372 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



off in this joint. The same thing happens in cases of injuries. The 

 wound caused by the breaking off of the leg is immediately closed with 

 a thin membrane already formed so that all loss of blood is avoided. 



Shortly before the next shedding takes place, a bud grows through 

 the scar where the leg was severed and in it is formed a regenerated 

 leg folded in two (pi. 5). It straightens out in the next shedding but 

 is at first somewhat smaller than the discarded limb and lacks always 

 the characteristic pilroe, which makes the fishermen think that they 

 here have an entirely different animal when they find a mitten crab 

 with two regenerated pincers in their by-catch. This lack of pilroe 

 on the regenerated limb is interpreted as a retrogression to an original 

 hairless form, but proof to this effect is lacking (pi. 5). 



How much of this self-mutilation is dependent on the ability to 

 renew discarded limbs is realized by the fact that the crabs are very 

 little inclined to self-mutilation when the time for the next shedding 

 is still remote. 



MITTEN CRAB BURROWS 



It is known that many tropical crustaceans that live in tidal regions 

 on the coast or in the river mouths dig burrows for themselves into 

 which they retire during ebb tide. The mitten crabs do it also in the 

 tidal regions of German rivers. We find their burrows in firm marsh 

 bottoms everywhere on the banks of the Elbe tributaries and in 

 canals which dry out in ebb tide. It is easy to recognize their low 

 and wide entrances and not to confuse them with the roimd openings 

 to the burrows of the water voles. The burrows are always dug to 

 slant downward and filled with water, which makes it possible for the 

 crabs to await here the return of the water with high tide. Where the 

 burrows are numerous, the undermined shore finally caves in and 

 thus the mitten crabs are the cause of considerable damage in many 

 places (pi. 6). 



DAMAGE CAUSED TO FISHING 



Fishermen maintain that the mitten crab catches and eats fishes in 

 open waters. However, this does not tally. The healthy fish is 

 much too quick and the mitten crab much too slow for that. Fisher- 

 men maintain also that the crab destroys the spawn and the fry. 

 This could hardly be the case either. But in other ways they do a 

 lot of damage, as for instance when fishes like flounders are caught 

 in place nets. When the net reaches the bottom the crabs crawl 

 high up on the net, eating the defenseless fish and becoming entangled 

 with their many legs in the fine net threads. In their attempts to 

 escape they tangle up the nets and finally cut them into pieces with 

 their jaws. To the loss in catch there is added the destruction of 

 nets and the loss of time caused by the constantly necessary mending 



