INTERNAL ANATOMY 



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of the proboscis and spreading out as a thin plexus under the glandular part of the ventral 

 wall; (3) nerves to the arms; (4) a pair of lateral nerves; (5) a post-oral ring from the 

 posterior edge of the collar and (6) nerv^es into the stolon. I was not able to find all the 

 nerves which Masterman described and the main course of the nerve tracts which I have 

 determined seems to be somewhat difi"erent. 



Fig. 7 is a drawing of the nervous system. From the anterior end of the main ganglion 

 arises a thin plexus of nerves which spreads out laterally between the basement mem- 

 brane and coelomic epithelium of the dorsal wall of the proboscis, the separate nerves 

 become fused, round the lateral edges, with a thin plate of nerve plexus found under the 



Fig. 7. C.densus. Nervous system. A, sagittal section; B, frontal section. 6, ganglion; c, gonad; c/), collar 

 pore; /, stomach; pn, pre-oral nerve ple.xus; pn^ , nerve plexus in ventral wall of proboscis; In, post-oral 

 nerve; In^, nerve to pharj'nx; /n,, nerve to post-oral lamella; In^, nerve to ventral body wall; iig, nerve to 

 gonad; dn, nerve to dorsal body wall; na, nerve to arms; r, rectum. 



glandular region of the ventral wall. This pre-oral nerve plexus does not extend to the 

 anterior tip of the proboscis, so that Masterman's description of its course is incorrect. 

 From the dorsal side of the ganglion arise the nerves to the arms ; from the posterior 

 end, a pair of post-oral nerves and a median nerve which runs in the dorsal wall of the 

 trunk. This median nerve gives off a pair of small branches which enter the ducts of 

 the gonads. The post-oral nerves, homologous with the "post-oral ring" of Masterman, 

 proceed backwards on either side, and at the base of the collar pores each divides into 

 three branches which enter the pharynx, post-oral lamella and body wall respectively. 

 PI. XXXVI 1 1 , figs . I to 8 are transverse sections which show the course of the main nerve 



