Morphogenesis of Cyrtohymena tetracirrata (Ciliophora, Hypotrichia, Oxytrichidae) during binary fission

Morphogenesis during the binary fission of the oxytrichid Cyrtohymena tetracirrata was investigated using protargol silver impregnation. The main process reveals the following characteristics, which generally resemble those of its congeners: (1) the proter retains the parental adoral zone of membranelles in its entirety, while the old undulating membranes join to form the UM-anlage in the proter; (2) eight frontal, five ventral, and four transverse cirri are derived from six streaks, namely, the UM-anlage and five FVT-cirral anlagen, which are segregated in the pattern of 1:2:3:3:4:4 from these primordia from left to right, respectively; (3) the generation of the dorsal kineties is of typical Oxytricha-pattern; and (4) one caudal cirrus is formed at the posterior ends of the 1st, 2nd and 4th dorsal kinety anlagen.