256 Annals Entomological Society of America  [Vol. XIV, 
water-surface and climbed up onto the surfaces of the stones. 
Very soon the leaders were followed by others, until, eventually, 
the majority of the gerrids had left the water. The entire 
upper surfaces of the stones were covered by the water-striders, 
sometimes several layers in thickness, so that they presented 
the appearance of dark brown masses extending above the 
surface of the water. The insects remained motionless, with 
their legs and bodies entangled in clusters. If undisturbed, 
they often stayed in these compact groupings for hours and 
even for days. The solid surfaces of the stones and the contact 
of the bodies of the hemipterons appeared to act as stimuli, 
inhibiting movements and resulting in the gerrids lying motion- 
less for long periods of time. 
Many of the insects left the surface of the water and crawled 
up the perpendicular glass faces of the aquaria, a response 
probably due to gravity. However, they did not remain in such 
situations, for within one or two hours they were all assembled, 
with the exception of a few individuals that were still leaving the 
surface of the water, in the angles formed by the meeting of 
two of the glass sides of the aquaria. Frequently, in these 
angles, there were formed tangled masses of gerrids, extending 
from a point one or two inches above the water-surface to the 
very tops of the aquaria. Several of the aquaria had metal 
flanges, extending inwards, placed at right angles to the upper 
edges of the upright glass sides. The juxtaposition of these 
flanges and the perpendicular sides of the aquaria formed 
right angles, and, often, many of the insects were found in 
these angles. Pearl (1903, pp. 560-562), experimenting with 
planarians, applied the name goniotaxis to responses of a similar 
character. The gerrids climbed to the very tops of the 
aquaria and formed tangled groups all round their upper 
edges and especially in the corners formed at the meeting 
points of the flanges and of two upright glass surfaces. Responses 
of this character were first observed when conducting experi- 
ments with some half dozen gerrids in each aquarium. It was 
noticed that the water-striders had disappeared. After search- 
ing for them carefully, it was found that they had crawled to 
the tops of the aquaria and had taken up positions such as 
already have been described. In a number of the aquaria, 
stones were placed close together, but with small spaces between 
them. It was observed that the gerrids crowded into these 
