CCELENTERATA : ALCYONARIA. 125 



Both these forms of corallum " are liable to become massive by 

 the union of several rows or tufts of corallites throughout the 

 whole or a portion of their height. An illustration of this is 

 afforded by the large gyrate corallum of Meandrina, over the 

 surface of whose spheroidal mass the calicine region of the 

 combined corallites winds in so complex a manner as at once 

 to suggest that resemblance to the convolutions of the brain 

 which its popular name of Brain-stone Coral has been devised 

 to indicate." 



CHAPTER XIV. 

 ALCYONARIA. 



Order II. Alcyonaria. — -The second great division of living 

 Actinozoa is that of the Alcyonaria, defined by the possession 

 oi polypes with eight pinnately-fringed tentacles, the mesenteries 

 and somatic chambers being also some multiple of four. The co- 

 rallum, when present, is usually sclerobasic, or spicular; if "theccs" 

 are present, as is rarely the case, there are no septa. 



The Alcyonaria or "Asteroid Polypes" differ numerically 

 from the Zoantharia in having their soft parts arranged in 

 multiples oifour, instead oifive or six, as in the latter. Their 

 tentacles, too, are pinnate, and are not simply rounded. 

 Numerically the Alcyonaria agree with the extinct order 

 Rugosa, but the latter invariably possess a well-developed 

 sclerodermic corallum, the thecas of which exhibit either septa 

 or tabulae, or both combined. 



With the exception of the single genus, Haimeia, the Alcyon- 

 aria are all composite, their polypes being connected together 

 by a common ccenosarc, " through which permeate prolonga- 

 tions of the somatic cavity of each, forming a sort of canal 

 system, whose several parts freely communicate," and permit 

 of a free circulation of nutrient fluids. As a rule, the entire 

 colony forms a lobate or branched mass. Anatomically the 

 polypes of the Alcyonaria do not differ in any essential par- 

 ticular from those of the Zoantharia ; the numerical distinc- 

 tion being the one by which they are chiefly separated from 

 one another. The Alcyonaria are divided into four families, 

 viz.; the AlcyonidcB, the Tubiporida, the Pennatulidce, and the 

 GorgonidcB. 



Family I. ALCYONiDiE. — This family is characterised by the 

 possession of a fixed actinosoma, which is provided with a 



