286 Annals Entomological Society of America  [Vol. XIV, 
Gerris remigis responds positively to an oscillating electric 
light of 44 ca. m. in the experimental field. The light oscillated 
in a plane parallel to the end of the aquarium containing the 
gerrids. Thirty water-striders were used in the experiments, 
the majority of them orienting with their heads pointed toward 
the oscillating hight and also moving promptly to the positive 
end of the aquarium. They appear to orient to and also to 
move toward the source of illumination more promptly than 
was the case with respect to the stationary light of a similar 
intensity. Before reaching the positive end of the aquarium, 
their path becomes oblique to the longitudinal axis of the 
vessel, this being due, apparently, to the oscillations of the 
light. On nearing the lighter end of the aquarium, there 
appears to be some “‘indecision’’ as to their direction of move- 
ment. There are some attempts to follow the swinging light, 
but, in the main, many of them make only slight changes in 
position, after reaching this end of the vessel. Some remain 
practically stationary, in so far as locomotion is concerned, 
being engaged in cleaning responses. Others move close to the 
glass end of the aquarium and attempt both to orient to and ~ 
also to follow the lght. 
The responses of water-striders to an oscillating electric 
light of approximately 22 ca. m. in the field of experimentation, 
in general, are very similar to those described in the experiments 
when the stronger light was employed. Twenty gerrids were 
used in the experiments. Their responses to the source of 
illumination are positive, but there is-neither quite the same 
promptness in orienting to, nor in moving toward the light as 
was the case in the experimental work with the light of greater 
intensity. After nearing the positive end of the aquarium, 
while their responses are much the same as in the former 
experiments, with the electric light of stronger illumination, 
yet in general the responses are rather less definite and precise. 
A number of experiments were conducted with a moving, 
but non-oscillating, electric light of 44 ca. m. in the experimental 
field. Forty gerrids were used in the experiments and they 
readily move around the aquarium in which they are confined, 
in response to a moving light. They either follow just behind 
the light or else retain positions almost parallel to it. However, 
these positions vary, for there is not much regularity about this 
