INHIBITORY RESPIRATORY REFLEX IN FROG 291 



depending upon the plugging of the nostrils and stoppage of the 

 flow of air through the respiratory passages. Both these may 

 come into play when the frog is submerged. 



Doctor Herrick has pointed out to us that there are "four 

 different types of innervation of the nasal region, the functional 

 limitations of no one of which have been clearly shown. These 

 are: 



1. Trigeminal nerve endings. 



2. Olfactory nerve. 



3. The vomeronasal nerve, with the same type of peripheral 

 endings as the olfactory, but limited to the vomeronasal organ 

 (Jacobson's organ) peripherally and with a special part of the 

 olfactory bulb (the bulbus accessorius) centrally. 



4. The nervus terminalis — peripheral endings unknown and 

 central endings independent of the olfactory bulb. 



"Ayers (Jour. Comp. Neur., June 15, 1919, vol. 30, 323) has 

 suggested some of the physiological problems here. The ter- 

 minal nerve is found in all vertebrates from fishes up and is 

 therefore probably not specifically concerned with air breathing. 

 On the other hand, Jacobson's organ and its nerve are well 

 developed in air breathers. Their reduction in birds may 

 account for some of the peculiarities of these animals." 



Since we shall find it impossible to pursue this line of investi- 

 gation any further, we can only hope that the above observa- 

 tions may at any rate serve the purpose of suggesting a field for 

 comparative physiological research. 



Some of the experiments above described were carried out by 

 Mr. K. J. Austmann under our direction. 



