Freshwater snails and mussels, in cold weather, bury
themselves in the mud of ponds or rivers; and land-snails hide
themselves in the ground or under moss and leaves. The heart then
ceases perceptibly to beat, but respiration continues in a very faint
degree. The common garden snail closes the mouth of his shell when he
wants to hibernate, with a slimy covering; but he leaves a very small
hole in it somewhere, so as to allow a little air to get in, and keep up
his breathing to a slight amount. My experience has been, however, that
a great many snails go to sleep in this way, and never wake up again.
Either they get frozen to death, or else the respiration falls so low
that it never picks itself up properly when spring returns. In warm
climates, it is during the summer that mollusks and other mud-haunting
creatures go to sleep; and when they get well plastered round with clay,
they almost approach in tenacity of life the mildest recorded specimens
of the toad-in-a-hole.
For example, take the following cases, which I extract, with needful
simplifications, from Dr. Woodward.
'In June 1850, a living pond mussel, which had been more than a year out
of water, was sent to Mr. Gray, from Australia. The big pond snails of
the tropics have been found alive in logs of mahogany imported from
Honduras; and M. Caillaud carried some from Egypt to Paris, packed in
sawdust. Indeed, it isn't easy to ascertain the limit of their
endurance; for Mr.
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