COE : NEMERTEANS OF WEST AND NORTHWEST COASTS. 195 



Proboscis remarkably large and strong ; provided with a |)air of 

 very large nerves, which arise from ventral brain lobes near the 

 commissure and pass forward to enter tlie ventral side of the pro- 

 boscis at its attachment immediately in front of the bi'ain ; they then 

 spread out to form a remarkably conspicuous plexus, situated directly 

 beneath the internal epithelium. There are but two distinct layers 

 of muscles, an internal longitudinal musculature l)eing wanting. 

 The cii'cvilar layer, however, shows an indication of two layers, the 

 outer half being composed of libers which run somewhat diagonally 

 to those of the inner half of the layer. The muscular crosses are 

 well developed. 



Body icalls. — Cutis remarkably thin, its glands extending inward 

 for only about one sixth to one fourth the distance fi'om surface of 

 integument to circular muscular layer. Outer longitudinal muscula- 

 ture much thicker than the other two muscular layers combined ; 

 it projects laterally beyond lateral nerve to form an acutely pointed 

 lateral ridge, or keel, the muscles being several times as thick in this 

 region as elsewhere on the circumference of the body. Inner longi- 

 tudinal musculature very thin, in many places being less than one 

 tenth as thick as the outer longitudinal muscular laver. 



Blood and nephridial systems.— A single pair of large lacunae 

 in the head unite anteriorly above the rh^^nchodaeum as in many 

 related species. Esophageal lacunae remarkably large, surrounding 

 esophagus on all sides except dorsally. 



The nephridia extend forward nearly to the mouth as ])rofusely 

 branched tubules lying on the lateral borders of the esophageal 

 blood laciinae. Anteriorly most of the tubules lie above the level 

 of the lateral nerves, but extend ventrally theieto in the middle 

 nephridial region. Posteriorly all the tubules collect into a single 

 large longitudinal canal on each side, at the posterior end of which 

 a single large efferent duct opens to the exterior on the dorso-lateral 

 surface of the body. The position of the ])air of nej)lii-idiopores is 

 at about one third the distance from mouth to intestinal region. 



Nervous system and sense organs. — All the nervous structures 

 of the body are remarkably conspicuous. The lobes of the brain 

 and their commissures, the esophageal, proboscidial, and dorso- 

 median nerves, as well as the plexus outside the circular muscles of 

 the body, are all I'emarkably well developed. 



The cerebral sense organs are unusually large, their glandular 



