FROG 



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The stomach in turn leads into a narrow, much-coiled small in- 

 testine, which widens to form the large intestine, the last part of 

 which is the cloaca (Latin, sewer). The kidneys, urinary bladder, 

 and reproductive organs {ova- N 



ries or testes) open into the 

 large intestine. Several glands, 

 the gastric glands, the liver, and 

 the pancreas, produce digestive 

 fluids. These digestive fluids 

 by means of enzymes change 

 insoluble food materials into a 

 soluble form which may be ab- 

 sorbed and become part of the 

 blood. 



Breathing. The frog takes 

 air into its mouth by lowering 

 the floor of the mouth and 

 drawing air in through the two 

 nostril holes. Then the little 

 valve-like flaps over the holes 

 are closed, the floor of the 

 mouth is raised, and the frog 

 forces the air down into the 

 baglike lungs. When the nos- 

 tril flaps are lifted the air is forced back to the mouth by the 

 pressure of the body wall and the contraction of the lungs. 

 Then the mouth floor is raised and the air is forced to the 

 exterior. The lungs contain air spaces surrounded by walls filled 

 with small blood vessels, by means of which oxygen is taken up 

 and carbon dioxide is given off. The skin also is provided with 

 many tiny blood vessels which absorb oxygen and give off carbon 

 dioxide. 



Explain how the frog captures its food. 



Practical Exercise 13. How does a frog breathe during his winter sleep at 

 the bottom of a pond? 



Circulation. The frog has a well-developed heart, composed 

 of a thick-walled muscular ventricle and two thin-walled auricles. 



