of the Fishery Board for Scotland. 



115 



They were caught on July 12, when the creels were shot close inshore 

 near low-water mark. The next smallest, viz. two at 3|in. and 3|in. 

 respectively, were caught in November in 24 fathoms. The fishermen 

 agree in saying that they never get any crabs smaller than 3in. across 

 offshore ; but that such crabs are often seen when the creels are 

 shot in summer near low-water mark. They are, however, able to 

 escape through the meshes of the net covering the creel. These crabs 

 may be seen in the pools at the edge of the tide during big ebbs. The 

 curves of the beach and creel crabs only overlap very slightly ; in fact 

 they may be said to be quite distinct. Now, it is impossible that the 

 crabs in the beach group could by one casting enter the creel group of 

 crabs. There is a very large gap between the two, which must be filled 

 by another group of crabs which is not represented, except by one or 

 two examples. This group is to be found neither on the beach nor in 

 the creels, except when they are shot close inshore. There is every 

 probability that these crabs, which may for convenience be labelled 

 the 2^ to 4 inches group, will be found just outside low- water mark, 

 and this is rendered the more probable since certain members of the 

 group appear among the beach crabs and occasionally with the creel 

 crabs. They are littoral, but they do not appear to allow themselves to 

 be left dry at low water. In the Report of the Crab and Lobster 

 Commission, Mr Roach, a witness, said he has been to a place behind 

 the breakwater (Plymouth) every year, and caught small crabs, but no 

 large ones ; therefore concludes that the small crabs are a distinct 

 species : he thinks the place a nursery for them " (p. 56). To complete 

 the cycle, then, there are two groups wanting — viz., Group I. from the 

 Megalopa stage to the crab of one inch across, and Group TIL, those 

 from 2^ to 4 inches in size. 



The distribution of the crab may then be tentatively described as 

 follows : — Group I., the postlarval stages and earliest young stages up 

 to ^-inch in breadth, which is probably restricted to the shallow shore 

 waters where it was hatched ; Group II., the beach crabs, from \ to 

 2| inches, which are to be found between tide-marks, usually left 

 dry by the ebb; Groups III., the crabs from 2| to 4 inches, which 

 appear to be confined to the littoral waters just outside low- water 

 mark; Group IV., crabs of 4 inches and upwards, which may be termed 

 the mature group, and which are to be found in winter offshore beyond 

 the twenty fathom line, and in spring and summer in the inshore waters 

 sometimes even within tide-marks. The sizes which have been given 

 to the groups are only intended as approximate. It is very unlikely 

 that the various groups are separated sharply. 



As to the age at which a crab becomes mature, I can furnish no data. 

 That can only be determined when it is known how often a crab casts 

 before it arrives at a size of 4 inches, and also how often the young 

 crabs may cast each year. These facts, and the rate of increase at each 

 cast, remain to be discovered. 



The irregularity in the rate of growth may be due to two factors — 

 (1) a difference in size between individuals in the same larval stages, 

 which difference would be perpetuated, and probably increased, with 

 each moult ; and (2) the possibility of more frequent casting in the 

 case of certain individuals during the early stages. The moulting 

 is probably directly due to the supply of food, and this is no doubt 

 subject to considerable variation in the case of different individuals. 



A general description of the life-history of the crab may be here pro- 

 posed. It rests directly on the conclusions come to above with regard 

 to Groups I. and ILL, and remains or falls with the future proof of their 

 reliability or error. The crab hatched in the inshore waters, when it 



