The Processes in Mating 113 



What significance is to be attached to the dissolution of 

 three of the eight nuclei originally present in the ex-con- 

 jugant is not clear; nor is it clear what is meant by the 

 diverse method of origin and distribution of the new mac- 

 ronuclei as compared with the new micronuclei ; to this point 

 we return later. 



The many details in these processes that occur after sep- 

 aration of the ex-con jugant must not be allowed to obscure 

 the essential features. These are simply that the new 

 micronucleus formed by union of the half nuclei divides so 

 as to produce new active macronuclei and new reserve mi- 

 cronuclei (Figure 30, G to L) ; and the animals continue to 

 divide by fission, as they did before conjugation, each of 

 the offspring getting a single active nucleus and a single 

 reserve nucleus. 



In this process of conjugation are involved all the prob- 

 lems of sex and of mating. It is of interest to examine it 

 in connection with the general questions which we proposed 

 in our introduction to this lecture, and with some of the 

 commoner answers to these questions. To this we turn. 



What are the results of this mating? What difference 

 does it make to the organisms or to the race which they 

 make up? 



As we saw in our first lecture, the best known theory as 

 to the effect of such conjugation is that it rejuvenates the 

 organism ; that it gets rid of the effects of age. But in 

 what way can it have this effect? There are two possible 

 answers to this question. One is that the rejuvenescence is 

 a result of the replacement of the old active nucleus by the 

 reserve nucleus. But for this no union of two individuals 

 is necessary, either logically or in fact ; we know now that 

 such replacement occurs without union. This answer there- 

 fore gives no explanation of the fact of union ; what we are 



