EXPERIMENTS ON WORMS 



75 



conduction of stimuli would still be possible through 

 the side nerve-plexus. 



Such an animal was placed after the operation on 

 the bottom of the aquari- 

 um ; the anterior piece im- 

 mediately began to move, 

 while the posterior piece 

 attempted to attach itself 

 to the bottom. The latter 

 soon yielded to the tugging 

 of the oral piece, however, 

 and took part in its pro- 

 gressive movements in an 

 entirely coordinated man- 

 ner, as though no incision 

 had been made. After a 

 time the oral piece turned 

 around and crawled over 

 the back of the posterior 

 piece, which was dragged behind passively, and was 

 turned on its back. It righted itself immediately and 

 moved off actively in the same direction as the oral 

 piece. Changes of direction originated only in the 

 piece containing the brain and were never transmitted 

 directly to the posterior piece. But if the oral piece 

 continued for a time to move in the same direction 

 and with the same rapidity, the same movement would 

 soon take place in the posterior piece. Hence the 

 posterior piece did not behave entirely like a piece 

 from which the brain had been removed, for it made 



FlG. 22. THYSANOZ06N WITH 



TRANSVERSE INCISION. 



