70 MOULTING OF CRUSTACEANS. 



ment, if it did not fall off when it had become too small to con 

 veniently accommodate them : therefore, crusta'ceans change their 

 skin as long as they continue to grow, and it appears that most 

 of these animals grow during their whole lives. The manner of 

 getting rid of the old envelope is very curious. Generally they 

 succeed without producing any deformity, and when they leave 

 it, the surface of the whole body is already provided with a new 

 sheath; but it is still soft, and becomes hard at the expiration of 

 some days. Crabs which have recently cast their old shell or 

 skin, and while the new skin remains soft, are considered a great 

 delicacy. 



" We are indebted to Reaumur, who watched the process in the cray-fish 

 (Astacus Jluviatilis), for what little is known concerning the mode in which 

 the change of shell (in crustaceans) is effected. In the animal above men- 

 tioned, towards the commencement of autumn, the approaching moult is 

 indicated by the retirement of the cray.fish into some secluded position, 

 where it remains for some time without eating. While in this condition, 

 the old shell becomes gradually detached from the surface of the body, and 

 a new and soft cuticle is formed underneath it, accurately representing of 

 course all the parts of the old covering which is to be removed ; as yet, but 

 little calcareous matter is deposited in the newly formed integument. The 

 creature now becomes violently agitated, and by various contortions of its 

 body seems to be employed in loosening thoroughly every part of its worn- 

 out covering, from all connection with the recently secreted investment. 

 This being accomplished, it remains to extricate itself from its imprison, 

 ment; an operation of some difficulty ; and, when the nature of the armour 

 to be removed is considered, we may well conceive that not a little exertion 

 will be required before its completion. As soon as the old case of the 

 cephalo-thorax has become quite detached from the cutis by the interposi 

 tion of the newly formed epidermic layer, it is thrown off after great and 

 violent exertion ; the legs are then withdrawn from their cases- after much 

 struggling; and, to complete the process, the tail is ultimately by long con- 

 tinued efforts extricated from its calcareous covering, and the entire coat of 

 mail which previously defended the body is discarded and lefl upon the 

 sand. The phenomena which attend this renovation of the external skeleton 

 are so unimaginable, that it is really extraordinary how little is accurately 

 known concerning the nature of the operation. The first question which. 

 presents itself, is, how are the limbs liberated from their confinement? for, 

 wonderful as it may appear, the joints even of the massive chela of the 

 lobster do not separate from each other ; but, notwithstanding the great size 

 of some of the segments of the claw, and the slender dimensions of the 

 joints that connect the different pieces, the cast-off skeleton of the limb 

 presents exactly the same appearance as if it still encased the living mem- 

 bcr. The only way of explaining the circumstance, is to suppose that the 

 individual pi ces of the skeleton, as well as the soft articulations connect- 

 ing them, split in a longitudinal direction, and that, after the abstraction of 

 the limb, the fissured parts close again with so much accuracy that even 

 the traces of the division are imperceptible." T. Rymer Jones. 



It is said that a lobster will throw off its claws it' alarmed by the report 

 of a cannon. This singular power of breaking off their own limbs, pos- 

 sessed by many crustaceans, is a very indispensable provision in their 

 economy. Should the claw of a lobster, for example, be damaged by acci- 

 dents to which creatures encased in such brittle armour must he perpetually 



