THE ACTINIAE'S OF PORTO RICO. 
339 
term, namely, the variability in size and outline of the polyps. Some are short and thickset, while 
others are long and slender. Mature polyps vary in length from 1 cm. to 2.5 cm. 
Preserved in alcohol the polyps are now a dirty gray, due to the presence of dark incrusting 
particles. They are mostly free, as if torn from some other object, while a few are adherent to pebbles 
and shells, with a very limited development of ccenenchyme. Two or three small specimens rise 
directly from a broad base, as if grown from larvfe, but more likely from a separate fragment of ccenen- 
chyme. All are in the retracted condition; the capitular region is swollen, and the capitular ridges, 
about thirty in number, are very distinct. On adding a few drops of acid to the liquid in which the 
polyps are placed a slight effervescence is set up, showing that some of the incrusting particles are 
calcareous; but in sections a large quantity of siliceous sand grains and a few sponge spicules and 
radiolarian tests remain, mainly limited to the outer half of body-wall. Not only is the greater part 
of the column-wall impregnated with foreign particles, but many are also found within the endoderm 
of the disk, although the two outer layers — ectoderm and mesogloea — are here quite devoid of them. 
Although charged to such a degree with sand grains and sponge spicules, it was possible to cut 
moderately thin sections from specimens embedded in paraffin. In vertical sections the sphincter 
muscle was found to be more strongly developed than in the polyp from which its form was originally 
represented (1889, pi. xvm a, fig. 7), more nearly corresponding with that of Gemmaria fusca on the 
same plate. The sphincter muscle of the Porto Rican polyps is represented in fig. 27 to show the 
possible variation within the species. Transverse sections through a polyp displayed the microtypal 
arrangement of the mesenteries; seventeen complete mesenteries occur on one side of the dorso-ventral 
axis and fifteen on the other, while on each side of the sulcar directives three incomplete mesenteries 
are present in the region of active, growth at the ventral aspect. Below are the more detailed char- 
acters of the species. 
External characters . — The polyps are erect, firm, smooth, and rise independently from a lamellar 
coenenchyme, or from around the base of one another, or rarely are solitary. They may be cylin- 
drical in retraction, swollen a little above, or more usually are clavate. Preserved specimens are often 
transversely wrinkled. The capitulum usually presents about thirty capitular ridges and furrows. 
The tentacles are acuminate, arranged in two alternating rows of about thirty in each. The peristome 
may be considerably raised, and the mouth is elongated and slit.-like. The disk and upper part of the 
column are greatly enlarged on expansion, and the margins of contiguous polyps come into contact 
and by mutual pressure produce a polygonal outline. 
The ccenenchyme is thin and very sparingly developed. As a flattened band or ribbon it 
connects the different members of a colony, but individuals can be seen in process of separation, the 
coenenchyme becoming constricted and ultimately breaking down. 
The lower part of the column is light buff in color, while the upper part is dark brown. The 
tentacles are usually dark brown, but may be olive or green. The outer part of the disk may be dark 
brown with green radiating lines, and the peristome a bright green; or the disk may be green and the 
peristome brown; in others the whole of the disk is bright green. The stomodamm is colorless. In 
alcohol the brown coloi is first extracted, leaving the colony a uniform dark green; later, this gives 
place to a dirty buff color, due to the i pc rusting foreign particles. 
The dimensions of the polyps vary greatly, even in the same colony. The length of the column 
of one of the largest polyps was 5 cm., diameter 1.2 cm; an average height is 1.5 cm. and diameter 
0.7 cm. The diameterof the fully expanded disk is 2.3 cm. ; the tentacles are about 0.3 cm. in length. 
Anatomy and Histology. — The cuticle of the column-wall is thickly coated below with a layer of 
foreign material, principally diatoms. The ectoderm is continuous and presents irregular internal 
limitations, partly due to the occurrence of incrustations, but also as a result of the ectoderm passing 
insensibly into the cell-inclosures of the mesogloea. Zooxanthelke and large oval nematocysts occur. 
The incrustations consist mostly of sand grains, sponge spicules, and radiolarian tests, and extend 
from the inner border of the ectoderm beyond the middle of the mesogloea. Sponge spicules are 
specially aggregated at the most distal part of the column (fig. 27). Von Heider (1899, pi. xvir, 
fig. 28) also represents a similar accumulation of spicules in the Singapore specimens. 
The mesogloea is thicker above and below than in the middle; numerous isolated cells and cell- 
inclosures occur, and among the cells of the latter are zooxanthelhe and oval nematocysts as in the 
ectodermal layer. Many small rounded or oval vacuolated spaces are present containing only a single 
nucleus. 
