CHINESE MITTEN CRAB — PANNING 371 



second year, and 2 to 3 times during their third year. The older 

 crabs shed only once a year. 



As the hatching of the larvae is usually completed in July, I count 

 the years of life of the mitten crabs as running from July to July. 

 Thus, according to my investigations, the average length of the crabs 

 is: the 1-year-olds about 13 mm; the 2-year-olds about 25 mm; the 

 3-year-olds about 36 to 38 mm. I estimate that the crabs about 56 

 mm long in the spawning swarms are 5 years old. 



NUTRIMENT 



In discussions on the evil of the mitten crabs the question has 

 always been an important one as to whether they attack and eat 

 fishes. It is easy to imderstand that every fisherman whose catch 

 falls off in vicinities where there are mitten crabs vows that they are 

 wanton destroyers of fishes. But the question is not so easily solved. 

 Timid fishes lose out, to be sure, where there are mitten crabs, and 

 the crabs do attack fishes that have been caught in nets, thus having 

 lost freedom of movement. They are omnivorous and eat whatever 

 they can get. That does not prove, however, that slow mitten crabs 

 catch speedy fishes at liberty. We have, in fact, kept fishes and 

 mitten crabs together for long periods in the same aquarium, a 

 mitten crab and a perch occupying the same corner, the fish directly 

 above the crab without being molested by it. Dr. H. Thiel has 

 proved through examinations of contents of stomachs of mitten 

 crabs that the largest portion of their food comes from the vegetable 

 kingdom, but they must to some extent get their food from the 

 animal kingdom as the lime that is necessary to harden the shell 

 otherwise would be lacking. They eat worms, especially Tubifex, 

 mussels and snails, inferior crustaceans, water insects, insect larvae, 

 and even dead substance of organic origin. Remains of fishes were 

 found only in 4 to 5 stomachs of 1,000 mitten crabs, and these came 

 from a region with huge swarms of young fishes. It may have been 

 the remains of cadavers of young fishes that had served the crabs 

 as food. 



VOLUNTARY MUTILATION AND REGENERATION 



The mitten crabs, like all higher Crustacea, are able to throw off 

 their pincer and walking legs and grow new ones at the same time with 

 their next new shell. This ability enables them often to save them- 

 selves when they are attacked. With lightning speed they discard 

 the leg the attacker has seized and then rush off. At the base of all 

 10 legs, between two joints which have grown together, there is another 

 joint with a very thin shell. Through certain muscular contraction 

 whereby the adjoining leg serves as lever, the endangered leg is broken 



114728—39 25 



