195 REPORT—1850. 
claws as if supplicating food. Thus the perfection regained is permanent; nature 
preserves the symmetry she originally designed. 
A weaker specimen of the Cancer Menas, H, had been mutilated of both claws and 
six limbs by the preceding animal when first taken. Crabs are in general extremely 
contentious, many species waging a war, even to extermination, against each other. 
This mutilated specimen survived several weeks, and died apparently of abortive 
exuviation, not of its wounds,—when I thought the new animal to be produced might 
be discovered lying with the limbs folded over the breast. 
Another small crab, I, having lost five limbs, including one of the claws, was 
diligently preserved. As reproduction is first announced by a papilla rising from 
the remaining stump in the mutilation of fleshy animals, I watched the several 
stumps here preserved, without adverting totheimprobability of the same process when 
there was a casement of shell; yet I wasso much influenced by what I had heard and 
read, that I began at length to believe papille actually perceptible ; but in due time 
the illusion was dispelled by the appearance of the new animal with all its ten limbs 
perfect, on exuviation. No regenerating limb ever protrudes from the vacant stump, 
Under all these circumstances, it is evident that the new subject—the shell and 
animal—to be produced on exuviation, must be concentrated within the smallest 
possible bounds, lying with the limbs crossed over the breast in the original shell, 
which sunders or gapes between the hind pair of limbs, to allow its exit when 
mature. 
Precisely the number of defective organs is presented by exuviation along with the 
rest. A specimen of the Cancer (or Portunus) pusillus, whose limbs expanded two 
inches between the opposite extremities, had lost both the claws. From this defect 
it fed itself with difficulty, for the claws of all crabs, lobsters, and such animals are 
employed just as the human hands. Both claws however appeared perfect in the 
new animal introduced on exuviation. The same occurred where only one pincer 
of the forceps of a claw was defective. Taking everything in view, therefore, the 
whole parts constituting the entire animal must be produced or reproduced within 
the original or subsisting shell; but generated or regenerated. The time and mode 
whereby this is effected, I must leave more skilful physiologists to determine. 
The course of exuviation of the lobster-tribe may be conveniently followed in the 
Crangon or shrimp, which is easily kept and fed, and becomes very tame ; also the 
process is frequent, The integument separates entire and is almost colourless. 
The Cancer Bernhardus, the Soldier or Hermit Crab, is intermediate between the 
Cancer and Astacus. As only the upper half is invested by a shelly covering, its 
exuviation is limited in correspondence, there being nothing to separate from the 
lower, the fleshy portion. The peculiarities of exuviation by the other crustacean 
genera, being sought from themselves, will be found extremely interesting by the 
practical naturalist. 
In as far as I have been able to ascertain, prolific females are exempt from exuyiation 
during the period of gestation. The spawn or roe adhering externally to the shell 
would be endangered by such a process. This spawn, which is seen in beautiful 
variety, in colour and quantity, often resembles luxuriant clusters of currants or 
grapes, each capsule containing a foetus, which is discharged on maturity, while the 
spawn still remains zz situ. The young has no resemblance whatever to the parent, 
The preceding facts, combined with many other observations, lead to the following 
conclusions :— 
1. The crustacean tribes are invested by a rigid inexpansible shell, 
2. As the existing shell cannot dilate to allow the increment of the animal, it is 
wholly cast off hy e«uviation, to make way for another, which is always of larger 
dimensions. 
3. This exuviation, commencing at very early age, is repeated at irregular intervals 
during the progress of increment, each successive shell with its animal exceeding the 
size of its precursor. 
4, The larger or new shell and animal is generated or regenerated within the 
existing shell, which opens for its exit when mature. 
5. No enlargement of the new subject is sensible after production. 
6. Whatever the mutilation may be which the existing shell and animal haye un- 
dergone, the new subject is always produced entire and perfect by exuyiation, 
