Nephrostomes 



Pronephros 



Glomerulus 



Pronephric duct 



Glomeruli 



Mesonephros 



FIG. 341. THE EXCRETORY SYSTEM OF A Petromyzon fluuiatilis, 22 MM. IN 

 LEXGTH, from the inner side. (After Wheeler.) About half the entire 

 length of the primary urinary duct is represented, and behind the pronephros 

 it is greatly coiled. Four pronephric nephrostomes and a folded glomerulus 

 are present, and between the pronephros and mesonephros is a portion 

 wanting in tubules. 



