COE: NEMERTEANS OF WEST AND NORTHWEST COASTS. 191 



as thick as the main circular layer. Integiimental muscles conspicu- 

 ous. Outer longitudinal muscular layer nearl}' disappears toward 

 posterior end of hody, but inner longitudinal muscles remain as a 

 well developed layer to the very end of body. 



Alimentary ca«a? show^s the usual division into esophagus proper, 

 stomach, intestine and rectum. 



Nephridia extend through whole of region of esophagus proj^er, 

 reaching forward as far as the mouth. In their anterior portions 

 numerous tine branches lie on the lateral walls of the blood lacunae, 

 but farther back unite into a single large longitudinal canal on each 

 side, which is situated close beside the proboscis sheath. Near its 

 posterior end the canal becomes much smaller and opens by a single 

 efferent duct to the dorso-lateral surface of body at about the region 

 where the esophagus enters the stomach. 



fSense ortjans. — Frontal sense organs present, but not highly 

 specialized. Cephahc furrows very shallow, not reaching half the 

 distance from surface to rhynchodaeum. Cerebral sense organs highly 

 developed, connected with dorsal ganglia by very large nerve cores. 



Habitat. — A single specimen was dredged by the Albatross south 

 of Alaska Peninsula (Sta. 3210, 54° 00' N. Lat., 162° 40' W. 

 Long.) at a depth of 483 fms., the bottom being composed of sand 

 and green mud. Bottom temperature, 38.5° F. This is the greatest 

 depth at which any of the nemerteans of these collections were 

 obtained, and is much greater than that at which nemerteans are 

 usually found, although a number of forms have been taken at even 

 greater depths. Species of Micrura are the most common of these 

 abyssal forms. 



Cerebratulus Renier. 

 Prospetto della Classe dei Vermi, 1804. 



The species of this genus are distinguished by long, flattened 

 bodies, the lateral margins of which are thin, adapted for swim- 

 ming. Most species are very active, swim readily with undulatory 

 motion, can roll up spirally and become twisted, but aie only moder- 

 ately contractile in length, and do not draw^ together into a tangled 

 mass. The dorso-ventral musculature is highly developed, as are 

 likewise the longitudinal and obli(jue muscles. 



Head usually pointed anteriorly, but very changeable in shape ; 



