One singular part of the history of these creatures is, the power that is possessed by them, of changing their shell once in every year; this power is providentially bestowed upon them, to enable them to increase in size, a thing that would otherwise be utterly impossible, from the peculiar nature of the hard coat in which they are enclosed.
The Crab, in order to prepare for the extraordinary change it is about to undergo, when shifting its shell, chooses a close and well-secured retreat, in the cavities of rocks, or under great stones, where it creeps in and remains during the operation. The time of the year when this occurs is about the beginning of the Summer, at which time their food is in plenty, and their strength and vigour in the highest perfection. But soon all their activity ceases; they are seen forsaking the open parts of the deep, and seeking some retired situation among the rocks, or some outlet where they may remain in safety from the attacks of their enemies. For some days before their change, the animal discontinues its usual voraciousness; it is no longer seen laboriously harrowing up the sand at the bottom, or fighting with others of its kind, or hunting its prey; it lies torpid and motionless, as if in anxious expectation of the approaching change. Just before casting its shell, it throws itself upon its back, strikes its claws against each other, and every limb seems to tremble; its feelers are agitated, and the whole body is in violent motion; it then swells itself in an unusual manner, and at last the shell is seen beginning to divide at its junctures, particularly at those of the belly, where it was before seemingly united. It also seems turned inside out; and its stomach comes away with its shell. After this, by the same operation, it disengages itself of its claws, which burst at the joints; the animal, with a tremulous motion, casting them off, as a man would kick off a boot that was too big for him.
Thus, in a short time, this wonderful creature finds itself at liberty; but in so weak and enfeebled a state that it continues for several hours motionless. Indeed, so violent and painful is the operation, that many of them die under it; and those which survive, are in such a weakly condition for some time, that they neither take food, nor venture from their retreats. Immediately after this change, they have not only the softness, but the timidity of a worm. Every animal of the deep is then a powerful enemy, which they can neither escape nor oppose; and this, in fact, is the time when the dog-fish, the cod, and the ray, devour them by thousands. But this state of weakness continues for a very short time; the animal, in less than two days, is seen to have the skin that covers its body almost as hard as before; its appetite appears to increase; and, strange to behold! the first object, it is said, that tempts its gluttony, is its own stomach, which it was lately disengaged from. This it devours with great eagerness. In about forty-eight hours, in proportion to the animal’s strength, the new shell is perfectly formed, and as hard as that which was but just thrown aside. Previous to the time of moulting or changing their skin, a flat chalky stone is found on each side of the stomach; this is believed to form a store of earthy matter for the renewal of the shell. These stones, popularly known as crabs’ eyes, were long highly esteemed for their medicinal properties, but in reality are not superior to so much chalk.
When completely equipped in its new dress, the dimensions of the old shell being compared with those of the new, it will be found the creature has increased in size nearly one-third, and it appears wonderful how the old shell could have contained it.
Many of the cold-blooded animals have the power of reproducing a limb, or a portion of one, if by any accident it has been lost. This faculty of reproduction is possessed by the Crab in great perfection; but it has also a surprising power in itself, voluntarily to break off its own legs and claws. It seems this takes place when any serious injury, by bruising, has happened to any of its members. After it has received the hurt it bleeds, and gives signs of pain, by moving the wounded limb from side to side, but afterwards holds it quite still, in a direct and natural position, without touching any part of its body or its other legs with it. Then, on a sudden, with a gentle crack, the wounded part of the leg drops off at the next joint to the one injured; this appears to be more easily done with respect to the smaller legs, than in the case of an injury occurring to those which bear the pincers.
When the leg has dropped off, a mucus, or jelly, is discharged on the remaining part of the joint next the body, which, as a natural styptic, instantly stops the bleeding; this gradually hardens and grows callous, becoming a new leg in miniature, which at every change of the creature’s shell increases rapidly in size.
Crabs are naturally very quarrelsome, and with their claws fight and kill each other; and if by chance any of their limbs should be so bruised, as to have taken away from the creature the power of breaking off its claws, the protecting jelly is not produced, and the animal bleeds to death. An experiment was made to give some idea of the tenacious disposition of this creature, by obliging a Crab, with one of its great claws, to lay hold of one of its smaller ones; the silly creature did not distinguish that itself was the aggressor, but exerted its strength, and soon cracked the shell of its own small leg, which bled freely; but feeling itself wounded it succeeded in breaking off its limb in the usual manner,—still, however, holding fast for a length of time the part of the wounded leg which had come away.
The curious shuffling walk of the Crab is well known, but it does not, as it is said, walk exactly backwards.
The Land Crab, ([Gecarcinus ruricola].)
Although nearly all the Crab tribe are inhabitants of the water, there is a species found in the West Indies, a native of the Bahama Islands, whose habits are unlike those of the rest of its class, and highly curious in themselves.