PLATE X. 



ORBICELLA ANNULARIS (Ellis & Solander). 



Fk;. 73. — Vertical section through the skeletotrophic tissue lining an interseptal chamber at its basal termination. 

 In situ the basal part of the loculus would rest upon a skeletal dissepiment. The endoderm at the 

 sides is greatly thickened, measuring 0.1 mm. in section, and is largely vacuolated with but few 

 protoplasmic contents; the calico-blast layer of the lateral walls has nearly disappeared. The endoderm 

 at the flattened termination of the loculus is much narrower, and closely resembles the layer in the 

 upper parts of the polyps. The calicoblast ectoderm [ml. ) is also a well-developed columnar epithelium, 

 resting upon the skeletal membrane (si. m.). The latter is well shown, and in some places is united 

 with the ectoderm and in others free from it. At the left edge it is continued along the lateral wall. 

 Desmoidal processes from the mesoglcea are developed, extending across the calicoblast layer to the 

 skeletal membrane. The active condition of the calicoblast probably denotes that the formation of a 

 dissepiment was in process when the polyp was preserved. X 300. 



SOLENASTRJEA HYADES (Dana). 



Fig. 74. — Group of rive polyps. The uppermost is nearly fully expanded; the others are in different states of 

 retraction. In some the tips of the tentacles are just visible, while in others they are completely covered 

 by the overfolded column wall, only the middle of the peristome being visible. Enlarged. 

 Fig. 75. — Transverse section through a portion of the upper region of a retracted polyp. The section includes a 

 knobbed tentacle, and showsthe lateral nematocysts arranged in projecting groups. The nerve hbersare 

 also clearly seen at the base of the knob. The ectodermal and endodermal musculatures of the tentacles 

 are cut obliquely, and the latter is seen in continuity with the musculature of the mesenteries. The 

 skeletotrophic endoderm is here a very narrow layer i ,■/. fig. 7!» |, and the calicoblast layer has almost 

 disappeared. X 300. 



-Vertical section through the column wall, showing the arrangement of the clear gland cells in the ectoderm. 

 X 900. 



-Tangential section through the ectoderm of the column wall, to the outside of the nuclear zone. The 

 interstitial supporting cells only partly separate the gland cells, which are polygonal in transverse 

 section. X 900. 



-Tangential section through the ectoderm of the column wall at the level of the middle nuclear zone. 

 X 900. 



-Longitudinal section through the skeletotrophic layers toward the lower termination of the polyp. The 

 endoderm is greatly thickened, and contains many large granules, either scattered or aggregated within 

 distinct cells. The calicoblast layer is finely granular, and presents no cell outlines. X 300. 

 618 



