82 



ESSENTIALS OF ZOOLOGY 



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. 



Ostium — 



Postcaval V-/F 



Ovary — 



— Mdrenal cjland 

 - - Renol vein 



■':y^- W\dr)2\j 



-nesonephric duct 



Urinary 31 



Fig. 23. — Urogenital system of the frog from ventral view. Male organs shown 

 on right side of figure and female on the left. The single urinary bladder is present 

 in both sexes. 



Another function is in maintaining the concentration of body 

 fluids. Frogs absorb water through their skin at a rather constant 

 rate, varying with the temperature. The kidney in turn expels 

 water at the same rate and thus maintains the proper balance. In 

 addition to its usual function the urinary bladder may be used as a 

 storage reservoir for water during temporary drought. The water 

 may be absorbed from it by other tissues until the proper osmotic 

 equilibrium of the tissues with the blood is produced, 



