Correlation of Ciliary and Nuclear Development in the Life Cycle of Euplotes

SYNOPSIS. Kinetosomal changes, as indicative of cytoplasmic reorganization in binary fission and during and after conjugation, were followed in a zoochlorellae-bearing species of Euplotes. The preconjugant peristome, designated the first generation peristome, breaks down partially after the conjugants have paired; the basal section, comprising the shorter adoral membranelles and the undulating, membrane, is resorbed. A new peristome, the second generation peristome, arises as a small pit near the left ventral margin, in midline, at the time when the micronuclei are in the first meiotic prophase. By the time of the second meiotic division a single set of new cirri, the second generation cirri, has formed in each conjugant. This second set is not perfect, lacking one of the frontals. Neither the second generation peristome nor cirri develop very far, or migrate, until after separation of the conjugants. Then the new peristome replaces the old one and the new cirri become functional. However, the new peristome lacks an undulating membrane and does not complete its development, bearing only a fraction of the normal number of membranelles. At its posterior termination, at the time of condensation of the macronuclear anlage, another peristome, the third generation peristome, is formed and develops as a granular, and later striated, invagination extending posteriorly. It appears to integrate with its predecessor and, as its constituent membranelles develop, a third generation single set of new cirri arises. These replace the imperfect previous set, all of the cirri being represented. In anticipation of the first postconjugant fission, all of the cirral apparatus is discarded again and two new sets (fourth generation cirri) originate; the old (combination second and third generation) peristome is retained by the proter while a new one is provided for the opisthe. It is evident, therefore, that a rather far-reaching cytoplasmic reorganization accompanies the nuclear changes of conjugation, seeming, for the most part, to follow the nuclear changes. The old macronuclear fragments have been found not to fuse with the macronuclear anlage.