All sandy and muddy coasts of the tropical seas, affording sufficient protection against a heavy sea, swarm with crabs. In the East and West Indies the Gelasimi bore in every direction circular holes in the moist black soil of the coast. One of the claws of these remarkable creatures is much larger than the other, so as sometimes to surpass in size the whole remainder of the body. They make use of it as a door, to close the entrance of their dwelling, and when running swiftly along, carry it upright over the head, so that it seems to beckon like an outstretched hand. One might fancy the crab moved it as in derision of its pursuers, telling them by pantomimic signs, "Catch me if you can!" [Illustration: Large-Clawed Calling-Crab.] As soon as the ebbing flood lays bare the swampy grounds of the mangrove woods, myriads of animals are seen wallowing in the pestiferous mud. Here a fish jumps about, there a holothuria crawls, and crabs run along by thousands in every direction. The black mud along the coast of Borneo assumes quite a brilliant blue tinge, when, at low water, during the heat of the day, the cœrulean Gelasimi come forth to feed. [Illustration: Calling-Crab of Ceylon.] The Venetian lagoons also harbour a vast number of the common Shore-Crab (_Portunus Mænas_), the catching of which affords a profitable employment to the inhabitants of those swampy regions. Whole cargoes are sent to Istria, where they are used as bait for anchovies. The fishermen gather them a short time before they cast their shell, and preserve them in baskets, until the moulting process has been effected, when they are reckoned a delicacy even on the best tables. On attempting to seize this crab, it runs rapidly sideways, and conceals itself in the mud; but when unsuccessful, it raises itself with a menacing mien, beats its claws noisily together, as if in defiance of the enemy, and prepares for a valiant defence, like a true knight. The most valuable short-tailed crustacean of the North Sea is undoubtedly the Great Crab (_Cancer pagurus_), which attains a weight of from four to five pounds, and is consumed by thousands in the summer, when it is in season and heaviest. It is caught in wicker-baskets, arranged so as to permit an easy entrance, while egress is not to be thought of. The legs of the crabs are very differently formed in various species. In those which have been called sea-spiders they are very long, thin, and weak, so that the animal swims badly, and is a slow and uncertain pedestrian. For greater security it therefore generally seeks a greater depth, where, concealed among the sea-weeds, it wages war with annelides, planarias, and small mollusks. Sea-spiders are often found on the oyster-banks, and considered injurious by the fishermen, who unmercifully destroy them whenever they get hold of them.