116 REPORT—1850. - 
the new shell, which is developed from a repetition of these layers, into which even- 
tually the whole pulp is converted. 
Il. Shedding the Exuvie.—As the period approaches for the completion of the 
new shell, it, being larger in extent than that which it is about to replace, is there- 
fore compressed into wrinkles or folds. It is by this compression, arising from the 
internal growth of the crab, acting upon the principle of the lever, that the old shell 
is removed ; the first external sign which I have observed of the approaching change 
in the animal’s mconomy, is an increase in the thickness, whereby the sections of the 
abdomen become more conspicuous from above ; as this increases, the crab wanders 
about in search of a resting-place, and often becomes very savage, darting at any 
and everything that approaches it, until when the moment draws near it hitches the 
point of one of its feet into some crack or crevice and withdraws itself from its old 
skin, escaping between the carapace and the abdomen. The moment after it is free 
the full size is obtained. 
I cannot help here remarking, that in the case alluded to by Reaumur it is stated, 
that with the crayfish (Astacus fluviatilis) the process was one of great labour and 
difficulty as well as duration, whereas in every case that I have watched of the crab 
(Carcinus Menas), the operation has been very quick and easy; and also up to the 
moment of their throwing off their extraneous skeleton, they have the use of all their 
limbs with perfect freedom, and display as much activity upon being disturbed as at 
any other time. They also seem to have the power of retaining the old shell at will 
until a suitable moment occurs for them to cast it with security; for although in 
many instances I have seen them before and after the process had commenced, and 
patiently watched for hours at a time, yet they have endeavoured to take advantage 
of a temporary absence of sometimes a few minutes to get rid of the shell. At this 
time they are very liable, in their defenceless state, to be preyed upon by larger 
animals both of their own and other ‘species, of which they themselves seem to be 
aware, and being excited by fear, are much more active and less easily caught than 
at any other period. 
Ill. The Reproduction of Limbs.—When a limb is injured all crustacea have the 
power of rejecting it (provided it be not below the last joint) ; this is done by a violent 
muscular contraction, and ultimately a blow from another limb or against some ex- 
ternal body ; the amputation is performed in a few seconds, except when they have 
but recently cast the exuvize, when for the first few days (while the new skeleton is 
being hardened) they have not that easy capability, and the wounded limb will 
sometimes remain for perhaps half an hour or more before it is thrown off. I once 
cut the large didactyle claw of a crab through the joint, so as to remove only the 
thumb and finger; and although the animal exhibited signs of severe suffering for 
some hours, yet it did not throw off the limb, and when the exuvie in its regular time 
were shed, the limb continued a maimed member and never was produced. The new 
limb is formed within the old carapace in connexion with the zew shell, and lies 
folded up until the old coat is thrown off, and becomes apparent only at the period 
of the development of the new shell, and is larger or smaller in accordance with the 
duration which existed between the period of the amputation of the limb and the 
shedding of the exuvie. The condition in which the limb is then in remains, as the 
rest of the animal, stationary in growth, until the shell is again cast, when the whole 
creature advances in size, but the newer-developed limb more rapidly in proportion 
than the remainder of the animal, until the new limb is equal to the others in size 
and importance. It is to this variety of sizes (dependent upon the period which 
occurs to atlow the new limb to be developed previously to the next succeeding moult), 
that the commonly received idea of the continual growth of the limb is based. 
IV. On the use of the False Feet in Male Brachyura.—These appendages, which 
consist of two pair, the anterior being the larger and more important, are attached 
to the first annular segment of the abdomen, the posterior or less belongs to the 
second ring, and in all that I have observed, the second or less pair is inserted pos- 
teriorly into the first or larger pair, except in Cancer Pagurus, in which the posterior | 
is of equal length, though less in other proportions. 
In the female, as is well known, the false feet are the appendages by which the 
ova are supported. by the parent during their development. But in the male they 
assume a more important function, being no other than the intromittent organ of 
