34 A MANUAL OF ZOOLOGY 



fastened in any way to the walls of the cavity? If possible 

 find some communication of this cavity either with ■ th^ 

 interior or exterior of the body. 



Divide the head vertically along the median line and 

 find the following: the opening of the mouth, the horned 

 beak, one part shutting under a larger. Which is dorBal? 

 Which is ventral? 



Notice the somewhat spherical buccal body. Of what 

 is it composed? What is its use? Find the oesophagus 

 running back through the bucca;i body. Find the lingual 

 ribbon. Follow the oesophagus posteriorly through the 

 head to the body. Which side of the liver does it pass? 



Around the oesophagus posterior to the head, notice 

 the cartilaginous cranium. What does this cranium con- 

 tain? Are there any ganglia elsewhere around the oesoph- 

 agus? Find the stellate ganglia referred to before. Trace 

 the radiating nerves to the differnt parts of the mantle. 

 The anterior branches may be traced through the retrac- 

 tors to the infra-oesopliageal ganglion. 



Find the large optic ganglia by removing the ventral 

 side of the head. Look for the auditory chambers as the 

 cartilage is cut away. The pedal, the pleural, and the 

 visceral ganglia are fused and lie ventrally, between the 

 optic ganglia. They together make up the infra-oesoph- 

 ageal mass. This mass is prolongated anteriorly into the 

 pro-pedal ganglia, from these ten nerves pass to the arms. 

 From the lower position of the infra-oesophageal maSs 

 the siphon neryes are given oft. The pleural and the 

 visceral lierves pass off further back. 



Make a drawing of the free surface of a .vecUeal 

 se ctioTT'pufting '-in alh the -mouth parts, the oesophagusr 

 and the oesophagaerneFve~mass. - ,_ _._^- 



The study of microscopirr mounts through the anterior 

 part of the body will give better results than can be had 

 by the dissection of a larger specimen, especially for the 

 nervous system. Notice the following points under the 

 microscope, they being the most important. The series 

 of slides should be taken in order from the anterior toward 

 the posterior- part of the head. ' 



1. Cut surface of five pairs of arms. 

 ■ 2. Nerve ganglia near center of each Arm. 



