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Annals Entomological Society of America [Vol. XIV, 
Although no quantitative data were obtained, the general 
behavior of the water-striders, with respect to the source of 
illumination, was very similar to that recorded in connection 
with their responses to the electric light of 44° ca. m. in the 
field of experimentation. If there was any difference of impor- 
tance, it was that the gerrids appeared to respond with some- 
what less promptness to the stimuli of the weaker light than 
they did to those of the stronger illumination. According to 
Essenberg (1915a, p. 400) who observed the light responses of 
a closely allied species, Gerris orba, she found that: 
It is more phototactic in strong light . . . less so in a weaker 
light. 
5. RESPONSES TO OSCILLATING ARTIFICIAL LIGHT OF 
MODERATE INTENSITY. 
Not only does Gerris remigis respond positively to a 
stationary electric light, but it also responds to a moving electric 
light. In these experiments the source of stimulation was an 
incandescent electric light of 44 ca. m. in the field of experi- 
mentation. The gerrids were placed on the surface-film in an 
aquarium of the usual kind, containing water a few inches in 
depth. The bulb of the electric light was hung directly in 
front of one end of the aquarium and made to oscillate as a 
pendulum, its plane of motion being parallel to the end of the 
receptacle. 
Thirty gerrids were used in the experiments. When the 
light was set in motion, the majority of the insects oriented 
with their heads pointing in the direction of the source of 
illumination. Then they moved promptly across the surface- 
film toward the positive end of the aquarium, in much the same 
manner as they did with respect to the stationary light of equal 
intensity. While no quantitative results were obtained, it 
was evident that the responses of the water-striders were more 
prompt with regard to the oscillating light than was the case 
with respect to the stationary one. They seemed to orient 
themselves to the source of illumination and also to move 
toward it more readily, perhaps, than was observed to be the 
case in their responses to the stationary light. 
After reaching a point in the aquarium A ORToRserele 
eight to ten inches away from the glass end, nearest the source 
