CCELENTERATA I ALCYONARTA. 137 



hat resemblance to the convolutions of the br 

 4 >pular name of Brain-stone Coral has hp^n rW,' 

 to indicate. 53 



v-r t 



to suggest that resemblance to the convolutions of the brain 

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



CHAPTER XIV. 



ALCYONARIA. 



ORDER II. ALCYONARIA. The second great division of living 

 Actinozoa is that of the Alcyonaria, defined by the possession 

 of polypes with eight pinnately -fringed tentacles, the mesenteries 

 and somatic chambers being also some multiple of four. The 

 corallum, when present, is usually sclerobasic, or spicular; if 

 " thecce " are prese?it, 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 of four, instead si five or six, as in the latter, whilst 

 the septa are not in pairs. 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 thecae 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 tubular polypes being connected 

 together by a common ccenosarc, " through which permeate 

 prolongations 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 

 particular from those of the Zoantharia ; the numerical dis- 

 tinction being the one by which they are chiefly separated from 

 one another. The Alcyonaria are divided into four families 

 viz., the Alcyonidce, the Tubiporidce, the Pennatulidce, and the 

 Gorgonidce. 



FAMILY I. ALCYONID^:. This family is characterised by 

 the possession of a fixed actinosoma, which is provided with 

 a sclerodermic corallum in the form of calcareous spicula 

 embedded in the tissues. The spicules are mostly fusiform in 

 shape, and are generally present both in the polypes them- 

 selves and in the connecting ccenosarc ; but there is no central 

 solid axis. 



