286 Annals Entomological Society of America [Vol. V, 
animals may be held in check by contact stimuli, as stated in 
the following quotation (1905, p. 325): ‘‘Contact stimuli not 
only inhibit positive phototaxis, but they produce a negative 
reaction as we have already seen; the latter tendency, however, 
is often held in check by the same cause by which it is brought 
about.”’ 
RESPONSE TO LESS INTENSE ARTIFICIAL LIGHT. 
My experiments on dragon-fly nymphs with a 16 c. p. 
incandescent light show that the animals respond negatively, 
their movements taking them to the end of the glass trough 
farthest from the source of illumination. Frequently the 
organisms walk from one end of the vessel to the other in a 
rather leisurely fashion. In such cases the swimming mode of 
locomotion seems to be inhibited. The reactions are often 
lacking in promptness and precision as the following experi- 
ments will show: 
Experiment A. The nymph is placed, by means of a camel’s hair 
brush, in the glass trough facing the light. The creature is slightly 
nearer to the left than it is to the right side of the vessel. Immediately 
the animal turns slowly half way around. This movementis slow. Now, 
the anterior pair of legs come in contact with the side of the dish. It 
walks entirely onto the side of the trough. At the same time it contin- 
ues the turning movement, until the head points away from the light. 
It walks slowly along the side for half the length of the vessel. The 
nymph stops for 5 seconds. Again it moves forward until within 
4 cm. of the end of the trough. It stops and performs cleaning reactions. 
In a few seconds, the animal walks slowly to the end of the trough. 
Experiment B. The nymph is placed in the center of the glass dish, 
at the end near the source of light. It remains stationary for 7 seconds. 
The animal then turns slowly to the right until in a position oblique to 
the direction of the rays. It again remains quiet for 3 seconds. It 
turns slowly further to the right and at the same time moves slightly 
toward the right side of the vessel. The front legs come in contact with 
the glass side and the nymph stops for 4 seconds. The creature turns 
very slowly until it is in a position at right angles to the rays of light. 
As it turns, 1t walks slowly up the side of the dish. It remains here for 
5 seconds in a position perpendicular to the floor of the trough. The 
animal turns slowly, the long axis of its body becoming parallel with 
the rays of light. It moves away from the light for a distance of 5 cm. 
It then stops for 2 seconds. It again moves forward for a distance of 
5 em. The nymph now stops for 8 seconds. It moves forward slowly 
for 2 cm. It stops for 2 seconds and then goes ahead a distance of 
4cm. The creature remains quiet for 3 seconds, after which it walks 
forward for 1 cm. It again stops; this time for a period of 16 seconds 
and performs cleaning reactions. It then moves slowly to the end of 
