236 History of Luminescence 



tivorous mammals and birds. Hence it is in accordance with Mr. Bates' 

 view, hereafter to be explained, that many insects mimic the Lampyridae 

 closely, in order to be mistaken for them, and thus to escape destruc- 

 tion. He further believes that the luminous species profit by being at 

 once recognised as unpalatable. It is probable that the same explanation 

 may be extended to the Elaters, both sexes of which are highly luminous. 

 It is not known why the wings of the female glow-worm have not been 

 developed; but in her present state she closely resembles a larva, and as 

 larvae are so largely preyed on by many animals, we can understand 

 why she has been rendered so much more luminous and conspicuous 

 than the male; and why the larvae themselves are likewise luminous. ^^ 



It is indeed surprising that Darwin rejected the undoubted use of 

 lampyrid light as a sex attraction. 



Later advocates of evolution have been little more successful in 

 visualizing the evolution of luminous organs, which must be of use 

 if natural selection is to operate. The subject was discussed by 

 A. R. Wallace in Tropical Nature and Other Essays (London, 1878) , 

 using practically the same argument as Darwin, by E. B. Poulton in 

 The Colours of Animals (1890) , by J. T, Cunningham in Sexual 

 Dimorphism in the Animal Kingdom (1900) and by A. Weismann 

 in his Decendenztheorie (1902) . 



Poulton held that the bright red of the tentacles of the worm, 

 Polycirrus, was a warning color, since Garstang had observed that 

 the worms were eaten by fish only if the tentacles had been cut off. 

 As the tentacles are limiinous at night, Poulton suggested that the 

 light may also be a warning to predators, and hence of selection 

 value. 



Cunningham was concerned with the wingless glowworm. In dis- 

 cussing wingless females and winged males among the lampyrids, he 

 held that " it would be difficult to prove that the wings became a 

 positive disadvantage to the female. On the view that disuse of 

 the wings in the female only has led directly to their degeneration, 

 the evolution becomes intelligible " since nocturnal species " are 

 naturally apt to develop to the extreme their retiring and inactive 

 habits . . . and the wings are therefore only required [by males] in 

 seeking the females." He added: " I do not profess to be able to 

 explain the origin of the property of phosphorescence in Lampyris." 



Finally, in August Weismann's Vortrdge ilber Descendenztheorie 

 (Jena, 1902) , attention was directed to the large numbers of deep- 

 sea animals with complicated lantern-like photophores, which Chun 

 held must be used to allure small animals, which were then eaten. 

 The fact that these lanterns had developed in such diverse groups 



" C. Darwin, The descent of man. Part II: 277, New York, 1889. Not in 1871 ed. 



