370 SUPPLEMENT 
animal closes its shell. It must be confessed, however, that 
the majority, being fixed more or less completely, according 
to age, and always by their inferior valve, they are obliged 
to live in the places where they are born. Some species form, 
by a successive accumulation of individuals, strata, or banks, 
often very much extended and very thick, while others re- 
main more or less free and solitary. 
They are found, as it would seem, in all seas, but never at 
very great depths, nor at a great distance from the shore. 
The gulfs formed by the mouths of great rivers, or those in 
which the waters are more tranquil, constitute their usual 
habitation. But it does not appear that oysters ever live 
entirely in fresh water, or delight in it, as Pliny is pleased to 
inform us. Certain species, it is true, live in those parts of 
rivers where the sea comes up, so that they remain dry during 
low-water. 'This especially takes place with the Ostrea para- 
sitica, which attaches itself to certain shrubs and trees in the 
torrid zone, vulgarly called Mangliers in the French Antilles, 
Conocarpus of Linneus. 'Then they close their shell ex- 
actly ; but in their ordinary state, z.e. in the water, they 
leave it half open, the marginal line of their tentacular papillze 
edging almost the entire of the cleft. On the slightest contact 
of a foreign body, with these tentacula only, they close the 
shell more or less completely, and can also enclose there some 
of the smaller crustacea, especially of the genus Pinnothera, 
but which do not serve them as food. In fact, the nutriment 
of oysters, is, in all probability, composed of animals much 
smaller, of infusoria, of animated molecules, and even of ani- 
mal matters so abundantly spread in the waters of the sea; 
for, in spite of the size of their buccal aperture, the softness 
of its edges, and its position, will not allow us to believe that — 
oysters can feed upon substances at all resisting ; and the con- 
fidence with which we ourselves eat these animals, must in- — 
duce the belief that their stomach contains no hard sub- 
