62 THE EAKTHWOEM 



a. In each of the segments vii. to xi. a pair of large 



vessels arise from the dorsal vessel in the hinder 

 part of the segment. These ' hearts ' run round 

 the sides of the oesophagus to open into a median 

 vessel below : during life they are rhythmically 

 contractile, the contractions passing along them 

 from above downwards. In the fresh state each 

 has a moniliform appearance. 



b. Smaller vessels in the same region run from the 



walls of the oesophagus to the dorsal vessel. 



C. Two pairs of lateral vessels are present in each 

 segment of the intestinal region, returning blood 

 from the sides of the intestine, and opening into 

 the dorsal vessel. 



d. A pair of vessels in each segment run round the sides 

 of the coelom, and put the sub-neural vessel into 

 direct communication with the dorsal vessel. 



3. The sub-intestinal vessel runs backwards below the 



alimentary canal. The ' hearts ' open into it. 



a. The intestinal arteries arise from the sub-intestinal 



vessel and supply the intestine. Corresponding 

 arteries supply the oesophagus, crop, and gizzard. 



b. The nephridial arteries arise from the sub-intestinal 



vessel, one pair in each segment. They supply 

 the nephridia. 



4. The sub-neural vessel is a median vessel running under- 



neath the nerve-cord. It is connected in each seg- 

 ment with the dorsal vessel by a pair of vessels 

 already mentioned (2, d.), which run round the sides 

 of the coelom close to the border of the anterior 

 septum, each receiving on its way a large vessel 

 from the nephridium of its side, and several smaller 

 ones from the body-wall. 

 6. The lateral neural vessels are a pair of longitudinal 

 vessels running along the sides of the nerve-cord. 

 Paired vessels running in the ventral body-wall 

 communicate with them. 



