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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The endoderm is of medium height and contains symbiotic algae and pigment granules; the 
circular endodermal muscle is clearly recognizable. 
The ccenenchyme contains numerous inclosures similar to those of the column-wall. Ccelenteric 
canals occur with a regular epithelial lining and a weak musculature. 
The sphincter muscle is single and mesogloeal. It extends for a considerable distance down the 
column, situated a little nearer the endodermal border. The upper mesoglceal chambers toward its 
distal extremity are large, and a gradual diminution takes place toward the proximal end. 
The tentacular ectoderm is broad, the periphery being crowded with small narrow nematocysts. 
The mesoglcea is thick in retracted tentacles, and contains isolated cells and foreign incrusting matter. 
Ectodermal and endodermal musculatures occur. 
The disca-t ectoderm is also very broad and includes zooxanthellae and glandular cells. The 
mesogloea is nearly as broad as that of the tentacles, and contains cells with elongated processes 
and cell-inclosures, but no foreign matter. The endoderm is low and the cells contain zooxanthelke. 
The layer may also be impregnated with foreign matter of the same character as that occurring in the 
column-wall. 
The stomodseum is oval-shaped in transverse section, with a well-marked truncated gonidial 
groove, the sulcar directives extending from the corners. The ectoderm is thrown into vertical folds, 
12 to 18 on each side. Large nematocysts and pigment granules are also present, and indications of a 
nerve layer. The cells are longer at the groove, and the mesogloea thickens toward the same place. 
The mesenteries are normally brachytypic, but occasionally the macrocnemic condition may 
occur on one side or the other. About thirty pairs of mesenteries are present, but the number may 
be either greater or less. Each mesentery contains a hasal canal a little beyond the origin, and in the 
upper part other canals extend almost across the mesentery. In the complete mesenteries the canal 
is compressed, and more circular in the incomplete mesenteries. The cellular tissue in the canals 
contains zooxanthellae and large oval nematocysts. Beyond the basal portion the mesenteries are 
very thin and the endoderm is provided with zooxanthellae. The imperfect mesenteries are very short 
radially, appearing in transverse sections as goblet-shaped projections of the column-wall. The 
parieto-basilar muscle is well developed on both the perfect and imperfect mesenteries. 
The reflected ectoderm and mesenterial filaments are of the usual Zoanthean type. 
Both male and female gonads may occur within the same polyp, either separately or on the same 
mesentery. 
Localities . — Jamaica (Duerden), Singapore (von Heider), Porto Rico (U. S. Fish Commission). 
Genus PALYTHOA Lamouroux. 
Brachycnemic Zoanlhidx with a single mesoglceal sphincter muscle. The body-wall is incrusted. 
The ectoderm is continuous. The mesogloea contains numerous lacume, and occasionally canals. 
Dioecious, rarely hermaphrodite. Polyps immersed in a thick ccenenchyme, which forms a massive 
expansion. 
Contrary to all other species previously examined a Javan Palythoa has been found by Carlgren 
(1 00a, p. 110) to be hermaphrodite. 
In the paper on the Jamaican Zoanlhex I have already discussed the practical absence of reliable 
taxonomic characters for the species of this genus. The external features available — color, number of 
tentacles and capitular ridges, form of the colonies and individual polyps, extent of immersion within 
the ccenenchyme, and dimensions — seem of little assistance; while, judging from the number of species 
already described, not much help is likely to be forthcoming from the characteristics of their internal 
anatomy and histology, including the nature and distribution of the, incrusting particles, the form of 
the sphincter muscle, the arrangement of the mesoglceal canal system, thickness of the ccenenchyme, 
and presence or absence of pigment granules. In none of these features has specific differentiation 
proceeded very far, and I consider it very doubtful whether the best course would not be to regard all 
the forms as but one species. Such a conclusion has been forced upon Professor Hickson (1898) as a 
result of his extensive studies of the Hydrozoan coral Millepora. He believes that all the numerous 
species of this well-defined genus already described are hut variations in the manner of growth, and 
that no reliable specific differences are forthcoming when the colonies with their zooidal tissues are 
compared in detail. A similar study of the recognized species of the genus Palythoa will be only 
possible where colonies from widely separated regions are available for comparison. 
