430 LIFE : OUTLINES OF GENERAL BIOLOGY 



organ is embedded in the musculature, and it is by contraction of 

 the muscles that the luminous secretion is shot out. 



In reference to this special case, standing by itself among fishes, 

 let us test the various theories of the possible utility of bio- 

 luminescence. 



{a) For some cases it has been suggested, £is above, that the 

 light produced by an animal may serve as a sex-signal, as in fire- 

 flies and glow-worms. The toadftsh (Porichthys) is luminous only 

 at the breeding season. But the light of Malacocephalus is shared 

 by both sexes, and the luminous organ was well-developed in the 

 smallest specimens collected. Therefore the probability is that the 

 sex-signal interpretation does not hold in this case. 



(6) In some other animals, as in certain deep-sea fishes with 

 the luminous organ dangling on the end of a rod rising from the 

 top of the head, it has been not unreasonably suggested that its 

 use may be to guide the animal in the darkness or semi-darkness. 

 But one can hardly think of a lantern being stowed away on the 

 under side of the body between the pelvic fins! It is not as if Malaco- 

 cephalus were a motor-car, requiring a rear light. 



(c) It has also been suggested that the luminescence of marine 

 animals, especially sedentary and sluggish ones, may serve as a 

 lure that attracts booty. Mr. Hickling thinks that this not unreason- 

 able interpretation may perhaps hold in the case of the "Softhead". 

 It feeds on crustaceans, such as small crabs, shrimps, and amphipods, 

 and it is quite possible that they are attracted to the light. In this 

 connection it is of interest to notice that one of the Banda luminous 

 fishes, Anomalops, is used by fishermen as bait. But it does not 

 necessarily follow that its value as bait is due to its luminosity. It 

 is obviously difficult to obtain definite experimental evidence for 

 or against these utilitarian interpretations. 



(d) There is a fourth possibility, namely that the luminescence 

 may confuse enemies, and this is the view that Hickling most 

 favours for his Malacocephalus. Speaking of the musculature sur- 

 rounding the gland, he says: "Contraction of these muscles 

 would cause the secretion to be shot out, and its use would seem 

 to be exactly analogous to the ink-sac of Cephalopods, but 

 whereas the latter emit a cloud of ink, this fish emits a cloud 

 of light." 



Captain Jones, of one of the trawlers, reports that a large specimen 

 of the fish, that was thrown overboard while still alive, emitted 

 a cloud of fire, which spread "like a dinner-plate" and remained 

 visible for some time. Thus a Malacocephalus pursued by a Hake 

 may puff out its luminous secretion and at the same time change 

 its direction. The Hake is confused or may pause to investigate 

 the strange halo. Meanwhile the "Softhead" is far away. To other 

 enemies the light may be alarming, and the result would be the 



