THE BEANCHING-SYSTEMS OF THE ALCYONACEA. 



523 



the XenlidcB the anthocodife are not retractile, but in the Alcyonidce the anthocodia is 

 introversible within the distal part of the anthostele. It shoukl be borne in mind that 

 "retractility " in Alcyonarians properly means the introversion of the anthocodia within 

 the anthostele. The latter is often strengthened at its distal end with spicules arranged 

 en chevron to form a crown of eight points, usually called the calyx or verruca. It will 

 be better to call it the anthocrypt. The anthocrypts are rudimentary in the Alcyomd(B, 

 but are well developed in other orders of the Alcyonaria, e. g. the Gorgonidce. As will 

 be more particu.larly described in the latter part of this paper, some Alcyonarian zooids 

 whicli have been described as " retractile " or " j)artially retractile " by various authors 

 are not introversible, but simply have the power of folding over or withdrawing the 

 tentacles into the oral disc. In such cases the bases of the tentacles are usually protected 

 by a special development of spicules, which may either be disposed en chevron (as in. 

 Siphoiiogorgia among the Alcyonacea), or developed into large shield-like plates as in 

 Prlmnoa. Such spicular defences are sometimes called calices, sometimes opercula ; it 

 may be useful to give them a special name, anthopoma, from xw«a, a lid. 



Fig. 2. 



Diagram of an Alcyonid colony in wliieh five chief members are represented as branching in one plane. — The 

 branching-system of each chief member may be described as a corymb ; but in the diagram, which is 

 much simplified, the anthocodi;B of the two outside members do not lie in the same plane. They may be 

 said, however, to bo corymbs, if the surface of the syudete is regarded as the plane to which all the 

 branches attain. 1,1. Anthocodia! of the chief zooids. 



The family Alct/onidce differs from the Xeniidce chiefly in the following respects : — The 

 anthosteles of the zooids are very intimately united by fusion of their mesogloeal walls ; 

 only a few of them reach to the base of the colony, the xuajority ending at various 

 depths in the thickness of the syndete in solenia which put them into communication 

 with adjacent anthosteles. Returning to the analogy of a bunch of flowers, we may 

 compare the Alcyonid anthodete to a bunch of corymbs, in wliich not only the main 

 axes, but also the proximal parts of the secondary, tertiary, and other axes, are fvised 

 together ; scarcely more than the flowers with very short lengths of peduncle remaining 

 free. If we imagine, as before, that all the axes are hollow and communicate one with 



72* 



