26 



THE BIOLOGY OF THE FROG 



CHAP. 



which the tongue is covered enables it to adhere to the 

 objects it strikes against, so that they may be conveyed to 

 the mouth. 



The frog has an instinct to snap at small moving objects 

 that come sufficiently near. This action is determined more 

 by the motion and size of the objects than their form. Un- 

 less a thing is moving, the frog pays little attention to it. 

 Frogs may often be caught by danghng small bits of red 

 yarn before them on a hook. When the yarn is seized, the 

 animal may be jerked out of the water. According to 

 Knauer, frogs and toads have the power of ejecting indigest- 

 ible bodies from the stomach by way of the mouth. Bits of 

 grass or moss accidentally swallowed with the food are gotten 

 rid of in this way. 



Protrusion of the Tongue. — The frog is able to throw 

 out its tongue with remarkable rapidity, but the method by 



which this feat is ac- 

 complished was, until 

 recently, but inade- 

 quately understood. 

 Hartog y and Gaupp ^ 

 have found that the 

 protrusion is brought 

 about by the pressure 

 of the lymph in the 

 large sublingual lymph 

 sac. This may be 

 readily shown if we cut 

 off the upper jaw of the frog and inject air or liquid through 

 the mylohyoid muscle, which extends beneath the tongue. 

 The lymph spaces become filled, and this causes the tongue 



1 Hartog, Ann. Nat Hist., May, (7), 7, 1901. 



2 Gaupp, Anat. Anz., 19, 1901. 





FlG. 6. — Figure sliowing the tongue of the 

 frog in three different positions. (After 

 Wiedersheim.) 



