EFFECT OF CONJUGATION 369 



This part of the theory of rejuvenescence which holds that the 

 vigor of reproduction is increased by conjugation appears to be 

 definitely a mistake, for the infusoria, as we have already shown 

 (page 359). We shall therefore consider it no farther. 



The experimental results of the present paper of course do not 

 alter the facts as to the 'structural rejuvenescence' if one desires 

 so to call it. Certain points are worthy of notice in this connec- 

 tion. 



1. So far as the 'rejuvenescence' or renewal of structures other 

 than the macronucleus is concerned (locomotor organs, et cetera), 

 this takes place equally in vegetative reproduction. It furnishes 

 therefore no foundation for a theory that conjugation is in any 

 special way a rejuvenating process. 



2. The replacement of the macronucleus by parts of the 

 micronuclei of the two individuals of the pair is of course thor- 

 oughly in consonance with the results of the present study, 

 furnishing not the slightest difficulty for interpretation. The 

 micronuclei are to be conceived as corresponding to the nuclear 

 apparatus of the germ cells of higher organisms, each one con- 

 sisting of a certain combination of 'determinants' or 'genes.' 

 When the macronucleus is replaced by parts of two micronuclei, 

 a new combination of 'determinants' is thus produced; the progeny 

 may therefore differ from the parents. In other words, 'varia- 

 tion' is induced in conjugation — through the production of many 

 new combinations, in different cases. Again, since the new ma- 

 cronucleus is produced by the union of parts from two diverse 

 individuals, the progeny may inherit from these two; in other 

 words, conjugation results in biparental inheritance, as we have 

 actually found to be the case. 



Now, it is a priori not impossible that the effects of the renewal 

 of the macronucleus are completed in those two results; it is not 

 a priori certain that the new macronucleus must otherwise func- 

 tion any better than the old one. 



We must therefore inquire as to the experimental ground for 

 the assertion made in the quotation given above from Maupas, to 

 the effect that this new apparatus acts on the entire organism as a 



