144 J. E. DurrpEen—Jamaican Actiniaria : 
still remains attached to the stomodzum and hangs freely from it, while the 
longer portion is connected with the column-wall and appears as a free mesentery. 
Histologically, the stomodzeal ectoderm consists mainly of ciliated supporting cells 
and long, narrow gland cells with finely granular contents; the nuclei of the 
former give rise to a brightly-staining middle zone. A weak longitudinal 
ectodermal musculature and a nervous layer are distinctly recognizable. Nemato- 
cysts cannot be detected in sections. The mesogloea is folded on its endodermal 
border for the support of the weak endodermal muscle. The endoderm itself is 
an extremely narrow layer, displaying nerve fibrille. 
In polyps small enough to be sectionized as a whole, twelve pairs of perfect 
mesenteries are present, of which two pairs are directives. These constitute the 
first and second cycles; and it is usually found that the members of the second 
cycle become free in advance of the others; the directives, as already stated, 
extend much below the others, retaining their attachment to the prolonged 
gonidial grooves. A third cycle of twelve mesenteries alternates with the com- 
plete members, and extends some distance within the ccelenteron, while a fourth 
cycle of twenty-four mesenteries extends but a little beyond the column-wall. In 
dissections of large polyps, a fifth cycle of forty-eight pairs of mesenteries occurred, 
the fourth cycle now stretching well within the ccelenteron, and the third cycle 
becomes connected with the stomodzeum for some distance. 'Trilobed mesenterial 
filaments are borne by the members of the first three cycles. ‘The mesenteries 
are exceptionally narrow, and, as a whole, occupy but a small proportion of the 
celenteron. The perioral stomata are very pronounced, but the marginal stomata 
are small and not readily distinguished. 
The retractor muscle is arranged on very narrow, bifureating, mesogloeal pro- 
cesses and gives rise to a thickened band, distally situated at a considerable 
distance from the column-wall (Pl. x1., fig. 1), but nearer proximally. In sections 
it commences as a rounded or acute enlargement, and centrally diminishes gra- 
dually. The musculature beyond the region of the retractor is very feeble, 
except towards the origin of the mesentery in the column-wall, where, in 
the region below the stomodzeum, a parieto-basilar muscle is well developed, and a 
strongly plaited pennon is present. ‘The endodermal muscle is continued between 
the mesogloea at the base of the mesentery, and that of the column-wall. The 
retractor is developed on all the cycles of mesenteries .except the lowest ; while in 
the proximal region a muscular layer is continued all round the smallest mesen- 
teries, the mesogloea being folded. The oblique musculature is very feeble. 
The mesenterial epithelium is narrow, except towards the origin of the mesen- 
teries, where it broadens, and what appears to be nerve fibrille become very 
obvious; the cell contents are here aggregated mostly peripherally (Pl. x1., fig 1). 
For a short distance both above and below the inner termination of the 
