UROGENITAL SYSTEM OF MYXINOIDS 89 



mass continues around the duct to section 380 and there ends, 

 remaining in the lumen of the vein. The duct proceeds posteri- 

 orly, and in section 385 divides into three tubules, each of which 

 leaves the pronephric vein and enters the Bowman's capsule of 

 the Malpighian body of the pronephros, opening into the capsule 

 by a nephrostome. There are no lobules connected with the 

 eighth segment of the duct. 



Price ('14) suggests that perhaps each lobule of the pronephros 

 represents a single original tubule and its secondary branches. 

 This is scarcely probable, for there is a total of 31 lobules con- 

 nected with the first six segments of the duct in the above de- 

 scribed pronephros, while those of the seventh segment could 

 not be counted with accuracy but there are at least four. If the 

 most anterior original tubule lay in somite 11, then there could 

 be only 21 tubules at most to and including somite 32, the defin- 

 itive position of the tubules after they have been pushed pos- 

 teriorly by the gills. In the pronephros under discussion, how- 

 ever, there are at least 35 lobules. 



In Bdellostoma none of the tubules in any of the pronephroi 

 examined by the writer show any signs of degeneration, and the 

 lumen of each tubule opens into the pericardial .cavity at one end 

 and is continuous, either directly or indirectly, with the lumen 

 of the central duct. The lumen of almost every tubule is filled 

 with a coarsely granular coagulum which is more or less shredded 

 into long processes resembhng flagella (fig. 16). These processes 

 are attached at one end to the columnar cells, usually one to a 

 cell, and the free end extends inward toward the base of the tu- 

 bule, that is, toward the central duct. The lumen of the central 

 duct sometimes contains a comparatively small amount of this 

 coagulum. The writer was unable to demonstrate cilia in the 

 phonephric tubules, but it is probable that his material was 

 not suitably preserved to permit these to be seen if present. 



The tubules are very simple in structure. Each is a cyhnder 

 consisting of a single layer of columnar cells, which are continu- 

 ous at the mouth with the pericardium and, at the base, with the 

 columnar cells of the central duct. The mouths of the tubules 

 are sometimes funnel-shaped (fig. 13), but are usually constricted 



