164 T. THOMSON FLYNN 



It is difficult to suggest a cause for the degeneration and 

 resorption which has taken place in the case of these nuclei, 

 but it is a significant fact that associated with the degenerating 

 groups are to be found abundant leucocytes of the small and 

 large mononucleate types. 



Situated just internally to the allantois are to be found 

 occasional large trophoblastic cells, being remains of the 

 cytoblast. These also are undergoing degeneration. 



In places the homogeneous nature of the ground-tissue is 

 less evident, and here multinucleated masses of protoplasm are 

 still in evidence. Apparently the foetal chorionic cells have 

 performed their function, viz. the fixation .ind a portion of 

 the preliminary nutrition of the embryo, and are now in 

 a process of degeneration and disappearance. 



The maternal vessels are extremely numerous, and their 

 finer branches now ramify at the surface of the diploplasma, 

 where they come into intimate apposition with the vessels of 

 the allantois in the way Hill describes. 



The allantoic mesoderm has penetrated but little into the 

 trophodermic layer. No spaces are formed in which maternal 

 blood flows, all maternal vessels being contained in definite 

 endothelial walls. The two blood-systems, however, are 

 elaborately interlocked, and very often foetal and maternal 

 blood-streams are separated merely by the thickness of two 

 endothelial walls. 



As regards the glands of the placental area, they are now 

 characterized by the possession of a low cubical epithelium. 

 Their cavities are wide, particularly near the opening of the 

 gland. The cells are ciliated. The mouth of each gland is 

 sometimes closed by the allantois with its numerous vessels, 

 at other times by degenerating remains of the trophoblast. 

 The condition of the portion of the gland contained within the 

 diploplasma is similar to that characteristic of the preceding 

 stage. 



Outside the placental area the maternal nuclei of the epithe- 

 lium still take the form of rounded vesicles in which it is difficult 

 to distinguish even a nucleolus. The glands of this portion of 



