The visual system of Musca: Studies on optics, structure and function

Experiments were performed in order to obtain information on the function of receptive and neural structures, and to relate this to the histology. The study of the optical properties of the ommatidia, and the “wiring diagram” of the first optic ganglion as evaluated by means of histological methods (BRAITENBERG, 1967; TRUJILLO-CENOZ and MELAMED, 1966), lead to the hypothesis that the unfused rhabdoms of the Dipteran eye, combined with the special neural connexions between retina and lamina are a means of increasing the light gathering power in this type of compound eye by “neural superposition” of the output of receptors nos. 1 to 6. The concept of neural superposition predicts functional differences between the system composed of receptors 1 to 6 and, the other composed of receptors 7 and 8. These differences, concerning absolute and spectral sensitivity, sensitivity to polarized light, and contrast transfer, have been demonstrated by means of optomotor experiments. One other consequence of the concept of neural superposition is that one ommatidium alone should be able to analyze movement. This has been verfified by stimulation of pairs of receptors within one single ommatidium. By means of this technique it has been shown, furthermore, that movement detectors in the upper front region of the eye are arranged in two orthogonal directions. This information has been used in order to draw a network of connexions which are the least necessary and sufficient to explain the experimental results. These connexions are also the minimal ones that must be found in the histology of the information carrying channels