130 ELEMENTARY ZOOLOGY 



gizzard, and next the intestine wtyich opens externally in 

 the terminal segment through the anus. The anterior end 

 of the alimentary canal is more or less protrusible, while 

 the posterior portion is held more firmly in place by the 

 septa which act as mesenteries. Surrounding the narrow 

 oesophagus are the reproductive organs, three pairs of 

 large white bodies and two pairs of smaller sacs. 



Note the dorsal blood-vessel lying along the dorsal 

 surface of the alimentary canal, from the anterior por- 

 tion of which arise several circumcesophageal rings or 

 "hearts." These hearts are contractile and serve to 

 keep the blood in motion tfirough the blood-ve-ssels (see 

 later). In the most anterior of the body segments note 

 the pear-shaped brain or cerebral ganglion. 



TECHNICAL NOTE. Lilt carefully to right and left the repro- 

 ductive organs, thus exposing the oesophagus. 



Note three pairs of bag-like structures projecting from 

 the oesophagus. The front pair is the oesopJiageal pouches; 

 the next two pairs are the oesopJiageal or calciferous 

 glands. They communicate with the alimentary canal, 

 and their secretion is a milky calcareous fluid. 



Make a drawing that will show all the parts so far 

 studied. 



TECHNICAL NOTE. Cut transversely through the alimentary 

 canal in the region of the clitellum and carefully dissect the anterior 

 portion of the canal away from the surrounding organs. 



Note the dorsal fold of the intestine, typJilosole, ex- 

 tending into the lumen. This fold gives a greater surface 

 for digestion, and in it are a great many hepatic or special 

 digestive cells. The entire alimentary canal is lined with 

 epithelium. Observe just beneath the alimentary canal 

 the ventral blood-vessel, and still beneath this blood- 

 vessel the ventral nerve-cord. There is a slight swelling 

 on the nerve-cord in each segment of the body. These 



