THE CH ORION WITH TROPHOBLAST. 



343 



a large irregular mass of cells, Tro. This is the trophoblast. In many places it 

 has already disappeared, so that there are spaces, lac, in the trophoblastic mass. 

 On the edges of these spaces the trophoblast is undergoing degeneration, deg, and 

 where that is occurring it is marked in the figure by the deeper staining of the 

 degenerated material. Upon examination with a higher power (Fig. 199) it will 

 be noted that the mesodermic cells are stained much more deeply than the 



Mes. 



EC. 



lac. 



Tro. 



FIG. 198. SECTION OF A VERY YOUNG HUMAN CHORION. 



deg, Degenerating ectoderm. EC, Epithelial ectoderm, lac, Lacuna for maternal blood. Mes, Mesoderm. Tro, 



Trophoblast. Vi, Villi. X 5 diams. 



matrix. They have an elongated form and run in various directions, more or 

 less parallel to the epithelium, EC' . Many of them are cut transversely or ob- 

 liquely. Aside from the trophoblast, the ectoderm is everywhere two-layered. 

 The inner layer is distinctly cellular, the outlines of the cells being very 

 sharply marked and the nuclei being relatively large. In the outer layer, which 

 is stained more darkly, there are no cell boundaries to be recognized, the struc- 



