hitrodtiction to Animal Morphology. 123 



branches arise from the calcareous (Isis) or horny joints 

 (Mopsea). Parisis seems to be a passage form. 



Order 6. Briareacese. — The axis is never horny, 

 but may be hollow (Ccelogorgia), or filled with spongy 

 tissue, with siliceous (Solanderia), or calcareous 

 spicules (Briareus), and with large, nutritive canals,, 

 or none (Spongioderma). The polypes may be partly 

 (Solenogorgia), or wholly retractile, either embedded 

 in the cortex (Paragorgia), or in wart-like calyces 

 (Briareus). 



Order 7. Coralliaceae — axis rigid, unjointed, cal- 

 careous, branched, finely grooved on the surface ; 

 coloured deep red by iron oxide, with little or no. 

 organic matter. This is coated by a red coenosarc, 

 traversed by the canals extending fi-om the bodies of 

 the retractile, white polyps. These canals have per- 

 forate walls, and contain a milky, corpusculated fluid. 

 The precious red coral of the Mediterranean (Corallium 

 rubrum) belongs here. It lies in 10-30 fathoms of 

 water. 



CHAPTER XX. 



SUB-KINGDOM 4. ECHINODERMATA. 



Marine, never colonial animals ; each made up 

 of several (usually four or five) radially, often 

 bilaterally, symmetrical antimeres. The integu- 

 ment has a ciliated outer layer, beneath which 

 is a dermis containing calcified, never chitinous^ 



