Oral Regeneration in the Ciliate Stentor coeruleus: A Scanning and Transmission Electron Optical Study

SYNOPSIS. Elaboration of ciliated feeding organelles in the protozoon Stentor coeruleus was reinvestigated for the first time by scanning electron microscopy which gives the most realistic 3-dimensional images. Parallel transmission EM studies of synchronized regenerating stentors gave further ultrastructural details of stomatogenesis, while also confirming the expectation that in the structure of its kineties this now classical experimental object does not differ from other species of Stentor previously studied. Within 2 hr after the stimulus to regeneration, several generations of new kinetosomes for the oral primordium are produced, first in association with kinetosomes of kineties at the restricted primordium site. These kinetosomes rapidly sprout membranellar cilia as well as subpellicular microtubules but are still randomly oriented (anarchic field). The forming membranellar band increases from its center-line to both sides while it grows in length. Young cilia are blunt-ended. Recession of the early anlage occurs without rupture of the pellicle; soon apparent is the clear border stripe of unknown function along the right side of the membranellar band. Instantaneous fixation of beating cilia in early primordia revealed random beating, with coordination and presumably membranellar organization not yet attained. In late anlagen there are 2 types of metachronal rhythm: transversely from cilium to cilium across any given membranelle, as well as the easily observable serial beating of membranelles along the entire band. A single file of cilia leads the subsequent cytostomal invagination. The posterior end of the membranellar band then follows to line the cytopharynx.