ON ACEPHALA. re! 
stances. Accordingly, it is generally admitted, that the 
water of the sea in which they live, continually attracted and 
rejected by the mantle, brings at once both the matter of 
respiration and that of nutrition, 
The oysters having, like the other bivalve mollusca, only 
the female sex evident, they must be genuine hermaphrodites ; 
and, in fact, it appears quite certain that a single individual 
can reproduce and continue the species. The eggs are ex- 
pelled in the form of spawn, or white fluid, very similar 
to a drop of grease, in which may be perceived with the 
microscope, innumerable little oysters. This is called spats 
by our fishermen. This matter, in which they swim, doubt- 
less serves to agglutinate them to the submarine bodies, or to 
individuals of their own species ; then the new ones, in being 
developed, smother, as it were, the old ones, not permitting 
the water to reach them, or hindering them from opening 
their shel]. It is thus are formed those immense banks of 
oysters which are found upon our coasts, and which, in spite 
of the constant destruction wrought amongst them for cen- 
turies, never appear to be exhausted. The species which are 
not fixed, or are not so in a flat position, not being circum- 
stanced so favourably for the adherence of the spawn, appear, 
in general, to be less multiplied. 
We are entirely ignorant of the manner of growth in the 
oysters, and of the duration of their life. It would seem, 
however, that as the growth is rather slow, if an individual 
be placed in favourable circumstances, that is, without risk 
of being smothered by its progeny, it would live a very long 
time. But we have no certain data to go on here. However, 
if we give credit to what is asserted by the inhabitants of 
Marennes, on the coasts of the Atlantic, oysters do not live 
more than ten years. In three days after the deposition of 
the spawn, the shell of the little oyster is already three lines 
in breadth ; in three months, or six, it is nearly the size of a 
Bb2 
