processes are seen. We are able to 

 follow both their primary condition and further development. 



The ectoblast (in Fig. 18 ekt. and Ek^. Figs. 16 & 17 ekt. 

 and Figs. 26 & 27 Plate XVI) consists of a double row of cells. 

 The inner row is composed of round, in some places oval cells 

 adjoining each other with their pole ends and containing a dark 

 stained nucleus which almost fills the cell. (Langhans' cells Figs. 

 26 & 27 1. z.). On the outside of this cell layer we find much 

 larger cells which contain one or more nuclei. Many of these 

 cells are considerably swollen, showing a fine granulation of their 

 cellular substance (Syncytiurh). (Figs. 26 & 27 sy.) In fol- 

 lowing this ectoblastic band, which here and there is detached 

 from the mesoblast, in the sections 47 and 60 represented in Figs. 



16 & 17, we can establish several facts. At various places (e. g., 

 Fig. 17 k) by a proliferation of the Langhans' cells the inner 

 layer is thickened, forming small buds covered by the syncytium. 

 These buds gradually become thicker and longer (Figs. 16 & 



17 tr & Fig. 18 tr to the right), but almost everywhere remain 

 covered with syncytial cells, as can be recognized in Figs. 16 & 

 17 under high magnification from the double layered band 

 marked "ekt." (Fig. 27 sy.) 



The ectoblast in this stage of delevopment has already sent 

 out a number of short sprouts, but the mesoderm which is just 

 forming has not as yet entered these processes, so that one can- 

 not speak of villi in the usual meaning of this term. 



It must, however, be emphasized that these earliest buds as 

 well as the further developed processes (the ectoblastic band in 

 Fig. 16) are completely surrounded by maternal blood and do not 

 come in contact nor have any connection with the maternal tis- 

 sue, especially decidual cells. 



While this fact alone proves the close relationship of these two 

 cell layers to the ectoblast, furthermore, in this stage of devel- 

 opment of the ovum absolutely nothing speaks in favor of an as- 

 sumption that the ectoblast or possibly its external cover the 

 syncytium, etiologically has any relation to the maternal tissue. 

 The ectoblast is a part of the Eianlage, its buds are the expres- 

 sion of the development of the latter. Without an Eianlage neith- 

 er a formation of trophoblast nor a proliferation of syncytium is 

 conceivable. 



Following further the increase in the size of the trophoblastic 

 buds (e. g., Fig. 18 tr. to the left; Fig. 16 tr to the left; Fig. 21 



