248 WALTER N. HESS 



The question of the origin of these organs can be settled only 

 by a study of the development of the photogenic tissues. With 

 the exception of three recent papers, Vogel ('13), Williams ('16), 

 and Dahlgren ('17), this has not been done by any one except 

 Dubois. Dubois ('98) studied the embrj^ology 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 multiplied, and by proliferation formed directly 

 the photogenic organs of the larva. For some reason Dubois' 

 work has attracted little attention, and is practically ignored 

 in general discussions of the subject. Moreover, he misinter- 

 preted the normal structure of the body wall in Lampyris, and 

 for this reason his conclusions have been severely criticised by 

 the few who have discussed them. 



Wheeler and Wilhams ('15), in their study of a mycetophiUd 

 fly of the New Zealand caves, found that the light-organs were 

 a modified portion of the malpighian tubules. These structures, 

 as is well known, are of ectodermal origin, and this furnishes a 

 clear instance of light-organs from the ectoderm in insects. 



Dahlgren ('17) studied the development of the adult Ught- 

 organs in the pupa of Photurus pennsylvanica. He states that 

 the light-organs are formed by a proliferation of cells from the 

 ventral abdominal hypodermis, which multiply and later differ- 

 entiate into the two layers of the light-organs. He does, however, 

 express some doubt as to the possible origin of the reflector layer. 



Two different workers upheld the view that the light-organs 

 arise from both ectoderm and mesoderm. Gegenbauer ('74) 

 advanced the idea that the non-luminous, or reflector, layer of 

 the light-organs is derived from the fat-body, while the photo- 

 genic layer is formed from the h>i)odermis. Wielowiejski ('90), 

 in opposition to Dubois, states that the so-called reflective, or 

 urate, layer of the photogenic organs is derived from fat-cells, 

 while the light-giving, or luminous layer, on the contrary, is 



