pronephric funnels 



glomerulus 

 coelom 



pronephric tubule in 

 anterior cardinal sinus 



second 



pronephric funnel 



pyloric region of stomach 



lung bud 



B 



nephric duct 



glomerulus projecting into coelom 

 radix oortoe 

 esophagus 



spinal cord 



notochord 



coelom_ 

 posterior cardinal 

 subcardinal 



germ cells 



dorsal aorta 

 mesonephric blastema 



nephric duct 



Figure 10-16. Pronephric system of the torval frog. A, ventral view of entire system in a 1 2-mm 

 larva; B, cross section of a !0-mm larva at the vertical of the second pronephric funnel; C, cross sec- 

 tion of 10-mm larva showing mesonephric blastema and germ cells. (A after Kindahl, 1938) 



involved in the kidney, as suggested by the number of pri- 

 mary tubules, and the fact that development continues for 

 such a long period. These facts also support the view that 

 this is a much modified kidney as is attested to by the 

 nature of its peritoneal funnels. 



The pronephros degenerates with the establishment of 

 the excretory functioning of the mesonephros. The opistho- 

 nephros, or adult kidney, appears to be entirely of meso- 

 nephric origin. The Miillerian ducts arise as in the sala- 

 mander. 



Choanate fishes 



Actiniilian The soft anatomy of the crossopterygian is 

 known only for Latimeria. Here the kidney is a short, thick, 

 medial mass lying in the postcloacal part of the abdominal 

 cavity, not against the roof, but rather on the floor. Later- 



ally, the margins of this mass extend up along the walls of 

 the body cavity. From it come paired ureters which are di- 

 lated dorsally as the urinary bladders. These ducts open 

 into a urogenital sinus which opens at the tip of a papilla in 

 the cloaca. 



The kidney of this fish, by its position and the fact that it 

 is not associated with the testis, is comparable to the poste- 

 rior part of the opisthonephros of the amphibian. Histologi- 

 cally, it lacks the extensive lymphoid (blood-filtering) and 

 hemopoietic (blood-cell producing) tissue of the other fishes 

 and has many clumps of large glomeruli from which long 

 looped tubules extend. 



Dipnoan The kidney of the dipnoan is an opisthonephros. 

 The band-like organs of either side are fused posteriorly (Fig- 

 ure 10-41). Many vasa efferentia from the testis enter through- 

 out the length of the definitive kidney oi Neoceratodus — which 



THE EXCRETORY SYSTEM 



303 



