592 
G. HERBERT FOWLER. 
derm (extending in some specimens very much further down than 
is represented in the diagram, fig. 13). Between this and the 
theca lies a narrow space, in which run, parallel to the long 
axis of the corallum, lamellae of tissue, connected on the one 
hand with this external body wall, on tbe other with the tissues 
clothing the exterior surface of the theca (figs. 13, 14, 17, M.') 
These lamellae correspond externally to the attachments of the 
mesenteries on the interior surface of the theca, and are appa- 
rently continuous with them over the lip of the calyx (fig. 13). 
They thus divide the space between body-wall and theca into a 
series of long chambers, corresponding to the exocceles and ento- 
coeles, in each of which lies a costa. Between these chambers 
and the exocoeles and entocoeles, a system of ramifying canals 
permeates the theca, placing the two sets of cavities in com- 
munication with one another. The columella is perforated by 
a similar system of canals which unites the whole circle of 
entocoeles and exocoeles ; there is thus free communication 
throughout 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 the 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, stomodseum, 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 ecto- 
derm, endoderm, and mesoderm, agreeing with those of other 
Hexactinise. 
The outline of the stomodseum 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 
entocoelic only ; they are so invaginated into pockets on each 
side of the septum that it is impossible to make out their 
