376 



METAZOAN PHYLA 



is little power of accommodation. The auditory organ has been in a 

 general way described in the preceding topic. There are three semi- 

 circular canals. The olfactory epithelium hues cavities just within 

 each of the nostrils. 



401. Behavior. — Endeavors have been made to determine the 

 function of the different regions of the frog's brain by the removal of 



Olfactory lobe 



^t. ;■■ '•■ ' %<^ Cerebrum 



pineal 

 stalk 



Diencephalon 



Optic 

 lobe 



Cerebellum 



Medulloi 



Fig. 266. — Brain of European frog, Rana esculenta Linnaeus, viewed from above. 

 {From a Ziegler model, after Wiedersheim.) The roots of the cranial nerves are marked by 

 roman numerals. 



one after another in the living frog. It has been found that removal 

 of the cerebral hemispheres, together with the olfactory lobes, seems 

 to have little effect. When the mid-brain is removed the frog loses 

 its power of spontaneous movement, which is clearly connected with 

 the loss of sight. Also the spinal cord becomes more irritable, which 

 shows that the destruction of the mid-brain and the loss of sight have 

 removed a control which was necessary to nervous equilibrium. The 



