UROGENITAL SYSTEM OF MYXINOIDS 95 



none was found. Price ('10), also, found no blood vessels in the 

 central mass in Bdellostonia. 



When not surrounded by the central mass, the central duct 

 retains its columnar walls, but loses them upon entering the 

 mass. The walls break down completely and the cells become 

 scattered in the mass. The lumen of the duct may continue in 

 the mass, but it has no organized lining and is bordered by nuclei 

 and strands of cytoplasmic ground-work (fig. 29). The colum- 

 nar lining of the central duct is never continuous with the epi- 

 thelial sheath around the central mass. In view of this fact, 

 it is difficult to regard, as Semon ('96) does, the central mass as a 

 series of glomeruU into whose Bowman's capsules the tubules of 

 the pronephros enter through their Tnnentrichter,' for Semon 

 ('96, '97) himself has shown that, in the mesonephros, the col- 

 umnar wall of the tubule of a Alalpighian body is continuous 

 with the squamosal epithelial wall of the Bowman's capsule. 

 Furthermore, in Bdellostoma, the writer never found a tubule 

 entering the central mass. The tubules enter the central duct 

 and the latter alone enters the central mass, hence in Bdello- 

 stoma Semon's Tnnentrichter' of the pronephric tubules really 

 open into the central duct. Therefore, the inner ends of the 

 pronephric tubules cannot correspond to that end of the tubule 

 of a mesonephi'ic Malpighian body which opens into the Bow- 

 man's capsule, and hence the central mass of the pronephros can- 

 not correspond to the glomerulus of a Malpighian body of the 

 mesonephros. 



In every pronephros of Bdellostoma examined by the wTiter 

 the central mass has one or more openings, through which the 

 central duct communicates with the lumen of the pronephric 

 vein (figs. 12, 20, 21, 22). These openings are natural, and the 

 endothelial sheath which surrounds the central mass lines the 

 sides of the openings. In the lumen of the duct near these open- 

 ings, or even projecting into them, there is almost always a 

 rounded collection of nuclei and granules, which is more deeply 

 stained than the central mass. The nuclei and granules do not 

 resemble blood corpuscles, but have the appearance of waste 

 particles. These openings do not occur in the central duct at 



