60 STUDIES IN GENERAL PHYSIOLOGY 
before exposing them to the sunlight I covered them with a 
box of dark-blue glass. Within ten to twenty seconds these 
animals had also placed their median planes sharply and 
precisely in the direction of the rays of light, in which 
direction they moved toward the room side. When I tooka 
third lot of fresh animals and covered them with red glass, 
the orientation of the animals into the direction of the rays 
did not occur. They crept to the right and to the left, occa- 
sionally moving a short distance toward the source of light; 
but even after minutes under the red glass the precise orien- 
tation of the animals, which followed under the blue glass in 
a few seconds, did not occur. Under red glass the animals 
behaved toward direct sunlight just as they did under blue 
glass toward very weak daylight. That the rays which pass 
through red glass are not absolutely without effect seems to 
be shown by the fact that the animals avoided going to the 
window side, and that they finally collected at the room side 
of the board. The directing force of the red rays seems 
therefore to be limited to this, that the animals will not 
move for long distances toward the source of light. In con- 
sequence, the animals must collect ultimately on the room 
side of the vessel. 
In all the previous experiments the animals were on a 
plane board. When at the beginning of an experiment the 
animals were collected on the window side of a test-tube 
which lay horizontal and perpendicular to the plane of the 
window, in direct sunlight and under blue glass all the ani- 
mals turned their oral poles within ten seconds toward the 
room side of the tube. In about twenty seconds they 
migrated to the room end of the tube. When the same ani- 
mals were exposed in the same way to direct sunlight, but 
under red glass, they neither oriented themselves nor moved 
toward the room side of the tube during the next four 
minutes, even though they were very restless. 
Digitized by Microsoft® 
