IV 



PHYLUM CCRLENTERATA 



201 



tubes being united by horizontal calcareous platforms (pi.) formed 

 by deposits of spicules in the expansions of the same name already 

 referred to. The skeleton of Tubipora is, therefore, an internal 

 skeleton, and in the living state is covered by ectoderm. In the 

 Red Coral of commerce (Corallium, Fig. 146) the originally separate 

 spicules are embedded in a cement-like deposit of carbonate of 

 lime, the result being the production of an extremely hard and 



FIG. 155. Gorgonia verrucosa. A, entire colony; B, portion of the same magnified. 



(After Koch and Cuvier.) 



dense branched rod, which extends as an axis through the ccenosarc. 

 In the Blue Coral (Heliopom), on the other hand, the stony 

 calcareous skeleton is not made up of fused spicules, but is solid 

 from the first. 



Another type of skeleton is found in the Antipatharia (Fig. 151) 

 and in the Gorgonacea (Fig. 155). It also consists of an axial rod, 

 extending all through the colony and branching with it, but is 



