PLATE V. 



PORITES ASTRjEOIDES Lamarck. 



Fig. 40. — Vertical section through a polyp, a little to one side of the oral aperture. The laterally folded stomodieal 

 wall (st. ) is included in section, with three mesenteries attached. Portions of three introverted 

 tentacles (/. ) are also included, the one to the left showing the external opening and the thickened apex. 

 The column wall to the left rests directly upon the thecal wall, while to the right a narrow canal per- 

 mits of communication of the polypal cavity with the one adjacent. X 50.. 



Fig. 41. — Transverse section through the stomodieal region of a polyp with seven pairs of mesenteries — that is, one 

 pair (A, A) more than usual — situated within the entocoele of the ventral directives (III, III). (The 

 ventral surface is placed ahove and the dorsal is below, a reversal of the usual position throughout the 

 drawings.) X 100. 



Fig. 42. — Transverse section a little below the stomodieal region of a polyp having ten pairs of mesenteries — that 

 is, four pairs (A — 1>) more than usual (cf., rig. 11 b, p. 469). X 50. 



ASTRANGIA SOLITARIA Lesueur. 



Fig. 43. — Transverse section through the tentacular region of a retracted polyp, showing the relationship of the 

 mesenteries, and the tentacular outgrowths from each mesenterial chamber [cf., rig. 8g, p. 463). 

 The exocoelic tentacles are the smallest, and the others vary in size according to the order of the 

 entocoelic chamber from which each arises, the six largest communicating with the six primary 

 entocceles (I). X 50. 



Fig. 44. — Transverse section through a mesenterial filament, immediately below the stomodieal region, and part of 

 the skeletotrophic tissue lining the wall of the septal loculus (sk. I. At this level the filament does not 

 differ histologically from the stomodieal ectoderm, and the skeletotrophic endoderm is very narrow. 

 The calicoblast layer is practically absent, only a few nuclei occurring here and there. X 300. 



Fig. 45. — Transverse section through a mesentery, and part of the lining of the septal loculus in which it is inclosed. 

 The mesenterial filament is here more characteristic in form, ami the endodermal epithelium immedi- 

 ately behind is much swollen on each side. The skeletotrophic endoderm is now greatly thickened and 

 highly granular. The dark circular bodies are probably nutritive particles. X 300. 



PHYLLANGIA AMERICANA Milne Edwards t \; Haime. 



Fig. 46. — Two polyps, united only by a basal skeletal expansion. The column wall is so transparent as to allow the 

 skeleton to be seen through. The polyp to the left is nearly fully expanded, the peristome protruding 

 as high as the tentacles; the polyp to the right is partly retracted, the column wall nearly covering the 

 tentacles. The tentacles are knobbed and tubercular. 



608 



