ACTINOZOA. 



91 



processes, each of which bears numer- 

 ous polypes. Closely allied to Virgu- 

 laria is the " Cock's-comb " Pennatula 

 (Fig. 28) ; but in this the lower end 

 of the coenosarc is naked and fleshy, 

 and the polype -bearing fringes are 

 considerably longer, giving the whole 

 organism very much the appearance 

 of a feather. 



Another family of the Alcyonaria 

 is represented by the so-called " Or- 

 gan-pipe corals," of which Tubipora 

 musica is a well-known example. In 

 this there is a well-developed sclero- 

 dermic coral consisting of numerous 

 cylindrical tubes, which are not di- 

 vided by vertical partitions (septa), 

 but which are connected by strong 

 transverse plates. The coral is bright 

 red in color, and the polypes are usually 

 bright green. 



The best known, however, of the 

 Alcyonaria is the family Gorgonidw, 

 represented by the sea-shrubs, fan- rm^s.-Pennataiida!. The Cock's-' 

 corals, and the red coral of commerce. comb (PmnaiuZa phospM- 



Af {• j-t ^ c lA ' £ "1 rea\ (After Johnson.) 



few of the members of this family 



live in temperate waters, but they attain their maximum in 

 point of size and numbers in the seas of the tropics. In all 

 the Gorgonidm the organism consists of a composite structure 

 made up of numerous polypes united by a common flesh or 

 coenosarc (Fig. 39, b), the whole supported by a central 

 branched axis or coral. The coral varies in composition, be- 

 ing sometimes calcareous — as in red coral — sometimes horny, 

 and sometimes partly homy and partly calcareous, as in Isis 

 (Fig. 29). In all cases, however, the corallum differs alto- 

 gether from the sclerodermic corallum, which has been de- 

 scribed as so characteristic of the reef-building corals. The 

 coral in the present instance is always what is called " sclero- 

 basic " — that is to say, it always forms an internal axis, covered 

 by the ccenosarc with the polypes produced therefrom. It is, 

 therefore, outside the polypes, and bears to the coenosarc the 

 same relation that the trunk of a tree bears to its investing 

 bark. This is well shown in Fig. 29, b, where there is repre- 

 sented one of these sclerobasic corals in which the corallum 



