ON ACEPHALA. 391 
lose their brilliancy. It has been proposed, for the purpose 
of restoring them, to cause them to be swallowed by pigeons. 
Supposing that the art of jewellery possessed no other means 
than this, attention should be paid to prevent them from re- 
maining too long in the crop of these birds, otherwise they 
would soon diminish in bulk. Redi, who made this experi- 
ment, informs us, that having caused a pigeon to swallow 
twelve grains of pearl, they diminished one third in weight. 
This author also relates, that on the opening of the tomb, 
where the daughters of Stilicho had been interred, with all 
their ornaments, eleven hundred and eighteen years before, 
every thing was found in high preservation, except the pearls, 
which were so brittle as to be very easily crushed with the 
finger. 
The genus PINNA approximates very much to that of the 
mussels, the only difference of any import being in the thick- 
ness and fineness of the byssus. In manners and habits they 
are also very similar. ‘They live, as it would appear, con- 
stantly fixed by their byssus, in a vertical position, the 
summit of the shell being undermost, and the base, or pos- 
terior extremity, uppermost. But it is particularly in a sandy, 
or even muddy bottom, that they fix themselves in consider-- 
able troops, and by attaching the filaments of the byssus to 
surrounding bodies, and even to grains of sand, so as easily 
to resist the movements of the sea. ‘The ancients relate many 
things respecting these animals, which have not been con- 
firmed by modern observations ; among others, they tell us 
that these mollusca have many enemies, the presence of which 
is indicated to them by a small crustaceous animal, thence 
named pinnothera, and which shelters itself in their shell. 
The most common species exists in certain places in the 
Mediterranean, at the depth of from five to six fathoms. The 
inhabitants of Sicily and Calabria seek after them, not merely 
for eating, like the mussels, but also to gather their byssus, of 
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