FIG. 151. Conjugation in Param&cium. k, macronucleus: nk, micronucleus; o, cyto- 



stomes. 



I. Changes of micronucleus; left sickle stage, right spindle stage. 



II. Second division of micronucleus; into primary spindles (i, 5) and secondary 

 spindles (2, 3, 4; 6, 7, 8). 



III. Degeneration of secondary spindles (2, 3, 4; 6, 7, 8); division of primary spindle 

 nto male (im, $m) and female spindles (rz#, yu-'). 



IV. Exchange of male spindles nearly complete (fertilization), one end still in the 

 parent animal, the other united with the female spindle, im, with 5^- and $>n with i-ui 1 ; 

 macronucleus broken up. 



V. The cleavage spindle t formed by male and female spindles dividing into the 

 secondary cleavage spindles t', t". 



VI. VII. End of conjugation. The secondary cleavage spindle dividing into the 

 anlage of the new micronucleus (nk'\ and that of the new micronucleus, pt (placenta). 

 The fragments of the old macronucleus begin to degenerate. 



Since P. caudatum shows the earlier and P. aurclia the later stages better, thcx- 

 forms have been used, P. caudatum for I-III, P. aurclia for the rest. The differences 

 consist in the existence of one micronucleus in P. caudatum, two in P. aurclia and 

 that in the latter the nuclear degeneration begins in I. 



13 



