Mg.nu. 



FlG. 21. Stages in the Conjugation of Paramcecium. 



A, Commencement of conjugation : the meganuclei (mg. mi) of the 

 two gametes are almost unaltered : the micronuclei (mi. nu) are in an 

 early stage of karyokinesis. 



B, The micronuclei have divided twice, each gamete now containing 

 four. 



C, Two of the micronuclei (mi. nu', mi. nu")of each gamete are 

 degenerating : of the remaining two one the active pronucleus is 

 passing into the other gamete. 



D, The active pronucleus of each gamete has passed into the other 

 gamete and is conjugating with its stationary pronucleus. The mega- 

 nucleus (mg. mi) has begun to break up. 



E, Each gamete contains a single conjugation-nucleus formed by the 

 union of its own stationary pronucleus with the active pronucleus of 

 the other gamete. On the right side the conjugation-nucleus is beginning 

 to divide. 



F, Conjugation is over and only one of the separated gametes is shown. 

 It contains the fragments of the meganucleus (dotted) and four nuclear 

 bodies (mi. nu) produced by the division and re-division of the con- 

 jugation-nuc'eus. 



G, Two of the products of division of the conjugation-nucleus (Mg. nu) 

 are enlarging to form mega-nuclei, the other two (Mi.nu) are taking on 

 the characters of micronuclei. 



(After H'ortwig.) 



I 2 



