1912] Ecology of Dragon-fly Nymphs 287 
the dish, passing the concave corner, and comes to rest at the end of the 
trough at right angles to the rays of light. 
Experiment C. The nymph is placed in the glass dish at the end 
toward the light. It turns slowly toward the left until the body is at 
right angles to the rays of light. It remains in this position for 2 seconds. 
The animal turns further to the left. Its body is now oblique to the 
rays of light. It moves obliquely forward 1 cm. The nymph turns to 
the left so that its body is now parallel with the rays of light. It swims 
forward 8 cm. and then stops, resting on the bottom of the vessel. It 
remains stationary 6 seconds. Then it walks forward 4 cm. It stops 
for 3 seconds with its body slightly oblique to the light rays. The 
animal walks forward 6 cm. and then comes in contact with the side of 
the dish. It remains in a resting position for 25 seconds. It walks 
along the side of the vessel for 4 cm. and then reaches the water. It 
walks forward for 2 cm. and then stops, performing cleaning reactions. 
After remaining quiet for 20 seconds, it swims to the end of the dish. 
The responses of the nymphs as indicated in these experi- 
ments are suggestive of those described by Holmes (1902, 
p. 212) for Gammarus and Amphithée. This observer states 
that, “If a single individual be watched it will be seen to strug- 
gle for a time, to move away from the light; it will then rest, for 
a longer or shorter period, only to resume its struggle later.”’ 
The writer performed a large number of experiments similar to 
those described as A, B, and C. In each case different nymphs 
were used. It is evident that such photic responses are con- 
spicuously lacking in the factors of directness and precision. 
While the three experiments described are more or less similar 
in details, it is obvious that there are differences. The nymphs 
appear to possess some individuality. The movements are 
not so stereotyped, but that they allow of considerable mod- 
ification. 
A number of experiments were performed in which the same 
nymph was exposed to the light from the incandescent lamp. 
Usually there were ten trials in a series, and the same individual 
was used throughout each series. In referring to the details of 
my experiments, they indicate, in a general way at least, that 
in the first few trials of the series, the reactions to light were 
fairly definite—the animal moving away from the source of 
illumination. The animals frequently responded by the swim- 
ming movement. Toward the end of the series, there were 
more pauses as the organisms traveled from one end of the dish 
to the other. The cleaning reactions were performed from 
time to time as the nymph rested, and walking was the prin- 
cipal method of locomotion. 
