"
But _how_ does the house grow large so as to suit the growing tenant? Most
shells are made from a part of the animal called the mantle, and increase
round the rim; if the snail's house is broken, its slime will harden over
the injured part and repair it. Then, when the cold weather comes, and the
snail prepares to bury itself underground for several months, and take
its winter nap, it makes a strong cement of earth and slime, with which
it builds up the open part of its shell--but, wonderful to think of, the
clever little mason leaves, as it were, one brick out of the wall, and thus
there is a tiny opening, too small to let in the water, but large enough to
admit air sufficient to keep him alive during his long sleep.
Now that our snail has been good enough to put out those four horns of his,
let us ask what purpose they serve, and why they are placed' where they
are. The answer is very simple; these "feelers" are to the snail instead of
arms and legs; and the upper pair have eyes at the end, so that the wary
little traveller, as it drags itself along a broad cabbage leaf, leaving a
slimy track behind it, can tell, both by sight and touch, what obstacles
may lie in its path. I don't know whether you have ever seen the eggs of
snails; I have not, but I have heard that they are about the size of peas,
and are buried in the earth, as the crocodile's eggs are buried in the
sand.
Of the many families of Ringed or Jointed Animals, we will choose the Crabs
and Lobsters first.
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