ADAPTATIONS FOR DIGESTION, CIRCULA- 

 TION, AND ABSORPTION OF FOOD 



PROBLEM XLV 



To study the digestive system of a frog, in order better 

 to understand that of man. 



Materials. Frogs preserved in 4% formalin. Some with 

 ventral body wall removed, others for optional dissection by the 

 pupil. Split specimens of frogs' stomachs. Portable micro- 

 scope. Chart showing digestive system of frog. 



a. General Study and Adaptations 



Observations. 1. Note the looseness of the skin. Are the 

 muscles forming most of the ventral body wall thick or 

 thin? 



2. Find a large, reddish brown, lobed organ (liver) which 

 nearly covers the other organs. How many lobes has the 

 liver ? 



3. Lift the liver to one side, and find a small greenish body 

 (bile sac or gall bladder) on one side of the liver and between its 

 lobes. To what does it seem to be attached ? 



4. Open the mouth of the frog and force a small probe 

 down its throat into its continuation (the gullet or esophagus). 

 This leads to an enlargement (stomach) which in turn leads to a 

 long slender tube (small intestine). 



5. Look for a thin membrane (mesentery) holding the coils of 

 the small intestine in place. Is it along the full length of the 

 small intestine ? 



6. Note that the small intestine leads into a larger tube 



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