296 THE WORLD OF THE SEA. 
horn in the insect upon land, we find the hardest calcareous 
secretion in the ocean crustacea. They are generally provided 
with powerful pincers, which they use either to hold their prey, 
which has, indeed, little chance of escape when clutched in their 
formidable grasp, or they are weapons of defence. These knights 
of the sea live among the rocks, generally in the neighbourhood 
of the land; but they are also found at great depths. Some of 
them burrow in the sand; and there are crabs which love the air 
of the shore as much as they do the water of the sea; and, in 
order to enjoy both, take up their residence under some moist 
projecting rock which is washed by the high tides. The solidity 
of their carapace prevents the crustaceans from growing: for, unlike 
the shell of the echinus—which is composed of plates, and can be 
THE MANTIS CRAB. 
Sguilla mantis.) 
enlarged by additions to their edges—the shell of these crus- 
taceans, once formed, never afterwards alters its size; therefore, 
as the animal does not reach its full growth at once, the only 
way it has of solving the difficulty is to cast off the shell, and 
secrete another adapted to its increased size. 
At certain determined periods, Nature despoils the warrior of 
his cuirass; the creature moults; and the calcareous crust falls 
off, leaving in its place a thin and delicate tunic. When in this 
state, the animal does not deserve the name of crustacean, for it 
is as soft as any mollusk. It is quite conscious of its weakness, 
and, retiring into some lonely place, seeks to hide its shame in 
a narrow crevice until its new carapace has had time to grow, 
when, invested in its new suit of armour, it leaves its place of 
retirement, and frequents its usual haunts with all the dignity 
of a crustacean. An evil day is it for the moulting crab if one 
of his enemies happens to find him in his hiding-place. Helpless 
