IV. CILIATA 



193 



Fig. 151. — Conjugation in ParamcBcium. k, macronucleus; k/?, micronudeus; 0, cyto- 



stomes. 



I. Changes of micronudeus; left siclvle stage, right spindle stage. 



II. Second division of micronudeus; 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); di\'ision of primary spindle 

 nto male (i"f, ^m) and female spindles (iiti', 5^). 



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

 parent animal, the other united with the female spindle, im, with 5TO and ^m with iw; 

 macronucleus broken up. 



V. The cleavage spindle t formed by male and female »pindles di"viding into the 

 secondary cleavage spindles t', t" . 



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

 anlage of the new micronudeus (n^'), and that of the new micronudeus, pt (placenta). 

 The fragments of the old macronucleus begin to degenerate. 



Since P. caudatum shows the earlier and P. aurelia the later stages better, these 

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

 consist in the existence of one micronudeus in P. caudatum, two in P. aurelia and 

 that in the latter the nuclear degeneration begins in I. 



13 



