PLATE VIII. 



CLADOCORA ARBUSCULA (Lesueur). 



Fit;. 59. — Transverse section through a part of the discal region of a retracted polyp, with two attached mesenteries 

 (directives) and the entoccelic septal invagination (sep. inr.). The skeletogenic ectoderm (cal. ) 

 lining the inner calicinal wall is a very distinct layer at this level, and also along the innermost 

 part of the invagination, but is absent from the lateral surfaces. X 320. 



Fig. 60. — Transverse section through the elevated peristome of a bud polyp. Five pairs of complete protocnemes 

 are present; the incomplete sixth pair is represented below, along with the six pairs of first- 

 cycle metacnemes. The reflected stomodaeal ectoderm (r. eel.) is seen on the left side (e/., fig. 51). 

 X 120. 



Fig. 61. — Transverse section of a bud polyp with eight complete mesenteries, which at the level represented are 

 nlamentiferous. Two unilateral pairs of metacnemes (A. A) have appeared on the ventral, sulcar, or 

 outer border. X "0. 



Fig. 62. — Transverse section of a pentameral bud polyp, with the metacnemic pairs showing successive stages in 

 development from the lower (abaxial) to the upper (axial) aspect. X 70. 



Fig. 63. — Section of the upper skeletotrophic layer, where the calicoblast layer is well developed. Destnoidal 

 processes are indicated by the striated bodies, but in the section are free from the mesoglcea. X 320. 



ORBICFLTA ANNULARIS (Ellis & Solander). 



Fig. 64. — Radial section through the column wall, perforated for the passage of a mesenterial filament and the 

 mesentery to which it is attached. I See p. 475.) X 300. 



Fig. 65. — Radial section through the infolded edge of the column wall of a retracted polyp. The endodermal 

 musculature forms a weakly diffuse endodermal sphincter muscle; pigment granules occur in groups in 

 the ectoderm of the outer part of the wall. X 300. 



Fig. 66. — Section through the skeletotrophic tissue lining the upper part of the theca. The edge of the broad calico- 

 blast layer {eel. ) is irregularly jagged. X 400. 

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