ABSTRACT
Two fluorescent materials have been localized in the adult firefly light organ by fluorescence microscopy. One of these is located in photocyte granules, has a maximum emission between 510 and 540 nm, is more fluorescent in basic than acidic solution, and is unstable in ultraviolet light, phosphomolybdic acid, and potassium permanganate. It is thought to be luciferin. The fluorescence of this material is very dim in untreated fireflies but increases substantially following sustained light emission induced by synephrine or prolonged electrical stimulation. It is suggested that the luciferin of untreated animals is bound in the granules and that binding suppresses its fluorescence. The second fluorescent material is located in the dorsal layer of the light organ, particularly in the cells bordering on the photogenic layer. This material has a maximum emission between 510 and 520 nm, is relatively stable in ultraviolet light, and rapidly disappears when light organs are exposed to water. Its identity and function are unknown.