PLATE V. 



PORITES ASTR.-EOIDES Lamarck. 



Fio. 40. — Vertical section througli a Jiolyp, a little to one side of the oral aperture. The laterally folded stomodceal 

 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 tlie left rests ilirectly upon the thecal wall, while to the right a narrow canal per- 

 mits of communication of tlie polypal cavity with the one a<ljacent. X 50. 



Fig. 41. — Transverse section through the stomod:eal region of a polyp with seven pairs of mesenteries — that is, <nw 

 pair (A, A) more tlian usual — situated witliin the entocicle of the ventral directives (III, III). (The 

 ventral surface is placed above and the dorsal is lielow, a reversal of the usual iiosition throughout the 

 draw^ings.) X 100. 



Fig. 42. — Transverse section a little lieldw the stomodseal rcginn ni a jiolyp liaving ten pairs of mcienteries — that 

 is, four pairs (A — D) more than usual (cf., (ig. 11 li, p. 4(i'.i). y .'iO. 



ASTRANGIA SOLITARIA I.esueur. 



Fig. 43. — Transverse section tlirongh the tentacular region of a retracted ]"ily]i, showing the relatiimshii) of the 

 mesenteries, and tlie tentacular outgrowths from each mesenterial chamber ((•;'., tig. 8g, p. 463). 

 The exoco'Iic tentacles are the smallest, and the others vary in size according to the order of the 

 entoccelic chandler from which each arises, the six largest conimunicating with the si.x [irimary 

 entocceles (I). X SO. 



Fig. 44. — Transverse section througli a mesenterial fllament, immediately below the stomoda'al region, and jiart of 

 the skeletotrophic tissue lining the wall of the septal loculus (sk. ). At this level the filament <Ioes not 

 differ histologically from the stomodfeal ectoderm, and the skeletotrophic endoderui 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, and the endodermal epithelium immedi- 

 ately behin<l is much swollen on each side. The skeletotrophic' endoderm is now greatly thickened and 

 highly granular. The dark circular Viodies are jirobably nutritive jiarticles. X '^00. 



I'llYI.LANGIA AMERICANA Milne Edwards it Haime. 



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

 skeleton to Vie seen through. The polyp to the left is nearly fully expanded, the iieristome 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. 



aos 



