MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 575 



Under ordinary conditions the discal areas are deeply depressed, and flat <>r slightly concaye; 

 on ('nil expansion they are raised a great height above the corallum. The surface appears 

 vrr\ coarse, owing to the presence of much granular matter and the verruca' over the septal 

 spines; near the periphery, in the area more or less hidden by the overhanging column wall, 

 t'ne disk seems thinner, and the dense pigmentation is almost wanting. 



Usually the oral apertures appear as narrow slits, about 3 mm. in length, with the lone axis 

 alone- the length of the disk: at other times they are situated at the apex of a conical peristome. 

 When open the mouth is oval or nearly circular in shape, displaying the intense white stomodaeal 

 walN. The latter are strongly ridged and furrowed, the number of ridges varying indifferent 

 polyps from twelve to twenty-four; when the mouth is partly opened a sharp line of 

 demarcation exists between the disk' and stomodseum. The mouths are about 7 mm. apart in 

 the living condition, and about 5 nun. in preserved colonies. 



The prevailing colors are dark green, brown, and yellow, with minute, opaque white, 

 superficial granules, distributed practically all over. These latter interfere somewhat with the 

 distinctive characters of the other colors. The yellow color predominates alone the thecal ridges, 

 and the green alone- the valleys. Irregular, opaque white, cream, or green patches are sometimes 

 present on the disk, ending in streaks toward the periphery — that is. in the region covered by 

 the overfolding column wall." 



On irritation numerous pixffongations of the mesenteries and filaments are extruded through 

 various regions of the body wall; sometimes tin' greater part of the colony will be thus covered. 

 presenting a very beraggled appearance. < >n withdrawal, the apertures through which the 

 mesenteries protruded may be so large as to be visible with the aid of a lens, and remain open for 

 some time; afterwards they close and leave no external evidence of their former presence. The 

 thin transparent mesentery can be easily distinguished from the dense white filament in any 

 protruded portion, and the former is often greenish in color. 



Anatomy and histology. — The ectoderm of the superficial body wall is remarkable for the 

 abundance of a finely granular pigment substance within the cells, and for the comparative fewness 

 of the clear eland cells. This condition is no doubt the principal cause of the dense opacity of 

 the outer tissues already described. The pigment matter is unaffected by carmine stains and 

 hematoxylin, and appears yellowish brown or greenish in sections, and in macerated tissues. It 

 is mainlv restricted to the deeper regions of the layer, where it is either continuous or distributed 

 in more or less isolated irregular patches (tie. 122). Toward the tentacular region of the column 

 wall clear gland cells are more numerous than elsewhere. 



The mesoglcea is of moderate thickness, and contains numerous connective tissue cells 

 distributed throughout. Sometimes their processes are seen in connection with the endoderm. 

 sometimes with the ectoderm, or may even stretch across from one layerto tic other. A slight 

 difference in consistency in the mesoglcea is also apparent in preparations stained with aniline 

 blue; lighter, tube-like portions extend across the whole layer, or in other sections appear as 

 so many circular disks staining less deeply than the surrounding mesoglcea. 



Zooxanthelhe occur in large numbers in the endoderm of the column, while the musculature 

 is strongly developed in the upper region, more so than in any other species here described. 

 The inner surface of the mesoglcea, for some distance, forms pointed, rounded, or dendriform 

 plait- for. its support, and the muscular fibrils themselves are somewhat large in transverse 

 section, constituting what must be regarded as a definite endodermal sphincter muscle (tig. li'l ). 

 The whole form resembles what ha- been described in certain Actiniaria as a •'restricted" 

 sphincter muscle. 



The tentacle- in retracted polyp- are crowded under the overhanging thickened edge of 

 the column wall, and may or may not be introverted. Histologically they differ much from 

 the column wall. The ectoderm is a deep layer, containing numerous gland cells and a marginal 

 zone of very narrow nematocysts; the granular pigment matter is absent from the more 



oProf. A. K. Yen-ill i 1901) alludes to the very varied colors <■(' the Tsophyllia at Bermuda, lie notes that some 

 specimens were phosphorescent at night, and that this property seemed to he related to the white pigment. 



