Landing reaction of Musca domestica. IV. A monocular and binocular vision; B. relationships between landing and optomotor reactions.

1. The behaviours of monocular and binocular flies are compared with respect to the landing reaction. It is found that landing reaction is elicited through different mechanisms by stimulating the zones of single or of double vision: M onocular stim ulation in the field of single vision evokes reactions with both ipsilateral and contralateral legs; monocular stimulation in the field of double vision evokes reaction only with the ipsilateral legs. 2. The relationships between landing and optomotor reactions are analyzed. It is found that, a. When the fly is not free to turn itself, it may react to a lateral displacement in the visual field (optomotor stimulus) w ith a landing reaction; b. T he threshold for landing evoked by an ex­ pansion in the visual field (landing stim ulus) is much lower than the threshold for landing evoked by a lateral displacem ent; c. A horizontal lateral displacem ent in the visual field of an eye is adequate to evoke the landing reaction only if it is perceived in the direction from the front to the back of the eye; d. W hen the fly is free to turn itself, it can present both landing and opto­ motor reactions to a optomotor stim ulus; e. W hen the fly is fixed at a point, landing reaction can be evoked also by an escape stimulus.