| 1. | The neural mechanisms responsible for flashing in the firefly,L. lusitanica, were investigated by means of localized electrolytic lesions and electrical stimulations. |
| 2. | Restricted lesions of the median protocerebral neuropile produced the irreversible abolition of spontaneous flashing and of the associated photogenic volleys. Single electric shocks applied to the same structure were followed by a propagated action potential in the lanternal nerves; a short (40 ms) train of stimuli at 200/s evoked a fully developed photogenic volley and the related flash, both of which were identical in all respects to the spontaneous ones (Figs. 2, 3). |
| 3. | Separation of the protocerebrum from the optic lobes led to the disappearence of rhythmic flashing, which was replaced by a continuous, dull luminescence; at the same time the photogenic volleys of the lanternal nerves were replaced by a continuous, asynchronous discharge at low frequency (Fig. 15). |
| 4. | Ablation of theretina-lamina ganglionaris complex was followed by a marked increase of flashing frequency. Electrical stimulation of theretina at low repetition rate (5/s) was followed by depression of both frequency and intensity of spontaneous flashing; opposite effects (i.e. increase in flashing frequency and intensity) were obtained by high rate (30/s) retinal stimulation (Figs. 6–9). |
| 5. | Electrolytic lesions of the medulla performed after ablation of theretina-lamina complex, did not produce any change in the patterns of spontaneous flashing. Electrical stimulation of the medulla produced facilitatory effects on flashing at all repetition rates used, with the lowest threshold at 30/s. This effect disappeared after localized electrolytic lesion (Figs. 12–14). |
| 6. | These findings are discussed and it is concluded that (a) the photomotor neurons of the firefly's brain are located in the deep protocerebral neuropile; (b) their rhythmic activity is the result of the interaction with an oscillator located in the optic lobes, possibly in the lobula; (c) the retina-lamina complex exerts a tonic inhibitory influence on flashing; (d) a phasic facilitatory influence is exerted by neural structures located at the level of the medulla. |
