THE HISTOLOGY OF THE LIGHT ORCxANS OF 

 PHOTINUS MARGINELLUS.» 



Organic light has always been a subject of interest, both to 

 the scientist and to the casual observer of nature, and no other 

 photogenic organisms are of such wide range and easy access as 

 the fireflies. In some of its phases the light of the firefly comes 

 within the scope of the physicist and chemist. To the former 

 belongs the consideration of its nature, of its spectrum and other 

 physical properties ; to the latter come the problems of chemical 

 analysis concerned with the phenomenon, but to the student of 

 entomology remains the study of the delicate living structure in 

 which this wonderful process of photogeny takes place. 



In spite of the abundance of these insects, little work has 

 been done on the structure of the light-organs in our American 

 fireflies. During the past twenty years some careful investiga- 

 tions have been made upon European and Cuban forms, but 

 there is practically no literature upon those of our own country. 

 The purpose of my study has been to learn something of the 

 histology of the light-organs of Pliotiniis viargincllus, the most 

 common firefly about Ithaca during June and July This work 

 was begun at the suggestion of Dr. Wm. H. Seaman of Wash- 

 ington, D. C, whose advice during its progress has been most 

 helpful. I am also indebted to Professor Comstock and to the 

 members of his staff at Cornell University for their kindly 

 supervision of my work. 



The material from which this work was done was collected 

 near Cornell University during the summers of 1901 and 

 1902. The insects begin to appear by the middle of June, but 

 are not abundant until July. The height of the flying season is 

 during the first part of July. The large majority of the insects 



