J. E. Dueeden — Jamaican Actiniaria : Part I. — Zoanthece. 355 



Drunk enman Cay ; sometimes the polyps are partially embedded in sand and 

 debris. Numerous young individuals arising directly from the ccenenchyme, or 

 from the base of other polyps, are mingled with the older examples. 



Column-wall (PL xviii.a, fig. 10). — The ectoderm is continuous, and not much 

 broken up by incrusting matter. The cuticle is thin, with few adhering foreign 

 bodies. The ectoderm is broad in the distal part of the column, but narrows 

 below, and the nuclei of the cells are uniformly distributed except near the cuticle, 

 a regular columnar epithelium not being formed. Large oval nematocysts occur, 

 and large zooxanthellse are present in company with small narrow stinging cells 

 and cells containing highly refractive pigment granules. The inner boundaries of 

 the ectoderm are not well defined, and at the capituluru the layer becomes very 

 thick and still more irregular in its internal outline ; definite bays or growths into 

 the mesoglcea appear in sections, probably due to the presence of capitular ridges 

 and furrows. 



The mesoglcea is of medium thickness, enlarging a little both proximally 

 and distally ; the incrustations are limited to the outer portion and the adjacent 

 ectoderm. They occur very sparingly, not interfering with the cutting of thin 

 sections, and consist of calcareous and a few siliceous sand grains, sponge spicules, 

 and an occasional Foraminiferal or Eadiolarian test. The mesoglcea contains 

 isolated cells and cell-islets distributed with some uniformity, except in the lower 

 part where an irregular zone of larger in closures may be found a little nearer the 

 inner boundary. The larger islets contain zooxanthellse, large oval nematocysts, 

 and occasionally pigment granules similar to those in the ectoderm, from which 

 layer the cell-islets can be seen to originate. 



The endoderm is thin, more so than in G. variabilis, and contains many zoox- 

 anthellse. The circular endodermal muscle is well developed ; fine fibrils from it 

 stretch nearly across the mesoglcea, and others are seen connecting the various 

 cells and cell-islets. 



Sphincter muscle (PL xvm. A, fig. 10). — The sphincter muscle is single and 

 mesogloeal. It is long and situated near the endoderm. Proximally it commences 

 in small irregular cavities in groups of two or three, and arranged in a not very 

 regular row. The more distal cavities are much larger, irregular in form, and 

 extend further across the mesoglcea ; the muscle fibres are arranged obliquely, and 

 isolated spherical cells occur. The muscle is shorter, the cavities less regular in 

 arrangement, and not in such a single series as in G. variabilis ; while the upper 

 ones are closer, broader, and more irregular in outline. 



Tentacles. — The ectoderm of the tentacles is very thick, and consists of an 

 outer zone of small narrow nematocysts, and an inner zone of zooxanthellse and 

 nuclei irregularly arranged. A few pigment granules, a number of homogeneous 



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