THE CRAYFISH 



229 



sides this value as a food, they are also used by man, the shrimp fisheries 

 in this country aggregating ■ over $1,000,000 yearly. 



\The Blue Crab. — Another edible crustacean of considerable economic 

 importance is the blue crab. Crabs are found inhabiting muddy bot- 

 toms ; in such localities they 

 are caught in great numbers 

 in nets or traps baited with 

 decaying meat. They are, 

 indeed, among our most valu- 

 able sea sca\'engers, although 

 they are carnivorous hunters 

 as well. The body of the 

 crab is short and broad, be- 

 ing flattened dorso-ventrally. 

 The abdomen is much re- 

 duced in size. Usually it is 

 carried close to the under 

 surface of the cephalothorax ; 

 in the female the eggs are carried under its ventral surface, fastened to 

 the rudimentary swimmerets in the position which is usual for other 

 crustaceans. The young crabs differ considerably in form from the adult. 

 They undergo a complete metamorphosis (change of form), and their 

 method of life differs from the adult. Immediately after molting, crabs 

 are greatly desired by man as an article of food. They are then known 

 as " shedders," or soft-shelled crabs. 



Other Crabs. — Other crabs seen along the New York coast are the 

 prettUy colored lady crabs, often seen running along our sandy beaches at 

 low tide ; the fiddler crabs, interesting 

 because of their burrows and gre- 

 garious habits ; and perhaps most 

 interesting of aU, the hermit crabs. 



The edible blue crab. From photograph loaned 

 by the American Museum of Natural History. 



The fiddler crab. From photograph 

 loaned by the American Museum of 

 Natural History. 



Hermit crab, about twice natural size. 

 From photograph loaned by the Amer- 

 ican Museum ot Natural History. 



The hermit crabs use the shells of snails as homes. The abdomen is soft, 

 and unprotected by a Umy exoskeleton, and has adapted itself to its con- 



