428 LIFE : OUTLINES OF GENERAL BIOLOGY 



the corpuscles as luminescent partner-bacteria, the other regarding 

 them as luminiferous granules belonging to the Pyrosome itself. 

 The luminous organs of some cuttlefishes are complex eye-like 

 structures, including a lens, a reflector, a dark curtain, and a central 

 mass of light-producing cells. Inside the last Pierantoni finds myriads 

 of bacteria, sometimes hunting in couples. These he regards as the 

 source of the light. The subj^cct has been carefully discussed by 

 Buchncr in his comprehensive book, Die Symbiose, and he comes 

 to the conclusion that the luminescence of Fire-flies, Fire-flames, 

 and Cuttlefishes — three very diverse types — is due to luminous 

 bacteria which have entered into a partnership or symbiosis with 

 the animals, whose luminescence is thus a borrowed splendour. 

 This seems to us a sweeping generalisation, esp)ecially in those 

 luminous animals that have an elaborate eye-like organ. In any 

 case, the evidence cannot be called conclusive until the so-called 

 bacteria are proved to be luminescent in some environment away 

 from their dominant partner. 



Uses of Luminescence. — When an organism simply exudes a 

 luminous secretion or sparkles at numerous points all over its 

 surface, it is quite possible that the luminescence is a by-play 

 without any significance as such in the everyday life. As we have 

 said, it may be comparable to the electric discharge associated 

 with many vital processes. But this is not a satisfactory inter- 

 pretation when there is an elaborate luminous organ. The search 

 for a use is then imperative, but the suggestions that have been 

 made remain more or less speculative. 



(a) The light may serve as a lure, which attracts booty in the 

 darkness of deep waters. This seems plausible when the luminous 

 organ is near the mouth, notably when it dangles at the end of a 

 fishing-rod-like fin-ray extended from the roof of the skull, as in 

 some .\nglers. 



(b) The light may serve, on the other hand, as a warning, which 

 scares away intruders or distracts predaceous molesters. It might 

 be compared to what is called "warning coloration". 



(r) The light may serve as a lantern, helping abyssal squids and 

 fijshes to fin(l their way about. This idea is tenable when the luminous 

 organ is situated in the vicinity of the head, which is often not 

 the case. This interpretation would not apply to fixed animals like 

 sea-pens. 



{(i) The light may facilitate the recognition of kin by kin, and 

 .serve as a .sex-signal in mating. In fire-flies there appears to be an 

 interchange of luminous signals between the more active males 

 and the more sedentary females. It is noteworthy that the toad- 

 fish. Porichthys. is luminous only during the spawning season. 



It is evident that the chemical physiology of animal light has 

 outnm the theory of its ecological significance. In all probability 



