CENTRAL NERVOUS SYSTEM. 



265 



changes from one to the other without special stimulation. It hibernates like 

 a normal frog, retains its sexual instincts, and can feed by catching passing 

 insects, such as flies (see Fig. 116). A frog without its hemispheres is there- 

 fore capable of doing several things apparently in a spontaneous way. Such 

 frogs balance themselves when the support on which they rest is slowly turned, 

 moving forward or backward as the case demands, in order to maintain their 

 equilibrium. In doing this the frog tends first to move the head inthedirec- 



/V\ 



i \ 



UK 



Fig. 116. — Frog's brain; the parts in dotted outline have been removed : J, brain intact ; /•'. cerebral 

 hemispheres removed ; C, cerebral hemispheres and thalami removed; IK cerebellum removed'; /-.'. two 

 sections through the optic lobes ; /•', two sections through the right half of the bulb (Stein 



tion opposite to the motion of the support, and then to follow with move- 

 ments of the body. If the optic thalami arc removed (Fig. IK!, C), the power 

 of balancing is lost, because, although movements of the head still occur, those 

 of the body are abolished. A frog thus operated on and depriv sd of the h im- 

 ispheres and thalami exhibits the lack of spontaneity which is usually d iscrib sd 

 as following the loss of the hemispheres alone, but which is not a necessary 

 consequence of this operation, as the preceding experiments show. 



A frog possessed of the mid-brain and the parts behind it (Fig. 11<>, C) 



