352 J. EK. Dusrpen—Jamaican Actiniaria: Part I.—Zoanthee. 
length, and one to two feet broad. Incrusting sponges grow freely on the ccenen- 
chyme and amongst the polyps, and Ophiuroids meander around. 
The specific name has reference to the amount of variation met with in the 
various external features of the polyps. 
Column-wall (Pl. xvi. a, fig. 7).—The cuticle of the column-wall is thickly 
coated below with a layer of foreign matter, principally diatoms. The ectoderm is 
continuous, and presents irregular internal limitations, especially towards the upper 
part of the column. This is due partly to the presence of incrustations, but also to 
the ectoderm passing insensibly into the cell-enclosures of the mesogloea. Numerous 
zooxanthellz occur, and occasionally large colourless oval nematocysts, showing the 
coiled internal thread. The incrustations are sand grains, sponge spicules, and 
tests of Radiolarians, and extend from the inner border of the ectoderm to beyond 
the middle of the mesoglea. 
The mesogloea is thicker above and below than in the middle; numerous cells 
occur bearing elongated processes, and cell-enclosures of various dimensions 
uniformly distributed. Fine radiating processes extend from the endodermal 
boundary, apparently throughout the layer; the large cell-islets contain zooxan- 
thellz and large oval nematocyts, as in the ectoderm. 
The endoderm is of medium height, and contains zooxanthelle and pigment 
granules ; the circular endodermal muscle is easily distinguished. 
Sphincter musele (Pl. xvi. A, fig. 7).—The sphincter muscle is single and enclosed 
in an extended series of small mesogloeal cavities, varying but slightly in size, 
shape, and distance apart. It is situated nearer the endoderm. The cavities in 
the upper part are a little larger, and the lining muscle-fibres are arranged in 
various directions, many being cut obliquely. A few small spherical cells are also 
present in the middle of the cavities. 
Tentacles—The ectoderm is thick and has an outer layer of small narrow 
stinging cells, and below this abundant deeply staining oval nuclei and nume- 
rous glandular cells. The mesogloea is broad, and contains isolated cells and 
foreign incrusting matter. An ectodermal and an endodermal musculature occur. 
Disc.—The ectoderm is very broad and contains zooxanthelle and glandular 
cells. The mesogloea is nearly as thick as that of the column-wall, but contains 
no foreign inclosures ; minute cellular strands and a few cell-islets with large oval 
nematocysts occur in it. In the peripheral part of the disc, the mesoglcea is very 
thin, while the ectoderm is a little thicker than in the more central region. The 
endoderm is low and contains zooxanthellae; a weak endodermal muscle on plait- 
ings of the mesoglcea occurs. 
(sophagus.—The cesophagus is oval-shaped in transverse sections, with a well 
marked truncated cesophageal groove, the sulcar directives extending from the 
corners. The ectoderm is thrown into longitudinal folds, not followed by the 
