134 



With the further growth of tb e niegalokaryocytes, as we may 

 now fitly term these trophoblastic cells, the nuclei continue to 

 enlarge, while the nucleoli are now enormous; they become sub- 

 divided into lobes which may be separated from one another, fre- 

 quently bear a curious resemblance in size, shape and staining 

 reaction to maternal red blood corpuscles, and appear in some 

 cases to be actually extruded from the nucleus. Further these 

 nucleoli may be seen to be enclosed in special vacuoles of the 

 achromatic substance and to themselves contain one or more small 

 vacuoles in their interior (Pig. 25). 



The chromatin, with the exception of some finely divided gra- 

 nules is now in the form of irregularly shaped, often elongate 

 masses, which still retain their position near the nucleoli. The 

 nuclei of the megalokaryocytes developed in this way from ordi- 

 nary fiat trophoblastic cells subsequently undergo degenerative 

 changes. The nuclear membrane disappears, the chromatin runs 

 together into (Fig. 25) numerous coarse lumps, or large spherical 

 globules. In the omphaloidean trophoblast both cell-body and 

 nucleus become flattened out and destroyed (Fig. 24). In the 

 allantoidean trophoblast, where megalokaryocytes are also formed 

 at the periphery, the cell breaks up and the chromatin globules 

 are dispersed into the neighbouring blood lacunae (Fig. 25c). 

 Practically the whole of the omphaloidean trophoblast becomes thus 

 transformed, and in many places, especially where the ompha- 

 loidean passes into the allantoidean region, there are two or 

 more layers of megalokaryocytes, between which are lacunae filled 

 with blood extravasated from the underlying blood-vessels (Fig. 

 19). Internally this trophoblast borders on the outer, or distal 

 wall of the yolk-sac, a layer of low cells, semi-circular or obtu- 

 sely conical in section, separated by short intervals from one 

 another, and placed on a very definite basement membrane which 

 stains intensely with acid dyes and is much thickened in later stages 

 (Fig. 19). Externally the trophoblast abuts, of course, against the 

 subepithelial tissue of the uterus. We may now pass to the des- 

 cription of the changes that take place in this tissue. As "has 



