32 



This is the only Invertebrate of which we have actual know- 

 ledge of such a migration taking place, but it is probable that some 

 of the other and at all events the larger Crustacea and the Cepha- 

 lopod Mollusca have the same power. 



A summary may now be given of the growth of the crab, 

 as presented in fig. 8. 



TABLE in.— CANCER PAGURUS (FEMALE). 



The chart and the table may be and they are not intended 

 to be more than approximately correct, but even so what they 

 demonstrate is of importance with reference to a species of con- 

 siderable economic importance, for when all is said it is the mainstay 

 of the inshore fisherman. 



According to the scheme set forth in both the table and chart 

 a female crab bears berries three times between its fifth and its 

 fourteenth year. Apart from theoretical considerations relating 

 to growth we have facts to prove that such intervals actually 

 occur. It is well-known that the two-year period characterises 

 the smaller crabs. The evidence for this has been given in 

 previous reports ; the results of observations of crabs in confine- 

 ment and of markmg experiments. Even theoretically apart 

 £rom such facts it is plam that the annual spawning which has been 

 assumed to take place is impossible. At the period of casting, 

 which in the years immediately preceding maturity takes place 

 in the autumn and continues at and after maturity at the same 



