exuviation, the limbs expanded two
inches 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
colour, 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
colour. '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 n