3H THE BIOLOGY OF THE FROG CHAP 



mainly by creeping, but the frog is nevertheless capable 

 of springing in the ordinary manner. In the water it swims 

 by alternate movements of the limbs. The resting position 

 assumed is not quite normal, the body is more flattened 

 than usual, and the hind limbs are not drawn up to the sides. 

 The breathing and swallowing reflexes are still normal, but 

 the croaking reflex is no longer performed. The reflex of 

 snapping at food is not destroyed, although in the absence 

 of connection with the eyes it is not performed in response 

 to visual stimuli. If a piece of meat is rubbed against the 

 frog's nose, the animal snaps at it and uses the fore legs to 

 stuff it into the mouth. The same reaction may be brought 

 about by using the finger, but after the finger is seized and 

 it is found that the object is too large to be stuffed into the 

 mouth, the frog begins to reject the morsel, and uses the fore 

 legs to push it away. Truly a remarkable combination of 

 reflexes ! 



The snapping reflex is also brought about by contact 

 with the fore legs, or even other parts of the body. If sev- 

 eral frogs, whose brains are cut through just behind the 

 cerebellum, be placed together in a box, they frequently 

 snap at each other when they accidentally come into con- 

 tact, as if they were defending themselves against attack. 

 Flies creeping over the nose are usually not snapped at, but 

 the stimulus produces another reflex, the fore leg being 

 brought forward to brush the insect away. 



The snapping reflex is prevented if the facial nerve is cut, 

 or if the region of the medulla from which the fifth and 

 seventh nerves originate is destroyed. These nerves form 

 the afferent and efferent channels respectively of the nervous 

 impulses involved in the snapping reflex. The extrusion of 

 the tongue, which goes along with this process, is dependent 

 upon the hypoglossus nerve, which has its origin further 



