262 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



outer surface of the kidney of a rabbit or of a man is 

 quite smooth ; this fusion affects also the inner sub- 

 stances of the lobes, and in man three, or only two, 

 tubes open directly into the pelvis of the organ. 



Fig. 109. Diagrams of the Urinary Tubules of 



A, The frog; B, tortoise; c, pigeon (after Hufner); D, man (after Ludwig) ; I., 

 glomerulus ; u. to vii., various regions of the tubule. 



The duct that carries to the exterior the secretion 

 of the kidney is ordinarily known as the ureter ; 

 so long as the pronephros persists, the segmental 

 duct and the ureter are one and the same ; when 

 the mesonephros appears, the duct becomes divided 

 into two, the Miilleriaii duct (which has no con- 

 nection with the kidney, but forms the oviduct of the 



