H. B. Weiss.
Positive Thigmotropism of Culex pipiens in Hibernation.
Psyche 20:36, 1913.

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36 Psyche i~ebruary
POSITIVE THIGMOTROPISM OF CULEX PIPIENS IN HIBERNATION.
. BY HARRY B. WEISS,
New Brunswick, N. J.
Commencing about the middle of September, gravid females of Culex pipiens become strongly negatively phototropic and seek dark hibernation quarters which in the cities consist of cellars, basements, closed empty houses and the like. They must how- ever be dark. The activity of these hibernating individuals depends entirely upon the temperature of the cellar or other place selected. If the place be warm, they are quite active when dis- turbed and if cold they are more or less torpid. Positive thigmo- tropism is of course exhibited only by those hibernating in warm' places.
After having become acclimated to these surroundings, the negative phototropism seems to be entirely supplanted by positive thigmotropism. Phototropic stimuli no longer produce responses. Upon being disturbed, they fly readily, but not far from their place of rest which is usually the lower side of a wall and always return to a similar position.
A shaft of sunlight manipulated by mirrors and thrown upon specimens in these positions produced absolutely no reactions. A sixteen candle-power electric light placed a foot away from speci- mens and allowed to remain there for an hour, also produced no response. The insects made no attempt to fly into a region of less illumination or from a less to a greater, but remained clinging to the wall. Of course it must be remembered that they were in a slightly dormant condition. Nevertheless they responded actively to mechanical stimuli.
In addition to being positively thigmotropic, gravid hibernating females of Culex pipiens are negatively geotropic. They always assume a position with the long axis of the body perpendicular to the earth and the head pointing upward. Never have I seen one in a different attitude.
The tropisms of C. pipiens are varied and interesting. Taking the female, we find her during the summer to be normally nega-



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