ACTINOZOA. 



93 



outMe the polypes, and bears to the coeuosarc the same relation that 

 the trunk of a tree bears to its investing bark. This is well shown 

 in fig. 56, B, where there is represented one of these sclerobasic corals 

 in which the corallum consists of a branched horny stem. The 

 polypes of all the Gorgonidce agree, of course, with their order in 

 having eight tentacles each, and by this they are distinguished from 

 the few Zoantharia in which there is a sclerobasic coral. The tissues 

 of the coenosarc and polypes are usually charged with microscopic 

 spicules. 



^^ The best known of the Gorgonidce is the Corallium rubrum, or 

 " Eed Coral " of commerce, which is largely imported from the Medi- 

 terranean. In this species (fig. 57) there is a bright red, finely 



J. 56. — A, Portion of a coiiipouud sclerodermic Coral (Dendrophyllia), showing the 

 cups (a a) produced by the separate polypes, united by a common calcareous tissue. 

 B, Portion of a branched sclerobasic Coi-al (Gorgonia), showing the hard homy 

 skeleton in the centre, surrounded by a fleshy bark or rind (mostly removed in 

 the figure), in which the little polypes are embedded. 



grooved, calcareous sclerobasis, usually more or less repeatedly 

 branched. The corallum is invested by a, bright red ccenosarc or 

 bark, which is studded with numerous little apertures. The polypes 

 can be protruded from these openings at will, and are milk-white in 

 colour, with eight fringed tentacles each. The entire coenosarc is 

 excavated into a number of communicating canals, with which the 

 cavities of the polypes are connected, the whole system being filled 

 with a nutritive fluid known as the " milk.'' 



Another group of the Alcyonaria has recently been constituted 

 under the name of Helioporidm for the singular stony corals belong- 

 ing to the genus ffeliopora, formerly believed to belong to the 

 Zoantharia. In this genus, the corallum is compound, and is formed 



