110 



ANIMAL BIOLOGY 



83. Food, food-getting, and digestion. Frogs feed upon 

 insects, fish, and other frogs, and even birds have been found 

 in their stomachs. Insects are caught by the aid of the 

 slimy tongue, the tip of which can be quickly thrust out of 

 the mouth and then drawn back again with the insect adher- 

 ing to it (Fig. 79) . The tiny teeth that are found on the upper 



jaw and the two large teeth in the roof of 

 the mouth are useful only in preventing 

 the escape of the prey from the mouth. 

 Hence the food is swallowed without 

 being chewed, and after passing down 

 the short gullet it enters the tubular 

 stomach (Fig. 80), where it is partially 

 digested by ferments (P. B., 53) secreted 

 by certain cells found in the lining of 

 this organ. 



When the food leaves the stomach, 

 it enters the coiled small intestine where 

 the process of digestion is continued by 

 the bile secreted in the liver and the 

 FIG. 79. The method pancreatic juice prepared in the pan- 

 creas. 1 As the digested food slowly moves 

 along the small intestine, it is absorbed 

 by the capillaries (84) in the walls of this tube and so may 

 be carried by the blood to the various cells of which the 

 body is composed. Digestion not only prepares the food 

 for absorption, but as in plants (P. B., 51) or in the fish 

 (98), makes it ready to be used in the cells either for growth 

 and repair or for the production of energy. 



84. Blood and circulation. The blood of the frog, 

 when examined under the microscope, is seen to consist 



^oth of these digestive fluids are carried to the intestine by 

 ducts. 



by which a frog se- 

 cures insects. 



