108 JESSE LE ROY CONEL 



to the posterior end of the pronephros, as is shown in figures 1 

 and 2. When the anterior ends or the ducts of this animal were 

 sectioned, it was found that the lumen of the right duct ends be- 

 side the posterior end of the Bowman's capsule of the Malpighian 

 body of the pronephros, but there is no communication between 

 them. Some of the sections of the left duct were scraped off the 

 slide in this region, hence the duct could not be followed. Im- 

 mediately posterior to the pronephros the lumen of the right 

 duct of this animal abruptly enlarges, becoming a cavity which 

 measures 0.4875 by 0.6240 by 1.335 mm. This cavity is almost 

 entirely filled with a rounded, loose mass of nuclei which re- 

 sembles a disintegrating glomerulus. This mass is connected 

 here and there to the lining of the duct by narrow strands of 

 nuclei, but no blood vessels could be seen in them. The lining of 

 the duct here does not resemble that of a Bowman's capsule, 

 and is composed of short columnar cells hke those of the proneph- 

 ric. tubules. If this be a disintegrating glomerulus, it is dif- 

 ficult to explain why it should be in the lumen of the mesonephric 

 duct. Immediately posterior to this enlarged cavity the duct 

 becomes narrowed to a diameter of 0.117 mm. 



Mesonephros 



Bdellostoma. Mesonephric ducts. Except in specimen 22, the 

 mesonephric ducts of the Bdellostomae examined begin from 

 2 to 10 mm. back of the posterior end of the pronephros. Small 

 strands of tissue, resembling in structure the outer wall of the 

 duct, extend from the anterior end of the duct toward the pro- 

 nephros. Sometimes a lumen is present in one of these strands 

 for a varying, but short, distance. These strands may be the 

 only trace of pro- or mesonephric elements between the posterior 

 limit of the pronephros and the anterior end of the ducts, or, in 

 addition to these, there may be one or more isolated tubules or 

 traces of glomeruli in this intermediate region. 



The anterior ends of the right and left ducts in an individual 

 are seldom opposite each other. The duct does not start abruptly, 

 but is always narrowest at the anterior end, and presents the 



