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cast less frequently than once in two years, and a stage is 

 ultimately reached when the crab ceases to cast. 



It is my belief that after attaining a size of about six 

 inches carapace breadth the females, as a general rule, 

 only cast once in three years, but that the males continue 

 to cast biennially for a considerably longer period. It 

 must be admitted that the figures on which this 

 suggestion is based are not sufficiently large to warrant 

 any conclusive statements on the subject. So that, 

 although I feel that my explanation is a reasonable one, 

 and is, furthermore, supported by many facts, I bring it 

 forward merely as a provisional hypothesis. I further 

 recognise that, just as in the case of the younger stages, 

 there can be no rigid law regarding the frequency of 

 casting. It is quite possible that many males over six 

 inches cast less frequently than once in two years, and 

 that many females above this size may cast biennially.* 



" Granny " Crabs. 



The assumption that female crabs above six inches 

 cast only once in three years was first suggested to me 

 when examining into the nature of " granny " crabs. 

 This name is given by the fishermen of Port Erin to 

 crabs occurring in the late summer and early autumn 

 which have dirty and discoloured shells and broken claws. 

 These crabs, if eaten, have a bitter taste and a powerful 

 purgative effect. The fishermen believe they are diseased 

 crabs, and always kill such when captured. There 

 appears to be no adequate reason for believing that these 

 crabs are diseased. The fact that they occur in consider- 

 able numbers every year during the late summer and 

 early autumn is sufficient to render this suggestion 

 doubtful. The general condition of these crabs leads me 



* Williamson has pointed out that if the soft mature female fails 

 to be fertilised, it will probably cast again in the following year. 



