MUSEUM OF COMPARATIVE ZOOLOGY. 171 



the circular muscles of the pharynx, where it terminates in a distinct 

 ring at about the level of the middle of the brain. 



At the point where the splanchnic nei've forms a ring around the 

 pharynx one finds a few nerve cells, but they are few in number, and 

 hardly deserve the name of a ganglion. From this ring it is easy to 

 trace in serial sections the stems of the intestinal plexus, which are 

 here large. This plexus lies in the connective tissue of the intestinal 

 wall, and was first described by Andrews ('90, p. 405) for S. Gouldii. 

 However, he failed to find a splanchnic ring, or any anterior connection 

 of the plexus with the central nervous system. 



The muscular branch (re. mu. ret.) passes off laterally from the middle 

 of the oesophageal connective, and divides near the centre of the fused 

 mass of the dorsal and ventral retractors into two branches, one of 

 which traverses each retractor. Xot far behind this branch there is 

 upon the connective a small trunk (*, Fig. 22), which passes to the sur- 

 face of the muscular mass, but which could not be traced farther. It 

 remained doubtful w^hether this was a subsidiary muscular branch or of 

 other value. 



c. Ventral Nerve Cord and Plexi. 



After the union of the two connectives, the ventral nerve cord thus 

 formed floats a short distance free in the body cavity, and sends off nu- 

 merous long nerves to the body wall. The first of these, the composite 

 nerve of Audreae ('81, p. 248), is by no means always composed of eight 

 branches in a single sheath, as stated by that author. The number varies 

 from six to nine, and the size of the different trunks varies as well (Plate 

 II. Fig. 22, /.). In fact, the later branches, which according to him 

 consist of two trunks, one from each side of the nerve cord, not only show 

 great variability in the size of these trunks (Fig. 22, //.), but also at 

 times only a single trunk can be found, which then comes from but one 

 side of the nerve cord. All these frequent irregularities point to a lack 

 of metamerism in the nervous system. On reaching the body wall these 

 nerves branch in a digitate manner through the muscles of the intro- 

 vert, the main trunks being longitudinal, and do not form nervous rings 

 around the body as in other parts of the wall. From these longitudi- 

 nal stems large trunks pass outward through the musculature to the 

 dermal plexus. 



This dermal plexus lies in the cutis at its plane of union with the mus- 

 culature, and consists of large longitudinal trunks {plx. n. drm., Plate 

 I. Fig. 4) with lateral anastomoses. From this network, fibres {rm, gl.) 



