152 j. E. Duerden — Jamaican Actiniaria : 



tentacles does not, however, yield any stinging cells. Grland cells are not developed 

 in the marginal tentacles to the same extent as in the column-wall. The endodermal 

 muscle is continued into the tentacles only as a very thin layer, the mesoglcea not 

 being j)laited ; but, in the naked region of the disc, directly from the base of the 

 tentacles, it is again strongly developed on mesoglceal plaitings, and extends the 

 whole width of the naked area, practically disappearing again as the disc tentacles 

 are reached. The ectoderm of the disc, though still containing gland cells, is 

 narrow, but the endoderm becomes enormously thickened, and presents the 

 appearance of an extremely loose vesicular tissue. In the disc tentacles, the ecto- 

 derm and mesoglcea are thin, but the large cavity is almost filled with the loose 

 endodermal tissue, among which are numerous zooxanthellse and medium-sized 

 ovate nematocysts, with a loose thread thrown into four or five loops; an 

 extraordinarily large stinging cyst is met with here and there. These latter are 

 enormous, horn-coloured cysts when mature, and bear tubercular or spine-like out- 

 growths. They are by far the largest met with in any anemone described from 

 this region (PI. xi., fig. 4). 



The constituent cells of the endoderm readily separate on maceration. The 

 supporting cells are of the usual type, but longer, and the free extremity is 

 ciliated ; the small nucleus occurs about the middle of the length. In places 

 where one or more zooxanthellse are enclosed the cell is greatly swollen. 



The stomodseum is round in transverse section, but short vertically, and its 

 walls are very deeply folded in the latter direction. These foldings which are so 

 marked a feature amongst the external characters are seen on anatomical exami- 

 nation to be elevations of the ectoderm followed by the mesoglcea, but not by the 

 endoderm. They often branch even more than is shown in M°Murrich's figure 

 (1889, PI. iv., fig. 3). The ectoderm presents the usual characters, having a clear 

 peripheral zone ciliated on the outside, a broad middle zone of oval deeply- 

 staining nuclei, and a narrow fibrillar zone. Nematocysts of various sizes are 

 present, including the large, colourless cysts with a spiral thread. A feeble 

 longitudinal musculature can be detected. The endoderm is much like that of 

 the column-wall, but deeper, and fewer zooxanthellse and no nematocysts occur. 

 The endodermal muscle is clearly distinguished, and rather strong, arranged on 

 small mesoglceal plaitings. 



As already remarked by Prof. M c Murrich the arrangement of the mesenteries 

 is difficult to determine, and appears very irregular in the alternation of perfect 

 and imperfect pairs, as does also the number of pairs. In addition to the complete 

 mesenteries an imperfect series is well developed, extending some distance within 

 the coelenteron, and, in certain regions, a second incomplete order is also formed. 

 The pairs are closely situated at about equal distances all the way round, the 

 endoccsles and exocceles being of nearly equal width ; the endoderm of the column- 



