STRUCTURE OF CORALS. 119 



Figs. 6 & 7. — Diagrams of the arrangement of the septa in Zoantharia 

 sclerodermata and Rugosa. Transverse section of a simple 

 sclerodermic coral (Turbinolia), showing the theca, with its pro- 

 jecting ridges, or " costee," outside, the visceral chamber and 

 radiating septa inside, and the columella in the centre. Trans- 

 verse section of a simple Rugose coral (Cyathophyllum), showing 

 the wall, costae, and septa. 



Fig. 8. — Portion of four corallites of Favorites Gothlandica, enlarged, 

 showing the tabulae. 



Fig. 9. — Portion of a Sclerodermic coral; branch of Dendrophyllia 

 nigrescens, a compound sclerodermic coral (after Dana). 



Fig. 10. — Longitudinal section of Isis liippuris, a sclerobasic coral, exhibit- 

 ing the external bark or ccenosarc, with its embedded polypes, 

 supported by the internal axis or skeleton (after Jones). 



These figures are all taken, by permission, from Nicholson's " Manual of 

 Zoology " (5th Edition). 



