290 Annals Entomological Society of America [Vol. V, 
mechanical—contact—stimul bring about changes in the 
relative positions of some of the individuals in the various 
groups. At such times there is a slackening of the grip of the 
appendages, so permitting photic stimuli to be more effective. 
The disintegration of the groups, then, is due to mechanical— 
contact—stimuli plus the stimuli of the powerful electric light. 
Immediately after the disintegration of a group, there appears 
to be a lack of definiteness in the responses of the nymphs to the 
electric light. They swim away from the cluster at various 
angles to the rays of light. While the majority of them even- 
tually arrive at the end of the trough farthest from the source 
of light, certain individuals exhibit a tendency to positiveness 
in their photic responses. This result may be due to a change 
in bodily condition, induced, possibly, either by thigmotaxis or 
by the effect of photic stimuli. Agrionid nymphs respond 
negatively to a 16 c. p. incandescent light, swimming away to 
the end of the trough farthest from the source of illumination. 
When responding to such photic stimuli, the insects frequently 
walk from one end of the trough to the other. The swimming 
reaction appears to be inhibited. The responses often lack 
promptness and precision. When the same individual is used 
in a series of experiments, the responses in the first few trials 
prove to be fairly definite, the animal swimming away from 
the source of illumination. Toward the end of the series there 
are pauses as the animal moves from one end of the trough to 
the other, and cleaning reactions are performed. When diffuse 
daylight is used as a source of illumination, the nymphs exhibit 
practically no response either to light intensity, or to the direc- 
tion of the rays. A large majority of the insects appear indif- 
ferent to the light. A few individuals tend to exhibit a positive 
response to photic stimuli of this nature. 
It seems possible to the writer that the behavior of Agrionid 
nymphs with respect to light and contact, may not be entirely 
of a reflex, mechanical nature. Such reactions are not always 
precise and definite; sometimes they are considerably modified. 
May they not, as Holmes (1905, pp. 337-349) has shown with 
respect to Ranatra, possess some of the concomitants of the 
‘““nleasure-pain’’ type of reaction? This form of response has 
been excellently discussed by Holmes (1910), (1911), and 
(191la), in several suggestive papers. The thigmotactic and 
photic reactions of these dragon-fly nymphs appear to be bene- 
