76 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



progressive movements, nor yet like a normal Thy- 

 sanozoon for it had lost its spontaneity. This becomes 

 still more apparent from the following observation : 

 I threw a Thysanozoon similarly operated upon into a 

 tank of water. Both pieces performed synchronic 

 swimming movements. The oral piece soon reached 

 the vertical side of the aquarium and began to creep 

 upwards. As a result of the change of direction in 

 the anterior piece, the tissue connecting the two parts 

 became twisted and the back of the posterior piece 

 came in contact with the glass, while the ventral side 

 was turned toward the water. It then made swim- 

 ming movements and in this way followed the crawl 

 ing movements of the oral piece. The posterior 

 piece therefore is not simply dragged behind passively, 

 but takes an active part in the progressive movement 

 when the movements are continuous. This is also 

 evident from the fact that it would often crawl along 

 on the back of the oral piece, especially if the latter 

 suddenly began to move more slowly. 



These experiments show that a Thysanozoon from 

 which the brain has been removed no longer moves 

 spontaneously, nor is it possible to produce progress- 

 ive movements in it by any external stimulus. If 

 touched, local contractions, only, result. 



2. The brain and nervous system of the fresh-water 

 Planarians (Fig. 23, from Jijima) are so similar to those 

 of the marine Planarians that for our purpose it is un- 

 necessary to give a special description of them. The 

 principal difference is probably that the two longitu- 



