34 ENTOMOLOGICAL NEWS. [July, 'l 7 



Origin and Development of the Photogenic Organs 

 of Photuris pennsylvanica DeGeer (Col.).* 



By WALTER N. HESS. 



In spite of the fact that the light organs of fire flies have 

 been the object of much study during the past century, com- 

 paratively little has been done on their development. How- 

 ever, during the past few years this phase of the subject has 

 received more attention, though as yet, no one has definitely 

 demonstrated their embryonic origin. 



There are at present three conflicting views regarding the 

 origin of the photogenic organs. One view is that they are 

 modified hypodermal cells, another that they are formed from 

 both ectoderm and mesoderm, and lastly, that they are derived 

 from fat cells. Of these three views, that of the fat cell 

 origin has been the most generally accepted. 



Among the earlier workers who favored the idea of ecto- 

 dermal origin was Owsjannikow (1868), but his observations 

 are of little value since he studied only the adult organ. 



The question of origin can be settled only by a study of 

 the development of the photogenic tissues. With the excep- 

 tion of two recent papers, Yogel (1912), and Williams (1916), 

 this has not been done by any one except Dubois. Dubois 

 (1898) studied the development of both Lampyris noctiluca 

 and Pyrophorus noctiluca. He believed that he was able to 

 follow the development of the photogenic organs through the 

 different stages, from the beginning of segmentation, to the 

 adult insect. He discovered a close histological resemblance 

 between the blastoderm cells and the photogenic cells of the 

 larva, pupa and adult. Furthermore, he concluded that the 

 cells of the hypodermis multiply, and by proliferation form 

 directly the photogenic organ of the larva. 



For some reason Dubois' work has attracted little attention 

 and is practically ignored in general discussions of the sub- 

 ject. Moreover he misinterpreted the normal structure of 

 the body wall in Lampyris, and for this reason his conclu- 



* Contribution from the Entomological Department of Cornell Uni- 

 versity. 



