J. E. Dueeden — Jamaican Actiniaria : Part I. — Zoanthea?. 347 



In none of the specimens could the disc and tentacles be noted externally ; 

 the individuals, as appears to be usually the case, maintaining a retracted condition. 



Colour. — Coenenchymatous base colourless in some, irregularly greenish brown 

 in others ; column dark brown, mottled with green and black, the pigment appear- 

 ing in granular form. The green colouring matter seems largely external, and 

 due to adhering unicellular algse. 



Dimensions. — Diameter of base may be l - 7 cm. ; diameter at commencement 

 of column varies from 0'4 cm. to 1 cm. ; average diameter of column 0'6 cm. ; 

 height, from 2*2 cm. to 4*2 cm. ; tentacles, measured in sections, 0*3 cm. long. 



Locality. — Seven specimens were found associated and firmly adhering to a 

 small block of coral-rock on the south-east side of Drunkenman Cay. 



Column-wall. — The cuticle on the outside is devoid of adhering foreign matter, 

 except in places where a unicellular green alga is attached, giving rise to the 

 greenish patches seen on the living animal. The sub-cuticla is of regular thick- 

 ness, but enlarged a little where it communicates with the internal mesogloea by 

 strands across the ectoderm. The ectoderm is thick ; the nuclei of the individual 

 cells show no regular zonal arrangement ; it is broken up by the strands of 

 mesogloea into somewhat cubical or spheroidal blocks ; large, thick-walled, highly 

 refractive zooxanthellse, and occasional large colourless stinging cells are present 

 in places. In the uppermost part of the column the sub-cuticla is absent, and 

 the ectoderm continuous. The internal boundary is often not clearly denned, 

 portions being, as it were, cut off and isolated, and, as still smaller parts, often 

 only individual cells, sunk further into the mesogloea. 



The mesogloea is very thick, and contains abundant cell-inclosures, and uni- 

 formly distributed small cells with granular protoplasm. In the lower parts more 

 especially these take the form of small communicating canals. M° Munich refers 

 to the alteration in histological structure which some of the cells undergo in the 

 mesogloea, by which they become filled with refractive, deeply staining granules, 

 and suggests (p. 118) that they may be concerned in the formation of the 

 mesogloea, their granules being particles which will later on be added to the 

 matrix of the mesogloea. Many of the cells in my sections, generally in limited 

 areas, appear to go a stage beyond, and instead of the granules filling the cells, 

 they become arranged peripherally, giving the appearance of a thickened granular 

 cell- wall, a distinct central nucleus remaining (fig. 6, PI. xvm. a). 



The endoderm is thin, and contains abundant zooxanthellse and small stinging 

 cells. A circular endodermal muscle occurs along the greater part of the length 

 of the column. Endodermal bays are met with at different levels, extending 

 nearly as far as the ectoderm, and evidently correspond with the thin annuli 

 noticed amongst the external characters. The endodermal muscle follows the 

 outgrowths for only a short distance. Perhaps the bays serve to give flexibility 



3G2 



