694 



ZOOLOGY 



SECT. 



mentioned. A pair of buccal ganglia are connected by slender 

 nerves with the cerebral. At the base of each osphradium is 

 usually a small osphradial ganglion connected by a slender nerve 

 with the visceral. In all the Streptoneura (Fig. 598), in accord- 

 ance with the displacement of the anus and the coiling of the 



r.visc.com 



r.ct&n. 



l.clen 



visc.com- 



FIG, 598. Diagrammatic representation of the displacement of the mantle-cavity and associatec 

 parts in the Gastropoda. Enteric canal blue, blood-system red. A, rej 



symmetrical arrangement ; in B, C, I), are represented successive stages of displacement of 

 the mantle-cavity to the right and forwards ; in E, the anus and (primarily) right ctenidium 

 have passed the middle line. an. anus ; aort. aorta ; csr. g. cerebral ganglion ; /. cten. left 

 ctenidium ; /. cixc. com. left visceral commissure ; mant. mantle ; mo. mouth ; neph. up. nephri- 

 dial apertures ; pe<l. ;/. pedal ganglion ; pi., g. pleural ganglion ; /. cten. light ctenidium ; r. 

 vise. com. right visceral commissure ; rixc. com. visceral commissures. (After Korschelt and 

 Heider.) 



visceral mass, the visceral cords are twisted, as already descrii 

 in the case of Triton, into a figure of 8. 



In Patella (Fig. 597) the pedal ganglia give origin to a paii 

 of elongated pedal nerve-cords. In Haliotis and Fissurella there 

 is a similar pair of pedal cords which are connected together by 



