THE ACTINIANS OF PORTO RICO. 
349 
of the tentacles is often scarlet. The tentacles are yellowish gray, and nearly transparent on the outer 
surface; several opaque, yellow oval patches occur on the inner aspect, and also a vertical, elongated 
spindle-shaped patch of crimson. The disk exhibits thin, radiating scarlet lines; and yellowish bands, 
passing from around the mouth, surround the base of the tentacles. The peristome and upper part of 
the stomodweuin are a bright scarlet. 
The above is the coloration generally met with, but different examples of the species vary much, 
and some may be here noted. Usually the column is a bright red, but may be crimson, orange, brown, 
chocolate brown, or a grayish olive. This latter color, and the verrucse in light and dark bands, most 
nearly corresponds with McMurrieh’s Bahaman specimen. In the larger examples the alternate 
larger and smaller acrorhagi are well distinguished by the contrast of their opaque white tubercles 
with the rest of the column. The verrucae toward the top of the column are usually more opaque 
white than those below; toward the base they become more transparent, with one or two dark centers. 
The column-wall in any individual specimen appears to be of practically the same color throughout, 
the lighter and darker vertical zones depending mainly upon the intensity of the pigmentation of the 
apex of the verruese. 
Twelve series of radiating colored bands, each made up of three parts, the middle one much the 
broadest, may extend from around the mouth to the first and second cycles of tentacles, then each 
passing between the tentacular bases forms a cream-colored area on the antero-lateral portion of the 
base of the alternating tentacles in the outermost cycles. Often a narrow band of crimson passes up 
the anterior face of the tentacles. 
The length of the column is usually about 4.5 cm., but a polyp may elongate as much as 
7 or 8 cm. The diameter is from 4 to 5 cm., or may be even 7.5 cm. ; the length of the largest tentacles 
is 1.3 cm., the diameter 0.4 cm. The acrorhagi may extend 0.3 cm. beyond the margin. 
Anatomy and Histology . — In vertical sections the base is folded to an extraordinary degree; the 
foldings usually include all the three layers, long processes of the mesogloea accompanying the 
ectodermal folds. The ectoderm of the base is very deep, being constituted of long narrow cells — 
mainly gland cells, with tine granular contents. The mesogloea and endoderm are very thin; a weak, 
circular endodermal muscle is present, and fine black pigment granules occur in the inner layer. 
The column-wall seems also much folded in sections, the appearance being due mainly to the 
presence of the vesicular evaginations (fig. 34). These are all hollow, and arise from both the 
entocoelic and exocoelic chambers. The wall of the vesicles is thinner than that of the column gen- 
erally, and a short canal connects the cavity of the vesicle with the coelenteron, while the endodermal 
muscle is specially developed around the aperture (cp. Dixon’s figure of Bunodes thallia, 1889, pi. iv, 
fig. 4). The ectoderm of the vesicles is high, and medium-sized nematocysts are abundant, mainly 
limited to the outer apical region; numerous unicellular gland cells are present laterally. The gran- 
ular secretion is seen partially extruded from many of the cells. The mesogloea of the column-wall 
is very variable in thickness. 
Small dark-colored pigment granules occur abundantly in the endoderm of the vesicles, as well as 
in the other parts of the column-wall, and, indeed, throughout the endoderm of the polyp. I have not 
been able to distinguish any yellow cells in the endoderm of any part of the polyps, but McMurrich 
states that numbers are contained throughout the layer in his Bahaman specimen. The endodermal 
muscle is very strongly developed along the column-wall, arranged on branching outgrowths of the 
mesogloea. 
The acrorhagi are much like the verrucae in structure; nematocysts are abundant only at the 
tips of the tubercles, and the ectoderm is comparatively thin. No endodermal musculature can be 
recognized. 
The sphincter muscle (pi. ix, fig. 34) is a typical circumscribed endodermal representative, situated 
within the fossa, and attached by only a very short pedicle. The appearance usually presented by 
transverse sections differs a little from that in the figure given by McMurrich, which is drawn associated 
with a mesentery. 
In partial contraction the tentacles are fluted externally, and in transverse sections present a 
sinuous appearance similar to that described and figured by the brothers Dixon (1889, fig. 1 ) for B. 
thallia. The ectoderm is very broad, but the two other layers are narrow; the nematocysts in the 
former are small and slightly curved. The ectodermal muscle is arranged on dendriform mesogloeal 
