THE ANTHOZOA 



35 



ORDER 6. Coenothecalia. 



Characters Synalcyonacea with a calcareous skeleton composed of 

 lamellae of calcite forming a dense corallum resembling that of the 





FIG. XVIII. 



1. Surface view of a portion of a fully grown colony of Helinpora coerulea, Pall., showing 

 two calices with their pseudosepta ; the openings of the coenenchymal tubules, the superficial 

 echinulations, and the shallow canals between them in which the superficial network of soleniu 

 lies in the living condition. 



'2. A single zooid with the adjacent soft tissues of Heliopora coerulea, as seen after removal 

 of the skeleton by decalcifi cation ; semiaiagrammatic. Z 1 , the distal retractile moiety of the 

 zoo;d, bearing fight pinnate tentacles ; Z-, the proximal calicular moiety of the same ; ec, the 

 continuous sheet of ectoderm which clothes the surface of the colony ; sp, the superficial 

 network of solenia lying directly beneath the ectoderm ; ct, coenenchymal tubules. 



3. Diagram illustrating the mode of growth and architecture of a colony of Hdiopora. 7A, 

 calyx of mother zooid ; Z'\ //', etc., calices of daughter zooids successively formed amongst the 

 coenenchymal tubules ; tt, tabulae. 



4. Surface view of a tangential section through the surface of a colony of Helwlites porosns, 

 Goldfuss, showing three calices, each with twelve pseudosepta imbedded in a coenenchyme con- 

 sisting of numerous vertical coenenchymal tubules (solenia) of approximately hexagonal shape. 



5. Diagram illustrating the essential structure of the corallum in Heliopont and HcHnlltet. 

 Ct, coenenchymal tubules, the walls of each of which are composed of twelve separate laminae, 

 which take a share in the composition of the walls of six adjacent tubules. In the centre of the 

 figure a calicular cavity is indicated formed by the arrest, complete or partial, of a group of 

 nineteen coriiem-hyinal tubules numbered i-xix. The outlines of the arrested tubules are. 

 indicated by dotted lines. 



imperforate Madreporaria, and developed from a specialised layer of ecto- 

 derm cells (calicoblasts). The corallum exhibits a number of larger 

 calices, provided with a variable number of radial pseudosepta, sunk in a 

 coenenchyme composed of numerous closely set vertical tubules, with 

 calcareous walls, which are disposed vertically to the surface of the 



