35 JESSE LE ROY CONEL 



into tubules, the other continuing posteriorly in the central mass 

 and ending blindly in it at section 274. In section 276 the duct 

 begins again as a part of the sixth segment, just opposite the 

 blind ending of the fifth segment. There are six lobules con- 

 nected with the fifth segment of the duct. 



The sixth segment of the duct arises in section 273 from the 

 union of the tubules of one lobule. The duct enters the central 

 mass in the vein in section 300, and is here 0.12 mm. wide. A 

 small twig extends anteriorly in the mass to section 276 where it 

 ends blindly and is separated by only one section from the end 

 of the fifth segment of the duct. Undoubtedly at one time the 

 fifth and sixth segments of the duct were connected at this point. 

 The sixth segment extends posteriorly through the central mass 

 to section 380 where it ends as a single tubule which runs out of 

 the vein and opens into the pericardial cavity. In sections 318 

 to 323 the duct opens through the central mass into the pro- 

 nephric vein, and in this region the duct and neighboring tubules 

 contain many blood corpuscles. In section 350 the duct leaves 

 the central mass and the columnar cells of the walls of the duct 

 become double their usual length and are thrown into longitudi- 

 nal folds like those of the mesonephric duct, to be described later. 

 This folded condition of the epithehal walls of the duct contin- 

 ues to section 370; then the cells diminish in length to the nor- 

 mal size for the tubules, and the duct here ends as a single tubule, 

 as explained. There are six lobules connected with the sixth 

 segment of the duct. 



The seventh segment of the central duct begins in the central 

 mass in section 340 beside the sixth segment. It continues in 

 the mass, which still lies in the pronephric vein, to section 365 

 where it leaves the mass and vein and divides into two branches, 

 one of which ends by branching into the tubules of a lobule and 

 two single tubules, the other breaks up into the tubules of the four 

 most posterior lobules of the pronephros. The lobules con- 

 nected with this segment of the duct are in such a compact mass 

 that they can not be counted with any degree of certainty. 



The eighth and last segment of the central duct arises in the 

 central mass in section 370 beside the se\'enth segment. The 



