81 



have been determined by the observations on larger crabs watched 

 for periods long enough to allow of at least one ecdysis taking 

 place, and by the results of marking experiments. 



The chart of growth (fig. 8) which is submitted here to indicate 

 the mean growth of the female of this species may not be absolutely 

 accurate, but I do not think it is far from being so. It is almost 

 precisely the same as that given in 1905. In this case I have 

 ventured to picture growth over a large number of years, so as to 

 permit of the discussion of several points of interest connected 

 with this species and Crustacea in general. 



The spawning season of the crab appears to be practically 

 the same all round the British Islands. It may be said to last 

 from November to February, only varying in different regions 

 by being a little earlier or a little later. This at all events is true 

 of the Cornwall region according to Cunningham, of the east coast 

 of Scotland and the north-east coast of England from the informa- 

 tion derived by Williamson and by me. Hatching takes place 

 from July to October. From this it may be gathered that the 

 incubation is one of about eight months, and experiments made 

 on the Northumberland coast have demonstrated that this is about 

 the length of the period. 



After hatching, the protozoeae are subject to a drift along the 

 coast for about a month or six weeks, and as has already been stated, 

 the megalopa and the young stages which follow it reach the 

 bottom, not usually inshore but in moderate depths outside. They 

 gain the inshore region for the most part during the second year. 

 After November of the second year they leave the tide region, 

 and some return to the shore in the following summer. A few 

 may return in the next one or two summers, but the majority do 

 not again venture between tide marks. Outside, however, they 

 repeat on a larger scale the inward and outward migrations. The 

 population of crabs as a whole migrates offshore in winter and inshore 

 in summer, as is well-known to the fishermen. As a result of 

 marking experiments it has been proved that the mature female 

 crab migrates before coming into berry, that is to say, before 

 spawning, in a contranatant direction. The Northumberland 

 crabs, for example, migrate for the most part to the southern 

 side of the Firth of Forth, but some reach the north side, or a part 

 of the coast still further north ; two have been recaptured on the 

 southern shore of the Moray Firth, at Banff. 



