BRAIN PHYSIOLOGY OF WORMS 351 



upon its back. The posterior piece at once resumed the 

 ventral position, however, and then moved actively in the 

 same direction as the oral piece. Changes in movement, 

 therefore, were inaugurated only by the oral piece which 

 contained the brain and were never communicated directly 

 to the aboral piece. When, however, the oral piece 

 moved for some time in the same direction and with the 

 same velocity, the same movement soon took place in the 

 aboral piece also. The aboral piece therefore, behaved not 

 entirely as a piece without the brain, as it was still capable 

 of progressive movement, but not as a normal Thysanozoon 

 either, as it had lost its spontaneity. This becomes still 

 clearer from the following observations : 



I threw the animal into a basin of water. Both pieces 

 executed energetic, synchronous swimming movements. The 

 oral piece soon reached the vertical glass wall of the aqua- 

 rium. In consequence of a change in the direction of the 

 movement of the anterior piece, the connecting bridge 

 between the two halves of the animal was twisted and the 

 aboral piece came in contact with the glass wall with its 

 back, while the ventral surface of the same was turned 

 toward the water. The posterior piece now executed swim- 

 ming motions and so followed the creeping movements of 

 the oral piece. ' That when movement is constant the 

 posterior piece takes an active part in the progressive move- 

 ment, and is not merely dragged along passively, is further 

 shown by the fact that it often crept with its free edge upon 

 the back of the oral animal, especially when the latter sud- 

 denly moved more slowly. 



The experiments detailed thus far show that a brainless 

 piece of Thysanozoon no longer moves spontaneously, that is 

 to say without an appreciable external stimulus. I did not 

 succeed in bringing about progressive movements in a brain- 

 less Thysanozoon even by stimulating it. If the animal is 



