46 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



branches of the lateral blood vessels, which ramify in all directions 

 beside and beneath the esophagus. In some species of Cerebkatu- 

 Lus there is a most profuse brandling of both sets of tul)ules in the 

 middle esophageal region, the fine nephridial canals winding in and 

 out among the blood Aessels, and being intimately associated with 

 them. In several species of Micrura the nephridial canals branch 

 out close against the lateral wall of the large lateral blood vessel 

 which lies in the angle between the jaroboscis sheath and the esoph- 

 agus. 



In some forms the nephridial tubules extend the whole length of 

 the esophagus and stomach and are provided 'wdth numeroiis ducts 

 on each side. In all species of the order the excretory pores are 

 situated above the lateral nerves, and in Micrura verriUi are some- 

 times not far removed from the median line. The efferent ducts 

 when numerous are disposed without regularity, and although there 

 may be approximately the same number on each side yet they are 

 by no means in regular pairs. 



The ne])hridial canals are lined with a single layer of columnar 

 e])ithelium which rests on a homogeneous basement membrane. The 

 epithelium is comparatively tliin in the smaller tubules but is very 

 high in the larger canals and in the efferent ducts. These cells are 

 provided with delicate, rather short cilia sparsely scattered over the 

 free surface. In many forms, especially the hoplonemerteans, the 

 fine branches prol>ably end in slightly enlarged terminal Aesicles, 

 in each of which a tuft of long cilia is suspended. Such terminal 

 vesicles are described in detail liy Burger ('91). 



In a few forms (Cephalothrix, Prosadenoporus, and Pela- 

 GONEMERTEs) the nephridia have not been discovered as yet. In 

 Paranemertes californica the efferent diicts are very inconspicuous 

 so that I was unable to find their openings. In Taeniosoma melan- 

 ogramniuni (7\ (/umqiielineatum) Punnett (: 00, p. 116) describes 

 some of the efferent diicts as opening into the alimentary canal. 

 In a recent study of 2\ienlosoma nnUineatxni fi'om the Hawaiian 

 Islands I have found an exactly similar condition — fi-om 7 to 20 

 efferent ducts on each side opening directly into tlie lumen of the 

 esophagus, wliile a smaller number of perfectly similar ducts opened 

 on the dorso-lateral surface of the body. There are also a few 

 other cases where the nei)hridia do not conform to the types 

 described above. 



