Explanation of Plate. 



A. Photograph of the spectrum of a carbon glow-lamp, for different exposures. 



B. Spectra of: (i) helium vacuum tube; (2) "4-watt" carbon glow-lamp; (3) firefly 



Photinus pyralis, taken in 1909; (4) and (7) firefly Photuris pennsylvanica; 

 (5) and (6) firefly Photinus pyralis, taken in 191 1. 



C. Spectra of: (1) helium vacuum tube; (2) from 0.38891* to 0.4922^; fluorescence 



spectrum of a substance found in the blood of fireflies, e. g., in Photinus pyralis; 



(2) from 0.5015M to 0.6678,1*, spectrum of light emitted by Photinus pyralis; 



(3) same as (2) from 0.50151* to 0.6678JU, using a shorter exposure. 



D. Photographs obtained with short-focus spectrograph: 



Photuris pennsvlvanica, I: 8, 9, 12, 13. II: 9, 10. Ill: 10, n, 12. IV: 6, 7. 



V: 7,8,9' VI: 2,5,6. VII: 2,3,4- 

 Photinus pyralis,!: 2 to 7. II: 2 to 8 and 14. Ill: 2 to 9 and 13, 14. IV: 

 2 to 5 and 8 to 14. V: 2 to 6 and 10 to 14. VI: 7 to 14. VII: 10 to 14. 

 Photinus consanguineus, I: 11. II: 11, 12. VII: 5, 6, 7, 8, 9. 

 Photinus scintillans, I: 14. 

 Glow-worm, II: 13. 



Helium comparison spectrum, VI: 3, wave-lengths from left to right 0.471, 0.492, 

 0.501, 0.587, and 0.667**. I: 10, yellow helium line, X = 0.5876/*. (0.501/* is 

 faint.) 

 In D, column I is made up of two plates. The succeeding columns, II to VII inclusive, 

 are reproductions of single plates containing a dozen or more exposures to firefly 

 light, with the helium comparison spectrum at the beginning and the end of 

 each series. The original negatives are of course much stronger in the red than 

 here reproduced. 



