694 



ZOOLOGY 



SKCT. 



mentioned. A pair of Imceal ganglia are connected by slender 

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

 usually a small ospliradial 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 



.den 



TfLSC.COTTL 



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

 parts in the Gastropoda. Enteric canal blue, blood-system red. A, represents a nearly 

 symmetrical arrangement ; in B, C, D, 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 ; cv: ri. cerebral ganglion ; 1. ctcn. left 

 ctenidium ; /. vise. rum. left visceral commissure ; want, mantle ; mo. mmith ; ," ji/<. n/j. nephri- 

 dial apertures ; ped. <i. pedal ganglion ; pi. <t. pleura! ganglion ; /-. ct,-;i. right ctenidium ; r. 

 -;.. COM. right visceral commissure; risc.com. visceral commissures. (After Korschelt and 

 Heider. ) 



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

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



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

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

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



