558 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



tertian' mesenteries. The sequence of the mesenteries in this species has been already noticed 

 (p. 464.) 



The individual mesenteries arc characterized by the thickness of the mesogloea, and by the 

 intricacy and depth of the plaitings for the support of the longitudinal musculature. The 

 foldings are nearly as complicated on the incomplete mesenteries as on the members of the first 

 and second cycles, and continue thus throughout the length of the mesentery; slight variations 

 in details occur in different mesenteries. The cut ends of the fibrils of the retractor muscle are 

 verv minute. The oblique musculature on the opposite face is strongly developed, and the 

 fibrils appear to be nearly vertical in direction; in the case of the complete mesenteries a very 

 distinct plaiting of the mesogloea takes place in the stomoda?al region, thus increasing the effectual 

 surface. The cells of the mesenterial epithelium in the upper regions are mostly filled with 

 deeply-staining, protoplasmic contents, and only a few clear gland cells occur. In the lower 

 regions the layer thickens, and the contents become finely granular, the cell outlines disappearing. 



Filaments may occur on all the mesenteries, and closely recall those of Astrangia. The 

 first part of the filament on the complete mesentaries is cordate in transverse sections, and 

 histologically resembles the stomodseal ectoderm, the tissue being of a similar character all 

 round. Soon, however, the filament becomes circular, and nematocysts and gland cells are 

 more numerous on the anterior part of the filament; the mesenterial mesoghea on each side also 

 becomes swollen immediately behind the filament. Still lower the filament is strongly charged 

 with large, oval, thin-walled nematocysts. The organs are slightly convoluted below, and by no 

 means crowd the coelomic cavity. 



The septal invaginations extend centrally but a short distance, and only toward the 

 proximal region are both entoccelic and exoccelic invaginations represented. The skeletotrophic 

 endoderm is much thickened below, and is densely granular, the granules of different sizes being 

 somewhat uniformly distributed throughout the layer. The lateral walls of the invaginations 

 are deeply indented, corresponding with the granules on the septal faces. 



Within the edge-zone the mesenteries are mostly incomplete on the inner side, so that the 

 peritheeal chambers are but imperfectly divided. 



Genus CLADOCORA Milne Edwards and Haime." 



Polyps smooth, distant, forming- bush-shaped or fasciculate colonies, free or fixed, and often 

 separated into subcolonies of from two to five polyps; peritheeal continuation of the gastro-coelomic 

 cavity and mesenteries. Column wall smooth, cylindrical, elongated, on retraction may close over 

 nearly the whole of the disk. Tentacles hexamerous, entoccelic and exoccelic, tricyclic, or incompletely 

 tetracyclic, entacmseous, finely tuberculated, knobbed or rounded at end. Stomodseal walls ridged. 



Mesenteries regularly hexamerous, dicyclic or incompletely tricyclic, six pairs complete, two pairs of 

 directives, all filamentiferous, extrusible. Septal invaginations entoccelic and exoccelic, tricyclic or 

 incompletely tetracyclic, below unite centrally (columella), giving rise to twelve separate mesenterial 

 loculi. 



Asexual reproduction by lateral columnar gemmation, rarely by fissiparous gemmation. 



Example. — Cladocora arbuscula (Lesueur). 



CLADOCORA AEBUSCULA (Lesueur). 

 (Ply. VI- VI II, rigs. 48-63.) 



External characters. — Small bush-like colonies of this species occur in numbers in the 

 -hallow waters of Kingston Harbor, and at other points around the coast, either free or attached 

 to loose pebbles or shells. Larger colonies are found in water of from three to six feet, and 

 thickly incrust the wooden piles of wharfs and buoys, or even the bottoms of boats plying in the 

 harbors. 



""Colony bush-shaped or branched or fasciculate. Corallites variable in length, erect, often flexuous, cylin- 

 drical, and free laterally. Calices circular and shallow. Columella well developed. Septa exsert, subequal, rounded, 

 and finely dentated and granulated laterally. Pali exist before all the cycles except the last. Wall compact, 



derately thick. Costse simple, granular, or finely eehinulate, straight. An incomplete epitheca, which often gives 



to horizontal collarettes, may extend from one corallite to another. Endotheca scanty. Gemmation lateral and 

 often in pairs from the same height on thestem." i Duncan, 1885, p. 70. i 



