COE: NEMERTEANS OF WEST AND NORTHWEST COASTS, l-il 



There are no indications whatever of cerebral sense organs, as is 

 attested by several }3erfect series of sections. External to the brain 

 and lateral nerves the basement layer, which is elsewhere extremely 

 thin and inconspicuous, is comparatively well developed. 



Anterior to the brain are numerous cephalic nerves (PL 6, fig. 53), 

 which pass forward between the basement layer and the thin circu- 

 lar muscles as in some species of Carinella. In the nephridial 

 region the lateral nerves press closely against the outer circular 

 muscles which here bend inward to encroach on the longitudinal 

 muscular layer (PL 8, fig. 57). The fibrous core now lies close 

 against the muscles, while its sheath of cellular elements is situated 

 peripherally, and between the nerve core and the basement layer. 

 Behind the nephridial region, or the region of the thickening of the 

 inner circular muscles, the nerve core sinks fully half way through 

 the layer of longitudinal muscles which here closely suiTound it on 

 three sides (PL 9, fig. 60). On the outer side alone are the cellular 

 elements and sheath. 



A transverse section through this region (PL 8, fig. 58) is strikingly 

 like a similar section through Cakinojia so far as the muscular and 

 nervous layers are concerned. It can be demonstrated, however, 

 that a few delicate fibers from the outer circular muscles bend 

 inward and continue to lie actually internally to the nerve core (PL 

 9, fig. 60) . 



In the intestinal region the nerve core again approaches the base- 

 ment layer, and tlie cellular elements of the sheath lie both dorsal 

 and ventral to it (PL 10, fig. 63). It has plainly regained its posi- 

 tion between the outer circular muscles and the basement layer. 



The explanation for such an inward migration of the nerve cords 

 in a limited portion of the body is not immediately a])parent. Such 

 a change of i)Osition can hardly be due to the influence of mechani- 

 cal stresses. It represents perhaps a case of arrested migration of 

 the nerve cords, which in CAPaNOMA have assumed a similar position 

 throughout the bodj'. 



The proboscis nerves are as in related genera ; the pair of esopha- 

 geal nerves is well developed, as are also the upper and lower dorso- 

 raedian nerves as far back as the thickening of the inner circular 

 muscles. The median nerve found beneath the esophagus is fairly 

 conspicuous anteriorly, but none of these nerves deserves special 

 comment. 



