168 THE AMERICAN NATURALIST. (VoL. XXXIX. 
did not appear longer to respond to the directive influence. Its 
movements were hap-hazard, not guided by the direction of the 
light, as if the organism, in its state of extreme excitement, had 
lost for a time its tendency to place itself when in motion under 
conditions of symmetrical stimulation. This violent” kinetic 
effect of very intense light has been observed for several lower 
organisms by Pearl and Cole (:02). The conditions of their 
experiments did not permit them to note the effect on orienta- 
tion. Long exposure produced a paralyzing effect, so that the 
movements became more and more slow as the stimulus con- 
tinued to act. No insects were tested by them. 
The experiments with the 64 c. p. arc light made it clear that 
when the intensity is increased by lessening the distance of the 
light from 80 cm. to 40 cm. there is a marked increase in the 
rapidity of true phototropic responses. This result in the case 
of Drosophila is certainly not due merely to more precise orien- 
tation, as was suggested by Davenport ('97) to explain the 
increase in the rate at which Daphnia traveled under strong 
light. Itisinteresting to note that Yerkes (: 00), experimenting 
on the same organism (Daphnia), concluded that while the 
increase in rate depended chiefly upon precision and quickness 
of orientation, there was also evidence of a quickening of the 
“swimming motions. 
It was stated at the beginning of this paper that when the 
insects are exposed in a large cylindrical glass vessel, to direct 
sunlight from a window, many of them eventually come to rest 
on the sides of the vessel which are least illuminated. Their 
heads are in this instance directed away from the source of 
light. When disturbed by the vessel's being turned about they 
show positive phototropic responses by flying toward the light. 
This apparent negative orientation while at rest is not due, 
therefore, to a reversal of the directive influence of the light 
owing to continued exposure to a higher intensity. 
It seems probable that the behavior of the flies under these 
conditions is the result of the following causes. When first 
exposed to the strong kinetic influence of bright sunlight Droso- 
phila becomes very active. Its flying and creeping movements 
toward the light are limited by the wall of the vessel, and the 
