Apparatus for Investigating the Reactions of Land Arthropods to Humidity

ABSTRACT Apparatus for the investigation of the reactions of land arthropods to air humidity is described. A(1). A straight line gradient of humidity is obtained with a long closed channel, into which water vapour is diffusing at one end, while being absorbed from it at the other end. The undesirable ends present in the above apparatus are eliminated by constructing the channel in the form of a ring. A (2). Any two humidities may be presented to an animal as alternatives in a simple chamber which has the advantage of providing space in which the animal can manœuvre, as well as being very cheap and easy to make. The exact form of the gradient is not, however, known in this chamber. B (1). The effect of different air humidities on the general state of activity of an insect may be investigated in an “Aktograph” consisting of a delicately balanced box; the movements of an insect inside the box cause it to tip to one side or the other, and this tipping is recorded by a lever writing on a drum. B (2). The existence of an avoiding reaction to humidity may be determined in the apparatus described under A (2), arranged so as to provide a wall of suddenly rising humidity across the centre of the dish. B (3). A straight line gradient, which for convenience must be shorter than A (1), may be obtained across a wide area, suitable for the study of directed reactions.