COEALS FOEJI AND ACHIEVEMENTS. 145 



Coral Islands, and occur most numerously within the 

 tropics. They are, however, found in most of the warmer 

 seas, either north or south of the equator, and are very 

 plentiful in the Red Sea. 



How these tubes and their supporting laminae are pro- 

 duced no one as yet knows. It seems that there must be 

 vessels or secreting sacs, but none have as yet been found. 

 How the creature is able to protrude and retract itself, 

 spread or fold its tentacles, is another mystery. There 

 are no perceptible muscular fibres, still less any nerves, 

 by which the will of the animal for it evidently has a 

 will can be conveyed to them. We do know that the 

 membrane is capable of contraction and relaxation, but 

 there our knowledge ceases. 



The last of these wonderful beings that can be men- 

 tioned is the Sea Pen. 



These remarkable compound animals are not attached 

 to any object which could support them, but seem to lie 

 loosely at the mercy of the waves. They are all more or 

 less phosphorescent, and at night have a peculiarly 

 striking appearance, owing to their graceful and boldly 

 curved outlines. The Sea Pens are to be found in nearly 

 all the warmer seas, and are common in the Mediter- 

 ranean. 



