70 STUDIES IN GENERAL PHYSIOLOGY 
X. THE NEGATIVE HELIOTROPISM OF THE LARVE OF TENEBRIO 
MOLITOR 
The larve of a beetle Tenebrio molitor, which can easily 
be collected in large quantities, are also suitable animals 
upon which to demonstrate negative heliotropism. When 
such animals are placed on a plate, they creep to the room 
side of it; if the intensity of the light is sufficiently great, 
they remain there. If the plate be covered with dark-blue 
glass, the result of the experiment is the same. If the plate 
be covered with red glass, the animals move in the concave 
edge of the piate both toward the window and away from it; 
a definite orientation does not occur. Under red glass they 
behave just as in the dark; under blue glass, just as in the 
light. 
I covered one-half of a plate with blue glass and one-half 
with red glass, so that the boundary between them lay in the 
direction of the rays. The animals were distributed equally 
over the plate at the beginning of the experiment. All the 
animals in the blue half moved to the room side of the plate, 
but none in the opposite direction; in the red half they 
moved in all directions. The animals moved from the blue 
into the red, but never from the red into the blue. When I 
covered one-half of the plate with opaque cardboard, the 
other half with red glass, so that the boundary between them 
again coincided with the direction of the rays of light, the 
animals scattered in all directions in the two halves of the 
plate. After a long time, however, the greater number col- 
lected under the cardboard. 
The experiments which have been described were made in 
direct sunlight. If on a dark day the plate is some distance 
from the window and the light is not very intense, the ani- 
mals, which at the beginning of the experiment were in the 
middle of the plate, will gradually creep toward the room 
side; when, however, they reach the shallow groove in the 
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