160 J. E. Durerpen—Jamaican Actiniaria : 
The stomodeeal ectoderm is deeply folded, a salient feature being the com- 
paratively large mesogloeal processes, resembling those of the column-wall, which 
support the folds. As shown in the section figured (Pl. xt., fig. 6), these bear no 
relation to the attachment of the mesenteries on the inner side. There is no 
modification in structure indicating gonidial grooves. Large nematocysts, such 
as are met with in the mesenterial filaments, occur sparingly in the ectoderm, and 
a feeble ectodermal musculature can be discerned. 
The mesenteries are very irregular in their development, but the hexameral 
condition is evidently the normal; one or more incomplete pairs may occur in the 
exocceles between the perfect pairs, or a pair may consist of one perfect and one 
imperfect mesentery. This irregular arrangement is consonant with what has 
been already noted for the tentacles, and is likewise probably connected with the 
usual method of reproduction by fission. 
At least three distinct orders are indicated in most polyps, though many of 
the members of the third order may be wanting. The section (PI. x1., fig. 6), 
of a young specimen shows thirty-six mesenteries of varying degrees of 
development ; of these only thirteen reach the stomodeum. Another presented 
twenty-four pairs, of which eight pairs were perfect, though in two pairs one 
mesentery in each fell short of the stomodzeum. A very small example sectionized 
exhibited only seven complete mesenteries, all arising from a region embracing little 
more than one-half of the circumference of the column-wall, while those arising 
from the remainder were all incomplete. The mesenteries become very numerous 
and closely arranged in large specimens. 
Another polyp, sectionized later, is diagrammatically represented in transverse 
section in fig. 1, Pl. xi1.; two pairs of directives occur, with three pairs of com- 
plete mesenteries on one side and four on the other. The members of the third 
order are present in some of the exocceles, but never in two pairs, one on each 
side of the pairs of the second order, as in the case where the cycles are deve- 
loped regularly. 
The retractor muscles, though feeble, are sufficiently well developed to allow 
of the arrangement in pairs being easily followed. No directives were distin- 
guishable in two young specimens, but in another two pairs occurred. The parieto- 
basilar muscles are very distinct on each face, but the mesogloea is smooth, and 
affords no indication of any basal pennon. The retractor muscles are supported, 
in places, on rather considerable plaitings of the mesoglea, but the distribution of 
the plaitings is very irregular, and rarely presents the same appearance on any 
two mesenteries. In some cases they may form two or three thickened vertical 
bands. In the mesentery represented in fig. 2, Pl. xu1., only one of these was present. 
Beyond the retractor region, the mesogloea becomes extremely thin, sometimes 
appearing to originate from the side of the thicker part, instead of being a con- 
