142 J. EK. Durrpen—Jamaiean Actiniaria : 
the chief constituents, but a few gland cells are also intermingled, though 
not by any means so thickly as in the ectoderm of the column-wall. Towards 
the mesogloea a fibrillar layer is very clearly displayed. No ectodermal muscle 
is present, or is only of the weakest character. The mesogloea is typical 
of its condition throughout the polyp, being very fibrous, and containing numerous 
cellular constituents. To its shrinkage is perhaps due, in some degree, the fine 
display of both the ectodermal and endodermal fibrillar layers which occur 
throughout all the polyps sectionized. 
As shown in the ectoderm of PI. x1., fig. 1, very fine fibrils, arranged in an almost 
parallel manner, extend from the delicate muscular layer, and afterwards unite 
to form an extremely thin layer. This latter usually appears as if made up of 
very delicate interlacing fibrille; and on its outer side another series of fibrils, 
irregularly arranged, are given off, and are connected with the cells of the 
ectoderm. For the sake of distinction I restrict the term nerve layer to the 
delicate, interlacing layer, and speak of that between it and the muscle layer as 
the fibrillar layer. Sometimes, as is represented in the endoderm of the same 
figure, the fibrils extending from the muscle fibres do not unite to form a definite 
nerve layer, but interlace and are reticular in section. What appear to be 
Ganglionic cells are distributed among the fibrille. Appearances similar to the 
above are also represented in the section through a portion of the tentacle 
and also of the gonidial groove of Homostichanthus anemone (Pl. xv., fig. 1; 
Pl. x1v., fig. 2), and can be made out in sections of most species. 
The endoderm of the base contains many zooxanthelle, which, along with 
the cell protoplasm and nuclei, are mostly concentrated towards the free border of 
the layer. A well-marked fibrillar stratum extends for some distance from the 
endodermal muscle, and the latter is arranged on fine mesoglceal plaitings. 
The column-wall throughout is of only medium thickness, and becomes 
thinner towards the apex; the mesogloea is nowhere much broader than the 
ectoderm or endoderm. The ectoderm is very deeply ridged in places, the 
elevations being partly followed by long processes of the mesoglca, often 
branching, and much longer than the whole thickness of the wall. ‘The supporting 
cells are scarcely so long as at the base; but unicellular glands, some with 
granular contents and others quite clear, are abundant. Maceration preparations 
reveal the presence of numbers of small nematocysts. A very weak longitudinal 
ectodermal muscle is present, and a nervous layer is readily distinguishable in 
places. The endoderm is a deep layer containing zooxanthelle ; its constituent 
cells are considerably elevated between the mesenteries where these are closely 
arranged. Throughout the column the endodermal circular musculature is 
developed with exceptional uniformity, the mesogloea being finely plaited for its 
support, and a nervous layer is clearly seen in some parts (Pl. x1, fig. 1). 
