8 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



authors prefer to speak of reflexes in cases where 

 the reaction of single parts or organs of an animal 

 to external stimuli is concerned ; while they speak 

 of instincts where the reaction of the animal as a 

 whole is involved (as is the case in tropisms). 



4. If the mechanics of a number of instincts is 

 explained by means of the tropisms common to ani- 

 mals and plants, and if the significance of the gan- 

 glion-cells is confined, as in all reflex processes, to their 

 power of conducting stimuli, we are forced to ask 

 what circumstances determine the coordinated move- 

 ments in reflexes, especially in the more complicated 

 ones. The assumption of complicated but unknown 

 and perhaps unknowable structures in the ganglion- 

 cells served formerly as a convenient terminus for all 

 thought in this direction. In giving up this assump- 

 tion, we are called upon to show what conditions are 

 able to determine the coordinated character of reflex 

 movements. Experiments on galvanotropism of ani- 

 mals have proved that a simple relation must exist 

 between the orientation of certain motor elements in 

 the central nervous system and the direction of the 

 movements of the body which is called forth by the 

 activity of these elements. This perhaps creates a 

 rational basis for the further investigation of coordi- 

 nated movements. 



5. We must also deprive the ganglion-cells of all 

 specific significance in spontaneous movements, just 

 as we have done in the case of simple reflexes and 

 instincts. By spontaneous movements we mean 



