37^ Problem of Rejuvenescence in Prot 020a [June-September 



including reproduction do follow endomixis, it seems reasonable to 

 believe that accelerated vital phenomena follow conjugation — that 

 is, that both processes, broadly speaking, " rejuvenate " the organism 

 physiologically. Both processes afford opportunity f or a rearrange- 

 ment of the molecular Constitution of the cell, conjugation afford- 

 ing amphimixis and endomixis affording ^wc^omixis. 



To recent contentions that our conclusions were wrong, in reg-ard 

 to conjugation not being a necessity for the continued reproduction 

 of infusoria, we would reply that endomixis is not conjugation; 

 and no one had any other phenomenon than conjugation, involving 

 syncaryon formation, in mind until the discovery of endomixis, in 

 which a syncarj'^on is not formed. To say that endomixis fills essen- 

 tially the same röle as conjugation in the infusorian life-history is 

 to beg the entire question. In a word, the whole aspect of the prob- 

 lem of senescence and rejuvenescence in protozoa has changed with 

 our knowledge of endomixis. The question is now not whether 

 conjugation is necessary — for it is not — ^but whether endomixis is 

 necessary. If endomixis is necessary, as it may well be, and if one 

 feels justified in considering the physiological phenomena which 

 are synchronous with the start of endomixis as evidence of " se- 

 nescence " and those synchronous with the end of endomixis as in- 

 dicating " rejuvenation " — then, this is a radically new phase of the 

 old idea of protoplasmic senescence and rejuvenescence in the in- 

 fusoria. 



Osborn Zoological Laboratory, 

 Yale University. 



