Biol 



inninesccnce 



665 



Light jiroduction among the chordatcs is restricted to the protochordates 

 and hshcs. A kiminous slime is produced, for example, bv species of Valano- 

 glussxis. Among the tunicates, the best known example of a luminescent 

 form is Pyrosovia, a colonial species. The organism luminesces on stimulation, 

 and a wave of photogenic acti\ity spreads out o\'er this colonial organism.-"''' 

 Light definitely operates as a stimulus in this spread of activity from one 

 luminescing indix'idual of a colony to adjacent ones. Thus the wave of 

 activity has been reported to pass from one colony to another even when 

 glass walls separate the two colonies. Similarlv, acti\itv mav be induced in 

 a colonv by using a light flash as a stimulating agent. 



A 



B 



C 



Fig. 252. A female larva of the beetle, Phengodes. A, Dorsal view. B, Lateral view. 

 C, A luminous specimen in darkness (From Harvey 1940).''^ 



The elasmobranch and especially the teleost fishes have numerous lumi- 

 nescent representatives, particularly among those inhabiting the depths of 

 the seas. In some, like Photohlefharon, Anomalous, Physiciihis, EqiinJa, and 

 Monocentris, the light is due to the presence of symbiotic bacteria in special 

 organs found in the cheeks or lower jaw.-' In others, e.g., Malacocephalus, 

 luminescent granules, possibly bacteria, are expelled from ventral sacs onto 

 the ventral surface of the body when the fish is excited. Still others, as Astro- 

 nesthes and Stomias, possess well-differentiated eye-like organs with lenses 

 and pigmented cups. In some fishes the appearance of light on stimulation is 



