NERVOUS SYSTEM. INVERTEBRATA. 45 



region of the mantle-border. From each posterior corner 

 arises another bundle of nerves (posterior pallial), which 

 innervates the posterior adductor and the hinder sixth 

 of the mantle-border. The branches of the pallial nerves 

 just before their final distribution are united by a ganglionic 

 cord (not shown in the specimen) that runs completely 

 round the mantle parallel to its edge. 



The cerebro-visceral connectives lie for their posterior 

 third upon the surface of the adductor ; anterior to that 

 point they traverse the superficial parts of the gonad to 

 reach the small cerebral ganglia. The latter lie behind 

 the mouth, united prseorally by a very long and delicate 

 commissure; they give off nerves to the anterior part of 

 the mantle and labial palps. The pedal ganglia are small 

 and contiguous in the mid-line ; they lie above the foot, 

 between the cerebral ganglia. 0. C. 1303 E I). 



43. Two specimens of the nervous system of a Pond-Mussel 

 (Anodonta cygnea], shown respectively from the left side 

 in situ, and isolated. The ganglia are more marked than 

 in MytiluS) but show much the same relative proportions 

 to one another. The cerebral lie at the postero-lateral 

 margins of the mouth, and are united praeorally by a long 

 commissure ; each gives off the usual nerves to the mantle, 

 palps, and anterior adductor. The pedal ganglia are closely 

 applied to one another, and are situated in the upper part 

 of the foot embedded in the viscera ; they give off 

 numerous nerves to the pedal muscles and integument. 

 The cerebro-visceral connectives run one on either side of 

 the body on a level with the line of attachment of the gills; 

 at their anterior end they lie far apart near the surface of 

 the visceral mass, but towards the visceral ganglion run close 

 together, between the organs of Bojanus. The visceral 

 ganglia are larger than either cerebral or pedal ; they are 

 fused together to form a bilobed mass v situated on the 

 ventral surface of the posterior adductor. They give off 

 several small visceral filaments from their anterior surface, 

 and two pairs of larger nerves from their lateral and 

 posterior borders. The lateral pair supply the gills, and 

 have at their origin a ganglionic area that underlies a 



