J. E. Durrpen—Jamaican Actiniaria: Part I.—Zoanthee. 343 
the shore at Port Henderson, Kingston Harbour, and on the coral-rock at 
Drunkenman and other Cays. 
Range.—St. Thomas (Duchassaing and Michelotti). 
Column-wall (Pl. xvi. A, fig. 3)—The column is partially coated with a layer 
of foreign matter, mostly diatom frustules and fine mud. ‘The ectoderm 
is very thin, nearly continuous, and only slightly vacuolated. A sub-cuticla 
occurs, as in most species of the genus, more noticeable on the lower part ; 
transverse strands of mesogloea are rarely seen. The mesogleea is very variable 
in thickness, according to the state of extension or contraction of the polyp; it is 
best developed in the region of the sphincter muscle, and also as the eceenenchyme 
is approached ; isolated cells, with elongated processes, occur ; fine processes are 
seen extending across the mesogloea from the ectoderm to the endoderm. Some 
of the more peripheral cell-islets contain dark granular pigment matter. An 
irregular, partially encircling, canal system is present, situated in the upper part 
nearer the endoderm, among the cells of which are nematocysts. The canals, in 
some sections, are seen definitely connected with the ectoderm.* The mesogloea 
is much shrunk in preserved specimens, producing, especially in longitudinal 
sections, a very irregular external outline, followed by the ectoderm and foreign 
material. The endoderm is very narrow, crowded with zooxanthelle and small 
oval nematocysts, and gives rise to a weak endodermal muscle. 
At the base, the ectoderm is thinner; the sub-cuticla is more clearly seen, 
also the ectodermal canals in the mesogleea communicating with the ectoderm. 
Numerous irregularly distributed ccelenteric canals, lined with ciliated epithelium, 
pass along the base of the polyps through the coenenchyme, and connect the 
cavity of one polyp with that of another. The cells of the canals are somewhat 
glandular, and a thin lining musculature is present. 
Sphincter muscle (Pl. xvut.a, fig. 3).—The upper (distal) portion of the sphincter 
muscle is much smaller than the lower (proximal). It is contained in about 
twenty small mesogloeal cavities, arranged in an irregular row. The first 
section of the larger muscle is contained in an irregular series of small cavities 
stretching for some distance across the mesoglea. The cavities are largest about 
the middle ; lower they are again smaller, and located for the most part nearer 
the ectoderm. The lining of muscle cells is very thin, a few nucleated rounded 
cells are also present. In the figure of the muscle cavities, the latter are repre- 
sented as flattened and almost closed. This condition is evidently due to the 
method of preservation in alcohol. Specimens preserved later, in formalin, have 
* Hertwig (1882, p. 112) found a similar connexion in Zoanthus Dane (?). M°Murrich states that, 
in Z. sociatus, he has observed the basal canal in the mesentery communicating with one of these spaces, 
and considers it open to question whether the cells in the large cavities of the mesogloa are not in reality 
endodermal in their origin. 
