70 



THE NATURE OF ANIMAL LIGHT 



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

 siiied on stimulation. 



Some forms only produce light at certain seasons of 



1. Pyractomena 

 borealia. 



2. Pyractomena 

 angulata. 



3. Pyractomena 

 lucifera. 



4. Photinus 

 pyralis. 



5. Photinus 



consanguineus. 



6. Photinus 



ecintillauB. 



7. Photinus 



marginellus. 



8. Photinus 

 castus. 



9. Photuris 



pennsylvanica. 



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

 flies {after McDermott). One cm. vertically = approximately 0.02 candle power; one cm. 

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

 of females ( 9 ) at right of chart. 



the year. According to Giesbrecht (1895) this is true of 

 the copepods, which only light in summer and autumn, 

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



