DEVELOPMENT OF LIGHT-ORGANS 249 



composed of cells derived from oenocj'tes, and is, therefore, 

 ectodermal. Here again the conclusions were based on a study of 

 the 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 Peters ('41), Leydig 

 ('57), Schultz ('65), Emery ('84), Seaman ('91), Wheeler ('92), 

 Bongardt ('03), and Berlese ('09), 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 were 

 based upon a definite study of the developmental tissues; one 

 by Vogel ('13) and the other by Williams ('16). Vogel studied 

 the embryonic development of this organ in Lampyris noctiluca, 

 beginning with a stage in which the organ was already clearly 

 differentiated. He made a comparable histological study of 

 its cells with 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- 

 organs arise from fat-cells. 



WilHams ('16) worked upon our native species, Photurus 

 pennsylvanica and Photinus consanguineus, and apparently 

 confirmed the work of Vogel. Although he studied the develop- 

 ment of both the larval light-organs and the light-organs of the 

 adult, his observations were devoted almost entirely to the adult 

 fight-organs. In the case of the adult he found that the fat- 

 spheres broke do\\Ti, liberating their cells, and that these became 

 distributed along the hypodermis in the region where the light- 

 organs were to form. He also found that the cells of the early 

 organs formed a gradual gradation from the rather dark pig- 

 mented cells lying against the hypodermis, to those on the side 

 towards the fat-cells and continuous with them. 



