157 



regions, as soon as, by the rupture of the capsularis, the lumen of the 

 yolk-sac comes to commuuicate freely with the lumen of the uterus. 



Iu the placenta itself it seems to me to be of great interest 

 that the arterial blood passes through the trophoblastic glycogenic 

 tissue on its way to the lacunae and that when the encroach- 

 nient of this tissue on to the space previously occupied by the 

 degenerate maternal tissue begins it is the arteries which are first 

 surrounded by it. The glycogen in the trophoblastic cells I sup- 

 pose to be derived not altogether from the arterial blood but 

 also from the sugar liberated when the maternal cells disappear. 

 The amount of glycogen thus stored up in the trophoblast appears 

 to coudition in part the duration of pregnancy. When the gly- 

 cogen is used up the thin protoplasmic envelopes collapse; and 

 since it is exactly across this regiou that the break takes place, 

 it would seem quite possible that the disappearance of the gly- 

 cogen may be au important factor in determining the moment of 

 parturition. An explanation is thus suggested of the secretion of gly- 

 cogen by embryonic, subsequent to its secretion by maternal cells, for 

 it may well be supposed that the bulk of this glycogenic tropho- 

 blast, and, consequently, the amount of glycogen it contains, is 

 correlated with the size of the embryo itself. The trophoblast 

 which separates the lacunae from the foetal capillaries must not 

 be regarded as a mere coveriug or supporting sheet; the nuclei 

 are often large, rounded not flattened, and evidently fuuctional. 

 The fat which it contains may be the remains of' the fat found 

 in the trophoblast in earlier stages; but I would rather suggest 

 that it has been absorbed from the maternal, and will be passed 

 on again into the foetal blood. It seems that if so it must be 

 absorbed and discharged again as a soap, since no fat is found 

 in the maternal or in the foetal blood spaces. 



Lastly I have in one instance found the brown iron granules 

 in this region of the trophoblast; they are not normally present 

 here, but their presence in this one instance suggests that this 

 trophoblast is also concerned in the passage of an iron compound 

 from the maternal to the foetal blood. 



