72 WALTER N. HESS. 



grown larvae were found during July and August in association 

 with the mature ones, it seems very probable that the larvae 

 live for two years before transforming to adults. 



Pupation takes place from about June 10 to August i. The 

 larvae do not build an elaborate pupal-cell, as the larva of Pho- 

 turus pennsylvanica does, but on the other hand, they craw r l 

 back away from the edge of the water, three to ten feet, where 

 they go underneath stones, and there excavate little cells in 

 which the pupal period is spent. The mature larva shortens up 

 slightly and assumes an arcuate position. The cuticula splits 

 down the middle of the dorsal thoracic region and gradually 

 liberates the pupa. 



The pupa, except for the yellowish white head, appendages 

 and tip of the abdomen, is of a delicate roseate color. The 

 pleural regions, however, are decidedly pinkish. The abdominal 

 and thoracic tergites are drawn out ventro-laterally into rather 

 acute projections. At the end of each is a mass of setae. The 

 straightened out pupa measures 8 mm., and in an arcuate position, 

 6.5 mm. 



The pupal period is rather brief, extending for only seven or 

 eight days. 



The larval light-organs function throughout the pupal period, 

 but as the time for emergence approaches, the glow usually 

 becomes very faint. In a few specimens the light was observed 

 in the adults for a brief period after emergence. 



PURPOSE OF LUMINOSITY. 



There can be little doubt but that the chief function of light- 

 emission in insects is to assist in securing the mating of the sexes. 

 It is evident that this has come about as a secondary character 

 when one considers the varying degrees to w r hich the light-organs 

 are developed among Lamyprids. It was suggested by Blair 

 (1915) that possibly the light may be an indication of impalata- 

 bility. In the case of the adults of Photinus scintillans, this 

 does not seem probable, as one frequently finds the females of 

 Photurus pennsylvanica and numerous species of spiders feeding 

 upon them. Many adult fireflies when captured emit a pale 

 yellow fluid from between the last coxal joints and from the 



