PLATE X. 



ORBTC'ELLA ANNULAKLS (KWis & Colander'*. 



Fig. 73. — Vertical section lhroufi;h the skeletotrophic tis.sue lining an interseptal chamber at its basal termination. 

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

 sides is greatly thickened, measuring 0.1 mm. in section, and i.-^ largely vacuolated \\ith Init few 

 lirotoplasmic contents; the calicoblast 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 polyj)S. The calicoblast ectoderm {cal. ) is also a well-developed columnar epithelium, 

 resting upon the skeletal membrane {sk. m.). The latter is w-ell 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 mesogloea are developed, extending across the calicoblast layer to the 

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

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



S()LKXASTR.EA HYADES (Dana). 



Fiii. 74. — (iroup of live polyps. The uiipermost 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 

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

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

 knobbed tentacle, and shows the lateral nematocysts arranged in projecting groups. The nerve fibers are 

 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 (//. fig. 79), and the calic(.)blast layer has almost 

 disappeare<l. X 300. 



-Vertical section through the column wall, showing tlii> arrangement of the cleargland cells in the ectoderm. 

 X 900. 



-Tangential section thinugh tlie ectoderm of the cnhnun wall, to the outside of the nuclear zone. The 

 interstitial supporting cells oidy partly separate the gland cells, which arc polygonal in transverse 

 section. X 900. 



-Tangential section tbrnugh tlie ectoderm uf tlie column wall at the level of the middle nuclear zone. 

 X 900. 



-Longitudinal section through the skeletotrophic layers toward the lower termination of the J"ilyp. 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 



