FERTILIZATION 



195 



the pair (Fig. 102). In each cell the micrenucleus divides and the 

 daughter micro-nuclei immediately divide again forming four. Of 



FIG. 102. Nuclear history during conjugation in Param&cium putrinum. 

 After Doflein. The macronuclear structures are omitted in all except A. A. 

 Formation of spindle for first division of micronucleus. B. Telophase of first 

 division. C. Second division of the micronucleus. D. Degeneration of three 

 of the micronuclei; the fourth, or permanent micronucleus, preparing for another 

 division. E. Division of the permanent micronucleus into the stationary and 

 migratory micronuclei. The spindle is greatly elongated and has a characteristic 

 mid-body. F. Grouping of micronuclei and exchange of migratory micronuclei. 

 G. Fertilization (mutual). Fusion of migratory with stationary micronuclei. 

 H. Formation of spindle for first division of the fusion nucleus in each conjugant. 

 /. Late phase of second division of fusion nucleus. J. Third division of fusion 

 nucleus. K. Exconjugant with eight micronuclei, derived from the fusion 

 nucleus. (The degenerating micronuclei are omitted from G-K.) d, degener- 

 ating micronuclei; m, migratory micronucleus; ma, macronucleus; mi, micro- 

 nucleus; p, permanent micronucleus; s, stationary micronucleus; sp, spindle. 



these, three degenerate (cf. maturation), while the one remaining 

 divides once more, this time unequally, forming a larger and a smaller 



