2 3 o COMPARATIVE PHYSIOLOGY OF THE BRAIN 



experiences no such sensation. If we continue the ex- 

 periment and divide the posterior piece in the middle, 

 the anterior part crawls off calmly while the posterior 

 part again makes writhing movements. We obtain 

 the same results if we divide the anterior piece. No 

 matter how the worm is divided, the piece in front 

 of the place of division shows coordinated crawling 

 movements, while the piece behind the place of divis- 

 ion makes writhing movements. It is not even neces- 

 sary to cut the worm. If we only touch it with the 

 point of a pencil the posterior part wriggles, the ante- 

 rior part elongates. The only conclusion that can be 

 drawn is that the stimulus of cutting produces a dif- 

 ferent effect when it extends forward through the 

 worm, from the effect which it produces when it ex- 

 tends backward. The movements do not indicate 

 that the animal possesses sensations of pain. 



Similar observations can be made in other Annelids. 

 In Planarians I had already observed that they give 

 no evidence of pain when they are divided trans- 

 versely. The forward piece crawls or swims as if 

 nothing had happened, occasionally merely hasten- 

 ing its movements. 



But even in insects and Crustaceans pieces can be 

 cut off without any reaction from the animal which 

 might be interpreted as the expression of a pain- 

 sensation. 



Janet has observed that the abdomen of a bee can be 

 cut off while the bee is sucking honey without causing 

 any interruption in its occupation. In 1888 I noticed 



