526 Mollusca. 
Persian Gnlf and at Ceylon, where they form an impor- 
tant article of commerce. 
The Chinese form pearls by casting into the shell of a 
certain kind of muscle artificial beads, which at the end 
of a year become covered with a pearly crust, in such a 
manner that they cannot be distinguished from the 
natural pearl.* 
THE COMMON OYSTER, (Ostrea edulis,) 
Has long been in favour with man for its delicacy as an 
article of food ; the Lucrine lake used to be as much in 
renown among the Romans for the choicest kind of 
Oysters, as Cancalle Bay with the French, and the Col- 
chester beds with us. The two shells of the Oyster are 
generally unequal in size; the hinge is without teeth, 
but furnished with a somewhat oval cavity, and gene- 
rally with lateral transverse grooves. Oysters sometimes 
grow to a very large size ; in the East Indies they are 
said sometimes to measure nearly two feet in diameter. 
The principal breeding season of oysters is in the 
months of April and May, when they cast their young, 
which are enveloped in slime, and in this state called 
spats by the fishermen, upon rocks, stones, shells, or any 
other hard substance that happens to be near the place 
where they lie; and to these the spats immediately 
adhere. Till they obtain their film or crust, they are 
somewhat like the end of a candle, but of a greenish 
hue. The substances to which they adhere, of whatever 
* For a very interesting article on this subject, see Bockmann's 
" History of Inventions." vol. i. p. 259. (JBohn's Standard Library. | 
