94 



ANTHOZOA. ALCYONARIA 



stomodgeum there is only one groove with cilia, and the 

 longitudinal muscles on the mesenteries are all directed 

 toward the groove (fig. 37, 6). All the mesenteries reach 

 the stomodseum (l). The nature of the skeleton varies 

 Considerably ; in A Icyonium it consists of isolated spicules 

 of carbonate of lime embedded in the common gelatinous 



iff #?#i — 4 



If lor 



Fig. 36. Part of a colony of Alcyonium digitatum, showing thirteen 

 polyps in various stages of retraction and expansion. (From Shipley 

 and MacBride.) 1, mouth; 2, stomodasum; 3, mesenteries; 4, ten- 

 tacles, x 8. 



base in which the polyps are placed. In some cases it has 

 the form of an axial rod surrounded by the soft parts ; this 

 rod may consist of horny material (e.g. Gorgonia) or of car- 

 bonate of lime (e.g. Corallium, the red coral), or it may be 

 formed of alternating segments of horny and of calcareous 

 material as in Isis. In the ' organ-pipe coral ' (Tubipora 



