60 CORALS AND CORAL ISLANDS. 



crowded clusters of such stems branching variously and having 

 each branch surmounted with its one polyp (figure p. 54) ; or, if 

 there is lateral growth and but little of upward, it produces 

 leaf-like forms and graceful groups or clusters of leaves, vases. 

 and other shapes ; or, if the germ-polyp is capable of lateral 

 growth alone, the results are simple lines of polyps creeping 

 over the supporting rock, like the creeping stolons of a plant, 

 or else encrusting plates, spreading outward like a lichen. 



In the descriptions of corals the following terms have the significa- 

 tions annexed. Those already mentioned are here repeated to bring 

 them all together. 



Zoothome. — The compound animal mass produced by budding. 



Corallum. — The coral either of the compound mass, or of the solitary 

 polyp. 



Gorallet (In Latin, corallulum). — The coral of a single polyp in a com- 

 pound corallum. 



Galicle. — The polyp cell in the top of a corallet, or of a solitary 

 corallum, w^hin the walls of the cells ; it is sometimes flat at top, that is, 

 without the usual depression. 



Septa. — The radiated plates of the cell or calicle. 



Dissepiments. — Small cross plates between adjoining septa (sometimes 

 wanting). 



Synapticuloe. — Minute cross bars uniting the surfaces of adjoining 

 septa. 



Ccenenchyma. — The common mass of the corallum between its dif- 

 ferent polyp cells or corallets, as in the Madreporae, Gemmiporse and 

 Dendrophylliae. 



Epitheca. — The coral layer sometimes deposited over the exterior of 

 the corallum during the life of the polyp by the outer skin before it dries 

 away, as explained on page 44. 



Peritheca. — The epitheca of a compound group or zoothome (fig. p. 71). 



Exotheca. — The portion of the corallum outside of the walls of cells 

 in many coralla of the Astrsea family, and some others, in which the polyps 

 of the mass are properly in contact, and there is consequently no true 

 ccenenchyma. 



Endotheca. — The portion of the corallum inside of the walls of the cell. 



We may now state briefly the characteristics of the 

 grander divisions of the Actinoid polyps, several of which 

 have been illustrated in the preceding figures. 



