Abstract: Protargol staining technique and scanning electron microscopy are used to study the morphology of Oxytricha platystoma,and morphogenesis of the ventral ciliatures during asexual reproduction and physiological reorganization.During asexual reproduction,adoral zone of membranelles primordium (AZMP,future opisthe) occurs at first,then,undulating membrane primordium (UMP),frontal-ventral-transverse cirri primordia (FVTP) and left-& right marginal cirri primordia (LMP,RMP)(future proter and opisthe) appear in succession while old AZM renews.The result is that two sets of ventral ciliatures are developed and old ciliatures are disintegrated and disappeared.During physiological reorganization,AZMP,UMP,FVTP,LMP,and RMP formed in the same sequence as asexual reproduction.As a results,a set of ciliatures are produced and old ciliatures are replaced by the new ones.Because there are certain similar characters in the differentiation of new ciliatures and the degeneration of old ones,it is postulated that the regulation mechanism is same in occuring,developing and locating of the ciliary primordia for both the asexual reproduction and the physiological reorganization.