INTRODUCTION 9 



The basis for the postulation of the theory of Sjnnbionti- 

 cism rests upon the nature of mitochondria. Our first task, 

 then, in attempting to estabUsh the theory consists in 

 reviewing the evidence for the bacterial nature of mito- 

 chondria. It also becomes necessary to seek in nature for 

 further evidence of the manifestations of the principle, for, 

 if mitochondria represent the end adjustment of a biologic 

 process, then it appears that it should be possible to find in 

 nature examples representing various phases of this mani- 

 festation in actual operation. A large number of such 

 examples have been described in biological literature. The 

 morphologic and physiologic responses exhibited in many 

 of these symbiotic associations furnish concrete evidence of 

 the manner in which the principles of Symbionticism may be 

 operating in the origin of species. 



