662 H. SCHIFF AND N. SCHÔNENBERGER 



and discharge patterns of one type of fibers in the optic nerve (Trevino ancl 

 Larimer, 1970). 



In our research we combined a study involving the structure of the ganglicjj 

 with that of frequency patterns from single primary, secondary, tertiary, ancU 

 optic nerve-fibers. 



The gênerai structure of the eye and the ommatidia and the fine structure oll 

 the retina have been described in previous papers (Schiff, 1963, 1970). The firsl 

 of thèse also gives the techniques for extracellular single fiber recording and the j 

 results of an electrophysiological research concerning the discharge patterns oti 



Fig. 2. 



Response of a secondary nerve fiber to sudden " on " of light. 

 The initial higher frequency decreases exponentially to zéro. 

 The lower line shows the registration of a calibrated photocell. 

 Light intensity: 6 lux. Length of trace: 10 sec. 



secondary fibers in response to changing light intensities, wavelengths, and to 

 adaptation, contrast and moving objects. 



Figure la shows the arrangement of the lamina, primary and secondary 

 fibers, and medulla externa and of the neurommatidia (optic cartridges) in the 

 lamina. Figure \b shows an optical cartridge of the lamina according to our 

 preliminary results. 



Primary (?) and secondary fibers show "on" responses with a slow exponen- 

 tial décline to zéro and no "off" responses (fig. 2). Graduai light increase is 

 followed by a graduai frequency increase (fig. 3). 



Tertiary fibers respond instead with short " on " and/or " off " bursts with 

 a much higher frequency than secondary fibers as well to step function as to 

 graduai light changes (fig. 4). Five fiber types could be distinguished within the 

 tertiary fiber bundle: 1. IC— (irregularly continuously firing) fibers, 2. RC— (regu- 

 larly continuously firing) fibers, 3. "on" fibers, 4. "on-off" fibers, 5. "off" 

 fibers. IC — and RC — fibers are pulse-code-and position-modulated by light 

 changes (fig. 5). 



The few truly optic fibers in the optic nerve resemble in their response 

 pattern partly the secondary fibers and partly the tertiary fibers (fig. 6). 



