NATURAL HISTORY STUDIES 



discharge of a luminous secretion, may have a pro- 

 tective value. In the darkness of the great abysses 

 some animals may possibly use their luminous 

 organs as lanterns. Where the luminous organs are 

 arranged on a definite pattern which is sometimes 

 different in the two sexes it is quite likely that they 

 serve as recognition marks, helping members of the 

 same kind or species to know one another at once. 



There is plainly much of the " perhaps " about 

 all this, but the general idea stands out that a 

 transformation of energy comparable to the burn- 

 ing candle chemical reactions producing light- 

 is of frequent occurrence among animals, and that 

 though it is not in itself necessarily useful, it may be 

 seized upon, utilized, and elaborated towards 

 diverse advantageous ends in diverse kinds of 

 creatures. 



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