ABSTRACT
In a diffusion gradient of humidity at uniform temperature, some cockroaches (Blatta orientalis, L.) show a tendency to spend more time in the drier region. Other individuals appear to be indifferent to the stimulus of air humidity.
On desiccation, there is a tendency for cockroaches to become hygro-positive.
In a temperature gradient, those individuals which react to humidity have a slightly but significantly higher preferred temperature in somewhat moist air than they have in dry air.
It seems, then, that the observed preferred temperature represents a kind of balance between a pure temperature reaction and a humidity reaction. The change in humidity reaction resulting from desiccation is qualitatively satisfactory to explain the fall in preferred temperature which occurs at the same time.
This part of the experimental work was done by C. A. C.
