CLASS ACTINOZOA. 



17 



Fie. 25. 



CoralTium rU'brum. Red Coral. 



The hard central axis is seen projecting 



toward the left. 



ORDER ALCYONARIA (al SI O na'rl a). 



This order includes those Polyps which have the me- 

 senterial folds and tentacles 

 arranged on a plan of eight. 

 The growth is supported on a 

 horny or calcareous, often 

 branching axis, surrounding 

 which is a limy layer depos- 

 ited in plates, allowing consid- 

 erable flexibility. It is into 

 the minute pores of this outer 

 layer that the Polyps can contract.* The Red Coral, prized 



for jewelry, is the highly polished 

 central axis of an alcyonarian Polyp, 

 found growing, in small quantities, 

 in the Mediterranean Sea. The 

 Sea-fan is also a representative of 

 this or^ler. Its interlacing branches 

 are covered with a purple or a yel- 

 low calcareous layer which, on dry- 

 ing, may cleave off, exposing the 

 black horny axis. 



FIG. 26. 



GOT go' m a fla bel' lum. Fragment 

 of Sea-fan, showing the inter- 

 locking of the branches. S, The 

 central horny axis. 



FIG. 27. 



* An aberrant form classed 

 in this order is the Organ-pipe 

 Coral, which consists of cylin- 

 drical tubes arranged like the 

 pipes in a church organ. Each 

 one is the cell of a single polyp, 

 and the whole number in the 

 mass is the progeny of the one 

 that first became fixed at the 

 base. Cross-plates at intervals 

 preserve the unity of the mass. 

 The mouth is located between 

 the bases of the tentacles, 



Tutnp'ora fnus'ica Organ-pipe Coral. 



