THE ACTINIANS OF PORTO RICO. 
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larger. A shallow fossa intervenes between the acrorhagi and base of the tentacles. The column-wall 
is incapable of folding over the disk and tentacles. The marginal tentacles are arranged in numerous 
entacmseous cycles, and usually number between two and three hundred. They are shortly conical 
and overhanging, the oral face being longer than the aboral or outer. The members of the first and 
second cycles are situated some little distance from the other cycles. Normally the cycles are 
hexamerous, but irregularities are frequently met with. Usually the tentacles bear several transverse 
opaque thickenings, most strongly developed along the oro-lateral area, where a distinct bilobation is 
often observable. Six or seven pairs, arranged pinnately, the middle pairs being the largest, may 
occur on the larger tentacles, and a less number on the smaller tentacles. For some little distance 
from their origin the tentacles are smooth, and polyps occur in which the tubercles are altogether 
undeveloped. Among a number of polyps from one locality every stage could be obtained between the 
full development and total absence of the thickenings, some tentacles possessing the full number and 
others being wholly destitute of them. 
The inner tentacles are small papilliform projections of the discal wall, varying much in size, and 
arranged mostly radially. They correspond with the interspaces of the first and second cycles of 
mesenteries, and sometimes with those of the lower orders. 
The disk is large, thin-walled, and peripherally is thrown into eight to twelve sinuous folds, 
which overhang the column ; the middle region is flat or slightly convex. The gonidial grooves are 
clearly indicated, the lips being thicker and lighter than the rest of the stomodaeal wall. 
The coloration is very variable, and all gradations can be traced in a large series of polyps. 
The disk colors are mostly brown and green, with opaque white spots and 1 dotches; those of the column 
and base are scarlet and crimson on a white or cream ground. The center of the verrucse is deep 
crimson; the tentacular thickenings usually appear as white bands. When the tentacles are smooth 
they are brown or reddish brown, with light crimson tips, and three longitudinal lighter lines traverse 
the oral aspect. The peristome is usually iridescent green. 
The dimensions are likewise very variable, according to age. In many young specimens the 
column was only 1.1 cm. long, and the diameter 0.8 cm. The length of the column in adult specimens 
is about 6 cm., the middle diameter 1.7 cm., and the basal 2.5 cm. ; the diameter of the disk varies from 
5 to 9 cm.; the innermost tentacles are 0.7 cm. in length. 
Anatomy and Histology . — The ectoderm of the base is a very broad columnar epithelium, with a 
few gland cells, and is much folded in sections. The mesogloea appears strongly fibrous and contains 
numerous connective tissue cells. Numerous z'ooxanthellse occur in the endoderm, and muscle fibrils 
are present. 
The column-wall is of only medium thickness, becoming more delicate distally. The ectoderm 
is broad and deeply ridged, the elevations being followed by the mesogloea. Clear and granular gland 
cells are abundant, and also small nematocysts. A nerve layer occurs, and what I consider to be a 
very delicate muscle layer in the upper part of the column. The endoderm is a deep layer containing 
zooxanthellse, and the circular endodermal muscle is well developed on fine mesogloeal plaitings. 
The muscle is nowhere concentrated to form a special sphincter. The verrucal ectoderm shows an 
absence of gland cells and nematocysts. 
Both the ectodermal and endodermal musculatures are well developed in the peripheral tenta- 
cles, supported on mesogloeal plaitings. The nematocysts in the ectoderm are exceptionally small. 
The tentacular swellings are due mainly to an increase, in the thickness of the mesogloea. 
The disk is thin- walled and the endodermal circular muscle is well developed on mesogloeal folds. 
The discal papillae are simple hollow upgrowths; the mesogloea and endodermal musculatures become 
so thin as to be scarcely recognizable, and the ectoderm is thinner than elsewhere. 
The stomodaeum is very elongated in transverse sections, extending almost across the coelenteron, 
the pair of directives at each extremity being shorter transversely than the other mesenteries. The 
walls are thin and the ectoderm is thrown into irregular vertical folds. The two gonidial grooves are 
clearly indicated, their ectoderm unfolded, and the mesogloea not much thicker than elsewhere. 
Longitudinally the stomodseum is comparatively short, but the groove at each end is prolonged for 
some distance below the lateral walls. Narrow gland cells occur, and a weak longitudinal ectodermal 
musculature and ganglion layer are recognizable. 
In mature polyps the mesenteries of the first three orders reach the stomodfeum, though the 
third and second orders may not extend throughout its length; a fourth and a fifth order may also be 
developed, the formula being 6 6 12 24 48. The mesenteries are comparatively narrow in transverse 
