84 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



itive symbionts were algae, fungi or yeasts. Recorded 

 instances of bacterial symbiosis have not been so numerous 

 as one might expect. Various reasons may be given for 

 this apparent scarity of bacterial symbionts. Unless the 

 bacterial symbiont possesses definite stability, or has dis- 

 tinctive characteristics, it would not be detected readily 

 within the cell. Furthermore, when bacteria are present 

 in an intracellular position, they are usually called "mito- 

 chondria" and their bacterial nature has not been generally 

 recognized. 



Certain bacteria, however, have physical characteristics 

 as distinctive as have algae or yeast cells which may readily 

 be recognized in microsymbiosis. Among these bacteria 

 are the "phosphorescent" or luminiferous forms which have 

 been observed in symbiotic relationship in a large number 

 of animals. The biological relationships exhibited by these 

 symbionts in respect to their hosts, furnish perhaps one of 

 the most significant chapters in microsymbiosis. On ac- 

 count of their luminiferous properties, these organisms can 

 be "followed and watched," not only in the development 

 of the host, but also in experimental investigations. This 

 can not be done so easily nor with the same degree of ac- 

 curacy and certainty with microsymbionts that do not 

 have such outstanding characteristics. We are again 

 indebted to Buchner for an extensive review of the literature 

 on "Light Symbiosis," and for original observations in this 

 importaTtt branch of microsymbiosis. 



The question of the nature of the material that is lumi- 

 nous in plants and animals was formerly the subject of con- 

 siderable polemic discussion. Certain kinds of decaying 

 woods are known to emit light of a continuous nature. 

 Bacteriologists long ago demonstrated that the emission of 

 light in these cases is associated with bacteria, apparently 

 feeding on the decaying wood. In the common ''light- 

 ning bug" or "firefly," on the other hand, the light appears 



