BEING A WORM 



191 



anterior end of the body. Blood also passes tliroush two intestino- 

 integumentary vessels which pass off at the 10th segment to supply 

 the walls of the esophagus and the skin, and to nephridia of that 

 region. Parietal vessels connect the dorsal and subneural vessels, 



cross Section of typyosolar vessel 



/ 



'>_Jat^rccl-y2eu:ral vessel 



V nerve 

 CorcL 



The '"hearts" of the earthworm. How do they function in circulation.^ 



that branch from the ventral vessel to supply the body muscle walls 

 and nephridia. Blood also passes from the ventral vessel to the body 

 walls, and to nephridia, and returns to flow, after passing through 

 capillaries, into the lateral neural trunks. In the subneural vessel, 

 the blood flows posteriorly and thence up by way of the parietal 

 vessels into the dorsal vessel. Both dorsal and ventral vessels supply 

 the anterior part of the worm. 



The Blood and Its Functions 



The blood of the earthworm consists of a liquid plasma, carrying 

 colorless corpuscles which are flattened spindle-shaped bodies. The 

 red color is due to hemoglobin, the same oxygen-carrying substance 

 found in the blood of man. But in the earthworm the plasma is 

 colored rather than the corpuscles. The exchange of food and 

 oxygen, which the blood picks up in the intestine and body walls, 

 respectively, occurs in the tiny lymph spaces around the individual 

 cells. Respiration takes place through the moist outer membrane 



