POLYPES. 223 



and very small quantities of silica, fluoride of cal- 

 cium, fluoride of magnesium, phosphate of lime^ 

 alumina, and oxide of iron. The red colour I 

 believe to be entirely organic, though nothing is 

 yet known concerning it ; and though coral is gene- 

 rally of a fine red colour, it is sometimes found of a 

 rose tint, or even quite yellow. There is also a black 

 variety, which is very rare. Its gelatinous tunic 

 also varies in colour. 



The calcareous stem of these animals is formed 

 like the shell of the oyster and other mollusca, 

 i.e., by the secretion of a liquid containing a large 

 amount of lime, and which appears to be produced 

 by certain glands situated at the basis of the 

 polype* s tentacles. 



In the Red Sea and the Mediterranean, coral is 

 seen adhering to the rocks in all directions. The 

 greatest height that a stem of coral, with its 

 branches, will attain in the Mediterranean is about 

 a foot and a half, its greatest diameter being about 

 eight lines. 



At each extremity of the coast of Algiers very 

 fine coral is found. The annual production by coral 

 fisheries in these parts is estimated at about 

 100,000 sterling. But the French are complain- 

 ing, at the present moment, of the negligent 

 manner in which their Mediterranean coral pro- 

 duction is carried on. It should yield, according to 



