Heredity in Protozoa 513 



size in P. caudatum (10), the original size being retained in a hybrid 

 exconjugant line for 10-36 generations. Since the two lines derived from 

 a pair of conjugants were considered genotypically identical, this lag in 

 appearance of the new phenotypes supposedly represented the time re- 

 quired for elimination of the old cytoplasm and the production of new 

 cytoplasm under the influence of the heterozygous synkaryon. Assuming 

 that the volume of old cytoplasm is halved at each fission, a dilution of 

 at least 1:1,000 would seem to be required in these cases before the new 

 zygotic nucleus can assert itself by producing a new phenotype. 



1st division 



2d division 



potent i a 

 gametic 

 nuclei 



potential 

 zygotic 

 nuclei 



Fig. 9. 1. Theoretical genetic effects of conjugation in Parame- 

 cium aurelia, based on Dillcr's (11) account of micronuclear behavior. 

 In the diagram, it is assumed that the two conjugants are heterozygous 

 for some particular trait and that only two haploid nuclei undergo 

 the third pregamic division. Only the micronuclei are indicated. 



