REGIONAL DIFFERENTIATION OF CORTICAL STRUCTURES AND THEIR REORGANIZATION DURING CELL-DIVISION IN PARAMECIUM-TRICHIUM

We observed the fell surface of Paramecium trichium using three differ ent methods. A non-dividing paramecium's cell surface consisted of thr ee major regions outside of the oral apparatus: a) an oral groove regi on, with 2-cilia-2-basal-body (2C-2BB) units; b) a posterior region, o ccupying 1/4 to 1/5 of the cell surface, with 1-cilium-1-basal-body (1 C-1BB) units; c) the remainder, with 1-cilium-2-basal-body (1C-2BB) un its. Five kinds of region-specific cortical reorganization occurred pr ior to cytokinesis: the 2C-2BB and 1C-1BB units were not duplicated, w hile the 1C-2BB units were reorganized to 2C-2BB, 1C-2BB or 1C-1BB uni ts. These reorganizations of the cell surface progressed from the fiss ion line to the anterior in the prospective anterior daughter cell, an d to the posterior in then prospective posterior daughter cell, and bi laterally from the old and also newly developing oral apparatus in bot h daughter cells. In contrast, the development of cilia and their asso ciated structures in each of the cortical units always progressed from posterior to anterior. The present work also showed that two fission lines began to develop bilaterally from the oral primordium, and then they joined to become a single fission line at the dorsal surface.