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HANDBOOK OF PROTOZOOLOGY 



been recognized by several investigators (Fig. 136). In Myxo- 

 sporidia the spore possesses a binucleate sporoplasm. Most 

 observers agree that, prior to germination of the sporoplasm, 

 the two nuclei undergo fusion (Fig. 28). 



Endomixis 



By pedigree culture methods. Woodruff and Erdmann have 

 found that Paramecium aurelia undergoes, at an interval of 

 thirty days, a complete nuclear reorganization without cell 

 fusion. The macronucleus breaks up into a number of fragments, 

 which become completely absorbed by the cytoplasm later. 

 Each of the two micronuclei divides twice, some of the products 

 forming a new macronucleus and others forming two new micro- 

 nuclei. This nuclear reorganization which takes place period- 



Fig. 28 Stained spores of Myxosoma catostomi, showing two nuclei in the 

 sporoplasm (a), which later fuse into one (b). X2600. 



ically was termed endomixis by the above-mentioned authors. 

 The process has further been found to occur in Paramecium 

 caudatum, in which the micronucleus divides three times. Here 

 four of the division products form new macronuclei, two degen- 

 erate, and two persist as new micronuclei. Endomixis has been 

 found in several other ciliates. 



As to the significance of the fertilization and endomixis, the 

 generally accepted theory is that these processes probably re- 

 store the "vitality" of the individual in which they occur. 



References 



Belar, K. 1926 Der Formwechsel der Protistenkerne. Eine 

 vergleichend-morphologische Studie. Ergebnisse und Fort- 

 schritte der Zoologie. Vol. 6. 



