REPRODUCTION 



205 



vides into numerous uninucleate secondary cysts. Each secondary 

 cyst divides into two and remains together within a common cyst- 

 wall. In each the nucleus divides twice, and forms four nuclei, one of 

 which remains functional, the remaining three degenerating. The 

 paedogamy results in formation of a zygote in place of a secondary 

 cyst. Belaf (1923) observed a similar process in Actinophrys sol 

 (Fig. 90). This heliozoan withdraws its axopodia and divides into 

 two uninucleate bodies which become surrounded by a common 



Fig. 90. Paedogamy in Actinophrys sol, X460 (Belaf). a, withdrawal 

 of axopodia; b, c, division into two uninucleate bodies, surrounded by 

 a common gelatinous envelope; d-f, the first reduction division; g-i, 

 the second reduction division; j-1, synkaryon formation. 



gelatinous envelope. Both nuclei divide twice and produce four nu- 

 clei, three of which degenerate. The two daughter cells, each with one 

 haploid nucleus, undergo paedogamy and the resulting individual 

 now contains a diploid nucleus. 



In Paramecium aurelia, Diller (1936) found simple fragmentation 

 of the macronucleus which was not correlated with any special 

 micronuclear activity and which could not be stages in conjugation 

 or autogamy. Diller suggests that if conjugation or autogamy is to 

 create a new nuclear complex, as is generally held, it is conceivable 

 that somewhat the same result might be achieved by "purification 

 act" (through fragmentation) on the part of the macronucleus itself, 



