134 INVERTEBRATE ZOOLOGY 



join it with the suboesophageal mass, which is composed of the 

 visceral, pedal, and in front of the latter, the brachial ganglia. 

 Connected with the sides of the cerebral mass are the two optic 

 nerves, which widen out to form the large optic ganglia, and run- 

 ning forward from it are two small nerves which connect it 

 with the suprapharyngeal ganglia, a small mass above the hinder 

 end of the pharynx. From these ganglia small nerves pass 

 around the oesophagus to the pair of subpharyngeal ganglia. 

 From the forward surface of the suboesophageal mass, i.e., from 

 the brachial ganglia, ten nerves pass off to the arms. These 

 may be seen on the inner surface of the head after the removal 

 of the pharynx. From the hinder surface of the visceral 

 ganglia pleural nerves run to the stellate ganglia in the mantle. 

 Trace these nerves from the stellate ganglia to their source. 



The pen. Make a longitudinal slit in the mantle on the back 

 of the animal and remove the pen ; it will be seen to lie quite 

 loosely in its sac. 



Exercise 8. Draw the pen. 



