THE ARTHROPODS 



373 



Next to the lobster, the crabs are important as articles of 

 human food. The blue crab is the favorite. Spider crabs 

 and fiddler crabs are not used as food. The " soft-shelled " 

 crabs of our markets are simply individuals which have 

 recently shed their shells (i.e., molted), and the new shell 

 has not had time to harden by deposit of lime salts. 



Crayfishes have long been used for food in France and 

 elsewhere on the continent of Europe. More than thirty 

 years ago Huxley wrote that Paris paid over $80,000 per year 

 for crayfishes. In the United States they are found in 

 special markets of the large cities. Half a million are shipped 

 annually from the Potomac River. Oregon ships more 

 than 100,000 pounds. The demand is increasing, and it will 

 probably pay to have crayfish farms on which to raise them 

 for market. Land too wet for agriculture might be so used. 



The shrimps seen in our markets usually come from the 

 Pacific coast, and the trade in them is worth many hundred 

 thousands of dollars annually. Only the abdomens are com- 

 monly seen in the markets, and the bright red color is due 

 to their having been boiled. 



316. Other Crustaceans. Besides the decapods, there 

 are many thousand species of crustaceans, from which we 

 select a few for a brief study which will 

 give us a better appreciation of this type 

 of arthropods. 



The wood-lice or sow-bugs, and the 

 similar pill-bugs, which live under stones 

 and logs, are easily kept in a jar contain- 

 ing large pieces of bark. Small bits of 

 bread, butter, apple, and other foods 

 should be placed in the jar occasionally. 

 Keep the bark moist, not wet. The 

 most interesting adaptation of these animals is for breathing. 

 The appendages of the abdomen have been modified into 

 breathing organs and covers for them. They are thus fitted 



FIG. 123. Sow-bug seen 

 from dorsal side. 

 (From Morse.) 



