194 J. E. DuERDEN — Jamaican Actiniaria : 



To the naked eye the surface of the ccEnenchyme and column-wall is quite 

 smooth, but with a lens minute white granulations — the foreign inclusions — are 

 disclosed. The walls arc thick and firm, but in some cases superficial wrinklings 

 may be observed in preserved specimens. 



The polyps were examined only in their retracted or partly retracted state. 

 They are capable of complete retraction, in which condition they are usually 

 mammiform ; or they may be slightly longer, and flattened or rounded above, a 

 small aperture remaining in the middle. Towards the base the column enlarges 

 in diameter, especially in the most retracted individuals. 



The capitular ridges are small, and can be distinguislied and counted only with 

 the assistance of a lens ; they are wedge-shaped and acute, and vary in number 

 from 14 to 16. The ridges and furrows are most distinctly indicated during 

 partial extension. 



The tentacles are short, apparently rounded at their apex, and dicyclic, 

 fourteen to sixteen occurring in each cycle. The mouth is rounded or slit-like, 

 and the lips prominent. 



The colour of the coenosarc and column -wall is greyish, being determined by 

 that of the included particles ; the tips of the capitular ridges are a little lighter ; 

 the tentacles and disc are brown. 



The height of retracted polyps above the coenenchyme is about 2 mm., and the 

 diameter the same. 



Anatomy and Histology. 



The ectoderm of the column-wall is a continuous layer, that is, it is not broken 

 up by crossing strands of mesogloea, as is the case in many Zoantheje. Superficially, 

 it is devoid of any recognizable cuticle or sub-cuticle, and the constituent cells are 

 more rounded than columnar in outline. The internal limitations of the layer are 

 very irregular and indeterminate in places, most of the inclusions occurring 

 around its boundary with the mesogloea, while cells pass from it into the 

 mesogloea (PL xiii., fig. 7; PI, xv., fig. 4). 



Small colourless nematocysts occur, but are not very numerous. 



The mesogloea is moderately thick, and near its internal border contains a 

 narrow, interrupted, encircling sinus filled with cells closely resembling those of 

 the ectoderm ; in the distal region, where the sinus becomes broader, it includes 

 numerous nematocysts. 



Isolated cells and cell-islets are scattered throughout the mesogloea ; and a 

 few siliceous sponge spicules are included, in addition to the predominating 

 calcareous sand-grains. The latter are very small and practically limited to its 

 peripheral border ; they are dissolved out by acids leaving only irregularly-shaped 

 lacunae. In regard to the foreign inclusions, a decided selection is manifested in 



