70 



ZOOLOGY 



and outside the base of the animal. Some of the septa may- 

 coalesce in the centre of the body, and thus the columella is 



Fig. 48. — Caryopliyllia borealis, Fleming, a simple coral, twice the natural size. 

 After Sir WyTille Thomson. 



produced ; this is usually continued as a little, pillar pointing 

 towards the mouth. The outer wall of the theca frequently 



FiQ. 49. — Astraea pallida, Dana, a compound coral in its living condition. 

 After Dana. 



bears ridges, the costae, which do not necessarily correspond 

 with the septa ; the latter may be connected with their neigh- 

 bours by horizontal shelves, termed dissepiments. 



