PECULIAR TYPE OF NEPHRIDIA IN NEMERTEANS. 



49 



ance would indicate that the ducts opening into the esophagus 

 furnish the principal course for the discharge of the excretory 

 products, while those which pass externally are little more than 

 vestiges of the primitive condition, for many of the latter are 

 incomplete and fail to reach the surface. 



The efferent ducts which open into the esophagus exhibit a 

 distinct, though thin-walled, tube passing directly from one of 

 the larger nephridial canals to the surface of the epithelium lining 

 the esophagus (Figs. I, 2, 3). The presence of a distinct lumen 

 throughout the whole length of some of the ducts does not leave 

 the slightest doubt as to the actual communication between the 



o 



nephridial canals and the lumen of the esophagus. 



In all cases the openings of the nephridial ducts are on the 





FIG. 2. Tieniosoma cingttlatum. Portion of transverse section of body through 

 middle of esophageal region, showing efferent nephridial duct opening into lumen of 

 esophagus. Reference letters as in P'ig. I. 130. 



ventro-lateral borders of the esophagus and in the vicinity of the 

 lateral nerves (Figs, i, 2, 3). 



During the movements of the body the cavity of the esophagus 

 is continually changing in outline, and the epithelial lining is 

 thrown up into numerous temporary longitudinal ridges. Such 

 ridges may form either in the vicinity of the nephridial openings 

 or between them. In the former case the nephridial duct is 

 greatly elongated and very slender and opens on the side or 



