100 THE FRESHWATER MUSSEL. 



a third of the length of the foot from its anterior 



end. 

 To find the pedal ganglia, split the anterior part of the 

 foot with a scalpel in the median plane, and dissect the two 

 halves apart until the ganglia are met with. The junction 

 of the muscular and visceral portions is very clearly defined, 

 and the ganglia lie close to it, in the visceral portion. 



Each pedal ganglion gives nerves to the foot. 



The auditory organ or otocyst, which lies a little 



behind and below the ganglion, is innervated from 



the cerebral ganglion. 



3. The cerebro-pedal connectives are a pair of nerve-cords 



connecting the cerebral ganglia with the pedal 

 ganglia. They run in an almost straight course 

 between the two ganglia, and are easily exposed. 



4. The visceral or parieto-splanclmic ganglia are a pair 



of closely apposed ganglia, on the ventral 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 already been done. The visceral 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. 



5. The eerebro-visceral connectives are a pair of long 



nerve-cords which connect the cerebral with the 

 visceral ganglia. 



From each cerebral ganglion the connective 

 curves upwards and backwards through the visceral 

 mass, lying close to the surface. It then runs 

 backwards along the inner surface of the kidney 

 to the visceral 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. 



