106 GEORGE MATTHAI 



in the latter case it is an endodermal formation ; but, whether 

 ectodermal or endodermal in origin, the inner lining possesses 

 histological identity. It is raised into ridges over the attach- 

 ments of mesenteries (fig, 5) ; these ridges vary in thickness 

 and breadth in different species and frequently possess median 

 grooves as they approach the enterostome. The free border 

 of the inner lining shows the vertical striation better than in 

 the surface ectoderm. It is conspicuously ciliated, the cilia 

 being longer in the median grooves of the ridges and in the 

 sulci between the ridges ; these cilia would function in the 

 ingress and egress of currents of water.^ Below the striated 

 border is a somewhat finely granular non-nucleated stratum, 

 beneath which is a much thicker region containing massed 

 nuclei of varying length and size (mostly tapering at both ends). 

 Between the nucleated region and the middle lamina is a 

 fibrillar region which is thicker than all other regions and 

 comprises the lower half or two-thirds of the ridge ; it contains 

 a few small, round or oval nuclei, and the fibrils are continuous 

 with the middle lamina. At the base of the inner lining is 

 the fine granular stratum which shades off into the middle 

 lamina. The striated border and the non-nucleated stratum 

 underlying it are of uniform thickness over the entire stomo- 

 daeum, while the nucleated and fibrillar regions are consider- 

 ably thinner in the intermesenterial parts. Vacuoles are 

 usually present in the stomodaeal ridges and are fewer in the 

 intermesenterial region ; many of them contain granules which 

 ■ vary in their density, being quite fine in some vacuoles. The 

 vacuoles extend to the surface of the ridges and, in sections of 

 some polyps, the granules are seen to have actually passed 

 into the lumina of the stomodaea. Xematocysts are sometimes 

 present in the inner lining of the stomodaeum. At the entero- 

 stome the inner lining of the stomodaeum becomes continuous 

 with its outer endodermal lining. 



Since numerous stomodaea are present in a Madreporarian 



^ Finely powdered carmine, when put into sea -water containing a live 

 , colony of Manicina areolata was passed into the stomodaea and 

 subsequently ejected. 



