MICROSYMBIOSIS 89 



the accessory "nidamental gland," muscular tissue grows 

 in from the sides and is transformed into the contractile 

 reflector. Superficial to the region of the "nidamental 

 gland," connective tissue grows in, and becomes trans- 

 formed into the lens. The "nidamental gland" portion 

 contains the luminiferous bacteria, whereas other symbio- 

 tic bacteria, which are not luminous, are associated with 

 the formation of the lens. In one species the limiiniferous 

 bacteria do not appear in the organ until after it has com- 

 pletely formed. Here is an example of an organ, in which 

 the whole of its comphcated structure is essentially a re- 

 sponse to bacterial influence, and the entire structure ap- 

 parently is designed to utihze symbiotic bacteria. 



There are other instances of organ formation, associated 

 with symbiotic luminiferous bacteria, but these examples 

 sufficiently illustrate the physiological and morphological 

 responses to such organisms. Harvey ('20) has written 

 a monograph on ''The Nature of Animal Light" in which 

 various aspects of "bioluminescence" are considered. This 

 treatise abounds in observations and experiments on the 

 physiology and chemistry of fight production. In a num- 

 ber of organisms the fight producing materials, luciferin 

 and luciferase are present in the cytoplasm of the luminif- 

 erous organ cells, usually in the form of small bodies or 

 granules. The probable genetic origin of this granular 

 material is indicated in the symbiotic relationships that 

 have been discussed and will be considered more fully in a 

 later chapter. 



Microsymbiosis is not limited to associations with ani- 

 mal hosts. There are a number of well-known microsym- 

 biotic relationships in plants. The physiologic and mor- 

 phologic responses in these symbioses are as significant as 

 those in which an animal is the relative symbiont. We 

 shall only discuss at this time one of these symbioses — the 

 root nodules and their symbionts in the legumes. 



