THE SHEDDIKG OF THE SKIN. 35 



The operation is facilitated by the splitting of the old 

 integument of the limb along one side longitudinally. 



When the legs ai'e disengaged, the animal draws its 

 head and limbs completely out of their former covering ; 

 and, with a sudden spring forward, while it extends its 

 abdomen, it extracts the latter, and leaves its old skele- 

 ton behind. The cara^^ace falls back into its ordinary 

 position, and the longitudinal fissures of the sheaths of 

 the limbs close up so accurately, that the shed integu- 

 ment has just the appearance the animal had when the 

 exuviation commenced. The cast exoskeleton is so like 

 the crayfish itself, when the latter is at rest, that, except 

 for the brighter colour of the latter, the two cannot be 

 distinguished. 



After exuviation, the owner of the cast skin, ex- 

 hausted by its violent struggles, which are not unfre- 

 quently fatal, lies in a prostrate condition. Instead of 

 being covered by a hard shell, its integument is soft and 

 flabby, like wet paper ; though Reaumur remarks, that 

 if a crayfish is handled immediately after exuviation, its 

 body feels hard ; and he ascribes this to the violent con- 

 traction which its muscles have undei'gone, leaving them 

 in a state of cramp. In the absence of the hard skeleton, 

 however, there is nothing to bring the contracted muscles 

 at once back into position, and it must be some time 

 before the pressure of the internal fluids is so distributed 

 as to stretch them out. 



When the process of exuviation has proceeded so far 



D 2 



