AN ANALYSIS OF SYMBIONT BEACTIONS 97 



fied chitin cells, according to the authors who have investi- 

 gated them. Here is a morphologic response in which 

 not only chitin cells become modified by the microsjuibiont 

 but other cells (the "urate cells") are apparently attracted 

 to the bacteriocytes, take up a definite position, and con- 

 tribute to the formation of the luminous organ. This is a 

 comparatively simple organ, performing a definite func- 

 tion, but its origin is directly traceable to bacterial invasion. 

 The organ is a permanent and characteristic structure of 

 the species. The micros^mbiont is transmitted in the 

 egg cell from generation to generation. 



The organ associated with Ught production in the ceph- 

 alopods {Rondeletia minor, Sepiola intermedia, Pterygio- 

 theutis macidata) is rather more complex than the lumi- 

 niferous organ in the beetles. In these forms we recognize 

 four distinct tissues entering into the formation of the 

 organ. The bacterial s^mbionts associated with the first 

 structure to develop — the "accessory nidamental glands" — 

 do not at first possess luminescence in some species. It is 

 only after the organ is completely formed that the lumi- 

 niferous bacteria make their appearance in that part of the 

 organ formed from the "accessory nidamental glands." It is 

 not definitely known if these symbionts are a transforma- 

 tion of the original bacteria associated with the "nidamental 

 glands," or if they come from some other source after the 

 organ is formed. On the basis of experiments with cultured 

 luminiferous bacteria, it is safe to assume that the original 

 bacteria become modified during development and become 

 luminous. One of the accessory structures in the organ 

 (lens) is definitely known to be associated with bacteria in 

 its formation. 



The history of the development of the luminiferous organ 

 in the cephalopods illustrates the influence of microorgan- 

 isms in organ production. Various t^^Des of cells, appar- 

 ently under the influence of the essential symbionts, become 



