34 ON THE MOULTING OF THE COMMON LOBSTER AND SHORE CRAB. 



description. In the only examples of the exuviation of macrou- 

 rous Decapod Crustaceans, there exists a singular diversity in the 

 process itself. In Astacus, as described by Beaumur, the process 

 commences with the escape of the cephalothorax ; in Homarus, as 

 I have now described it, it begins by the emergence of the abdo- 

 men. In Astacus the carapace is detached and thrown oif bodily 

 and unbroken, being severed from its attachments with the lateral 

 portions of the cephalothorax, as is the case in the Brachyura ; 

 whereas in Homarus the lateral attachments of the carapace 

 remain, whilst the plate itself is split up the centre. In Astacus, 

 as is also the case in the Brachyura, the thrown- off slough is uni- 

 formly left resting on its dorsal surface ; in Homarus the reverse 

 is uniformly the case. But the most striking dissimilarity is 

 to be found in the circumstances stated to attend the liberation 

 of the chelae. Prof. Bell, in the Introduction to his ' History of 

 the British Stalk-eyed Crustacea,' remarks — " It is impossible to 

 imagine that the crust of the legs, and especially of the great 

 claws of the larger species, could be cast off, unless it were 

 susceptible of being longitudinally split" (p. 35), and he then 

 proceeds to give the account detailed by Beaumur of the longi- 

 tudinal splitting of the shell in the neighbourhood of the joints of 

 the claws in Astacus, so as to allow of the extrication of the hands. 

 Nevertheless, however impossible it may appear for the chelae to 

 escape without this splitting, no such circumstance occurs in the 

 exuviation of Homarus vulgaris ; and when we consider that the 

 hands of Astacus are small in proportion to the wrist-joints, and 

 that in Homarus they are larger in proportion to those joints than 

 in any other of the Macroura, this dissimilarity in the mode in 

 which the claws escape is the more remarkable, and, I confess, to 

 my own mind it suggests the suspicion that the distinguished and 

 usually most accurate Erench naturalist to whom I have referred 

 may possibly in this instance have been led to consider as a fact 

 that which was to him a supposed necessity*. 



Since the foregoing account of the moulting of the Lobster was 

 written, I have dredged a specimen of the common shore-crab 

 (^Carcinus mcenas), in the act of casting its shell. This little 

 crustacean had taken refuge, no doubt for the safe and secret per- 



* The suspicion above expressed has been fully confirmed by observations 

 made by Mr. J. J. Bennett, the Secretary of the Linnean Society. Mr. Bennett 

 informs me that, in an aquarium in his possession, an Astacus fiuviatilis has 

 twice cast its shell, and the process of moiilting was on each occasion accom- 

 plished without any sphtting of the shell at the joints of the claws. 



