128 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 



portions, a cardiac division and a pyloric division, similar 

 to the stomach of a starfish. The pyloric division opens 

 into the intestine, which runs almost straight to the anal 

 aperture on the ventral side of the telson. The pyloric 

 division of the stomach is surrounded by two pairs of large 

 digestive glands (Fig. 70), often called " Uvers," that open 



Dorsal bloodvessel Ifeart Ovaiy 



Brainganglkn 



Greengland 

 ^Mauth 

 'Digestive gland 

 Swimmereis ^ '^T^ntral bloodvessel 



Fig. 70. — Structure of a crayfish. 



through short ducts into the anterior end of .the intestine. 

 The stomach is lined by a chitinous layer, and projecting 

 from its inside walls are several dark brown, chitinous teeth. 

 Strong muscles also run from the outside of the stomach 

 to the walls of the body. 



The food and digestive process. — The food of the cray- 

 fish consists of both plant and animal matter, preferably 

 the latter. These animals sometimes destroy vegetables 

 in gardens, but their diet consists chiefly of worms, snails, 

 and insect larvae. The crayfish is also a scavenger and 

 devours dead fish, clams, and other substances that might 

 pollute the water. They sometimes eat their own cast 

 skins, the shells of snails, and occasionally, each other. 

 Sometimes the food is gnawed off directly by the mandibles, 

 and sometimes it is torn off in bits by the large pincers and 



