ARENICOLA. 187 



It should be noticed (i) that the hearts are paired, two- 

 chambered and independent in action; (2) that the hearts 

 are not on the main outer circle formed by the dorsal and 

 ventral vessels, but merely force blood into this current ; (3) 

 that the hearts pump blood to the gills and the body, and 

 hence they are not definitely either respiratory or systemic. 



Fig. 113.— View of Nerve-ring and Brain of 

 Arenicola. 



(After AsHWORTH and Gamble.) 





\ 



Note the Oesophagus cut across leavhig a hole round which the nerve-ring connects 

 the brain with the ventral nerve-cord. 



The nervous system in Arenicola consists of a paired 



brain in the prostomium, a ring round the pharynx in the 



Nervous peristomium and a ventral nerve cord running 



in the median ventral wall of the body. There 



are no ganglia. Arenicola has no eyes but is endowed with 



