36 A PHYSICAL STUDY OF THE FIREFLY. 
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 hasanything 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 
meastirements on these samples showed but a slight warming, if any, over 
the luminous segments. 
TABLE 4. 
. ‘Temperature Temperature 
ee of empty pola Aig At Remarks. 
test tube. fireflies, 
fo ° o 
8 20 30.6 30.6 o.o | Start; temperature read just before fill- | 
ing test tube. 
8 30 30.6 31.6 1.0 
8 40 30.4 31.3 0.9 | Insects less active. 
9 40 30.2 30.3 0.1 After return from field, nearly all insects 
inactive at bottom of test tube. 
g 48 30.2 30.7 o.5 | After shaking the test tube, covering the 
thermometer with lively insects, and 
waiting 8 minutes. No effect due to 
shaking. All but about a dozen 
insects inactive, active ones at top; 
put thermometer there. 
10 02 30.5 30.8 0.3 
lo 20 | *30.5 30.8 0.3 
10 25 30.3 30.6 0.3 | Interchanged places of test tubes. 
10 30 30.3 30.7 0.4 | Agitated test tube; inserted thermometer 
te Be: in living mass of insects. 
10 33 30.4 30.8 0.4 
10 35 30.4 30.8 0.4 
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 
