Macronuclear Events and Some Morphogenetic Details During the Excystment of Onychodromus acuminatus (Ciliophora, Hypotrichia)

Light microscopy of stained (protargol, Feulgen, aceto-orcein, methyl green-pyronin) specimens of Onychodromus acuminatus during excystment shows that the macronucleus appears during the first hour as a warped ribbon with variable density and width and with sharpened ends. One extraordinary point that reaches the cortex is frequently seen in front of a small granule where the bundle of positioning fibers arises. The macronucleus returns to its previous form, with rounded edges, at the end of cortical morphogenesis, and later divides twice. Some details of cortical morphogenesis during the excystment process are discussed.