ANTHOZOA. ALCYONARIA 



95 



musica, fig. 38) the skeleton consists of numerous parallel 

 tubes or corallites (a) which are not in contact but are 

 held together by horizontal calcareous plates or ' plat- 

 forms ' (b). The walls of the corallites, although apparently 

 quite compact, are really composed of spicules which have 

 serrated edges and are firmly fitted together. A single 



Fig. 37. Transverse section through a polyp of Alcyonium digitatum in 

 the region of the stomodaeum. x about 120. 1, cavity of stomodasum ; 

 2, ventral groove with cilia (siphonoglyph) ; 3, ectoderm ; 4, gelatin- 

 ous layer; 5, endoderm; 6, muscles of mesenteries; 7, cavity between 

 mesenteries. (After Hickson.) 



polyp lives at the summit of each corallite ; spicules occur 

 in the middle gelatinous layer of the polyp, and in the 

 lower part become interlocked to form the solid wall of the 

 corallite. The interior of each corallite is divided up by 

 tabulae which are often funnel-shaped (fig. 38 c). 



