36 



A PHYSICAIv STUDY OF THE IfIRElfI.Y. 



The preceding pages give an exact account of the observations, an expla- 

 nation of which is not attempted. However, in concluding this subject, it 

 may not be out of place to add that an explanation based on the assumption 

 that the dark segments are at a lower temperature than the luminous seg- 

 ments, due to their higher emissivity, does not appear satisfactory. As for 

 the oxidation theory, the present data do not refute it. Whether this tem- 

 perature difference has anything to do with the photogenic processes remains 

 an undecided question. It seems to be present all the time in a healthy 

 insect, but is not observable on a freshly killed non-glowing specimen. As 

 stated elsewhere, several dead specimens were found which had begun to 

 decompose, and the luminous organs emitted a faint glow. Thermo-couple 

 measurements on these samples showed but a slight warming, if any, over 

 the luminous segments. 



Table 4. 



As a final summary of this perplexing series of experiments, it may be 

 added that the temperature of the firefly is somewhat lower than the air, 

 but it is not known whether this body temperature has a fixed value ; that 

 the luminous segments are hotter than the adjoining dark segments, this 

 temperature difference being most marked on the ventral side of the insect ; 

 that it is uncertain whether this temperature difference is effected by the 

 flash (whether the flash is accompanied by an endothermic or exothermic 

 reaction) ; and that, if radiant energy (especially the infra-red) is emitted 

 by these insects, it is immeasurably small. No suggestions are offered as to 

 the cause of this difference in temperature between the luminous and the 

 non-luminous segments. Apparently there are slight discrepancies in the 

 two sets of measurements of the effect of the flash upon this temperature 

 difference ; but a study of the data and of the functions of the two types of 

 instruments used in these measurements does not indicate that this is a 



