166 PHYLUM C@LENTERA. 
pillar may be formed. ‘The outer wall of the theca may 
bear vertical ridges or cost, and these may be connected 
with neighbouring coste of other polyps by horizontal 
shelves or dissepiments. Both septa and costz correspond 
to intermesenteric spaces. (See Shipley’s Zoology of the 
Invertebrata, pp. 68-71.) 
ANTIPATHARIANS 
Usually arborescent, sometimes whip-like colonies, of wide distribu- 
tion in most seas, often called ‘‘black corals.” A spinose hollow 
horny axis is covered with coenenchyma and regularly arranged polyps, 
ae 
wees 
Fic. 83.—Structure of Antipatharians. 
1. A group of polyps—J/., mouth ; ¢., tentacles. 
2. Axis without polyps and ccenenchyma, covered with spines 
S; 
3. Vertical section of a polyp—A., axis; ¢., tentacle; g., gullet ; 
m., mesentery ; 0., ovary ; #2.., mesenteric filaments. 
4. Cross section of a polyp—ZC., ectoderm; /., mesoglcea ; 
EN., endoderm ; G., gullet; 17S., mesenteries. 
without any trace of spicules. A polyp is usually oval in section, with 
its long diameter in the line of the axis, and its gullet elongated at 
right angles to this. There are usually six simple non-retractile 
tentacles, ten mesenteries, and two ill-defined siphonoglyphes. The 
mesenteries are without muscle-banners. The two longest, running at 
right angles to the elongated stomodeum, bear gonads. The develop- 
ment is unknown. 
