114 SITMBIONTICISM AND THE ORIGIN OF SPECIES 



organism in Symbionticism may not be limited to a single 

 tissue or organ. If the particular microsymbiont has the 

 property of producing some chemical substance, this may 

 not only affect the particular group of cells in the produc- 

 tion of a new cell type harbormg the symbiont, but the 

 chemical substance may alter the physiology of a number 

 of distant tissues and organs. Such reactions are com- 

 monly found in connection with pathogenic microorganisms. 

 The pathogenic organism may be locahzed in a particular 

 group of cells producing abnormalities in the tissues of that 

 organ, but the toxins may affect specifically other tissues 

 of the host. The "nidamental gland," whose origin is as- 

 sociated with symbiotic bacteria, apparently influences 

 muscular tissue in such a way that it transforms or dif- 

 ferentiates into a reflector for the luminiferous organ in the 

 squid. It is possible that many tissues in an animal pre- 

 sent secondary modifications or responses to symbiont 

 influences. 



It appears to the author that Symbionticism offers a 

 rational explanation for many of the variations in the 

 morphology and physiology of plants and animals. When 

 these variations are of sufficient magnitude and permanence 

 they constitute new species. The fact that mitochondria 

 are universally present in the cells of all organisms higher 

 than the bacteria, that mitochondria are bacterial in nature 

 and that microsymbiosis can determine morphologic and 

 physiologic changes in organs and cells, can lead to no 

 conclusion other than that Symbionticism is a fundamental 

 causative factor in the origin of species. 



