Abstract
Records are reproduced showing various types of luminescence intensity-time curves for the prothoracic light organs of Pyrophorus. A small (5 per cent) rhythmic fluctuation of light intensity during the reflex emission of light is to be observed in many records, which because of its rapid rate is attributed to rhythmic nerve discharge from a photogenic centre. Longer "pulsations" of luminescence intensity (25 per cent change) can be detected by the eye.