A STUDY OF RESTITUTION MASSES. 



455 



are sharp and distinct, approximating the normal in size but slightly 

 larger ; they have a tendency to be fusiform in shape with sharply 

 pointed extremities, and are often joined end to end. Spaces between the 

 cells are frequent, but they are occasionally found arranged in compact 

 whorls or masses. The outline of the cells is well defined, the cytoplasm 

 clear but slightly vacuolated, the nuclear membrane and nucleolus dis- 

 tinct. 



. Sections of restitution masses at the end of 3 weeks (Fig. 8) 

 showed a still more definite arrangement of convoluted endodermal 



ect;. 



end, tub: 



Fig. 8. x 260. — Section through part of a restitution mass 20 claj-s old, showing forma- 

 tion of definite endodermal tubules ; all the cells in the mass are sharp and well 

 defined, and the plasmodial character noticeable in earlier stages is lost. Ect., 

 ectoderm cells ; end. tub., endoderm tubules ; p., perisarc. 



tubules. The cells forming these tubules were regularly arranged and 

 closely resembled those lining the enteric cavity of the normal polyp 

 with the exception that no flagella were seen. The cytoplasm of 

 these cells w^as crowded with large granules, which were often so plentiful 

 as to partially obscure the nucleus. The ectoderm cells were present in 

 even smaller numbers than in earUer stages, but were very definite in 

 structure. Occasional large spaces, corresponding to the spaces producing 

 the fenestrated appearance described as occurring in older masses, were 

 seen among the cells, and other areas in which the cells had degenerated 

 and left merely some granular debris were observed. 



At the end of 5 weeks (Fig. 9) the endodermal cells forming the 

 tubules had become crowded with darkly staining spherical granules of 



