Survey of Luminous Organisms: 

 Problems and Prospects 



E. Newton Harvey 

 Department of Biology, Princeton University, Princeton, New Jersey 



One of the first questions to be settled on discovery of a living lumi- 

 nous organism is whether the species is truly self-luminous, with 

 light from a chemiluminescent system of its own, or whether the light 

 comes from luminous bacteria. The answer is important because light 

 emission from luminous cells is usually associated with coccus-like 

 granules, which look like bacteria, and the existence of symbiotic 

 luminous bacteria in a number of species has been definitely estab- 

 lished. 



There are in fact three categories of luminous bacteria associated 

 with organisms. In addition to the saprophytic varieties, growing on 

 dead fish or flesh, parasitic bacteria occasionally attack living sand- 

 fleas, midges, and caterpillars, giving rise to a luminous disease which 

 is usually fatal to the infected individual. Nevertheless, the animals 

 are active while living, and have been reported as luminous species. 



A much more important and widespread type of luminescence re- 

 sults from bacterial symbiosis, common among the squid and the fish. 

 Every individual of a species whose light is associated with symbiotic 

 luminous bacteria must be luminous. In addition, the host often pos- 

 sesses complicated luminous organs in which the symbionts grow. 

 Although the luminous bacteria emit a continuous light, the fish or 

 squid may develop special devices, movable screens, or migrating 

 chromatophores by which the bacterial light can be obscured. 



The most striking instances of bacterial symbiosis occur in the 

 Indonesian fish, Photobleplioron and Anomalops, two genera of the 



