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TEXTBOOK OF ZOOLOGY 



over and over. It has been estimated that, while man excretes about 

 one-fiftieth of his weight per day, the frog excretes about one-third 

 of its weight. During hibernation and aestivation, however, in com- 

 mon with the slowing down of its other body functions, the kidney 

 function of the frog is practically stopped. 



Ostium -- 



Postcaval V 



Ovaty- 



Oviduct — 



L.intest'im — 

 Uterui 



Fig. 278.- 



Cloaca 1?- 



Anus 



-Urogenital system of the frog from ventral view. Male organs shown on 

 one side, female on the other. 



The kidney is not only concerned with the elimination of waste 

 products but also has other functions. One of these is the reabsorp- 

 tion by its tubules of useful substances, such as some of the salts 

 and glucose which have filtered out, and their reintroduction to the 

 blood stream. In their food frogs obtain less sodium chloride than 

 do mammals, and this is compensated for in part by a retention of 

 salts from the water taken in, while in mammals water is retained 

 and the salts are eliminated. 



