28o 



SWAN MUSSELS. PHYLUM MOLLUSCA 



NERVOUS SYSTEM 



The nervous svstem (Fig. 208) comprises three pairs of ganglia 

 with commissures uniting them. The cerebral gangHa are two 



i^a.ad. 



Fig. 208. — Details of the anatomy of the swan mussel. 



A, Diagram of a transverse section through the foot, showing the principal blood vessels and, by means 

 of arrows, the course of the circulation : each gill is cut at an interlamellar junction. — After Howes. 

 B. the mouth and neighbouring structures from in front ; C, a portion of the shell, in section ; D, a 

 plan of the nervous system from above, with the visceral commissures more widely parted than they 

 are in the animal. 



a.ad.. Position of anterior adductor ; aff.br., afferent branchial vessel ; au., auricle ; B, glandular part of 

 kidney ; c.p.c, cerebropedal commissure ; c.p.g., cerebral (cerebropleural) ganglion ; eff.br., efferent 

 branchial vessels ; /., foot ; g., gills ; i.p., inner labial palp ; K.o., Keber's organ ; m., mouth ; ml., 

 mantle ; ncr., nacreous layer ; o.p., outer labial palp ; p.g., pedal ganglion ; pern., periostracum ; 

 pl.n., pallial nerve ; prm., prismatic layer ; v., ventricle ; v.c, vena cava ; v.cm., visceral commissure; 

 v.g., visceral (parietosplanchnic) ganglion. 



small, orange-coloured bodies, placed one on each side behind the 

 mouth, above which they are connected by a cerebral commissure. 

 They are sometimes known by the name ' cerebro-pleural ', 

 because each contains the elements of two ganglia, the cerebral 



