Crustacea. 3491 



tron is effected in the course of a few hours, body and limbs being alike relieved from 

 their hard covering. Until the new shell acquires firmness and strength, the creature 

 is very shy, and, in the state of nature, retires into cavities below rocks or heaps of 

 protecting sea-weed. Sir John had kept for some time one of our smaller species of 

 shore-crabs (Carcinus Manas), of medium size, of a brown colour, with one white limb. 

 One summer evening it was put outside the window in a capacious glass vessel of sea- 

 water. In the morning a form exactly resembling its own, only somewhat larger, lay 

 in the vessel. This was the same animal, which had performed exuviation and extri- 

 cated itself from the old shell during the night. The resemblance between both forms 

 was complete — everything was the same, even the white limb was seen in both. Ano- 

 ther specimen kept was of smaller size, the opposite extremities of the limbs being 

 only 13 lines asunder ; its colour was green, with three white patches on the back. 

 In the course of little more than a year five exuviations took place at irregular inter- 

 vals, the new shell and animal becoming larger each time. The third shell came on 

 uniformly green, the white spots being entirely obliterated. On the fourth exuvia- 

 tion, the limbs expanded 2£ inches. From the long slender form of the limbs of Crus- 

 tacea, 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 colour, the claws tipped with 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 colour. * A young white specimen of the common crab was subjected to observa- 

 tion 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 dia- 

 meter. Its first exuviation ensued on the 8th of November, the second on the 30th of 

 April following, and the shell then produced subsisted till 12th September, when ano- 

 ther 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 ano- 

 ther 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 the 23rd of 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 while. 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 esta- 

 blished : was this perfection permanent, or was it only temporary ? Like its precur- 

 sor, this specimen was quite tame, healthy, and vigorous. In 102 days it underwent 



