UNICELLULAR FORMS 71 



follows: Two paramoecia which are not distinguishable as to sex, 

 fuse together along their oral surfaces (Fig. 21). The oral grooves 

 disappear in each, as do also the macronuclei. The micronuclei then 

 divide three times, giving eight in each of the conjugating animals. 

 Of these eignt, seven disappear. Then in each the remaining micro- 

 nucleus divides again into two, one of which is stationary and the 

 other migratory, moving across into the endoplasm of the other 

 coNjuGANT. The animals thus exchange micronuclear material. 

 Then in each the two micronuclei unite and the conjugating ani- 

 mals separate. The fact that the micronucleus of each of these ex- 

 con jugants is derived one-half from each member is important, for 

 this provides a vehicle whereby all future descendants of either 

 shall have inherited equally from both members of the conju- 

 gating pair. 



Following the fusion of the two micronuclei and the separation 

 of the pair, the micronuclei in each undergo rapid divisions fol- 

 lowed by a series of cell divisions and the division rate remains at 

 a higher level for some tim.e. The question now presents itself: Is 

 this fertilizing process of amphimixis a device that corrects the 

 effects of time, that is to say, the eiifects of old age, and brings about 

 rejuvenescence, a restoration to the condition of a young animal? 

 The answer is apparently in the affirmative, but this is not the only 

 method that will restore the original division rate. In some races 

 the animals singly undergo a periodic reorganization of the micro- 

 nuclear material that is comparable to the behavior of a single 

 member of a conjugating pair, called endomixis, which is followed 

 by an increase in division rate. Nor is the process of amphimixis 

 identical in all varieties of ciliate Infusoria. In some the micro- 

 nucleus is not visible. 



Metabolism. The metaboHsm of the paramcecium is holozoic 

 and the processes of oxygen intake and carbon dioxide outgo are, 

 as in the amoeba, directly through the body wall by diffusion. Non- 



