J. E. Dueeden — Jamaican Actiniaria : Part I. — Zoanthece. 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 xviii. 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 mesoglcea are rarely seen. The mesoglcea 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 ccenenchyme 

 is approached ; isolated cells, with elongated processes, occur ; fine processes are 

 seen extending across the mesoglcea 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 mesoglcea 

 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 zooxanthellse 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 mesoglcea communicating with the ectoderm. 

 Numerous irregularly distributed ccelenteric canals, lined with ciliated epithelium, 

 pass along the base of the polyps through the ccenenchyme, 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 (PI. xviii.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 mesoglceal 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 mesoglcea. 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 Bancs (?). M c Hurrieh 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 niesoglcea are not in reality 

 endodermal in their origin. 



