CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 129 



passed into the mouth by the small pmcers on the walking 

 legs. 



The food is partly masticated by the mandibles, maxillae, 

 and foot jaws. It then passes into the stomach, where it 

 is farther comminuted by the churning action of the 

 chitinous walls aided by the chitinous teeth. The stomach 

 is really a masticating organ and has no digestive fimction. 



As soon as the food leaves the stomach, it receives the 

 fluids from the digestive glands and the work of digestion 

 takes place at once m the anterior end of the intestine. 

 The food then passes through the walls of the intestiae 

 directly into the blood which chstributes it all over the 

 body. 



The circulatory system. — The circulation of the crayfish 

 is weU developed. The heart (Fig, 70) is situated in the 

 dorsal part of the thorax. Fi^'e arteries originate from the 

 anterior end of the heart. One goes forward to the eyes, 

 two (paired) supply the antennas, antemiules, and stomach 

 with blood, while two (paired) furnish blood to the diges- 

 tive glands. From the posterior end of the heart two single 

 arteries spring, one of which, the dorsal artery, passes back- 

 ward along the dorsal side of the iutestine and furnishes 

 blood to the intestine and dorsal muscles through many 

 Ijranches. The other passes directly downward and joins 

 the ventral artery which runs lengthwise of the body below 

 the nerve cord (Fig. 70). The A^entral artery sends branches 

 to the legs and abdominal appendages and muscles. All of 

 these arteries divide and subdivide into smaller and smaller 

 branches until they end in microscopic vessels called capil- 

 laries. The capillaries empty the blood into irregular 

 spaces, or sinuses, that occur all through the body between 

 the muscles and other organs. These sinuses communicate 



herkiok's zool. — 9 



