UROGENITAL ORGANS. 



123 



Ao 



last open into the collecting tubules ; but it is important to 

 note that at no time are nephrostomata developed in connec- 

 tion with them, and the body cav- 

 ity is without communication with 

 this nephridial system. While this 

 process is going on the whole met- 

 anephros pushes farther forward, 

 dorsal to the pronephric duct, the 

 ureter increasing correspondingly 

 in length. In the subsequent his- 

 tory the kidney becomes strongly 

 lobulated, the lobes corresponding 

 to the groups of collecting tubules 

 of which it is composed. This lob- 

 ular appearance is retained through- 

 out life in the sauropsida, but is 

 subsequently lost in all mammals 

 except the whales and some car- 

 nivores. 



The kidney never extends 

 through as many segments as 

 does the mesonephros, but forms a 

 relatively smaller and more com- 

 pact body lying within or a little 

 in front of the pelvic region. In 

 the mammals the anterior end of 

 the ureter becomes widened out, 

 inside of the mass of the kidney, 

 into a considerable chamber, the 

 pelvis of the kidney, into which 

 the collecting tubules empty, the 

 openings of these being placed on 

 one or more papillae, which extend 

 into the pelvis renalis, partially 

 dividing it into smaller chambers 

 or calyces. 



The ureter does not long retain its primary connection with 

 the distal end of the pronephric duct, but acquires its own open- 



FlG. 131. Urogenital system 

 of male heron (^Ardea')^ from 

 Wiedersheim. Ao, aorta; BF, 

 bursa Fabricii, opening at BF' into 

 the cloaca, Cc; Ep, epididymis; 

 Ho, testes ; A^, kidney ; Sr, opening 

 of ureter ; V, furrows for veins on 

 ventral surface of kidney ; Vd, vasa 

 deferentia ; Vd' , their opening into 

 cloaca. 



