BRAIN PHYSIOLOGY OF Worms 353 
differences in their physiological reactions. If a fresh-water 
Planarian is cut in two the aboral piece which contains no 
brain creeps about in just as lively a manner as the oral half. 
The spontaneity of the progressive movements in Planaria 
torva is therefore in no way a function of the brain. Every 
piece of the animal, not too small, possesses spontaneity. 
The decapitated animals creep with the oral end directed 
forward, as do normal animals. 
2. In a previous paper I have described the behavior 
of Planaria torva toward light. The animals are chiefly 
photokinetic, that is to say, changes in the intensity of the 
light alter their movements. If the animals are suddenly 
brought from darkness into light they begin to move. 
During the first few moments the direction of the move- 
ments is also influenced by the light. The animals move as 
do negatively heliotropic animals to the room side of the 
vessel, but they do not collect here as do negatively helio- 
tropic animals, but distribute themselves in all directions, 
and now begin to move in every direction, to come to rest 
finally in that region of the vessel which is more weakly 
illuminated than its surrounding. 
One receives the impression therefore that an increase in 
the intensity of the light causes the animals to move, while 
a decrease in the intensity of the light causes them to come 
to rest. For this reason one finds the animals through the 
day collected in relatively dark places in the vessel, or on the 
under-surface of stones. I suspect that the animals begin to 
move anew at night, and then at the approach of day again 
collect in relatively dark places. I repeatedly covered one- 
half of the glass vessel in which I kept the Planarians with 
black paper in the morning. No change occurred through 
the day. On the next morning, however, I found all the 
animals under the covered portion of the aquarium. This 
could be interpreted only as showing that the animals crept 
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