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THE FLATWORMS— PLATYHELMINTHES 



When the time comes for egestion, planaria is faced with the same 

 problem that hydra had ; there is only one opening to the digestive tract, 

 so the mouth must serve as an anus also and the indigestible food residue 

 is expelled through the mouth. 



Intestine 



Proboscis 



Mouth 



Diverticulum 



Intestine 



Fig. 10.3. Digestive system of planaria. The highly branched condition of the system 



is shown in this drawing copied from a photograph of a planaria that had been fed a 



dye that filled the intestine and its branches. 



