ANATOMY OF NEOHELIA PORCELLANA (mOSELEV). 593 



Coenosarc. The coenosarc extends over the surface of the corallum from polyp 

 to polyp but has the same poral interruptions as the peritheca. The coenosarc is 

 traversed by numerous branching and anastomising Endodermal canals which are con- 

 tinuous with the coelentera of the polyps. One canal is given off from each inter- 

 mesenterial space in a manner similar to that of Stylophora described by G. von 

 Koch (19), by Stanlej' Gardiner for Coenopsanimia (24), by Fowler for Rhudopsuniniia (10). 

 Neohelia being an Im]ierforate madrepore, these canals are necessarily confined to the 

 surface of the colony. 



There is nothing worthy of note about the general structure of the coenosarc, but 

 in the neighbourhood of the apertures in the wall of the colony, it is covered by a 

 .specialized epithelium which completely surrounds each aperture (Figs. .5 and 6, Ep. 1.). 

 This epithelial layer is seen to contain : — 



1. ^suraerous large nematocysts with long si^irally-barbed threads similar to those 

 occurring on the acontia (Fig. 7). 



2. Numerous gland cells, some of which, when stained with iron haematoxylin, 

 have a reticular appearance, while others contain granules (Fig. 6). 



3. Interstitial cells of two kinds (i) of a long narrow columnar tj'pe, lying between 

 the nematocysts and the gland cells, (ii) more or less triangular cells which fill up 

 the spaces, below the nematocysts and gland cells and above the Mesogloea (Mg). 



Below the epithelium and lying in the Mesogloea is an endodermal ring canal 

 which encircles the epithelium surrounding each aperture, this canal is lined by some- 

 what cubical cells with large nuclei, and sends off ramifications in the coenosarc which 

 comnuuiicate with the coelentera of the polyps (Fig. 5). 



Neohelia is like Madracis in that it has a well-developed peritheca, it is also 

 like it in the fact that the peripheral lamellae of the mesenteries extend into the 

 coenosarc covering the peritheca. It is supposed by Fowler in Madracis that with the 

 growth of the peritheca resulting in the formation of echinulations, the coelenteron 

 between the lamellae becomes broken up into canals which form the only communication 

 between the polyp cavities. The canals in the coenosarc of Neohelia may be accounted 

 for in a similar way. 



The important features noticed in the colony- are : — 



1. A Horny-membrane lines the hollow tube which forms the colony. 



2. There are certain apertures in the wall of the tube extending through coenosarc, 

 peritheca, and horny-membrane. As the colony grows older the apertures become smaller. 



3. An " epithelial layer " and an endodermal ring canal encircles each aperture, 

 the latter communicating with the coelentera of the polyps. It is probable that the 

 " epithelial layer " encircling each aperture is of the same nature as the free growing 

 edge of the colony, (which unfortunately has been broken off), in having the power of 

 growth, the growing coenosarc secreting horny membi-ane and calcareous skeleton, and 

 thus filling up the apertures. 



