TRANSACTIONS OF THE SECTIONS. 121 
tifal intermixture of green and white. On the first exuviation, the new shell appeared 
in perfect purity, with precisely the same colours distributed in the same manrer. 
This shell subsisted 210 days: The male survived but a short time; nor did the 
union of the animals prove prolific. ; 
Numerous other examples were afforded by the Cancer Menas, all to the same 
purport. The observer must feed the subject of experiment frequently, that is, every 
day or every second day, and renew the sea-water as often. Nothing prognosticates 
exuviation unless abstinence for one or more days previously, and greater quiescence. 
The colours are alike vivid on exuviation, as if the animal were at large ; butif it be 
a defective specimen, mutilated perhaps of both large claws, or of the eight limbs, all 
these ten organs will come in perfect and entire on the first subsequent exuviation, as 
an integral portion of the new shell. On the other hand, no subsisting shell which 
is mutilated seems ever to acquire a new limb. There is naturally a great disparity 
in the size of the claws of various genera. 
It is difficult to explain either the formation and position of the new shell within 
the existing animal, or how it escapes on exuviation. 
For a long time I concluded that the new parts were derived from the old, that a 
claw was generated within a claw, a limb within a limb, the eyes within the eyes; 
thence concurring in the prevalent opinion, that on exuviation each was withdrawn 
from the pre-existing organ as from a sheath. Nature seems to conduct her opera- 
tions otherwise. But the means are most obscure. 
The adult of the common Crab, Cancer Pagurus, is of a reddish brown colour, 
ἢ darker or lighter, the claws always tipped black ; but some of the young are naturally 
of the purest white, which remains long unsullied. This is not incident to confine- 
ment, which has no effect on colour. 4 
A young white specimen, C, was taken among others on September 29. The body 
might have been circumscribed by a circle, nine lines or three quarters of an inch in 
diameter, and the extended limbs by one and a half inch in diameter. Its first 
exuviation ensued on November the 8th; the second on the 30th of April following ; 
the shell now produced subsisted until September 12, when another exuviation took 
place, introducing a new shell of such pure and transparent white, that the interior 
almost shone through it. All the shells were white, and somewhat larger success- 
ively. This last shell of September 12 subsisted until March 29, being 197 days, 
when it was evacuated by another exuviation, introducing its contents, D, to view. 
The new animal, as I must call it, D, had only the two claws; all its eight limbs were ἡ 
deficient.. Resting on the breast, I did not at first discover the fact, but the creature 
presented a very strange and uncouth aspect. However, it fed readily and proved very 
tame, though helpless, often falling on its back, nor able to recover itself from wanting 
the limbs. I preserved this mutilated subject 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 
June 23. 
What was now disclosed? Still another animal, E, came forth, and in the highest 
perfection, quite entire and symmetrical, with all the ¢en limbs peculiar to its race, 
and of the purest and most beautiful white! I could not contemplate such a spe- 
cimen of Nature’s energies restoring perfection, and through a process so extra- 
ordinary, without admiration. Something yet remained to be established. Was 
this perfection permanent, or was it only temporary? Like its precursor, this spe- 
cimen, a very fine one, was quite tame, healthy, and vigorous besides. In 102 days 
it underwent exuviation, when the new animal, F, appeared in all perfection, with a 
shell of snowy white and a little red speckling on the limbs. Finally, its shell having 
subsisted 189 days, was succeeded by another, G, of equal beauty and perfection, 
the speckling on the legs somewhat increased. As all the shells had gradually aug- 
mented, so was this much larger than any. The limbs extended would have occu- 
pied a circle of four inchés diameter. About a month after this last exuviation, the 
animal perished accidentally, having been two years and eight months under obser- 
vation. This was a fine and interesting specimen, extremely tame and tranquil, 
always coming to the side of the vessel as I approached, and holding up its little 
