128 CitAYFiSll, LOBSTERS, SlTDEliS, AND INSECTS 



portions, a cardiac division and a pyloric division, similar 

 to tlic stomach of a starfish. Tlie pyloric division opens 

 into the intestine, whicli 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 " hvers," that open 



Dorsal blood v essel Heart Ovurtj 



Brain ganglion 



Greengland 

 Mouth 

 Digestive gland 

 Siiimmereis ' Ventral blood vessel 



Fig. 70. — Structure of a crayfish. 



through short ducts into tlie anterior eml 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 outsitle of the stomach 

 to the walls of the l^ody. 



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

 fish consists of botli plant ami animal matter, i:)referably 

 the latter. These animals sometimes destroy vegetables 

 in gardens, jjut their thet consists chiefly of worms, snails, 

 and insect larva\ Tlie crayfish is also a scavenger and 

 devours dead fish, clams, and other sulistances that might 

 pollute the wa,ter. Tliey sometimes eat their own cast 

 skins, tlie .sliells of snails, and occasionalh', each other. 

 Soiuetimes the food is gnawed off directly by the mandifiles, 

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



