6 A PHYSICAL, STUDY OF 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 andean be made 

 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 Avork. 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. 



A 



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 



tv ^:? '% a?=^ 1^ different-colored light. For 



'*'~^ '' " example, Photinus Pyralis 



has two small light organs, 

 L' L', Fig. I , 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 

 in L' L' is simply a question 

 of intensity. In the Photinus 

 Pyralis it appears to be a low- 

 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 Hght, 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. 



A = male. 



Fig. I. — Photinus pyralis. 



£=female. L and Z,' = luminous organs 



