208 THE WORLD OF THE SEA. 
—they reckon 600 to every square yard; the greater part of 
these are of a marketable size. The farms, at this calculation, 
bear at least 378,000,000 of the mollusks. 
The ocean is not the only scene of the useful experiments of 
M. Coste. Nearly 500,000 oysters were transported to the roads 
of Toulon and to the Lake Thau. A piece of clay pipe taken up 
from the former place in eight months, was found to be covered 
with numerous shells. This cultivation of the fruits of the sea is 
a most profitable undertaking, and ought to be encouraged by 
every government. 
Following the example of the Romans, oysters are placed in 
reservoirs where they grow larger, and assume a green tint. Is 
this why such oyster plantations are termed parks ? 
At Marennes these reservoirs are called claires. They are 
inundated fields, which stretch on each side the banks of the 
Seudre for many miles. The claires of Marennes differ. from the 
oyster parks of other localities in this—that while the parks are 
submerged by the rising waters of every tide, the claires are only 
covered at spring-tide. 
An oyster six or eight months old requires two years before 
it reaches the point of perfection; but it is very seldom that the 
oysters eaten in Paris undergo these conditions; generally the 
adult oyster is placed in the claires, and in a few days it begins 
to have the characteristic green tint. The green colour is not 
general, but is particularly shown in the region of the branchiae, 
upon the labial feelers, and in the intestinal canal. What this 
colour is has long been a subject of conjecture. It certainly differs 
from all other colouring matters; and Berthelot has shown, by a 
chemical analysis, that it has some peculiarities. Some naturalists 
believe that it is produced by a disease of the liver, caused by the 
unnatural position of the oyster; certainly this would give a green 
hue to the parenchyma. Another opinion is, that the colour is 
from an accumulation of animalcule, which are lodged in the 
tinted parts. Priestley suggests that it is the peculiar green colour 
which is generally produced in water exposed for long to the 
action of light; but the most probable solution of the difficulty 
appears to be that it is in some way due to the soil of the claires, 
