THE ACTINIANS OF PORTO RICO. 
335 
The ccenenehyme is very rarely band-like and incrusting; more often it is represented by stolons, 
variable in form and length, and constituting an irregular connection between the polyps. Sometimes 
the base of a polyp may be flattened or irregularly lobulated on one or more sides, as if forming 
ccenenehyme. Polyps all about the same size are often closely associated, incrusting some rock or 
stone. More often they are in practically free clusters, loosely attached to coral and shore debris, 
the polyps connected with one another in an irregular fashion by free, stolon-like coenenchyme. 
Polyps living on the upper surface of stones are usually short and cylindrical, while those on the 
sides and underneath, or in crevices, become more elongated, with a distinct peduncle. In any large 
group of polyps the individuals on expansion rise to practically the same level however they are 
disposed with regard to one another basally. 
The lower part of the column is usually sand-colored, the upper dark green or bluish; the 
tentacles are yellowish green, blue green, or brown. The disk presents various light and dark shades 
of blue and green, often mixed with yellow and black; the oral cone is bright yellow or green; a 
darker triangular area may be present at each angle of the mouth or at only one. McMurrich gives 
the column of the Bahaman specimens as usually flesh-colored, with the upper part purplish brown; the 
tentacles are the same in color as the upper part of the column. 
The height of the polyps is very variable; an average may be about 1 7 mm. ; the greatest diameter 
of the living retracted polyp is 5 mm. , of preserved polyps 3 mm. The diameter of the disk in expansion 
varies from 5 to 8 mm.; the inner tentacles are 2.5 mm. long. 
Anatomy and Histology . — The cuticle, subcuticle, and ectoderm are of the same character as in the 
previous species. The ectoderm is strongly vacuolated below, but less so above, and contains oval 
nematocysts; its mesogloeal boundary is often not well defined on account of the connecting mesogloeal 
strands, mesoglceal vacuoles, and cell-inclosures. 
The mesogloea is broad in the region of the lower sphincter muscle and thence narrows in both 
directions, becoming greatly constricted at the capitular groove. Large and small cell-inclosures 
occur, many of them containing fine pigment granules. Circular and oval vacuoles also occur, with 
but few cell contents. An interrupted encircling sinus is present, connected in places with the 
ectoderm. The endoderm is a very thin layer, loaded with zooxanthelke, and forms a delicate 
circular musculature. 
The sphincter muscle is double and mesogloeal; the smaller part consists of but a few distinct 
cavities, while the larger is very elongate and is represented by an enormous number of chambers 
variable in size and outline and becoming smaller below. 
The ectoderm of the tentacles is devoid of cuticle and subcuticle, and contains numerous small 
oval nematocysts in its lower parts. Internally, fine pigment granules may occur and a weak 
ectodermal muscle on fine mesogloeal plaitings. 
The mesogloea is thin and finely plaited on its endodermal border for the support of the 
musculature. The endoderm is very broad in the retracted tentacles, leaving only a small lumen, and 
is crowded with zooxanthelke. 
The ectoderm of the disk is much narrower than that of the tentacles, and nematocysts are few. 
Between the ectoderm and mesogloea appears a kind of intermediate layer in which are numerous 
oval granular cells with their long axis at right angles to that of the ectodermal columnar cells, 
some are partly free and partly embedded in the mesogloea. The ectodermal and endodermal 
musculatures are weakly developed. 
The stomodffium is usually oval in transverse section, with about six deep ridges on each side, 
less in number than the perfect mesenteries. The gonidial groove is rather wide, its ectodermal lining 
smooth, with few gland cells, and more strongly ciliated than the stomodteal ectoderm elsewhere. 
The rest of the ectoderm is broad and contains many small nematocysts in its deeper regions. A 
delicate nerve layer can be detected in favorable sections. The mesogloea is also comparatively broad, 
more so than in the disk and mesenteries. 
The mesenteries are normally brachytypic, but the macrotypic arrangement may occur on one 
side or another. The number of mesenteries is usually about 60. 
The endoderm contains many zooxanthelke and medium-sized oval nematocysts. The mesogkea 
is finely plaited for the support of the retractor muscle. In most cases a basal canal occurs some little 
distance from the insertion of the mesenteries in the column-wall, but is not present in all. The 
canals contain many small oval nematocysts. 
2d— F. C. B. 1900—22 
