PLATE VIT. 



CLADOCORA ARBUSCULA (Lesueur). 



Fig. 53. — Transverse section of an enlarged polyp, with a triangular st(mioda;al tube and three pairs of directives (D). 

 The alternation of complete and incomplete uiesenteries is irregular. X 50. 



Fio. 54. — Transverse section through the lower jiart of a polyp, showing how the polypal cavity is encroached uiion 

 and subdivided into more or less distinct chambers by the septal ingrowths. The skeletotrophic endo- 

 derm is somewhat thickened, compared with its condition in the upper region. The perithecal parts 

 of the mesenteries are now beginning to cease their connection with the skeletotropliic wall. X 50. 



Fig. 55. — Transverse section of the same polyp at a still lower level. The perithecal part of the polypal wall is 

 here absent, and the jiolypal cavity is liroken up into twelve distinct loculi by the middle union of the 

 septa. A remnant of the polypal cavity yet persists in the center. The mesenteries have nearly 

 disappeared. X 50. 



Fig. 56. — Vertical section through the middle part of tlie disk and tlie stomodicum, showing the folded character of 

 the latter in retracted polyps. <Jn the left side the stomodical wall is in connection with a mesentery, 

 while on the right it is free and narrowed. X 120. 



Fiii. 57. — a, Transverse section of the free extremity of a.mesentery of the second order, showing the earliest appear- 

 ance of the mesenterial filament, h, Transverse section through a mesenterial filament immediately on 

 becoming free from the stomoda^al region, c, The same filament some distance below the stomodseal 

 region. (8eep. 472.) X 320. 



Fi(4. 58. — Section of a jiart of a convoluted mesentery, with tlie filament at each end containing large oval nematocysts 

 with a s])iral threa<l. X 250. 

 612 



