PHYLUM ANNELIDA 99 



(3) The ventral blood vessel: Loosen up the intestine completely on the left 

 side so that it can be pressed over to the right side to enable you to see the 

 median ventral line. Look here on the underside of the intestine for a brownish 

 line, the ventral blood vessel. It is easiest to see under the dilated portion of 

 the intestine behind the region of the seminal vesicles. Look for branches of 

 the ventral blood vessel to the intestine, body wall, and the nephridia. Trace 

 the connection of the hearts with the ventral blood vessel and follow the latter 

 forward as far as you can. 



(4) The subneural vessel: Directly under the ventral blood vessel is a white 

 line, the ventral nerve cord. Cut this through at some convenient point back of 

 the region of the hearts, pull up a short strip of it backward, and look on the 

 underside for a longitudinal vessel looking like a dark line running down the 

 middle of the white cord. Its branches from the nephridia and the body wall 

 may sometimes be found. It is called the subneural vessel. 



(5) The intestino-tegumentary vessels: Extending from the tenth segment 

 forward, an extra vessel will be found on each side of the wall of the intestine. 

 Hearts and other structures should be removed to see it. 



Make a drawing from the side of the parts of the circulatory system which 

 you have been able to find. Some specimens will show more of the vessels than 

 others. 



On living earthworms observe the rhythmic contractions of the dorsal vessel. 

 In which direction do the contractions travel? Read Hegner (p. 175) on the 

 course of the circulation in the earthworm. 



c) The digestive system: It consists of the following parts (Hegner, 

 pp. 169-71): 



(1) Buccal pouch: This is a small tube extending from the mouth through 

 about three segments. White, slender, muscle fibers, the dilators of pharynx, 

 attach it to the body wall and allow of its expansion. On the dorsal surface 

 of the buccal pouch, just before the pharynx begins, note the small, white, 

 bilobed brain. 



(2) Pharynx: This is the thick-walled portion following the buccal pouch. 

 The muscular fibers attaching it to the body wall are much more numerous than 

 in the preceding division. 



(3) Esophagus: This long, slender tube extends through the region occupied 

 by the hearts and seminal vesicles. These should be removed from the left side, 

 if not already done, so that it can be clearly seen. In its wall in the region of the 

 seminal vesicles are three pairs of brownish projections, the calciferous glands, 

 said to secrete calcium carbonate into the digestive tract. 



(4) Crop: The esophagus leads into the large thin-walled crop, which acts 

 as a storage reservoir for food. 



(5) Gizzard: Immediately posterior to the crop is the very thick-walled 

 gizzard, in which the food is ground to small particles. 



