94 THE FEESH WATER MUSSEL 



4. The osphradial or parieto-splanchnic ganglia are a pair 



of closely apposed ganglia, situated on the under 

 surface of the posterior adductor muscle about the 

 middle of its length. 



Pass a seeker into the cloacal cavity, and along the median 

 supra-branchial passage, and lay open this latter, if it has 

 not been already done. The osphradial ganglia are then 

 readily found in the position noted above. 



From the ganglia nerves are distributed to the 

 posterior adductor, the mantle, and other parts. 

 These ganglia were named 'osphradial' by Spengel, 

 who believes them to correspond with the ganglia so 

 named in other molluscs, in which they supply special 

 sense-organs, presumably of smell. 



5. The cerebro-osphradial connectives are a pair of long 



nerve-cords which connect the cerebral with the 

 osphradial ganglia. 



From each cerebral ganglion the connective 

 curves upwards and backwards through the visceral 

 mass, lying close to the surface. It then runs 

 straight back along the inner surface of the kidney 

 to the osphradial ganglion. The part in relation 

 with the kidney is very easy to dissect : in front of 

 the kidney the dissection is more troublesome, but 

 presents no serious difficulty. 



F. The Digestive System. 



I. The alimentary canal is a convoluted tube, the greater 

 part of which lies in the visceral mass, imbedded in 

 the liver and generative organ, while the terminal 

 portion runs back through the pericardial cavity to 

 the anus. 



Insert a seeker into the mouth, and using this as a guide 

 slit up the oesophagus and stomach with scissors. Follow the 

 coils of the intestine in the same way to the point where the 

 rectum enters the pericardial cavity. Slit up the ventricle to 

 see tlie rectum, which it surrounds. 



