NERVOUS SYSTEM OF PELAGIC NEMERTEANS. 



125 



(Fig. i). The fibrous cores of these main nerves are connected 

 at the posterior end of the body by the broad posterior com- 

 missure, which passes on the dorsal side of the rectum. They are 

 also connected indirectly metamerically by the union of minute 

 branches from both dorsal and dorsal peripheral nerves in the 

 intermuscular plexus (Figs, i, 2, 4). 



Dorsolateral nerves. In the anterior part of the body of many 

 of the species studied a pair of nerves originating- from the dorsal 



FIG. 2. Portion of transverse section of body of Ncuroncmertes auran- 

 tiaca Coe, showing on one side the relations of the peripheral nerves to the 

 body musculature. The section passes between adjacent diverticula of the 

 intestine and shows on the left hand side a portion of the dorsoventral 

 musculature (dvn) ; dn, dorsal nerve, with bilobed ganglion (gl) ; dpn, Ipn, 

 and vpn, dorsal, lateral and ventral peripheral nerves ; ps, proboscis sheath ; 

 dv and Iv, dorsal and lateral blood vessels ; bm, basement layer underlying 

 the surface epithelium ; par, parenchyma ; cm and Im, the thin circular and 

 longitudinal musculatures of the body walls. Other letters as in Fig. I. 



brain lobes, pass backward along the internal border of the body 

 musculature near the dorsolateral edges of the probosis sheath. 

 These dorsolateral nerves (Figs, i, 2) are connected by means of 

 delicate fibres with both the dorsal nerves and the dorsal peri- 

 phereal nerves of the lateral nerve cords. Efferent branches sup- 

 ply the body musculature on the dorsolateral aspects of the body, 

 as well as the proboscis sheath. These nerves are evidently 

 homologous with the dorsolateral nerves of other Platyhelminths. 

 They do not occur in all the pelagic species, and where present 

 are limited to the anterior end of the body (Fig. i). In other 

 species, and toward the middle of the body in all species, their 

 place is taken by fibres from the dorsal peripheral nerves. 



