-EARTHWORM. 21 



(a) On the dorsal side of the pharynx in the 

 2d or 3d somite a pair of pyriform 

 white bodies united in the median line : 

 the cerebral ganglia. 



(b) From each lobe a nerve-cord, the circum- 



cesophageal commissure, passes down at 

 the side of the pharynx, in the con- 

 striction between the bnccal sac and 

 the pharynx, to the suboasophageal gan- 

 glion (first ventral ganglion) on the lower 

 side. 



(c) From the suboesophageal ganglion a long 



double ventral nerve-cord passes poste- 

 riorly in the mid ventral line. 

 Peripheral Nervous System. 



(d) Two large nerves which run anteriorly 



from the cerebral ganglia. 



(e) A nerve from each half of the circum- 



03sophageal commissure near the union 

 of the two halves on the ventral side. 

 (/) Typically three pairs of nerves in each 

 somite : two pairs arising from the gan- 

 glion and one pair (septal nerves) from 

 the cord immediately behind the dis- 

 sepiment. 

 Make a diagram (X 6) of the nervous system. 



(At this point the buccal sac, C. II. 5. (a), may 



be looked for.) 



