50G A. A. W. HUBRECHT. 



And we can definitely afiirm that this part is an active one 

 after inspection of such preparations as those of fig. 84. They 

 show us that the blood extravasate above alluded to, which is 

 such a constant and characteristic feature of the phase of 

 development that is here under discussion, is bodily absorbed 

 by the cells of the trophoblastic annulus. The blood-corpuscles 

 that have been set free between the uterine wall and the tro- 

 phoblastic annulus are seen to enter the cells of the latter to a 

 very considerable extent, and I have no doubt that during life 

 this process takes place on an extensive scale. Whether the 

 cells of the trophoblastic annulus which thus absorb maternal 

 blood-corpuscles in a phagocytical way produce other matter 

 out of them, thanks to a special activity of their protoplasm, 

 must be left an open question. Still it is an undoubted fact 

 that about this time the cavity of the yolk-sac gradually comes 

 to contain matter which forms a characteristic coagulum in 

 this and the next phases. 



This coagulum grows and increases, and is spread out against 

 the hypoblast that lines the mesometrical concavity of the yolk- 

 sac (fig. 56). It has a yellowish-green, glassy, and yet partly 

 granular appearance, sometimes with different shades of colour 

 disposed in parallel layers (fig. 57). It appears to be densest 

 in the immediate proximity of the hypoblast ; towards the 

 lumen of the yolk-sac it grows less dense, and in the phases of 

 fig. 13 and following it fills the yolk-sac more or less com- 

 pletely, the area vasculosa and its modified hypoblast, of which 

 we shall come to speak by-and-by, being bathed by it. 



In the early phases of development the cavity of the yolk- 

 sac does not contain similar coagulable matter. The first 

 appearance coincides (a) with the increased resorption and 

 final disappearance of the congested omphaloidean mucosa ; {b) 

 with the increase in size of the yolk-sac, which is then applied 

 with its whole surface against the mesometrical wall of the 

 uterus. 



These particulars should be borne in mind when we are 

 going to speculate upon the origin and significance of the 

 coagulum. And if we then see that the trophoblastic annulus 



