CCELENTERATA. iSS 



The majority of the Actinozoa secrete a hard sup- 

 porfcing structure known as " coral." Its importance 

 as the material of " coral reefs " is well known ; nor 

 has it been less in past ages of the world, for corals 

 are often abundant in. geological formations, and even 

 extensive reefs are not unknown. The gastric cavities 

 of the polyps often remain connected with one another, 

 so that the coral is channelled all through, the new 

 polyps not being closed off in budding. 



The two chief divisions of the Actinozoa are the 



■pig. 33. — The Snowy Anemone, Sagartia itivaa (from Claus and Sedgwick, 

 after Gosae), sliowing tentacles and mouth. 



Alcyonaria and Zoantharia (Madrepores), formerly 

 called Octocoralla and Hexacorulla. The commonest 

 English representative of the former is the Alcyonium, 

 popularly called Dead-man^s Fingers; the Sea-pen 

 {Pennatula) is sometimes found on our coasts; it is 

 so called from its shape^ which is something like that 

 of a quill feather, owing to the polyps being arranged 

 on the stock in a definite bilateral manner. The 

 Qorgonia, or sea-fan, the red coral of the Mediter- 

 ranean, and the organ coral, or Tuhipora, are among 

 the chief foreign representatives of the order. 



