122 MANUAL OF ZOOLOGY. 



and more slender than in the preceding, and the polype-bear- 

 ing fringes are short. The polypes have eight tentacles. The 

 sclerobasis is in the form of a long calcareous rod, like a knit- 

 ting-needle, and part of it is usually naked. No spicula are 

 found in the tissues of Virgularia. 



FAMILY IV. GORGONID/E. In the Gorgonidce, or " Sea- 

 shrubs/' there is an arborescent coenosarc permanently rooted 

 and provided with a grooved, or sulcate, branched sclerobasis, 

 which is sometimes associated with true tissue - secretions, 

 termed "dermo-sclerites." 



The sclerobasis of the Gorgonida varies a good deal in its 

 composition. In some it is corneous, and these have often 

 been confounded with the Antipathida, amongst the Zoantharia. 

 The distinction, however, between them is easy, when it is 

 remembered that the polypes in the Gorgonida have tentacles 

 in multiples of four, whilst in the Antipathidce they are in sixes. 

 The sclerobasis, too, in the former is always marked by grooves, 

 whereas in the latter it is always either smooth or spinulous. 

 In Isis (fig. 31, &) and Mopsea the sclerobasis consists of alter- 

 nate calcareous and horny segments, branches being developed 

 in the former from the calcareous, and in the latter from the 

 horny segments. 



In Cordllium rubrum, the "red coral" of commerce, the 

 sclerobasis is unarticulate, or unjointed, and is entirely cal- 

 careous. It is the most familiar member of the family, and is 

 largely imported for ornamental purposes. Red coral consists 

 of a branched densely calcareous sclerobasis, which is finely 

 grooved upon its surface, and is of a bright red colour. The 

 corallum is invested by a coenosarc, also of a red colour, 

 which is studded by the apertures for the polypes, which are 

 white, and possess eight pinnately- fringed tentacles. The 

 entire ccenosarc is channelled out by a number of anastomosing 

 canals, which communicate with the somatic cavities of the 

 polypes, and are said to be in direct communication with the 

 external medium by means of numerous perforations in their 

 walls. The entire canal system is filled with a nutrient fluid, 

 containing corpuscles, and known as the " milk." 



