of the Fishery Board for Scotland. 



79 



open, since, if they were decked, they would not be suitable for the 

 transport of the large fleet of creels. 



The present research* has been carried on with the view of adding to 

 the knowledge of the life-history of the crab, upon which legislative 

 interference with the fishery ought to be principally, if not altogether, 

 based. A number of new facts are brought to bear upon such 

 important questions as the size at maturity, the seasonal migrations, 

 distribution, the season of casting, and other points. 



Size of Crab at Maturity. 

 The Mature Female Crab. 



There are three characters by which a mature female may be recog- 

 nised, viz. (1) its being berried, (2) the ripeness of the ovary, (3) the 

 presence of sperms in the spermatheca. 



The first character is one which can only be applied as a test of 

 maturity in a comparatively small number of cases, owing to the fact 

 that the berried crab, unlike the berried lobster, is rarely captured in 

 the creels. Cunninghamf considers that the reason for this most 

 likely is " that the movements of the female crab are hindered by the 

 mass of spawn much more than are the movements of berried lobsters. ' 

 While this may be the case to some extent, it seems probable that the 

 berried crab is forced to keep in shelter, in some crevice or hole, where 

 it will not be exposed to the attacks of other crabs. When not berried 

 the abdomen (or tail) is the least vulnerable part of the body, but 

 when it carries the large mass of eggs it is kept extended from the 

 body, and could then be easily torn off. The berried crabs kept in the 

 tanks at Dunbar did not appear to move about much, for the food 

 (pieces of fish) which was scattered over the bottom of the tank was 

 often left untouched, while in the tanks which contained unberried 

 crabs the food was always devoured during the night, a fact 

 probably due to the reluctance of the former to leave their retreats, 

 where they lay half buried in the sand. This, no doubt, accounts for 

 their absence from the creels ; their occasional capture may have 

 resulted from the fact that the creel has fallen quite close to where 

 they lay hid. There is evidence, however, that the berried female 

 undertakes a journey from deep water to the shallows. 



If, then, the berried condition were the only standard, we should have 

 few data upon which to found our conclusions. But, fortunately, it is 

 possible, for several months afterwards, to recognise a crab which has 

 borne and hatched its eggs. As Spence Batej pointed out, after the eggs 

 hatch, the empty egg-capsules remain attached to the swimmerets for some 

 time. He added that they were got rid of when the crab cast. They 

 are, however, in many cases thrown off before casting. The main mass 

 of empty egg-capsules is sloughed off shortly after the eggs hatch, but 

 a few mav be detected on the bases of the endopodites (viz., on the 

 posterior surface of base of endopodite of 1st ai d inner surface of base 

 of 4th swimmeret) in some cases five months after that period. We 

 thus have a very useful distinguishing mark of a mature female, and, 



* I beg to .acknowledge my indebtedness to Mr. W. Hutchison, Dunbar, for much 

 valuable assistance. During my absence from Dunbar he took charge of the labelling 

 experiments, and of the different crab statistics kept at Dunbar in 1899. 



f Report of the Executive Committee for Fisheries, Cornwall County Council, for 

 1897 4898. Penzance, 1898, p. 5. 



X Reports of the Crab and Lobster Fisheries of England, Wales, and Scotland. Buck- 

 land, Walpole and Young [C. 1695], 1877, p. 56. 



