fd... OYSTER CULTURE. 767 
and of the same nature as the secretions which form the nacreous lining 
of the valves, but which in consequence of peculiar conditions, either a 
sickness of the animal or the presence of some strange body, assume a 
spherical or pyriform shape. It is certain that the presence of a foreign 
body, by irritating the mantle, produces an abnormal secretion of the 
nacreous material which soon entirely covers that body with a material 
identical in character with that forming the pearls. 
For a long time the Chinese have made use of this peculiarity of the 
pearl-oyster and of certain other mollusks. Among the class of pearl- 
producing or nacre-producing animals must be placed our fresh-water 
mussel. In order to have any ornament covered with nacre. it should 
be placed within the shell of a pearl-oyster and left there for several 
months, after which time it will appear as though entirely composed of 
pearly material. The most valuable pearls come from Ceylon and the 
Persian Gulf. The pearl-oysters are found in banks, like the common 
oyster, at a depth of from 5 to 20 meters. The pearl-oyster bears a gen- 
eral resemblance to the edible oyster, except that it is much larger, at- 
taining sometimes a diameter of 30 centimeters (between 9 and 10 inches). 
They are taken in Asia at four principal places: around the island of 
Bahren in the Persian Gulf, on the coast of Arabia near Carisa, in the 
Gulf of Manaar in Ceylon, and upon the coast of Japan. The fishing 
commences in February and ends in April; it is performed by native 
divers furnished simply with a knife to detach the shellsand a basket to 
gather them in. The fishing of the banks is subject to a sort of police 
supervision on the part of those who lease the right to fish for pearls. 
Only a certain number are taken, and the banks are carefully inspected 
at every fishing ; the divers are always careful to spare the young ones, 
and take only those which look as if they ought to contain pearls, since 
all do not contain them. The valves of the pearl-oyster are also objects 
of commerce, as they furnish nacre. But they are not the only ones 
which furnish this product; upon our coasts a great number of mollusks 
are found, among others the Haliotus, which furnish a very valuable 
nacre, more beautiful even than that of the pearl-oyster. In seeking 
conditions of soil, depth, and temperature as nearly as possible like those 
surrounding the pearl-oyster in Asia, it would seem possible to acclimate 
this mollusk in the waters of our coast and of the African shores of the 
Mediterranean; waters which even now contain much unexplored wealth, 
particularly vast beds of coral, and which would seem to cover naturally 
fertile places for the abode of the pearl-oyster. 
MUSSELS. 
Under the generic name of mussel (Mytilus) are united bivalve mol- 
lusks having a symmetrical shell and equal valves, and with the mantle, 
is divided into two similar lobes, entirely separated along the ventral 
edges, both of which are smooth, much thickened and attached to the 
