92 



INVERTEBRATE ANIMALS. 



consists of alternate horny and calcareous joints. The pol- 

 ypes of all the GorgonidoB agree, of course, with their order 

 in having eight tentacles each, and by this they are distin- 

 guished from the few Zoantharia in which there is a sclero- 

 basic coral. 



FIG. 29. Sclerodermic and Sclerobasic Corals, a Portion of branch of Dendrophyllia 

 nigrescens, a sclerodermic coral (after Dana) ; b Longitudinal section of Isis Mppuris, 

 a sclerobasic coral, exhibiting the external bark or coenosarc, with its imbedded polypes, 

 supported by the internal axis or skeleton (after Jones). 



The best known of the Gorgonidce is the Corallium rubrum, 

 or " red coral " of commerce, which is largely imported from 

 the Mediterranean. In this species there is a bright-red, 

 finely-grooved, calcareous coral, usually more or less repeatedly 

 branched. The coral is invested by a bright-red coenosarc or 

 bark, which is studded with numerous little apertures. The 

 polypes can be protruded from these openings at will, and are 

 milk-white in color, with eight fringed tentacles each. The 

 entire ccenosarc 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." 



ORDER III. HUGOS A (Lat. rugosus, wrinkled). This order 

 merely requires mention, as all its members are extinct, and 

 are therefore only known to us by their hard parts or skele- 



