EARTHWORM. 95 



On the middle line of the floor of the body find the 

 ventral nerve-cord, with its numerous enlargements (gan- 

 glia). Are these latter equal in number to the somites? 

 Do they occur in or between the somites? Trace the 

 nervous system forward and find out how it connects 

 with the brain. Draw the brain and twenty ganglia of 

 the ventral chain connected together. Just outside the 

 ventral nervous cord find in each segment (except a few 

 anterior) a minute coiled tube (nephridium) . These are 

 the excretory organs of the worm, and each opens sepa- 

 rately to the exterior between the rows of chsetae. 



