200 THE BIOLOGY OF THE ANIMAL 



How do they communicate with the ventricle? 

 What is the shape of their cavity? What is their 

 relation to the gills? Look for veins running 

 along the upper edges of the gills and communi. 

 eating with the auricles. 



0. — The Nervous System. 



Using an alcoholic specimen, and dissecting in 

 a dish of fifty per cent, alcohol, endeavor to make 

 out the following parts : 



a. The cerebral ganglia. — Separate the palpi on 

 each side of the mouth, and just under the skin, 

 between their bases, the ganglia will be found. 

 What is the position of the ganglia with regard 

 to the mouth ? How many are there ? What is 

 their shape? Size? Color? In Avhat direction 

 do nerves pass off ? Look for nerves passing to 

 the anterior adductor muscle ; to the palpi ; to 

 the mantle lobes ; to the foot, connecting with 

 the pedal ganglia, and hence called cerebro- 

 pedal connectives ; to the parieto-splanchnic 

 ganglia at the posterior end of the body, and 

 forming the cerebro-splanchnic connectives, 

 and from one cerebral ganglion across over the 

 mouth to the other ganglion, the inter- cerebral 

 commissure. Do you find that these gangha 

 are bilaterally symmetrical as regards position 

 and branches? 



I. The parieto-splanchnic or visceral ganglia. — 



To see these, separate the gills at the posterior 

 end of the body. Compare these ganglia with 

 the cerebral ganglia in all points of structure. 

 Endeavor to make out nerves running to the 



