232 Annals Entomological Society of America  [Vol. XIV, 
I, INTRODUCTION. 
Two of the most pronounced forms of behavior of many of 
the aquatic and semiaquatic Hexapoda are their responses to 
contact and to light stimuli. Study and observation of the 
aquatic species Gerris remigis Say, of the family Gerride, one 
of the common forms of aquatic Heteroptera, have demonstrated 
that it, also, evinces responses of this character. 
Gerris remigis is a typical water-film species (Figs. 1, 11), 
being widely distributed in the United States on the surfaces of 
brooks, creeks and rivers, with currents of moderate velocity. 
Fig. 1. The large water-strider, Gerris remigis Say, apterous form; 
a typical surface-film, stream inhabitant. Natural size. 
(Drawing by Beutenmiiller.) 
The rapidity with which it strides along the water-film, without 
breaking through the surface, its noticeably facile and agile 
movements, and the ease with which it obtains food, entangled 
in the surface-film, all tend to indicate the adequacy of its 
responses for living in a water-film habitat. Its elongated 
body and tapering, slender legs, spread widely apart, thus 
more equally distributing its weight over the water-surface, are 
plainly evident as this species of gerrid darts to and fro in its 
stream habitat. Such characteristics seem to suggest the 
suitableness of its bodily structure for a life on the surface 
of water. 
