and a half. From the long slender form of the limbs of crustacea, they are very liable to mutilation. Crabs are also a very pugnacious family, and in their battles limbs are often snapped off. These mutilations, however, are readily repaired; although, contrary to what was the common belief, the restoration takes place only at the next regular period of exuviation. The full-grown common crab (_Cancer pagurus_) is of a reddish-brown color, the claws tipped black; but some of the young are naturally of the purest white, which remains long unsullied. This does not arise from confinement, which, according to Sir John, has no influence on color. "A young white specimen of the common crab was subjected to observation on 29th September. The body might have been circumscribed in a circle three-quarters of an inch in diameter, and the extended limbs by one and a half inch in diameter. Its first exuviation ensued on 8th November, the second on the 30th of April following, and the shell then produced subsisted till 12th September, when another exuviation took place, introducing a new shell of such transparent white that the interior almost shone through it. All the shells were white, and increased somewhat in size successively. This last shell of 12th September subsisted until 29th March, being 197 days, when it was thrown off during another exuviation." But what was remarkable, the animal now had only the two large claws, the other eight limbs were deficient. "Resting on its breast as it was, I did not at first discover the fact, that the creature presented a strange and very uncouth aspect. However, it fed readily, and proved very tame, though helpless; often falling on its back, and not being able to recover itself from the deficiency of its limbs. I preserved this mutilated object with uncommon care, watching it almost incessantly day and night: expecting another exuviation which might be attended with interesting consequences, I felt much anxiety for its survivance. My solicitude was not vain. After the defective shell had subsisted eighty-six days, its tenant meantime feeding readily, the desired event took place in a new exuviation on 23d June. On this occasion a new animal came forth, and in the highest perfection, quite entire and symmetrical, with all the ten limbs peculiar to its race, and of the purest and most beautiful white. I could not contemplate such a specimen of nature's energies restoring perfection, and through a process so extraordinary, without admiration. Something yet remained to be established: was this perfection permanent, or was it only temporary? Like its precursor, this specimen was quite tame, healthy and vigorous. In 102 days it underwent exuviation, when it appeared again, perfect as before, with a shell of snowy white, and little red speckling on the limbs. Finally, its shell having subsisted 189 days, was succeeded by another of equal beauty and perfection, the speckling on the legs somewhat increased.