330 



MOLLUSCA 



that tlie pleural and parietal ganglia are separate. If the commissures 

 be sliort, the ganglia are coUeeieJ near ihe pharxaix and, thus freed from 

 the bodv torsion, are symmetrical (oi-lhoiiaiii>iis. fig. ,^30, //). If the 





\. 



■^*^ 



Fig. r.5.— Row of lecih from the radula of Trothus iiiurdiius y.\H-:r Schmarda). 



Fig. 336. 



l'"^- ,;37- 



Fig. 3^6. — /. s(ri'|ilonrur(His nervous system of Pdhidiiui (after TTerint;, from 

 Gegcnbaur). //, orllioiieuious s\slein of I.iiini,,,i lafler l.aea.'.e IHitliiers'l. .1. 

 visceral; /■>, Iniceal; ( ', eereliral; />, |H'ilal; /'/, pleural; ,s/i, .s/i, suli- ami supraintestinal 

 ganglia; n, olfaetor\" ner\-e; o, oloe\sl. 



Fig. 3,^7. — Itiagram oi eireulalion in Poris lafler l.euekarlV <;, aurlele; 

 c, gills around ;inus; /, tenlaek-; ■;'. \enlriele; .v, \essels reluming \'enous blood from 

 the body. 



ccrehrovisccral commissures he loirger, the result is almost always strep- 

 toneury. IMeural and \isceral ganglia hold their phice, liuf the right 

 parietal ganglion crosses aboye the intestine to the left side (hence called 



