ACTINOZOA. 



93 



outdde the polypes, and bears to tlie creuosarc tlie 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 tliese sclerobasie corals 

 in which tlie coralium consists of a branched horny stem. The 

 •polypes of all the Gorgonidw agree, of course, with their order in 

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

 the few Zoantkaria in which there is a sclerobasie coral. The tissues 

 of the cffintjsarc and polypes are usually charged witli microscopic 

 spicules. 



The best known of the Oorgonid(c is the CoraUium rahrmn, or 

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

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



Fly, 56. — A, Portion ot a eoiiipouiid sclerndennic Coi-al (DendropUylUaX sbowii]g the 

 ciip.'^(a a) produced by the separate polypes, united by a coniuion calcareous tissue. 

 B, Portion of a branched sclerobasie Coral (Gorgonia), showini^ the hard horny 

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

 the figure), in which the little polypes aie enibediled. 



grooved, calcareous sclerobasis, \isually more or less repeatedly 

 branched. The coraUum is invested by a bright red crenosarc or 

 bark, which is studded with numerous little apertures. The polyi:ies 

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

 colour, with eight fringed tentacles each. The entiie ooenosarc is 

 excavated into a number of communicating caiials, with which the 

 cavities of the polypes are connected, the whole system l^eing filled 

 with a nutritive fluid known as the "milk." 



Another group of the Alci/onan'a lias recently been constituted 

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

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

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



