74 ORGANISMS OF ONE CELL 



increases enormously in quantity and becomes drawn out in 

 the form of rods termed chromosomes, too numerous to count. 

 Each of these chromosomes is then divided into two equal parts, 

 after which the micronuclei divide through the center, each 

 daughter micronucleus receiving one-half the original chroma- 

 tin. There are now two micronuclei in each cell, and all four 

 divide once again, forming eight in all or four in each cell. Of 

 these four, three degenerate and are absorbed in the endoplasm, 

 leaving one micronucleus in each cell. These then divide once 

 again, forming what are called pronudei, one of which migrates 

 from its cell into the other cell so that a mutual exchange of 

 pronuclei takes place. Each wandering pronucleus unites 

 with the stationary pronucleus of the opposite cell and fuses 

 completely with it, forming a fertilization nucleus (Fig. 30, 

 A-H). 



In the meantime the macronucleus of each cell begins to 

 break into pieces and to degenerate, and sooner or later it en- 

 tirely disappears, although this final disappearance does not 

 occur until some time after the two cells separate and divisions 

 have begun. After separation of the conjugating cells the 

 fertilization nucleus gives rise, by divisions, to eight micro- 

 nuclei. Four of these begin to swell, change in character, 

 and develop into four new macronuclei. After twenty- 

 four to forty-eight hours the exconjugant divides. Two 

 macronuclei and two micronuclei pass into each daughter 

 cell, and after another twenty-four hours these cells divide 

 again, one micronucleus and one macronucleus going to each 

 daughter cell. With this final division the normal relations 

 of the cell are restored, and the processes of conjugation 

 are ended, the resulting cells having each one macronucleus and 

 one micronucleus (Fig. 30, I-P). 



With the breaking up of the old macronucleus the protoplasm 

 becomes loaded with nuclear stuffs, as in endomixis, and these 

 probably renew the supply of material for the production of 

 the various endoenzymes needed in the vital reactions. 



With the conjugation of Paramecium, therefore, the ordinary 

 cells are metamorphosed into germ cells with extraordinary 



