70 



THE NATURE OF ANIMAL LIGHT 



It lasts for hours, but may become more dim or be inten- 

 sified on stimulation. 



Some forms only produce light at certain seasons of 



1. Pyraotomena 

 borealis. 



2. Pyraotomena 

 angulata. 



3. Pyraotomena 

 lucifera. 



4. Photinus 

 pyralia. 



A. Photinus 



oonBanguineuB. 



6. Photinus 



eointillans. 



7. Photinus 



marginellus. 



8. Photinus 

 oastus. 



9. Photuris 



pennsylvanica. 



Fio. 16. — Chart showing relative intensities and durations of flashes of American fire- 

 flies (after McDermott). One cm. vertically ^approximately 0.02 candle power; one om, 

 horizontally = approximately one second. The nash of the males (^) is at the left; that 

 of females ( 9 ) at right of chart. 



the year. According to G-iesbrecht (1895) this is true of 

 the copepods, which only light in summer and autumn, 

 and according to Greene (1899) in the toad-fish, Porich- 



