218 Vertebrate Embryology 



of small pits or nephrostomes pushing into the 

 mesoblast from the body-cavity, a little below 

 and to the median side of the Wolffian duct 

 (Fig. 54, CWS). Between the bottoms of 

 these little nephrostomes and the Wolffian 

 duct small twisted rods of cells appear which 

 soon become hollow, and open into the Wolf- 

 fian duct, at one end, and into the nephros- 

 tomes at the other. Thus, through these 

 Wolffian tubules, the body cavity is brought 

 into communication with the Wolffian duct. 

 These tubules soon degenerate, and nearly all 

 of them disappear completely. 



The Wolffian tubules of that part of the 

 Wolffian body that lies back of the sixteenth 

 somite do not open into the body-cavity : that 

 is, there are no nephrostomes. The tubules 

 of this region begin as small vesicles in the 

 mesoblast between the Wolffian duct and the 

 body cavity. These vesicles become elon- 

 gated to form the tubules, and, at their inner 

 ends, acquire connection with the cavity of 

 the Wolffian duct, while their outer ends 

 become enlarged to form the Malpighian 

 bodies. By the increase in the number of 

 the tubules, and by the increase in the length 

 of each tubule, causing it to become greatly 



