On the method of macronuclear disintegration during endomixis in Paramecium aurelia

Abstract

In the original studies 1 of the nuclear phenomena involved in endomixis, it was found that macronuclear disintegration, both in Paramecium aurelia and Paramecium caudatum, was effected by the elimination of spherical chromatin-bodies from the macronucleus, instead of by the transformation of most of the macronucleus into long tangled chromatin-ribbons such as occurs during conjugation in these species. Regarding Paramecium aurelia, it was stated that the “differences between the macronuclear changes during conjugation and during the process (endomixis) are only morphological; on the one hand, the macronucleus forms 'wurstförmige Schlingen,' while on the other, the macronucleus eliminates its chromatin by extruding it in the form of spherical bodies.” 2

This contrast proved valid not only in Woodruff's pedigree race 3 (I) of Paramecium awelia in which endomixis was discovered, but also in animals from such diverse sources as Germany and Ohio. Only one cell (Paramecium aurelia, I), 4087th generation, December 6, 1913) was observed during endomixis which in any way even suggested ribbon formation and a figure was given of this animal with the legend “An atypical form of macronuclear disintegration, slightly resembling the ribbonilike formation characteristic of conjugation.” 4

It is therefore interesting to record that the study of animals from this same pedigree culture (I) of Paramecium aurelia at about the 8900th generation (November, 1921) showed some cells successfully undergoing endomixis with macronuclear disintegration by ribbon formation and others by chromatin-body formation.

Thus it is clear that although all the data thus far at hand indicate that chromatin-body formation is the typical method of destroying the macronucleus in endomixis, nevertheless under certain unknown conditions the formation of chromatin-ribbons, until now regarded as diagnostic of conjugation, occurs in endomixis. This fact, of course, in nowise narrows the significant and crucial difference between endomixis and conjugation the absence cif synkaryon formation in the former and its presence in the latter.