164 J. E. Dugrpen—Jamaican Actiniaria : 
the dise with the usual colours, demonstrating that we are dealing with a mere 
colour variety, between which and the normal every gradation may occur. 
The diameter of the base is about 5 cm., and the height of the column 4 em. 
The diameter of the disc is 10 to 12 em., or may be even more. ‘The tentacles are 
about 0°6 em. in length, and vary but little in different regions of the dise. ‘They 
are often largest in diameter at the tips, where they may measure 0°2 cm. 
across. The diameter of the naked part of the disc across the mouth is 2°5 cm. 
Prof. M°Murrich’s figure (1889, Pl. 1., fig. 8, Discosoma anemone) represents the 
usual appearance of the Jamaican specimens. 
ANATOMY AND HIsToLoay. 
The column-wall is of only moderate thickness, the mesoglcea being often 
narrower in section than the ectoderm. ‘The latter is deeply folded, the mesoglcea 
partly following. In the ectoderm the nuclei of the supporting cells are distri- 
buted with considerable uniformity 1 sections, not limited to a zone as is generally 
the case. Very numerous, long, granular gland cells are included among the 
supporting cells. There is no trace of any ectodermal musculature. The 
mesoglcea shows a delicate, fibrous structure, and numerous included cells. On 
its endodermal border it presents narrow, slightly branching plaits for the support 
of the circular musculature, and very fine fibrils pass into the denser peripheral 
part of the endoderm, in some places giving rise to a distinct nerve layer. 
Ganglionic cells are recognizable between the muscular and nervous layers. The 
endoderm is much thinner than the two other layers, and contains many zooxan- 
thellee and granular gland cells. 
Where sections pass through verruce, the ectoderm undergoes certain modifica- 
tions: gland cells are absent, and the region stains more densely than the ordinary 
ectoderm. Very delicate processes, like enidocils, also appear on the surface, and 
the remains of the layer of cilia are more obvious than elsewhere. 
The sphincter muscle is a strong, circumscribed, endodermal represen- 
tative. It is recognized as a large outgrowth from the column-wall, a little 
below the outermost cycle of tentacles, and is made up of several lobes. The 
pedicle is broad and short, and a narrow mesoglceal axis extends nearly the whole 
length. From this axis delicate processes are given off—sometimes on one side, 
sometimes on the other, or on both together—for the support of the musculature. 
The lobes are so deeply separated that often a portion of the ccelenteron is enclosed 
in sections. The surrounding endodermal layer resembles that of the column-wall, 
and contains numbers of gland-cells and zooxanthellae. Owing to the lobed 
character, the appearance presented by the muscle varies in different sections. 
As indicating the possible amount of this variation, the figure given by M’Murrich 
(1889, pl. m1. fig. 15) should be compared with that on (Plate x1v., fig. 1). 
