Spectral and polarization sensitivity measurements were made at several levels (retina, first and third optic ganglion, cervical connective, behavior) of the dipteran visual nervous system. At all levels, it was possible to reveal contributions from the retinular cell subsystem cells 1 to 6 or the retinular cell subsystem cells 7 and 8 or both. Only retinular cells I to 6 were directly studied, and all possessed the same spectral sensitivity characterized by two approximately equal sensitivity peaks at 350 and 480 nm. All units of both the sustaining and on-off variety in the first optic ganglion exhibited the same spectral sensitivity as that of retinular cells 1 to 6. It was possible to demonstrate for motion detection and optomotor responses two different spectral sensitivities depending upon the spatial wavelength of the stimulus. For long spatial wavelengths, the spectral sensitivity agreed with retinular cells I to 6; however, the spectral sensitivity at short spatial wavelengths was characterized by a single peak at 465 nm reflecting contributions from the (7, 8) subsystem. Although the two subsystems exhibited different spectral sensitivities, the difference was small and no indication of color discrimination mechanisms was observed. Although all retinular cells 1 to 6 exhibited a preferred polarization plane, sustaining and on-off units did not. Likewise, motion detection and optomotor responses were insensitive to the polarization plane for long spatial wavelength stimuli; however, sensitivity to select polarization planes was observed for short spatial wavelengths.

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u,' The authors describe a novel stereotaxic method for the removal of minute lesions of the central nervous system (CNS). With the development and refinement of computerized tomography (CT), such small lesions can be detected by noninvasive (x-ray) scanning with computer processing of the data. Using a G E 7800 scanner system and a PDP 11/45 computer, data processing of various kinds is possible. Multiple computer programs have been developed to enhance regions of interest on CT scans by magnification, threedimensional reconstruction, and digital processing. These data are then used to calculate a stereotaxic approach to a CNS lesion. A head fixation system has been devised to enable information transfer from a CT scan to the stereotaxic surgical system. Newly developed instruments are mounted on a micromanipulator for guidance at the operative site. These include stereo endoscopes with xenon arc illumination, a tissue expander for exposing the operative area, a radiation tracer probe, a rotary extractor, and instruments for operating and removal of blood from a small intracerebral hemorrhage. The micromanipulator for guiding the tactical instruments is, in turn, mounted on a stereotaxic guide mechanism which accurately defines all areas of the cranium in three-dimensional coordinates. The combination enables the site of the lesion, the three-dimensional coordinates of which have been located by CT scan, to be accurately approached by the stereotaxic guide/micromanipulator assembly.