PHOTOGENIC ORGANS OF LAMPYRIDS 169 



genie granules were bacteria, by trying to make cultures of these 

 granules in a number of different media. All his results were 

 negative.) 



Geipel ('15) who has published perhaps the best account of 

 the structure of the photogenic organs in beetles, agrees with 

 Bongardt when he 1 says that the nerves to the photogenic layer 

 terminate in the tracheal end-cells and not in the photogenic 

 cells. Thus it would seem that the oxidation process for photo- 

 genesis is activated through the agency of these end-cells. 



It seems clear that while the photogenic organ in the Lam- 

 pyridae is derived from adipose tissue, the luminous substance 

 itself is not fat-like, but is probably a protein contained in 

 modified fat cells (the luminous layer) in the form of minute 

 dark-staining granules. Such granules evidently occur in all true 

 photogenic tissue. 



Almost numberless experiments have been performed with 

 fireflies to determine if possible the manner as well as the pur- 

 pose of the light production. An old and important discovery 

 is that when the photogenic organ when dissected out and dried, 

 it will, months thereafter, shine in the presence of air and mois- 

 ture, showing that these substances are essential to luminescence, 

 and that the process may be independent of living protoplasm. 

 But the very fact that it is produced by protoplasm (plus oxida- 

 tion) which is not generally admitted to be a merely physico- 

 chemical combination, would necessarily entail a vital activity 

 of some sort. That the luminescence is controlled directly by 

 the nervous system and not immediately through muscular activ- 

 ity (abdominal respiratory movements) seems clear from experi- 

 ment as well as from the fact that glandular structures in general 

 (including the electric organs of fishes) are dependent for their 

 activity upon nerve control. Luminous organs may also respond 

 locally to mechanical stimuli. It is easy to determine that the 

 respiratory movements do not correspond to the periodicity of 

 the light, and as Lund and others have shown, there is no special 

 musculature for the photogenic tissue. Nor does it seem prob- 

 able that the light is controlled by the flow of blood, as claimed 

 by Dubois. This could hardly account for the rapid and well- 



