CCELENTERATA 



171 



SUBCLASS I. ACTINOZOA (Sea-anemones and Corals). 



In these the animal is usually fixed. It never swims 

 freely except in the embryonic stages. The body is more 

 or less columnar, with a base for attachment and an oral 

 disc inside the circle of tentacles, in the centre of which 

 is the oval or slit-like mouth. Inside, the septa are well 

 developed, and attached to these are, besides the mesen- 

 terial filaments, long cords of nettle-cells which can be 

 protruded through the mouth or through small openings 



FIG. 18. Diagram of a bit of coral to show 

 the way in which the polyps are con- 

 nected. The coral is black, the digestive 

 cavity shaded. In nature the digestive 

 cavity is divided into small canals con- 

 necting the different polyps. 



FIG. 19. Section of a 

 coral cup showing 

 the calcareous septa. 

 After Pourtales. 



in the walls of the body. In some the individuals 

 (polyps) are separate; in others the individuals repro- 

 duce by division or by budding, and the new polyps thus 

 formed never completely separate from their parents, so 

 that large aggregations or colonies result. In these one 

 ran distinguish the mouths, and usually the tentacles, of 



