Cuvier describes the Burrowing Crab as displaying wonderful instinct:--"The animal closes the entrance of its burrow, which is situated near the margin of the sea, or in marshy grounds, with its largest claw. These burrows are cylindrical, oblique, very deep, and very close to each other; but generally each burrow is the exclusive habitation of a single individual. The habit which these crabs have of holding their large claw elevated in advance of the body, as if making a sign of beckoning to some one, has obtained for them the name of Calling Crabs. There is a species observed by Mr. Bosc in South Carolina, which passes the three months of the winter in its retreat without once quitting it, and which never goes to the sea except at the epoch of egg-laying." The same observations apply to the Chevalier Crabs (so called from the celerity with which they traverse the ground). These are found in Africa, and along the borders of the Mediterranean. Some Crabs, truly aquatic, as the Vaulted Crab of the Moluccas, have the power of drawing back their limbs, and concealing them in a furrow, which they closely fit; and thus, in imitation of a tortoise, which retracts its feet and head within its shell, they secure themselves, when alarmed. Other aquatic species have their limbs adapted for clinging to weeds and other marine objects. Of these some have the two or four hind pairs of limbs so placed as to appear to spring from the back; they terminate in a sharp hook, by means of which the Crab attaches itself to the valves of shells, fragments of coral, &c., which it draws over its body, and thus lurks in concealment. Allied, in some respects, to the Hermit or Soldier Crabs, which tenant empty shells, is one which, from its manners and habits, is one of the most extraordinary of its race. The Hermit Crabs are voracious, and feed on animal substances. The Hermit, or Bernhard Crab, is so called from its habit of taking up its solitary residence in deserted shells, thus seeking a protection for its tail, which is long and naked. It is found in shells of different dimensions, and from time to time leaves its abode, as it feels a necessity, for a more commodious dwelling. It is said to present, on such occasions, an amusing instinct as it inserts the tail successively into several empty shells until one is found to fit. We learn from Professor Bell, however, that it does not always wait until the home is vacant, but occasionally rejects the rightful occupant with some violence. On the contrary, the Crab, or rather Lobster-Crab (for it takes an intermediate place between them), is more delicate in its appetite, and feeds upon fruits, to obtain which it is said to climb up certain trees, at the feet of which it makes a burrow. This species is the Purse Crab, or Robber Crab, of Amboyna and other islands in the South Pacific Ocean.