154 ACTINOZOA. 



Actinozoa, Most frequently its texture is simply- 

 corneous, but in Coralliiiin proper and a few 

 other forms, it becomes calcareous by deposition ; 

 and in Hyalonema and Hyalopcdhes, if these be 

 true Actinozoaf it is siliceous. In Isis and 

 Mopsea it consists of alternately disposed calca- 

 reous and horny segments, thus, as it were, com- 

 bining strength with a yielding pliancy. In Isis 

 branches are developed from the calcareous, in 

 Mopsea from the horny segments of the sclero- 

 basis. Melitcea presents a like structure, save 

 that, in it, the corneous segments are replaced by 

 others which assume a porous and suberous as- 

 pect. 



Section of a sclerobasis shows it to be, in some 

 cases, solid or nearly so; in others, distinctly 

 resolvable into concentric layers, which serve, 

 also, to illustrate the manner in which it has been 

 produced; while, more rarely, it is composed of an 

 aggregation of separate fibres. 



Two principal modifications of form distinguish 

 the sclerobasis. In some Adinozoa it constitutes 

 a free axis, virgate or pinnately divided, and 

 varying much in composition and thickness. In 

 others it is attached, simple or branched, and 

 often singularly plant-like in physiognomy, as in 

 those Gorgonidce to which the name of Sea-shrubs 

 has been applied. 



The relations of such structures to the soft 

 parts of the animal are, with little difficulty, 

 discerned. The sclerobasic corallum is, in fact, 

 outside the bases of the polypes and their con- 

 necting coenosarc, which, at the same time, receive 

 support from the hard axis which they serve to 

 conceal. Thus the ccenosarc of these corals ap- 



