238 Annals Entomological Society of America  [Vol. XIV, 
2. VARIATION OF RESPONSES UNDER SIMILAR 
CONDITIONS. 
The fact has been pointed out that although Gerris remigis 
responds to contact usually by a decrease or a cessation of its 
locomotory movements, yet the manner in which it responds, 
apparently, varies at different times. Similar facts have been 
observed when two or more gerrids, moving about on the 
surface-film, come in contact with each other, for under such 
conditions their responses also vary at different times. As 
they touch each other, the stimuli of contact may result in 
increased movement, the insects darting away from each other, 
in different directions, with great speed. This rapid loco- 
motion may continue for several minutes before it subsides. 
At such times the behavior of the water-striders appears as if 
due to some strong or unpleasant stimuli. After the subsidence 
of the immediate effects of the stimuli, they continue their 
usual movements. In connection with the statement that the 
gerrids, after coming in contact with each other, may continue 
to stride about rapidly for sometime after contact has occurred, 
a quotation from Jennings (1906, p. 285) may be of interest. 
He states that: 
Often, of course, stimulation does rouse an organism to increased 
activity. But even in this case the activity is due to the release of 
internal energy. It may, therefore, continue long after the stimulation 
which inaugurated the release has ceased to act. Such continuance 
thus does not necessarily imply continued action of the stimulus. In 
many cases the specific stimulus to action is only the change of 
conditions. 
The responses are not always as have been described, for on 
touching each other, the gerrids may not stride rapidly away, 
but, on the other hand, they may do so in a manner which is 
very slow and appears to be deliberate. Sometimes, when such 
contact occurs, while striding about on the water-surface, they 
pause for a few seconds and then move forward or backward 
again, usually the former movement taking place. 
It is rather difficult to understand, at least from direct 
observation and without definite experimental evidence, why 
these water-striders should respond in different ways at different 
times, for careful and repeated observations in the field seem 
to indicate that they respond differently, even when the stimuli 
