Lobster — Devclopincni, Moulting, 2 I 



adult animal. An enlarged drawing oi! this stage is hung in Wall- 

 Wall-case No. 2. The most important diiferences from the adult ^^g^^_3 

 are the absence of all the abdominal appendages (pleopods and 

 uropods) and the presence on each of the legs of an exopoditc. 

 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 wall 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 limbs are gradually withdrawn through the opening, leaving the 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. H. 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 



