Eye Movements in the housefly, Musca domestica

“Clock-spikes” in Musca are produced by a motoneurone which lies in the subesopha-geal ganglion. It innervates a small muscle, attached to the inner frontal margin of the retina. In the frontal eye region, muscular activity causes the distal rhabdomere tips to move perpendicular to the ommatidial axes. Slow angular movements of the optical axes of the retinula cells result herefrom. The spike rate can be slightly changed by a variety of gross visual stimuli. The adequate visual stimulus as well as the functional significance of the eye muscle system with respect to the behaviour of the unrestrained insects are still unknown.