388 The Commercial Products of the Sea. 



ing coral, to which to attach itself, free from sand or drift, 

 and a considerable influx and outflow of the sea at the 

 rise and fall of the tide. That they are not absolutely 

 confined to lagoons, but exist also in great quantity under 

 the tremendous breakers which beat upon the outer reefs 

 (as also, probably, at greater depths in the sea beyond 

 them), is a fact not generally known, but is nevertheless 

 true. As a proof of this, there are to be found, chiefly on 

 the windward side of all coral reefs enclosing lagoons 

 (and especially at certain seasons of the year), incredible 

 numbers of microscopic pearl oysters, and others of larger 

 size, up to the diameter of a shilling, tossed about in the 

 foam of the breakers, and travelling with the flood tide over 

 the reef towards the calm waters of the lagoon. These 

 have been spawned in the deep sea, or in the coral caves 

 under the foaming surf, which thunders on the outer reef, 

 and seek by some instinct of their nature to make their 

 own way into the placid waters enclosed within that stony 

 barrier. The oysters which are spawned within the lagoon 

 are formed in congeries attached to the parent shells, or 

 clustered in vast numbers, fastened to one another, in the 

 holes of the rocks. The shell comes to maturity in about 

 seven years, at which time its average weight is one 

 pound, exclusive of the fish contained in it. The usual size 

 is about that of a soup-plate, or 10 inches in diameter, 

 although in rare instances they arrive at as much as 18. 

 After this the creature perishes, detaches itself from the 

 rock, opens to close no more, the animal decays, and the 

 shell, becoming coated with coral and other stony parasites 

 within and without, loses all value. 



The pearl oyster is gregarious. Wheresoever one is met 

 with, there are of a surety vast -numbers somewhere irr the 

 immediate vicinity. They are found in coral caverns, hang- 



