Complete periodic nuclear reorganization without cell fusion in a pedigreed race of Paramaecium

This preliminary communication presents the main results derived from the cytological study of specimens preserved throughout the life of a pedigreed race of Paramaecium aurelia, as well as of a series of specimens preserved daily, during the past four months, from subcultures of this race carried under constant environmental conditions.

During the past six and three quarter years this pedigreed race has been carried with the following chief results:

1. More than 4,250 generations have been attained to date (February 18, 1914) without the fusion of individuals or the advent of periods of marked physiological depression, though periodically well-defined normal morphological changes have occurred. 1 This demonstrates that the so-called “life cycle” of Paramaecium is nonexistent when proper environmental conditions are supplied. 2

2. Minor periodic fluctuations in the division rate, termed rhythms, have been demonstrated, recovery from which is autonomous. 3

3. The rhythms have been shown to be independent of environmental changes and due to inherent phenomena in the cell. 1

The present cytological study demonstrates that:

1. The rhythms in the division rate of Paramaecium are the physiological expression of profound nuclear changes.

2. These periodic nuclear phenomena involve the formation of a complete new nuclear apparatus by a definite sequence of morphological changes disintegration of old macronucleus; multiple division of micronuclei, formation of new macronuclear Anlagen which simulate typical conjugation. This results in the reorganization of the cell without the fusion of two animals.

This nuclear reorganization is evidently a normal substitute for typical conjugation in this race, but does not preclude its occurrence for the latter process has occurred in subcultures from this race subjected to environmental conditions suitable for its consummation 2

Details of this remarkable process, together with a discussion of its theoretical importance from the standpoint of the sexual potentiality of unicellular organisms and the physiological behavior of long pedigreed races of Infusm-ia, will be presented in another paper.