PLATE IX. 



ORBICELLA ANNULARIS (Ellis* Solander). 



Fig. 67.— Radial vertical section of a decalcified, partly expanded-, polyp. The column wall on each side passes 

 uninterruptedly into a tentacle, bearing nematocyste at the apex; the disk is elevated around the mouth, 

 and is partly indrawn, the actual stomodseal ectoderm commencing a little within the tube. The 

 mesenteries are represented by sections in different directions, and are limited in their distribution 

 to the upper half of the polyp. On the left side a mesentery is cut obliquely, stretching from the 

 column wall to the disk, and on the right side one stretches from the disk to the skeletotrophic lining 

 of a septum. The two oval bodies a little above the middle are sections of the modified glandular 

 mesenterial filaments, found within this and other species. The lower half of the polypal cavity is 

 practically empty, but is largely intruded upon by the thickened endoderm of the skeletotrophic tissues. 

 On the left side the polypal cavity is continued over the thecal edge, but its communication with the 

 adjacent polyp is interrupted, while on the right side the continuity is preserved. Desmoidal processes 

 ( des. /»/'. ) are strongly developed at the point of separation of the polyp and the others adjacent. X 70. 



Fis. lis. — Transverse section through a complete and incomplete mesentery and the entoseptal invaginations which 

 inclose them. The larger mesentery stretches from the thecal wall to the inturned column wall, and 

 about the middle its mesoglcea is deeply folded on both faces for the support of the retractor and oblique 

 musculature. Toward its insertion on the skeletotrophic tissues the mesoglceal foldings are more 

 normal, and occur only on the face bearing the retractor muscle. The small incomplete mesentery 

 bears a single ovum. No exoseptal invagination are present at this level. X 110. 



Fio. 69. — Transverse section through a portion of a mesenterial filament which has become wholly glandular and 

 greatlv enlarged. Drops of the secretion are represented oozing out in places. The glandular cells are 

 supported behind upon the swollen mesenterial endoderm. X 320. 



Fig. 70. — Tangential section of a similar glandular filament. The middle gland cells are cut transversely, and are 

 polygonal in outline, while the marginal are cut obliquely. X 320. 



Fio. 71. — Free glandular and supporting cells from a mesenterial filament. X 450. 



Fio. 72. — Transverse section through a mesenterial filament, showing the more usual structure, tor comparison with 

 the glandular modification iu fig. 69. X 320. 

 616 



