THE JOINTED-FOOT ANIMALS 



163 



given to the distribution and habits of this crab. It is caught 

 most easily soon after the molting, which takes place in early 

 summer, and is then called a soft-shell crab ; at this time 

 also the species is considered most valuable as food. 



The blue crab is not confined to the salt water, for it is 

 found frequently in rivers some distance from bays. Wher- 

 ever they are, they devour much 

 of the organic waste that flows 



V [x 



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XL 



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Fig. 88. Fiddler crabs. (Slightly reduced) 



down to the sea. They 

 are therefore impor- 

 tant as scavengers. 



The most noticeable 

 thing in the structure 

 of the fiddler crab 



(U'ca pugila'tor, Fig. 88) is the presence in the males of a 

 large cheliped. Sometimes it is the right one that is larger, 

 and sometimes the left one ; the females have their chelipeds 

 small and of equal size. The name "fiddler" is supposed to 

 have been derived from the fancied resemblance of the large 

 cheliped to a fiddle, and of the small one to a bow. 



The Sow Bug. The sow bug, and a related species called 

 the pill bug because of its habit of rolling up into a ball, are 

 found under stones, boards, logs, and in other dark, moist 



