ENDOSKELETON. ANIMALS. 7 



coral at the base of the zooids simulates the columella of 

 the Anthozoan. PI. I. fig. 1. 



Moseley, Phil. Trans., vol. clxix. 1879, p. 449. 



ANTHOZOA. 



Chemical Composition. 



The coral is in most cases composed of calcium carbonate 

 associated with a varying amount of organic matter; minute 

 traces of other salts are present. In some Gorgonacea (e. g. 

 Gorgonia flabellum, G. setosd) calcium phosphate is the chief 

 inorganic constituent of the axis, although none is found in the 

 crust. 



A. 15. Horny axis of Antiputhes politum. It has been ma- 

 cerated in acid : this has caused a partial separation of its 

 constituent lamellae. 0. C. 85 G. 



A. 16. Small portion of Organ-pipe Coral (TuUpora musica). 

 It has been treated with dilute nitric acid which has removed 

 all colour, and the calcium carbonate that alone renders the 

 coral stiff and hard. The polyps may be seen at the mouths 

 of the tubes. 0. C. 84. Hunterian. 



A. 17. A similar specimen in which the tubes are somewhat 

 larger and the polyps absent. 0. C. 85. Hunteiian. 



A. 18. The axis of a main stem of a Coral (Melitodes ochracea). 

 The lower portion has had its surface acted upon by dilute 

 hydrochloric acid. This has partly removed the calcium 

 carbonate, leaving the organic matter. In the " nodes " 

 the organic matter is more abundant : they accordingly 

 project above the level of the more eroded internodes, 

 which are of a bright red colour. Besides the calcium 

 carbonate there is a small trace of calcium phosphate. 

 0. C. 85 A. 



A. 19. Smaller branches of the same Coral (Melitodes ochracea) 

 similarly treated. O.C. 85 B. 



