Bioluminescence 205 



fill amount of illumination for the individuals producing it as well 

 as for other inhabitants in the immediate neighborhood. In shallow 

 water and on land during the night animals may similarly use their 

 photophores as lanterns. The employment of luminescence in recog- 

 nition of one sex by another is clearly exemplified by the firefly. 

 Among the American Lampyridae each species has a characteristic 

 code of flashing by which the females can recognize males of the 

 same species and distinguish them from males of other species. After 

 dark the female climbs up on a blade of grass and when a flying male 

 signals in her vicinity she attracts him to herself by recognizable 

 flashes in response (Harvey, 1952, Ch. 13). 



In the abyssal depths of the sea, fish can perhaps locate each other 

 by recognizing the pattern of lights presented by the luminescent 

 organs. It has also been suggested that squid are able to keep to- 

 gether in a school during the dark hours of the night by means of 

 their characteristic flashing. 



Animals may lure prey by means of their luminescent organs. 

 Since many small fish and planktonic invertebrates are attracted to 

 light, these animals would be expected to move toward the lumi- 

 nescent organs of predatory fish, many of which are located near the 

 jaws or even on filaments dangled in front of the mouth. On the 

 other hand, the sudden flash of luminescent organs may act as a 

 warning to scare off predators. Certain deep-sea shrimps produce 

 a luminescent secretion that may be discharged into the water. This 

 is an interesting counterpart to the sepia produced by squid and 

 cuttlefish in shallow water. When the latter are attacked, they can 

 discharge the black secretion into the water and escape from their 

 enemies in the "smoke screen" thus produced. In the inky blackness 

 of the deep sea the shrimps that produce a luminous discharge when 

 attacked may be able to escape in a "cloud of light" (Fig. 6.9)— or 

 these sudden emissions may act simply by distracting or frightening 

 the enemy. 



The possession of luminescence may be a definite disadvantage for 

 some organisms if it gives away their presence to enemies. For other 

 species the emission of light may be an accidental by-product of 

 metabolism and hold no ecological significance whatsoever. We can- 

 not imagine, for example, any possible benefit for bacteria that could 

 be derived from their production of luminescence. 



A correlation has been thought to exist in the marine environment 

 between the occurrence of eyes, the type of coloration, and the pres- 

 ence of daylight or luminescence. Eyes are well developed among 

 animals inhabiting the upper layer of the ocean, and luminescent 



