236 



PROTOZOOLOGY 



mating types. Sonneborn's view (p. 233) that the macro-nucleus is 

 the determiner of the mating types in Paramecium aurelia appears to 

 hold true in Euplotes also. 



The relation between the cytoplasm and nucleus in respect to in- 

 heritance has become better known in recent years in some ciliates. 

 Sonneborn (1934) crossed two clones of Paramecium aurelia differing 

 markedly in size and division rate, and found the difference persisted 



Type VI 



Type J 



Type I 



Type I 



Type VI 



Fig. 98. Diagram showing conjugation between a double (type IV) 

 and a single (type VI) of Euplotes patella (Powers), a, a double organism 

 with one micronucleus (genotype mt'mt 1 ); b, a normal single with a mi- 

 cronucleus (genotype mt 2 mt 2 ); c, conjugation of the single with the ami- 

 cronucleate half of the double (one of the pronuclei produced in the sin- 

 gle migrates into the double, while the two pronuclei of the double un- 

 dergo autogamy); d, the exconjugant double is shown to be type I 

 (mtmit 2 ); e, exconjugant single remains type VI; f, the double divides 

 into two type I doubles; g, occasionally the anterior half of the double 

 is widely "split," and division produces a double and two singles, the 

 latter testing as type IV and type VI; h, line of exconjugant single. Newly 

 formed macronuclei are stippled. 



