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circulation. This animal is furnished with three blood 

 vessels, of considerable size extending from the head 

 to the tail. The largest runs along the back, and the 

 other two along the belly. The one that passes along 

 the back sends off a great number of ramifications on 

 each side, opposite to each other, nearly at right an- 

 gles ; each annular section has from it two branches, 

 one running to the right and the other to the left, 

 appearing to terminate in the largest that runs along 

 the belly. Probably the vessel that is situated on the 

 back is the artery which brings the blood from near 

 the head ; and the largest one on the belly is the cor- 

 responding vein, which carries the blood back near 

 the head, to the commencement of the artery. By a 

 minute attention to the bloodvessels, when the animal 

 is in motion, I think the blood may be seen to move. 

 This motion of the blood is not uniform as in the 

 more perfect animals ; but flows only at intervals dur- 

 ing the motion of the worm. May we not infer the 

 circulation from the inspection of the distribution of 

 the blood vessels ? We know that these vessels are 

 given them for important purposes, and to reason 

 from analogy, we can ascribe no other office to them 

 than the circulation of that fluid which they evidently 

 contain. The small vessel that runs along the belly 

 lies more superficially, and is confined to the skin. 



There is a curious fact relative to their blood ves- 

 sels : Tliey form a strait canal when in a state of 



