III. CILIATA. 



207 



borhood of the cytostome at right angles to the surface and divides 

 into two nuclei, the superficial being called the wandering or 



Fig. 146.— Conjugation in Parama^cium. /.-, macronuclens; Jt/c, micronucleus; o, cyto- 



stomes. 



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



II. Second division of mioronucleus into primary spindles (1, :>) and secondary 

 spindles (2, 3, 4; Ij, 7, »). 



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

 into male (1'h, hm) and feniale spindles (l?y, ^w\. 



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

 parent animal, the other united with the female spindle, \ni with Sic and hm with lw\ 

 maeronncleus hrolien up. ^ i ■ . 



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

 secondary cleavage spindles (', i''. 



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

 anlage of the new micronuoleus (u/l'), and that of the new macronucleus, p« 

 (placenta). The fragments of the old macronucleus begin to degenerate. 



Since F rnudatum shows tlie earlier and P. aure/in the later stages better, these 

 forms have been used, P. cmidahnn for I-III, P. aurdia for the rest. The differences 

 consist in the existence of one mioronucleus in P. rai/(iu(Mm, two m P. fimtda, and 

 that in the latter the nuclear degeneration begins in I. 



male nucleus, the deej^er, the stationary or female nucleus. The 

 male nuclei of the two coiuilating animals are exchanged, travers- 



