FOECED MOVEMENTS 31 



is blackened. Circus motions after destruction of one 

 cephalic ganglion in an insect are a general occurrence 

 and have been known for a long time. 



The importance of these forced movements caused by 

 lesion of the brain for the explanation of the conduct of 

 normal animals lies in the fact that the latter is essen- 

 tially a series of forced movements. The main difference 

 between the forced movements after brain lesion and the 

 conduct of a normal animal lies in the fact that the 

 former are more or less permanent ; while in the normal 

 animal conduct the changes in the relative tone of sym- 

 metrical muscles leading to a temporary forced movement 

 are caused by a difference in the velocity of chemical^ 

 reactions in symmetrical sense organs or other elements 

 of the surface. 



