196 



Fig. 23. A megalokaryocyte showing cytoplasmic granules oi' various sizes. 



From an embryo of about eiglit days. 

 (Aceto-corrosive). 

 Fig. 24. The flattened out and crushed nucleus of a megalokaryocyte from 



the omphaloidean trophoblast in the later stage of degeneration. 



The chromatin is in the form of coarse clumps and strands. 

 Fig. 25. Five stages in the degeneration of the nuclei of the megalokary- 



ocytes in the allantoidean region. 



The chromatin becomes aggregated into large irregular masses, 



which may be vacuolated: while the nucleoli (also vacuolated) lie 



in special clear vacuoles of the achromatic substance. The nuclear 



membrane then disappears, chromatin and nucleoli both break up 



into small spherical globules, and are dispersed. 



(«. Aceto-corrosive, b. Flemming, c. d. and e. Foa). 

 Fig. 26. Cells from the flattened layer of connective tissue underneath the 



muscularis. From the stage represented in Figs. 6 and 11. 



The surfaces of the cells are inden ted ; between them is a matrix 



which may be stained blue with nigrosin, or indigo-carmine. 

 (Foa). 

 Fig. 27. Subepithelial tissue of the allantoidean region, showing the diffe- 



rentiation into supporting and giycogenic cells; some of the latter 



are making their way through the ruptured endothehum into a 



maternal artery. 



From a stage a little earlier than that figured in Fig. 10. 

 (Aceto-corrosive). 

 Fig. 28. A small part of the section across the border between maternal 



and embryonic tissues; from the preparation figured in Fig. lü. 



Above are seen the maternal glycogen cells, with their character- 



istic shape, and vacuolation; between these and the trophoblast 



are the remains of the layer of flattened (previously vacuolated) cells. 



The cytoplasm of the trophoblast, besides containing cellular and 



nuclear débris, is also vacuolated. The nuclei are oval and irregular 



and have large nucleoli. 



At the bottom of the figure is a maternal glycogen cell enclosed 



in the trophoblast. 

 (Aceto-corrosive). 

 Fig. 29. Section across the boundary between maternal and embryonic 



tissues at stage intermediate between those represented in Figs. 



5 and 6. 



Above is the disintegrating maternal tissue; blood vessels are seen, 



and between them supporting cells, and a few glycogen cells. 



Below is the giycogenic trophoblast, forming a compact mass in 



which maternal glycogen cells (distinguishable by their shape and 



nuclei) and débris are embedded. 



In the lower part of the figure is a sinus in which a maternal 



glycogen cell is floating. 

 (Foa). 



