IXVEUTEBEATE AXI^[ALS. 



belonging to the individual zooida, without any common calcareous 

 basis secreted by a ccenosarc. 



As before said, the " septa " are vertical partitions, which divide 



Fig. 5?. — A compound Coral (Astr(sa pallida) in its living state. (After Dana.) 



the space contained within the walls (the so-called " theca ") of the 

 coral into a series of compartments. The septa spring from the 

 inner surface of the " theca " (fig. 51), and advance towards its 



Fig. 51. — A, Transverse section of a simple sclerodermic coral, showing how the 

 space included within the wall or "theca" is subdivided by the radiating septa, 

 the centre being occupied by the coluTnella ; B, Transverse section of a simple 

 Rugose coral, showing the wall and the radiating septa. 



centre. Often the septa unite centrally with a calcareous pillar or 

 rod, the " columella " ; and they are of different breadths. A certain 

 number of them extend quite to the centre of the coral, where they 



