BRAIN PHYStoLoGy oF Worms 851 
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 
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