256 G. HERBERT FOOLER. 



of cavities in communication with one another. The columella is 

 perforated by a similar system of canals, which unites the whole circle 

 of entocceles and exocoeles ; there is thus free communication through- 

 out the whole of the polyp, despite the comparative preponderance of 

 skeleton over soft tissue. The canals are' composed of endoderm and 

 mesoderm, continuous with the same layers that clothe all the rest of 

 skeleton ; and in the meshes of the network lies the corallum, theca 

 or columella. 



The polyp thus consists of an external body-wall, mouth-disc with 

 tentacles, stomatodseum, and mesenteries ; with a coelenteron divisible 

 into columellar canal system, exocoeles, entocoeles, thecal canal system, 

 and chambers exterior to the theca, corresponding to and continuous 

 over the lip with the mesenterial chambers. 



The body-wall and mouth-disc are composed of simple ectoderm, 

 endoderm, and mesoderm, agreeing with those of other Hexactinite. 



The outline of the stomatoda3um is oval, as usual ; but I have not 

 observed any trace of gonidial grooves at the ends of the longer axis. 



The tentacles, which are simple evaginations, appear to be entoccelic 

 only ; they are so invaginated into pockets on each side of the septum 

 that it is impossible to make out their exact size and shape. This 

 condition is probably due merely to alcoholic contraction, and does 

 not imply that involution is the normal method of tentacular con- 

 traction. A similar invagination had taken place at the bases of the 

 tentacles of Flabellum. They are covered with nematocysts, which 

 are not so sharply denned into batteries as was the case in Flabellum. 



At a varying depth below the lip of the calyx (but generally at a 

 lower j>oint than is represented in fig. 13, which is considerably 

 shortened in the longer axis) the external body-wall perishes, owing 

 probably to the various parasites that infest the external surface of 

 most coral thecse and polyps ; notably a sponge, which in some places 

 eats its way right into the theca. The cavity marked /in fig. 15 is 

 thus filled with sponge spicules. Below the point at which the body- 

 wall ends there is visible in some places a thin line of tissue indicated in 

 fig. 15, g, which may or may not be a part of the polyp. The appear- 

 ance of the periphery of the theca in such a section suggests very 

 strongly that a secondary line of corallum has been deposited round 

 the circumference to protect the canals from communication with the 

 sea water and against the parasites. At the top of fig. 15 the semi- 

 circular outline of the canals seems to indicate such a formation. 



