LUMINESCENCE 577 



produced by an animal when disturbed by a predator may in turn attract 

 an enemy of the predator. In this way luminescent planktonic animals 

 may expose predator to predator along the length of the food chain. It is 

 well known that active creatures, swimming through swarms of luminescent 

 protozoa or other small planktonic forms, leave a luminous wake behind, 

 and this may be a signal to call larger predators to the scene. Luminescence, 

 in this wise, would have general survival value for the species and not 

 necessarily for the individual. Somewhat similar is the suggestion that 

 when one individual in a group of actively swimming animals is stimulated 

 into luminescence, it might serve as a warning to the others and cause their 

 flight. 



The inference seems fairly strong that in certain bottom forms the display 

 of luminescence may have the role of a sacrifice lure. In the polynoid 

 worms the scales of the back flash on tactile stimulation and are easily 

 detached, and it has also been observed that when a worm is transected 

 the posterior fragment alone luminesces. This behaviour could permit the 

 anterior portion to escape or be overlooked, while the shining posterior 

 fragment engaged the attention of the attacker. Subsequently the anterior 

 fragment would regenerate the missing segments. A similar explanation 

 may possibly serve for Chaetopterus, in which the anterior luminous 

 region can be autotomized and is readily regenerated. 



There are certain animals which discharge a luminous cloud into the 

 surrounding sea water when irritated, such as the deep-sea shrimp Sys- 

 tellaspis, the squid Heteroteuthis, the mysid Gnathophausia and the teleost 

 Malacocephalus. The light produced by these animals may have protective 

 value by confusing or bewildering the attacker. The littoral terebellid 

 Poly cirrus caliendrum, which Garstang has shown to be distasteful to fish, 

 may employ its light as a warning device. Remarkably enough, there are 

 some blind luminescent animals. The majority of luminescent copepods 

 are blind, and the deep-sea ray Benthobatis moresbyi, which possesses a 

 series of light-producing spots on the margin of the head, has rudimentary 

 eyes. In these animals a visual function is definitely excluded (32). 



It is uncertain whether luminescence in any animal is concerned with 

 securing food. The light-organs on the tips of barbels and anterior dorsal 

 fin rays in stomiatoid fishes such as Eustomias and Chirostomias and in 

 Ceratias and other ceratioid angler-fishes, are suggestive of fishing lures 

 (Figs. 13.8(c) and 13.18). The peculiar arrangement by which photophores 

 illuminate the interior of the oro-pharyngeal cavity of certain teleosts 

 (e.g. Chauliodus) may serve to attract prey into the mouth of the fish. Those 

 absyssal animals with well-developed eyes and photophores may be able 

 to detect weak light reflected from the surfaces of other organisms. Tell- 

 tale gleams of this kind would provide valuable clues of the presence 

 nearby of possible prey in bathypelagic waters where the population 

 density is relatively low. The dark brown and black coloration of deep-sea 

 fish, and the reds of bathypelagic Crustacea, may be an adaptation to 

 reduce such reflexion to a minimum (2, 34, 53). 



M.A.— 19 



