470 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



The crabs probably stay in the offshore waters from 

 December to February, and it is here that the females 

 spawn. The inshore migration begins in February, and 

 in May the bulk of the crabs are probably back in the 

 inshore waters again. The hatching of tin 4 larvae takes 

 place in the warm inshore waters, and casting process is 

 performed, and, in the case of the females, fertilisation is 

 effected immediately after ecdysis. In the autumn the 

 offshore migration again commences, and the cycle is 

 repeated. 



Inshore migration 



Spawrana time 

 M Hotckina time, 

 til Casting time 



October 

 fessaa 



December 

 November 



^r 



Fig. 13. — Diagram illustrating the annual migratory cycle of mature 

 crabs. The three processes — casting, spawning and hatching — 

 probably do not take place in one cycle. 



It must be remembered, however, that in the mature 

 female crab casting and fertilisation in the autumn is not 

 necessarily followed by spawning in the same winter. 

 Furthermore, casting w T ill only take place once in two or 

 three years. But when spawning does take place it is in 

 the offshore waters, and the hatching is always in the 

 inshore waters. 



As suggested by Williamson, the main reason for 



