94 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



circumstances, but if it has lost the supraoesophageal 

 ganglion, the presence of the other worm in the tube 

 has no inhibitory effect. It tries to force its way into 

 the tube even if it perishes in the attempt. If both 

 worms have lost the supraoesophageal ganglion, they 

 rub their heads together until they are sore. If we 

 wish to keep them alive, they must be separated by 

 breaking the tube. If we compare the conduct of a 

 Nereis whose brain has been amputated, with that of 

 a normal worm, the difference seems to be of the 

 same nature as that between an insane and a rational 

 human being. It would be erroneous, however, to 

 conclude that the normal, brain-endowed Nereis pos- 

 sesses reason or intelligence. The peculiar irritability 

 by means of which the Nereis draws its head back and 

 moves backward out of the tube depends upon organs 

 which are located in the forward end of the body and 

 whose sensory nerves go to the supraoesophageal 

 ganglion. Hence, if the supraoesophageal ganglion 

 is extirpated, the connection between these organs 

 and the rest of the body is interrupted, and the stimuli 

 which affect the forward part of the body can no 

 longer produce backward movements in the posterior 

 portion of the animal. 



This does not, however, explain the change of 

 character, the restlessness of the Nereis which has 

 been deprived of its brain. It is maintained that, if 

 the spontaneous activity or the reflex irritability of 

 an animal is increased after the loss of a part of the 

 brain, that part is an inhibitory mechanism. Nothing 



