Quarterly Journal of Microscopical Science, Vol s2-74, 537-546, Copyright © 1931 by Company of Biologists

Memoirs: Micronuclear Variation Paramecium bursaria

¹ Osborn Zoological Laboratory, Yale University

Studies on a race of P. bursaria, in pedigree culture for more than seven years, lead to the following chief results:

1. Marked variations occurred in the micronuclear number. Originally bimicronucleate, the race later assumed the unimicronucleate condition characteristic of the species, and finally became amicronucleate.

2. No marked variation in the vitality of the race has been observed throughout its life in culture, so that whatever function the micronuclear apparatus plays in the somatic life of the race is not obviously influenced by profound changes in the volume and distribution of the micronuclear material.

3. Evidence of endomixis or conjugation has never been observed in this race.

4. The viability of amicronucleate animals, without the power to undergo endomixis or conjugation, further supports the identification of the macronucleus and micronucleus as a segregation of somatic and generative elements into discrete bodies within the cell.