J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthece. 367 



Tentacles. — The tentacles have a very broad ciliated ectoderm crowded with 

 narrow elongated nematocysts, zooxanthellse, and pigment granules ; the meso- 

 glcea and the endoderm are thin. The longitudinal ectodermal muscle is well 

 developed on small mesoglceal plaitings. 



Disc. — The ectoderm of the disc is broad and contains nematocysts, zooxan- 

 thellse, and pigment granules in the deeper parts. The mesoglcea thickens 

 towards the middle, and incrustations are there present. The endoderm is like 

 that of the column-wall. 



(Esophagus. — The outline of the oesophagus varies in different regions and in 

 different specimens. In most polyps it is the usual pyriform, truncated shape, 

 with the ectoderm thrown into seven or eight longitudinal folds on each side, and 

 the oesophageal groove well marked and occupying nearly one-third of the trans- 

 verse diameter ; but in others, it may be almost circular in outline with none of 

 the folds showing. The ectoderm is very thick, stains deeply, is richly ciliated, 

 and loaded internally with yellow pigment granules, and outwardly with elon- 

 gated nematocysts. The mesoglcea is narrow, thickening a little at the groove ; 

 the endoderm is like that of the column-wall. 



Mesenteries (PI. xix., fig. 7). — The mesenteries present the usual brachycnemic 

 arrangement in most cases ; but, as already mentioned, irregularities may occur, 

 so that a polyp may be brachycnemic on one side and macrocnemic on the other, 

 while one polyp has been met with which has the latter arrangement on both sides. 

 The number of pairs is variable, and the two lateral halves do not always corre- 

 spond. In a portion of one colony two polyps have eight perfect mesenteries 

 on each side; two have eight on one side and seven on the other ; while another 

 has six on one side and eleven on the other. The imperfect mesenteries are well 

 developed. The endoderm is very thick, and contains zooxanthellee, nematocysts, 

 and abundant pigment matter. The parieto-basilar muscle is clearly seen on 

 each side, but the retractor muscle layer is scarcely distinguishable. The mesoglcea 

 is extremely thin, except towards the column-wall, where the canals or sinuses 

 extend nearly the whole vertical length ; they occupy almost the whole transverse 

 width in the uppermost region, but are elongated or oval below. The basal canals 

 are well developed in both the perfect and imperfect mesenteries, and are 

 crowded with oval nematocysts and pigment particles, and connected below 

 with the sinuses in the coenenchyme. The ectoderm of the oesophagus is 

 reflected and folded on the mesenteries. The endoderm on the lower part of 

 the mesenteries is enormously thickened and loaded with granules ; the mesen- 

 terial filaments become nearly circular. 



Gonads (PI. xix., fig. 6). — Spermaria, arranged in vertical and transverse 

 rows, were present in the mesenteries of some of the polyps examined. 



