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Vol. XXVlii] ENTOMOLOGICAL NEWS. 305 



sions have been severely criticised by the few who have dis- 

 cussed them. 



Wielowiejski (1890), in opposition to Dubois, states that 

 the so-called reflective or nrate layer of the photogenic organ 

 is derived from fat cells ; the light giving or luminous layer, 

 on the contrary, is composed of cells derived from oenocytes, 

 hence ectodermal. Here again the statements are based on a 

 study of mature organs, and hence are not conclusive. 



With the exception of the two previously mentioned papers 

 by Vogel and Williams, all authors who favor the theory of 

 fat cell origin have based their conclusions only on a study of 

 the adult organs. Many of these, including Leydig (1857), 

 Schultze (1865), Wheeler (1892) and Berlese (1909) seem 

 to be of this opinion, largely because the structure of the 

 mature organ resembles somewhat that of fat cells, and also 

 because certain cells of the photogenic organs secrete urates 

 and other products, comparable with fat cells. 



Recently two important papers have appeared which ap- 

 parently definitely settle the question in favor of the fat cell 

 origin, one by Vogel (1912), the other by Williams (1916). 



Vogel studied the embryonic development in Lampyris noc- 

 tiluca, beginning with a stage in which the organ was already 

 clearly differentiated. He made a comparative histological 

 study of its cells and those of the neighboring tissues, from 

 which he concluded that the cells of the photogenic organ, in 

 this stage, agree with the neighboring fat cells in shape, size 

 and relations of their nuclei. On this he based his conclusions 

 that the light organ arises from fat cells. 



It should be noted that Vogel found the organ in its early 

 development closely applied to the hypodermis, while at a 

 later stage it was definitely separated from it. 



Williams (1916) worked upon our native species, Photuris 

 pennsylvanica, and apparently confirmed completely the work 

 of Vogel. He maintains that the cells of the photogenic organ 

 form a gradual gradation from the rather dark pigmented 

 cells lying against the hypodermis, through those on the side 

 towards the fat cells and continuous with them. 



