ACTINOZOA. 87 



be "sclerobasic." (For illustrations of these different kinds of 

 corals, see figs. 49 and 5G.) In the typical form of sclerodermic 

 coral, the skeleton is in the form of a conical cup (fig. 49), the upper 

 part of which is hollow, and is called the " calice." The lower part 

 is divided into a series of compartments by vertical jjlates, which 

 are called the " septa," and which correspond to the mesenteries of 

 the living animal. Sometimes the space contained within the walls 

 of the cup or " corallite " is broken uji by horizontal plates called 

 "tabulse"; but when these are present, there are often no septa. In 

 the coral just described we have a single corallite, produced by one 

 polype, and this simple condition may be maintained throughout 



Fig. 49. — The skeleton of CarynphyVia horrnll^, a simple sclerodermic coral, twice 

 the natural size. (After Sir C. Wyville Thoinsrm.) 



life. In the great majority of cases, hov. ever, the polj'pes bud or 

 divide, so as to form a colony all bound together by a common flesh 

 or coenosarc. When such a colony (fig. 50), therefore, produces a 

 sclerodermic coral, in place of a single corallite, we have a composite 

 skeleton composed of a numljer of little cups or corallites, each of 

 which was produced by one polype, and all of which are united by 

 means of a common calcareous basis, secreted by the ccenosarc. In 

 other cases, the colony is produced simply by the budding forth of 

 new polypes from the sides of the old ones, or by cleavage of the 

 original poly]ies; so that there is no true cienosarc. In these cases, 

 the compound skeleton is composed simply of the separate corallites 



