330 



THE BIOLOGY OF STENTOR 



e 



f 



e 



©■ 



Fig. 94. Conjugation in S. polymorphus, following the account 



of Mulsow, 1913. (Early stages are like those numbered i to 6 



in coeruleus, Fig. 93.) 



a: Both migratory and stationary pronuclei surrounded by 

 halos of cytoplasm excluding chlorellae, that of the female 

 nucleus being stellate. Immediately preceding maturation 

 divisions apparently reduced the chromosomes from 56 

 to 28 and from 28 to 14, the latter by seemingly transverse 

 division. Male pronucleus flattens as a disc against the 

 partition. 



b: Male nucleus breaks through and unites with partner's 

 stationary pronucleus. 



c: First mitotic division of the amphinucleus. 



d: Products retain cytoplasmic halos and have karyosomes 

 with achromatic fibers connecting to nuclear membranes. 



e: Second division, halos disappeared and 56 pear-shaped 

 chromosomes, producing — 



/; Four nuclei with karyosomes. 



g: Third division, simultaneous, yielding 8 nuclei, 6 of which 

 usually form macronuclear anlagen and have karyosomes, 

 and usually 2, becoming granular, form the new 

 micronuclei. 



h: Division and reduction in size of progenitors of 

 micronuclei. 



/.• Separation of partners, each usually with 6 macronuclear 

 anlagen and 4 micronuclei. 



j: Karyosome of macronuclear anlage forms chromatic 

 spireme. 



