590 TEXT-BOOK OF EMBRYOLOGY. 



At an early stage large masses of cells appear among the villi, sometimes being 

 attached to the villi (Figs. 496 and 498) . The origin of these masses is not known 

 with certainty. They may represent thickenings of the syncytium in which the 

 cell boundaries have reappeared, or they may represent outgrowths from 

 Langhans' layer. In some cases the cells are small with darkly staining nuclei, 

 in other cases large and homogeneous with large vesicular nuclei. Large 

 multinuclear cells, or giant cells, with homogeneous cytoplasm, also appear. 

 In some cases they apparently lie free in the intervillous spaces although 



Hofbauer's celJ 



Capillary 



FIG. 497. Transverse section of chorion villus from human embryo of two months, showing meso- 

 dermal core of villus and surrounding cellular layer (cyto-trophoderm) and syncytium (plas- 

 modi-trophoderm). Hofbauer's cell is an example of large cells found in the villi, but the 

 significance of which is not known. From retouched photograph. Grosser. 



it is claimed by some investigators that they merely represent sections of 

 tips of the syncytial masses. A structure known as canalized fibrin (which 

 takes a brilliant eosin stain) begins to develop in the earlier months of preg- 

 nancy and gradually increases in amount during the later stages. It is found 

 in relation with the large cell masses among the villi and is probably a degen- 

 eration product of these masses. 



In the later months of pregnancy the covering layer of the villi loses its 

 distinctly epithelial character, the cyto-trophoderm or cellular layer disappearing 

 and the plasmodi-trophoderm or syncytial layer becoming reduced to a thin 



