21 
L obster — Development, Moulting. 
adult animal. An enlarged drawing of this stage is hung in Wall- 
Wall-case No. 2. The most important differences from the adult g 
are the absence of all the abdominal appendages (pleopods and 
uropods) and the presence on each of the legs of an exopodite. 
These exopodites are fringed with hairs and are used as swimming 
organs, by means of which the larvae move rapidly about at the 
surface of the sea. At a later stage (see drawing), the exopodites 
of the legs are lost and the young animal, which has now assumed 
the essential structure of the adult, sinks to the sea-bottom. In 
many Crustacea the changes of form between the larval and the 
adult state are much greater than they are in the Lobster, but 
in some cases they are less marked, and the animal is hatched in 
what is practically the adult form. 
Moulting. — As already mentioned, the outer covering of the 
Lobster is quite continuous over the whole surface of the body 
and limbs. It consists of a substance known as “ chitin,” which 
resembles horn and is hardened by the deposition of lime-salts to 
form the shelly parts of the exoskeleton. At the joints the covering 
is thin and soft and contains no lime. As this covering will not 
stretch to any great extent, the Lobster, like all other Arthropoda, 
requires to cast its shell at intervals as it grows. In this process 
of moulting (or ecdysis) the integument of the back splits between 
the carapace and the first abdominal somite ; and the body and 
limbs are gradually withdrawn through the opening, leaving the 
cast shell with all its appendages almost entire. The new shell, 
which had been formed underneath the old before moulting, is at 
first quite soft, and the animal rapidly increases in size by the 
absorption of water. The shell gradually becomes hardened by 
the deposition of lime-salts. 
Several series of specimens illustrating the process of moulting 
are exhibited in Wall-case No. 3. These have been prepared and 
presented to the Museum by Mr. and Mrs. EL J. Waddington, of 
Bournemouth, who have been very successful in keeping marine 
animals alive for long periods in aquaria. Two cast shells, obtained 
successively from a single Lobster, and the Lobster itself preserved 
in the “ soft ” condition immediately after escaping from the 
second of these, show very clearly the increase in size at each 
moult, and the same point is illustrated in a different way by a 
drawing hung in this case, in which are superposed the outline of 
a Lobster before moulting and the outline of the same animal a 
few hours after the moult. 
In a jar in the centre of the case are shown several specimens 
