A STUDY OF RESTITUTION MASSES. 447 



cell mass tubules lined with large columnar endoderm cells can be seen, 

 and these tubules are covered on the side where they project somewhat 

 into the hollow cavity of the stem with a single layer of small cubical 

 cells, which form a complete inner lining to the hollow stem. In longi- 

 tudinal sections the tubules can be traced up into the individual polyps, 

 and it can readily be seen that their cells are directly continuous with 

 the endotlerm cells lining the enteric cavity of the polyps. Similarly the 

 smaller cells in which these tubules are embedded in the coenosarc can 

 be seen to be directly continuous with the ectoderm cells of the polyps. 

 Neither in sections of the coenosarc nor of the polyps were we able to 

 distinguish any structure or structureless layer corresponding to the 

 mesoglsea. 



In Fia". 2 a tubule with surrounding ectoderm cells is shown under 

 a higher power of magnification. It will be noticed that the endoderm 



endtub. 



Fig. 2. X 500. — A normal tubule under higher power of magnification. Ed., ectoderm 

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



cells are distinctly columnar, with broad bases, and that they are con- 

 siderably larger than the ectoderm cells. Their nuclei are relatively 

 large, and usually situated near the base of the cell : the nuclear mem- 

 brane is sharp and well defined and the nucleoli are remarkably distinct ; 

 strands of chromatin are present, radiating from the nucleolus towards 

 the nuclear membrane. The cytoplasm is distinctly granular, and fre- 

 quently darkly staining vacuoles, presumably food vacuoles, were seen. 

 Flagella do not appear to be present on these cinosarcal endoderm cells. 



