COMMON SHORE-CRAB, ETC. 97 



time as a new shell becomes secreted, and by harden- 

 ing assumes the form and efficiency of its predecessor. 

 " We are indebted to Reaumur, who watched the 

 process in the Cray-fish (Astacus flaviatilis), for what 

 little is known concerning the mode in which the 

 change of shell is effected. In the animal above 

 mentioned, towards the commencement of autumn, 

 the approaching moult is indicated by the retirement 

 of the Cray-fish into some secluded position, where it 

 remains some time without eating. While in this 

 condition, the old shell becomes gradually detached 

 from the surface of the body, and a new soft cuticle 

 is formed underneath it, accurately representing, of 

 course, all the parts of the covering which is to be 

 removed; but as yet little calcareous matter is de- 

 posited 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 connexion with the recently secreted 

 investment ; this being accomplished, it remains to 

 extricate itself from its imprisonment an operation 

 of some difficulty and when the nature of the armour 

 to be removed is considered, we may well conceive 

 that no 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 interposition of the new-formed epidermic layer, 

 it is thrown off in one piece, after great violent 

 exertion ; the legs are then withdrawn from their cases. 



