Physiological Control 



of Luminescence in Animals 



J. A. C. Nicol' 

 Marine Biological Laboratory, Plymouth, England 



Luminescence appears to be almost universally subject to some degree 

 of regulation in animals (Harvey, 1953). As an initial approach w^e 

 can distinguish two main categories of luminescence, namely extrinsic 

 or bacterial, in which the light is produced by bacteria harbored by 

 the animal; and intrinsic, in which photogeny depends upon the 

 animal's own biochemical accomplishment. In either event, overt ap- 

 pearance of light, i.e., light emission to the exterior, is usually con- 

 trollable. 



If luminescence is considered in terms of effector systems, then I 

 think we can concede the following classification: (1) continuous 

 production of light by symbiotic bacteria; (2) discharge of luminous 

 secretion into a surrounding aqueous medium; (3) intracellular lumi- 

 nescence by the animal's photocytes. This is the foundation of my 

 discussion, and in this paper I shall review certain aspects of lumi- 

 nescence from the viewpoint of neuro-effector control. 



It would appear that symbiosis with luminescent bacteria is rela- 

 tively rare. The most interesting and best authenticated instances of 

 symbiosis are encountered in certain marine teleosts, in which lumi- 

 nescent bacteria are harbored in special circumscribed organs. By the 

 use of screening devices the light emitted by the bacteria can be 

 occluded or revealed. A few instances are also known of continuous 

 light emission on the part of the animal, e.g., in pelagic squid Spirula, 

 a millipede Luminodesmtis, the larva of the beetle Phengodes, and 



* Guggenheim Canadian Fellow. 



299 



