of the Fishery Board for Scotland. 



113 



obtained iu August showed small buds of new limbs. These had been 

 evidently present when casting took place. The loss of the limbs had 

 in these cases occurred too soon before casting to enable the new limb 

 to be completely formed. 



In adult crabs also, which, from their dirty condition, could not have 

 cast for two or three years, the brown scar on the second joint has been 

 Found to be covered with large barnacles, Anomia, and zoophytes, which 

 clearly indicated that the renewal of the limb was not a process which 

 was inaugurated immediately on the injury being sustained. 



A crab does not always throw off an injured limb. Many crabs are 

 found which have lost the last joint of a limb, viz. the dactylopodite. 

 In these cases a black scar covers the place of injury. Sometimes the 

 muscle is shrunk away from the shell, leaving it to project in front of 

 the black scar. This not unfrequently happens in cases of injury to the 

 last joint of the biting claw. A soft crab showed a rather unusual 

 condition. A limb had been broken off near, but not at, the fracture 

 plane. The shell had grown inwards over the scar, reducing the aperture 

 very much. A female in one of the tanks at Dunbar had received 

 an injury to one of the walking limbs ; it had been broken off about 

 the middle of the fifth joint, the propodite. The muscle was decay- 

 ing ; there was no appearance of a scar. Even in this case the crab 

 had not got rid of the injured member. 



As to the repair of injuries to the carapace, this seems to be depend- 

 ent on the activity of the chitinogenous epithelium, and only occurs at 

 the time of casting or while the crab is still soft. When the fishermen 

 are testing the soft crabs in autumn they are more than likely to push 

 the thumb through the shell. The crab is then often thrown into the 

 water, and numerous examples of the repair of the injury have come 

 under my notice. It is not at all difficult to get during the winter, in 

 the catches of the fishermen, some of the crabs which had been thus 

 treated. Some of these show a complete, and others a partial repair of 

 the shell. Old -looking crabs are from time to time captured which 

 show more or less severe injuries to the carapace. In these the parts 

 where the flesh has been exposed are covered simply by a soft black 

 scar, beneath which a thin live skin is found. It is therefore apparent 

 that the renewal of the shell over the injured part does not take place 

 during the whole interval between two castings, but only during the 

 time the dermis is active in thickening the shell, a period of, on the 

 average, four months probably. Again, the chance of repair to the 

 injury will be the greater the sooner it occurs after casting. Even on 

 casting the old injuries are not always completely repaired. The 

 injured area may, in the soft crab, be of less extent, but cases have 

 been noticed where soft crabs showed injuries which had evidently been 

 present before casting. In such cases it has probably happened that 

 the chitinogenous epithelium had at that part been destroyed, and at 

 the time of casting it had not been completely renewed by the ingrowth 

 of the epithelium surrounding it. 



The regeneration of the limbs only takes place when the crab is 

 preparing to cast. The repair of injuries to the carapace only take* 

 place at the same period, or during the time the crab is soft. The 

 presence of buds of new limbs may be regarded as an indication that it 

 is about to cast. 



In the case of adult crabs the new limb cannot reach the size of the 

 other limbs until after at least two moults. Crabs which have diminu- 

 tive chelae are not uncommon. 



Kate of Growth and Distribution. 



With the view of arriving at some determination of the rate of growth 

 of the crab, the method which has been used by Petersen in connection 



