Older ones change
only once a year. All the different kinds of Crab begin life as _larvae_
or _zoeas_, and cast their shells as we have seen.
Crabs can see and hear and smell; and they must also have a fine sense
of touch. I was once watching a big Crab eating his dinner under a rocky
ledge in a large glass tank. As he tore his food, some of the bits, no
larger than crumbs, fell and settled on the rocks below. Then I saw that
a smaller Crab, with long pincers, was hiding under a rock. As the
crumbs fell, he reached out his pincers and picked them up, one by one.
Each bit was gravely carried to his mouth, and tucked in, and then he
reached out for another. Though I was very close to the Crab, I could
hardly see the tiny scraps which he was able to pick up so easily.
One of the strangest Crabs is the Hermit. You would think that Nature
had played a joke on him, for he has only half a suit of armour. His
tail part is soft. He would have a bad time in the sea, but for a dodge
he has learnt.
The baby Hermit takes the empty home of a periwinkle. As he grows he
needs a larger house, and so leaves the tight shell and pops his tail
into a bigger one, generally a whelk shell.
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