

322 THE WORLD OF LIFE 



or spots of blue or green on the upper pair, while the lower 

 have a band of spots near the posterior margin of a brilliant 

 crimson. Among perhaps a hundred species with this 1 

 general style of coloration, there are a few (perhaps a | 

 dozen) in which the red of the hind wings, when viewed very | 

 obliquely from behind, changes into opalescent and then! 

 into a curious bluish phosphorescence of intense brilliancy. 



I am informed by Dr. K. Jordan (of the Tring Zoological 

 Museum) that in these insects the black ground of the wing| 

 changes also into metallic blue, which seems to spread over 

 the red and to aid in the production of the phosphorescent! 

 effect. This is so marked that Mr. Bates gave to one of the 

 new species he described, the name of Papilio phosphorus, 

 One of the small Erycinidae {Euselasia prceclard) found in the 

 Upper Amazon valley, is of a yellow buff colour, with al 

 wonderful opalescent reflection which is said to be the mos 

 intense and brilliant in the whole order of Lepidoptera an 

 probably the most brilliant colour known. 



All metallic reflections in the animal world are what ar> 

 called interference-colours, and are produced by excessively 

 fine lines or rugosities on polished surfaces, or by equally 

 thin transparent laminae. It is probable that in the remark-, 

 able changing glows now described, both these causes may 

 come into play, producing, when viewed at certain angles, 

 an intensity of hue resembling those of the finest opalsf 

 or sometimes imitating the most brilliant glow - worms 

 or fire-flies by means of reflected light. It seems probable 

 that these rare hues may be of a protective nature, since <; 

 pursuing bird might be startled by the sudden flashing out o| 

 so brilliant a light and thus allow the insect to escape ; bu'i 

 that does not render it more likely that the infinitel} 

 complex arrangements by which such structures are produce^ 

 and transmitted unfailingly to offspring, should have beer; 

 brought about for this purpose alone, when thousands o 

 other species arrive at the same end by simpler means. 



Now if there was a difficulty in the view that all th< 

 wealth of colour and beauty in birds has been developec 

 solely on account of its utility to themselves, that difficult} 

 becomes greatly increased in the case of these insects. Th( 

 described butterflies alone are already far more numeroui 



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