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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
larger specimens the annuli on the inner cycles are few in number, the proximal portion of the tentacles 
being quite smooth. In preserved polyps the tentacular rings remain very evident as thickened bands. 
Microscopic examination proves that they represent special urticating areas. In all the examples of 
this species which McMurrich obtained at the Bahamas, the tentacles were arranged octamerously, 
the mesenteries likewise corresponding. In Jamaican specimens a hexamerous arrangement prevailed, 
both in the tentacles and mesenteries. There is no doubt, therefore, that the species varies in this 
important character, and an explanation is thus given to Lesueur’s statement (1817, p. 172) that “the 
centre tentacula are about six or eight in number.” 
The naked portion of the disk is small; the peristome and lips are slightly crenulate, six ridges 
and grooves occurring on each side, corresponding with insertion of the mesenteries. The two 
stomodreal grooves are not distinctly shown. The lips often approach laterally, leaving an aperture at 
each end. 
The base is white; the column is white or cream colored below, flecked with opaque white; above 
it is pale or dark brown and more strongly flecked. The tentacles are a granular brown; the numerous 
incomplete spirals or rings are gray or white with the internal brown granules showing through. The 
color of the innermost tentacles, when the annuli are almost absent, is a pale blue. The surface of the 
disk is dark brown; opaque white or brownish patches occur near the base of the innermost tentacles, 
and another series, corresponding with the tentacles, may be present around the mouth; the disk may 
also be flecked in other places with opaque bluish white. 
At Port Antonio, Jamaica, a specimen was obtained nearly devoid of any brown color, the walls 
being perfectly transparent, or with only opaque white or cream flecks. The tentacular annulationsin 
this example were not very perfect, the urticating areas being more in patches. Verrill describes the 
color of the Bermudan specimens as light green. The brown or green color is altogether endodermal 
in origin, and is due to the presence of numbers of zooxanthellae within the cells of the endoderm. 
The white or cream opaque flecks are wholly superficial. 
The column of large living specimens is 4 to 5 cm. in height; the diameter across the middle 
from 2 to 3. cm.; the inner tentacles are usually 4 to 5 cm. long; the outer 1 to 2 cm. Some polyps 
when fully expanded may be nearly double these amounts. 
Anatomy and Histology . — The base is very thin- walled, the ectoderm being the broadest of the three 
layers. The latter is formed of long columnar cells, most of which have clear contents. The nuclei 
are mostly in a subperipheral zone, and the nerve layer is occasionally displayed. The inesogloea 
is extremely narrow, and the endoderm is but a little thicker; many of the cells of the latter contain 
zooxanthelUe. A very weak basal endodermal musculature occurs. 
The ectoderm of the column-wall in sections is thrown into deep folds as a result of contrac- 
tion, the foldings being followed by long processes of the mesoglcea. Like those of the base, the 
ectoderm cells are largely glandular, and small nematocysts occur in places. A weak endodermal 
muscle, on slight mesoglceal plaitings, extends all the way from the base to the apex (tig. 42). It 
becomes a little stronger in the upper region, being best developed in the region corresponding with 
the external constrictions, that is, a short distance below the apex. In this position McMurrich 
found in Aiptasia sp.? (1889, p. 103) what he regarded as a second sphincter. Distally the endodermal 
musculature undergoes no increased development, such as can be regarded as a sphincter muscle. 
Zooxanthelke are abundant in the endoderm of the upper region, but less so below; hence the 
light color of the living polyp proximally, and the brown distally. McMurrich records a total absence 
of “yellow cells” in one of his specimens, and, as already mentioned, a colorless variety has been 
found around Jamaica. 
A great difference is apparent in the walls of the tentacles according as the organs are retracted 
or fully extended. In the former state all the three layers are rather broad, the mesoglcea least so, 
and ectodermal and endodermal muscles are very evident on long processes of the mesoglcea. In the 
extended condition the wall is so thin that the three layers can scarcely be distinguished individually, 
except where the section passes through urticating areas. Here the ectoderm and endoderm are 
swollen, and nematocysts occur in the former, while the endoderm is crowded with zooxanthellae 
(tig. 41). The nematocysts are of two kinds, large and small; the latter are arranged peripherally, 
and occur also in the intervening areas; the elongated examples extend wholly across the ectoderm 
and are restricted to the swellings. The zooxanthellse present a curious distribution. Instead of 
being arranged uniformly throughout the endodermal layer, they are aggregated within restricted areas, 
and project some distance beyond the ordinary level of the endoderm (fig. 41). No doubt it is this 
