Crustacea. 



cidedly useful as a scavenger, disposing of a 



great amount of dead and decaying material 



which would pollute the water, 



such as dead fish, clams, etc. In 



eating, the big pinchers may 



tear the food to pieces, 



and then the smaller pinch- 



rn 



ers of the second and third 

 pairs of legs may transfer 

 the pieces to the mouth, the 

 entrance to which is sur- 

 rounded by the maxillipeds. 

 Or, instead of this process, 

 the crayfish may apply the 

 mouth directly to the foopl, 

 and gnaw it off in bits by 

 means of the mandibles and 

 maxillipeds. Crayfishes 

 are frequently guilty of 

 cannibalism. 



The Digestive System of 

 the Crayfish. The mouth 

 of the crayfish is on the 

 under surface instead of at | 

 the front of the head, as 

 in many animals. There 

 are six pairs of mouth parts, the 

 mandibles, two pairs of maxillae, and 

 three pairs of maxillipeds. These 

 jaws all move sidewise ; and when all of them 

 are closed, the third or hindmost pair of 

 maxillipeds cover all the others. The short 

 gullet passes straight up from the mouth to 



