LUMINESCENCE 



559 



appear to be bacteria, and the origin of the light is still in some doubt 

 (10, 28). 



Among teleosts many examples of symbiotic relationships with lumines- 

 cent bacteria are known. In Malacocephalus laevis luminescent granules 

 resembling bacteria are located in large glandular sacs lying in the ventral 

 surface of the body, and this luminescent material can be expelled by the 

 fish (Fig. 13.22). Similar conditions occur in Coelorhynchus japonicus, 

 Physiculus japonicus and Hymenocephalus striatissimus, where the luminous 

 bacteria are housed in a gland beneath the skin and the light shines through 

 the body wall. In the Japanese kingfish Monocentris japonicus the organ 

 harbouring the luminescent bacteria is located in the lower jaw, and in 

 Gazza and Leiognathus (=EqimIa) a ring-shaped gland envelops the oeso- 

 phagus into which it opens. The luminescent organ of Acropoma 



Light 

 gland 



Hyaline 

 body 



heath 



gland 



Fig. 13.22. Luminous Organ of the Teleost Malacocephalus. The Light- 

 gland OPENS ON THE VENTRAL SURFACE CLOSE TO THE RECTUM. 



(From Hickling (32).) 



japonicum is embedded in the muscles of the ventral body wall and is 

 provided with a long duct leading to the exterior. In some of these animals 

 the tissues bordering the light-organ are organized into reflectors and lenses 

 so as to direct the emission of light. An open gland containing what may 

 prove to be luminescent bacteria is also found in the bathypelagic teleost 

 Ceratias and other angler-fishes in the esca at the tip of the anterior dorsal 

 fin-ray (Fig. 13.8(c)). Finally, we may mention two interesting East Indian 

 fish Photoblepharon palpebratus and Anomalops katoptron which have a 

 conspicuous white light-organ located immediately underneath each eye 

 (Fig. 13.23). The interior of these organs is occupied by epithelial tissue 

 containing rod-like bacteria (11, 23, 24, 26b). 



BIOCHEMISTRY OF LIGHT-PRODUCTION 



The chemical substances responsible for bioluminescence have been 

 subjected to intensive study, and the chemical reactions have been followed 

 and measured by the light that is emitted. The luminescent substances are 

 highly specific materials, available only from animal sources; nevertheless, 



