Tissues of animals and plants that show marked fluorescence in near ultraviolet light are described and a special study made of fluorescence of the photogenic material of luminous animals. Beroe, Amphiura, Ophiopsila, Acholoe, and cope-pods show marked fluorescence of the luminous tissue, after a strong luminescence, even when the luminescent light has completely subsided, probably due to fluorescence of the oxidation product of luminescent material. Fire-flies, Pyrophorus and Myctophum, always show fluorescence of the luminous organ but this may be due to continual presence of the oxidation product of luminescent material. Luminous bacteria, fungi (Panus), radiolarians, Pennatula, Funiculina, Thelepus, Tomop-teris, Pholas, Cypridina, Heteroteuthis and Balanoglos sus show no special fluorescence. Chaetopterus and Microscolex are doubtful; their luminous slime is quite fluorescent but non-luminous slime is often fluorescent also. Many luminous fish preserved in formalin show markedly fluorescent luminous organs. The luminous organ of the fire-fly is fluorescent after boiling and when dried (even after 10 yrs.). Ophiopsila and Acholoe show fluorescence but not bioluminescence in absence of O. The color of the fluorescence is usually about the same as that of the luminescence, but in the fire-fly, Photinus pyralis, the fluorescence is decidedly more yellow than the orange luminescence.