Ultrastructure of Nuclear Division in Paramecium Aurelia I. Mitosis in the Micronucleus

Abstract

Ultrastructural details of micronuclear mitosis in the ciliate P. aurelia are described. Throughout mitosis the nuclear membrane remains intact and centrioles are not associated with the dividing nucleus. At late interphase the micronucleus has a peripheral layer of microtubules, a fibrous zone, and a core of condensed chromatin. This core fragments at prophase, the peripheral microtubules disappear, and microtubules extend from the fibrous zone. At metaphase, over 100 chromosomes could be seen, each attached to a bundle of microtubules though kinetochores were indistinct.