BRANCH YERMES: THE WORMS I3 1 



swellings are the ganglia. How many pairs of nerves 

 are given off from each ganglion ? Observe in each seg- 

 ment, posterior to the first three or four, the successive 



Dorsal blood vessel 



lyphlosole 



intestine 



nepkrostome 



ventral nerve cord 



FIG. 26. Dissection to show alimentary canal in section and nephridia 

 of earthworm. 



pairs of convoluted tubes, the nephridia, or organs of 

 excretion. Each nephridium opens internally through a 

 ciliated funnel, the nepJirostome, within the body-cavity, 

 while it opens externally by a small excretory pore 

 between the setae on the ventral surface of the segment 

 behind that in which the nephridium chiefly lies. The 

 function of the nephridia is to carry off waste matter 

 from the fluid which fills the body-cavity. 



Trace the ventral nerve-cord forward to its connection 

 with the cerebral ganglion. Note the threat nerve-ring 

 or circumccsophageal collar connecting the ventral cord 

 with the brain. 



Make a drawing of the nervous system showing its 

 relation to other organs. 



Life- history and habits. The earthworm lives in soft 

 moist soil which is rich in organic matter. Its food is 



