354 STUDIES IN GENERAL PHYSIOLOGY 
about in the vessel during the night, and came to rest in the 
morning in the darkest regions. 
These animals possess at the oral pole not only a brain 
but also comparatively well-developed eyes. I decided to 
test whether a decapitated Planarian still shows the same 
reactions toward light as normal Planarians, in spite of the 
loss of brain and eyes. This is true in a most surprising 
way. About sixty specimens of Planaria torva were cut 
across transversely, close behind the brain and the eyes, in 
the evening. All the pieces were put into a vessel having 
vertical sides and half covered with black paper. On the 
next morning nearly all the posterior pieces as well as the 
oral pieces were found in the covered part of the aquarium. 
They were fairly uniformly distributed here. A few were 
found in the uncovered portion of the vessel, but among 
these there were head pieces as well as aboral pieces crowded 
together in one corner in the room side of the dish. In this 
corner the intensity of the light was relatively low. In 
repeating this experiment with normal animals I obtained 
the same results as with the decapitated animals. When the 
decapitated animals had collected in the covered portion of 
the vessel and had become perfectly quiet, their quiet was 
quickly disturbed when the dark paper was suddenly removed 
without jarring the vessel. The animals began to move, crept 
at first toward the room side, and finally collected again in 
regions where the light was least intense. This reaction also 
occurred as in normal animals, with this difference, however, 
that the reaction time of the brainless animals to changes in 
the intensity of the light was greater than in normal animals. 
In the animals possessing a brain and eyes the reaction began 
about one minute after light struck them; in the brainless 
pieces after about five minutes. In these experiments only 
diffuse daylight was used as a stimulus. 
I have pointed out before that when uninjured Planarians 
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