264 S. O. MAST 



appear as though the males produced more intense flashes than 

 the females, but if several of each sex were put into different 

 glass jars, placed side by side and observed from a distance of 

 two or three meters, as was repeatedly done, I was never able, 

 by focusing attention on the character and the amount of light 

 alone to distinguish one from the other with any degree of 

 certainty. 



The male fire-flies, however, seldom if ever respond to the 

 glow of other males. In some way they appear to be able to 

 distinguish between the flashes of light produced by the two 

 sexes, as the following experimental observations clearly indicate. 



A number of males were put into one glass liter jar and three 

 females into another. Both were sealed and set in the garden 

 50 cm. apart. Thirty minutes later six free males had collected 

 about the jar containing the females and none around the other 

 jar. The two jars were then interchanged in position. Ten 

 minutes later all of the males had again collected about the jar 

 containing the females. These experiments were repeated with 

 slight modifications on nine different evenings and the results in 

 all cases were essentially like those stated above. Moreover, if 

 a female and several males are put on a plane surface and closely 

 watched, as was repeatedly done, the males seldom if ever make 

 the mistake of turning toward other males. And again that 

 the males recognize the glow of the females is clearly shown by 

 the difference in the effect produced upon them by the glow of 

 the two sexes as shown in the following experiment. 



Five males were put into each of two glass liter jars labeled 

 A and B respectively. The jars were then sealed and placed 

 50 cm. apart on a sheet of paper spread out on the ground. 

 Four females were put into a 50 cc. bottle and placed 50 cm. 

 from each of the two jars. Two free males soon came and lit 

 on the paper. An opaque screen was then so arranged that the 

 glow of the females could be seen by the males in one jar (A) 

 but not by those in the other jar (B). The males in jar (A) 

 and the two free males soon glowed freely, as did also the females. 

 In fact they glowed so freely that there was almost a continuous 

 flashing. The males in jar (B), however, presented a very 

 different spectacle. They were watched carefully for fifteen 

 minutes and during this time produced a total of only three 

 flashes. It should be emphasised here that these males could 



