THE ACTjNOZOA. 145 



calcification of the axial connective tissue of the zoantho- 

 deme, occurs. It is an unattached simple rod in Pennatula 

 and Veretillum, but fixed, tree-like, branched, and even retic- 

 ulated, in the Gorgonice and the red coral of commerce ( Co- 

 r allium). In the Alcgonia, or " Dead-men's-fingers," of our 

 own shores, there is no sclerobase, nor is there any in Tubi- 

 pora, the organ-coral. But, whereas in all the other Octoco- 

 ralla the bodies of the polyps and the ccenosarc are beset with 

 loose spicula of carbonate of lime, Tubipora is provided with 

 solid tubiform thecae, in which, however, there are no septa. 



Dimorphism has been observed by Kolliker to occur exten- 

 sively among the Pennatulidce. Each zoanthodeme presents 

 at least two different sets of zooids, some being fully devel- 

 oped, and provided with sexual organs, while the others have 

 neither tentacles nor generative organs, and exhibit some 

 other peculiarities. 1 These abortive zooids are either scat- 

 tered irregularly among the others (e. g., Sarcophyton, Vere- 

 tillum), or may occupy a definite position (e. g., Virgularia). 



In the other chief division of the Coralligena — the Hexa- 

 coralla — the fundamental number of enteroccele chambers and 

 of tentacles is six, 2 and the tentacles are, as a rule, rounded 

 and conical, or filiform. 



The Actinozoon developed from the egg in some of the 

 Hexacoralla remains simple, and attains a considerable size. 

 Of these — the Actinidm — many are to some extent locomo- 

 tive, and some (Mim/as) float freely by the help of their 

 contractile pedal region. The most remarkable form of this 

 group is the genus Cereanthus, which has two circlets, each 

 composed of numerous tentacles, one immediately around the 

 oral aperture, the other at the margin of the disk. The foot 

 is elongated, subcorneal, and generally presents a pore at its 

 apex. Of the diametral folds of the oral aperture, one pair is 

 much longer than the other, and is produced as far as the 

 pedal pore. The larva is curiously like a young hydrozoon 

 with four tentacles, and, at one time, possesses four mesen- 

 teries. 



The Zoanthidce differ from the Actinidce in little more 

 than their multiplication by buds, which remain adherent, 

 either by a common connecting expansion or by stolons ; and 

 in the possession of a rudimentary, spicular skeleton. In the 

 Antipatliidw there is a sclerobasic skeleton. The proper 



1 " Abhandlungen der Senkenbergischen naturforschenden Gesellschaft," 

 Bd. vii., viii. 



2 That is to say, in the adult, they are either six or some multiple of six. 



7 



