



(a 



HOW THE LIGHT OF THE FIREFLY IS PRODUCED 



Cross-section of lower part of a firefly's abdomen, magnified about three hundred times. 

 The dark tissue at the bottom produces the hght; it is backed up internally by a reflecting 

 layer, which appears very light in the photograph. The small dots in this layer are the 

 nuclei of the cells of which it is composed. The reflecting layer diffuses the light and may 

 also serve to guard the insect from injury by its own illumination. Throughout the two 

 layers can be seen the canals or trachea which conduct air — for oxygen appears to be necessary 

 to oxidize the light-producing substance of the fireflv. Photomicrograph by John Howard 

 Paine. (Fig. 16.) 



other unparalyzed parts will go on 

 flashing as usual. 



Between the hght organs and nervous 

 system intervenes what is called a 

 reflecting layer. This layer does not 

 directly reflect, however, but rather 

 diffuses the light so as to make the 

 entire abdomen appear as though glow- 

 ing. This layer may protect the nerv- 

 ous system from some possible bad 

 effects of the direct light, and many 

 think it serves still another purpose of 

 being the storehouse for some substance 

 which plays an active part in the light 

 production. Whether or not it con- 

 tains the stored-up supply of oxidizable 

 materials, however, must still remain 

 in the realm of conjecture. 



The photogenic property of the 

 abdominal segments is independent of 

 life, for if the organs are dried and 



ground to powder, light reappears under 

 the influence of air and moisture. 



Often the photogenic properties may 

 be observed in the eggs while they are 

 still in the ovaries, and nearly all the 

 larvae of the illuminating species show 

 fluorescence. Does the insect store up 

 "fuel" in its earlier stages which 

 gradually becomes exhausted during 

 the use of the light-emitting apparatus 

 when adult? There is some sHght 

 evidence to show that this might be 

 the case, but sufficient knowledge has 

 not yet been gained to make it possible 

 to reach any definite conclusion. 



INTENSITY OF THE LIGHT 



The intensity of the insect's light is 

 remarkable. It varies greatly, but the 

 most rehable tests made on the insects 

 frequenting Washington, D. C, place 



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