356 J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthem. 



deeply staining bodies, and glands filled with clear contents, are met with, and 

 an occasional large oval stinging cell. Transverse sections show a well developed 

 ectodermal muscle on mesoglceal plaitings. The mesoglcea has small cells 

 scattered throughout. The endoderm is made up of small regularly arranged 

 cells; an endodermal circular muscle is supported on fine mesoglceal plaitings; 

 and zooxanthellse are present. 



Disc. — The ectoderm of the disc is even thicker than that of the tentacles, and 

 exhibits an outer zone of clear gland spaces and small narrow nematocysts. The 

 deeper part is largely composed of zooxanthellse, glandular cells or spaces, and an 

 occasional large oval stinging cell. An ectodermal muscle occurs on mesoglceal 

 plaitings, and an endodermal muscle is present. The mesoglcea is thick and 

 contains cells and cell-islets, but is devoid of incrustations. 



(Esophagus. — Only a slight oesophageal groove is indicated, the mesoglcea 

 being a little thickened and truncate, and the directives extend from the two 

 corners. Below it is oval-shaped in section, and the ectoderm remains unfolded ; 

 distally the latter is thrown into eight or nine well marked folds on each 

 side, only exceptionally followed by the mesoglcea. In a second specimen, the 

 number of folds was fifteen on each side. Immediately on passing, in longitu- 

 dinal sections, beyond the lips of the mouth, the ectoderm undergoes a great 

 alteration from that of the disc. It is richly ciliated, a narrow zone immediately 

 below is colourless ; then follows a thick zone of narrow, closely-arranged nuclei, 

 gland cells, and nematocysts, which together form a dense deeply staining band, 

 extending the whole length of the oesophagus. A zone below this has only a few 

 scattered nuclei, and, in })laces, the large oval stinging cells and pigment granules. 

 The mesoglcea is a homogeneous layer with rarely an enclosed cell, and the 

 endoderm is extremely thin. A weak endodermal but no ectodermal musculature 

 occurs. Terminally the ectoderm is reflected upwards on the mesenteries for 

 a short distance, and folded in a double pinnate manner, and then descends, 

 constituting the mesenterial filaments. 



Mesenteries. — The mesenteries are brachycnemic in arrangement. Twelve 

 perfect pairs occur on each side in one specimen, and sixteen in another. In the 

 middle oesophageal region each is extremely delicate, scarcely showing any 

 enlargement towards the insertion at the body -wall or oesophagus ; the usual 

 basal canal is often absent, especially distally. The imperfect mesenteries are 

 broad above, but very short below, not being readily distinguishable in places. 

 The parieto-basilar muscle is present on each side ; the retractor muscle is weak. 

 A little beyond the insertion of the mesenteries is the flattened or oval-shaped 

 basal canal filled with deeply-staining tissue, and now and then a large oval 

 nematocyst. The endoderm is poorly developed, and has large zooxanthellse. 



Gonads. — No reproductive cells were present in the examples studied. 



