Conjugation 



same as 

 singlet 

 on left 



b* 



e* 



FIG. 5. Diagram of experiment to test whether macronuclear differentiation is the 

 basis of the singlet-doublet difference. Hollow symbols represent nuclei originally 

 in singlet parents; solid symbols represent nuclei originally in doublet parents; 

 stippled symbols represent hybrid nuclei formed at fertilization and their deriva- 

 tives. The largest nuclei are macronuclei; the smallest are micronuclei; inter- 

 mediates are fragments of the prezygotic macronuclei. The diagram is simplified 

 by showing only a few of many fragments of a prezygotic macronucleus; actually 

 the many fragments are not completely segregated until several fissions later, 

 o, singlet subclone with macronucleus regenerated from fragment of singlet pre- 

 zygotic macronucleus. 

 b*, singlet subclone with macronucleus regenerated from fragment of doublet 



mate's prezygotic macronucleus. 

 c, singlet subclone with macronucleus of normal kind, developed from product of 



fertilization nucleus. 

 (/, doublet subclone with macronucleus regenerated from fragment of doublet s 



prezygotic macronucleus. 

 e*, doublet subclone with macronucleus regenerated from fragment of singlet 



mate's prezygotic macronucleus. 

 /, doublet subclone with macronucleus of normal kind, developed from product of 



fertilization nucleus. 



b* and e* are the critical cases; their functional nuclei (macronuclei) are de- 

 rived from their mate's prezygotic functional macronuclei. 



All types (a through /) have hybrid micronuclei, but these do not affect the 

 phenotypes. The latter correspond to the macronuclear genotypes. 



177 



