myomeres 



sheath of notochord 



reticular tissue 



(interrenol and suprarenal) 



renal sinus with trobeculae 



renal artery 



lymphoid tissue 



glomerulus 

 excretory part of kidney 



nephric duct 

 ovary 

 typhlosole 

 Figure 10-26. Cross section of adult lamprey to show interrelationships. 



well as in the posterior "metanephric" region. The origin 

 of the Mijllerian duct by the splitting of the nephric duct 

 is also unmatched elsewhere. 



Cyclostomes 



lamprey The kidney of the adult lamprey is an opistho- 

 nephros. It is band-like, hanging down on either side of the 



body cavity (Figure 10-26). That of the left side is larger. 

 Anteriorly each kidney is narrow, beginning at the duct of 

 Cuvier (posterior end of the pronephric region) where it is 

 only a band of tissue in the roof of the coelom; posteriorly 

 it increases in depth. Near the anal region it tapers to the 

 nephric duct. The nephric ducts of either side join just 

 before reaching the tip of the urogenital papilla which ex- 

 tends into the cloaca (Figure 10-27). 



radials 



spinal cord 

 .notochord 

 caudal artery 



ncter muscle ' 



ng into coelom 

 rem urinary sinus 



le between joined 

 nephric ducts 



onus urogenital papilla 



radials 

 JT^ — Spina! cord 

 notochord 

 caudal artery 



sphincter muscle 

 urogenital sinus 



radial 



abdominal pore 

 anus 



Figure 10-27. Semidiagrammatic sagittal sections of the cloacal region of the lamprey, A, and 

 Myxine, B. 



THE EXCRETORY SYSTEM • 313 



