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 



