MICROSYMBIOSIS 85 



to be intermittent in character. An anatomical investiga- 

 tion of the "hghtning bug" reveals a definite body or organ 

 in the abdomen that is associated with the production 

 of Ught. This organ is supphed with branches from the 

 tracheal respiratory system, as well as with blood vessels. 

 It has been thought that the cells of this organ contain a 

 material of fatty nature, sometimes called "noctilucine" 

 or "luciferin," which when oxidized produces light. The 

 intermittent character of the light was supposed to be pro- 

 duced by contractions and relaxations of the tracheal tubes 

 under the influence of nerves. Dubois ('86, '87) found 

 that the eggs in two famihar famihes of beetles, while still 

 in the oviduct and before fertiUzation had taken place, 

 were luminous. He also noticed that after the egg had 

 been laid it retained luminescence a much longer time than 

 did segregated bits of the luminiferous organ. Dubois 

 saw minute granulations in the cytoplasm of the luminif- 

 erous organ, as well as in the egg cell. These granula- 

 tions which he observed increasing by division, he also 

 found to be associated with luminescence. He named the 

 granules "Vacuoloids," and considered them as elementary 

 and highly significant parts of the hving substance which 

 might be bearers of a number of other functions. 



Regarding the finer structure of the luminferous organs 

 in the beetles, there are two types of cells entering into the 

 formation of the organ, a deeper opaque and a superficial 

 layer. The opaque layer is made up of cells filled with 

 urates, which performs a secondary function in the organ, 

 acting as a condensor and reflector. The superficial layer 

 of cells is transparent and represents a modified portion of 

 the chitin cells. According to M. Schultze ('65), Dubois 

 and others, it is only the superficial cells that contain the 

 luminous substance. Pierantoni, in 1914, demonstrated 

 the presence of two kinds of bacteria in the cells. One 

 variety is rod-shaped and about 10 micra in length. The 



