166 THE AMERICAN NATURALIST. | (Vor. XXXIX. 
sometimes through the entire distance. Since it was impossible 
to obtain pure creeping responses in all cases, those involving 
both creeping and flying were taken into account. Pure flying 
responses were not timed. 
Observations were made on four flies, two males and two 
females, and the average time of twenty responses (five for each 
fly) at each of the four distances from the arc light was 
obtained. At 800 cm. and 300 cm. and even at 80 cm. the 
results did not materially differ, the average times of the 
responses at these three positions being respectively, 18 sec., 
I8 sec., 16.7 sec. At 40 cm. there was a marked increase in 
the rapidity of the movements of the flies, the average time 
of the responses being 7.4 sec. 
The behavior of a fly under continued exposure to the highest 
intensity of light available for these experiments seemed to be 
of considerable interest. The apparatus used was the same as 
for the experiments last described, except that an arc light of 
greater candle power (250 c. p. approx.) was used. The pro- 
cedure was also unchanged, the insect being brought up from a 
distance of 300 cm. to 80 cm. and finally to 40 cm. from the 
light. For each of the first two positions time records for five 
excursions were obtained, although those for 80 cm. required 
patient manipulation and many repetitions of the excursions, so 
numerous did the flying responses become. At 40 cm. the 
behavior of the fly was such that a full set of five readings 
could not be taken. Under the influence of the intense light 
the insect became extremely active, flying and leaping about 
spasmodically in all directions, and giving little or no evidence of 
directive responses. That is to say, the directive influence of 
the light was no longer effective enough to cause the fly to make 
excursions back and forth along the cylinder in accordance with 
the position of the illumination. While the fly was in this con- 
dition of great muscular activity, the screening off of thearc light 
and the turning on of the incandescent lamp, were followed by 
less activity on the part of the animal, but not by a progression 
toward the illuminated end of the vessel. The directive influ- 
ence seemed to be for the time inhibited. 
It appears, then, that continued exposure to a high intensity 
