. Discovery reports. Discovery (Ship); Scientific expeditions. INTERNAL ANATOMY 253 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
. Discovery reports. Discovery (Ship); Scientific expeditions. INTERNAL ANATOMY 253 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. Nervous system. A, sagittal section; B, frontal section. 6, ganglion; c, gonad; c/), collar pore; /, stomach; pn, pre-oral nerve ; 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. XXXVI11, figs. I to 8 are transverse sections whic
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectscientificexpedition
