6 A PHYSICAL STUDY OI THE FIREFLY. 
The Photinus scintillans and the Photinus consanguineus were found 
together among shrubbery, in small isolated spots of an acre or less in area. 
The scintillans is only about 3 to 5 mm. long and is therefore very difficult 
to handle. On the spectrometer slit it would flash but a few times, when 
fortunately it would emit a rich glow. A female scintillans was caught while 
flying about during the daytime. As in the female pyralis, the light organ 
occupies one-third of the ventral area of the third abdominal segment. Both 
male and female have the appearance of diminutive pyralis, the color of the 
wings being more grayish. 
The consanguineus is somewhat larger than the scintillans andcan bemade 
to flash for a longer time before it begins to glow. Both of these species 
become active early in the evening, but cease their flashing some time before 
dark. ‘The flash is a beautiful orange-red, which is emitted at long intervals. 
The fewness of these two species and the infrequency of the flash made it 
difficult to obtain specimens in sufficient number for the requirements of the 
present work. In work like the present it is necessary to have alarge number 
of insects to last three hours. Only once was work undertaken (this on the 
small spectrograph to be described subsequently) with less than a dozen 
insects, and of this number only two were very active. 
III. COMPOSITION OF THE LIGHT OF FIREFLIES. 
The question of the composition or “color”’ of the light emitted by vari- 
ous species of fireflies is of considerable interest, and may prove of great 
importance in the theory of radiation. ‘The color of the light may vary 
according to the species that produces it and from different parts of the body 
the same animal may emit 
different-colored light. For 
example, Photinus pyralis 
has two small light organs, 
L’ L’, Fig. 1, on the last ab- 
dominal segment which emit 
light of a decidedly more 
greenish color than the light 
emanating from the rest of 
the luminous organs. 
It would be interesting to 
know whether the maximum 
emission is different in the 
two luminous organs or 
whether this greenish color 
Fic. 1.—Photinus pyralis. in L’ L’ is simply a question 
A=male. B=female. L and L’=luminous organs. of intensity. Inthe P hotinus 
pyralisit appears to bealow- 
intensity effect. Whether there is an actual variation in the composition of 
the light emitted by any one luminous organ is of considerable interest, as 
this would show that not only the act of emitting the light, but also the com- 
position of the light, is under control of the insect. Whether there is such 
a variation in the composition, subject to the control of the insect, would 
be difficult to establish. = 
