145 



frequently crossed by strands or trabeculae of cytoplasni. But in 

 additiou there are large sinuses lined by the trophoblastic pseudo- 

 endothelium already referred to. They course right through this, 

 the allantoic regiou of the placenta, and only open into lacunae 

 on the foetal side. On the maternal side they arise from sirailar 

 sinuses which traverse the non-allantoic glycogenic portion of the 

 trophoblast next to be described (Figs. 5, 11). 



The boundary line between this portion of the placenta and 

 that which we have just been considering is exceedingly irregular 

 and consequently the glycogenic layer is produced into processes 

 which dip down into the allantoic portion. In these processes the 

 cells become elongated (Fig. 33a) as though they were being 

 stretched by the growth of the neighbouring tracts of the allan- 

 toic region. The elongation becomes much more niarked as pla- 

 centation advances. The nuclei of these cells resemble, as we have 

 seen, the ordinary nuclei of the allantoidean trophoblast, many of 

 them, especially in the deeper layers, nearer the foetal side, may 

 be seen to be in a state of karyokinesis. 



The glycogenic vacuolation is now well developed in the cells 

 on the maternal side of this layer, and all transitions in the pro- 

 cess may be found in passing down to the cells on the deep side 

 in which the vacuoles are only just beginuing to appear (Fig. 33). 

 The whole of this layer shows a progressive increase in thickness, 

 and though this is no doubt due in part to the actual distension 

 of the cells with glycogen, still, taking into account the occur- 

 rence of mitoses in the deeper parts and the progress of the 

 vacuolation from below upwards, I thiuk it must be conceded 

 that this is a tissue in which active growth is proceeding, suffi- 

 ciently active indeed to give rise in the next period to a mass 

 of glycogenic cells occupying the whole of the upper region of 

 the placenta. 



The glycogenic tissue is traversed by sinuses leading into the 

 sinuses which pass directly through the placenta, and, like these, 

 lined by a pseudo-endothelium of flattened trophoblastic cells. 

 These cells are always larger than the endothelial cells of the 



