204 J. E. DurrpEN—Jamaican Actiniaria : 
relations of one cavity to another. More internal than these cell-spaces the 
mesogleea is practically homogeneous, and affords a sharp boundary line with the 
endoderm. 
The endoderm is broad and contains numerous zooxanthelle ; its cells are 
much elongated in the narrow mesenterial spaces. Only faint indications of an 
endodermal circular musculature can be made out. It is unfortunate that in the 
capitular region, where the sphincter muscle should occur, the walls are so thin 
and the large sponge spicules so closely aggregated, as to render suitable sections 
a matter of practical impossibility. The delicate walls in every case readily 
break away with the inclusions. 
From a knowledge of related forms it can, I think, be safely inferred that if 
a sphincter is developed it will be of an endodermal, diffuse, and extremely weak 
type. ‘The power of retraction is not possessed to the same degree as in the 
previous species. 
The ectoderm of the tentacles is a broad, columnar layer; small, narrow 
nematocysts occur peripherally, and occasionally one of the larger oval forms 
similar to those in the column-wall. The merest traces of an ectodermal and 
also of an endodermal musculature can be detected. The mesogloea is extremely 
narrow; the endoderm is loaded with zooxanthelle and with deeply-staiming 
granules of various sizes, and, in retracted examples, completely fills the lumen. 
The dise in all its three layers is a very thin structure. In retracted 
specimens it is deeply concave outwardly, affording space above for the tentacles, 
while below it comes almost in contact with the floor of the ccelenteron, nearly 
obliterating the ccelenteric cavity. In consequence of the extreme shortness of 
the polyps as a whole, and of this approximation of the disc and base, the study 
of the paired arrangement of the mesenteries is almost fruitless. 
The peristome remains elevated, and the stomodzeum is comparatively large 
in sections. As shown in PI. xm, fig. 9, transverse sections pass at the same 
time through the column-wall, tentacles, elevated peristome, and stomodzeum ; only 
exceptionally can a mesentery be traced from the column-wall to the stomodzeum. 
The stomodzeum is usually oval-shaped in tranverse sections, and the single 
gonidial groove is clearly indicated ; the lateral walls may be thrown into a few 
vertical folds. The ectodermal epithelium consists mainly of ciliated supporting 
cells with nematocysts and gland cells; the two latter are practically absent at 
the sulcar end where the groove occurs. Large granular gland cells, the contents 
of which do not stain in borax carmine, are also met with. The mesoglea is a 
very thin layer, thickening somewhat at the groove; the endoderm is broad and 
crowded with zooxanthellee. 
In vertical sections the stomodzeal ectoderm is seen to be in continuity with the 
filamental tissue of the mesenteries. The lower termination of the stomodzeum is 
