Among the Mollusks, not only the highly organized Cephalopods
(Cuttle-fish, Octopus, etc.), but even the lowly Oyster, and the more
active Snail and Slug appear to possess associative memory.
Prof. A. H. Cooke (Cambridge Natural History, Vol. III), declares that
Oysters can learn from experience. Says he:--
“As soon as an Oyster is taken out of the sea, it closes its shells,
and keeps them closed until the shock of removal has passed away, or
perhaps until the desirability of a fresh supply of water suggests
itself. The men take advantage of this to exercise the Oysters,
removing them from the sea for longer and longer periods. In time this
has the desired effect; the well-educated Mollusk learns that it is
hopeless to ‘open’ when out of the water, and so keeps his shell closed
and his gills moist, and his general economy in good condition.”
A certain degree of intelligence has been attributed to Snails. Miss
Elizabeth Lockwood Thomson, for example, experimented extensively with
these Mollusks and found that they are educable--that they can learn by
experience.[9]