THE ANTHOZOA 



n 



each stolon contains, not one, but several solenia, which branch 

 and anastomose with one another. In many Clavulariae the stolons 

 are flattened and band -like, and anastomose freely with one 

 another so as to form a close meshwork ; and this process of fusion 

 and anastomosis being carried still further, the stolons form a close 

 feltwork, which, like a membrane, adheres to the surface of 

 attachment. In all these forms the stolons and the solenia which 

 they contain are, with one exception, given off from the basal 

 region only of the zooid, and the zooids appear to, and do in fact, 

 stand upon the meshwork or feltwork of stolonic tubes. 



A further differentiation is established when, as in Sarcodictyon, 

 the solenia are not confined to the base, but are also given off from 

 the lateral walls of the proximal extremity of the zooid. In such 

 a case, fusion of the walls of adjacent solenia gives rise to a 

 cushion-like thickening at the base of each zooid. 



In Sympodium the zooids are frequently crowded together to 

 form dense tufts, and in such tufts (Pseudobushes of von Koch) 

 the cushion-like thickenings surrounding the bases of the zooids 

 become fused together so as to form a crust, in which numerous 

 solenia ramify. The proximal portions of the cavities of the 

 individual zooids extend through the thickness of the crust. 



By further differentiation along the same lines, the colonial 

 forms characteristic of the Xeniidae and Alcyonidae are arrived at. 

 In the Xeniidae the zooids are crowded together to foi-m bundles ; 

 the surface of attachment is relatively small, and the fused proximal 

 portions of the zooids assume the character 

 of a stout stem, from the flat summit of 

 which the distal portions of the zooids 

 project. 



In the Xeniidae the zooids are not 

 very intimately fused together in each 

 bundle. Each zooid and each solenium is 

 typically limited by three layers — endo- 

 derm, mesogloea, and ectodei'm — passing 

 from within outwards. In Xenia the zooid 

 bundles are formed chiefly by fusion of 

 the ectoderm of adjacent zooids and their 

 solenia, the mesogloeal lamina of each 

 remaining distinct. In Heteroxenia the 

 mesogloea takes a share in the fusion. In 

 the Alcyonidae the fusion of the meso- 

 gloeal layers is complete. The colonies 

 form lobose, generally bluntly branching 

 masses, from the whole surface of which 



the distal moieties of the zooids, when fully expanded, project. 

 The fused mesogloea forms a thick mass, honeycombed by the 



Fio. VII. 



Clavularia cdehcnsis, Hick.soii. 



