74 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



sharp knife while the Planarian is crawling on a 

 glass plate, the oral piece (a, Fig. 21) crawls on un- 

 disturbed, while the progressive movement of the 

 posterior piece ceases entirely. The spontaneity of 

 the progressive movement of the Thysanozoon is 

 then a function of the part of the body containing 

 the brain (2). 



In a Thysanozoon that has been divided, both pieces 

 live and regenerate the lacking parts. The oral piece, 

 however, regenerates more rapidly than the aboral 

 piece, which has to form a head. I have not investi- 

 gated whether the latter also forms a new brain. I 

 kept such pieces alive for four months. The spon- 

 taneity of the posterior piece never returned ; the 

 spontaneity of the anterior piece remained. 



If we put a normal Thysanozoon on its back it soon 

 rights itself. The question now arises whether, like 

 the progressive movements, these righting movements 

 are a function of the brain. This is not the case. A 

 Thysanozoon from which the brain has been removed 

 rights itself if laid on its back, only the reaction pro- 

 ceeds more slowly than in the normal animal, or even 

 in a piece of an animal if this piece contains the brain. 

 We see here again that the nervous system only 

 serves to bring about a quicker reaction. 



If, instead of dividing the Thysanozoon completely, 

 we leave the two parts on one side connected by a 

 thin piece of tissue in such a way that (Fig. 22) the 

 posterior piece can receive no direct innervations 

 from the brain through the longitudinal nerves, 



