PLATE XXV
CRAB CHRYSALIDS (3 and 3 A)
When the caterpillar of an insect has reached its full size it throws off its skin and appears as a chrysalis, or pupa. And the caterpillar, or zoea, of a crab does exactly the same thing. It casts its skin, and appears in quite a different form. Only we do not call it a chrysalis, as a rule. We call it a “Megalopa.”
1. PEA CRAB (life-size).
2. CRAB CATERPILLAR (enlarged).3. CRAB CHRYSALIDS (enlarged).
2A. ” ” (life-size).3A. ” ” (life-size).
The word “megalopa” means “a creature with big eyes,” and it is given to the crab chrysalis because it has eyes which are enormously big in proportion to the size of the head. They are set on long footstalks, which project on either side, so that the head looks rather like a hammer. Then the long curved horns which the zoea had are to be seen no longer, and the carapace is shaped much more like that of the perfect animal, while the great claws begin to show, and the legs increase in length. The tail, however, is still quite free, like that of a lobster, and the little animal still swims by turning somersaults in the water, and lives on the same tiny scraps of decaying matter on which it fed as a zoea. After a few weeks it throws off its skin once more, and appears in the world as a perfect crab.
PLATE XXVI
HERMIT CRABS (1 and 2)
If you go down among the rocks when the tide is out, and hunt about in the pools, you may often find the shell of a whelk in which a small crab is living, with one of his great claws carefully guarding the entrance. This is a Hermit Crab, and a very curious little creature he is. For, in the first place, his long tail is quite free, like that of a lobster, instead of being fastened down to the lower surface of his body; and in the second place, it is quite soft, without any shelly covering at all. His body and limbs are covered with armour, just like those of other crabs, but his tail has none at all.