Luminous Organs of Fish Which Emit Light Indirectly

INTRODUCTI9N THERE ARE MANY REPO~TS of luminous fishes, all of which, in earlier days, were taken from the deep seas. Luminous organs were found on the sides of the bodies, on the barbels, or on the antennae. In ourward 'appearance these fishes were strangely shaped and feebl y developed, with soft bones and loose muscles, and it was assumed that such 'unusual fishes belonged exclusively to the deepsea fauna. The material examined was invariably dead and damaged. It might have been newly .caught, or else had been preserved in formalin or in alcohol for an indefinite period. There seems to be very little record of observations on living material , 'and only the , morphology of the organs of these fishes was studied. The organs were never really understood, and were mistaken for sensory organs, electric organs, or secondary eyes, or they were simply referred to as eye-like organs. , In the early days bacteriological knowledge, especially knowledge of luminous bacteria was not far advanced, and fish which became luminous after death as a result of contamination by saprophytic luminous bacteria were mistaken for true luminous fishes. Recent advances in the study of these interesting problems of luminosity have shown that luminous fishes are not confined to the deep-sea fauna, but may be found among the fauna of the shallow and coastal waters of the sea, and that luminosity may be caused by luminous bacteria. Moreover these studies have revealed that luminous bacteria play an important role in the production of light in